Environmental correlates of toad abundance and population genetic diversity

Knowledge of factors that affect population demographic and genetic charact eristics is of importance to the development of conservation strategies. Us ing field and remote sensing of microgeographic and landscape-level feature s of the aquatic and terrestrial environment, we examined the degree to whi ch 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-isol ated breeding populations of B. bufo from Leicestershire, Great Britain, ba sed 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 frequ encies over inter-breeding pond intervals of less than or equal to2 km. Suc h estimates of "patch size" which are inferred from correlograms, may be us eful in defining the extent of effective gene flow and spatial scales over which landscape-level features could plausibly be used to characterize ecol ogical attributes of importance to individuals from specific local breeding populations. Toad presence or absence at amphibian breeding ponds, populat ion size, and population estimates of observed heterozygosity, allelic rich ness, and Wright's inbreeding coefficient (F) were individually used as dep endent variables in analyses with aquatic and terrestrial habitat character istics. Inter-population variation in inbreeding coefficients was significa ntly related to presence of additional ponds near each breeding site. Allel ic richness, population size, and toad presence/absence were primarily asso ciated with terrestrial habitat variables, including pond density and veget ative characteristics reflecting surrounding land use (e.g. presence of woo dlands; hedgerows, extent of area in livestock [sheep] pasture, and anthrop ogenic development). In the absence of definitive population demographic da ta, specific habitat characteristics may offer predictive potential for inf erring population characteristics and future viability. However, the choice of ecologically and evolutionarily relevant habitat characteristics should be made with care. (C) 2001 Elsevier Science Ltd. All rights reserved.