The pattern of nested species subsets has been reported for many taxa
in naturally or anthropogenically fragmented habitats. Of continued in
terest to ecologists is whether nestedness is mure frequently and stro
ngly associated with either selective extinction or selective coloniza
tion. We studied patterns of amphibian incidence at 118 ponds in south
western Ontario from 1992 to 1994. Our objectives were to determine if
individual species, groups of species, or the entire fauna was nested
, and at what spatial scales, to examine patterns of species associati
on, and to evaluate causal hypotheses. The entire fauna was significan
tly nested at the geographic, region and sub-region scales. Most speci
es were highly nested, but differences occurred among regions for some
species. Species grouped by their requirement for woodland habitat or
susceptibility to fish predation showed a high degree of nestedness.
Historic deforestation and introduction of predatory fish are the like
ly mechanisms of extinction in this fauna. Species grouped as ''good d
ispersers'' were less nested than ''poor dispersers''. Species inciden
ce was positively correlated with potential dispersal abilities. Our r
esults suggest the importance of both selective extinction and selecti
ve colonization in contributing to the degree of nestedness in this fa
una. Nested patterns may be the rule for faunas having high turnover o
n mainlands. Species poor sites were dominated by the same assemblage
of three species, suggesting that single large reserves are preferable
to several small reserves for conservation of temperate zone pond-dwe
lling amphibian assemblages.