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Recovery Strategy for the Mormon Metalmark (Apodemia mormo) Prairie Population in Canada (Proposed)
- 1.1 Species Assessment Information from COSEWIC
- 1.2 Description
- 1.3 Populations and Distribution
- 1.4 Needs of the Mormon metalmark
- 1.5 Threats
- 1.6 Knowlege Gaps
1.1 Species Assessment Information from COSEWIC
Common Name: Mormon metalmark (Prairie population)
Scientific Name: Apodemia mormo
COSEWIC Status: Threatened
Reason for designation: The Prairie population of the Mormon Metalmark is a small, northern outlier of the species' main ranges in the southwestern US. Known populations are not currently directly threatened by human activities and half the known sites are within the boundaries of a National Park. However, the total population is quite small, likely undergoes extreme fluctuations in size, is a habitat specialist, and occurs in a highly restricted area, making it vulnerable to stochastic events.
Canadian Occurrence: Saskatchewan
COSEWIC Status History: Designated Threatened in May 2003. Assessment based on a new status report.
The Prairie population of Mormon metalmarks (or interchangeably "metalmarks"), Apodemia mormo, is part of a northern population that occurs along portions of the Milk and Missouri Rivers and their tributaries in North Dakota, Montana and Saskatchewan. This population is spatially separate from the main range of metalmarks in the southwestern U.S. (Opler 1999). Known sites for the Canadian Prairie population occur along the lower Frenchman River and Rock Creek. Most of these localities are on land managed by the Parks Canada Agency and only three privately managed cattle ranches have known Mormon metalmarks on or near them and all are within the proposed Grasslands National Park boundaries (COSEWIC 2002). To date, neither biology nor population dynamics of the Mormon metalmark Prairie population have been investigated. Only two limited metalmark surveys have ever been conducted for the Prairie population (Hooper 2002, A. Henderson, Grasslands National Park, unpublished data 2006); therefore knowledge of habitat requirements for the Canadian Prairie population are extremely limited and most of the current information comes from the United States. Additionally, no surveys have been conducted in suitable habitat in Alberta so the presence of metalmark butterflies in that province remains unknown (G. Anweiler, University of Alberta Strickland Museum, pers. comm. 2006).
The Mormon metalmark is the only Canadian representative of the tropical Riodinidae family of butterflies (Layberry et al. 1998). COSEWIC (2002) noted that Canadian population morphology has not been studied in detail and used the description of the nominate1 subspecies A. m. mormo which appears to be generally consistent with the appearance of specimens from both British Columbia and Saskatchewan.
The Mormon metalmark is a medium sized butterfly with a 25 to 35 mm wingspan (Figure 1). The common name 'metalmark' for many species in this family refers to the predominance of metallic-like markings on the wings. The upper side has an orange brown background colour with multiple white patches and black marks, while the underside is grey with white spots; the forewings have a reddish-brown area on both the upper and lower surfaces (Layberry et al. 1998, Southern Interior Invertebrates Recovery Team 2005). The eyes are green, the body is grey with white markings along the sides, and the antennae have alternating black and white rings (COSEWIC 2002). Metalmark eggs are flattened spheres, pink turning purple, laid in small groups of 2-4 on the larval host plant, the branched umbrella plant, Eriogonum pauciflorum (Scott 1986, Pyle 2002). Scott (1986) describes the larvae as "dark violet (lighter beneath), with six rows of clustered cactus-like spines, the dorsal rows black at their bases, the lateral rows ochre." The pupae are usually mottled brown, somewhat stout and hairy, and are found in the plant litter at the base of the host plant (Environment Canada 2006).
Adult male and female metalmarks develop different size and structural characteristics (i.e., sexual dimorphism). Females are larger with broader wings and three pairs of functioning legs; the male's forelegs are not used for walking (COSEWIC 2002). Adult butterflies only live about 10 days. They are typically in flight from mid-August to late September (Guppy and Shepherd 2001) with peak activity from mid-to-late August. In the 2006 survey of GNP, metalmark adults were observed in flight at the end of July until late September (A. Henderson, Grasslands National Park, unpublished data 2006).
