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Barraquand F.,University of Tromsø | New L.F.,University of St. Andrews | New L.F.,Us Marine Mammal Commission | Redpath S.,University of Aberdeen | And 2 more authors.
Theoretical Population Biology | Year: 2015

We develop a theory of generalist predation showing how alternative prey species are affected by changes in both mean abundance and variability (coefficient of variation) of their predator's primary prey. The theory is motivated by the indirect effects of cyclic rodent populations on ground-breeding birds, and developed through progressive analytic simplifications of an empirically-based model. It applies nonetheless to many other systems where primary prey have fast life-histories and can become superabundant, thus facilitating impact on alternative prey species and generating highly asymmetric interactions. Our results suggest that predator effects on alternative prey should generally decrease with mean primary prey abundance, and increase with primary prey variability (low to high CV)-unless predators have strong aggregative responses, in which case these results can be reversed. Approximations of models including predator dynamics (general numerical response with possible delays) confirm these results but further suggest that negative temporal correlation between predator and primary prey is harmful to alternative prey. Finally, we find that measurements of predator numerical responses are crucial to predict-even qualitatively-the response of ecosystems to changes in the dynamics of outbreaking prey species. © 2015 Elsevier Inc.


New L.F.,Us Marine Mammal Commission | Moretti D.J.,Naval Undersea Warfare Center | Hooker S.K.,University of St. Andrews | Costa D.P.,University of California at Santa Cruz | Simmons S.E.,Us Marine Mammal Commission
PLoS ONE | Year: 2013

Mass stranding of several species of beaked whales (family Ziphiidae) associated with exposure to anthropogenic sounds has raised concern for the conservation of these species. However, little is known about the species' life histories, prey or habitat requirements. Without this knowledge, it becomes difficult to assess the effects of anthropogenic sound, since there is no way to determine whether the disturbance is impacting the species' physical or environmental requirements. Here we take a bioenergetics approach to address this gap in our knowledge, as the elusive, deep-diving nature of beaked whales has made it hard to study these effects directly. We develop a model for Ziphiidae linking feeding energetics to the species' requirements for survival and reproduction, since these life history traits would be the most likely to be impacted by non-lethal disturbances. Our models suggest that beaked whale reproduction requires energy dense prey, and that poor resource availability would lead to an extension of the inter-calving interval. Further, given current information, it seems that some beaked whale species require relatively high quality habitat in order to meet their requirements for survival and reproduction. As a result, even a small non-lethal disturbance that results in displacement of whales from preferred habitats could potentially impact a population if a significant proportion of that population was affected. We explored the impact of varying ecological parameters and model assumptions on survival and reproduction, and find that calf and fetus survival appear more readily affected than the survival of adult females.


New L.F.,Us Marine Mammal Commission | New L.F.,University of St. Andrews | New L.F.,U.S. Geological Survey | Harwood J.,University of St. Andrews | And 8 more authors.
Functional Ecology | Year: 2013

Behavioural change in response to anthropogenic activities is often assumed to indicate a biologically significant effect on a population of concern. Disturbances can affect individual health through lost foraging time or other behaviours, which will impact vital rates and thus the population dynamics. However, individuals may be able to compensate for the observed shifts in behaviour, leaving their health and thus their vital rates and population dynamics, unchanged. We developed a mathematical model simulating the complex social, spatial, behavioural and motivational interactions of coastal bottlenose dolphins (Tursiops truncatus) in the Moray Firth, Scotland, to assess the biological significance of increased rate of behavioural disruptions caused by vessel traffic. We explored a scenario in which vessel traffic increased from 70 to 470 vessels a year in response to the construction of a proposed offshore renewables' facility. Despite the more than sixfold increase in vessel traffic, the dolphins' behavioural time budget, spatial distribution, motivations and social structure remain unchanged. We found that the dolphins are able to compensate for their immediate behavioural response to disturbances by commercial vessels. If the increased commercial vessel traffic is the only escalation in anthropogenic activity, then the dolphins' response to disturbance is not biologically significant, because the dolphins' health is unaffected, leaving the vital rates and population dynamics unchanged. Our results highlight that behavioural change should not automatically be correlated with biological significance when assessing the conservation and management needs of species of interest. This strengthens the argument to use population dynamics targets to manage human activities likely to disturb wildlife. © 2013 British Ecological Society.


Pirotta E.,University of Aberdeen | New L.,Us Marine Mammal Commission | Harwood J.,University of St. Andrews | Lusseau D.,University of Aberdeen
Ecological Modelling | Year: 2014

Agent-based models can be used to simulate spatially-explicit animal behavioral processes and their interactions with human activities. This approach can be applied to predict the potential effects of such activities on animal behavior and individual condition that could lead, in turn, to alterations in vital rates and, ultimately, long-term population change. We developed an agent-based model to describe the effect of interactions with tourism on the behavior of bottlenose dolphins in Doubtful Sound (New Zealand). The model describes the temporal variation of the individuals' hidden motivational states, the way in which these states interact to determine the activity of groups of dolphins, and the feedback influence of the group's activity on individual motivations and condition. Moreover, it realistically simulates the movement of dolphin groups in the fiord. The model also includes tour boat behavior, incorporating the way key geographical features attract these boats. In addition to tourism effects, we accounted for the spatial heterogeneity in both dolphin activities and shark predation risk. The final simulation platform generated a realistic representation of the social and behavioral dynamics of the dolphin and boat populations, as well as observed patterns of disturbance. We describe how this tool could be used to ensure effective management of the interactions between anthropogenic factors and bottlenose dolphins in Doubtful Sound, and how it could be adapted to evaluate the effects of human disturbance on other comparable populations. We then fitted the dolphin component of the model to data collected during visual studies of the Doubtful Sound dolphin population between 2000 and 2002 using a Bayesian multi-state modeling framework. However, when the parameter estimates from this fitting process were used in the agent-based model, biologically realistic representations of the population were not generated. Our results suggest that visual data from group follows alone are not sufficient to inform such agent-based models. Information on the spatial structure of the animals' activities and an appropriate measure of individual condition are also required for successful model parameterization. © 2014 Elsevier B.V.

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