Northwestern cellar spider (Psilochorus hesperus): COSEWIC assessment and status report 2014
NOT AT RISK
2014
Table of Contents
- Document Information
- COSEWIC Assessment Summary
- COSEWIC Executive Summary
- Technical Summary - DU1: Southern Mountain Population
- Preface
- Wildlife Species Description and Significance
- Distribution
- Habitat
- Biology
- Population Sizes and Trends
- Threats And Limiting Factors
- Background
- Residential or Commercial Development (Threat 1)
- Agriculture and Aquaculture (Threat 2)
- Energy Production and Mining (Threat 3)
- Transportation and Service Corridors (Threat 4)
- Natural System Modifications (Threat 7)
- Pollution (Threat 9)
- Geolodical Events (Threat 10)
- Limiting Factors
- Number of Locations
- Protection, Status, and Ranks
- Acknowledgements and Authorities Contacted
- Information Sources
- Biographical Summary of Report Writer(s)
- Collections Examined
List of Figures
- Figure 1. Male (lacking three legs, two from left side, one from right side) on a human forearm. Note copulatory organs (modified pedipalps) in front of the male's face. Length, exclusive of legs, is approximately 2.5 mm. Photograph: Darren Copley
- Figure 2. Female with pale abdomen and carrying an egg sac. White and black lines indicate approximate lengths of body and first leg tibiae respectively. Female photographed as found clinging to the undersides of rocks. Length, exclusive of legs, is approximately 3.3 mm. Photograph Darren Copley
- Figure 3. Global range of Psilochorus hesperus. Sites within the United States are approximated from the distribution map in Slowik (2009)
- Figure 4. Canadian range of Psilochorus hesperus. Dark circles = all known sites; pale circles = searched sites. Green arrow = cemetery site at Summerland. Red arrows = Okanagan Valley sites with recent surveys (listed from north to south): east shore Skaha Lake (present 1996, undetected 2012), McIntyre Rd. (undetected 2001-2011, present 2012), Kennedy Flats (present 1995, undetected 2009), Haynes Lease/"The Throne" (present 1992 (Haynes Lease), 2001 and 2009 ("The Throne"), undetected 2012), Osoyoos Indian Reserve 1 (present 1995, converted to vineyards later that decade), and Kilpoola Lake (present 2007, undetected 2012)
- Figure 5. Map of British Columbia showing all Psilochorus hesperus records (orange squares); all records of related native cellar spider Pholocophora americana in BC (blue triangles; many of these dots also represent a minimum of 1.5 hours search effort) and general spider surveys in British Columbia from 2006 – 2013 (black dots; each dot represents at least 1.5 hours search effort per site). Map created by Alain Filion
- Figure 6. South Okanagan Grasslands Protected Area Chopaka East site, ~ 2 km southwest of Kilpoola Lake (west of Osoyoos), July 2012. This population was first recorded in 2008. Many of these rocks harbour P. hesperus with northeast exposure and shading from shrubs providing good environmental protection
- Figure 7. Suitable habitat for Psilochorus hesperus along Old Hedley Road just east of Hayes Creek, ~ 12.5 km east of the junction with Highway 5A near Princeton, July 2012. East view. Many rocks in this image harbour P. hesperus
- Figure 8. Suitable and unsuitable habitat for P. hesperus at the McIntyre Road bluffs immediately east of Vaseux Lake, July 2012. Rocky slope faces southwest. This site has been surveyed for pholcids and other spiders several times between 2001 and 2012. Psilochorus hesperus was first observed here in 2012 and only at one site (yellow oval) where rocks are afforded environmental protection by a dense thicket of Saskatoon Serviceberry. Other areas of this slope (white oval) contain unsuitable exposed habitat as well as a significant area of apparently suitable habitat shaded by shrubs and Ponderosa Pines; no P. hesperus have been found in those unsuitable or apparently suitable habitats. Presumably the very hot southwestern exposure makes this site and its rock habitats generally unsuitable for P. hesperus
- Figure 9. Artificial rock wall supporting P. hesperus in otherwise unsuitable habitat, Peach Orchard Cemetery, Summerland, July 2012. The cemetery is located on an exposed, hot, east-facing steep slope; adjacent habitat is primarily sagebrush (Artemesia sp.) on fine silt soil with no rock. At this site, specimens of P. hesperus occur only on the undersides of some of the capping slabs on the cement block retaining walls (other available interstitial spaces are packed with silt). This is the northernmost known site for P. hesperus and is more than 35 km north of the McIntyre Road bluffs, the nearest known occupied site. A single mature female (carrying an egg sac) and several juveniles were observed in 2012
List of Tables
- Table 1. General data on xeric areas of British Columbia surveyed for pholcid spiders 2001-2012. All surveys conducted by R.G. Bennett et al. Pholcophora americana was broadly distributed through most of the surveyed area; Psilochorus hesperus was restricted to the Similkameen River and parts of the southern Okanagan Valley. See Figure 5 for additional survey sites in BC.
- Table 2. Psilochorus hesperus records in southern British Columbia with 2012 search effort. Abbreviations: CDD – C.D. Dondale; GGES – G.G.E. Scudder; LR – L. Ramsay; RGB – R.G. Bennett; WDC – W.D. Charles. Latitude, longitude, and elevation data from Google Earth 6.1 (Google Inc. 2011). All specimens deposited in the Royal British Columbia Museum (Victoria, BC) except for collections by WDC and GGES identified by CDD which are in the Canadian National Collection of Insects and Arachnids (Ottawa, Ontario).
- Table 3. Search effort within P. hesperus habitat where no specimens were found during targeted surveys. Abbreviations: CC – C. Copley; DC – D. Copley; MF – M. Fairbarns; RGB – R.G. Bennett. Latitude, longitude, and elevation data from Google Earth 6.1 (Google Inc. 2011). Voucher specimens of other species collected at these sites are deposited in the Royal British Columbia Museum, Victoria, BC
- Table 4. Psilochorus hesperus summary of IUCN-CMP Threats applicable to each site
- Table 5-a. Level 1 Threat Mesures Impact Counts Scope and Severity Levels Calculation
- Table 5-b. IUCN-CMP (World Conservation Union–Conservation Measures Partnership) unified threats classification system. Threats may be observed, inferred, or projected to occur in the near term. Threat "impact" is calculated from scope and severity. For information on how the values are assigned, see Master et al. (2009) and for threat classification see CMP (2010)
Document Information
COSEWIC status reports are working documents used in assigning the status of wildlife species suspected of being at risk. This report may be cited as follows:
COSEWIC. 2014. COSEWIC assessment and status report on the Northwestern Cellar Spider Psilochorus hesperus name in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. x + 42 pp (Species at Risk Public Registry).
Production note:
COSEWIC would like to acknowledge Dr. Robb Bennett for writing the status report on the Northwestern Cellar Spider , Psilochorus hesperus, in Canada, prepared under contract with Environment Canada. This report was overseen and edited by Jennifer Heron, Co-chair of the COSEWIC Arthropods Specialist Subcommittee.
For additional copies contact:
COSEWIC Secretariat
c/o Canadian Wildlife Service
Environment Canada
Ottawa, ON
K1A 0H3
Tel.: 819-953-3215
Fax: 819-994-3684
COSEWIC E-mail
COSEWIC web site
Également disponible en français sous le titre Ếvaluation et Rapport de situation du COSEPAC sur le Pholcide de l'Ouest (Psilochorus hesperus) au Canada.
Cover illustration/photo:
Northwestern Cellar Spider -- Photo provided by Darren Copley.
©Her Majesty the Queen in Right of Canada, 2014.
Catalogue No. CW69-14/693-2014E-PDF
ISBN 978-1-100-21531-0
COSEWIC Assessment Summary
Assessment Summary - May 2014
- Common name
- Northwestern Cellar Spider
- Scientific name
- Psilochorus hesperus
- Status
- Not at Risk
- Reason for designation
- This small, rare spider is one of only two native cellar spiders in Canada. The species has a restricted range within bunchgrass- and Ponderosa Pine-dominated ecosystems and is found only within a specific habitat within these ecosystems. It requires cool, humid microhabitats beneath large rocks that enable its survival in otherwise hot and dry environments. This species has limited dispersal ability and small population sizes within isolated rocky habitats. Sites and habitats are potentially at risk from urban and agricultural development, road construction, and utility corridor maintenance activities. However, overall threats to the specific rocky habitats of the species are considered to be low at present. Furthermore, there is extensive potential habitat in the Similkameen and Okanagan Valleys that has not been surveyed for the species. These considerations resulted in the designation of Not at Risk.
- Occurrence
- British Columbia
- Status history
- Designated Not at Risk in May 2014.
COSEWIC Executive Summary
Northwestern Cellar Spider
Psilochorus hesperus
Southern Mountain population
Prairie population
Wildlife Species Description and Significance
Psilochorus hesperus (Northwestern Cellar Spider) is a cellar spider (Family Pholcidae) characterized by specialized copulatory structures, basally fused jaws and six of their eyes arranged in a pair of distinctive triads. The species has long and spindly legs, a small body size, Y-shaped groove on the head, distinctive spurs on the male jaws and bovine-udder-like female genitalia. This spider has limited dispersal abilities.
Cellar spiders derive their name from the human structures in which some of the species in this family are commonly found: undisturbed dark crevices within buildings, homes, basements and cellars. However, only a fraction of the 1350 named species occur within anthropogenic habitats. Most species live in natural habitats that include caves, under rocks and in abandoned mammal burrows. Psilochorus hesperus has not been found in basements or cellars.
Distribution
Psilochorus hesperus ranges from eastern California through Nevada, Idaho, Utah, Washington to southern interior British Columbia. In Canada the spider is restricted to the Western Interior Basin within British Columbia in a small area of the lower Similkameen and south Okanagan Valleys. The species is one of only two native pholcid spiders in Canada. An additional non-native pholcid species ranges in BC.
Habitat
Psilochorus hesperus inhabits low-elevation valley bottoms within the hot dry bunchgrass, Douglas-fir and Ponderosa Pine ecosystems of the southern interior of British Columbia. The species’ microhabitat includes the undersurfaces of relatively large, stable rocks, which provide some protection from temperature extremes. Occupied rocky areas are typically those situated in cooler habitats that are north- or east-facing and have a component of open forest or shrub which provides shading. The species likely wanders from its rocky residences in the cooler night temperatures and thus requires vegetation or other unqualified habitat elements adjacent to occupied rocky areas.
Biology
Psilochorus hesperus has a one-year life cycle. Individuals spend their lives within small territorial spaces under the surface of suitable rocks. Adult females and juveniles overwinter although adult females are present year-round (various age classes) and some may overwinter twice; adult males and new adult females mature in early spring; adult males are unlikely to be encountered after late summer. Mated females may produce several egg sacs, one at a time. Each egg sac is a loosely bound ball of up to two dozen eggs carried in the mother’s jaws. The extended egg production period results in a series of juvenile age classes within a population. Dispersal to new rock habitats is by nocturnal wandering for relatively short distances from areas of occupied rock habitat.
