Small Mammal Communities and Urban Land Cover Associations in San Marcos, Hays County, Texas




Cody, Lauren C.

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The importance of understanding small mammal diversity in urban areas is multifaceted. Small mammals affect predator population dynamics, habitat structure, and the spread of zoonotic diseases. Small mammal populations can help evaluate habitat fragmentation and quality and can potentially delineate habitat management strategies. My objectives were to determine the composition and diversity of small-mammal communities within the city of San Marcos, and to evaluate relationships between composition and diversity by meteorological seasons and land cover type. I surveyed 20 sites within urban San Marcos between August 2013 and May 2014 for a total of 11,490 trap nights over 4 seasons. I captured 280 small mammals among 12 species; the hispid cotton rat (Sigmodon hispidus), house mouse (Mus musculus), and northern pygmy mouse (Baiomys taylori) were captured more than expected overall (P ≤ 0.001). The hispid cotton rat was captured more than expected in all seasons, and in all land cover types (P = 0.007 for spring, P ≤ 0.001) except urban developed, where the house mouse was captured more than expected (P ≤ 0.001). The northern pygmy mouse was also captured more than expected in the fall (P = 0.004). An ANOVA and Tukey’s post hoc analysis show differences in captures between grassland and woodland sites (P ≤ 0.001) and between grassland and urban sites (P = 0.011). Grassland sites showed the highest trap success in both the fall (P ≤ 0.001) and winter (P = 0.001) seasons. Species richness was higher in urban sites, in the summer season, and at site 10. Site 10, the spring season, and urban sites had higher Shannon-Weiner indices of diversity. An ANOVA and Tukey’s post hoc analysis showed a difference in species diversity between grassland and woodland sites (P = 0.004). Analyses for urban sites may have been overinflated by the captures of 2 rock squirrels (Spermophilus variegatus) and a Virginia opossum (Didelphis virginiana), which are not typical for the size of Sherman trap used. The variety of species captured shows that even small pockets of natural areas and manicured parks in urban areas can support several small-mammal species. More studies should be done to better understand predator/prey population dynamics in urban San Marcos. The presence of species that are reservoirs for zoonotic diseases suggest that these populations should be monitored for disease prevalence, especially due to their proximity to human recreation areas and residences. The presence of non-native house mice and roof rats (Rattus rattus) in non-urban sites suggest poorer habitat quality due to habitat fragmentation and degradation. Species such as the hispid cotton rat can also be used to evaluate habitat quality by testing for environmental toxins. Sites that support native species should be protected from habitat degradation, and sites that sustain populations of non-native species should be targeted for the removal of those individuals. Now that areas with high numbers and diversity of small mammals have been identified in San Marcos, these sites can provide opportunities for future surveys and projects, and can be used to further assess and monitor the habitat quality of this urban area.



Small mammal, Urban, San Marcos, Rodent, Land cover, Habitat quality


Cody, L. C. (2015). Small mammal communities and urban land cover associations in San Marcos, Hays County, Texas (Unpublished thesis). Texas State University, San Marcos, Texas.


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