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Newton, GA, United States

Steen D.A.,Auburn University | Steen D.A.,Joseph W. Jones Ecological Research Center
Herpetological Conservation and Biology | Year: 2010

Standardized efforts to passively sample for upland snakes often result in low detection probabilities, yet this methodology is often used to determine differences in relative abundance. Estimating abundance of upland snakes using a model that incorporated detection probabilities did not generate useful results because detection rates were too low. These results indicate researchers interested in quantifying relative abundances of upland snakes should focus on increasing sampling efforts in an attempt to raise detection probabilities, regardless of the preferred analysis. Source

Cherry M.J.,University of Georgia | Conner L.M.,Joseph W. Jones Ecological Research Center | Warren R.J.,University of Georgia
Behavioral Ecology | Year: 2015

Costs associated with antipredator behaviors can have profound effects on prey populations. We investigated the effects of predation risk on white-tailed deer foraging behavior by manipulating predator distributions through exclusion while controlling for effects of habitat type. In 2003, we constructed predator exclosures on 4 of 8 approximately 40-ha study plots in southwestern Georgia, USA. We examined the seasonal and sex-specific effects of predator exclusion, and group size and composition on the behavioral state (i.e., feeding or vigilant) of foraging white-tailed deer at baited camera traps during 2011-2012. Predator exclusion resulted in a 5% increase in the time females spent feeding during the summer, concurrent with fawning; and 13.4% increase in the time males spent feeding during winter, while in postrut condition. Males were more vigilant than females and demonstrated a stronger response to predator exclusion. Males showed no response to group size or composition, whereas females and juveniles decreased foraging when males were present during the summer. Our results suggest that white-tailed deer alter vigilance levels in response to predator distributions independent of habitat cues. We propose that expanding coyote populations in the southeastern USA influence white-tailed deer numerically through predation of juveniles, and behaviorally by inducing antipredator responses that likely carry foraging costs. This emerging predator-prey dynamic may have strong nonconsumptive effects on naive white-tailed deer populations that experienced little nonanthropogenic predation risk for decades. © The Author 2015. Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. All rights reserved. Source

Thomas J.R.,South Florida Water Management District | McCormick P.V.,Joseph W. Jones Ecological Research Center
Fundamental and Applied Limnology | Year: 2012

Sulfate biochemistry is of particular interest in south Florida, USA, due to its role in mediating mercurymethylation rates in the Florida Everglades. Discharges from Lake Okeechobee - a subtropical, polymictic, and eutrophic lake in south Florida - are a source of sulfate to the Everglades, but it remains unclear whether this large shallow lake is simply a passive reservoir for watershed sulfate loads or an active sink or source. We evaluate hydrologic, chloride and sulfate budgets to answer this question and to clarify Lake Okeechobee's role in sulfate loading for south Florida. Evaporative losses accounted for 62 % of the water removal from Lake Okeechobee and explain the 40 % higher sulfate concentrations within the lake compared to inflowing waters. Three lines of evidence suggest the lake is a small net sink for sulfate: 1) the in-lake ratio of sulfate to chloride is lower than the inflow ratio (0.6 vs. 0.7), 2) average sulfate budget residuals (an estimate of missing sources or sinks) represent 9 % of the in-lake mass, 3) the best fit for a simple sulfate model included a removal rate of 0.061 per year. Sulfate in the lake has declined significantly over the past three decades, a result of declining sulfate loads from the Everglades Agricultural Area (EAA) and Kissimmee subwatersheds. This suggests that sulfate within the lake can be further reduced through management of the loads to the lake. In the past five years, the average net-load of sulfate discharged to the EAA from Lake Okeechobee was approximately 13,000 t year-1 representing between 16 and 20 % of the EAA sulfate budget as compared to previous estimates of 31 to 50 %. Lake Okeechobee is a much smaller contributor of sulfate to the EAA and thus to the Everglades than previously determined. © 2012 E. Schweizerbart'sche Verlagsbuchhandlung. Source

Brooks M.L.,Joseph W. Jones Ecological Research Center | Chambers J.C.,Rocky Research
Rangeland Ecology and Management | Year: 2011

Settlement by Anglo-Americans in the desert shrublands of North America resulted in the introduction and subsequent invasion of multiple nonnative grass species. These invasions have altered presettlement fire regimes, resulted in conversion of native perennial shrublands to nonnative annual grasslands, and placed many native desert species at risk. Effective management of these ecosystems requires an understanding of their ecological resistance to invasion and resilience to fire. Resistance and resilience differ among the cold and hot desert shrublands of the Great Basin, Mojave, Sonoran, and Chihuahuan deserts in North America. These differences are largely determined by spatial and temporal patterns of productivity but also are affected by ecological memory, severity and frequency of disturbance, and feedbacks among invasive species and disturbance regimes. Strategies for preventing or managing invasive plant/fire regimes cycles in desert shrublands include: 1) conducting periodic resource assessments to evaluate the probability of establishment of an altered fire regime; 2) developing an understanding of ecological thresholds associate within invasion resistance and fire resilience that characterize transitions from desirable to undesirable fire regimes; and 3) prioritizing management activities based on resistance of areas to invasion and resilience to fire. Source

Stuble K.L.,University of Tennessee at Knoxville | Kirkman L.K.,Joseph W. Jones Ecological Research Center | Carroll C.R.,University of Georgia | Sanders N.J.,University of Tennessee at Knoxville | Sanders N.J.,Copenhagen University
Conservation Biology | Year: 2011

The degree to which changes in community composition mediate the probability of colonization and spread of non-native species is not well understood, especially in animal communities. High species richness may hinder the establishment of non-native species. Distinguishing between this scenario and cases in which non-native species become established in intact (lacking extensive anthropogenic soil disturbance) communities and subsequently diminish the abundance and richness of native species is challenging on the basis of observation alone. The red imported fire ant (Solenopsis invicta), an invasive species that occurs throughout much of the southeastern United States, is such an example. Rather than competitively displacing native species, fire ants may become established only in disturbed areas in which native species richness and abundance are already reduced. We used insecticide to reduce the abundance of native ants and fire ants in four experimental plots. We then observed the reassembly and reestablishment of the ants in these plots for 1 year after treatment. The abundance of fire ants in treated plots did not differ from abundance in control plots 1 year after treatment. Likewise, the abundance of native ants increased to levels comparable to those in control plots after 1 year. Our findings suggest that factors other than large reductions in ant abundance and species density (number of species per unit area) may affect the establishment of fire ants and that the response of native ants and fire ants to disturbance can be comparable. ©2011 Society for Conservation Biology. Source

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