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1.
Integr Comp Biol ; 2021 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-33744919

RESUMO

SynopsisMany large predators are also facultative scavengers that may compete with and depredate other species at carcasses. Yet, the ecological impacts of facultative scavenging by large predators, or their "scavenging effects", still receive relatively little attention in comparison to their predation effects. To address this knowledge gap, we comprehensively examine the roles played by, and impacts of, facultative scavengers, with a focus on large canids: the African wild dog (Lycaon pictus), dhole (Cuon alpinus), dingo (Canis dingo), Ethiopian wolf (C. simensis), gray wolf (C. lupus), maned wolf (Chrysocyon brachyurus), and red wolf (C. rufus). Specifically, after defining facultative scavenging as use or usurpation of a carcass that a consumer has not killed, we (i) provide a conceptual overview of the community interactions around carcasses that can be initiated by facultative scavengers, (ii) review the extent of scavenging by and the evidence for scavenging effects of large canids, (iii) discuss external factors that may diminish or enhance the effects of large canids as scavengers, and (iv) identify aspects of this phenomenon that require additional research attention as a guide for future work.

2.
J Anim Ecol ; 2021 Feb 23.
Artigo em Inglês | MEDLINE | ID: mdl-33624313

RESUMO

Extreme climatic events (ECEs) and predator removal represent some of the most widespread stressors to ecosystems. Though species interactions can alter ecological effects of climate change (and vice versa), it is less understood whether, when and how predator removal can interact with ECEs to exacerbate their effects. Understanding the circumstances under which such interactions might occur is critical because predator loss is widespread and ECEs can generate rapid phase shifts in ecosystems which can ultimately lead to tropicalization. Our goal was to determine whether loss of predation risk may be an important mechanism governing ecosystem responses to extreme events, and whether the effects of such events, such as tropicalization, can occur even when species range shifts do not. Specifically, our goal was to experimentally simulate the loss of an apex predator, the tiger shark Galeocerdo cuvier effects on a recently damaged seagrass ecosystem of Shark Bay, Australia by applying documented changes to risk-sensitive grazing of dugong Dugong dugon herbivores. Using a 16-month-field experiment established in recently disturbed seagrass meadows, we used previous estimates of risk-sensitive dugong foraging behaviour to simulate altered risk-sensitive foraging densities and strategies of dugongs consistent with apex predator loss, and tracked seagrass responses to the simulated grazing. Grazing treatments targeted and removed tropical seagrasses, which declined. However, like in other mixed-bed habitats where dugongs forage, treatments also incidentally accelerated temperate seagrass losses, revealing that herbivore behavioural changes in response to predator loss can exacerbate ECE and promote tropicalization, even without range expansions or introductions of novel species. Our results suggest that changes to herbivore behaviours triggered by loss of predation risk can undermine ecological resilience to ECEs, particularly where long-lived herbivores are abundant. By implication, ongoing losses of apex predators may combine with increasingly frequent ECEs to amplify climate change impacts across diverse ecosystems and large spatial scales.

3.
Ecol Lett ; 2020 Sep 29.
Artigo em Inglês | MEDLINE | ID: mdl-32990363

RESUMO

Non-consumptive predator effects (NCEs) are now widely recognised for their capacity to shape ecosystem structure and function. Yet, forecasting the propagation of these predator-induced trait changes through particular communities remains a challenge. Accordingly, focusing on plasticity in prey anti-predator behaviours, we conceptualise the multi-stage process by which predators trigger direct and indirect NCEs, review and distil potential drivers of contingencies into three key categories (properties of the prey, predator and setting), and then provide a general framework for predicting both the nature and strength of direct NCEs. Our review underscores the myriad factors that can generate NCE contingencies while guiding how research might better anticipate and account for them. Moreover, our synthesis highlights the value of mapping both habitat domains and prey-specific patterns of evasion success ('evasion landscapes') as the basis for predicting how direct NCEs are likely to manifest in any particular community. Looking ahead, we highlight two key knowledge gaps that continue to impede a comprehensive understanding of non-consumptive predator-prey interactions and their ecosystem consequences; namely, insufficient empirical exploration of (1) context-dependent indirect NCEs and (2) the ways in which direct and indirect NCEs are shaped interactively by multiple drivers of context dependence.

