Abstract
Habitat split is a major force behind the worldwide decline of amphibian populations, causing community change in richness and species composition. In fragmented landscapes, natural remnants, the terrestrial habitat of the adults, are frequently separated from streams, the aquatic habitat of the larvae. An important question is how this landscape configuration affects population levels and if it can drive species to extinction locally. Here, we put forward the first theoretical model on habitat split which is particularly concerned on how split distance – the distance between the two required habitats – affects population size and persistence in isolated fragments. Our diffusive model shows that habitat split alone is able to generate extinction thresholds. Fragments occurring between the aquatic habitat and a given critical split distance are expected to hold viable populations, while fragments located farther away are expected to be unoccupied. Species with higher reproductive success and higher diffusion rate of post-metamorphic youngs are expected to have farther critical split distances. Furthermore, the model indicates that negative effects of habitat split are poorly compensated by positive effects of fragment size. The habitat split model improves our understanding about spatially structured populations and has relevant implications for landscape design for conservation. It puts on a firm theoretical basis the relation between habitat split and the decline of amphibian populations.
Highlights
One-third of the world’s amphibian species are threatened, more than 40% have declining populations, and 168 species probably went extinct in the last five centuries [1]
We explore the theoretical consequences of habitat split for the conservation of amphibian species with aquatic larvae
Insects with indirect development, such as dragonflies and damselflies, have been recently demonstrated to suffer from alterations in the physical structure of the riparian vegetation that disconnect the aquatic habitat of the larvae from the terrestrial habitat of the adults [33]
Summary
One-third of the world’s amphibian species are threatened, more than 40% have declining populations, and 168 species probably went extinct in the last five centuries [1]. Since amphibian species exhibit marked ontogenetic habitat shifts, being strongly affected by habitat split [16], the predictive power of such models is limited. For forest-associated amphibians with aquatic larvae, deforestation causes spatial disjunction between the habitat of the larvae, ponds and streams, and the habitat of the adults, the forest fragments. Habitat split compels adults to traverse the anthropogenic matrix to reach breeding sites and recently metamorphosed juveniles to walk haphazardly through the matrix searching for an isolated forest fragment. This compulsory bi-directional migration causes drastic declines on amphibian populations [17]
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