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At least 811 records · Page 45Linked to original sources

USGS2005

Artificial nest experiments in a fragmented neotropical cloud forest

We conducted artificial nest experiments in a Neotropical montane forest in the eastern Andes, Colombia, in order to test the effect of placing the nests in forest fragments or continuous forests, at two nest heights and for two different climatic seasons. Predation was not consistently different between nests placed in fragments and controls. However, we found that nests on the ground had a higher daily probability of being predated than nests in the understory. Also, daily nest mortality rate (DNM) was higher in the wet season than in the dry season. Most of the predated nests were attributed to mammals (56%), and predation occurred mostly on the ground (78%). Our estimates of DNM are quite low (= 0.023) and similar to another Neotropical montane forest and other Neotropical sites. Comparisons of DNM between Neotropical and temperate sites suggests that predation rates are similar. Our results suggest that fragmentation may not have a large negative impact in nest predation for bird populations breeding in fragments compared to other sites in tropical and temperate regions. ?? The Neotropical Ornithological Society.

Ornitologia Neotropical↗

USGS2017

Acoustic assessment of pelagic planktivores, 2016

Alewife ( Alosa pseudoharengus ) and Rainbow Smelt ( Osmerus mordax ) are the most abundant pelagic planktivores in Lake Ontario (Weidel et al 2017), and the most important prey for salmon and trout, making up greater than 90% of the diet of the top predator, Chinook salmon (Lantry 2001, Brandt 1986), and supporting a multimillion dollar sportfishery. Alewife are also important prey for warm water predators, notably Walleye ( Sander vitreus ). Abundance of Alewife and smelt has declined since the 1980s, likely due to reduced nutrient loading, proliferation of invasive dreissenid mussels, and predation by stocked salmon and trout. Cisco ( Coregonus artedi ), a native planktivore, historically dominated the offshore pelagic prey fish of Lake Ontario, but their populations were severely reduced in the mid-20th century due to overfishing and competition with Alewife and smelt. Remnant populations of Cisco still exist, mostly in the eastern basin, and Cisco produce periodic strong year classes once or twice per decade (Owens et al 2003, most recently in 2012 and 2014 (OMNRF, 2017). Alewife ( Alosa pseudoharengus ) and Rainbow Smelt ( Osmerus mordax ) are the most abundant pelagic planktivores in Lake Ontario (Weidel et al 2017), and the most important prey for salmon and trout, making up greater than 90% of the diet of the top predator, Chinook salmon (Lantry 2001, Brandt 1986), and supporting a multimillion dollar sportfishery. Alewife are also important prey for warm water predators, notably Walleye ( Sander vitreus ). Abundance of Alewife and smelt has declined since the 1980s, likely due to reduced nutrient loading, proliferation of invasive dreissenid mussels, and predation by stocked salmon and trout. Cisco ( Coregonus artedi ), a native planktivore, historically dominated the offshore pelagic prey fish of Lake Ontario, but their populations were severely reduced in the mid-20th century due to overfishing and competition with Alewife and smelt. Remnant populations of Cisco still exist, mostly in the eastern basin, and Cisco produce periodic strong year classes once or twice per decade (Owens et al 2003, most recently in 2012 and 2014 (OMNRF, 2017).

Lake Ontario↗

USGS2018

Demographic drivers of a refugee species: Large‐scale experiments guide strategies for reintroductions of hirola

Effective reintroduction strategies require accurate estimates of vital rates and the factors that influence them. The hirola ( Beatragus hunteri ) is the rarest antelope on Earth, with a global population size of <500 individuals restricted to the Kenya–Somali border. We estimated vital rates of hirola populations exposed to varying levels of predation and rangeland quality from 2012 to 2015, and then built population matrices to estimate the finite rate of population change (λ) and demographic sensitivities. Mean survival for all age classes and population growth was highest in the low‐predation–high‐rangeland‐quality setting (λ = 1.08 ± 0.03 [mean ± SE]), and lowest in the high‐predation–low‐rangeland‐quality setting (λ = 0.70 ± 0.22). Retrospective demographic analyses revealed that increased fecundity (the number of female calves born to adult females annually) and female calf survival were responsible for higher population growth where large carnivores were absent. In contrast, variation in adult female survival was the primary contributor to differences in population growth attributable to rangeland quality. Our analyses suggest that hirola demography is driven by a combination of top‐down (predation) and bottom‐up (rangeland quality) forces, with populations in the contemporary geographic range impacted both by declining rangeland quality and predation. To enhance the chances of successful reintroductions, conservationists can consider rangeland restoration to boost both the survival and fecundity of adult females within the hirola's historical range.

Ecological Applications↗

USGS2025

Dynamic riskscapes for prey: Disentangling the impact of human and cougar presence on deer behavior using GPS smartphone locations

Prey species adjust their behavior along human-use gradients by balancing risks from predators and humans. During hunting seasons, prey often exhibit strong antipredator responses to humans but may develop tolerance in suburban areas to exploit human-mediated resources. Additionally, areas with high human activity may offer reduced predation risk if apex predators avoid such locations. This study examined mule deer Odocoileus hemionus behavioral responses to risks from humans and their primary predators, cougars Puma concolor , contextualized by differences in risk levels between study sites, individual risk exposure, and human habituation. We framed our investigation using three non-mutually exclusive hypotheses: (H1) neutral impact, (H2) human shielding (human tolerance driven by cougar avoidance), and (H3) super-additive risk (human avoidance dominating behavior). We controlled for deer phenology and diel period, recognizing that deer behavior varies with these temporal dynamics. Spatiotemporal cougar encounter risk was quantified using GPS collar data, while spatiotemporal human encounter risk and use intensity were quantified using GPS smartphone data. Our results supported H2 and H3, emphasizing the significance of site- and individual-level variation in risk exposure and human use intensity. Deer managed cougar risk adaptively, but humans emerged as the dominant perceived risk, varying by study site. At the site with higher cougar density and lower human hunting pressure, deer exhibited antipredator responses to humans based on individual exposure to human activity, except during hunting season, when tolerance for cougars increased. Conversely, humans were the dominant risk at the site with lower cougar density and greater human hunting pressure. Deer behavior varied significantly across a gradient of human use, influenced by nuanced human presence and predation risks, which were discernible using human smartphone data.

Colorado, Utah↗

USGS2016

Larval long-toed salamanders incur nonconsumptive effects in the presence of nonnative trout

Predators can influence prey directly through consumption or indirectly through nonconsumptive effects (NCEs) by altering prey behavior, morphology, and life history. We investigated whether predator-avoidance behaviors by larval long-toed salamanders ( Ambystoma macrodactylum ) in lakes with nonnative trout result in NCEs on morphology and development. Field studies in lakes with and without trout were corroborated by experimental enclosures, where prey were exposed only to visual and chemical cues of predators. We found that salamanders in lakes with trout were consistently smaller than in lakes without trout: 38% lower weight, 24% shorter body length, and 29% shorter tail length. Similarly, salamanders in protective enclosures grew 2.9 times slower when exposed to visual and olfactory trout cues than when no trout cues were present. Salamanders in trout-free lakes and enclosures were 22.7 times and 1.48 times, respectively, more likely to metamorphose during the summer season than those exposed to trout in lakes and/or their cues. Observed changes in larval growth rate and development likely resulted from a facultative response to predator-avoidance behavior and demonstrate NCEs occurred even when predation risk was only perceived. Reduced body size and growth, as well as delayed metamorphosis, could have ecological consequences for salamander populations existing with fish if those effects carry-over into lower recruitment, survival, and fecundity.

Montana↗

USGS2016

Efficacy of GPS cluster analysis for predicting carnivory sites of a wide-ranging omnivore: the American black bear

The capacity to describe and quantify predation by large carnivores expanded considerably with the advent of GPS technology. Analyzing clusters of GPS locations formed by carnivores facilitates the detection of predation events by identifying characteristics which distinguish predation sites. We present a performance assessment of GPS cluster analysis as applied to the predation and scavenging of an omnivore, the American black bear ( Ursus americanus ), on ungulate prey and carrion. Through field investigations of 6854 GPS locations from 24 individual bears, we identified 54 sites where black bears formed a cluster of locations while predating or scavenging elk ( Cervus elaphus ), mule deer ( Odocoileus hemionus ), or cattle ( Bos spp.). We developed models for three data sets to predict whether a GPS cluster was formed at a carnivory site vs. a non-carnivory site (e.g., bed sites or non-ungulate foraging sites). Two full-season data sets contained GPS locations logged at either 3-h or 30-min intervals from April to November, and a third data set contained 30-min interval data from April through July corresponding to the calving period for elk. Longer fix intervals resulted in the detection of fewer carnivory sites. Clusters were more likely to be carnivory sites if they occurred in open or edge habitats, if they occurred in the early season, if the mean distance between all pairs of GPS locations within the cluster was less, and if the cluster endured for a longer period of time. Clusters were less likely to be carnivory sites if they were initiated in the morning or night compared to the day. The top models for each data set performed well and successfully predicted 71–96% of field-verified carnivory events, 55–75% of non–carnivory events, and 58–76% of clusters overall. Refinement of this method will benefit from further application across species and ecological systems.

New Mexico↗

USGS2017

Detect and exploit hidden structure in fatty acid signature data

Estimates of predator diet composition are essential to our understanding of their ecology. Although several methods of estimating diet are practiced, methods based on biomarkers have become increasingly common. Quantitative fatty acid signature analysis (QFASA) is a popular method that continues to be refined and extended. Quantitative fatty acid signature analysis is based on differences in the signatures of prey types, often species, which are recognized and designated by investigators. Similarly, predator signatures may be structured by known factors such as sex or age class, and the season or region of sample collection. The recognized structure in signature data inherently influences QFASA results in important and typically beneficial ways. However, predator and prey signatures may contain additional, hidden structure that investigators either choose not to incorporate into an analysis or of which they are unaware, being caused by unknown ecological mechanisms. Hidden structure also influences QFASA results, most often negatively. We developed a new method to explore signature data for hidden structure, called divisive magnetic clustering (DIMAC). Our DIMAC approach is based on the same distance measure used in diet estimation, closely linking methods of data exploration and parameter estimation, and it does not require data transformation or distributional assumptions, as do many multivariate ordination methods in common use. We investigated the potential benefits of the DIMAC method to detect and subsequently exploit hidden structure in signature data using two prey signature libraries with quite different characteristics. We found that the existence of hidden structure in prey signatures can increase the confusion between prey types and thereby reduce the accuracy and precision of QFASA diet estimates. Conversely, the detection and exploitation of hidden structure represent a potential opportunity to improve predator diet estimates and may lead to new insights into the ecology of either predator or prey. The DIMAC algorithm is implemented in the R diet estimation package qfasar.

Ecosphere↗

USGS2024

Evaluating mountain lion diet before and after a removal of feral horses in a semiarid environment

Non-native species can affect ecosystems by influencing native predator-prey dynamics. Therefore, management interventions designed to remove non-natives may inadvertently lead to increased predation on native species. Feral horses are widely distributed throughout the arid parts of western North America. A growing body of research indicates that horses can be an important prey species to mountain lions in ecosystems where they overlap. In December 2020, the Bureau of Land Management removed 455 horses from the Delamar Mountains, Nevada, USA. We leveraged this management intervention to implement a before–after–control–impact study to test hypotheses about predation on horses and native ungulates. We predicted (1) that horses would comprise an important part of the diet in this mixed-prey community, (2) following removal, the proportion of horses in the diet would decrease and native ungulates would increase, and (3) mountain lion home ranges overlapping the treatment areas would increase in response to decreased prey availability. From 2018 to 2022, we investigated 1360 clusters from 29 GPS-collared lions and identified 1056 prey items. To model the probability of a predation event (a kill), we fit a mixed-effects logistic regression model for ungulate prey as a function of lion sex, treatment area (in/out), and treatment period (pre-/post-removal). We used a log-linear regression model to evaluate changes in home range size. The most common prey were mule deer (55%), feral horses (32%), and coyotes (4%). Twenty-two of 29 lions consumed horses, although the rate of horse consumption was highly variable across individuals. Horses of both sexes and all age classes were predated. In contrast to predictions, our models detected no effect of removals on diet composition (β interaction = 0.30 ± 1.1), nor did the removal influence home range size (β interaction = 0.02 ± 0.02). Despite a 46% reduction in horse abundance, we found no evidence for prey-switching following the horse removal treatment. Removal magnitude, rapid horse immigration, and/or behavioral specialization of individual mountain lions may help explain these results. Our findings have important implications for mountain lion and feral horse management in arid environments characterized by high prey diversity, but low prey abundance.

