Sand-verbena Moth (Copablepharon Fuscum)
- Assessment Summary
- Executive Summary
- COSEWIC History, Mandate, Membership and Definitions
- Lists of Figures, Tables and Appendices
- Species Information
- Population Sizes and Trends
- Limiting Factors and Threats
- Special Significance of the Species
- Existing Protection or Other Status
- Summary of Status Report
- Technical Summary
- Acknowledgements and Literature Cited
- Biographical Summary of the Report Writer, Authorities Consulted, and Collections Examined
Because of the relationship of Copablepharon fuscum with its host-plant, Abronia latifolia, habitat requirement information is provided for both species in this section.
Copablepharon fuscum Habitat Requirements
C. fuscum occurs in association with A. latifolia in spits, dunes and other sand-dominated coastal sites. These sites occur where coastal erosion and transport of glacially derived sand deposits has created and sustained large depositional coastal features (e.g., dunes, spits, etc.) over the long term. Sand-dominated coastal sites are generally rare in B.C. and are typically clustered spatially because of shared physiographic conditions and coastal processes.
The specific habitat requirements of C. fuscum are poorly understood. Available information on its habitat requirements is based on Troubridge and Crabo’s (1996) species description, personal observations made by N. Page and published information on coastal dune ecosystems. Three points are noteworthy:
- C. fuscum has consistently been found in close spatial association with A. latifolia. The moth and the plant appear to have a parasite/host relationship. C. fuscum has not been captured in a variety of coastal sites lacking A. latifolia. Similarly, C. fuscum has not been captured more than 25 m from A. latifolia plants.
- Anecdotal observations indicate that A. latifolia is used for all phases of C. fuscum’s lifecycle: adult nectaring, egg-laying and larval development. While other polyphagous moths and insects use A. latifolia flowers for nectaring or feed on the leaves as larvae, C. fuscum is considered a monophagous species with high fidelity to its host-plant. Few other plant species found in coastal beaches have the combined resources (i.e., large, nectar-rich flowers and succulent leaves) found in A. latifolia.
- Only large, flowering patches of A. latifolia appear to support C. fuscum. Estimates of A. latifolia patch size (visual estimates of total foliar cover in m2) and the presence/absence of C. fuscum in these patches suggests that C. fuscum is only found above a threshold of resource availability. C. fuscum was only present in sites where the total foliar cover of A. latifolia was greater than 400 m2. The total A. latifolia cover in the three Canadian sites with C. fuscum was estimated 450 m2, 620 m2 and 680 m2 respectively based on field visits and air photo assessment. Host-plant quality and density also appears to be important for sustaining populations. C. fuscum was not captured or observed in sites or portions of sites with diffuse or non-flowering A. latifolia patches. For example, light-trapping in a grass-dominated meadow with remnant A. latifolia plants on San Juan Island did not result in capture of C. fuscum despite its presence in nearby open dune areas. Thresholds of resource availability for population persistence have been demonstrated for other insects (Forare and Solbreck, 1997; Grez and Gonzalez, 1995).
Abronia latifolia Habitat Requirements
Abronia latifolia is a long-lived perennial plant with distinctive prostrate growth form, bright yellow umbellate flowers and succulent leaves, stems and roots (Tillet, 1967; Wilson, 1972) (Figure 6a). It is found in coastal, sand-dominated habitats that lack dense herbaceous or bryophyte plant cover (Figure 6b and c). A. latifolia is endemic to the Pacific Coast of North America and is distributed from Santa Barbara County, California to the Queen Charlotte Islands, British Columbia (Tillett, 1967; Barbour and Breckon, 1974). In Canada, A. latifolia is restricted to dunes and sandy spits, islands and beaches in the Strait of Georgia, the west coast of Vancouver Island and the Queen Charlotte Islands. A review of herbarium records in British Columbia and intensive fieldwork by N. Page in 2001 and 2002 indicated that A. latifolia has been recorded or observed at approximately 25 sites in British Columbia (Page, 2003) (see Figure 5). It is currently designated by the BC Conservation Data Centre with a global rank of G5 (“demonstrably widespread, abundant and secure”) and a provincial rank of S3 (“vulnerable to extirpation or extinction”) (BC Conservation Data Centre, 2002).
