Gold-edged gem (Schinia avemensis) recovery strategy 2014: chapter 1

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3. Species Information

3.1 Species Description

The Gold-edged Gem is a member of the Order Lepidoptera (butterflies and moths) and Family Noctuidae (owlet or cutworm moths). The Gold-edged Gem is one of about 150 North American species belonging to the subfamily Heliothinae or flower moths, many of which are colorful in appearance and cryptic against the flowers on which they feed and rest (Hardwick 1996).

Figure 1. Adult Gold-edged Gem resting on a sunflower  © J. Dombroskie.

Adult Gold-edged Gems are relatively small with a stout body and a 16-20 mm wingspan (Figure 1; Hardwick 1996, COSEWIC2006). The forewings are maroon and each is crossed with two yellow bands. The species’ common name refers to the distinctive pale yellow fringe along the forewings. The head is pale yellow while the hindwings and thorax are predominantly black. Both sexes are similar in appearance, but females tend to be larger and darker than the males (COSEWIC2006).

The Gold-edged Gem is a diurnal moth typically observed resting or nectaring on flowers of its larval host plant, or rapidly flying among blossoms of other composite plants. The moth is univoltine (one generation per year) and the average lifespan of an adult is less than a week (Hardwick 1996). The flight period in Canada can range from July 10 to August 20 (COSEWIC2006). The early life-stages (i.e., egg, larva, and pupa) of the Gold-edged Gem have not yet been described. 

3.2 Population and Distribution

The Gold-edged Gem is native to North America and its known range extends across the southern Prairie Provinces of Canada south into central Colorado, United States (Figure 2). Within this range, the species is confined to a few isolated pockets of open sand dunes^[2] and blowouts^[3]. The Canadian population is separated by over 1000 km from the American population (COSEWIC2006). However, additional undocumented occurrences are speculated to exist throughout its range (G. Anweiler, pers. comm. 2008; NatureServe 2011).

In the United States, Gold-edged Gems are known only from three occurrences, all within south-central Colorado (C. Harp, pers. comm. 2008). As of 2008, information on population abundance and trends in the United States was not available (NatureServe 2011). However, the population at the Great Sand Dunes National Park, Colorado, was thought to be stable (C. Harp, pers. comm. 2008).

Figure 2. Known distribution of the Gold-edged Gem.

Canadian distribution and population

The known Canadian Gold-edged Gem range extends from southeastern Alberta through Saskatchewan and into southwestern Manitoba, south of the 52^nd parallel (Figure 2). The species was not found during surveys of active dunes in sand hills^[4] north of this parallel (i.e., North Battleford sand hills, Saskatchewan and Wainwright sand hills, Alberta) (M. Curteanu 2011, M-C. Bélair, unpubl. data).

Since the COSEWICstatus report was prepared in 2006, several new occurrences have been discovered in Saskatchewan and as of 2011 the Gold-edged Gem was known to occur in nine sand hills in Canada, including three occurrences in southeastern Alberta, five occurrences in Saskatchewan, and one occurrence in southwestern Manitoba (Table 1). Further investigation in unsurveyed sand hills in Saskatchewan (e.g., Pelican Lake, Westham, Great Bigstick, Piapot and Seward sand hills) and Manitoba (e.g., Lauder sand hills) may uncover additional occurrences.

Generally, occupied habitat patches cover less than 50 hectares and Gold-edged Gem abundance is relatively low (10-50 moths per hectare) (COSEWIC2006). COSEWIC(2006) roughly estimated the Canadian Gold-edged Gem population to be between 700 and 6,000 individuals. However, this is likely an underestimate. There is a high degree of uncertainty associated with the COSEWICestimate, given the scant amount of survey work that has been done. New occurrences have been discovered since this estimate was made. The timing of surveys is critical as the presence of Gold-edged Gems is difficult to detect in occupied habitat patches. Adult moths of the Heliothinae subfamily are short lived (i.e., live less than a week) (Hardwick 1996), adult emergence period is variable on an annual basis (COSEWIC2006) and hourly basis within the same sand dune (M-C. Bélair, unpubl. data). In addition, none of the field surveys conducted to detect this species’ presence were designed to estimate population size.