Population Sizes and Trends
Population size and trends are unknown.
Threats and Limiting Factors
The primary threat is the conversion of natural habitat to urban and agricultural development, and road construction and maintenance activities along transportation and service corridors. A combination of wildfires, water management activities, landslides, and pesticides also threaten the species. Limiting factors include small population sizes at occupied sites and isolation from other populations; widely separated areas of unsuitable habitat; and limited dispersal abilities that may prevent recolonization of new areas.
There are at least 16 locations: eight in the lower Similkameen Valley and eight in the south Okanagan Valley. One site at Summerland (Okanagan Valley) is situated in an artificial rock wall within a cemetery and considered a result of movement of material by humans. This site is still considered extant and included in the number of locations. An additional site in the Okanagan Valley was converted to agricultural use and is presumed extirpated, although the area has not been re-surveyed. There is a small possibility of unrecorded populations in adjacent habitats.
Habitat Protection and Ownership
Psilochorus hesperus has been recorded within provincially owned protected areas including the South Okanagan Grasslands Protected Area (East Chopaka site) and Haynes Ecological Reserve. One site is on a roadway adjacent to a private conservation property owned by The Nature Trust, and the spider is likely also present within this protected area. Most sites are on unprotected provincial Crown (e.g., roadsides or forestry land) or First Nations land.
Psilochorus hesperus is not protected by federal or provincial legislation. The species does not have a global rank (GNR). The Canadian and British Columbia General Status ranks of “2” (may be at risk) applied. The draft national status rank is N2 (imperilled) and the provincial is S2 as well.
Technical Summary
Psilochorus hesperus
Northwestern Cellar Spider
Mormon(French name)
Pholcide de l'Ouest
- Range of occurrence in Canada:
- British Columbia
Demographic Information
- Generation time
- 1 year
-
Is there an [observed, inferred, or projected] continuing decline in number of mature individuals?
Inferred decline based on cumulative habitat loss and degradation within the Okanagan Valley; magnitude unknown. - Inferred decline, but magnitude unknown.
- Estimated percent of continuing decline in total number of mature individuals within [5 years or 2 generations]
- Unknown
- [Observed, estimated, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over the last [10 years, or 3 generation].
- Unknown
- [Projected or suspected] percent [reduction or increase] in total number of mature individuals over the next [10 years, or 3 generations].
- Unknown
-
[Observed, estimated, inferred, or suspected] percent [reduction or increase] in total number of mature individuals over any [10 years, or 3 generations] period, over a time period including both the past and the future.
No temporal data on populations are available. Inferred reduction based on threats from urban and agricultural land conversion. - Inferred reduction based on habitat loss and degradation
-
Are the causes of the decline clearly reversible and understood and ceased?
Causes of decline not reversible; partially understood and not ceased. - Causes of decline not reversible; partially understood and not ceased.
- Are there extreme fluctuations in number of mature individuals?
- Unknow
Extent and Occupancy Information
-
Estimated extent of occurrence
2376 km² - all Canadian records
1773 km² - excludes north Okanagan cemetery site - 1773 - 2376 km2
-
Index of area of occupancy (IAO)
(2x2 grid value)
68 km² based on 17 known sites;
5-10 potential unrecorded sites expected from future surveys - 68 km2
- Is the population severely fragmented?
- Unknown
-
Number of locations
Extent and Occupancy Information Footnote1
The species is likely with an additional ten locations. - > 16
-
Is there an [observed, inferred, or projected] continuing decline in extent of occurrence?
Inferred decline based on habitat loss and degradation - Yes, inferred.
-
Is there an [observed, inferred, or projected] continuing decline in index of area of occupancy?
Inferred decline based on some habitat loss and degradation, although there is potential unchecked habitat. - Yes, inferred.
- Is there an [observed, inferred, or projected] continuing decline in number of populations?
- Unknown.
-
Is there an [observed, inferred, or projected] continuing decline in number of locations
Extent and Occupancy Information Footnote1?
Similkameen Valley sites are likely stable. Okanagan Valley sites have inferred decline based on some habitat loss and degradation. - Unknown.
-
Is there an observed continuing decline in and/or quality of habitat?
Observed decline in habitat quality and habitat area, with destruction of habitat for residential, industrial, and (especially) agricultural uses ongoing. - Yes, observed and inferred.
- Are there extreme fluctuations in number of populations?
- Not likely.
- Are there extreme fluctuations in number of locations Extent and Occupancy Information Footnote1?
- Not likely.
- Are there extreme fluctuations in extent of occurrence?
- No
- Are there extreme fluctuations in index of area of occupancy?
- No
Population | No. of Mature Individuals |
---|---|
Total | Unknown |
Quantitative Analysis
- Probability of extinction in the wild is at least [20% within 20 years or 5 generations, or 10% within 100 years].
- Unknown
Threats (actual or imminent, to populations or habitats)
The predominant threat is habitat destruction resulting from conversion of land to residential, industrial, and agricultural uses. Habitat loss could include large-scale land clearing (e.g., housing subdivision) or specific rocky substrate extraction (e.g., road construction materials) or road building (e.g., blasting). Other significant threats applicable to most sites are wildfire, landslides, gas pipeline construction and maintenance, and pesticide application.
Rescue Effect (immigration from outside Canada)
-
Status of outside population(s)?
The species has not been assigned conservation status ranks for adjacent states (WA, OR).
There are more widely distributed records in the US. - Unknown.
-
Is immigration known or possible?
Transportation by humans may be possible. Immigration via natural dispersal mechanisms is unknown. - Unknown, but possible.
-
Would immigrants be adapted to survive in Canada?
Survival of immigrants inferred from records at Peach Orchard Cemetery site within otherwise unsuitable habitat. - Yes
- Is there sufficient habitat for immigrants in Canada?
- Yes
- Is rescue from outside populations likely?
- Unknown. but possible.
Data-Sensitive Species
- Is this a data-sensitive species?
- No
Status History
- COSEWIC:
- COSEWIC: Designated Not At Risk (2014)
Status and Reasons for Designation
- Status:
- Not at risk
- Alpha-numeric code:
- Not applicable.
- Reason for Designation:
- This small, rare spider is one of only two native cellar spiders in Canada. The species has a restricted range within bunchgrass- and Ponderosa Pine-dominated ecosystems and is found only within a specific habitat within these ecosystems. It requires cool, humid microhabitats beneath large rocks that enable its survival in otherwise hot and dry environments. This species has limited dispersal ability and small population sizes within isolated rocky habitats. Sites and habitats are potentially at risk from urban and agricultural development, road construction, and utility corridor maintenance activities. However, overall threats to the specific rocky habitats of the species are considered to be low at present. Furthermore, there is extensive potential habitat in the Similkameen and Okanagan Valleys that has not been surveyed for the species. These considerations resulted in the designation of Not at Risk.
- Criterion A (Decline in Total Number of Mature Individuals):
- Not applicable. No data on decline.
- Criterion B (Small Distribution Range and Decline or Fluctuation):
- Not applicable. While the EO and IAO are below the thresholds for Endangered, and the overall habitat quality is declining, there are more than 10 locations, the population is not severely fragmented, and there are no extreme fluctuations as far as it is currently known.
- Criterion C (Small and Declining Number of Mature Individuals):
- Not applicable. No data available on population sizes of mature individuals.
- Criterion D (Very Small or Restricted Population):
- Not applicable. No data on population numbers.
- Criterion E (Quantitative Analysis):
- Not applicable. No data available.
COSEWIC History
The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list. On June 5, 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.
COSEWIC Mandate
The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.
COSEWIC Membership
COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal entities (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature), three non-government science members and the co-chairs of the species specialist subcommittees and the Aboriginal Traditional Knowledge subcommittee. The Committee meets to consider status reports on candidate species.
Definitions (2014)
Wildlife Species
A species, subspecies, variety, or geographically or genetically distinct population of animal, plant or other organism, other than a bacterium or virus, that is wild by nature and is either native to Canada or has extended its range into Canada without human intervention and has been present in Canada for at least 50 years.
- Extinct (X)
- A wildlife species that no longer exists.
- Extirpated (XT)
- A wildlife species no longer existing in the wild in Canada, but occurring elsewhere.
- Endangered (E)
- A wildlife species facing imminent extirpation or extinction.
- Threatened (T)
- A wildlife species likely to become endangered if limiting factors are not reversed.
- Special Concern (SC)Footnotea
- A wildlife species that may become a threatened or an endangered species because of a combination of biological characteristics and identified threats.
- Not at Risk (NAR)Footnoteb
- A wildlife species that has been evaluated and found to be not at risk of extinction given the current circumstances.
- Data Deficient (DD)Footnotec
- A category that applies when the available information is insufficient (a) to resolve a species’ eligibility for assessment or (b) to permit an assessment of the species’ risk of extinction.
The Canadian Wildlife Service, Environment Canada, provides full administrative and financial support to the COSEWIC Secretariat.
Wildlife Species Description and Significance
Name and Classification
- Class:
- Arachnida
- Order:
- Araneae
- Subordinal:
- Opisthothelae: Araneomorphae: Haplogynae
- Family:
- Pholcidae
- Subfamily:
- Modisiminae
- Genus
- Psilochorus Simon 1893
- Species
- Psilochorus hesperus Gertsch and Ivie 1936
- English Common Name
-
Northwestern Cellar Spider
Northwestern Longlegged Pholcid - French Common Name
- Pholcide de l'Ouest
The genus Psilochorus is part of a New World clade of pholcid (cellar) spiders (Huber 2005, 2011a) and includes over 40 described species (Platnick 2012). The majority of these species have small and restricted ranges within the Nearctic region. Simon (1893) described the genus; Gertsch and Ivie (1936) described Psilochorus hesperus; and Slowik (2009) revised the Nearctic species occurring north of Mexico. Huber (2000, 2011a) has analyzed the global phylogeny of pholcids. No subspecies of P. hesperus are described.
Although Psilochorus hesperus is called a cellar spider, the name is due to taxonomic history rather than habitat association. The first genus described in the family was its namesake taxon, the European Pholcus (in 1805). Because of its close association with human habitation, Pholcus phalangioides has accidentally been introduced around the world where they are found in undisturbed areas such as basements and cellars. It is for this reason the family is often referred to as cellar spiders, despite the fact that most of the 1300+ named species occur in natural habitats that include caves, under rocks, and in abandoned mammal burrows. In Canada, the only pholcid recorded in homes is this non-native pholcid, Pholcus phalangioides. There are no records of P. hesperus or the other native pholcid species occurring in association with human habitation.
Morphological Description
Pholcid spiders lack a cribellum (a broad, flat silk production organ located in front of the spinnerets in a variety of spiders) and have haplogyne genitalia (male genitalia feature an exposed genital bulb) on the tarsal (last) segment of each pedipalp (paired leg-like structures in front of the first pair of legs of all spiders, modified for copulation in males, unmodified in females, Fig 1). Female genitalia have a simple plate ventrally on the abdomen and lack the complex copulatory apparatus typical of most female spiders. In addition, pholcids are distinguished by the possession of basally fused chelicerae (jaws) and eyes arranged in three groups with the anterior median eyes occurring as a pair (or absent in some pholcids; specimens of Psilochorus have a full complement of eight eyes) and the other six eyes as distinctive triads.
Psilochorus have long and spindly legs (length of each tibia of the first pair of legs > body length [versus < body length]; Figure 1 and 2), small body size (< 4 mm [versus > 4 mm]; 3), carapace with a Y-shaped dorsal median groove and each male pedipalp with a pointed structure on the tip of a slender femur (versus pointed structure lacking and femur enlarged) and a simple slender procursus (a basal outgrowth on the tip of the pedipalp) (versus a much larger and complex procursus).
Males have a sharply pointed, inwardly curved, pair of elongate spurs projecting from the bases of the fused jaws and resembling steer horns; and females have a pair of closely spaced humps on a large prominence projecting ventrally from the copulatory region of the abdomen and resembling a bovine udder.
The following description of P. hesperus is summarized from Slowik (2009). Specimens are small (body length 2.5 mm [males, Figure 1] to 3.3 mm [females; Figure 2]). Colouration ranges from pale (almost translucent) yellow to dark brown with the abdomen darker than the carapace; most specimens are pale. Y-shaped mid-carapace groove makes the eye region appear somewhat elevated. Clypeus (between the jaws and eyes) projects strongly forward. Abdomen dorsally with lightly contrasting pattern of dark “heart mark” (central elongated dark mark anteriorly on abdomen) bracketed by several pairs of darkened spots laterally against a paler background. Abdominal pattern may be indistinct or absent. Further morphological details are provided in Gertsch and Ivie (1936), Huber (2000), and Slowik (2009).
Two native pholcids occur in Canada. Pholcophora americana is common and widespread in the southern interior of British Columbia (BC) and a small portion of southern Alberta (AB). Psilochorus hesperus occurs only in south central BC (see Distribution). A third non-native pholcid, Pholcus phalangioides (Fuesslin), ranges throughout southern BC within anthropogenic structures and buildings. The morphological characters separating these three species are clear. Psilochorus hesperus can be distinguished from other cellar spiders in this genus by its distribution. It is the only species occurring north of central Oregon in western North America (Figure 4).
Population Spatial Structure and Variability
No population structure or genetic studies have been conducted on P. hesperus. There is good potential for the species to exist in discrete, genetically distinct populations (e.g., see Keith and Hedin 2012).
Designatable Units
Psilochorus hesperus is being assessed as one designatable unit, in the absence of information on discreteness or evolutionary significance among populations. The species occurs within the COSEWIC (2011) Southern Mountain Ecological Area.
Special Significance
Pholcidae is a large family of spiders (1300+ species) (Platnick 2012) characterized by a high degree of habitat specialization. The majority of species have restricted ranges ( e.g., Huber 2000, 2001, 2011b; Slowik 2009) within cooler and humid tropical climates.
Psilochorus hesperus is one of two native pholcids in Canada. The majority of the species’ global range is within the Great Basin (Slowik 2009), a hot and dry ecosystem that extends through west-central North America, the northernmost extent within the Western Interior Basin of BC. The species is adapted to cool, humid microhabitats provided by the undersurface of large rocks within an otherwise hot, dry environment.
The range of P. hesperus within the Okanagan and Similkameen areas of BC overlaps with at least 204 additional species at risk (British Columbia Conservation Data Centre 2013), of which at least 65 have been assessed by COSEWIC (COSEWIC 2013).
The species is not known to have cultural significance to First Nations in the region (Jones pers. comm. 2012).
Distribution
Global Distribution
The global range of Psilochorus hesperus is primarily within North America’s hot, dry Great Basin, and stretches from extreme southcentral BC through central Washington (WA) to eastern California and southwestern Idaho (Figure 3) (Slowik 2009). The species is recorded through the arid interior of WA east of the Cascade Range, and narrows in the north to a single drainage, the Okanogan River Valley (Okanogan County, WA). At Oroville the distribution follows both the Similkameen and Okanagan River drainages north into BC. The approximate global range extent is less than 700 000 km2.
Canadien Distribution
In Canada, P. hesperus is at the northern edge of its range in south-central BC (Slowik 2009). The speciesis recorded from 17 sites (sixteen extant and one presumed extirpated; Table 2) within lower elevations (280 – 760 metres elevation above sea level [asl]) of the Similkameen and Okanagan valleys (Figure 4). Less than 5% of the species’ global range occurs in Canada.
In the Similkameen Valley (Figure 4, Table 2), P. hesperus is recorded from eight sites within a 75 km corridor of the Similkameen River from the vicinity of the Hayes Creek drainage (~10 km east of Princeton, site 2) to the international boundary in the South Okanagan Grasslands Protected Area East Chopaka (site 5).
In the Okanagan Valley (Figure 4), the species is recorded at nine sites from Summerland (site 12, northernmost site) to Osoyoos (site 11, southernmost site). The Summerland site is within a cemetery and may be an outlier (see Special Significance and Dispersal and Migration).
The Similkameen and Okanagan valley sites may represent disjunct populations. These drainages are tributaries of the Columbia River system and join approximately 12 km south of the international border at Oroville, WA. The spiderhas been recorded in WA near Oroville (Table 2) and sites approximately 30 km southward to the Columbia River Valley (see Figure 3).
Extent of Occurrence and Area of Occupancy
Based on all records (17 sites) the extent of occurrence (EO) in Canada is 2376 km2 (Filion pers. comm. 2012). If the cemetery site (site 12 Summerland) and a site now presumed extirpated from agricultural development (site 11 Osoyoos Indian Reserve 1) are excluded the EO is reduced to 1429 km2.
The index of area of occupancy (IAO), based on a 2 X 2 km grid for all 17 sites, is 68 km2 (Filion pers. comm. 2012). Excluding the presumed extirpated site the IAO is 64 km2. The IAO is likely an underestimate; there are potential sites on the east side of the Okanagan Valley between Oliver and Osoyoos and in the Similkameen Valley, particularly on First Nations land between Hedley and the international border. Using Google Earth imagery (Google Inc. 2011), and “rock/talus/sandbar” mapping in Vegetation and Habitat Types in Public Utility District No. 1 of Okanogan County (2009), an estimated 2 km2 of potentially suitable specific rock habitat is available (Bennett pers. comm. 2012).
Search Effort
Targeted spider sampling (in general) began in the 1970s. Pholcid spiders were unrecorded in BC before the 1980s (see West et al. 1984, 1988). From 2001 to 2012 Pholcid surveys across southern BC (Table 3; Figure 5) targeted habitats known to have P. hesperus, including grasslands, open Douglas-fir (Pseudotsuga menziesii)and Ponderosa Pine (Pinus ponderosa) woodlands, and rocky areas in relatively xeric landscapes (Table 1). Most survey sites involved hiking within suitable habitats or were adjacent to or within a few hundred metres of roadways.
Table 1. Table summarizing general data on xeric areas of British Columbia surveyed for pholcid spiders from 2001 to 2012. Information includes drainage name, waterway name, and general area surveyed.
Drainage | Waterway | General Area Surveyed |
---|---|---|
Fraser/Thompson | Fraser River | Lytton to Williams Lake including some minor tributaries |
Fraser/Thompson | Thompson River | Lytton to Cache Ck., Kamloops, and Salmon Arm, incl some minor tributaries |
Fraser/Thompson | Nicola River | Spences Bridge to Stump and Douglas Lks. |
Fraser/Thompson | Chilcotin River | Riske Ck./Beecher Prairie to Farwell Canyon |
Fraser/Thompson | Seton River | Anderson Lake to Mission Ridge |
Fraser/Thompson | Bridge River | Carpenter Lake dam to Lillooet |
Fraser/Thompson | Yalakom River | Ore Ck. to Moha |
Similkameen | Similkameen River | Whipsaw Ck. to Chopaka |
Similkameen | Tulameen River | Otter Lake/Tulameen to Princeton |
Similkameen | Allison Creek | 7 Mile to Princeton |
Similkameen | Ashnola River | Buckhorn Rec. Site to Similkameen River |
Okanagan Valley | Okanagan River | Numerous sites from Armstrong to Osoyoos |
Kettle | Kettle River | Christian Valley to Rock Ck. and Grand Forks to Christina Lake |
Kettle | Granby River | Volcanic Ck. to Grand Forks |
Columbia / Kootenay | Columbia River | Trail to Waneta |
Columbia / Kootenay | Kootenay River | Whiteswan Lake/Canal Flats to Lake Koocanusa/Grasmere; Grohman Narrows (Nelson); including various tributaries |
Canada’s native pholcids are small, inconspicuous spiders that move quickly and therefore require focused search effort and specific sampling techniques. Psilochorus hesperus surveysare done through a combination of hand-collection (physical examination of habitat) and pitfall trapping. Hand-collection is the best method for determining pholcid presence and is the primary method in pholcid surveys (Bennett unpubl. data). Pitfall trapping is a passive method that involves burying a cup flush with the ground, filling the cup with preservative and leaving the cup for up to a month in order to record arthropod presence. This method is effective for long-term pholcid monitoring and detection of unrecorded populations.
More than 195 hours of hand searching for P. hesperus has accumulated in the past fifteen years, most of this search effort within the past few years by one to three spider specialists who specifically targeted habitats for this species. Pitfall trapping in suitable habitats (within at least 12 sites) spanning at least three field seasons (1991, 1994 and 1995) has also revealed some results (Table 2 and 3).
Table 2. Table summarizing Northwestern Cellar Spider records in southern British Columbia. Information includes site number, collection date, whether site was searched in 2012, site location, geographic coordinates, habitat description, collector's name, and search effort.
