Habitat Selection Under Predation Hazard: Test of a Model with Foraging Minnows

Abstract

Animals commonly choose among habitats that differ both in foraging return and mortality hazard. However, no experimental study has attempted to predict the level of increase in resources, or the decrease in mortality hazard, which will induce a forager to shift from a safer to a more hazardous (but richer) foraging area. Here we present and test a model that specifies the choice of foraging areas ("habitats") that would minimize total mortality risk while allowing collection of some arbitrary net energy gain. We tested the model with juvenile creek chubs (Semotilus atromaculatus) in an experimental field stream in which the foragers could utilize a foodless refuge and choose between two foraging areas that differed in experimentally manipulated resource densities (Tubifex spp. worms in sediments) and mortality hazard (adult creek chubs). For the case tested, the model specified a simple rule: "use the refuge plus the site with the lowest ratio of mortality rate (μ) to gross foraging rat (f)," i.e., "minimize μ./f." Independent prior measurements of mortality hazard (as a function of predator density) and gross foraging rate (as a function of resource density) allowed us to predict the resource level in the more hazardous foraging site that should induce a shift from the safer to the more hazardous site. The chubs' preferences in subsequent choice experiments agreed well with the theoretical predictions. The "minimize μ/f" rule (deaths per unit energy), perhaps in modified form, provides a simple alternative to the "maximize f" (energy per unit time) criterion that applies to long-term rate maximization when predation hazard does not differ among choices.

Predators select against high growth rates and risk–taking behaviour in domestic trout populations

“…With increases in predation risk, there was a corresponding decline in survival advantage and an increase in growth advantage for the domestic trout. These results are consistent with theory which predicts that growing quickly and minimizing mortality represents a trade-off that is mediated through foraging behaviour (Werner & Gilliam 1984;Gilliam & Fraser 1987;Houston et al 1993;Werner & Anholt 1993). Domestication has proved that salmonid fishes are physiologically capable of elevated growth rates that are not observed in nature (Gross 1998;Devlin et al 2001).…”

“…Studies in the laboratory (e.g. Gilliam & Fraser 1987;Anholt & Werner 1995 and in the field (Biro et al 2003a,b) support these predictions and show substantial increases in prey activity, use of risky habitats and greater predation mortality with declines in food abundance. Risk-taking behaviour probably results from constraints that force individuals to take risks, such as time constraints to reach a particular body state, or a baseline risk of predation that is independent of behaviour (Rowe & Ludwig 1991;Walters & Juanes 1993;Werner & Anholt 1993).…”

State–dependent shifts between nocturnal and diurnal activity in salmon

“…Therefore, while foraging by night may o¡er the lowest ratio of mortality risk to food gained (see Gilliam & Fraser 1987;Clark & Levy 1988), this is not necessarily the optimal time-period of feeding for all ¢sh, as the strategy that will maximize their long-term survival varies. Thus, some must achieve a higher intake than is possible from purely nocturnal foraging, and so must forage more by day even though that is riskier in the short-term.…”

Abiotic and biotic factors influence the habitat use of an estuarine fish

“…bottlenose dolphins Tursiops truncatus) primarily occur in deeper waters in North Carolina (Gannon 2003). Further work with telemetry in areas that bottlenose dolphins frequent may help determine how subadult red drum balance feeding and predation risk (Gilliam & Fraser 1987). The response of organisms to estuarine water quality variables can be complex (Eby & Crowder 2002, Bell et al 2003.…”