Two spatial patterns have been observed in local-scale A. latifolia distribution: 1) small patches or isolated plants often occur near the margin of the upper beach where water-dispersed seeds are deposited; and 2) contiguous or isolated patches occur on beach ridges and open dunes (Figures 6b, c and e) (Wiedemann, 1984). These patches can be either sparse (2-25% cover (Figure 6e)) or dense (>25% cover (Figure 6b)). C. fuscum was only captured in dense patches by N. Page in 2000–2001.
A. latifolia can be considered either a beach or dune obligate-species and is found near sea-level (Tillet, 1967; Wiedemann et al., 1999). Only two of more than twenty-five sites with A. latifolia observed in the 2000-2001 study were located more than 5 m above the high tide line: one had extensive populations above 50 m asl on a sand-dominated coastal prairie, while the other had a small population approximately 15 m asl on a coastal bluff. In only one site was A. latifolia found more than 100 m from the shore.
A. latifolia populations are maintained by the unique natural disturbance regime of coastal sites that sustains open sand areas through wave, tide and wind disturbance. Observations by N. Page suggest that vigour and flowering decline when the sand stabilization promotes development of bryophyte or herbaceous communities. A. latifolia is sometimes found in grass-dominated areas; however, flowering and growth is only vigorous in patches where A. latifolia is the dominant species on open sand. It is not known if the lower growth rate and flowering is caused by reduced light, competition for soil resources (e.g., nutrients, water), or other factors. Succession in dunes is generally initiated by surface stabilization by bryophytes followed by development of grass- and shrub-dominated communities (Kumler, 1969; Page, 2003).
One site in the Queen Charlotte Islands is shown in the smaller map to the top right. Populations in Washington are not shown.
Based on the 2000-2001 study, A. latifolia occurs in sites with sand soils (dominant particle size is 0.25 – 0.15 mm) that are weakly acidic (pH 5.5 to 6.3) and nutrient poor (total nitrogen <0.01%) (Page, 2003). This is characteristic of sandy dune soils that experience precipitation-induced leaching and soil development (Ranwell, 1972). A. latifolia has unique adaptations to this environment, including deep tap roots with high water storage capacity, prostrate growth and succulent leaves with thick epidermis.
The leaves and flowers of A. latifolia are a rich resource for a variety of moths and other insects. A. latifolia flowers from early May to early October and peaks in June and July. Numerous browsing scars (Figure 6g) were observed in all A. latifolia populations regardless of whether C. fuscum was present. A total of 18 moth species were captured in light-traps with C. fuscum by N. Page in 2000–2001.
Based on the lack of seeds in A. latifolia seed husks in a variety of sites, seed predation appears to be high. Alternately, poor pollination or other factors may reduce seed set. C. fuscum may be an important pollinator of A. latifolia in some sites, particularly given its long proboscis; however, successful pollination of A. latifolia in many sites lacking C. fuscum indicates that their relationship is not an example of exclusive mutualism as occurs in yucca moths (Parategeticula spp., Tegeticula spp.).
Photo by N.A. Page.
Photo by N.A. Page.
Photo by N.A. Page.
Photo by N.A. Page.
Photo by N.A. Page.
Photo by N.A. Page.
Photo by N.A. Page.
Sand-dominated coastal sites in British Columbia have been rapidly and extensively modified throughout the known range of C. fuscum over the past 100 years. Detrimental effects vary in intensity and range from recreational disturbance, construction of roads and buildings, modification of disturbance regimes (e.g., shoreline armouring) and vegetation stabilization. Dunes, spits and other sparsely vegetated communities were the most poorly represented of seven sensitive ecosystem types that were inventoried on southeastern Vancouver Island between 1993 and 1997; only 39.5 ha of dune and 111.3 ha of spit were identified by air photo analysis and field assessment (Ward et al., 1998).