Site # | Year | Coll. Date | 2012 Survey | Site | Owner ship | Elevation (m) | Habitat | Collector (C) and Identifier (ID) | Search Effort (Hours) |
---|---|---|---|---|---|---|---|---|---|
1 | 2001 | 26.ix. 2001 |
Not surveyed | CAN: BC: East of Hedley, near small stream crossing south end of Hedley / Nickelplate Road | Unknown | 540 | underside of rocks, open Ponderosa Pine, lots of Latrodectus | RGB | 1 |
2 | 2008 | 1.v. 2008 |
Positive | CAN: BC: East of Princeton, Bromley Rock, Old Hedley Road, ~8km West of highway bridge | BC Crown; Park | 571 | underside of rocks in loose pile, roadside, open D-fir woods | RGB | 1 |
- | 2012 | 17.vii. 2012 |
Positive | CAN: BC: East of Princeton, Bromley Rock, Old Hedley Road, ~8km West of intersection w highway 3 | BC Crown; Park | 571 | underside of rocks in loose pile, roadside, open D-fir woods, south-facing shaded by firs and shrubberies | CC, DC, RGB | 3 |
3 | 2012 | 17.vii.2012 | Positive | CAN: BC: East of Princeton, Old Hedley Road, ~ 12.5 km east of junction with highway 5A | Likely BC Crown (MoTH) | 600 | underside of rocks, at base of stabilized talus slope along access road, open D-fir woods, southwest-facing shaded by firs and tall grasses | CC, DC, RGB | 3 |
4 | 2010 | 20.vii.2010 | Positive | CAN: BC: East of Princeton, Old Hedley Road, ~ 2 km NW of Bromley Rock, access road @ intersection of gas and hydro lines | Likely BC Crown (MoTH) | 580 | underside of rocks | RGB, CC, DC (C) RGB (ID) |
3 |
- | 2012 | 17.vii.2012 | Positive | CAN: BC: East of Princeton, Old Hedley Road, ~ 2 km NW of Bromley Rock, access road @ intersection of gas and hydro lines | Likely BC Crown (MoTH) | 580 | underside of rocks, at base of stabilized talus slope along access road, open D-fir woods, south-facing shaded by firs and shrubberies | CC, DC, RGB | 3 |
5 | 2008 | 3.v.2008 | Positive | CAN: BC: East Chopaka, South Okanagan Grasslands Protected Area, ~2 km southwest of Kilpoola Lake | BC Crown; Park | 890 | underside of rocks, rocky outcrop, east-facing slope | RGB | 1 |
- | 2012 | 17.vii.2012 | Positive | CAN: BC: East Chopaka, South Okanagan Grasslands Protected Area, ~2 km southwest of Kilpoola Lake | BC Crown; park | 890 | underside of rocks, rocky outcrop, east-facing slope (west-facing slope on opposite side of this ridge did not have P. hesperus) | CC, DC, RGB | 3 |
6 | 1996 | 8.viii. 1996 |
Not detected | CAN: BC: East shore Skaha Lake, ~ 4.5 km south of Penticton | Unknown; Very close to Nature Trust property | 346 | pitfalls in antelope brush | GGES (C) RGB (ID) |
unknown |
7 | 2007 | 31.v. 2007 |
Not detected | CAN: BC: North shore of Kilpoola Lake, West of Osoyoos, near road access | Likely BC Crown | 821 | underside of rocks in pile, open area | RGB | 3 |
8 | 1992 | 9.iv-8.ix.1995 | Not surveyed in 2012; not detected in 2009 | CAN: BC: near Oliver, Kennedy Flats / McIntyre Canyon | Unknown. | 340-450 | pitfalls in antelope brush, several sites centred on area of stated lat/long | GGES (C) RGB (ID) |
unknown |
9 | 2001 | 28.ix. 2001 |
Not detected | CAN: BC: off Road 22, Haynes Lease, rock face of "The Throne", South of Oliver | BC Crown; Ecological Reserve | 390 | underside of rocks, southerly open exposure | RGB | 2 |
- | 2009 | 23.vi. 2009 |
Not detected | CAN: BC: off Rd 22, Haynes Lease, rock face of "The Throne", S of Oliver | BC Crown; Ecological Reserve | 390 | underside of rocks, southerly open exposure | RGB | 2 |
- | 1992 | 8.viii-9.ix. 1992 |
Not detected | CAN: BC: Oliver, Haynes Lease | BC Crown; Ecological Reserve | 360 | pitfall in antelope brush/cactus | GGES (C) CDD (ID) |
unknown |
10 | 1992 | 7.ix-4.x. 1992 |
Not surveyed | CAN: BC: Osoyoos, East Bench | Private? | 393 | pitfall in antelope brush by irrigation line in mixed agricultural/residential area | GGES (C) CDD (ID) |
unknown |
11 | 1995 | 7.vii-3.x. 1995 |
Site now agricultural | CAN: BC: Osoyoos, Osoyoos Indian Reserve 1 | Federal; Indian Reserve | 350 | pitfalls in antelope brush, several sites centred on area of stated lat/long | GGES (C) RGB (ID) |
unknown |
12 | 1982 | 10.viii.1982 | Positive | CAN: BC: Summerland, Peach Orchard cemetery | Private | 372 | pitfall in sagebrush above graveyard | WDC (C) RGB (ID) |
unknown |
- | 2012 | 16.vii.2012 | Positive | CAN: BC: Summerland, Peach Orchard cemetery | Private | 372 | underside of concrete landscaping blocks | CC, DC, RGB | 3 |
13 | 2012 | 16.vii.2012 | Positive | CAN: BC: Vaseux Lake, McIntyre Road, talus ~ 0.2 km east of highway | Unknown; may be within a protected area | 376 | underside of rocks, southwest-facing scree, shaded by dense saskatoons ( Amelanchier alnifolia). Site surveyed many times 2001-2011 with negative results for P. hesperus. | CC, DC, RGB | 3 |
14 | 2012 | 17.vii.2012 | Positive | CAN: BC: W of Hedley, Old Hedley Road, ~1 km West of intersection with highway 3 | BC Crown (MoTH) | 548 | underside of rocks, s of powerline right of way, open D-fir woods, shaded, south-facing slope | CC, DC, RGB | 3 |
15 | 2005 | 30.viii.2005 | Positive | CAN: BC: W of Hedley, Old Hedley Road, ~2 km W of intersection with highway 3 | BC Crown (MoTH) | 549 | underside of rocks, s of powerline right of way, open D-fir woods | RGB | 2 |
16 | 2006 | 29.v.2006 | positive | CAN: BC: W of Hedley, Old Hedley Road, 3.2 km W of highway bridge | BC Crown (MoTH) | 552 | underside of rocks, s of powerline right of way, open D-fir woods | RGB, LR (C) RGB (ID) | 2 |
- | 2012 | 17.vii.2012 | Positive | CAN: BC: W of Hedley, Old Hedley Road, Forest Service Rec. Site, ~3.2 km West of intersection with highway 3 | BC Crown | 552 | underside of rocks, s of powerline right of way, open D-fir woods | CC, DC, RGB | 3 |
17 | 2012 | 17.vii.2012 | Positive | CAN: BC: w of Keremeos, Ashnola River Rd, east-facing slope, west bank of river above gorge, ~1.7 km above first bridge | BC Crown (MoTH) | 571 | underside of rocks, open Douglas-fir habitat, shaded, east-facing exposure | CC, DC, RGB | 3 |
- | 2012 | 17.vii.2012 | Positive | CAN: BC: w of Keremeos, Ashnola River Rd, west-facing slope, east bank of river near mouth | BC Crown (MoTH) | 469 | underside of rocks, shaded, west-facing exposure | CC, DC, RGB | 3 |
Not applicable. | 1995 | 7.vii-10.ix.1995 | not checked | USA: WA: Oroville, just south of international boundary | Not applicable. | 360 | pitfalls, unknown habitat | GGES (C) RGB (ID) |
unknown |
Table summarizing search effort within Northwestern Cellar Spider habitat where no specimens were found during targeted surveys. Information includes date range, site searched, geographic coordinates, elevation, remarks, surveyor(s), and search effort.
Date Range | Site Searched | Elevation (m) | Remarks | Surveyors | Search Effort (hours) |
---|---|---|---|---|---|
- | - | - | - | Total Hours | 147 |
2001-2011 | CAN: BC: vicinity White Lake, Fairview/White Lake Road | ~ 540 | Many collections from underside of rocks and other suitable habitat, | RGB et al. | 12 |
1994 - 2011 | CAN: BC: White Lake Ranch | 630 | Undersides of rock, wood, and ranch debris | RGB | 1 |
1994 - 2011 | CAN: BC: Highway 3A, South shore Yellow Lake | 800 | Undersides of rock and wood | RGB | 4 |
1994 - 2011 | CAN: BC: White Lake Rd shale beds, north of radio telescope site | 572 | Undersides of rock | RGB | 1 |
1994 - 2011 | CAN: BC: vicinity Mahoney Lake, Green Lake Road | 475 | Undersides of rock and wood | RGB | 3 |
1994 - 2011 | CAN: BC: vicinity Okanagan Falls Provincial Park | ~ 340 | Undersides of rock and wood | RGB | 2 |
1994 - 2011 | CAN: BC: along west shore Vaseux Lake | 340 | Undersides of rock and wood | RGB | 3 |
2001-2011 | CAN: BC: Vaseux Lake, McIntyre Road, talus ~ 0.2 km East of Highway | ~350-390 | Many collections from underside of rocks and wood, (site produced P. hesperus in 2012 – see Table 2) | RGB | 9 |
1994 - 2011 | CAN: BC: near Oliver, Kennedy Flats / McIntyre Canyon | 450 | Undersides of rock and wood | RGB | 3 |
1994 - 2011 | CAN: BC: nr Vaseux Lake, various sites along McIntyre Ck. Road | ~ 360-500 | Undersides of rock and wood | RGB et al. | 12 |
1994 - 2011 | CAN: BC: Oliver, vicinity of UBC geology field camp | ~ 480 | Undersides of rock and wood | RGB et al. | 3 |
1994 - 2011 | CAN: BC: Osoyoos, var. locations along east side Osoyoos Lake ("Nk'Mip Pocket Desert") | ~ 340 | Undersides of rock and wood | RGB et al. | 6 |
1994 - 2011 | CAN: BC: Osoyoos, locations along e slope of Mt Kruger above golf course | ~ 360-470 | Undersides of rock, wood, rotting cow | RGB, MF | 3 |
1994 - 2011 | CAN: BC: Osoyoos, Richter Pass to Mt. Kobau summit | ~ 660-1800 | Undersides of rock and wood. (Also Blades and Maier 1996 study.) | RGB, MF | 6 |
1994 - 2011 | CAN: BC: nr SE shore of Kilpoola Lake, W of Osoyoos, nr road access | 830 | Undersides of rock and wood | RGB | 1 |
1994 - 2011 | CAN: BC: ~1.1 km S of Kilpoola Lake, disturbed grazed area, nr road access | 800 | Undersides of rock and wood | RGB | 1 |
1994 - 2011 | CAN: BC: ~1.3 km S of Kilpoola Lake, ridge top, west of road | 990 | Undersides of rock and wood | RGB, MF | 4 |
1994 - 2011 | CAN: BC: East Chopaka Protected Area, ~3.5 km SW of Kilpoola Lake | 940 | Undersides of rock | RGB | 1 |
1994 - 2011 | CAN: BC: East Chopaka Protected Area, ~4.5 km W of Kilpoola Lake | 1000 | Undersides of rock | RGB | 1 |
1994 - 2011 | CAN: BC: East Chopaka Protected Area, ~3.6 km W of Kilpoola Lake, at abandoned homestead | 940 | Undersides of wood and homestead debris | RGB | 1 |
1994 - 2011 | CAN: BC: East Chopaka Protected Area, ~3.6 km W of Kilpoola Lake, just w of abandoned homestead | 950 | Undersides of rock | RGB | 1 |
1994 - 2011 | CAN: BC: East Chopaka Protected Area, ~3.4 km W of Kilpoola Lake | 970 | Undersides of rock and wood, disturbed area (logging debris and cattle grazing) | RGB | 1 |
1994 - 2011 | CAN: BC: Chopaka, Highway 3 @ Chopaka/Nighthawk Rd, west of rd | 470 | Undersides of wood, debris in heavily grazed area | RGB, MF | 2 |
1994 - 2011 | CAN: BC: just NW of Chopaka/Nighthawk border crossing | 460 | Undersides of rock and wood in shallow ravines | RGB, MF | 3 |
1994 - 2011 | CAN: BC: Cawston, var locations along Old Fairview Rd / Blind Ck. | ~ 490- 900 | Undersides of rock and wood | RGB et al. | 8 |
1994 - 2011 | CAN: BC: Hedley, Hedley/Nickelplate Rd, top of slide above 1st set of switchbacks | 980 | Undersides of rock, wood, and debris | RGB, CC, DC | 3 |
1994 - 2011 | CAN: BC: nr. Keremeos, various sites along Ashnola River Valley | ~ 700-1000 | Undersides of rock, wood, and debris | RGB et al. | 18 |
1994 - 2011 | CAN: BC: Princeton, ~ 14 km north on Highway 5a | 760 | Undersides of rock | RGB, CC, DC | 3 |
1994 - 2011 | CAN: BC: Princeton, ~ 9 km north on Highway 5a @ Summers Ck. Road | 725 | Undersides of rock and wood | RGB, CC, DC | 3 |
1994 - 2011 | CAN: BC: Tulameen, south entry to town along Trans-Canada trail | 780 | Undersides of rock and wood | RGB | 1 |
1994 - 2011 | CAN: BC: Coalmont, n side of town along Trans-Canada trail | 750 | Undersides of rock and wood | RGB | 1 |
16.vii. 2012 |
CAN: BC: Summerland, Giants Head Peak | 820 | Searched underside of rocks and wood, north and south-facing slopes near peak, open Douglas-fir, shaded | C. Copley, D. Copley, and R.G. Bennett | 3 |
16.vii. 2012 |
CAN: BC: Penticton, Madeline/Max Lake | 500 | Searched underside of rocks, wood and debris, east-facing slope at edge of overgrown field, open Douglas-fir, shaded | C. Copley, D. Copley, and R.G. Bennett | 3 |
16.vii. 2012 |
CAN: BC: east shore Skaha Lake, ~ 4.5 km s of Penticton, Nature Trust property at roadside pond | 346 | Searched underside of rocks, wood and debris, west and northwest-facing slopes south of pond, open Douglas-fir, disturbed site | C. Copley, D. Copley, and R.G. Bennett | 3 |
16.vii. 2012 |
CAN: BC: Okanagan Falls, Allendale Rd, n of Blue Mtn Vineyards | 446 | Searched underside of rocks and wood, west-facing slopes , open Douglas-fir, shaded | C. Copley, D. Copley, and R.G. Bennett | 3 |
17/vii. 2012 |
CAN: BC: off Rd 22, Haynes Lease, rock face of "The Throne", S of Oliver | 390 | Underside of rocks, southerly open exposure ( P. hesperus records in previous years) | C. Copley, D. Copley, and R.G. Bennett | 2 |
17.vii. 2012 |
CAN: BC: Oliver, Haynes Lease | 360 | Searched underside of wood and other debris, cactus field to w of Throne ( P. hesperus records in previous years) | C. Copley, D. Copley, and R.G. Bennett | 1 |
17.vii. 2012 |
CAN: BC: N shore of Kilpoola Lake, W of Osoyoos, nr road access | 82 | Underside of rocks in pile, open area ( P. hesperus records in previous years) | C. Copley, D. Copley, and R.G. Bennett | 3 |
17.vii. 2012 |
CAN: BC: East Chopaka Protected Area, ~2 km SW of Kilpoola Lake | 890 | Underside of rocks, rock outcrop, west-facing slope (east-facing slope on opposite side of this ridge supports P, hesperus) | C. Copley, D. Copley, and R.G. Bennett | 3 |
Table 4. Table identifying threats to Northwestern Cellar Spider sites (17 sites) in Canada based on the IUCN-CMP threats assessment calculator.
Site Number | Site Name | Land Ownership | 1.1 | 2.1 | 3.2 | 4.1 | 4.2 | 7.1 | 8.2 | 9.3 | 10.3 | 11.3 |
---|---|---|---|---|---|---|---|---|---|---|---|---|
Total Sites | - | - | 4 | 1 | 9 | 11 | 8 | 17 | 17 | 3 | 6 | 17 |
1 | CAN: BC: East of Hedley, near small stream crossing south end of Hedley / Nickelplate Road | Unknown | - | - | x? | x | x | x | x | - | x | x |
2 | CAN: BC: East of Princeton, Bromley Rock, Old Hedley Road, ~8km West of highway bridge | BC Crown | - | - | x? | x | x | x | x | - | x | x |
3 | CAN: BC: East of Princeton, Old Hedley Road, ~ 12.5 km east of junction with highway 5A | Likely BC Crown (Ministry of Transportation) | - | - | x? | x | x | x | x | - | x | x |
4 | CAN: BC: East of Princeton, Old Hedley Road, ~ 2 km NW of Bromley Rock, access road @ intersection of gas and hydro lines | Likely BC Crown (Ministry of Transportation) | - | - | x? | x | x | x | x | - | - | x |
5 | CAN: BC: East Chopaka, South Okanagan Grasslands Protected Area, ~2 km southwest of Kilpoola Lake | BC Crown | - | - | - | - | - | x | x | - | - | x |
6 | CAN: BC: East shore Skaha Lake, ~ 4.5 km south of Penticton | Unknown; close proximity to The Nature Trust private conservation property | x | - | - | x | - | x | x | - | - | x |
7 | CAN: BC: North shore of Kilpoola Lake, West of Osoyoos, near road access | Likely BC Crown | - | - | - | - | - | x | x | - | - | x |
8 | CAN: BC: near Oliver, Kennedy Flats / McIntyre Canyon | Unknown | - | - | - | x | - | x | x | - | - | x |
9 | CAN: BC: off Road 22, Haynes Lease, rock face of "The Throne", South of Oliver | BC Crown Ecological Reserve | - | - | - | - | - | x | x | x | - | x |
10 | CAN: BC: Osoyoos, East Bench | Private? | x | - | - | - | - | x | x | x | - | x |
11 | CAN: BC: Osoyoos, Osoyoos Indian Reserve 1 | Federal; Indian Reserve | x? | x? | - | - | - | x? | x? | x? | - | x? |
12 | CAN: BC: Summerland, Peach Orchard cemetery | Private | x | - | - | - | - | x | x | - | x | x |
13 | CAN: BC: Vaseux Lake, McIntyre Road, talus ~ 0.2 km east of highway | Unknown; may be within protected area | - | - | x? | x | - | x | x | - | x | x |
14 | CAN: BC: W of Hedley, Old Hedley Road, ~1 km West of intersection with highway 3 | BC Crown | - | - | x? | x | x | x | x | - | x | x |
15 | CAN: BC: W of Hedley, Old Hedley Road, ~2 km W of intersection with highway 3 | BC Crown | - | - | x? | x | x | x | x | - | x | x |
16 | CAN: BC: W of Hedley, Old Hedley Road, Forest Service Rec. Site, ~3.2 km West of intersection with highway 3 | BC Crown | - | - | x? | x | x | x | x | - | x | x |
17 | CAN: BC: w of Keremeos, Ashnola River Rd, west-facing slope, east bank of river near mouth | BC Crown | - | - | x? | x | x | x | x | - | x | x |
Surveys confirm P. hesperus is restricted to rocky habitats in a narrow low-elevation band along the Similkameen Valley and at scattered sites in the southern Okanagan Valley (Figure 5). Surveys have been done in urban environments in the region and the species has not been recorded in cellars or human-made structures within urban areas historically, or in recent, dedicated surveys.
To date surveys in the lower Similkameen Valley have focused on the northeastern side of the valley, including the Ashnola Valley. The distribution of P. hesperus is not known in the First Nations lands (Lower Similkameen Indian Band) on the southwestern side of the valley (more than 17,000 ha from Hedley to Keremeos to Cawston and the international border [Statistics Canada 2012a]). However, suitable rock habitat may be widely separated south of the Cawston area (see “Other” habitat types, in Public Utility District No. 1 of Okanogan County [2009]).
Surveys in the Okanagan Valley have focused on known sites and habitats where permission to survey was obtained. Large portions of habitat on the east side of the valley (e.g., approximately 13 000 ha of First Nations land around Oliver, Osoyoos, and Osoyoos Lake areas [Statistics Canada 2012a]) may have potential habitat for P. hesperus, based on previous collection records (e.g., Osoyoos Indian Reserve 1).
Loose talus habitats are considered unsuitable and the majority of rock habitat in the Okanagan and Similkameen Valleys that is talus does not appear suitable. The Similkameen Valley in WA has not been well surveyed (Crawford pers. comm. 2012). However there is also much unsuitable habitat, such as the alkali flats south of Chopaka/Nighthawk international border crossing, open sagebrush grassland and eroded silt slopes between the community of Nighthawk (international border) and Shanker’s Bend (United States) (see Vegetation and Habitat Types in Public Utility District No. 1 of Okanogan County [2009]).
Conversely, the more common and broadly distributed Pholcophora americana is recorded widely in southern BC (Figure 5). Since 2006 there has been substantial search effort that has specifically targeted spiders throughout BC (Copley pers. comm. 2013) (Figure 5). Each dot shown in Figure 5 represents search effort of at least 1.5 hours per site since 2008.
Habitat
Habitat Requirements
Psilochorus hesperusis associated with hot, dry and arid environments characteristic of the Great Basin ecosystem. In BC ecosystems are described as biogeoclimatic zones, a vegetative classification system developed by the BC Ministry of Forests (2009). Psilochorus hesperus habitat is within the Bunchgrass (sagebrush-steppe) and Ponderosa Pine (open parkland) biogeoclimatic zones of the Southern Interior Ecoprovince in the southernmost parts of the Similkameen and Okanagan valleys (Demarchi 2011; Figure 4). The species occupies xeric sites of the driest variant of the Bunchgrass zone (BGxh1 Very Hot Dry Bunchgrass) and margins of the Ponderosa Pine zone (PPxh1subzone Very Hot Dry Ponderosa Pine) (BC Ministry of Forests 2009).
Psilochorus hesperusis associated with specific rock undersurfaces that provide stable, cool and humid microclimatic conditions within an otherwise hot external environment (Figure 7 – 12 and 14) (Bennett unpubl. data; Crawford pers. comm. 2013). Spatially, rocky undersurfaces have open space for territorial and individual movement and are not flush with the underlying substrate (Bennett unpubl. data). Occupied rocks are stable and unlikely to be dislodged (i.e., rocks in active talus slopes are unsuitable habitat). The dimensions of suitable rock habitat are difficult to generalize. However, individual females appear to require a territorial area of about 10-15 cm diameter (Bennett unpubl. data).
