Evol Ecol Res 1: 611-633 (1999) Full PDF if your library subscribes.
What factors shape sexual size dimorphism in ungulates?
Anne Loison,‡ Jean-Michel Gaillard,* Christophe Pélabon and Nigel Gilles Yoccoz§
Laboratoire de Biométrie, Génétique et Biologie des Populations, UMR CNRS 5558, Université Claude Bernard Lyon 1, F-69622 Villeurbanne Cedex, France
Author to whom all correspondence should be addressed.
Studies of sexual size dimorphism among mammals have in the main focused on whether body weight, level of polygyny or ecological variables account for dimorphism patterns. Unfortunately, the use of different methods and indices of dimorphism has led to confusion and a failure to assess the relative role of the variables. We studied the effect of body weight, level of polygyny, feeding type and habitat type on sexual size dimorphism in ruminants. Three patterns emerged: first, dimorphism increases with body weight; second, this positive relationship is accounted for by the positive association between level of polygyny and weight; and third, the effect of feeding type is weak, and habitat type has no detectable effect. These results demonstrate that allometry is unimportant for shaping sexual size dimorphism in ungulates, and that degree of polygyny alone can almost entirely account for the phenomenon that sexual size dimorphism increases with increasing body size in ungulates. Level of polygyny increases with weight and this correlation leads to the observed positive correlation between weight and dimorphism when polygyny is not accounted for. The possibility that the relationship between weight and level of polygyny can be explained by density and spacing systems is discussed, and some other hypotheses concerning mechanisms of selection are presented.
Keywords: allometry, feeding habits, habitat, level of polygyny, sexual size dimorphism, ungulates.
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