For the reasons mentioned above, the size of the Canadian Gold-edged Gem population is currently unknown. There are also no data available with which to monitor changes in population and distribution for Gold-edged Gem. In Canada, open sand dunes and associated habitats have been stabilizing at a rate of 10% to 40% per decade (Wolfe et al.2000). The progressive stabilization and loss of active dune complexes across the Great Plains in the past 100 years (Wolfe et al. 2000), suggest long-term population declines and a decrease in the ability to recolonize isolated remnant dunes.

AlbertaPopulations

Gold-edged Gems have been found in the Pakowki Lake, Middle and Empress Meander (Dune Point) sand hills in Alberta (Table 1). Frequent surveys of the Pakowki Lake sand hills have established that individuals at this location are thriving (Jensen et al. 2009, Curteanu 2011). The Middle sand hills occurrence, found within the Suffield National Wildlife Area (NWA), Alberta, was discovered in 1939 (Table1). Within the Suffield NWA, Gold-edged Gems have been found at a dozen small sand dunes and blowouts (Jensen et al. 2009, Curteanu 2011). The remaining occurrence is found in the Empress Meander (Dune Point) sand hills near Bindloss, Alberta.

SaskatchewanPopulations

In Saskatchewan, the species has been observed in the Burstall, Tunstall, Cramersberg, Elbow and Dundurn sand hills (Table 1). Gold-edged Gems were recently found in two different sand dunes in the Cramersberg sand hills on Carry the Kettle Nakoda First Nation Indian Reserve (G. Anweiler, unpubl. data, M-C. Bélair, unpubl. data), one sand dune in the Dundurn sand hills, five sand dunes in Elbow sand hills within Douglas Provincial Park (DPP) and Elbow Community Pasture, and three sand dunes in the Tunstall sand hills on Bitter Lake Community Pasture (Curteanu 2011, M-C. Bélair, unpubl. data,). The remaining occurrence is found in the Burstall sand hills.

ManitobaPopulation

In Manitoba, Gold-edged Gem occurs at one location within the Spirit Sands. The Spirit Sands is a 4 km² active sand dune located partly in Spruce Woods Provincial Park and partly in the adjacent Canadian Forces Base Shilo.  The sand dune is part of the Brandon sand hills (Schykulski and Moore 1996). Gold-edged Gems were first reported in the Brandon sand hills in 1903 (Table 1) where they likely had a broader historical distribution. The species has not been observed in the past 80 years in some sand dunes (e.g., Aweme, MB) (COSEWIC2006).

¹ The information in this table represents the best information available to Environment Canada at the time this recovery strategy was written. The sources for this table are: M-C. Bélair, unpubl. data, M. Curteanu, unpubl. data, COSEWIC2006, Jensen et al. 2009, Curteanu 2011.
²Sand hill names according to Wolfe 2010.
³ Minimum counts.

3.3 Needs of the Gold-edged Gem

General habitat requirements

The Gold-edged Gem is a sand dune prairie obligate moth; it is restricted to naturally occurring active (wind-moving) sand dunes or blowouts where colonies of Prairie Sunflower (Helianthus petiolaris) occur (Hardwick 1996, COSEWIC2006). Anthropogenic roadside areas of open sand where Prairie Sunflowers were abundant have been found to be devoid of Gold-edged Gems during the adult emergence period (M-C. Bélair, unpubl. data, M. Curteanu, unpubl. data), suggesting that the species does indeed require the natural active sand dune areas where it has been found. Based on sampling records and field observations, Gold-edged Gem habitat consists of open, barren or sparsely vegetated sand dunes, sand flats, or sandy hill areas that are actively eroding and being moved by wind. Active sand dunes and blowouts currently occur as isolated patches on the crests of partially or fully stabilized sand hills (Wolfe 1997) that are scattered within a vast landscape of established grassland.

Reasons why Gold-edged Gems rely on active sand dunes or blowouts are poorly understood and require further investigation. Avoiding predation and/or parasitism or coping with subfreezing winter conditions is a common adaptation exhibited by a wide range of desert invertebrates (Crawford 1981). The sand substrate offers burrowing insects a humid and stable microclimate important during the resting stage (Crawford 1981). Although there are no data specific to Gold-edged Gem, it is probable that the sand provides a secure environment during the pupal stage and facilitates the burrowing activity during the larval and adult emergence stage.

Oviposition and larval resources

Female Gold-edged Gems deposit eggs within the blossoms of the Prairie Sunflower, the only plant known to be utilized by the larva for its development. Female Gold-edged Gems insert their eggs into the florets and the eggs hatch within a few days. The larvae (caterpillars) feed inside the flower heads of the host plant specifically consuming its floral parts and developing seeds (Hardwick 1996). The last larval instar ceases to feed and pupates at or below soil surface. The pupa remains in a state of diapause throughout the winter and spring although diapause can last up to several years (Hardwick 1996).

The Prairie Sunflower is an annualand is recognized by its bright yellow blossoms and alternate lance-shaped leaves; the plant can reach up to 2 m in height and blossoms from June to September (Heiser 1969, Moss 1994). The plant is native to North America and is widely distributed throughout Canada and United States (Heiser 1969). Prairie Sunflowers inhabit sand dunes, sandy river banks, eroded slopes, coulees, roadsides, and fallow fields; the plant is considered an early colonizer of disturbed areas (Moss 1994).

Monophagous moths and butterflies (i.e., species that feed on a single plant species) have to be selective in choosing plants for oviposition as the timing of larval development must coincide with that of the host plant (Dempster 1997, Peterson 1997). Starvation caused by the larvae’s inability to consume the hard coated seed pods due to late oviposition and development has been reported as a cause of mortality in some butterfly species (Dempster 1997). Gold-edged Gem may suffer higher mortality rates and lower reproductive success if adult emergence, oviposition, and larval hatching do not coincide with larval host plant blossoming and seed development.  Currently, very little is known about the ecology of the Prairie Sunflower or how environmental and climatic conditions influence this plant’s distribution and germination. For example, the number of Prairie Sunflowers at some occurrences has been observed to vary greatly from year to year (G. Anweiler, pers. comm. 2008), in turn affecting Gold-edged Gem abundance at these occurrences.

Adult food resources

Similar to other moths and butterflies, adult Gold-edged Gems depend on an adequate supply of nectar as a source of energy for metabolic functions, flying, and reproduction (Heinrich and Raven 1972). The Prairie Sunflower and Common Skeletonweed (Lygodesmia juncea) are the primary nectar sources for Gold-edged Gems (COSEWIC2006, C. Harp, pers. comm. 2008). Common Skeletonweed is a perennial and is widely distributed throughout the Great Plains. In Colorado Gold-edged Gems have been observed perched on Common Skeletonweed blossoms when Prairie Sunflowers were still in bud. Gold-edged Gems have been observed resting on Rhombic-leaved Sunflowers (Helianthus pauciflorus subsp.subrhomboideus) in the Middle sand hills which suggests that this plant may be an additional nectar source or larval host plant (S. Westworth, pers. comm. 2011). However, further investigation is required to confirm this because Gold-edged Gems have never been observed mating or feeding on Rhombic-leaved Sunflowers.

Limiting Factors

Gold-edged Gem distribution and abundance is inherently limited by the scarcity of open active sand dunes or blowouts where colonies of Prairie Sunflower exist. Thorpe et al. (2001) identified 125 sand hills throughout the Canadian Prairie Provinces but these comprise only a small fraction of the total land-cover. Within sand hills, Gold-edged Gems also show microhabitat preferences based on sand dune topography, moisture, sand particle size and plant community (COSEWIC2006, Jensen et al.2009). Given Gold-edged Gem’s habitat and host plant specificity and the scarcity of current active dunes in Canada, availability of suitable habitat is the primary biological factor limiting this species’ recovery.

Additionally, Gold-edged Gem distribution might be limited by dispersal and colonization ability. Although the species’ dispersal has not yet been assessed, monophagous moths generally display strong host plant fidelity, thus they are generally not found outside of the immediate vicinity of host plant colonies (Hardwick 1996, COSEWIC2005). While at a local scale, adults may disperse along a ridge, or among open sandy patches, or among sand dunes or blowouts in close proximity to one another, it is highly unlikely that Gold-edged Gems are able to disperse at the landscape level given the lengthy distances of unsuitable habitat separating major sand hills. Furthermore, the short life span of Gold-edged Gems suggests that its dispersal and colonization potential may be limited or non-existent. The home range for the genus Schinia is estimated at 1 km² (NatureServe 2011). Consequently, if the Canadian populations were extirpated, natural recolonization from the American populations is presumed impossible (COSEWIC2006).

4. Threats

4.1 Threat Assessment

¹ Level of Concern: signifies that managing the threat is of (high, medium or low) concern for the recovery of the species, consistent with the population and distribution objectives. This criterion considers the assessment of all the information in the table.

² Severity: reflects the population-level effect (High: very large population-level effect, Medium, Low, Unknown).

³ Causal certainty: reflects the degree of evidence that is known for the threat (High: available evidence strongly links the threat to stresses on population viability; Medium: there is a correlation between the threat and population viability e.g. expert opinion; Low: the threat is assumed or plausible).

4.2 Description of Threats

The progressive stabilization of active sand dunes and blowouts is the most prevalent threat to the Canadian Gold-edged Gem populations (COSEWIC2006, Jensen et al.2009). Other factors such as elimination of host and nectar plants by exotic, invasive or introduced species, trampling of host and nectar plants, oil and gas development ungulate herbivory, pest control, military activities and stochastic events also have the potential to negatively impact Gold-edged Gem populations. Threats are listed in order of decreasing level of concern.

Dune stabilization

In the last century, the North American Great Plains land-cover has changed dramatically in response to climatic variations and land use regimes resulting in several active sand hills being nearly or completely stabilized by vegetation (Wolfe et al. 1995, Geological Survey of Canada 2001, Mangan et al. 2004). An increase in precipitation in the prairies during the last century has been a major factor contributing to sand dune stabilization (Wolfe et al. 1995, Hugenholtz and Wolfe 2005). Dune stabilization occurs during moist warm periods when the rate of vegetation growth is faster than the rate of dune migration (Wolfe et al. 1995, Hugenholtz and Wolfe 2005).  Established vegetation prevents the wind from moving the dune and eventually stabilizes it; drier conditions such as droughts and significant disruptions to vegetation growth can cause dunes to reactivate and migrate.

Natural disturbances such as extreme weather patterns, large ungulate grazing, flooding, animal burrowing activities, pest outbreaks, and fires, have played significant roles in the evolution of North America’s prairies (White 1979, Sousa 1984, Axelrod 1985). Historically, these disturbances occurred frequently, randomly, and at different scales and magnitudes across the landscape, and have contributed to plant community composition and structure, and the overall ecological integrity of the prairie (Garren 1943, Daubenmire 1968, White 1979, Leisica and Cooper 1999).  Grazing of sand dunes by Plains Bison (Bison bison) combined with the periodic burning of the prairies contributed to disturbance and the overall maintenance of active sand dunes; the absence of bison grazing and reduction in prairie fires since European settlement may have accelerated the rate of sand dune stabilization across the Prairie Provinces. Finally, intensive seeding or re-vegetation of active sand dunes in order to decrease soil erosion and improve land use productivity was historically encouraged and practiced up to the early 1990s. Species of grass that thrive in dry nutrient-poor soils have been planted at the Burstall sand hills, Saskatchewan to accelerate dune stabilization (David 1977), while flax bales were used at the Middle sand hills, Alberta, to prevent soil erosion.