Rocks occupied by P. hesperus are typically protected from full-day sun exposure (Figure 6-9) (Bennett unpubl. data) provided by open forest cover dominated by Douglas-fir (Pseudotsuga menziesii), Ponderosa Pine [Pinus ponderosa]), shrubs such as Oceanspray (Holodiscus discolor) and other vegetation characteristic of these ecosystems. The spider is less commonly recorded from similar rocky areas within open bunch grass vegetation with no forest cover. In the absence of shading factors, rocks on north- and east-facing slopes will host P. hesperus while similar rocks on south- or west-facing slopes will be less likely to.
Psilochorus hesperusrecords from woody substrates are considered anomalous (Bennett unpubl. data; R. Crawford pers. comm. 2013).
Habitat Trends
Substantial historical habitat loss has been documented within the lower-elevation grassland ecosystems of the Okanagan and Similkameen valleys (see Lea 2008). The habitat trends within the range of P. hesperus that apply specifically to the rock habitat (for residence) and suitable wandering/dispersal habitat needed to link these rocky sites are difficult to quantify. The current and historic use of rocky outcrops and other rock habitats for road construction materials and other resource extraction purposes is not well documented for the Okanagan and Similkameen valleys.
However, some general habitat trends can be inferred. The majority of the Canadian range of P. hesperus overlaps with the Okanagan-Similkameen Regional District, which has a current human population of 81,000 that is projected to increase 34% to 108,000 by 2031 (Regional District of Okanagan-Similkameen 2012; Statistics Canada 2012b). With this human population increase comes the need for further urban, rural and agricultural development. Historic ecosystem mapping for some of the Antelope-brush bunchgrass ecosystems shows a 67.4% loss to development (Iverson 2012).
Agriculture is one of the major economic drivers in the range of P. hesperus. For example, the lower Similkameen and south Okanagan Valleys have the largest concentration of vineyards in Canada (Regional District of Okanagan-Similkameen 2012). Vineyard area (ha) in BC increased between 1989 (445 ha) and 2011 (3946 ha) by almost 900% (British Columbia Ministry of Agriculture, Food and Fisheries 2004; Lea 2008; Simms 2012). The majority of vineyard development has been in the south Okanagan and lower Similkameen Valleys (see Threats).
Biology
Information on P. hesperus is summarized from Huber (2005) and Slowik (2009) and from unpubl. data (Bennett pers. comm. 2012; Huber pers. comm. 2012; Slowik pers. comm. 2012).
Life Cycle and Reproduction
Pholcid life cycles are poorly understood. Collection and search effort data (see Table 2 and 3) suggest P. hesperus has a one-year life span, although adult females are generally present year-round. Adult females and juveniles overwinter; adult males and new adult females mature in early spring; adult males are unlikely to be encountered after late summer (Bennett unpubl. data; Slowik 2009).
Psilochorus spiders live in small webs composed of a few lines of silk (Bennett unpubl. data; Huber 2005; Slowik 2009). Mating has not been observed. As in most spider species, a mature male spins a small sperm web, deposits a drop of sperm and transfers it to the genital bulbs of his palpi prior to courtship of females and mating. Mated female pholcid spiders generally produce and guard a series of egg sacs over several months resulting in a series of juvenile age classes (Huber pers. comm. 2012). Female P. hesperus produce and guard one egg sac at a time and each sac is a loosely bound ball of up to about two dozen eggs carried in the mother’s jaws.
Physiology and Adaptability
There is no information on the physiology or adaptability of P. hesperus. Artificial objects such as cement blocks (see Figure 9) may mimic microclimatic conditions and spatial territory requirements (e.g., site 12 Summerland site).
The general public as well as arachnologists regularly and routinely sample non-natural habitats throughout the world. While this search effort is not quantifiable, it is significant and assumed synanthropic records of P. hesperus would be recorded during such widespread searches. Within its Canadian range (as well as in the Okanogan Valley in WA) the only synanthropic record for the species is Peach Orchard Cemetery in Summerland (site 12). This population may be the result of passive anthropogenic dispersal via artificial substrate (concrete landscaping blocks, origin unknown). The cemetery is the northernmost P. hesperus site, surrounded by unsuitable habitat which has been searched (Copley pers. comm. 2013), and the nearest extant site is more than 35 km to the south.
Dispersal and Migration
Psilochorus hesperusis known to disperse short distances from occupied sites by wandering overland (Bennett unpubl. data). Pitfall trapping data (Site 6, 8, 9, 10 and 11, Table 2) suggest adult males, females and juveniles wander from rock substrates at night during the summer months. Dispersal is likely in response to crowding (which leads to cannibalism) and/or a lack of suitable prey; both of which are known behaviours for spiders (Duffey 1998; Foelix 2011). Mature males wander in search of receptive mature females (Foelix 2011).
Several species of pholcids, including at least one species of Psilochorus, are well-known synanthropes and easily dispersed by humans (Bennett unpubl. data; Huber 1994, 2005, pers. comm.; Slowik 2009, pers. comm.). Psilochorus hesperus may be dispersed passively through the transportation of rocks or artificial substrates (Bennett unpubl. data; J. Slowik pers. comm. 2013) (see Physiology and Adaptability). Synanthropic dispersal of P. hesperus is an unlikely occurrence in northern parts of its range, mainly because of widely separated areas of occupied habitat and overall small populations.
The ability of P. hesperus to recolonize large rocks within disturbed habitats has not been studied. Within BC, at least 10 of the 17 sites (59%) are adjacent to roadsides, suggesting the species may have an ability to slowly recolonize the undersurfaces of large suitable rocks within disturbed habitats, from adjacent natural habitats. In WA, P. hesperus has been recorded from under rocks within disturbed habitats such as roadside and railroad right-of-ways, at nine out of 82 collection sites (approximately 11% of sites). It is assumed the species colonized these disturbed habitats from adjacent natural habitats.
Aerial ballooning is a common dispersal mechanism in many spider families (Greenstone et al. 1987; Bennett unpubl. data 2003; Foelix 2011) but has not been observed nor is likely in pholcids (Huber pers. comm. 2012; Bennett unpubl. data).
Interspecific Interactions
Interspecific interactions for P. hesperus have not been well documented. Psilochorus spiders are often found in close association with the webs of other spiders (Gertsch 1979), especially cobweb weavers (Family Theridiidae), which may be common in the same rocky habitats. For example, Slowik (2009) documented P. imitatus living within the web of a species of Steatoda. P. hesperus has also been recorded living in the webs of Western Black Widows (Latrodectus hesperus) (R. Bennett (unpubl. data).
Psilochorus hesperusare generalist predators and consume insects and other spiders. Spider wasps (Hymenoptera: Pompilidae) are significant predators of spiders (Gertsch 1979; Foelix 2011). Other predators of spiders include insects, other spider species, frogs, birds and small mammals such as shrews. Fungal infections and nematodes often affect spiders (Gertsch 1979; Foelix 2011). Specimens of P. hesperus dispersing from the protection of their rock habitats at night are especially vulnerable to predation by bats and other nocturnal species.
Population Sizes and Trends
Sampling Effort and Methods
There are no studies on population sizes and trends. Targeted P. hesperus sampling to date (2012) has primarily been to record the species’ presence and range in BC (Table 2).
Abundance
Abundance estimates are not possible to calculate based on existing data.
Fluctuations and Trends
Population fluctuation and trends are unknown. However, inferences from presence/not detected data (Table 2 and 3) are available. Sites in the Similkameen Valley have remained occupied between 2001 and 2012. However, populations at four sites in the Okanagan Valley were not detected in 2012: Site 7 Kilpoola Lake (present 2007, not recorded 2012); Site 9a Haynes Lease (present 1992, not recorded 2012); Site 9b Haynes Lease “The Throne” (present 2001 and 2009, not recorded 2012); Site 8 Kennedy Flats (present 1995, not recorded 2009); Site 6 East shore Skaha Lake (present 1996, not recorded 2012). Similarly Site 13 McIntyre Road (undetected 2001 – 2011)was not recorded until 2012. Known populations of P. hesperus in the Okanagan Valley are in open, exposed rocky habitats (e.g., Figure 6, 8) while those in the Similkameen are in rocky habitats with some vegetative protection (Figure 7). These factors may contribute to presence/not-detected records at Okanagan valley sites.
Rescue Effect
The Okanagan and Similkameen valleys span the US border and join at Oroville to become Okanogan Valley in WA. Psilochorus hesperus was caught by pitfall trapping in 1995, less than 1.5 km south of the international border (Table 2). The next nearest P. hesperus site in WA is 35 km south near Tonasket (Crawford unpubl. data) (see Distribution). Potential habitat in the Okanogan Valley from the international boundary south of Tonasket is agricultural (Google Inc. 2011). However, that corridor and its tributaries have not been well surveyed, especially in the US portions of the Similkameen Valley between Oroville and the international boundary. This area does contain a small amount of potential habitat that could provide important linkages between populations in the US (see Vegetation and Habitat Types in Public Utility District No. 1 of Okanogan County [2009]).
Threats And Limiting Factors
Background
The International Union for Conservation of Nature-Conservation Measures Partnership (2006) (IUCN-CMP) threats calculator was used to classify and list threats to P. hesperus (Salafsky et al. 2008; Master et al. 2009). Results of the calculator suggest an overall low threat impact (Table 5). Threats applicable to P. hesperus are discussed below.
Table 5-a. Level 1 Threat Impact Counts for Southern Mountain Population
- Species Name:
- Northwestern Cellar Spider ( Psilochorus hesperus)
- Date:
- September 10, 2013; updated February 28, 2014
- Assessed by:
- Jennifer Heron (Arthropods SSC Co-chair), Claudia Copley (Royal British Columbia Museum), Orville Dyer (BC Ministry of Forests, Lands and Natural Resource Operations), Dave Fraser (BC Ministry of Environment).
Threat Impact | Level 1 Threat Impact Counts high range |
Level 1 Threat Impact Counts low range |
---|---|---|
Calculated Overall Threat Impact: | Low | Low |
Very High | 0 | 0 |
High | 0 | 0 |
Medium | 0 | 0 |
Low | 3 | 3 |
Table 5-B. Matrix summarizing the results of IUCN-CMP threats calculator applied to the Northwestern Cellar Spider.
