Academic journal article The American Midland Naturalist

Habitat Characteristics within a Zone of Separation between the Ranges of Two Species of Pocket Gophers

Academic journal article The American Midland Naturalist

Habitat Characteristics within a Zone of Separation between the Ranges of Two Species of Pocket Gophers

Article excerpt

ABSTRACT.-

Gaps between distributions of closely related species have been noted in the literature but little empirical research exists to explain these patterns. One hypothesis is poor habitat quality occurs within the gaps and therefore prevents species from inhabiting these areas. Multiple examples of gaps between species distributions can be found among different species of pocket gophers. The objective of this research was to analyze a zone of separation between Geomys bursarius and Cratogeomys castanops in southwest Kansas. Habitat suitability maps were produced using Maxent (3.3.2) for each species throughout the study area. Values of habitat suitability and important habitat variables were compared between locations within the zone of separation and presence localities. The most important variable for predicting habitat suitability for G. bursarius was percent sand, while both percent sand and clay were important for C. castanops. Habitats within the zone of separation were significantly less suitable compared to presence localities. Also, important habitat variables (percent sand and clay) were significantly different at presence localities for both species compared to within the zone of separation. These results suggest the zone of separation between populations of G. bursarius and C. castanops is maintained by a trough of lesser quality habitat.

Pocket gophers (family Geomyidae) are subterranean rodents found throughout North America. Their solitary lifestyles, limited dispersal capabilities, and similar habitat requirements makes them ideal models for investigating patterns of distributions and ecological interactions. Species of pocket gophers generally are not sympatric in their distributions and when their distributions overlap, they tend to separate themselves ecologically. This distributional pattern is commonly referred to as parapatry (Key, 1982; Bull, 1991). Several studies have identified patterns of parapatry among pocket gophers (Miller, 1967; Vaughan, 1967; Thaeler, 1968). Specifically the distributional patterns of the plains pocket gopher ( Geomys bursarius) and yellow-faced pocket gopher ( Cratogeomys castanops) have received much attention where the geographic ranges of these species overlap primarily in portions of New Mexico, Colorado, and Kansas (Hall, 1981). In these areas of overlap, both species separate themselves by inhabiting areas with different soil types and land cover (Best, 1973; Moulton et al., 1983; Lovell et al., 2004; Hoffman and Choate, 2008).

Although populations of G. bursarius and C. castanops do not co- exist in the same habitats, the spatial characteristics of the zones of contact between the two species appear to be highly variable across the landscape. In some cases the distributions of each species do not contact each other but rather a gap is present between the populations. Hoffman and Choate (2008) noted a gap existed between the distributions of G. bursarius and C. castanops in certain areas of southwestern Kansas. This phenomenon has also been observed among other species of pocket gophers. Kennedy (1959) found a 17.7 km gap between populations of the Texas pocket gopher (Geomys personatus) and G. bursarius. Likewise, Best (1973) documented a 29 km gap between populations of Botta's pocket gopher (Thomomys bottae) and C. castanops. Because these distances are beyond the normal limits of pocket dispersal (Vaughan, 1963; Smolen el ai, 1980; Daly and Patton, 1986), any contact among these populations seems unlikely. Although these gaps between populadons of pocket gophers appear to be a common occurrence, they are not indicative of all pocket gopher distributions. Both Kennedy (1959) and Best (1973) noted several instances where the occurrences of different species of pocket gophers approached within less than 100 m. In southeastern Colorado Moulton et aL, (1979) trapped C. castanops and T. bottae from mounds 20 m apart and noted instances where the distributions of each species overlapped by approximately 800 m. …

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