A Demographic Study of an Isolated Population of the Gopher Tortoise, Gopherus polyphemus; and an Assessment of a Relocation Procedure for Tortoises

It is acknowledged that the gopher tortoise is declining in numbers throughout its geographic range primarily from degradation and loss of suitable habitat. This research project is part of a pilot program to study the effectiveness of relocation as a mitigation method for the conservation of gopher tortoises. There was an opportunity to gather information about the tortoise population prior to its relocation, and for that reason this thesis is presented in two sections. The first section of this work involved the analysis of the tortoise population prior to its removal from the development site. Results of two methods for the estimation of population density from burrow counts seem to indicate that in some cases, those procedures may over estimate tortoise density. Excavated burrows of hatchling and juvenile tortoises showed a significant correlation between carapace length and burrow length. A von Bertalanffy interval growth equation fit to carapace length and age data produced predicted ages from specific sized tortoises that were similar to previously published data. The second section of this thesis describes the methods used to relocate a tortoise population and evaluates the success of that procedure. Use of enclosures around burrows when releasing the tortoises did not lead to their becoming permanently established in those areas. The enclosures probably served to increase the survival rate of the tortoises by establishing a source of shelter. Twenty-five tortoises (12 relocated and 13 resident) were fitted with radio transmitters to document movements. The relocated tortoises generally moved greater overall distances than the residents. However, the differences were significant only in number of moves per tortoise and not in distances per movement. The relocated tortoises did not always use burrows during their movements and often sought shelter in shallow pallets and forms

Comparison of traps and baits for censusing small mammals in Neotropical lowlands.

Snap-traps, live-traps, and baits affect the ability to capture small mammals, but few previous studies have involved sampling communities of small mammals in tropical environments. We tested differences in captures of small marsupials and rodents by Victor snap-traps versus Sherman live-traps and by two types of bait in lowland rainforest at Reserva Cuzco Amazónico, southeastern Peru. Snap-traps took ca. 3.5 times as many individuals as live-traps. Snap-traps also captured more species (and more rare species), but we attribute this to more numerous captures overall because the relative proportions of species captured by the two traps generally were the same. Type of bait had little impact on our trapping results

Effects of Supplemental Food on Population Dynamics of Cotton Rats, Sigmodon Hispidus

Variation in resource abundance affects population dynamics by altering demographic processes and interactions among individuals in the population. For small mammals, food is likely to be a critical resource. Population densities should vary directly with food abundance, but the underlying demographic changes are more difficult to predict. We experimentally increased food available to populations of hispid cotton rats, Sigmodon hispidus, to examine how rates of recruitment and disappearance varied with food abundance. We expected supplemental food to increase winter survival and to increase recruitment, perhaps advancing the date of first reproduction in the spring. We also thought larger, behaviorally dominant animals might dominate the point sources of supplemental food, altering age or size ratios and producing an excess of transient animals. Supplemental food increased population densities but did not dampen pronounced seasonal fluctuations. Supplemented populations contained proportionately more juveniles and small adults than did controls; social behavior may have limited increases in numbers of large adults. Survival rates did not change; density increases were due to increased reproduction and immigration. In supplemented populations, reproductive effort by females increased, but the proportion of reproductive females decreased. Reproductive females and nonreproductive animals of both sexes were less likely to be transients than were reproductive males. Transients constituted higher proportions of control populations because of successful settlement, primarily by juveniles and small adults, into supplemented areas. The strongly seasonal climatic conditions under which northern S. hispidus populations exist produce contrasting selective pressures which might favor season-specific foraging strategies. Our data support a scenario of territorial females and wandering males in the reproductive season, with females maximizing resource acquisition for production of offspring. During winter, both sexes may restrict foraging time (and exposure to predators and weather) to the minimum required for survival

Tricolored bats at a southern range edge exhibit partial migration northward in autumn

Abstract Background Animal migration is a widespread global adaptation by which individuals move in response to environmental conditions to reach more favorable conditions. For bats in temperate climates, migration and hibernation are often associated with each other when these bats must migrate to reach suitable overwintering sites. However, differences in movement across the geographical range of a species and the degree to which hibernation drives migratory behavior of bats in subtropical climates, where conditions may remain warm with available prey year-round, remains incomplete. Understanding the migratory strategies of subtropical bats during winter is of increasing importance as they are threatened by stressors such as disease and environmental change. Methods We evaluated migration patterns of tricolored bats (Perimyotis subflavus) in Florida, USA, through analysis of stable hydrogen isotope ratios of the fur. We inferred the summer geographic origins of the fur samples and estimated the minimum distance and likely direction traveled by hibernating individuals. We used linear models to examine whether hibernation region, colony size, and an individual’s sex affected the distance traveled. Results We sampled 111 bats hibernating at 40 sites and found that more than half (54.1%) of individuals were residents of the area in which they hibernated. We found that almost half of the sampled bats (43.2%) traveled from southern Florida to overwinter in North Florida. We also documented three individuals that traveled > 100 km from northerly origins, one of which had traveled an estimated minimum distance of 1382 km. We also found that tricolored bats moved farther to reach hibernacula in Northwest Florida and hibernacula with more populous colonies, with no difference in movement between sexes. Conclusions Our results indicate a pattern of northward autumnal movements of tricolored bats in the subtropical southeastern portion of their range. We suggest that bats are differentially constrained at the edge of their geographical range, resulting in movement contrary to what is expected. Even though we found that few (2.7%) bats moved into Florida from farther north, those migrants can potentially transfer the fungus that causes the deadly white-nose syndrome, which does not currently occur in the state. Our results support the characterization of tricolored bats as flexible partial migrators, with a rarely exercised capacity for long-distance movements

Investigating Niche And Lineage Diversification In Widely Distributed Taxa: Phylogeography And Ecological Niche Modeling Of The Peromyscus Maniculatus Species Group

The relationship between lineage formation and variation in the ecological niche is a fundamental evolutionary question. Two prevailing hypotheses reflect this relationship: niche conservatism and niche divergence. Niche conservatism predicts a pattern where sister taxa will occupy similar niche spaces; whereas niche divergence predicts that sister taxa will occupy different niche spaces. Widely distributed species often show distinct phylogeographic structure, but little research has been conducted on how the environment may be related to these phylogenetic patterns. We investigated the relationship between lineage divergence and environmental space for the closely related species Peromyscus maniculatus and P. polionotus utilizing phylogenetic techniques and ecological niche modeling (ENM). We estimated the phylogenetic relationship among individuals based on complete cytochrome b sequences that represent individuals from a majority of the species ranges. Niche spaces that lineages occupy were estimated by using 12 environmental layers. Differences in niche space were tested using multivariate statistics based on location data, and ENMs were employed using maximum entropy algorithms. Two similarity indices estimated significant divergence in environmental space based on the ENM. Six geographically structured lineages were identified within P. maniculatus. Nested within P. maniculatus we found that P. polionotus recently diverged from a clade occupying central and western United States. We estimated that the majority of the genetic lineages occupy distinct environmental niches, which supports a pattern of niche divergence. Two sister taxa showed niche divergence and represent different ecomorphs, suggesting morphological, genetic and ecological divergence between the two lineages. Two other sister taxa were observed in the same environmental space based on multivariate statistics, suggesting niche conservatism. Overall our results indicate that a widely distributed species may exhibit both niche conservatism and niche divergence, and that most lineages seem to occupy distinct environmental niches. © 2011 The Authors