Potential habitat available for Gold-edged Gem has been decreasing at a rapid rate. Several open dunes in the Brandon sand hills, Manitoba, were active during the late 1920s but are now mostly stabilized by parkland type vegetation including Aspen (Populus spp.), Spruce (Picea spp.), Tamarack (Larix spp.), Dwarf Oak (Quercus spp.) and native grasses and shrubs (David 1977, Schykulski and Moore 1996). It was estimated from aerial photographs that dune stabilization of the Brandon sand hills has occurred at a rate of 10-20% per decade since the early to mid 1900s despite periods of drought (Wolfe et al. 2000, Hugenholtz and Wolfe 2005). At Pakowki Lake sand hills, Alberta, the amount of bare sand has declined by almost 75% since the 1950s (Wallis and Wersher 1998).  

Dune stabilization alters the physical and functioning structure of active dunes and ultimately renders the habitat unsuitable for sustaining Gold-edged Gems; dune stabilization is a serious threat to the recovery of the species in Canada.

Invasion and Establishment of Exotic Plants

Exotic species that escape cultivated areas have the potential to invade and out-compete native vegetation, and over time, dominate and alter ecosystem properties and functions (Gordon 1998, Henderson and Naeth 2005). Specifically, invasive species exclude native flowering plants, conceivably limiting both nectar and larval food resources which are critical for Gold-edged Gem reproduction and survival. Invasive species also render Gold-edged Gem habitat unsuitable by accelerating the process of dune stabilization. At Pakowki Lake sand hills, Crested Wheatgrass (Agropyron cristatum) and Tall Baby’s breath (Gypsophila paniculata) were observed growing in dense stands near Gold-edged Gem habitat (Jensen et al. 2009). Within Spruce Woods Provincial Park, Manitoba, sweet clover (Melilotus sp.), Smooth Brome (Bromus inermis), and particularly Leafy Spurge (Euphorbia esula) are considered major problems for the long-term integrity and sustainability of the native prairie (Schykulski and Moore 1996). Owing to their invasive nature and habitat-altering qualities, invasive species are considered a prominent threat to Gold-edged Gem recovery and survival.

Trampling of host and nectar plants

Activities such as off-highway vehicle (OHV) use, livestock movement, horseback riding, and hiking can contribute to dune destabilization and potentially benefit Gold-edged Gem habitat. According to Lemauviel and Roze (2003), active and semi-stabilized dune vegetation showed higher resilience over a short term to tourist pressure than stabilized dunes. However, consistent, heavy use of an area without periods of recovery may lead to extensive trampling and eventual eradication of Gold-edged Gem larval host and nectar plants. Specifically, OHVrecreational activities can cause significant lasting damage to the landscape including dispersal of invasive species and destruction of native and establishing vegetation (Ouren et al. 2007) leading to changes in the plant community. Currently, OHV recreational activities have been observed at the Burstall (Saskatchewan) and Pakowki Lake (Alberta) sand hills (G. Anweiler, pers. comm. 2008). The Manitoba Gold-edged Gem occurrence is not threatened from OHV recreational activities or trampling as a result of livestock movement since OHV and livestock are not permitted in the area occupied by the species (Schykulski and Moore 1996). Gold-edged Gems within the Elbow sand hills within Douglas Provincial Park, Saskatchewan and Spirit Sands of Spruce Woods Provincial Park, Manitoba may be subject to disturbance from tourists. More than 40,000 visitors can visit Douglas Provincial Park within a summer (Lake Diefenbaker Tourism Destination Area Planning Committee 2008). Grazing by livestock occurs in the immediate vicinity of several sand dunes and blowouts in the Pakowki Lake and Empress Meander (Dune Point) sand hills in Alberta, and the Burstall, Tunstall, Cramersberg, Elbow and Dundurn sand hills in Saskatchewan. Host and nectar plants at these occurrences could be threatened by trampling if overgrazing occurs within dune and blowout critical habitat. Some active sand dunes in the Elbow sand hills appeared to be heavily used by cattle and were devoid of Prairie Sunflowers (M-C. Bélair, pers. obs.). However, whether this relationship was one of cause-and-effect or merely circumstantial was not determined.

Other Threats

Activities associated with petroleum development such as exploration and extraction may threaten suitable Gold-edged Gem habitat. Roads divide landscapes leading to habitat fragmentation and alteration, population isolation and facilitation of the introduction and spread of exotic species (Clifford 1959, Forman et al. 2003). Several studies (e.g. Rao and Girish 2007) have shown that increases in traffic and speed inadvertently kill butterflies and moths. In the Middle sand hills, Alberta, and Cramersberg sand hills, Saskatchewan, oil and gas activities are ongoing and there is potential for further development which may contribute to Gold-edged Gem mortality and habitat loss. Based on analysis of historical aerial photographs and satellite imagery of the northeast corner of Middle sand hills in Suffield NWA, the density of oil and gas wells has increased from 0 well sites/km² to 2 well sites/km² between 1949 and 1998 (Bender et al. 2005). By 2007, a density of 6.25 well sites/ km² occurred in some areas of Suffield NWA (EnCana 2007). Additionally, Rowland (2008) has shown that diversity and cover of introduced plants species, which may accelerate sand dune stabilization and outcompete host plant (see Table 4), was greater at pipelines and well sites than in native prairie at Suffield NWA. The relative significance of petroleum development as a threat to Gold-edged Gem recovery is difficult to quantify at this time, especially since the extent to which the open, active sand dunes themselves have been damaged by oil and gas development remains unknown. Moreover, modern techniques such as horizontal drilling, which would preclude the need for directly disturbing the surfaces of open, active sand dunes, and restricting exploration and drilling activities to wintertime should limit the threat that petroleum development poses to Gold-edged Gems.

Ungulate herbivory likely represents a continuum of possible effects on Gold-edged Gem ranging from beneficial to potentially deleterious depending on the intensity and timing. On the one hand, grazing by domestic and wild ungulates may benefit Gold-edged Gem habitat by destabilizing sand dunes and initiating sand movement (Lesica and Cooper 1999, Hugenholtz and Wolfe 2005). On the other hand, grazing during critical periods of growth and flowering could result in the removal of host and/or nectar plants, which may in turn be detrimental to Gold-edged Gems particularly during periods of drought (COSEWIC2006). Although it has been shown that different ungulate species will select different plant species when grazing (Lloyd et al. 2010) and may not prefer the Gold-edged Gem’s host and/or nectar plants, ungulates may not be selective during periods of drought when their preferred forage is unavailable or is in short supply which could result in the grazing of the moth’s host and/or nectar plants. Gold-edged Gem eggs and larvae are concentrated within the blossoms and developing seeds of the host plant, and as such, intensive long-term grazing by both domestic and wild ungulates can lead to direct mortality of individuals. The effect of grazing on the most important host and nectar plant for Gold-edged Gems, the Prairie Sunflower, is unclear. One study reported a reduction in density and cover of the Prairie Sunflower in grazed short-grass prairie compared to ungrazed sites (Ruthven et al. 2000). Another study reported that grazing by bison had no effect on forbs, among which the Prairie Sunflower was included, in sand hill prairie habitat (Pfeiffer and Steuter 1994). Dempster (1997) reported that grazing of Orange-tip Butterfly (Anthocharis cardamines) host flowers accounted for up to 19% of larval mortality. Evidence of grazing by native ungulates on Prairie Sunflowers was observed at the Middle and Pakowki Lake sand hills, Alberta (M. Curteanu, pers. obs., M-C. Bélair, pers. obs.)