1.3 Populations and Distribution
The Mormon metalmark ranges from northern Mexico, through the western United States to southern British Columbia and Saskatchewan in Canada (Figure 2) (COSEWIC 2002). Globally, NatureServe (2006) has designated this species as G5 which indicates that it is demonstrably widespread, abundant, and secure, although it may be quite rare in parts of its range, especially at the periphery as evidenced in Canada. California has the greatest number of subspecies and the range expands eastward through Nevada, Utah, and Colorado (COSEWIC 2002). Separated populations tend to occur north of these states and Opler (1999) and Pyle (2002) show a cluster of four populations in the Pacific Northwest, which includes the sites in British Columbia, as well as an isolated northeastern population in eastern Montana, western North Dakota and southwestern Saskatchewan (Figure 2). In northwestern North America the Mormon metalmark is found primarily in habitats along the valleys of the Columbia and Missouri rivers and their tributaries (COSEWIC 2002).
Figure 2. Known North American Range of Apodemia mormo, the Mormon metalmark butterfly. Populations in regions shown in grey were considered another subspecies and were removed from A. mormo range by Opler 1999. Map adapted from Opler 1999 and Pyle 2002 (Taken from COSEWIC 2002).
1.3.1 Canadian distribution
The Canadian range of this species includes two separate populations (COSEWIC 2002). The Prairie population is found within and adjacent to GNP in southwestern Saskatchewan. The Southern Mountain population occurs in southcentral British Columbia near the town of Keremeos in the Lower Similkameen River Valley and is extirpated from the South Okanagan River Valley (Cannings et al.1998, Southern Interior Invertebrates Recovery Team 2005). The conservation ranking of this species in both British Columbia and Saskatchewan is S1 (Critically Imperiled, extremely rare).
Only two limited Saskatchewan metalmark surveys have ever been conducted for the Prairie population and none have been conducted in Alberta (Hooper 2002, A. Henderson, Grasslands National Park, unpublished data 2006). A 2002 survey of metalmarks in Saskatchewan identified locations in the East and West Blocks of GNP, in the Killdeer badlands, and along the slopes of the Frenchman River Valley (Hooper 2002). Two weeks of survey work for metalmarks during the summer of 2006 resulted in the discovery of two new metalmark colonies in the West Block of GNP (A. Henderson, Grasslands National Park, 2006 (unpublished data)). Insufficient information exists to estimate population number, size, or trend. More thorough surveys of Mormon metalmark populations in Canada are planned for 2007.
1.3.2 Percent of Global Distribution and Abundance in Canada
Canada has less than 1% of both the Mormon metalmark's global range and population (Cannings et al. 1998). The Canadian population probably varies from year to year, and is currently estimated at less than 250 individuals in the Southern Mountain population and probably less than 1000 in the Prairie population (COSEWIC 2002). It is not unusual for numbers of invertebrates in a population to vary by orders of magnitude from season to season, depending on factors such as weather, predator population sizes, etc. (G. Anweiler, University of Alberta Strickland Museum, pers. comm. 2006).
Figure 3. Map of sightings of Mormon metalmarks in Saskatchewan (Hooper 2002 and A. Henderson, Grasslands National Park, unpublished data 2006). Badland habitat has not been systematically searched for Mormon metalmarks. The badland areas on the map indicate regions where future populations might be discovered.
