Geology topics

Mathew J. Denton

Publications and source records attributed to Mathew J. Denton.

4 recordsLinked to original sources

USGS2018

Stable isotope analysis enhances our understanding of diamondback terrapin Malaclemys terrapin foraging ecology

Dietary studies on generalist predators may provide valuable information on spatial or temporal changes in the structure of ecological communities. We initiated this study to provide baseline data and determine the utility of stable isotope analysis (SIA) to evaluate the foraging strategies of an opportunistic reptilian predator, the diamondback terrapin ( Malaclemys terrapin ), which specializes in salt marshes and mangrove estuaries along the Atlantic and Gulf coasts. We evaluated stable carbon (δ 13 C) and nitrogen (δ 15 N) isotope values of multiple tissues from terrapins inhabiting mainland and island mangrove habitats in south Florida and potential food sources to examine spatial and temporal variations in terrapin resource use. We fit linear regression models to determine the best predictors of isotopic values for both terrapins and their prey, and Stable Isotope Bayesian Ellipses in R (SIBER) analysis to examine terrapin isotopic niche space and overlap between groups. We identified differences in terrapin isotopic δ 13 C and δ 15 N values among all sites. Blood and scute tissues revealed different isotopic compositions and niche overlap between sites, suggesting diets or foraging locations may change over time, and amount of variation is site specific. Niche overlap between size classes was larger for blood (short term) versus scute (long term), suggesting greater variability in food habits or resource isotopes over the long term versus short term. These results demonstrate the usefulness of SIA in examining the spatial and temporal variability in diamondback terrapin resource use within estuary systems and further define their niche within these dynamic food webs.

Estuaries and Coasts↗

USGS2016

Diet of diamondback terrapins (Malaclemys terrapin) in subtropical mangrove habitats in South Florida

Unique among turtles as the only exclusively estuarine species, the diamondback terrapin’s (Malaclemys terrapin) life history predisposes it to impacts from humans both on land and in the near-shore environment. Terrapins are found in salt marshes and mangroves along the Atlantic and Gulf coasts from Massachusetts to Texas. Whereas previous dietary studies have elucidated terrapins’ role in temperate salt marsh food webs, food resources for terrapins inhabiting subtropical mangrove habitats have not been studied. We examined dietary resource use for diamondback terrapins in subtropical mangrove creek and island habitats within Everglades National Park, Florida, to determine foraging strategies of terrapins inhabiting south Florida (SF) mangrove systems. Fecal analysis revealed 6 categories of food items, with gastropods, crabs, and bivalves being the dominant food items. Multivariate analysis revealed differences in food sources based on habitat more so than by terrapin size class. Our results revealed that like their counterparts in temperate salt marshes, SF terrapins consume similar prey categories but with different species and abundances comprising each category.

Florida↗

USGS2015

Malaclemys terrapin rhizophorarum (mangrove diamond-backed terrapin)

MALACLEMYS TERRAPIN RHIZOPHORARUM (Mangrove Diamond-backed Terrapin). DIET. Malaclemys terrapin rhizophorarum, one of seven subspecies of M. terrapin, inhabits subtropical mangrove habitats in South Florida, USA. In temperate climates M. terrapin is largely carnivorous, feeding primarily on gastropods, bivalves, and decapod crustaceans (Tucker et. al. 1995. Herpetologica 51:167–181; Butler et. al. 2012. Chelon. Conserv. Biol. 11:124–128). In addition to its preferred prey, M. t. rhizophorarum has also been reported to consume barnacles, fish, and vegetation (Tucker et. al. 1995, op. cit.; Butler et. al. 2012, op. cit.; Tulipani 2013. Ph.D. Dissertation. The College of William and Mary, Williamsburg, Virginia. 224 pp.). Herein, we report observations regarding the diet of M. t. rhizophorarum from the southernmost extent of their range in the Florida Keys, USA.

Herpetological Review↗

USGS2014

Home range and movements of American alligators ( Alligator mississippiensis ) in an estuary habitat

Background Understanding movement patterns of free-ranging top predators throughout heterogeneous habitat is important for gaining insight into trophic interactions. We tracked the movements of five adult American alligators to delineate their estuarine habitat use and determine drivers of their activity patterns in a seasonally-fluctuating environment. We also compared VHF- and satellite-tracks of one of the alligators to examine tradeoffs in data quality and quantity. Results All tracked alligators showed high site fidelity in the estuary, but estimated home range size and core-use areas were highly variable. Two alligators were relatively sedentary and remained in the upper stream zone. One alligator traveled to a transition zone between freshwater marsh and estuary habitat, but primarily remained in the upstream area. Two alligators traveled to the downstream zone into saline conditions and showed high salinity tolerance. Overall movement rates were highly influenced by salinity, temperature, and season. Both satellite and VHF radio telemetries resulted in similar home range, core-use area, and activity centers. Conclusions This study reveals consistent use of estuary habitat by American alligators. The alligators showed variations in their movement pattern and seasonal habitat, with movement attributable to environmental factors. Although satellite-derived locations were more dispersed compared to locations collected using VHF radio-tags, data collected from VHF tracking omitted some habitat used for a short period of time, indicating the effectiveness of satellite telemetry to continuously track animals for ecosystem-scale studies.

Florida↗