Md. Meyer et Tj. Valone, Foraging under multiple costs: the importance of predation, energetic, andassessment error costs to a desert forager, OIKOS, 87(3), 1999, pp. 571-579
We investigated spatial and temporal variation in the use of resource patch
es by Chaetodipus penicillatus by documenting changes in foraging activity
over several seasons, under two moon phases, and in two resource patch type
s. In particular, we examined the influence of nocturnal illumination (a su
rrogate for predation risk) and ambient temperature on: (1) foraging effort
(which is inversely proportional to the giving-up density, GUD), and (2) G
UD equality, i.e. the ability of foragers to accurately assess patch qualit
y by equalizing heterogeneous resource patches to the same GUD. There were
significant positive relationships between foraging effort and relative GUD
equality, ambient temperature and foraging effort, and ambient temperature
and GUD equality. In contrast, despite having a strong effect at the begin
ning of our study, moonlight did not have a consistent or significant impac
t on foraging effort and GUD equality when analyzed over several seasons. O
ur results indicate that as energetic or predation costs decline, foraging
effort rises, which in turn, leads to an increase in GUD equality and a red
uction in assessment error costs. This increased harvesting equality is due
to both enhanced functional harvest rates and increased accuracy of patch
assessment by foragers as more time is spent within a patch. In addition, p
redation risk and energetic costs appeared to switch in relative importance
in C penicillatus over the course of several seasons. These results emphas
ize the importance of considering multiple foraging costs and their additiv
e effects in studies of foraging and patch use.