Nj. Welton et Ai. Houston, A theoretical investigation into the direct and indirect effects of state on the risk of predation, J THEOR BIO, 213(2), 2001, pp. 275-297
As well as there being a direct physical effect of the state (for example f
at reserves, or size) of an animal on the risk of being caught by a predato
r, state also has an effect on predation risk indirectly through changes in
behaviour. We present a mathematical model which looks at these two compon
ents of the effect of state on predation risk. We focus on two different mo
dels, (i) where the animal must achieve a fixed state and its fitness depen
ds on the time at which this state is reached and (ii) where the animal mus
t survive until a fixed time and its fitness depends on its final state. We
investigate conditions under which the indirect effect of increased state
is to increase or decrease predation risk, and give some numerical illustra
tions. Under certain conditions in the fixed-state model, the indirect effe
ct of state is to increase predation risk, whereas under certain conditions
in the fixed-time model the indirect effect of state is to decrease predat
ion risk. We discuss the implications of our results for empirical investig
ations into the effect of state on predation risk. (C) 2001 Academic Press.