Nevada↗

USGS2016

Annual elk calf survival in a multiple carnivore system

The realized effect of multiple carnivores on juvenile ungulate recruitment may depend on the carnivore assemblage as well as compensation from forage and winter weather severity, which may mediate juvenile vulnerability to predation in ungulates. We used a time-to-event approach to test for the effects of risk factors on annual elk ( Cervus canadensis ) calf survival and to estimate cause-specific mortality rates for 2 elk populations in adjacent study areas in the southern Bitterroot Valley, Montana, USA, during 2011–2014. We captured and radio-tagged 286 elk calves: 226 neonates, and 60 6-month-old calves. Summer survival probability was less variable than winter ( P = 0.12) and averaged 0.55 (95% CI = 0.47–0.63), whereas winter survival varied more than summer and significantly across study years ( P = 0.003) and averaged 0.73 (95% CI = 0.64–0.81). During summer, elk calf survival increased with biomass of preferred forage biomass, and was slightly lower following winters with high precipitation; exposure to mountain lion ( Puma concolor ) predation risk was unimportant. In contrast, during winter, we found that exposure to mountain lion predation risk influenced survival, with a weak negative effect of winter precipitation. We found no evidence that forage availability or winter weather severity mediated vulnerability to mountain lion predation risk in summer or winter (e.g., an interaction), indicating that the effect of mountain lion predation was constant regardless of spatial variation in forage or weather. Mountain lions dominated known causes of elk calf mortality in summer and winter, with estimated cause-specific mortality rates of 0.14 (95% CI = 0.09–0.20) and 0.12 (95% CI = 0.07–0.18), respectively. The effect of carnivores on juvenile ungulate recruitment varies across ecological systems depending on relative carnivore densities. Mountain lions may be the most important carnivore for ungulates, especially where grizzly bears ( Ursus arctos ) and wolves ( Canis lupus ) are rare or recovering. Finally, managers may need to reduce adult female harvest of elk as carnivores recolonize to balance carnivore and ungulate management objectives, especially in less productive habitats for elk.

Journal of Wildlife Management↗

USGS2018

Landscape‐level patterns in fawn survival across North America

A landscape‐level meta‐analysis approach to examining early survival of ungulates may elucidate patterns in survival not evident from individual studies. Despite numerous efforts, the relationship between fawn survival and habitat characteristics remains unclear and there has been no attempt to examine trends in survival across landscape types with adequate replication. In 2015–2016, we radiomarked 98 white‐tailed deer ( Odocoileus virginianus ) fawns in 2 study areas in Pennsylvania. By using a meta‐analysis approach, we compared fawn survival estimates from across North America using published data from 29 populations in 16 states to identify patterns in survival and cause‐specific mortality related to landscape characteristics, predator communities, and deer population density. We modeled fawn survival relative to percentage of agricultural land cover and deer density. Estimated average survival to 3–6 months of age was 0.414 ± 0.062 (SE) in contiguous forest landscapes (no agriculture) and for every 10% increase in land area in agriculture, fawn survival increased 0.049 ± 0.014. We classified cause‐specific mortality as human‐caused, natural (excluding predation), and predation according to agriculturally dominated, forested, and mixed (i.e., both agricultural and forest cover) landscapes. Predation was the greatest source of mortality in all landscapes. Landscapes with mixed forest and agricultural cover had greater proportions and rates of human‐caused mortalities, and lower proportions and rates of mortality due to predators, when compared to forested landscapes. Proportion and rate of natural deaths did not differ among landscapes. We failed to detect any relationship between fawn survival and deer density. The results highlight the need to consider multiple spatial scales when accounting for factors that influence fawn survival. Furthermore, variation in mortality sources and rates among landscapes indicate the potential for altered landscape mosaics to influence fawn survival rates. Wildlife managers can use the meta‐analysis to identify factors that will facilitate comparisons of results among studies and advance a better understanding of patterns in fawn survival.

Journal of Wildlife Management↗

USGS2015

Causes of mortality and temporal patterns in breeding season survival of lesser prairie-chickens in shinnery oak prairies

