Abstract
Spatial relationships between predators and prey have important implications for landscape processes and patterns. Highly mobile oceanic birds and their patchily distributed prey constitute an accessible model system for studying these relationships. High-frequency echosounders can be used together with simultaneous direct visual observations to quantitatively describe the distributions of seabird consumers and their resources over a wide range of spatial scales, yielding information which is rarely available in terrestrial systems.Recent fine-scale investigations which have used acoustics to study the distribution of foraging marine birds have reported weak or ephemeral spatial associations between the birds and their prey. These results are inconsistent with predictions of optimal foraging, but several considerations suggest that traditional foraging models do not adequately describe resource acquisition in marine environments. Relative to their terrestrial counterparts, oceanic ‘landscapes’ are structurally very simple, but they generally lack visual cues about resource availability.An emerging view assumes that perceptually constrained organisms searching for food in multiscale environments should respond to patterns of resource abundance over a continuum of scales. We explore fractal geometry as a possible tool for quantifying this view and for describing spatial dispersion patterns that result from foraging behavior. Data on an Alaskan seabird (least auklet [Aethia pusilla]) and its zooplanktonic food resources suggest that fractal approaches can yield new ecological insights into complex spatial patterns deriving from animal movements.
Highlights
The landscape ecological perspective focuses on interactions between spatial patterns and the ecological processes influencing and influenced by patterns at different scales (Risser et al 1984; Risser 1987)
We suggest that if such 'behavioral cascades' accurately describe the responses of individual predators to prey distribution across a wide range of scales, an ensemble of such predators should collectively exhibit a spatial distribution with a fractal dimension that is correlated to the fractal dimension of the prey distribution
We repeated our fractal analyses with the data grouped into bins of increasingly larger size. This kind of data aggregation essentially increases the observational scale of our study, but in retrospect. These analyses showed that fractal dimensions were relatively constant (e.g., Fig. 5), indicating that spatial patterns of auklet and zooplankton distributions were nearly scale-invariant over the range of relatively fine scales examined here
Summary
The landscape ecological perspective focuses on interactions between spatial patterns and the ecological processes influencing and influenced by patterns at different scales (Risser et al 1984; Risser 1987). Predator-prey interactions constitute an important class of such ecological processes because: 1) most organisms live in environments where food resources are distributed heterogeneously The ocean can be viewed as a 'landscape' in the sense that it can be described by patterns with different temporal and spatial scales (Haury et al 1978; Steele 1989). Oceanic birds and their marine prey constitute an excellent model system for examining the interplay between resource distribution, foraging behavior, and trophic exchange. Unlike terrestrial environments, where complex landscape structure may be an important constraint on movement (e.g., rock piles, dense vegetation, mountains, bodies of water), the oceanic environments of seabirds are vast and open; the movements of foraging seabirds are potentially directly reflective of their assessment of spatial variation in resource abundance or availability
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