Environmental correlates of toad abundance and population genetic diversity

Abstract

Knowledge of factors that affect population demographic and genetic characteristics is of importance to the development of conservation strategies. Using field and remote sensing of microgeographic and landscape-level features of the aquatic and terrestrial environment, we examined the degree to which habitat characteristics were correlated with population demographic and genetic characteristics in the common toad ( Bufo bufo). Measures of genetic diversity and departures from random mating are described for 20 semi-isolated breeding populations of B. bufo from Leicestershire, Great Britain, based on three species-specific single locus variable number of tandem repeat minisatellite loci. Spatial autocorrelation of allele frequencies revealed significant population structuring or lack of independence in allele frequencies over inter-breeding pond intervals of ⩽2 km. Such estimates of “patch size” which are inferred from correlograms, may be useful in defining the extent of effective gene flow and spatial scales over which landscape-level features could plausibly be used to characterize ecological attributes of importance to individuals from specific local breeding populations. Toad presence or absence at amphibian breeding ponds, population size, and population estimates of observed heterozygosity, allelic richness, and Wright's inbreeding coefficient ( F) were individually used as dependent variables in analyses with aquatic and terrestrial habitat characteristics. Inter-population variation in inbreeding coefficients was significantly related to presence of additional ponds near each breeding site. Allelic richness, population size, and toad presence/absence were primarily associated with terrestrial habitat variables, including pond density and vegetative characteristics reflecting surrounding land use (e.g. presence of woodlands, hedgerows, extent of area in livestock [sheep] pasture, and anthropogenic development). In the absence of definitive population demographic data, specific habitat characteristics may offer predictive potential for inferring population characteristics and future viability. However, the choice of ecologically and evolutionarily relevant habitat characteristics should be made with care.