Leigh G. Torres

National Institute of Water and Atmospheric Research, Wellington, Wellington, New Zealand

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Publications (6)10.71 Total impact

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    Leigh G. Torres, Andrew J. Read
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    ABSTRACT: Observations of bottlenose dolphins (Tursiops truncatus) in Florida Bay, Florida, between 2002 and 2005 revealed the use of three distinct foraging tactics. The goal of this study was to identify ecological correlates with tactic use and describe the impact of foraging specializations on the overall habitat use and distribution patterns of this dolphin population. Foraging tactics showed strong association with contrasting environmental characteristics, primarily depth. Locations of two of these tactic groups were spatially repulsed. Analyses of sighting histories of individual dolphins observed at foraging events determined that dolphins which employed one tactic never employed the other, and vice versa. Although bottlenose dolphins have plastic foraging behaviors, dolphins in Florida Bay appear to specialize in one tactic and subsequently limit their overall distribution patterns to coincide with habitats that facilitate success using that foraging tactic. This study demonstrates how foraging behavior can be an ecological determinant of overall dolphin habitat use patterns and works to create spatial structure within a population due to consistent mapping of tactics onto environmental variation. These foraging specializations potentially impact the social and demographic patterns of this dolphin population. The possible evolutionary mechanisms behind this intraspecific variation, including resource limitation and social learning, are considered.
    Marine Mammal Science 09/2009; 25(4):797 - 815. · 2.13 Impact Factor
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    LG Torres
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    ABSTRACT: Habitat selection by top predators that are largely free from predation pressures is a function of prey availability and interspecific competition. Such competition can be minimized through niche dimensions: mechanism of resource partitioning based on prey choice and foraging tactic. This study compared habitat use patterns of 5 top predators (bottlenose dolphins, double- crested cormorants, osprey, brown pelicans and terns) within Florida Bay with respect to each other, their prey and habitat variability. Foraging dolphins, osprey and pelicans exhibited similar habitat use patterns in shallow, turbid, productive waters with high proportions of mud and mudbank bottom types. These same habitat characteristics also described the distribution of their major prey items: mullet and catfish. Competition between these 3 predators is likely diluted by foraging tactic varia- tion. Conversely, the habitat use patterns of cormorants showed strongest association with deeper water, with low chlorophyll a and turbidity levels, less mud and mudbank habitat, and greater pro- portions of hardbottom and seagrass bottoms. Those prey items of cormorants with less competition from other predators examined displayed the same habitat associations. Cormorants in Florida Bay may concentrate their foraging efforts on less competitive prey, occurring more frequently in habitats where these prey items dominate. Despite Florida Bay's limited bathymetric relief, habitat use pat- terns of top predators are significantly influenced by depth, and subsequently bottom type. Sighting rates of all predators, except non-foraging dolphins, peaked in shallow mudbank habitats. This pat- tern of strong habitat overlap among predators implies currently adequate resource availability and/or niche dimensions among interspecific competitors.
    Marine Ecology-progress Series - MAR ECOL-PROGR SER. 01/2009; 375:289-304.
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    Leigh G Torres, Andrew J Read, Patrick Halpin
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    ABSTRACT: Predators and prey assort themselves relative to each other, the availability of resources and refuges, and the temporal and spatial scale of their interaction. Predictive models of predator distributions often rely on these relationships by incorporating data on environmental variability and prey availability to determine predator habitat selection patterns. This approach to predictive modeling holds true in marine systems where observations of predators are logistically difficult, emphasizing the need for accurate models. In this paper, we ask whether including prey distribution data in fine-scale predictive models of bottlenose dolphin (Tursiops truncatus) habitat selection in Florida Bay, Florida, U.S.A., improves predictive capacity. Environmental characteristics are often used as predictor variables in habitat models of top marine predators with the assumption that they act as proxies of prey distribution. We examine the validity of this assumption by comparing the response of dolphin distribution and fish catch rates to the same environmental variables. Next, the predictive capacities of four models, with and without prey distribution data, are tested to determine whether dolphin habitat selection can be predicted without recourse to describing the distribution of their prey. The final analysis determines the accuracy of predictive maps of dolphin distribution produced by modeling areas of high fish catch based on significant environmental characteristics. We use spatial analysis and independent data sets to train and test the models. Our results indicate that, due to high habitat heterogeneity and the spatial variability of prey patches, fine-scale models of dolphin habitat selection in coastal habitats will be more successful if environmental variables are used as predictor variables of predator distributions rather than relying on prey data as explanatory variables. However, predictive modeling of prey distribution as the response variable based on environmental variability did produce high predictive performance of dolphin habitat selection, particularly foraging habitat.
    Ecological Applications 11/2008; 18(7):1702-17. · 3.82 Impact Factor
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    ABSTRACT: Cetacean–habitat modeling, although still in the early stages of development, represents a potentially powerful tool for predicting cetacean distributions and understanding the ecological processes determining these distributions. Marine ecosystems vary temporally on diel to decadal scales and spatially on scales from several meters to 1000s of kilometers. Many cetacean species are wideranging and respond to this variability by changes in distribution patterns. Cetacean–habitat models have already been used to incorporate this variability into management applications, including improvement of abundance estimates, development of marine protected areas, and understanding cetacean–fisheries interactions. We present a review of the development of cetacean–habitat models, organized according to the primary steps involved in the modeling process. Topics covered include purposes for which cetacean–habitat models are developed, scale issues in marine ecosystems, cetacean and habitat data collection, descriptive and statistical modeling techniques, model selection, and model evaluation. To date, descriptive statistical techniques have been used to explore cetacean–habitat relationships for selected species in specific areas; the numbers of species and geographic areas examined using computationally intensive statistic modeling techniques are considerably less, and the development of models to test specific hypotheses about the ecological processes determining cetacean distributions has just begun. Future directions in cetacean–habitat modeling span a wide range of possibilities, from development of basic modeling techniques to addressing important ecological questions.
    Marine Ecology Progress Series. 01/2006; 310:271-295.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Cetacean–habitat modeling, although still in the early stages of development, represents a potentially powerful tool for predicting cetacean distributions and understanding the ecological processes determining these distributions. Marine ecosystems vary temporally on diel to decadal scales and spatially on scales from several meters to 1000s of kilometers. Many cetacean species are wideranging and respond to this variability by changes in distribution patterns. Cetacean–habitat models have already been used to incorporate this variability into management applications, including improvement of abundance estimates, development of marine protected areas, and understanding cetacean–fisheries interactions. We present a review of the development of cetacean–habitat models, organized according to the primary steps involved in the modeling process. Topics covered include purposes for which cetacean–habitat models are developed, scale issues in marine ecosystems, cetacean and habitat data collection, descriptive and statistical modeling techniques, model selection, and model evaluation. To date, descriptive statistical techniques have been used to explore cetacean–habitat relationships for selected species in specific areas; the numbers of species and geographic areas examined using computationally intensive statistic modeling techniques are considerably less, and the development of models to test specific hypotheses about the ecological processes determining cetacean distributions has just begun. Future directions in cetacean–habitat modeling span a wide range of possibilities, from development of basic modeling techniques to addressing important ecological questions.
    Marine Ecology Progress Series 01/2006; 310:271-295. · 2.64 Impact Factor
  • Source
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    ABSTRACT: In the Northwest Atlantic the distribution of coastal bottlenose dolphins (Tursiops truncatus) overlaps with that of the offshore ecotype. We hypothesized that the distribution of the two ecotypes could be delineated by depth and/or distance from shore, facilitating their identification during surveys. We obtained 304 skin biopsy samples and identified each as either coastal or offshore using analysis of mitochondrial DNA. We then interpreted the spatial distribution of coastal and offshore forms using spatial analysis. Using a Classification and Regression Tree (CART) analysis, we found a statistically significant break in ecotype distribution at 34 km from shore. In waters beyond 34 km from shore and deeper than 34 m, all bottlenose dolphins were of the offshore ecotype. Within 7.5 km of shore, all 65 samples were of the coastal ecotype. Between these two areas only nine samples were collected, so the genetic composition of bottlenose dolphins in this area remains poorly known. To enhance our understanding of the spatial distribution of the two ecotypes, future research should obtain more biopsy samples in this zone. Nevertheless, our results indicate that a conservative abundance estimate for the coastal ecotype could be generated from surveys of bottlenose dolphins within 7.5 km of shore.
    Marine Mammal Science 06/2003; 19(3):502 - 514. · 2.13 Impact Factor

Publication Stats

158 Citations
10.71 Total Impact Points

Institutions

  • 2009
    • National Institute of Water and Atmospheric Research
      Wellington, Wellington, New Zealand
  • 2003–2008
    • Duke University Marine Lab
      North Carolina, United States
  • 2006
    • Duke University
      Durham, North Carolina, United States