1.4 Needs of the Mormon Metalmark
1.4.1 Habitat and Biological needs
Throughout their range, Mormon metalmark habitat includes hillsides, slopes, and embankments with eroded clay or heavy clay soils and moderate to high densities of branched umbrella plant and rubber rabbitbrush (Ericameria nauseosus) (COSEWIC 2002). However, only two limited metalmark surveys have ever been conducted for the Prairie population (Hooper 2002, Henderson 2006 (unpublished data)); therefore knowledge of habitat and requirements for the Canadian Prairie population are extremely limited and most of the current information comes from the United States. Metalmarks produce one generation per year and require branched umbrella plants to complete their life cycle, thus healthy branched umbrella plant populations are critical to metalmark survival. Upon emergence, adults live in colonies and have limited dispersal, reportedly remaining close to their larval host plant (the branched umbrella plant), to feed on its nectar (Arnold and Powell 1983, COSEWIC 2002). Adults use rubber rabbitbrush (COSEWIC 2002) as a secondary nectar source. Though still unclear, the quality of metalmark habitat is likely influenced by the density and quality of both nectar sources.
Mating occurs within three days of adult emergence (COSEWIC 2002). Adults require mature umbrella plants for egg laying and flowering umbrella plants and rabbitbrush for nectaring (COSEWIC 2002). While waiting for females to copulate, males perch on host or nectar plants or nearby shrubs. Females reportedly lay fertilized eggs on leaves at the base of robust branched umbrella plants and eggs are deposited singly or in clusters of two to four (Arnold and Powell 1983). It is not known if eggs hatch in the spring or fall, but a staggered emergence is most likely (COSEWIC 2002). The larvae are known to hibernate in stems, on flower heads, or under leaf litter of their host plants and emerge in the spring to feed (Arnold and Powell 1983). Larvae are nocturnal (Arnold and Powell 1983) and rest during the day in nests made of leaf litter and silk at the base of the branched umbrella plant where they are also thought to pupate (COSEWIC 2002). Healthy populations of branched umbrella plants are critical to metalmark development.
Mormon metalmark habitat in and around GNP is stable and relatively abundant with little threat of disturbance. More detailed surveys of GNP are required to quantify the amount of available and occupied habitat. Studies of both the Southern Mountain and Prairie populations are planned for 2007 to improve the knowledge of metalmark developmental biology, habitat requirements, and dispersal (S. Desjardins, University of British Columbia, pers. comm. 2006).
1.4.2 Limiting Factors
The following are the biologically limiting factors for the Prairie population of Mormon metalmarks, although many of these factors are not yet fully understood:
- Food plant specificity: Adult metalmarks in Saskatchewan reportedly nectar only on branched umbrella plants and rubber rabbitbrush (Hooper 2002). Larvae and pupae depend solely on branched umbrella plants for development (Scott 1986, Pyle 2002). It is not known whether metalmarks use another plant, Eriogonum flavum (i.e., alpine golden buckwheat, Piper's buckwheat, yellow buckwheat), which is closely related to E. pauciflorum and is reported to occur in GNP. Even though metalmarks have highly specific host plant requirements, both branched umbrella plants and rubber rabbitbrush are common on eroded clay soils of badlands habitat in GNP, and thus play only a partial role as a limiting factor in the distribution of this species.
- Flowering period of the food plant: The flowering period of the food plants must coincide with the metalmark flight period to ensure nectar is available. If the timing of flowering is delayed or changed, food plant senescence could impact adult survival and has the potential to cause species extirpation for particular locations. Since the Prairie population of metalmarks is at the northernmost extent of the range for this species (Opler 1999, Pyle 2002), it may be particularly susceptible to changes in climatic factors that influence the blooming period of their nectar plants.
- Dispersal capability: Mormon metalmarks have a short adult lifespan and only one annual flight period, which limit their dispersal potential in the naturally fragmented landscape of GNP (COSEWIC 2002). Most of the habitat that metalmarks occupied in 2002 and 2006 occurred on eroding slopes, which may be limited in distribution or separated by long distances. For this reason, populations may be vulnerable to natural stochastic events and extirpations, and re-colonization probability may be limited (COSEWIC 2002).
