Friday, August 6, 2010 - 10:50 AM

COS 116-9: Does area-restricted search lead to density-dependent foraging?

Travis M. Hinkelman, University of Nebraska and Brigitte Tenhumberg, University of Nebraska-Lincoln.


Area-restricted search is a foraging tactic characterized by reduced speeds and frequent turns that is found in taxa as diverse as insects, fish, birds, and mammals. The effectiveness of area-restricted search has primarily been studied in the context of resource distributions (e.g., clumped, uniform), but it is often assumed that area-restricted search will lead to density-dependent foraging (i.e., searching biased toward high density resource patches). We used a simulation approach to test the performance of area-restricted search mechanisms in a landscape where patches differed in resource density. The searching mechanisms were based on generalizations of empirical observations of searching behavior as described in Bell’s (1991) seminal book. Turning behavior was modeled as (1) zigzagging, (2) looping, (3) spiraling, and (4) patch edge (where forager turns back into patch when edge is detected). The effect of reducing speed and increasing turns were considered separately and together for a total of nine searching mechanisms involving area-restricted search, which were compared to a random searching behavior (i.e., movement not affected by resource consumption).


All of the searching mechanisms were more efficient (efficiency = resources consumed · time-1 · distance-1) than random movement and all mechanisms generated at least weak density-dependence. The most efficient mechanism (spiraling with reduced speed) also generated strong density-dependence, but generally there was weak concordance between efficiency and density-dependence. Indeed, the time spent moving between patches was a better predictor of efficiency than time spent moving within patches. Surprisingly, there was similarly weak correspondence between foraging efficiency of the consumer and per capita predation risk for resources. Searching mechanisms that included slowing down were more efficient for the consumer but less of a threat to resources than mechanisms that involved only turning behavior. Overall, the search mechanisms varied greatly in efficiency and strength of density-dependence, but the hypothesis that area-restricted search leads to density-dependent foraging was supported.