Baseline survival and mortality data for lesser prairie-chickens ( Tympanuchus pallidicinctus ) are lacking for shinnery oak ( Quercus havardii ) prairies. An understanding of the causes and timing of mortalities and breeding season survival in this ecoregion is important because shinnery oak prairies have hotter and drier environmental conditions, as well as different predator communities compared with the northern distribution of the species. The need for this information has become more pressing given the recent listing of the species as threatened under the U.S. Endangered Species Act. We investigated causes of mortality and survival of lesser prairie-chickens during the 6-month breeding season (1 Mar–31 Aug) of 2008–2011 on the Texas Southern High Plains, USA. We recorded 42 deaths of radiotagged individuals, and our results indicated female mortalities were proportionate among avian and mammalian predation and other causes of mortality but survival was constant throughout the 6-month breeding season. Male mortalities were constant across avian and mammalian predation and other causes, but more mortalities occurred in June compared with other months. Male survival also varied by month, and survival probabilities were lower in June–August. We found predation on leks was rare, mortalities from fence collisions were rare, female survival did not decrease during incubation or brood-rearing, and survival was influenced by drought. Our study corroborated recent studies that suggested lesser prairie-chickens are living at the edge of their physiological tolerances to environmental conditions in shinnery oak prairies. As such, lesser prairie-chickens in our study experienced different patterns of mortality and survival that we attributed to hot, dry conditions during the breeding season. Specifically, and converse to other studies on lesser prairie-chicken survival and mortality, drought positively influenced female survival because females did not incubate eggs during drought conditions; the incubation period is when females are most vulnerable to predation. Male mortalities and survival were negatively influenced by drought later in the breeding season, which we attributed to rigorous lekking activities through late May combined with lack of food and cover as the breeding season progressed into summer.

Texas↗

USGS2019

Resource concentration mechanisms facilitate foraging success in simulations of a pulsed oligotrophic wetland

Context Movement of prey on hydrologically pulsed, spatially heterogeneous wetlands can result in transient, high prey concentrations, when changes in landscape features such as connectivity between flooded areas alternately facilitate and impede prey movement. Predators track and exploit these concentrations, depleting them as they arise. Objectives We sought to describe how prey pulses of fish rapidly form and persist on wetland landscapes, while enduring constant consumption by wading birds, without being fully depleted. Specifically, we questioned how is the predator–prey relationship mediated by interactions between animal movement and dynamic landscape connectivity? Methods Two models were developed of the predator–prey-landscape system with qualitatively different representations of space, to identify and quantify prey pulsing dynamics that were robust across modeled assumptions. The first included a homogeneous landscape described by simple geometry, and implicit fish movement as wetland volume contracts. The second modeled transverse movement across a heterogeneous landscape, with isolated drying patches. Results Both models produced rapid fish prey concentrations as the wetland dried to shallow water depths. These conditions are critical for making prey available to wading birds. Fish were also rapidly depleted by birds, representing daily caloric intake supporting birds. Model 1 provided average estimates across the modeled domain. Model 2 mapped locations of emerging prey hotspots on the landscape through time. Conclusions Our models tracked predator, prey, and landscape dynamics in parallel, inducing systems dynamics from empirical observations. Explicit inclusion of dynamic wetland hydrologic connectivity, a key landscape mechanism, allowed for a comprehensive picture of links between landscape dynamics and the adapted predator–prey system.

Landscape Ecology↗

USGS2016

Should fatty acid signature proportions sum to 1 for diet estimation?

Knowledge of predator diets, including how diets might change through time or differ among predators, provides essential insights into their ecology. Diet estimation therefore remains an active area of research within quantitative ecology. Quantitative fatty acid signature analysis (QFASA) is an increasingly common method of diet estimation. QFASA is based on a data library of prey signatures, which are vectors of proportions summarizing the fatty acid composition of lipids, and diet is estimated as the mixture of prey signatures that most closely approximates a predator’s signature. Diets are typically estimated using proportions from a subset of all fatty acids that are known to be solely or largely influenced by diet. Given the subset of fatty acids selected, the current practice is to scale their proportions to sum to 1.0. However, scaling signature proportions has the potential to distort the structural relationships within a prey library and between predators and prey. To investigate that possibility, we compared the practice of scaling proportions with two alternatives and found that the traditional scaling can meaningfully bias diet estimators under some conditions. Two aspects of the prey types that contributed to a predator’s diet influenced the magnitude of the bias: the degree to which the sums of unscaled proportions differed among prey types and the identifiability of prey types within the prey library. We caution investigators against the routine scaling of signature proportions in QFASA.