Pest control through the indiscriminate or careless application of chemicals to control agricultural pests and mosquitoes has played a significant role in the decline of pollinators in industrialized regions (Kevan 1999). Pesticide drift, particularly though not exclusively from aerial applications, could be a potential threat to Gold-edged Gem recovery through the direct mortality as well as the removal of adult nectar and larval host plants (Longley and Sotherton 1997). Studies have shown that effects of herbicides on non-target plants in field margins dissipate rapidly with distance from the target. While adverse effects have routinely been documented within 10 m of a field’s edge, few such effects have been documented at much greater distances (Wolfe and Cessna 2004). In contrast, even relatively small amounts of off-field drifting insecticides were predicted to pose a significant mortality risk to larval butterflies living in field margins (Davis et al. 1991, Cilgi and Jepson 1995). In Canada, the pesticide regulatory and labelling processes are intended to take into consideration and minimize the potential for environmental impacts due to spray drift (Felsot et al. 2011). While it is unlikely that sand dunes where the Gold-edged Gem is known to occur would be directly targeted for pesticide application, it remains unknown whether the same is true of farmland that lies adjacent to those dunes and from which pesticides could drift into Gold-edged Gem habitat. In summary, while chemical pest control may be a threat to Gold-edged Gem, its magnitude remains unknown.

The Gold-edged Gem is known to occur in certain sand dunes located within three military bases: CFBSuffield in Alberta, CFBDundurn in Saskatchewan and CFB Shilo in Manitoba. The Department of National Defence does not use sand dunes at CFB Shilo and Suffield for military training. Access to these areas is limited to periodic inspections, and forest fire response. The impact of these activities on the Gold-edged Gem should be minimal. However, some sand dunes at CFB Dundurn are located within the military training area. It is unknown whether the species occurs at those dunes.

Stochastic events can threaten specialist species. Specialized species with a short flight period and fluctuating populations are more prone to local extinctions from random (stochastic) events (i.e., severe storms, winter conditions, or fires), than generalist species with stabilized populations (Tscharntke et al. 2002, Nilsson et al. 2008). Gold-edged Gems have a narrow habitat breadth. Known Canadian occurrences are small and localized which make them vulnerable to extirpation due to environmental stochasticity. Additionally, genetic effects attributed to habitat fragmentation, isolation, and stochastic events have been suggested to play a significant role in local extinction of Lepidoptera (Packer and Owen 2001). Natural recolonization is unlikely given that the nearest known Gold-edged Gem population in the United States is approximately 1,200 km away (COSEWIC2006).

5. Population and Distribution objectives

The population and distribution objectives for the Gold-edged Gem are to maintain or increase the distribution of all known occurrences in the Canadian range of the species, and any additional occurrence(s) discovered in Canada in the future.

At this time, it is not feasible to establish quantitative population objectives because the size of the Canadian population has not been accurately estimated due to the difficulty associated with detecting the presence of the species and the limited data available on the species (see section 3.2).

Gold-edged Gems are specialists and their distribution in Canada is restricted to active open sand dunes and/or blowouts that contain larval host plants and/or adult nectar sources. Suitable habitat for the species is limited as it exists only in small isolated occurrences separated by large areas of unsuitable habitat and is declining as sand dunes are stabilizing. Even if the species is eventually down-listed to a lesser category as knowledge gaps are filled and new occurrences are discovered it is reasonable to assume that it will probably always remain at risk in Canada.

² A sand dune is a “mound, hill or ridge of windblown sand, either bare or variously covered by vegetation, capable of movement from place to place through the development of a slip face, but always retaining its own characteristic shape for an extended period of time” (David 1977).

³ A blowout “refers to a small, typically less than 1 hectare in size, area of wind blown sand, which is commonly bowl shaped and somewhat elongated in the direction of transporting winds. Thus, road tracks, all-terrain vehicle trails, cattle trails, oil/gas well pads, dugouts, cattle-disturbed areas around water wells sites and ranches, and sand pits” are not considered to be natural wind blown blowouts (Wolfe 2010).