Evolution in the hypervariable environment of Madagascar

Abstract

We show that the diverse ecoregions of Madagascar share one distinctive climatic feature: unpredictable intra- or interannual precipitation compared with other regions with comparable rainfall. Climatic unpredictability is associated with unpredictable patterns of fruiting and flowering. It is argued that these features have shaped the evolution of distinctive characteristics in the mammalian fauna of the island. Endemic Herpestidae and Tenrecidae and members of five endemic primate families differ from closely related species elsewhere, exhibiting extremes of "fastness" and "slowness" in their life histories. Climatic features may also account for the dearth of frugivorous birds and mammals in Madagascar, and for the evolutionary prevalence of species with large body mass.

Fig. 1.

Residuals from a global nonlinear regression of interannual rainfall variation against mean annual rainfall at 15 stations in Madagascar, as in ref. : stations with variation, adjusted for mean, that is >75% of global stations are shown in red, stations with variation that falls between the median and the 75th percentile are shown in yellow, and those with variation between the 25th percentile and the median are shown as green.

Fig. 2.

Colwell's P in relation to mean rainfall for 15 Madagascar stations (triangles) and 15 matching stations from continental Africa (circles).

Fig. 3.

Colwell's C (constancy) vs. Colwell's M (contingency) for 15 Madagascar stations (triangles) and 15 matching stations from continental Africa (circles).

Fig. 4.

Interbirth interval and litter size for Malagasy herpestids (triangles) and continental African and Asian herpestids (circles). The slight random jitter has been added for clarity.