Ecological Research↗

USGS2004

The distribution of seabirds and pinnipeds in Marguerite Bay and their relationship to physical features during austral winter 2001

The distribution of seabirds and pinnipeds and their relationship to physical oceanographic variables were investigated as part of the US Southern Ocean Global Ocean Ecosystem Dynamics field program along a study grid centered around Marguerite Bay on the west Antarctic Peninsula during late fall (April-May) and winter (July-August), 2001. Sea-ice conditions during the cruises provided an opportunity to compare the relationship among physical oceanographic variables and species distributions before and after the development of pack ice. During the fall cruise before pack ice development, both sea-ice-affiliated species and open-water-affiliated were observed in the area. The most common ice-affiliated species observed at this time were snow petrel (Pagodroma nivea, 0.7 individuals km-2) and Antarctic petrel (Thalassoica antarctica, 0.2 individuals km-2) and the most common open-water-affiliated species were blue petrel (Halobaena caerulea, 0.4 individuals km-2), cape petrel (Daption capense, 0.2 individuals km-2), and southern fulmar (Fulmarus glacialoides, 0.1 individuals km-2). In addition, Antarctic fur seals (Arctocephalus gazella, 0.1 individuals km-2) and crabeater seals (Lobodon carcinophagus, 0.4 individuals km-2) were observed in low numbers. Akaike's information criterion was used to assess competing models that predicted predator distributions based on physical oceanographic variables proposed to structure predator distribution in previous research. These analyses indicated that predator distributions were primarily associated with water-mass structure and variability in bottom depth during the fall cruise. Crabeater seal, snow petrel, Antarctic petrel, and southern fulmar had higher densities in Inner Shelf Water, particularly near Alexander Island where a coastal current was present. Blue petrel, kelp gull (Larus dominicanus), and southern giant petrel (Macronectes giganteus) were positively associated with variability in bottom depth in April-May, suggesting that hydrographic processes influenced by bathymetry may have been important in structuring bird distributions. After the development of pack ice, during July and August, only sea-ice-affiliated species, including snow petrel (1.0 individuals km-2), Antarctic petrel (0.1 individuals km-2), Ade??lie penguin (Pygoscelis adeliae, 0.4 individuals km-2), and crabeater seal (0.3 individuals km-2), were observed. Seabirds were primarily associated with sea-ice characteristics (e.g. sea-ice concentration, sea-ice type) rather than the water-column environment later in the winter. Results from this study suggest that the timing and extent of sea-ice development in the fall may influence over-winter predation by seabirds and pinnipeds on zooplankton and fish on the western Antarctic Peninsula. Delays in sea-ice development may allow seabirds and pinnipeds access to biologically important areas such as the Inner Shelf Water for a longer period of time thereby increasing predation on zooplankton and fish. ?? 2004 Elsevier Ltd. All rights reserved.

Deep-Sea Research Part II: Topical Studies in Ocea↗

USGS2005

Assessing uncertainty in ecological systems using global sensitivity analyses: A case example of simulated wolf reintroduction effects on elk

Often landmark conservation decisions are made despite an incomplete knowledge of system behavior and inexact predictions of how complex ecosystems will respond to management actions. For example, predicting the feasibility and likely effects of restoring top-level carnivores such as the gray wolf ( Canis lupus ) to North American wilderness areas is hampered by incomplete knowledge of the predator-prey system processes and properties. In such cases, global sensitivity measures, such as Sobol’ indices, allow one to quantify the effect of these uncertainties on model predictions. Sobol’ indices are calculated by decomposing the variance in model predictions (due to parameter uncertainty) into main effects of model parameters and their higher order interactions. Model parameters with large sensitivity indices can then be identified for further study in order to improve predictive capabilities. Here, we illustrate the use of Sobol’ sensitivity indices to examine the effect of parameter uncertainty on the predicted decline of elk ( Cervus elaphus ) population sizes following a hypothetical reintroduction of wolves to Olympic National Park, Washington, USA. The strength of density dependence acting on survival of adult elk and magnitude of predation were the most influential factors controlling elk population size following a simulated wolf reintroduction. In particular, the form of density dependence in natural survival rates and the per-capita predation rate together accounted for over 90% of variation in simulated elk population trends. Additional research on wolf predation rates on elk and natural compensations in prey populations is needed to reliably predict the outcome of predator–prey system behavior following wolf reintroductions.

