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Wirsing, Aaron J.; Heithaus, Michael R.; Dill, Lawrence M.
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2011 |
Predator-induced modifications to diving behavior vary with foraging mode.
Oikos 120(7): 1005-1012. 4 tables. 1 fig. DOI: 10.1111/j.1600-0706.2010.18844.x. July 2011.
–ABSTRACT: Breath-hold divers are strongly interacting species whose top–down influence on aquatic communities is shaped by factors governing their diving decisions. Although some of these factors (e.g. physiological constraints, energetic needs) have been scrutinized, the possibility that predation risk influences diving behavior has been largely overlooked, and no study to date has asked if anti-predator responses by divers depend on foraging mode. We contrasted dive cycle changes by herbivorous dugongs Dugong dugon using two foraging tactics – cropping, which always permits anti-predator vigilance, and excavation, which limits surveillance at depth – in response to temporal variation in tiger shark Galeocerdo cuvier abundance. Dugongs responded to increasing shark abundance (one component of predation risk) by diving more frequently without changing their surface times and thereby spending a greater proportion of time at the surface, but only while excavating. When threatened, in other words, excavating dugongs sacrificed foraging time at depth to facilitate shark detection. In contrast, cropping dugongs at risk from sharks were able to continue diving and foraging normally. By implication, future studies should consider the influence of predation risk on diving decisions, even by large-bodied species, and the possibility that behavioral responses by divers to predators may vary with foraging mode.
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Wirsing, Aaron J.; Ripple, William J.
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2011 |
A comparison of shark and wolf research reveals similar behavioral responses by prey.
Frontiers in Ecology and the Environment 9(6): 335-341. 3 figs. DOI: 10.1890/090226. Aug. 2011.
–ABSTRACT: Marine and terrestrial ecologists rarely exchange information, yet comparing research from both sides of the land–sea boundary holds great potential for improving our understanding of ecological processes. For example, by comparing the interaction between tiger sharks (Galeocerdo cuvier) and dugongs (Dugong dugon) to that between gray wolves (Canis lupus) and elk (Cervus elaphus), we show that top predators in marine and terrestrial ecosystems trigger three similar types of anti-predator behavior: (1) encounter avoidance, (2) escape facilitation, and (3) increased vigilance. By implication, the ecological roles of top predators in both ecosystems may be more similar than previously thought, and studies that fail to account for multiple modes of anti-predator behavior are likely to underestimate these roles and the consequences of eliminating predators from ecosystems. We encourage more communication between marine and terrestrial ecologists, in the interest of generating further insights into ecosystem dynamics and conservation.
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Nowicki, Robert J.; Thomson, Jordan A.; Fourqurean, James W.; Wirsing, Aaron J.; Heithaus, Michael R.
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2021 |
Loss of predation risk from apex predators can exacerbate marine tropicalization caused by extreme climatic events.
Jour. Animal Ecology DOI: 10.1111/1365-2656.13424 Feb. 22, 2021.
–ABSTRACT: 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.
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Bibliography and Index of the Sirenia and Desmostylia 