Progressive loss of open sand habitats from vegetation stabilization is the primary cause of habitat decline for C. fuscum in Canada. Sand-dominated coastal sites develop from sand accretion which is controlled by sediment transport processes (Thomson, 1981). Vegetation stabilization rates show similar temporal variability, and the recent stabilization trend in many dunes and spits in the Strait of Georgia may reflect a period of reduced sediment transport. It is more likely, however, that much of the recent vegetation stabilization is caused by anthropogenic impacts. In particular, the introduction of invasive exotic plant species, such as Cytisus scoparius (Scotch broom) and a variety of exotic grasses (e.g., Bromus tectorum, Ammophila arenaria, Dactylis glomerata, Holcus lanatus, Bromus hordeaceus, Vulpia myuros, Anthoxanthum odoratum), have accelerated stabilization. Native mosses (Tortula ruralis, Racomitrium canescens, Ceratodon purpureus and Bryum capillare) function in concert with vascular plants rapidly colonizing the sand surface. C. scoparius is the most important of the exotic species in sand-dominated coastal sites because of its rapid growth and ability to fix nitrogen in low fertility sand soils (Parker, 2002). A. arenaria, a widespread invasive grass species of outer west coast beaches from B.C. to California (Wiedemann and Pickart, 1996), is also present in some dune sites in the southern Strait of Georgia. Increased log debris in some coastal sites may also contribute to stabilization.
Direct habitat loss from land development (e.g., roads, buildings, etc.) or recreational use has also caused habitat decline. Recreational uses may have contributed to localized damage to A. latifolia, although in other areas limited disturbance has maintained open sand areas.
Finally, it is difficult to evaluate if changes to coastal sediment transport have affected sites with C. fuscum populations. Shoreline modifications, including erosion protection, may reduce sand supply and change transport and deposition patterns. This may contribute to stabilization of dunes.
Historic air photos were used to evaluate land cover change in the three Canadian sites in which C. fuscum occurs. Photos were scanned, adjusted to a common scale, and land cover types (urban, tree and shrub, grass and bryophyte, and open dune) were measured. For the two northern sites, photos from 1957 were compared to 1995 or 1997 photos. For the southern site, photos from 1932 were compared to 1995.
|Site||Date||Total Area||Urban||Forest/Shrub||Grass/Bryophyte||Open Dune|
|Site 1 (Comox area, B.C.)||1957||27.5||2.6||3.5||17.0||4.4|
|Site 2 (Comox area, B.C.)||1957||5.4||0.0||1.3||3.3||0.8|
|Site 3 (near Sidney, B.C.)||1932||6.8||0.0||0.5||4.0||2.3|
In general, all three sites show relatively little overall change in total area and similar, but variable, loss of open dune habitat (Table 1). Two sites enlarged slightly (0.7 ha and 0.1 ha increases) because of sand accretion, while the other remained stable. Open dune areas declined in all sites; two sites lost 50% of their open dune area (loss of 2.2 and 0.4 ha), while the other lost 21% (loss of 0.5 ha). Grass and bryophyte areas also declined in all sites; one site lost over 52%, while the others lost 6% and 13%. Forest and shrub cover increased substantially in all sites: 134% in one site, 46% in another and 220% in the third (gain of 4.7, 0.6 and 1.1 ha). Only one site has urban land use and increased from 2.6 ha to 9.2 ha (254% increase) since 1957.
Ownership and protection status of Canadian sites with C. fuscum populations is variable, but all have some form of public ownership (Table 2). None are privately owned. Relative to many species of conservation concern, a high proportion of C. fuscum habitat is located within parks or other publicly owned lands. One site recently transferred to Parks Canada has a relatively large population of A. latifolia, but sampling for C. fuscum did not result in the capture of any specimens.
US sites with C. fuscum populations also have a high level of public ownership: one site is in a national park, one is in a wildlife refuge, two are in state parks and one is in a military reserve.
|Site||Park||Indian Reserve||Other Federal Land (DND)||Private Land||Total Area1|
|Site 1 (Comox area, B.C.)||1.5 ha (park)||5.6 ha||21.1 ha||0.0 ha||28.2 ha|
|Site 2 (Comox area, B.C.)||5.4 ha (park)||0.0 ha||0.0 ha||0.0 ha||5.4 ha|
|Site 3 (near Sidney, B.C.)||0.9 ha (reg park)|
1.8 ha (mun. park)
|4.2 ha||0.0 ha||0.0 ha||6.9 ha|
1 Total Area includes the entire site rather than just the portion in which C. fuscum has been captured or A. latifolia has been observed.
- Date Modified: