Newton, GA, United States
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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.

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.

Conner L.M.,Joseph W. Jones Ecological Research Center | Morris G.,Joseph W. Jones Ecological Research Center
PLoS ONE | Year: 2015

Declining large carnivore populations, increased habitat fragmentation, declining interests in fur trapping, and other anthropogenic factors can all lead to increased mesopredator populations and these may negatively impact biodiversity. Lethal mesopredator control potentially mitigates some of these effects but can be controversial, largely because impacts on mesopredator populations have not been evaluated. Estimating these impacts may reduce controversies while increasing our understanding of when lethal control may be beneficial. Therefore, we analyzed published mesopredator removal data to determine if mesopredator removal rates changed over time. Removals of medium,(e.g., raccoons (Procyon lotor)or red foxes (Vulpes vulpes), and large, i.e., bobcats (Lynx rufus) or coyotes (Canis latrans), mesopredators were consistent from year to year and over the duration of study (i.e., number removed during the first and last years of studies were similar). In contrast, removals of small mesopredators, e.g., weasels (Mustela spp.) or spotted skunks (Spilogale putorius), declined over the duration of study. Study area size, number of species targeted for removal, and duration of removal effort were poor predictors of removal rates. Our analyses suggest that: (1) control, as typically implemented, is unlikely to cause negative long-term impacts on populations of medium and large mesopredators but may negatively impact small mesopredators, (2) if mesopredator control benefits prey, recurring removals will generally be needed to maintain benefits, and (3) timing of removals will be important to achieve management goals. We suggest that mesopredator control efforts are frequently spatially structured harvests from continuously distributed populations. This may explain (1) why removal of small mesopredators declined over time; whereas, medium and large mesopredator removals remained consistent, and (2) why some prey failed to respond to mesopredator control efforts. © 2015 Conner, Morris. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Morris G.,Joseph W. Jones Ecological Research Center | Conner L.M.,Joseph W. Jones Ecological Research Center
Forest Ecology and Management | Year: 2016

Nest predation is often the primary cause of avian nest failure, and factors influencing nest predation are diverse. To better understand how forest management practices, weather, and indices of nest predator abundance influence nest predation, we set artificial ground nests at 100 sites for 2 weeks each summer from 2002 to 2013 in a longleaf pine/wiregrass ecosystem. We modeled effects of prescribed fire, hardwood removal, rainfall, temperature, indices of mammalian and avian nest predator abundance, and proximity to wildlife food plots and agriculture, edges, and roads on nest predation. Annual nest predation rates ranged from 30% to 74% and averaged 53%. Occurrence of prescribed fire at a nest site <2 months prior to nest placement had a strong, positive association with nest predation but prescribed fires carried out ≥2 months prior to nest placement had little effect. Hardwood removal was also associated with increased rates of nest predation, but this effect appeared most prevalent 4-9 years following removals. Nest predation rates also increased when food plots or agricultural fields were within 50 m of nest sites. Higher temperatures were associated with greater rates of predation, but rainfall did not have a significant influence. There was a general lack of support for effects of predator indices on nest predation rates, except for a weak, negative association with raccoon relative abundance. This study shows the wide range of factors which may influence nest predation and importance of viewing effects of forest management practices on nest predation over the long term. © 2016 Elsevier B.V.

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.

Stober J.M.,Joseph W. Jones Ecological Research Center | Smith L.L.,Joseph W. Jones Ecological Research Center
Journal of Wildlife Management | Year: 2010

Status and trends of gopher tortoise (Gopherus polyphemus) populations are a critical information need for natural resource managers, researchers, and policy makers. Many tortoise populations are small and isolated, which can present challenges for deriving population estimates. Our objective was to compare abundance and density estimates for a small tortoise population derived using a total burrow count versus estimates obtained with line transect distance sampling (LTDS) using repeated surveys. We also compared results of the 2 survey methods using standard burrow-to-tortoise correction factors versus assessing occupancy of all burrows with a camera scope. In addition, we compared LTDS data obtained using a compass and measuring tape to define transects to those obtained using a Global Positioning System (GPS) and Personal Data Assistant (PDA) field computer to navigate transects. Line transect distance sampling with repeated surveys (both with a measuring tape and compass and with a GPSPDA) yielded sufficient observations of tortoises to calculate population estimates. From 18 to 31 of burrows were occupied by tortoises as determined with the burrow camera. We found 25 burrows during the LTDS survey that we did not find in the total count survey, which demonstrated that the assumption of 100 detection for the total count was not met; hence, density or abundance measurements derived with this method were underestimates. We recommend using GPSPDA technology, scoping all burrows detected, and using LTDS with repeated surveys to estimate abundance and density for small gopher tortoise populations. © 2010 The Wildlife Society.

Conner L.M.,Joseph W. Jones Ecological Research Center | Rutledge J.C.,Joseph W. Jones Ecological Research Center | Smith L.L.,Joseph W. Jones Ecological Research Center
Journal of Wildlife Management | Year: 2010

Although nest predation is often the single largest source of mortality in avian populations, manipulative studies to determine predator impacts on nest survival are rare, particularly studies that examine impacts of mid-size mammalian predators (hereafter, mesopredators) on nest survival of shrub-nesting birds. We quantified nest survival and identified nest predators of shrub-nesting songbirds within 4 large (approx. 40-ha) exclosures and 4 control sites within a longleaf pine (Pinus palustris) ecosystem. During 2003-2006, we located and monitored 535 shrub nests (222 with videography) for 4,804 nest-days to quantify daily nest survival and document predation events. We found no support for a treatment effect, suggesting mesopredators had little impact on daily nest survival (0.9303 in controls and 0.9260 in exclosures) of shrub-nesting songbirds. For the 5 most commonly monitored species, daily nest survival within species was constant. Our analysis suggested that shrub nests were most vulnerable during the nestling stage and presence of cameras on nests increased survival with the increase in survival being more pronounced during the incubation stage. We filmed 107 nest predation events, identifying predators at 88 nests. Of these 88 nests, snakes caused 33%, red imported fire ants (hereafter fire ants, Solenopsis invicta) 28%, raptors 17%, corvids 8%, mesopredators 6%, and small mammals 8% of nest predations. Cause-specific nest predation in controls and exclosures did not differ from expectation, providing evidence that compensatory predation did not occur. Nest predators differed from expectation with regard to nest stage; fire ants and raptors only depredated nests during the nestling stage. Presence of cameras had no effect on nest abandonment. Fire ants were the most prevalent nest predator, and nest predation by fire ants was only observed on nestlings, potentially reducing likelihood of renesting. Magnitude and timing of fire ant predation suggests that fire ants may be the most influential nest predator of shrub-nesting birds within the longleaf pine ecosystem. Our data suggest that controlling mesopredators will have no effect on nest success of shrub-nesting birds within longleaf pine forests. © 2010 The Wildlife Society.

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.

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.

Kaeser M.J.,Joseph W. Jones Ecological Research Center | Kirkman L.K.,Joseph W. Jones Ecological Research Center
Forest Ecology and Management | Year: 2012

Restoring the fire-maintained longleaf pine (Pinus palustris Mill.) ecosystem in the southeastern United States has become a regional conservation priority in recent years and development of cost-effective approaches to restoration is a major objective. An improved understanding of the potential role of persistent seed banks in the longleaf pine ecosystem and reliance on the seed bank for restoration efforts could contribute to reduced costs associated with restoration. We used a buried seed bag method to determine seed banking potential of species within three common families (Poaceae, Fabaceae, and Asteraceae) and a rare, endangered member of the Orobanchaceae family native to the longleaf pine ecosystem. Seeds were exhumed 1, 2, 4, and 8. years after burial and tested for viability. Species within the Fabaceae showed the greatest potential for forming long-term persistent seed banks with seed viability 50% or greater after 8. years of burial. Some species in the Poaceae, Asteraceae, and Orobanchaceae form transient or short-term persistent seeds banks. The ability of some species to form short- or long-term persistent seed banks may in some cases make it possible to rely on the seed bank for native species re-introductions on sites scheduled for restoration. © 2012 Elsevier B.V.

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