Threat Number |
Threat Classification |
Impact (calculated) |
Scope (next 10 Yrs) | Severity (10 Yrs or 3 Gen.) | Timing | Comments |
---|---|---|---|---|---|---|
1 | Residential & commercial development | Low | Small (1-10%) | Slight (1-10%) | High (Continuing) | Cumulative impacts of housing and industrial development surrounding the urban centres of Canada, specifically in southern regions approximately 200km from the US border. |
1.1 | Housing & urban areas | Low | Small (1-10%) | Slight (1-10%) | High (Continuing) | Some sites are within private land and there is potential for urban development. Areas around Skaha Lake, Osoyoos East bench and within Osoyoos Indian Reserve1 (although this site is presumed extirpated). |
1.2 | Commercial & industrial areas | - | Unknown | Unknown | Unknown | Applies to potential unchecked habitat. For example, a prison is being constructed in some open grassland habitat, between Oliver and Osoyoos on the east side of the Okanagan Valley. Other forms of commercial development, such as an industrial park (within the same area as the prison) are ongoing. Impacts to specific rocky habitats are unknown. |
1.3 | Tourism & recreation areas | - | - | - | - | Not applicable. |
2 | Agriculture & aquaculture | Low | Small (1-10%) | Extreme (71-100%) | High (Continuing) | - |
2.1 | Annual & perennial non-timber crops | Low | Small (1-10%) | Extreme (71-100%) | High (Continuing) | Applies to potential unchecked habitat. Agricultural intensification in lower-elevation areas surrounding urban centres of Canada. Although this threat is historical, intensification of agricultural practices has occurred within these agricultural areas. |
2.2 | Wood & pulp plantations | - | - | - | - | Not applicable. |
2.3 | Livestock farming & ranching | - | - | - | - | Not applicable. |
2.4 | Marine & freshwater aquaculture | - | - | - | - | Not applicable. |
3 | Energy production & mining | Negligible | Negligible (<1%) | Moderate (11-30%) | Moderate (Possibly in the short term, < 10 yrs) | - |
3.1 | Oil & gas drilling | - | - | - | - | Not applicable. |
3.2 | Mining & quarrying | Negligible | Negligible (<1%) | Moderate (11-30%) | Moderate (Possibly in the short term, < 10 yrs) | Possible minor gravel and road materials extraction from areas along roadways. This is likely to not impact the entire habitat polygon. |
3.3 | Renewable energy | - | - | - | - | Not applicable. |
4 | Transportation & service corridors | Low | Small (1-10%) | Slight (1-10%) | Moderate (Possibly in the short term, < 10 yrs) | - |
4.1 | Roads & railroads | Low | Small (1-10%) | Slight (1-10%) | Moderate (Possibly in the short term, < 10 yrs) | Road maintenance and construction materials within rock areas adjacent to roadways. The threat has the potential to destroy a specific occupied habitat, although it is unlikely to destroy all rocky potentially occupied habitats along an entire stretch of roadway. Threat is large (11/16 sites) but severity was scored lower because the entire rocky habitat will not likely be impacted. |
4.2 | Utility & service lines | Low | Small (1-10%) | Slight (1-10%) | Moderate (Possibly in the short term, < 10 yrs) | Pipeline construction and maintenance can directly impact P. hesperus habitat, especially within the pipeline right-of-way. In some cases, vegetation and debris that has accumulated in the right-of-way could be deposited on the adjacent areas and impact dispersal and occupied sites. Where undisturbed P. hesperus habitat occurs adjacent to the pipeline and hydroelectric corridors, observational data suggest the species is able to disperse into and occupy suitable new habitat in the corridors following construction/maintenance disturbance events and once sufficient time has passed. For example, P. hesperus is recorded in stabilized rocks adjacent to pipeline and hydroelectric corridor access roads at two sites (site 1 and 2) along the Old Hedley Road. More study is required. This threat is likely to impact eight sites. |
4.3 | Shipping lanes | - | - | - | - | Not applicable. |
4.4 | Flight paths | - | - | - | - | Not applicable. |
5 | Biological resource use | - | - | - | - | Not applicable. |
5.1 | Hunting & collecting terrestrial animals | - | - | - | - | Not applicable. |
5.2 | Gathering terrestrial plants | - | - | - | - | Not applicable. |
5.3 | Logging & wood harvesting | - | - | - | - | Not applicable. |
5.4 | Fishing & harvesting aquatic resources | - | - | - | - | Not applicable. |
6 | Human intrusions & disturbance | - | - | - | - | - |
6.1 | Recreational activities | - | - | - | - | Not applicable. |
6.2 | War, civil unrest & military exercises | - | - | - | - | Not applicable. |
6.3 | Work & other activities | - | - | - | - | Not applicable. |
7 | Natural system modifications | Not a Threat (in the assessed timeframe) |
Small (1-10%) | Extreme (71-100%) | Low (Possibly in the long term, >10 yrs) | - |
7.1 | Fire & fire suppression | - | Pervasive (71-100%) | Unknown | Moderate (Possibly in the short term, < 10 yrs) | Fires are possible within the species' range. Fires would impact the trees and shrubs shading occupied rocky areas, thus affecting the cooling affect these plants have on occupied rocky substrates and the microclimatic conditions needed for these spiders. |
7.2 | Dams & water management/use | Not a Threat (in the assessed timeframe) |
Small (1-10%) | Extreme (71-100%) | Low (Possibly in the long term, >10 yrs) | Proposed dam sites within the lower Similkameen, in the US. |
7.3 | Other ecosystem modifications | - | - | - | - | Not applicable. |
8 | Invasive & other problematic species & genes | - | Pervasive (71-100%) | Unknown | High (Continuing) | - |
8.1 | Invasive non-native/alien species | - | Pervasive (71-100%) | Unknown | High (Continuing) | There are likely invasive plants at all sites but the impact of invasive plants is unknown. |
8.2 | Problematic native species | - | - | - | - | Not applicable. |
8.3 | Introduced genetic material | - | - | - | - | Not applicable. |
9 | Pollution | - | Restricted (11-30%) | Unknown | High (Continuing) | - |
9.1 | Household sewage & urban waste water | - | - | - | - | Not applicable. |
9.2 | Industrial & military effluents | - | - | - | - | Not applicable. |
9.3 | Agricultural & forestry effluents | - | Restricted (11-30%) | Unknown | High (Continuing) | Pesticide drift from adjacent agricultural areas into occupied sites is a potential threat. This threat applies to three sites. |
9.4 | Garbage & solid waste | - | - | - | - | Not applicable. |
9.5 | Air-borne pollutants | - | - | - | - | Not applicable. |
9.6 | Excess energy | - | - | - | - | Not applicable. |
10 | Geological events | Negligible | Restricted (11-30%) | Negligible (<1%) | Moderate (Possibly in the short term, < 10 yrs) | Over the short-term small landslides, debris, silting and slumping may cause the local extirpation of populations. Over the longer term, populations may be able to recolonize suitable rocks from areas in the habitat polygon that were not disturbed. |
10.1 | Volcanoes | - | - | - | - | Not applicable. |
10.2 | Earthquakes/tsunamis | - | - | - | - | Not applicable. |
10.3 | Avalanches/landslides | Negligible | Restricted (11-30%) | Negligible (<1%) | Moderate (Possibly in the short term, < 10 yrs) | Small landslides and slumping are possible at some sites. The type of debris that is in the landslide will determine the impact to the spider. If the debris is silt or clay, the landslide could fill or seep into the territorial spaces under occupied rocky sites. This threat is possible at six sites. |
11 | Climate change & severe weather | - | - | - | - | Not applicable. |
11.1 | Habitat shifting & alteration | - | - | - | - | Not applicable. |
11.2 | Droughts | - | - | - | - | Not applicable. |
11.3 | Temperature extremes | - | Unknown | Unknown | High (Continuing) | Temperature extremes at some sites, especially if areas are cleared or exposed from other threats (e.g., road construction, maintenance, wildfire, etc.). |
11.4 | Storms & flooding | - | - | - | - | Not applicable. |
Residential or Commercial Development (Threat 1)
1.1 Housing and Urban Areas.
Population growth in the Okanagan-Similkameen Regional District from 2011- 2031 is projected at more than 30% (Regional District of Okanagan-Similkameen 2012) (see Habitat Trends). The Regional Growth Strategy aims to protect sensitive habitats; however, this region has some of Canada’s most desirable real estate and there is constant pressure to build ( e.g., see http://www.regalridge.com/). Although trend data are not available for specific rocky areas, residential development continues on open slopes (dispersal habitat) and rocky outcrops (nest habitat).
This threat applies to potential habitat. For example, unsurveyed rock habitat on the western slopes of Anarchist Mountain has been converted to residential development. Blasting and filling of rock outcrops occurred on the east side of Skaha Lake (Dyer pers. comm. 2013).
Agriculture et Aquaculture (Threat 2)
2.1 Annual and Perennial Non-Timber Crops
Agricultural development (specifically vineyard development) has increased substantially from 1989 and 2011 (see Habitat Trends) (British Columbia Ministry of Agriculture, Food and Fisheries 2004; Lea 2008; Simms 2012). During this development, significant dispersal habitat for P. hesperus was also converted. For example, low elevation bunchgrass grasslands have decreased by about 70% since the 1800s (see Lea 2008) particularly along the east side of the Okanagan Valley from Vaseux Lake to Osoyoos (see Figures 8, 9 in Lea 2008). This area also corresponds to all recorded sites for P. hesperus in this valley. Valley bottom areas of the lower Similkameen Valley between Keremeos and the international boundary have also been converted to agricultural purposes (Google Earth 2011).
This threat applies to potential habitat. In the past, agricultural development eliminated site 11 (Osoyoos Indian Reserve 1).
Energy Production and Mining (Threat 3)
3.2 Mining and Quarrying
Sites with proposed mining and gravel extraction within the range of P. hesperus are currently under review, and government staff are regularly asked to review potential applications for conservation values. Staff are most likely not aware of this species and the importance of conservation of rocky habitats for the species.
This threat applies to sites adjacent to roadways, where sites could be designated as a source of gravel, rock or road materials that are necessary for road maintenance in the area. This threat also applies to potential habitat.
Transportation and Service Corridors (Threat 4)
4.1 Roads and railroads.
The major highways of the lower Similkameen Valley (Highway 3), Okanagan Valley around Skaha Lake, Vaseux Lake and McIntyre Bluffs (Highway 97) and at Osoyoos (Highway 3 and 97) are dispersal barriers for P. hesperus. Highway 3 traverses known or potential habitat from Princeton to the west side of Richter Pass and crosses the Okanagan Valley between the west side of Richter Pass on Mount Kobau to Anarchist Mountain. In the Okanagan Valley, particularly on the approaches to Anarchist Mountain west of Osoyoos, the highway traverses P. hesperus sites. Highway 97 at Skaha Lake/Vaseux Lake/McIntyre Bluffs for P. hesperus sites and potential habitat.
Highway maintenance and expansion may destroy roadside habitats. For example, about 6 km upstream from Hedley, P. hesperus occupies habitat immediately adjacent to the Similkameen River bridge. Replacement of this bridge and the associated rerouting of Highway 3 in the 1990s likely destroyed rocky habitat.
This threat applies to most sites adjacent to roadways or along transportation corridors (11 sites). At some sites, the occupied rock habitat is not likely suitable but adjacent dispersal and surveyed areas (where no specimens have been recorded) may be impacted in the future.
