Population ecology and genetics of the eastern cottontail rabbit on West Texas Playa Basins
Scribner, Kim Thomas
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Spatial and temporal changes in population number, density distribution, and genetic attributes of eastern cottontails (Sylviligus floridanus) were studied on 2 playa lake basins in the Texas Panhandle. Live-trapping was conducted from February through November, 1981, resulting in 1,857 captures of 931 individuals in the course of 7450 trap nights. Seven successive litters were produced on both areas from late March through early September, 1981. Prereproductive populations were estimated at 8.2 and 11.6 cottontails/ha on playa basins A and B respectively. Subsequent monthly estimates of population numbers and densities varied with reproductive increment and dispersal, which was related to crop phenology and harvest. Animals were concentrated during periods of limited cover and flooding. A sign;ificantly (P<0.05) high proportion of individuals were found on playa peripheries prior to new spring growth and during periods of dispersal than on playa basin interiors. Surrounding wheat and cotton fields provided cover and forage for dispersing animals, causing playa densities to decrease. Population increases were noted after crop harvest. Little change in adult and juvenile mortality rates occurred throughout the study, except during periods of dispersal. Spatial and temporal changes in allele frequency, genotypic proportions, and total and single locus heterozygosity were studied on both playa basins. Prereproductive adult cottontail populations had observed genotypic proportions that deviated significantly from expected Hardy-Weinberg equilibrium, seemingly the result of heterozygote deficiencies related to differential overwinter selection and/or nonrandom genotypic dispersal. These findings are inconsistent with previous studies in which heterozygosity increases were shown to correlate with superior fitness characteristics. Significant (P_<0.05) changes in population allele frequencies, genotypic proportions, and heterozygosity were related to population demographic characteristics. Apparent random matings by individual parental genotypes and subsequent juvenile recruitment dampened or eliminated the disequilibrium in Hardy-Weinberg proportions. Changes in population number due to reproductive recruitment and dispersal were accompanied by changes in gene frequency and heterozygosity. Spatial differences in population genetic attributes were maintained between the two playa basins throughout the study because of the large distances between breeding groups. However, parallel trends were observed in population genetic and demographic characteristics on both playa basins.