- Soil, slope and aspect habitat requirements: Known locations of metalmark colonies appear to occur in host plant patches on hillsides and slopes with exposed, eroding clay soils (Hooper 2002; A. Henderson, Grasslands National Park, unpublished data 2006). These sites are common in GNP and may be important habitat characteristics. Although apparently suitable habitat is available, very few of these locations are occupied by metalmarks. The requirement for these habitat characteristics and details of differences between available but unoccupied and occupied habitat are not well understood and may therefore be limiting.
1.5.1 Threat classification
The following factors, (Table 1), may pose a threat to the Mormon metalmark Prairie population but are not well understood. Each will be addressed in the action plan for this species.
Identification and ranking of current threats to the survival and habitat of the Mormon metalmark Prairie population (1= severe/widespread, 2= moderate/potentially widespread, 3= limited threat in scope and severity, 4= unknown).
|1||Habitat loss, degradation, and fragmentation|
|2||Invasive exotic species|
|4||Climate change and natural disasters|
1.5.2 Description of threats
Habitat loss, degradation and fragmentation
As demonstrated for other butterfly species (Franco et al. 2006, Schultz and Dlugosch 1999), habitat loss and degradation poses a potential threat to the metalmark Prairie population (COSEWIC 2002). While the probability of it occurring is low, there is the potential for habitat loss and degradation to have a severe localized effect on metalmark colonies. For this reason, it is ranked relatively high.
Examples of human activities that have the potential to destroy or degrade Mormon metalmark habitat include the following:
- Ranching activities such as locating winter-feeding, salt blocks, or calving sites on metalmark habitat could affect Mormon metalmark habitat; and
- The development of a backcountry campground or infrastructure.
The risk of habitat degradation or destruction caused by the above activities is already quite low and could be reduced almost to zero if all the colony locations are documented and made known to land managers.
Similarly, oil and gas exploration and development could cause destruction and degradation of metalmark habitat. However, as part of the Grasslands National Park establishment agreement, all the land within the proposed boundary of Grasslands National Park has had the oil and gas leases extinguished. Oil and gas exploration and development may become a larger issue if future metalmark surveys identify new metalmark locations outside of the proposed boundaries of Grasslands National Park.
Prairie fires are a relatively common and important source of disturbance in the northern mixed-grass ecosystem of Grasslands National Park. The loss of metalmark habitat by prairie fire is, however, unlikely because badland habitat is very sparsely vegetated.
Invasive exotic species
Habitat loss and degradation due to invasive exotic plant species is an important driving force for butterfly population declines (Keeler et al. 2006). Yellow sweet clover, Melilotus officinalis, is an exotic species that can outcompete native species and has already invaded badland habitat within GNP (Michalsky et al. 2005). The presence of yellow sweet clover in known metalmark habitat has not been confirmed. The potential for yellow sweet clover to alter metalmark habitat suitability by competing with branched umbrella plants or rubber rabbitbrush requires further clarification.
Pollution (i.e. agrochemicals)
In studies of other butterfly systems, agrochemical drift has resulted in direct butterfly mortality or overall reduced fitness in adults, larvae, pupae, host plants, and food plants (Davis et al. 1991a, Davis et al. 1991b, Davis et al. 1993, Longley et al. 1997). Pollution related to agrochemical drift from nearby agricultural lands, in particular grasshopper control during outbreak years is a potential threat. All metalmark populations on Parks Canada land are safe from direct spraying and privately managed rangelands are rarely sprayed but the direct application of pyrethroids and chlorpyrifos on metalmarks would likely have severe localized affects. The distance that these chemicals can drift and have toxic effects on butterflies is poorly studied but could range from 150 m to 500 m (D. Johnson, Univ. of Lethbridge, pers. comm. 2006). There are agricultural crops within 500 m of some Mormon metalmark colonies located within GNP.
