Introduction

The life histories and reproductive strategies of vertebrates are closely linked to the pattern of seasonality of the environment in which they live (May & Rubenstein, 1984). In mammals, this allows females to synchronize the energetically costly gestation and lactation with the period in the year when resources are abundant. Depending on the particular strategy and especially on the development of the young at birth, the timing may maximize resources for the mother during gestation or for the young after birth (May & Rubenstein, 1984; Bronson, 1989; Clutton–Brock, 1991). In general, however, lactation requires a greater energy investment than gestation (Oftedal, 1984a).

In some tropical regions, seasons may be virtually non–existent or at least much less marked than in temperate ecosystems. In others, seasonality may be more apparent in rainfall than in temperature and photoperiod. Such rainfall has an important effect on primary production, causing herbivores to adjust their annual cycle of reproduction to the cycle of rains. Thus, there are examples of tropical mammalian herbivores that reproduce only once a year (e.g. the Greater kudu, Tragelaphus strepsiceros, at the end of the rains: Perrin & Allen Rowlandson, 1995), although the reproductive season may be longer than in temperate regions (e.g. Mastomys rats: Leirs et al., 1994).