4.
Ecol Appl ; 30(3): e02061, 2020 04.
Artigo em Inglês | MEDLINE | ID: mdl-31863535

RESUMO

Ecosystem-based management requires consideration of overlapping resource use between humans and other consumers. Pacific salmon are an important resource for both fisheries and populations of wildlife around the Pacific rim, including coastal brown bears (Ursus arctos); salmon consumption has been positively linked to bear density, body size, and reproductive rate. As a case study within the broader context of human-wildlife competition for food, we used 16-22 yr of empirical data in four different salmon-bearing systems in southwestern Alaska to explore the relationship between sockeye salmon (Oncorhynchus nerka) availability and consumption by bears. We found a negative relationship between the annual biomass of salmon available to bears and the fraction of biomass consumed per fish, and a saturating relationship between salmon availability and the total annual biomass of salmon consumed by bears. Under modeled scenarios, bear consumption of salmon was predicted to increase only with dramatic (on the order of 50-100%) increases in prey availability. Even such large increases in salmon abundance were estimated to produce relatively modest increases in per capita salmon consumption by bears (2.4-4.8 kg·bear-1 ·d-1 , 15-59% of the estimated daily maximum per capita intake), in part because bears did not consume salmon entirely, especially when salmon were most available. Thus, while bears catching salmon in small streams may be limited by salmon harvest in some years, current management of the systems we studied is sufficient for bear populations to reach maximum salmon consumption every 2-4 yr. Consequently, allocating more salmon for brown bear conservation would unlikely result in an ecologically significant response for bears in these systems, though other ecosystem components might benefit. Our results highlight the need for documenting empirical relationships between prey abundance and consumption, particularly in systems with partial consumption, when evaluating the ecological response of managing prey resources for wildlife populations.


Assuntos
Ursidae , Alaska , Animais , Ecossistema , Pesqueiros , Humanos , Rios , Salmão
5.
Oecologia ; 189(2): 487-500, 2019 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-30539299

RESUMO

The non-consumptive effects of predators on prey are now widely recognized, but the need remains for studies identifying the factors that determine how particular prey species respond behaviorally when threatened with predation. We took advantage of ongoing gray wolf (Canis lupus) recolonization in eastern Washington, USA, to contrast habitat use of two sympatric prey species-mule (Odocoileus hemionus) and white-tailed (O. virginianus) deer-at sites with and without established wolf packs. Under the hypothesis that the nature and scale of responses by these ungulates to wolf predation risk depend on their divergent flight tactics (i.e., modes of fleeing from an approaching predator), we predicted that (1) mule deer would respond to wolves with coarse-scale spatial shifts to rugged terrain favoring their stotting tactic; (2) white-tailed deer would manage wolf risk with fine-scale shifts toward gentle terrain facilitating their galloping tactic within their current home range. Resource selection functions based on 61 mule deer and 59 white-tailed deer equipped with GPS radio-collars from 2013 to 2016 revealed that habitat use for each species was altered by wolf presence, but in divergent ways that supported our predictions. Our findings add to a growing literature highlighting flight behavior as a viable predictor of prey responses to predation risk across multiple ecosystem types. Consequently, they suggest that predators could initiate multiple indirect non-consumptive effects in the same ecosystem that are transmitted by divergent responses of sympatric prey with different flight tactics.


Assuntos
Cervos , Lobos , Animais , Ecossistema , Comportamento Predatório , Washington
6.
Ecol Evol ; 8(22): 11158-11168, 2018 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-30519433

RESUMO

Top predators have cascading effects throughout the food web, but their impacts on scavenger abundance are largely unknown. Gray wolves (Canis lupus) provide carrion to a suite of scavenger species, including the common raven (Corvus corax). Ravens are wide-ranging and intelligent omnivores that commonly take advantage of anthropogenic food resources. In areas where they overlap with wolves, however, ravens are numerous and ubiquitous scavengers of wolf-acquired carrion. We aimed to determine whether subsidies provided through wolves are a limiting factor for raven populations in general and how the wolf reintroduction to Yellowstone National Park in 1995-1997 affected raven population abundance and distribution on the Yellowstone's Northern Range specifically. We counted ravens throughout Yellowstone's Northern Range in March from 2009 to 2017 in both human-use areas and wolf habitat. We then used statistics related to the local wolf population and the winter weather conditions to model raven abundance during our study period and predict raven abundance on the Northern Range both before and after the wolf reintroduction. In relatively severe winters with greater snowpack, raven abundance increased in areas of human use and decreased in wolf habitat. When wolves were able to acquire more carrion, however, ravens increased in wolf habitat and decreased in areas with anthropogenic resources. Raven populations prior to the wolf reintroduction were likely more variable and heavily dependent on ungulate winter-kill and hunter-provided carcasses. The wolf recovery in Yellowstone helped stabilize raven populations by providing a regular food supply, regardless of winter severity. This stabilization has important implications for effective land management as wolves recolonize the west and global climate patterns change.

