EXTINCTION AND OUTBREAKS ACCOMPANY FRAGMENTATION OF A REPTILE COMMUNITY

Abstract

Land clearing depletes and fragments habitat, resulting in the loss of biodiversity. Corridors of native vegetation can ameliorate the impacts of land clearing by reducing isolation of remnant vegetation. However the effectiveness of linear remnants as corridors or connecting habitat is influenced by remnant size and condition. In central New South Wales, Australia, 84–95% of native vegetation has been cleared, with remnants occurring as isolated reserves and interconnecting strips beside roads and paddocks. Do the linear remnants provide connectivity throughout the landscape for reptile populations? In three 100-km2 agricultural locations, I classified all remnants into one of 10 “landscape elements” based on shape, management, and vegetation. I used generalized linear models and permutation tests to examine differences in reptile abundance among landscape elements. Only two blind snakes were captured in paddocks, suggesting that the matrix between remnants is virtually devoid of reptiles. Remnant shape had a strong effect, with fewer species in linear remnants than in square reserves. Five species were significantly less abundant (two of these species were absent) in linear remnants. Three species had significantly lower abundance in grazed linear remnants, and one species had lower numbers on roadsides. In contrast, five species were more abundant on roadsides, with one skink tripling in number. Limited evidence suggested that food specialization, body size, and range size were not correlated with species declines. However, allozyme electrophoresis results indicated that two declining species had stronger isolation-by-distance effects than two widespread species, implying that the decliners had weaker dispersal powers or smaller effective population sizes. Comparisons with the reptile fauna from an uncleared landscape suggested that two species may be locally extinct and that three other species had inflated population sizes in the farming locations. In addition to substantially altering the reptile community, the cumulative impact of remnant management was to increase fragmentation beyond that expected from the distribution of remnant vegetation alone. At two locations, 22% of remnant vegetation was suitable for the Nobbi dragon Amphibolurus nobbi, and the suitable remnants were subdivided into an additional 2–4 fragments. Extensive landscape restoration is now needed to help arrest reptile declines from highly cleared agricultural landscapes.