Understanding when and how animals use their performance capacities can yield insights into the selection pressures driving high performance. Using two species of cursorial spiders, Schizocosa ocreata (Hentz 1844) and Rabidosa rabida (Walckenaer 1837) (Araneae: Lycosidae), we investigated the escape speeds exhibited by individuals of various body sizes in response to three aversive stimuli (jets of air, seismic cue, prodding) to determine how individuals use their performance capacity in response to different stimuli. We found that large individuals of both species exhibited their highest observed escape speeds in response to jets of air, whereas smaller individuals exhibited their fastest observed escape performances in response to prodding. We hypothesized that differences in escape behavior may reflect differences in risk associated with each cue type: fast moving jets of air may announce the arrival of an avian predator, and large individuals may be at greater risk of avian predation owing to their more conspicuous body size; whereas smaller individuals may be more susceptible to arthropod predators, which attack from the level of the spider, similar to a prod. We then performed an unreplicated mark-recapture, avian-exclosure experiment for both species, where we tracked individuals' persistence for 30 d. Consistent with our predictions, we found that larger individuals enjoyed greater persistence in our avian exclosure treatment, but their advantage was lost when avian predators were allowed to enter. Our results suggest that these spiders express their highest performances in only their most dire situations.
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Vol. 42 • No. 1