![]() If predators increase their search rate while exploring an unfamiliar habitat, prey at high densities will be encountered when search rate is relatively low in contrast, low-density prey will be encountered after a longer period of time, when search rate has accelerated to higher levels. Ruxton (2005) proposed an alternative, but not mutually exclusive, mechanism. First, when prey are aggregated, increasing density should not proportionally reduce the average distance to the nearest prey and thus the time to first encounter prey ( Travis and Palmer 2005). Two untested hypotheses have recently been presented to explain this result. However, a recent experimental study using great tits ( Parus major) searching for winter moth caterpillars explicitly tested this assumption for the first time and found that the time to first encounter did not decline with increasing density as steeply as would be expected from a directly proportional relationship between prey density and encounter rate ( Mols et al. This assumption seems initially reasonable and follows from analogy with physicists' models of collisions between randomly moving gas particles (e.g., Denny and Gaines 2000). 2004), an assumption forming the basis of many classical models in ecology (e.g., the Lotka-Volterra predator–prey model Lotka 1925). In numerous models using encounters between predator and prey, a central assumption is that the encounter rate of a predator with potential prey is directly proportional to prey density ( Mols et al. Once prey were encountered, the probability of attack increased with the number of cells already visited, leading to a higher probability of attacking first-encountered prey at lower prey densities.Īn encounter between 2 agents is the first step in any interaction between them, whether they are predator and prey, parasite and host, or randomly moving molecules. We also found an interesting effect of prey density on the likelihood that an encounter with a prey would lead to an attack. There was no evidence found, however, that spatial autocorrelation had any effect. Moreover, the greater this acceleration the less prey density and encounter rate were directly proportional. ![]() In the majority of our trials, the search rate accelerated as more of the arena was searched. The relationship between prey density and encounter rate was found to be less than directly proportional, confirming the findings of a previous study using great tits searching for caterpillars. Hence, the arena was effectively one dimensional, simplifying the recording of search paths and removing edge effects. The fish explored a novel apparatus of 16 cells (15 × 16 cm) arranged in a ring, with each cell connected to the 2 adjacent cells by small openings. Here, three-spined sticklebacks were used to test 2 recently proposed mechanisms based on predator search behavior that may induce this nonlinearity: the effect of increasing search rate over the course of the search and the effect of spatial correlation in areas searched. Although numerous influential models in ecology assume a directly proportional relationship between prey density and prey encounter rate, a recent test of this assumption found that the actual relationship was nonlinear (rising slower than proportionately). ![]()
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