7.
Ecol Evol ; 8(17): 9048-9061, 2018 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-30271565

RESUMO

The interaction between brown bears (Ursus arctos) and Pacific salmon (Oncorhynchus spp.) is important to the population dynamics of both species and a celebrated example of consumer-mediated nutrient transport. Yet, much of the site-specific information we have about the bears in this relationship comes from observations at a few highly visible but unrepresentative locations and a small number of radio-telemetry studies. Consequently, our understanding of brown bear abundance and behavior at more cryptic locations where they commonly feed on salmon, including small spawning streams, remains limited. We employed a noninvasive genetic approach (barbed wire hair snares) over four summers (2012-2015) to document patterns of brown bear abundance and movement among six spawning streams for sockeye salmon, O. nerka, in southwestern Alaska. The streams were grouped into two trios on opposite sides of Lake Aleknagik. Thus, we predicted that most bears would forage within only one trio during the spawning season because of the energetic costs associated with swimming between them or traveling around the lake and show fidelity to particular trios across years because of the benefits of familiarity with local salmon dynamics and stream characteristics. Huggins closed-capture models based on encounter histories from genotyped hair samples revealed that as many as 41 individuals visited single streams during the annual 6-week sampling season. Bears also moved freely among trios of streams but rarely moved between these putative foraging neighborhoods, either during or between years. By implication, even small salmon spawning streams can serve as important resources for brown bears, and consistent use of stream neighborhoods by certain bears may play an important role in spatially structuring coastal bear populations. Our findings also underscore the efficacy of noninvasive hair snagging and genetic analysis for examining bear abundance and movements at relatively fine spatial and temporal scales.

10.
Proc Natl Acad Sci U S A ; 114(40): 10678-10683, 2017 10 03.
Artigo em Inglês | MEDLINE | ID: mdl-28923917

RESUMO

Extinction risk in vertebrates has been linked to large body size, but this putative relationship has only been explored for select taxa, with variable results. Using a newly assembled and taxonomically expansive database, we analyzed the relationships between extinction risk and body mass (27,647 species) and between extinction risk and range size (21,294 species) for vertebrates across six main classes. We found that the probability of being threatened was positively and significantly related to body mass for birds, cartilaginous fishes, and mammals. Bimodal relationships were evident for amphibians, reptiles, and bony fishes. Most importantly, a bimodal relationship was found across all vertebrates such that extinction risk changes around a body mass breakpoint of 0.035 kg, indicating that the lightest and heaviest vertebrates have elevated extinction risk. We also found range size to be an important predictor of the probability of being threatened, with strong negative relationships across nearly all taxa. A review of the drivers of extinction risk revealed that the heaviest vertebrates are most threatened by direct killing by humans. By contrast, the lightest vertebrates are most threatened by habitat loss and modification stemming especially from pollution, agricultural cropping, and logging. Our results offer insight into halting the ongoing wave of vertebrate extinctions by revealing the vulnerability of large and small taxa, and identifying size-specific threats. Moreover, they indicate that, without intervention, anthropogenic activities will soon precipitate a double truncation of the size distribution of the world's vertebrates, fundamentally reordering the structure of life on our planet.


Assuntos
Evolução Biológica , Tamanho Corporal/fisiologia , Bases de Dados Factuais , Extinção Biológica , Modelos Biológicos , Vertebrados/fisiologia , Animais
11.
Nat Commun ; 8: 15469, 2017 05 23.
Artigo em Inglês | MEDLINE | ID: mdl-28534486

RESUMO

Top predators can suppress mesopredators by killing them, competing for resources and instilling fear, but it is unclear how suppression of mesopredators varies with the distribution and abundance of top predators at large spatial scales and among different ecological contexts. We suggest that suppression of mesopredators will be strongest where top predators occur at high densities over large areas. These conditions are more likely to occur in the core than on the margins of top predator ranges. We propose the Enemy Constraint Hypothesis, which predicts weakened top-down effects on mesopredators towards the edge of top predators' ranges. Using bounty data from North America, Europe and Australia we show that the effects of top predators on mesopredators increase from the margin towards the core of their ranges, as predicted. Continuing global contraction of top predator ranges could promote further release of mesopredator populations, altering ecosystem structure and contributing to biodiversity loss.

