Sand-verbena moth (Copablepharon fuscum) COSEWIC assessment and status report: chapter 6
Distribution
Copablepharon fuscum has been recorded in eight sand-dominated coastal sites such as spits and dunes surrounding the Strait of Georgia of British Columbia and Puget Sound of Washington State (Figures 3 and 4). All population records are based on light-trap or hand-net captures from three sources: Troubridge and Crabo (1996) from the type localities; Troubridge and Woodward (2000) for one site in the northern Strait of Georgia; and records collected by N. Page in 2001 and 2002 from one new site in the northern Strait of Georgia and four new sites in Puget Sound. Collections by N. Page were made using a modified Robinson light-trap or by hand-netting in proximity to a light-trap between the middle of May and early July. In most cases, a single light-trap was placed adjacent to patches of A. latifolia prior to dusk and was operated for the full dusk to dawn period. Two traps were used occasionally. This sampling method and intensity has been used successfully to capture Copablepharon species (J.T. Troubridge, pers. comm., 2002). Additional coastal sites that did not support C. fuscum were also sampled but provide contextual information on habitat preferences (see Figure 4). Detailed sampling records from 2001 and 2002 are provided in Appendix 2 (note: sites with known C. fuscum populations are not identified by name or geographic coordinates). All known specimens of C fuscum have been identified by J.T. Troubridge.
Figure 3: North American Range of C. fuscum Based on Confirmed Specimens
Figure 4: Copablepharon fuscum Populations and Sampling Sites in the Strait of Georgia – Puget Sound and West Coast of Vancouver Island
Sites with confirmed populations of C. fuscum are shown with black dots. Sites with A. latifolia that were sampled in 2001/2002 without capturing C. fuscum are shown with squares. Sites without A. latifolia that were sampled in 2001/2002 without capturing C. fuscum are shown with triangles.
Each location is believed to encompass one population. The extent of occurrence of all known sites with C. fuscum is 4850 km2, which is a maximum of 220 km long and 45 km wide. The extent of the three Canadian populations is approximately 3700 km2. The maximum distance between known populations is 220 km.
C. fuscum has been recorded at three sites in Canada in the past eight years (Figure 4). Two populations are located in the northern Strait of Georgia in the Comox area, B.C. A single population is located in the southern Strait of Georgia near Sidney, B.C. The southern Canadian population is proximate to populations in Washington described below.
Based on the presence of its host-plant, Abronia latifolia, C. fuscum may occur in up to four additional sites in the Canadian portion of the southern Strait of Georgia. One potential site was sampled in June 2002 without success and more intensive sampling is needed in that locality. A privately owned island near Sidney, B.C. has recent records of A. latifolia from one to three sand spits or dunes (Clement, 1998). It has not been sampled for moths. Three sites with small patches of A. latifolia (< 25 m2) in the southern Strait of Georgia were also sampled in 2002 without success. In addition, C. fuscum was not captured in three other sites that do not support A. latifolia. No additional sites with suitable habitat (e.g., open dunes with A. latifolia) for C. fuscum were found in the northern Strait of Georgia. Dunes on the west coast of Savary Island were visited on June 2002. No A. latifolia plants were observed, and light-trapping in dune meadow areas did not result in capture of C. fuscum. Five dune sites on the west coast of Vancouver Island with A. latifolia populations were sampled between May 15 and July 10, 2001. No C. fuscum were captured or observed at these sites.
It is unknown if C. fuscum has been extirpated from any sites in Canada.
C. fuscum has been recorded from five sites in the Puget Sound region of Washington: two on Whidbey Island (including the type locality at Deception Pass State Park), one on San Juan Island, and two on the eastern side of the Strait of Juan de Fuca (Figure 4).
C. fuscum may occur in up to 6 additional sites in the Puget Sound area. These potential sites have not been visited, and the presence of C. fuscum was inferred from inspecting oblique air photos for suitable open dune habitat. Other than the visually confirmed presence of A. latifolia on one spit on Lopez Island, it is unknown if these additional sites support large patches of A. latifolia. Two other sites with small patches of A. latifolia in the Puget Sound area were sampled in June 2002 using light-traps. No C. fuscum were captured or observed at either site.
There is no indication that C. fuscum populations in the Strait of Georgia - Puget Sound region are peripheral to a larger population on the Oregon and California coasts. A review of collections from the western U.S. by J.T. Troubridge did not reveal any additional collection records of C. fuscum (J.T. Troubridge pers. comm., 2002). One site in Oregon with A. latifolia was visited in June 2002. No light-trapping was possible, and C. fuscum was not found during hand searches of patches of flowering A. latifolia. A. latifolia has declined throughout its range on the Oregon and California coasts because of exotic species invasion, intensive recreational use and urban development (A. Wiedemann, pers. comm., 2002). However, additional sampling is needed to determine the presence or absence of C. fuscum in coastal sites in Oregon and California.
The distribution of C. fuscum appears to be structured at two spatial scales. The geographic isolation of sand-dominated coastal sites with large A. latifolia patches creates a fragmented regional distribution pattern of C. fuscum populations. It is unclear if C. fuscum exhibits a metapopulation1 structure in which infrequent dispersal increases population persistence, or if the populations are better described as isolated populations without dispersal. The northern Strait of Georgia populations are approximately 6.7 km apart and may have infrequent immigration (e.g., < 1 migrant per year). The southern populations are more geographically isolated (mean, minimum and maximum distance between the six southern populations: 32.6, 3.9, 59.9 km respectively). The population near Sidney, B.C. is the most isolated Canadian population and the closest known population is 33.2 km away on San Juan Island.
Within sites, A. latifolia plants are also patchily distributed. Dense patches may be separated by open sand or grass areas without A. latifolia, or by sparse nonflowering A. latifolia plants. In some sites, C. fuscum was captured among relatively small patches of A. latifolia (+/-50 m2) that are up to 200 m from large, contiguous patches. Each C. fuscum population may be composed of a series of subpopulations with regular migration between subpopulations.
Footnotes
1 A metapopulation is a complex of connected populations whose persistence as a whole depends on limited migration between the isolated populations (Hanski, 1997). An important assumption for metapopulations is that habitat patches are not too isolated to prevent immigration.
Page details
- Date modified: