UVM Theses and Dissertations
Format:
Print
Author:
Rinehart, Kurt
Dept./Program:
Wildlife and Fisheries Biology Program
Year:
2007
Degree:
M.S.
Abstract:
Amphibians are often thought to signal the ecosystem health of a locale, due to their sensitivity to pollution, pH, and fluctuating climatic conditions. However, the degree to which they also signal degrading landscape patterns is unclear. To measure the effects of landscape-level patterns on salamander abundance, we surveyed populations of Eastern newts (Notophthalmus viridescens) at 551 stations across Vermont, and modeled salamander distribution as a function of environmental variables hypothesized to influence site occupancy. We developed a set of 13 a priori models based on seven hypotheses of site occupancy: (1) amount of habitat at a landscape level, (2) arrangement of breeding and non-breeding habitats at a landscape level, (3) abiotic conditions, (4) housing density, (5) road density, (6) landscape change, and (7) stand structure. For hypotheses 1-5, we assessed the performance of these variables across two different landscape extents (0.5 km, 1 krn, or 5 km). We used a single-season occupancy model to rank and compare the 13 models.
In total, 232 Eastern newts were detected at 82 of 551 stations. Of the 13 models, two represented over 90% of the weight in the model set: Abiotic NORTH (weight = 0.74) and Arrangement 0.5 km (weight = 0.17). In both models, YEAR was the strongest effect, with probability of occupancy dropping significantly between 2003 and 2004, and occurring across all sites. Newts had a higher probability of occupancy in southern Vermont, where northern hardwoods dominated. Occupancy probability increased as average distance between breeding and non-breeding habitat decreased. However, sites with significant amounts of wetland edge density decreased probability of occupancy, suggesting that both breeding and non-breeding habitat should be spatially juxtaposed, but not thoroughly integrated. Wetland edge density was negatively correlated with forest cover and positively correlated with developed land use classes, suggesting that these arrangement metrics could be largely influenced by cover amounts. Further research is needed to determine the direct role of development on occupancy patterns, and to disentangle the spatial habitat requirements of this species.
In total, 232 Eastern newts were detected at 82 of 551 stations. Of the 13 models, two represented over 90% of the weight in the model set: Abiotic NORTH (weight = 0.74) and Arrangement 0.5 km (weight = 0.17). In both models, YEAR was the strongest effect, with probability of occupancy dropping significantly between 2003 and 2004, and occurring across all sites. Newts had a higher probability of occupancy in southern Vermont, where northern hardwoods dominated. Occupancy probability increased as average distance between breeding and non-breeding habitat decreased. However, sites with significant amounts of wetland edge density decreased probability of occupancy, suggesting that both breeding and non-breeding habitat should be spatially juxtaposed, but not thoroughly integrated. Wetland edge density was negatively correlated with forest cover and positively correlated with developed land use classes, suggesting that these arrangement metrics could be largely influenced by cover amounts. Further research is needed to determine the direct role of development on occupancy patterns, and to disentangle the spatial habitat requirements of this species.