Frequency of Encounter with Risk and the Tradeoff between Pursuit and Antipredator Behaviors in Crayfish: A Test of the Risk Allocation Hypothesis

Abstract

Prey animals encountering multiple stimuli must often make behavioral tradeoffs. Many environmental cues may influence the tradeoff observed, but recent theoretical work suggests that temporal variation in risk should influence how prey animals behave during any given period of risk. As time spent under risk of predation increases, prey animals will increase their allocation of foraging during periods of risk. This model is known as the risk allocation hypothesis (RAH) (Lima & Bednekoff 1999). We tested the RAH using the crayfish Orconectes virilis. We selected two frequency regimes (exposure to risk every 6 or 12 h) and three cues suggestive of increasing risk (water, snapping turtle cue, and conspecific alarm cue). Test animals were exposed to one of the six frequency × risk combinations for 24 h, followed immediately by the simultaneous introduction of a food and a risk cue. Three behaviors (burrow use, non‐ambulatory motion, and locomotion) were then recorded for 5 min. Responses were significantly influenced by the interaction of risk and frequency. Further analysis indicated that responses were not consistently influenced by frequency alone. While our results do not support the predictions of the RAH for our frequency regimes, qualitative comparison with an earlier, similar study (Hazlett 1999) suggests that risk allocation is occurring in this system. We recommend that frequency of encounter with risk be considered in future studies. Ignoring temporal variation may lead to over‐ or underestimation of the subject's natural responses.

Variation in predation risk and vole feeding behaviour: a field test of the risk allocation hypothesis

“…They noticed that foraging of field voles was lower in high-risk situations than in lowrisk situations at a high attack ratio, but not at a low attack ratio. Pecor and Hazlett (2003) exposed crayfish to two frequencies of predation risk and also varied the level of predation risk. Their results did not support the risk allocation hypothesis, as crayfish did not respond to the frequency variation according to the predictions of the hypothesis.…”

“…Previous experiments testing the predation risk allocation hypothesis have been conducted using invertebrates (Hamilton and Heithaus 2001;Sih and McCarthy 2002;Pecor and Hazlett 2003), or lower vertebrates (amphibians) in aquatic systems (Van Buskirk et al 2002). The behaviour of higher vertebrates, like voles, is probably much more flexible than that of invertebrates or amphibians, and voles are likely to adjust their behaviour in a much more complicated way.…”

“…high attack ratio, sensu Lima and Bednekoff 1999) prey should increase their foraging effort during the low-risk situation and decrease it during the high-risk situation compared to conditions with a low attack ratio. Experiments testing the model of Lima and Bednekoff (1999) have yielded mixed results (Hamilton and Heithaus 2001;Sih and McCarthy 2002;Van Buskirk et al 2002;Pecor and Hazlett 2003). The studies were conducted mainly under laboratory conditions and a clear taxonomic bias towards aquatic invertebrates prevents one from making generalisations about the validity of the hypothesis.…”

The mate pursuit-predation avoidance tradeoff in the virile crayfish,Orconectes virilis

“…This method caused the total stimulus volume to differ among the treatments. We chose not to make the volumes equal through injection of 20 mL of a water blank in the pheromone and alarm treatments because of the spurious results obtained with this species in an earlier study using such a method (Pecor and Hazlett 2003).…”

“…Lowered posture was considered any posture in which the chelipeds touched the substrate. These behaviors, excluding proximity to the stimulus pipette, form a consistent suite of responses for O. virilis (Hazlett 1999(Hazlett , 2003Pecor and Hazlett 2003). We added proximity to the stimulus pipette to the existing suite based on personal observations of O. virilis behavior.…”