Demography, Topographic Orientation, and Migratory Patterns of Two Ambystomatid Communities on the Southern Cumberland Plateau in Franklin County, Tennessee.

Abstract

Habitat degradation and loss has been identified as one of the major causes of amphibian declines worldwide. Alterations to the terrestrial landscape can alter or eliminate migrations of amphibians and disrupt amphibian assemblages. Degradation of the upland habitat surrounding wetlands can have severe consequences for emigrating juvenile amphibians, decreasing gene flow within metapopulations. Analyses of topographic orientation of migratory amphibians can indicate habitat used and the occurrence migratory corridors on the landscape. This study occurred simultaneously at two wetlands located on the Southern Cumberland Plateau. The primary goals were to (1) determine the amphibian and reptile assemblages, (2) determine if migrations of ambystomatid salamanders were uniformly oriented, and (3) determine, through the use of telemetry, if current habitat management is impacting salamander migration patterns.

Two wetlands, 26007 and 26031, of differing habitats on Bear Hollow Mountain Wildlife Management Area were completely encircled with polypropylene fencing material. Pitfalls and box-style funnel traps were placed along both sides of the drift fence. Demographic and topographic orientation data were gathered between 07 December 2007 and 04 May 2010, encompassing a minimum of two breeding seasons for ambystomatid salamanders. Telemetry data were collected during the spring of 2011.

Four species of ambystomatid salamanders were captured at each site: Ambystoma opacum, Ambystoma maculatum, Ambystoma talpoideum, and Ambystoma tigrinum. Ambystomatid salamanders dominated the capture total at each site. Size and ratio of males to females varied between sites. Female A. opacum were larger than males at 26007, but males outnumbered females at the site. Male A. opacum were larger and occurred with less frequency than females at 26031. Female A. maculatum were larger and outnumbered males at both 26007 and 26031. Male A. talpoideum were larger than females at both sites and out outnumbered females at 26007, but not 26031. Recruitment of juvenile ambystomatid salamanders was stochastic between species, sites, and years.

The uniformity of migratory patterns for both male and female A. opacum varied between years at site 26007. Female and male A. maculatum immigrations were not uniform at site 26007, but emigrations were uniformly distributed across the site. Uniform migrations varied across years for male and female A. talpoideum, but emigrations were uniformly distributed across site 26007.

The immigration of male, female, and emigration of adult A. opacum were not uniform at 26031. Migratory patterns of male and female A. maculatum were not uniform at 26031, but uniform emigration was observed during Year 3. A. talpoideum male and female migrations were uniformly distributed at site 26031.

Straight-line migratory distances of A. maculatum averaged 388.18 m (range 80 - 840 m) at site 26007 and 310.67 m (range 94 - 480 m) at site 26031. The terrestrial buffer zone at each site necessary to protect 95% of the breeding population is 557.89 m (97.78 ha) at site 26007 and 439.27 m (60.62 ha) at site 26031.

Surveys indicate that large populations of ambystomatid salamanders exist in the terrestrial habitat surrounding each site. The size of these populations varied between sites and the habitat modifications surrounding site 26031 potentially impacting juvenile recruitment resulting in the differences in population sizes detected; however, it is not know if habitat management is the sole reason for differences in population size. Migratory distances observed during telemetry are the longest recorded for A. maculatum and indicate this species can migrate across open habitat during one night. Although A. maculatum has the ability to migrate across open habitat given certain environmental conditions exist, the removal of vast areas of surrounding terrestrial habitat may prove detrimental to juvenile recruitment and the overall population stability.