Dynamics of Peripheral Populations of Great Basin Pocket Mice, <em>Perognathus parvus</em>, and Western Harvest Mice, <em>Reithrodontomys megalotis</em>, in Southern British Columbia

Abstract

The Great Basin Pocket Mouse (Perognathus parvus) and Western Harvest Mouse (Reithrodontomys megalotis) are two peripheral species occurring in the southern Okanagan Valley of British Columbia, Canada. Both species are listed as vulnerable to extirpation because of habitat loss, primarily due to conversion of natural habitat to agricultural uses and suburban expansion. Population dynamics of these two species were studied in three habitat types: old field, sagebrush, and pine forest. The Great Basin Pocket Mouse occurred at densities ranging from 12 to 28/ha in sagebrush habitats and at 2-8/ha in old fields and Ponderosa Pine forest. The Western Harvest Mouse occurred at variable densities up to 10/ha in old fields and up to 5/ha in sagebrush habitats. Mean number of lactating females for Great Basin Pocket Mice ranged from 4-8 in sagebrush, 1-5 in old fields and pine forests combined. Mean juvenile survival to adulthood ranged from 3.28 young Great Basin Pocket Mice per pregnant female in sagebrush, 4.67 in old field, and 1.82 in pine forest habitats. Mean juvenile survival to adulthood of Western Harvest Mice ranged from 1.46-1.72 young per female in old field and sagebrush habitats. Conservation of habitat features (high biomass and structural diversity of grasses and forbs) in linear habitats has the potential to maintain populations of Western Harvest Mice. The Great Basin Pocket Mouse needs features of sagebrush and old field habitats that need to be conserved as natural non-linear components in mosaics of natural and anthropogenic habitats. Both species could act as “indicators” of habitat integrity for a wide range of other vertebrate, invertebrate, and plant species in the Okanagan Valley.

Abundance and diversity of small mammals in response to various linear habitats in semi-arid agricultural landscapes

“…This pattern was clear for P. parvus which inhabited the orchard-sagebrush margin to a significant degree, followed by the orchard-old field margin. Mean abundance per line was 3.9 times higher in the sage than old field margin; a similar magnitude of difference was reported for non-linear examples of these two habitats (Sullivan and Sullivan, 2008). Tattersall et al (2002) reported no difference in small mammal abundance or diversity when linear and nonlinear habitats in an agricultural setting were compared.…”

“…Two small mammals considered at risk are the Great Basin pocket mouse (Perognathus parvus Peale) and the western harvest mouse (Reithrodontomys megalotis Baird) (Sullivan and Sullivan, 2008). Both species occupy big sagebrush (Artemisia tridentata Nutt.)…”

“…and old field/perennial grassland habitats with occasional forays by the pocket mouse into ponderosa pine (Pinus ponderosa Dougl.) forest (Sullivan and Sullivan, 2008). Although these two species have peripheral ranges in BC and wider distributions in the United States, their persistence is an indicator of the health and integrity of natural habitats.…”

An Addition to the Mammalian Fauna of Saskatchewan: The Western Harvest Mouse, <em>Reithrodontomys megalotis</em>

“…This is particularly true when one considers that success in live-trapping Western Harvest Mice may vary considerably from year to year in areas where it is known to occur (Heske et al 1984;Reynolds et al 1999*). Sullivan and Sullivan (2008) suggested that the Western Harvest Mouse could persist among habitats of diverse quality through dispersal, which is generally <300 m (Clark et al 1988;Skupski 1995). However, long-distance movements of 375-3200 m have been reported by Clark et al (1988).…”

Conservation, Connectivity, and Coexistence: Understanding Corridor Efficacy in Fragmented Landscapes

“…Western harvest mouse (Reithrodontomys megalotis) populations are common across the western United States and central Mexico in rangeland, prairies, and deserts with elevations between -77 and 4000 m (Webster and Jones 1982;Ruff and Wilson 1999). While habitat generalists, R. megalotis populations are abundant in rangeland and old fields, as the 20 species require dense vegetative cover and tall grass for foraging, nesting, and protection from predators (Kaufman and Fleharty 1974;Sullivan and Sullivan 2008). Frequently found bordering riparian and agricultural areas and using linear habitats as corridors, the species is not sensitive to edge effects.…”