Ecological Modelling↗

USGS2020

The economics of territory selection

Territorial behavior is a fundamental and conspicuous behavior within numerous species, but the mechanisms driving territory selection remain uncertain. Theory and empirical precedent indicate that many animals select territories economically to satisfy resource requirements for survival and reproduction, based on benefits of food resources and costs of competition and travel. Costs of competition may vary by competitive ability, and costs of predation risk may also drive territory selection. Habitat structure, resource requirements, conspecific density, and predator distribution and abundance are likely to further influence territorial behavior. We developed a mechanistic, spatially-explicit, individual-based model to better understand how and why animals select particular territories. The model was based on optimal selection of individual patches for inclusion in a territory according to their net value, i.e., benefits (food resources) minus costs (travel, competition, predation risk). Simulations produced predictions for what may be observed empirically if such optimization drives placement and characteristics of territories. Simulations consisted of sequential, iterative selection of territories by simulated animals that interacted to defend and maintain territories. Results explain why certain patterns in space use are commonly observed, and when and why these patterns will differ from the norm. For example, more clumped or abundant food resources are predicted to result, on average, in smaller territories with more overlap. Strongly different resource requirements for individuals or groups in a population will directly affect space use and are predicted to cause different responses under identical conditions. Territories are predicted to decrease in size with increasing population density, which can enable a population’s density of territories to change at faster rates than their spatial distribution. Due to competition, less competitive territory-holders are generally predicted to have larger territories in order to accumulate sufficient resources, which could produce an ideal despotic distribution of territories. Interestingly, territory size and overlap are predicted to show a parabolic response to increases in predator densities, and territories are predicted to be larger where predators are more clumped in distribution. Our model’s predictions are consistent with many empirical observations, providing support for optimal patch selection as a mechanism for the economical territories of animals commonly observed in nature.

Ecological Modelling↗

USGS2013

Intra-population variation in activity ranges, diel patterns, movement rates, and habitat use of American alligators in a subtropical estuary

Movement and habitat use patterns are fundamental components of the behaviors of mobile animals and help determine the scale and types of interactions they have with their environments. These behaviors are especially important to quantify for top predators because they can have strong effects on lower trophic levels as well as the wider ecosystem. Many studies of top predator movement and habitat use focus on general population level trends, which may overlook important intra-population variation in behaviors that now appear to be common. In an effort to better understand the prevalence of intrapopulation variation in top predator movement behaviors and the potential effects of such variation on ecosystem dynamics, we examined the movement and habitat use patterns of a population of adult American alligators ( Alligator mississippiensis ) in a subtropical estuary for nearly four years. We found that alligators exhibited divergent behaviors with respect to activity ranges, movement rates, and habitat use, and that individualized behaviors were stable over multiple years. We also found that the variations across the three behavioral metrics were correlated such that consistent behavioral types emerged, specifically more exploratory individuals and more sedentary individuals. Our study demonstrates that top predator populations can be characterized by high degrees of intra-population variation in terms of movement and habitat use behaviors that could lead to individuals filling different ecological roles in the same ecosystem. By extension, one-size-fits-all ecosystem and species-specific conservation and management strategies that do not account for potential intra-population variation in top predator behaviors may not produce the desired outcomes in all cases.

Estuarine, Coastal and Shelf Science↗

USGS2023

Telescoping prey selection in invasive Burmese pythons spells trouble for endangered rodents

The allometric scaling of predators and their prey is well established within snakes (i.e., gape-width limits maximum prey sizes). However, while some species exhibit ontogenetic shifts to larger prey as they grow, others exhibit telescoping prey selection and continue to consume small prey in addition to larger prey. The Burmese python ( Python bivittatus ) is a large dietary generalist constrictor native to Southeast Asia that is established in South Florida (USA). As part of survey efforts at the southern invasion front in the Florida Keys, we used camera traps to document predation on endangered Key Largo cotton mice ( Peromyscus gossypinus allapaticola ) by an adult female Burmese python. These images represent the first photo documentation of predation attempts upon a federally endangered species in the python's invasive range, but we note three additional instances of Key Largo cotton mice in the gut contents of euthanized pythons from Key Largo. These observations suggest Burmese pythons exhibit telescoping prey selection behavior where even small rodents (<30 g) are viable prey for adult snakes. However, based on the number of documented strikes with failed predation events and low frequency of occurrence in gut contents, we suspect mice may be less common prey items for adult (i.e., >185 cm SVL) pythons relative to cotton mouse abundance in the environment. However, we also documented endangered Key Largo woodrats ( Neotoma floridana smalli ) and Key Largo cotton mice collecting and consuming the shed skins of pythons, which suggests the two rodent species remain naïve to the threat of these invasive predators. Further understanding of the impact of Burmese pythons on native prey communities can help inform efforts to minimize biodiversity loss along their invasion fronts.

Food Webs↗