Climate and natural disasters
Climate change, associated with an increase in frequency and intensity of extreme and periodic climatic events such as droughts, may affect species by: shaping species' ranges and distributions; altering competitive interactions; causing resource asynchrony; and inducing phenological2 changes and extinctions (Easterling et al. 2000, Forchhammer et al. 1998, Hughes 2000, Lemmen et al. 1997, Thomas et al. 2001, Stenseth et al. 2002). Some obvious conservation planning implications are shifts in species' ranges outside of protected area boundaries as well as maintaining populations of rare and endangered species in cases where climatic conditions for them may be deteriorating (Peters and Darling 1985, Hannah et al. 2002 a, b).
Single small populations such as the Canadian Mormon metalmark Prairie population are especially vulnerable to extinctions due to random climatic events or loss of representation due to species' range shifts with climate change (Williams and Araujo 2000). Extreme weather events such as hailstorms, severe frost or flooding pose a threat to metalmarks. Although it is difficult to predict with certainty, general circulation model (GCM) simulations suggest that the trend throughout the Northern Great Plains will be decreased precipitation and increased mean annual temperatures (Karl et al. 1991, Lemmen et al. 1997). Models of climate and vegetation changes by Rizzo and Wiken (1992) suggest that southern Alberta and Saskatchewan will become a semi-desert. Such predicted changes may alter the timing of host plant flowering or cause insufficient moisture for healthy host plant growth or larval development, thereby affecting metalmark populations. Since the Canadian metalmark Prairie population is at the northernmost extent of the range for this species, this area may actually become progressively more important in maintaining the species as the climate changes (Channell and Lomolino 2000) and core ranges potentially shift north.
1.6 Knowledge Gaps
1.6.1 Inventory and Monitoring Gaps
An inventory of available and occupied habitat, population size, and distribution around and within GNP is incomplete and requires additional surveys. To date, only two limited surveys have been completed in Saskatchewan and none have been conducted in Alberta. A monitoring program is required to gather details of population parameters, including changes in population size, immigration, recruitment, persistence, and dispersal distance, which are not yet available. In order to establish a reliable monitoring program, further research is required to determine how counts of adults in flight correlate to actual abundance determined with mark-recapture methodology. Opportunities will be sought, whenever possible, to collaborate with biologists developing monitoring methodology for the Lower Similkameen River Valley population (Southern Interior Invertebrates Recovery Team 2005).
1.6.2 Biological/Ecological Knowledge Gaps
Knowledge of biological characteristics and habitat requirements for the Canadian metalmark Prairie population is extremely limited and most of the current information comes from the United States. Therefore, future research is necessary to improve knowledge of the general biological characteristics and ecological requirements of the metalmark Prairie population. More specifically, studies are required to identify specific metalmark habitat requirements, clarify mortality factors for different life stages and population demographics, and determine why apparently suitable habitat is currently unoccupied.
Very little is also known about the genetics of this species throughout its Canadian range. There is no information on the degree to which the Canadian Prairie population is linked by dispersal to metalmark populations in northern Montana. The proximity of the nearest Montana population is not known. Genetic studies to clarify rates of dispersal among Saskatchewan populations and between Saskatchewan and Montana populations are required to assess connectivity between these sites. COSEWIC (2002) noted that a detailed examination of the nominate subspecies A. m. mormo in Canadian populations in comparison to those in the U.S. has not been undertaken and that such a study may well reveal important differences between these populations. In addition to proposed genetic studies, careful observations of adult morphology will be documented during the ongoing surveys to confirm the subspecies' identity.
1.6.3 Threat Clarification
The potential risk to the Prairie populations of metalmark butterflies from agricultural herbicide and insecticide drift needs to be better-understood so best management practices can be developed. The potential for exotic invasive plants to invade metalmark habitat and the degree that it negatively affects habitat also needs to be assessed.
1 The nominate subspecies is indicated by the repetition of the specific name (e.g. Apodemia mormo mormo)
2 Relating to periodic biological phenomena, such as flowering, breeding, and migration, in relation to climatic conditions (The American Heritage® Dictionary of the English Language, 2007).
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