4.2 Utility and Service Lines.
Pipeline construction and maintenance can directly impact P. hesperus habitat. A natural gas pipeline crosses the Okanagan Valley at Manuel Flats/Oliver, enters the lower Similkameen Valley at Keremeos, and follows two routes north through the valley (Fortis BC 2011). One route crosses the mouth of the Ashnola Valley and travels overland via the Paul Creek drainage to rejoin the Similkameen Valley near Princeton. The other route follows the valley bottom on the northeast side to Princeton, parallel with Highway 3 and the Old Hedley Road. This route travels through all the Old Hedley Road sites occupied by P. hesperus (site 1, 2, 3, 4, 14, 15, 16). For example, the Oliver to Ashnola River/Paul Creek pathway is included in 161 km of pipeline upgrading scheduled to commence in late 2014 (FortisBC 2011). This will involve extensive excavation and other forms of significant habitat disruption in or adjacent to P. hesperus habitat, especially in the vicinity of the mouth of the Ashnola River (site 17). This threat is likely to impact eight sites, although slow natural colonization may occur if the species inhabits suitable adjacent and undisturbed habitats.
A hydroelectric transmission corridor travels through P. hesperus habitat between Keremeos and Princeton and maintenance activities may impact sites.
Where undisturbed P. hesperus habitat occurs adjacent to the pipeline and hydroelectric corridors, observational data suggest the species is able to disperse into and occupy suitable new habitat in the corridors following construction/maintenance disturbance events and sufficient time has passed to allow the disturbed sites to stabilize (Bennett unpubl. data). For example, P. hesperus is recorded in stabilized rocks adjacent to pipeline and hydroelectric corridor access roads at sites 1 and 2 along the Old Hedley Road.
Natural System Modifications (Threat 7)
7.1 Fire and Fire suppression
Wildfires occur in the southern third of the province and consume large tracts of forest and grasslands annually in the interior including the Similkameen-Okanagan Regional District (see BC Ministry of Forests and Range 2012c). For example, the 2500 wildfires recorded in BC in 2003 were concentrated in the southern interior of the province and burned large amounts of habitat in the south Okanagan Valley including important P. hesperus habitats in the vicinity of Vaseux Lake (British Columbia Ministry of Forests and Range 2012b), McIntyre Road (British Columbia Ministry of Forests and Range 2012a) and Haynes Lease in the mid-1990s. Fires in dispersal habitat destroy individual spiders as well as the cover objects and other habitat that provide protective retreats for them during dispersal. Hot ground fires destroy spiders in their residences.
7.2 Dams and Water Management/Use and 7.3 Other Ecosystem Modifications
Historically, the Okanagan River and many of its tributaries were altered through dam construction, stream bed alteration, and other water management activities. Today approximately 7% of the Okanagan River remains in undisturbed condition (Lea 2008).
It is not possible to quantify the impact of historic water management activities on P. hesperus. Within the Similkameen Valley, water storage and hydroelectric dam projects are under consideration at Shanker’s Bend (upstream from Oroville in WA) and Copper Mountain (upstream from Princeton in BC). The Copper Mountain site (Garstin 2012) will not impact P. hesperus habitat. Shanker’s Bend has been a proposed dam site since the 1920s and could have significant impact on P. hesperus habitat in Canada. In 2006 the Okanogan Public Utility District began steps towards a dam (Boyer 2009; Washington State Department of Ecology 2011). However, plans for these dam options were shelved in 2011 due to widespread opposition (Washington State Department of Ecology 2011).
Pollution (Threat 9)
9.3 Agricultural and forestry effluents
The application of pesticides in the McIntyre Bluff and Osoyoos corridor are ongoing. The study of pesticide impacts on spiders began only recently; however, the negative impacts are now well documented ( e.g., see review in Maloney et al. 2003). The combination of land conversion and operational activities likely renders agricultural areas unusable as dispersal habitat and prevents the migration of individuals and establishment of populations in previously unoccupied suitable habitat.
Geological Events (Threat 10)
10.3 Avalanches/Landslides.
Psilochorus hesperus does not occupy unstable rocky habitats, such as steep talus slopes or areas with frequent falling rock. Most known sites occur in stabilized habitats on the margins of active rock habitat. Summerland Peach Orchard Cemetery is within a steep silt slope surrounded by some residential development and at risk from silt washouts or slumping.
Limiting Factors
Psilochorus hesperushas limited natural dispersal abilities, small population sizes, may be isolated due to the rocky habitat associations, and in crowded populations may exhibit cannibalism.
Numbers of Locations
There are at least 16 locations of P. hesperus in Canada, corresponding to the 16 extant sites: eight in the lower Similkameen Valley and eight in the south Okanagan Valley. One location at Summerland (site 12) is situated in an artificial rock wall within a cemetery and likely a result of human movement. This site is still considered extant and included in the number of locations. An additional site in the Okanagan Valley was converted to agricultural use, and the species is presumed extirpated. This site has not been resurveyed; however, there is a possibility the species could remain within small rocky areas surrounding the agricultural area that have not been converted. Based on search effort data and areas of potential habitat, there are an estimated 5 to 10 additional locations.
Protection, Status, and Ranks
Legal Protection and Status
Psilochorus hesperusis not protected under provincial or federal legislation. Invertebrates assessed by COSEWIC as Threatened, Endangered or Extirpated will be protected through theBritish Columbia Wildlife Act and Wildlife Amendment Act once the regulations listing these species are completed. The British Columbia Parks Act and Ecological Reserves Act protect species at risk within these areas, and when P. hesperus is assigned a conservation status rank the species will be protected under these acts. The species is a potential Identified Wildlife candidate under the provincial Forest and Range Practices Act due to the possibility of rock substrate extraction for road construction.
Non-Legal Status and Ranks
Psilochorus hesperusis provisionally assigned a conservation status rank of N2S2 (nationally and provincially imperilled) in Canada (NatureServe Canada 2010). The species has not been assigned a global conservation status rank. The 2010 Canada and BC General Status rank for P. hesperus is “2” (may be at risk) (Wild Species 2012). The species has not been assigned a global (Natureserve 2013) or provincial conservation status rank (British Columbia Conservation Data Centre 2013). The species has not been assigned a conservation status rank at the national or subnational level in the United States. There are currently no international laws that protect this spider in other parts of its global range.
Habitat Protection and Ownership
Psilochorus hesperusis recorded within three provincial protected areas: Haynes Lease Ecological Reserve, Bromley Rock Provincial Park and South Okanagan Grasslands Protected Area (East Chopaka Site); one private conservation area (Skaha Conservation Area owned by The Nature Conservancy); and one federal protected area (the Northeast and Southeast Uplands Units of the Vaseux-Bighorn National Wildlife Area).
Sites on provincial Crown land are managed under the British Columbia Forest and Range Practices Act; however, the species is not listed as Identified Wildlife under this act and thus not protected (e.g., Old Hedley Road sites 3 and 4 [other than at Bromley Rock], Kilpoola Lake [site 7], and Ashnola River [site 17]).
A few sites are managed by First Nations (Site 17 Ashnola River and Site 11 Osoyoos Indian Reserve 1) or are private property ( e.g., Site 10 Osoyoos East Bench and Site 12 Summerland Peach Orchard Cemetery).
A Regional Growth Strategy (RGS) has been developed (Regional District of Okanagan-Similkameen 2012) that provides guidelines and policies for the protection of sensitive ecosystems. The document focuses on wetland protection and includes caveats such as “the right to farm”. However, the conservation value of the lower Similkameen and south Okanagan Valleys as a national biodiversity hotspot is well known, and the Strategy Steering Committee includes representation from Environment Canada, Natural Resources Canada, and the BC Ministry of Environment.
Acknowledgements and Authorities Contacted
The following people are gratefully thanked for their contributions to the preparation of this status report in the form of background information, logistical support, shared data, mapping, expert opinion, and/or field assistance. From the British Columbia provincial government – Orville Dyer (Ecosystems Biologist, Ministry of Forests, Lands and Natural Resource Operations, Penticton, BC), Dave Fraser (Scientific Authority Assessment, Ministry of Environment, Victoria, BC), Jennifer Heron (Invertebrates Specialist, Ministry of Environment, Vancouver, BC), and Leah Ramsay (Program Zoologist, Conservation Data Centre, Victoria, BC); from the COSEWIC Secretariat, Gatineau, QC – Angele Cyr (Scientific Project Officer), Wendy Dunford (Recovery Management), Alain Filion (Scientific and GIS Project Officer, mapping support), Monique Goit (Scientific Project Officer), Neil Jones (Scientific Project Officer and ATK Coordinator), Sonia Schnobb (Program Support Specialist), and Shirley Sheppard (Administrative Specialist); from the Royal British Columbia Museum, Victoria, BC – Rob Cannings (Curator of Entomology), Claudia Copley (Collections Manager), and Darren Copley; from the University of British Columbia – Launi Lucas (Department of Zoology), Karen Needham (Collections Manager, Spencer Entomological Museum), and Geoff Scudder (Professor Emeritus, Department of Zoology).
From elsewhere – Paul Catling (COSEWIC Arthropods Specialists Subcommittee, Ottawa, ON), J. Coddington and D. DeRoche (Entomology, Smithsonian Institution, National Museum of Natural History, Washington, DC), R.C. Crawford (Pacific Northwest regional spider expert, Burke Museum of Natural History and Culture, Seattle, WA), B. Huber (world Pholcidae expert, Zoologisches Forschungsmuseum Alexander Koenig, Bonn, Germany), L. Leibensperger (Invertebrate Zoology, Museum of Comparative Zoology, Harvard, MA), N. Platnick and L. Sorkin (Entomology, American Museum of Natural History, New York, NY), J. Slowik (Nearctic Psilochorus expert, University of Alaska Museum of the North, Fairbanks, AK), and D. Ubick (California Academy of Sciences, San Francisco, CA). All spider photographs by Darren Copley.
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Biographical Summary of Report Writer(s)
Robb Bennett holds MSc and PhD degrees earned from the study of spider taxonomy and systematics. He is a Fellow of the Entomological Society of Canada and currently works as a research associate at the Royal British Columbia Museum, and an entomology/arachnology and invasive species consultant. Previously he worked as a forest insect management specialist, mentored over two dozen graduate and an undergraduate student, served on a variety of professional administrative committees and boards of directors, and was a member of the COSEWIC Arthropod Specialists Subcommittee and Editor-in-Chief of The Canadian Entomologist.
Collections Examined
American Museum of Natural History. E-mail correspondence between R. Bennett and N. Platnick and L. Sorkin, October 2012 (no Canadian specimens).
California Academy of Sciences. E-mail correspondence between R. Bennett and D. Ubick, October 2012 (no Canadian specimens).
Canadian National Collection of Insects and Arachnids (Ottawa, ON). Collections examined by R. Bennett, May 2012.
Museum of Comparative Zoology. E-mail correspondence between R. Bennett and L. Leibensperger, October 2012 (no Canadian specimens).
Royal British Columbia Museum, Victoria, British Columbia. Collections examined by R. Bennett and C. Copley, September 2012.
Smithsonian Institution. E-mail correspondence between R. Bennett and J. Coddington and D. DeRoche, October 2012 (no Canadian specimens).
Spencer Entomological Museum. Collections examined by R. Bennett and D. Copley, August 2010 (no specimens).
University of Washington Burke Museum. E-mail correspondence between R. Bennett and R. Crawford, September 2012 (no Canadian specimens).
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