Resource Allocation: Exploring Connections between Foraging and Life History

Abstract

Foraging determines an organism's intake of resources (water, nutrients or energy), while life-history patterns (survival, reproduction, growth) result from resource expenditure on fitness-related activities. Allocation of a limited resource pool among competing life-history traits links foraging and lifehistory strategies (Fig. 1). Although foraging, allocation and life history can be studied independently, they must be integrated in order to understand an organism's ecology and population dynamics in contrasting or variable environments (Pianka 1976; Boggs 1981; Mooney & Chiariello 1984; Gatto, Matessi & Slobodkin 1989). In particular, integration allows us to study ecological dynamics via the effects of input and output variation on the whole system through time. Allocation is arguably both the most important and least understood element in the chain from foraging to life-history strategy. The physiological processes and the life-history effects of allocation have been studied extensively, but they have generally been examined separately. For example, life-history studies have examined correlations between offspring size and number, or among reproduction, storage, maintenance and growth, but have assumed a given resource intake and utilization efficiency (e.g. Cohen 1971; Smith & Fretwell 1974; Snell & King 1977; Reznick 1985; Parker & Begon 1986; Lloyd 1987; Reekie & Bazzaz 1987a-c). Physiological studies have focused on efficiencies of resource utilization, and resultant rates of growth or reproduction, but usually do not relate the results to integrated life-history strategies (e.g. Lei & Armitage 1980; Milne 1987; Briegel 1990; Glazier 1990). Foraging studies have considered patterns of resource intake in variable environments, but generally do not address resource use, even on further foraging effort (e.g. Chapin 1980; Real & Caraco 1986; Hutchings 1988; Tuttle, Wulfson & Caraco 1990). Here I argue that these three sorts of studies must be blended and expanded if we are to understand life-history strategies in variable resource environments. Much life-history and resource allocation work has recently focused on the evolution of specific strategies, for which an understanding of the underlying