Species diversity and mammalian succession in conservation reserve program grasslands

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1992-05

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Abstract

Species diversity and composition, of small mammals, were compared between Conservation Reserve Program (CAP) grasslands and native shortgrass prairie on the Southern High Plains of Texas. Six CAP fields (1, 2 and 3 years of age) in Hockley County, and two control fields at Muleshoe National Wildlife Refuge in Bailey County were sampled. Small mammals were systematically live trapped, in all four seasons of a one-year interval (May, 1990 to February, 1991). A total of 6000 trap nights was compiled: 1200 trap nights during the Spring, Summer, and Fall, and 2400 trap nights in the Winter. Three factors (vegetational heterogeneity, predation, and age of habitat) known to affect species diversity were analyzed by a variety of quantitative methods. Differences in species diversity (Fisher's log series ct) were evaluated by comparing the 95% Cl of this index among fields. Nonparametric correlations were calculated to test for associations between diversity and vegetational heterogeneity, predation, or field age. Vegetational heterogeneity (Shannon-Wiener information index) was measured using a variation of the step-point method. Predation was estimated for both vertebrate predators, and for ectoparasites. Field age was defined as the time since the establishment of the fields (for CAP fields), or since the establishment of the Refuge (for control fields). No significant differences in diversity were found between fields, and diversity was not significantly correlated with vegetational heterogeneity, predation, or field age. Species composition (proportional density of species) was significantly different among all fields in each season. Regardless of season, a priori hierarchical comparisons revealed significant differences in the proportional abundances of species in all CAP fields as a group, and in the control fields. Most of the a posteriori comparisons of particular CAP fields and the control fields similarly yielded significant differences in proportional species abundances. The CAP grasslands simulate shortgrass prairies in species diversity, but not in species composition. Differences in species composition between CAP grasslands and shortgrass prairie may be a result of the lack of natural disturbances (i.e., grazing, fire) on the CAP grasslands.

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Keywords

Mammal populations -- Texas, Grassland ecology -- Texas, Rodents -- Habitat -- Texas, Rodents -- Speciation

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