12.
Oecologia ; 183(2): 415-429, 2017 02.
Artigo em Inglês | MEDLINE | ID: mdl-27873066

RESUMO

The relationship between prey abundance and predation is often examined in single habitat units or populations, but predators may occupy landscapes with diverse habitats and foraging opportunities. The vulnerability of prey within populations may depend on habitat features that hinder predation, and increased density of conspecifics in both the immediate vicinity and the broader landscape. We evaluated the relative effects of physical habitat, local, and neighborhood prey density on predation by brown bears on sockeye salmon in a suite of 27 streams using hierarchical Bayesian functional response models. Stream depth and width were inversely related to the maximum proportion of salmon killed, but not the asymptotic limit on total number killed. Interannual variation in predation was density dependent; the number of salmon killed increased with fish density in each stream towards an asymptote. Seven streams in two geographical groups with ≥23 years of data in common were then analyzed for neighborhood density effects. In most (12 of 18) cases predation in a stream was reduced by increasing salmon abundance in neighboring streams. The uncertainty in the estimates for these neighborhood effects may have resulted from interactions between salmon abundance and habitat that influenced foraging by bears, and from bear behavior (e.g., competitive exclusion) and abundance. Taken together, the results indicated that predator-prey interactions depend on density at multiple spatial scales, and on habitat features of the surrounding landscape. Explicit consideration of this context dependency should lead to improved understanding of the ecological impacts of predation across ecosystems and taxa.


Assuntos
Teorema de Bayes , Ursidae , Animais , Ecossistema , Comportamento Predatório , Salmão
14.
J Anim Ecol ; 83(2): 319-21, 2014 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-24428597

RESUMO

A caribou wearing an animal-borne video camera (a) and animal-borne video footage taken from systems deployed on mule deer (Odocoileus hemionus) in north-central Washington state, USA (b-d). When paired with tracking technology, animal-borne video can reveal detailed information about behaviour and environmental features at each location: (b) feeding, (c) vigilant in the open, (d) vigilant in cover, (e) resting in the open. Accordingly, animal-borne video systems should allow for analyses of habitat selection by individuals in particular behavioural states. In Focus: DeCesare, N.J., Hebblewhite, M., Bradley, M., Hervieux, D., Neufeld, L. & Musiani, M. (2014) Linking habitat selection and predation risk to spatial variation in survival. Journal of Animal Ecology, 83, 343-352. Resource selection is often assumed to confer enhanced fitness, but this assumption is rarely examined. In a study involving woodland caribou subject to grey wolf predation, DeCesare et al. (2014) show that while patterns of selection by caribou did correspond with a fitness proxy (survival probability), individuals did not avoid wolf predation risk to the extent that would minimize mortality. Here, we use the results of this paper as a springboard for discussing the choice of fitness proxies and the need to account for individual behavioural variation in studies of resource selection.


Assuntos
Ecossistema , Cadeia Alimentar , Longevidade , Rena/fisiologia , Animais , Feminino
15.
Science ; 343(6167): 1241484, 2014 Jan 10.
Artigo em Inglês | MEDLINE | ID: mdl-24408439

RESUMO

Large carnivores face serious threats and are experiencing massive declines in their populations and geographic ranges around the world. We highlight how these threats have affected the conservation status and ecological functioning of the 31 largest mammalian carnivores on Earth. Consistent with theory, empirical studies increasingly show that large carnivores have substantial effects on the structure and function of diverse ecosystems. Significant cascading trophic interactions, mediated by their prey or sympatric mesopredators, arise when some of these carnivores are extirpated from or repatriated to ecosystems. Unexpected effects of trophic cascades on various taxa and processes include changes to bird, mammal, invertebrate, and herpetofauna abundance or richness; subsidies to scavengers; altered disease dynamics; carbon sequestration; modified stream morphology; and crop damage. Promoting tolerance and coexistence with large carnivores is a crucial societal challenge that will ultimately determine the fate of Earth's largest carnivores and all that depends upon them, including humans.


Assuntos
Carnívoros , Fenômenos Ecológicos e Ambientais , Ecossistema , Extinção Biológica , Animais , Carnívoros/anatomia & histologia , Carnívoros/classificação , Carnívoros/fisiologia , Humanos , Produtos da Carne/estatística & dados numéricos , Oceanos e Mares , Plantas , Dinâmica Populacional
16.
Oecologia ; 168(4): 977-88, 2012 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-22009341

RESUMO

There has long been interest in the influence of predators on prey populations, although most predator-prey studies have focused on prey species that are targets of directed predator searching. Conversely, few have addressed depredation that occurs after incidental encounters with predators. We tested two predictions stemming from the hypothesis that nest predation on two sympatric freshwater turtle species whose nests are differentially prone to opportunistic detection-painted turtles (Chrysemys picta) and snapping turtles (Chelydra serpentina)-is incidental: (1) predation rates should be density independent, and (2) individual predators should not alter their foraging behavior after encountering nests. After monitoring nest survival and predator behavior following nest depredation over 2 years, we confirmed that predation by raccoons (Procyon lotor), the primary nest predators in our study area, matched both predictions. Furthermore, cryptic C. picta nests were victimized with lower frequency than more detectable C. serpentina nests, and nests of both species were more vulnerable in human-modified areas where opportunistic nest discovery is facilitated. Despite apparently being incidental, predation on nests of both species was intensive (57% for painted turtles, 84% for snapping turtles), and most depredations occurred within 1 day of nest establishment. By implication, predation need not be directed to affect prey demography, and factors influencing prey crypsis are drivers of the impact of incidental predation on prey. Our results also imply that efforts to conserve imperiled turtle populations in human-modified landscapes should include restoration of undisturbed conditions that are less likely to expose nests to incidental predators.


Assuntos
Cadeia Alimentar , Comportamento de Nidação/fisiologia , Tartarugas/fisiologia , Animais , Água Doce , Ontário , Densidade Demográfica , Comportamento Predatório/fisiologia , Modelos de Riscos Proporcionais , Guaxinins/fisiologia , Especificidade da Espécie , Tempo (Meteorologia)
17.
J Anim Ecol ; 78(3): 556-62, 2009 May.
Artigo em Inglês | MEDLINE | ID: mdl-19076259

RESUMO

1. Risk effects of predators can profoundly affect community dynamics, but the nature of these effects is context dependent. 2. Although context dependence has hindered the development of a general framework for predicting the nature and extent of risk effects, recent studies suggest that such a framework is attainable if the factors that shape anti-predator behaviour, and its effectiveness, in natural communities are well understood. 3. One of these factors, the interaction of prey escape tactics and landscape features, has been largely overlooked. 4. We tested whether this interaction gives rise to interspecific variation in habitat-use patterns of sympatric large marine vertebrates at risk of tiger shark (Galeocerdo cuvier Peron and LeSueur, 1822) predation. Specifically, we tested the a priori hypothesis that pied cormorants (Phalacrocorax varius Gmelin, 1789) would modify their use of shallow seagrass habitats in a manner opposite to that of previously studied dolphins (Tursiops aduncus Ehrenberg, 1833), dugongs (Dugong dugon Müller, 1776), and green turtles (Chelonia mydas Linnaeus, 1758) because, unlike these species, the effectiveness of cormorant escape behaviour does not vary spatially. 5. As predicted, cormorants used interior and edge portions of banks proportional to the abundance of their potential prey when sharks were absent but shifted to interior portions of banks to minimize encounters with tiger sharks as predation risk increased. Other shark prey, however, shift to edge microhabitats when shark densities increase to take advantage of easier escape despite higher encounter rates with sharks. 6. The interaction of landscape features and escape ability likely is important in diverse communities. 7. When escape probabilities are high in habitats with high predator density, risk effects of predators can reverse the direction of commonly assumed indirect effects of top predators. 8. The interaction between landscape features and prey escape tactics can result in a single predator species having differential effects on their sympatric prey that could cascade through ecosystems and should be incorporated into a general framework for context dependence of risk effects.


Assuntos
Aves/fisiologia , Ecossistema , Reação de Fuga , Comportamento Predatório/fisiologia , Tubarões/fisiologia , Animais , Golfinhos/fisiologia , Dugong/fisiologia , Fatores de Risco
18.
Trends Ecol Evol ; 23(4): 202-10, 2008 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-18308421

RESUMO

Recent studies document unprecedented declines in marine top predators that can initiate trophic cascades. Predicting the wider ecological consequences of these declines requires understanding how predators influence communities by inflicting mortality on prey and inducing behavioral modifications (risk effects). Both mechanisms are important in marine communities, and a sole focus on the effects of predator-inflicted mortality might severely underestimate the importance of predators. We outline direct and indirect consequences of marine predator declines and propose an integrated predictive framework that includes risk effects, which appear to be strongest for long-lived prey species and when resources are abundant. We conclude that marine predators should be managed for the maintenance of both density- and risk-driven ecological processes, and not demographic persistence alone.


Assuntos
Ecossistema , Dinâmica Populacional , Comportamento Predatório , Água do Mar , Animais , Biodiversidade , Conservação dos Recursos Naturais , Peixes , Cadeia Alimentar , Medição de Risco , Tubarões , Frutos do Mar , Tartarugas
19.
J Anim Ecol ; 76(5): 837-44, 2007 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-17714261

RESUMO

1. A predictive framework of community and ecosystem dynamics that applies across systems has remained elusive, in part because non-consumptive predator effects are often ignored. Further, it is unclear how much individual-level detail community models must include. 2. Previous studies of short-lived species suggest that state-dependent decisions add little to our understanding of community dynamics. Body condition-dependent decisions made by long-lived herbivores under risk of predation, however, might have greater community-level effects. This possibility remains largely unexplored, especially in marine environments. 3. In the relatively pristine seagrass community of Shark Bay, Australia, we found that herbivorous green sea turtles (Chelonia mydas Linnaeus, 1758) threatened by tiger sharks (Galeocerdo cuvier Peron and LeSueur, 1822) select microhabitats in a condition-dependent manner. Turtles in poor body condition selected profitable, high-risk microhabitats, while turtles in good body condition, which are more abundant, selected safer, less profitable microhabitats. When predation risk was low, however, turtles in good condition moved into more profitable microhabitats. 4. Condition-dependent use of space by turtles shows that tiger sharks modify the spatio-temporal pattern of turtle grazing and their impacts on ecosystem dynamics (a trait-mediated indirect interaction). Therefore, state-dependent decisions by individuals can have important implications for community dynamics in some situations. 5. Our study suggests that declines in large-bodied sharks may affect ecosystems more substantially than assumed when non-lethal effects of these top predators on mesoconsumers are not considered explicitly.


Assuntos
Comportamento Animal/fisiologia , Ecossistema , Comportamento Predatório , Tubarões/fisiologia , Tartarugas/fisiologia , Animais , Constituição Corporal/fisiologia , Conservação dos Recursos Naturais , Meio Ambiente , Geografia , Dinâmica Populacional , Especificidade da Espécie
20.
Oecologia ; 153(4): 1031-40, 2007 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-17636333

RESUMO

Predators can influence plants indirectly by altering spatial patterns of herbivory, so studies assessing the relationship between perceived predation risk and habitat use by herbivores may improve our understanding of community organization. In marine systems, the effects of predation danger on space use by large herbivores have received little attention, despite the possibility that predator-mediated alterations in patterns of grazing by these animals influence benthic community structure. We evaluated the relationship between habitat use by foraging dugongs (Dugong dugon) and the threat of tiger shark predation in an Australian embayment (Shark Bay) between 1997 and 2004. Dugong densities were quantified in shallow (putatively dangerous) and deep (putatively safe) habitats (seven survey zones allocated to each habitat), and predation hazard was indexed using catch rates of tiger sharks (Galeocerdo cuvier); seagrass volume provided a measure of food biomass within each zone. Overall, dugongs selected shallow habitats, where their food is concentrated. Foragers used shallow and deep habitats in proportion to food availability (input matching) when large tiger sharks were scarce and overused deep habitats when sharks were common. Furthermore, strong synchrony existed between daily measures of shark abundance and the extent to which deep habitats were overused. Thus, dugongs appear to adaptively manage their risk of death by allocating time to safe but impoverished foraging patches in proportion to the likelihood of encountering predators in profitable but more dangerous areas. This apparent food-safety trade-off has important implications for seagrass community structure in Shark Bay, as it may result in marked temporal variability in grazing pressure.


Assuntos
Dugong/fisiologia , Comportamento Alimentar , Comportamento Predatório , Tubarões/fisiologia , Animais , Ecossistema , Medo , Densidade Demográfica
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