Sharon M. Hermann

Sampling on private property to evaluate population status and effects of land use practices on the gopher tortoise, Gopherus polyphemus

Abstract Although private properties are predicted to play an increasingly significant role in conservation, surveys of species of special concern are rare on these lands. We created a template for a multi-county survey of randomly selected sites and sampled for burrows of the gopher tortoise (Gopherus polyphemus) in south-central Georgia, USA. Current land use was strongly correlated with tortoise population condition. The highest densities of tortoise burrows were found on lands with open-canopied pine stands that were managed with prescribed fire, a practice associated with types of selection forestry and/or wildlife management. Agricultural sites and unburned areas provided poor habitat and pine plantations were only slightly better. Our estimates of tortoise population densities indicated that the current landscape supports less than 20% of the animals present before implementation of modern land use practices. In addition, our estimate for density of active burrows was approximately one third of that projected for the entire state range 20 years ago by Auffenberg and Franz [Auffenberg, W., Franz, R., 1982. The status and distribution of the gopher tortoise (Gopherus polyphemus). In: Bury, R.B. (Ed.), North American Tortoises: Conservation and Ecology (US Fish and Wildlife Service Wildlife Research Report 12). pp. 95–126]. However, some good sites for gopher tortoises remain in south Georgia and our data also suggested that extraordinary conservation actions may not be required if ways can be developed to retain traditional land management practices on private property.

Patterns of Folivory and Seed Ingestion by Gopher Tortoises (Gopherus polyphemus) in a Southeastern Pine Savanna

Abstract This study documents the ingestion of leaves and seeds by gopher tortoises (Gopherus polyphemus) in a relatively intact pine savanna habitat. Fifty-three species of seeds were identified. Species richness of seeds ingested was highest during spring and fall and was lowest during summer. Grass seed and foliage were consumed consistently by tortoises throughout the year. Despite being found in only 12% of all scats, Rubus seed comprised half of all seeds recovered. Based on seeds in scats, tortoises ingested the fruits of plants in the same proportions in which the plants occurred immediately around active burrows. Although some kinds of leaves were less prevalent in scats than predicted by their availability near active tortoise burrows, this may have occurred because these leaves were digested and, therefore unrecognizable in scats. The role of the gopher tortoise as a generalist herbivore and an opportunistic frugivore was confirmed.

Effects of Population Density On Patterns of Movement and Behavior of Gopher Tortoises (Gopherus polyphemus)

Abstract:  Patterns of burrow size, tortoise size, home range size and overlap, movement distances, and mating rates were compared among six sites that differed in density of Gopher Tortoises. Burrow sizes differed among sites because tortoise size distributions differed among sites, but this was due principally to the unusually small size of animals on the Conecuh National Forest. A linear relationship between tortoise density and burrow density was documented from the six sites, suggesting that tortoises, on average, created 2.5 burrows per site or that the burrow-to-tortoise conversion factor for our sites was 0.40. The average distance from a burrow to its nearest three neighbors was greater for low-density sites than for high-density sites, indicating that animals probably were more isolated from each other on sites with low tortoise densities. Tortoise home ranges were larger in males than females, a feature documented in other studies of tortoise movements. Home range sizes were greatest for densities of approximately 0.4 tortoises/ha and decreased in size above and below this density. This suggests that animals moved to visit close neighbors in areas of high density, expanded movements to maintain contact with neighbors that became more widely dispersed as density decreased, and then restricted movements to a few close neighbors as density reached extremely low levels. Home range overlap increased linearly with increasing density, suggesting that opportunities for social interactions decreased with decreasing density. When tortoises moved between burrows, males moved longer distances than females and tortoises of both sexes moved shorter distances on high-density sites than did tortoises on low-density sites, suggesting greater movement costs for males than females and for tortoises on low-density sites. Males traveled up to 500 m to visit female burrows, but most movements were < 80 m. Median movement distances of males to visit females were negatively correlated with burrow density, suggesting that cost of male movements to find mates increased as population density decreased. Based upon patterns of 95% confidence limits, rates of mountings of female tortoises approached zero when females occupied burrows approximately 200 m from neighboring burrows. If burrows were uniformly distributed 200 m apart, then reproductive failure would be a statistically supportable outcome at a density of 0.3 burrows/ha (0.12 tortoises/ha). These values are similar to the values of 0.4 tortoises/ha (1.0 burrows/ha) that our data suggest is the density at which social structure associated with movements within home ranges are altered.

Effects of Forest Management on Amphibians and Reptiles: Generalist Species Obscure Trends Among Native Forest Associates

In the future, land stewards are expected to increase their use of fire surrogates to manage longleaf pine forests. Varying land management strategies may have disparate effects on wildlife and the strength of these effects may depend upon the degree to which each target species is associated with the longleaf pine forest. To determine how amphibian and reptile assemblages respond to prescribed burns and fire surrogates, we sampled these animals within plots of land managed under four common management practices (burning, thinning, thinning and burning, and application of herbicide) and on unmanaged reference plots. We analyzed these data first by examining the entire herpetofauna and then by repeating all analyses for only taxa exhibiting some evidence of an evolutionary association with longleaf pine forests. We found that estimates of species richness of all amphibians did not differ significantly among treatments. These trends were altered when the pool of taxa was restricted to amphibian species known to be associated with longleaf pine forests. For associated amphibians, species richness was elevated on plots that were exposed to herbicide and burn, hardwood thinning, and hardwood thinning plus prescribed fire, relative to reference plots. No significant trends were identified for squamates in general or those squamate species known to be associated with longleaf forests. Fire surrogates may facilitate conservation for individual species of the ancestral biota of longleaf pine forests, but these trends may be obscured when entire assemblages are considered.

Patterns of Dispersion and Burrow Use Support Scramble Competition Polygyny in Gopherus polyphemus

Abstract Gopher tortoises spend most of their time in burrows from which they emerge to forage and perform behaviors such as courtship and mating. Previous literature is divided regarding the mating system of this species; some assert that gopher tortoises conform to female defense polygyny, and others assert that scramble competition polygyny is more likely. Here, telemetry data were used to record the frequency with which pairs of tortoises shared burrows and the frequency with which they apparently chased each other from burrows. Additionally, telemetry locations were used to estimate patterns of dispersion of individuals. If gopher tortoises conformed to female defense polygyny, then males should have: (1) moved frequently to share burrows with females, (2) rarely shared burrows with males, (3) infrequently displaced females from burrows, and (4) frequently displaced males from burrows. Similarly, females should have: (1) infrequently moved to share burrows with either sex, and (2) infrequently chased either sex. Also, females should have shown an aggregated dispersion relative to other females. On the contrary, we found that males moved equally frequently to share burrows with adults of both sexes and chased females from burrows more frequently than they chased other males. Females moved more frequently to share burrows with males than with females and chased males more often than they chased other females. Females did not have an aggregated pattern of dispersion relative to other females. These data were most consistent with scramble competition polygyny.