SPONTANEOUS EMERGENCE OF A RELATIONSHIP BETWEEN HABITAT OPENNESS AND MEAN GROUP-SIZE AND ITS POSSIBLE EVOLUTIONARY CONSEQUENCES IN LARGE HERBIVORES

Group size generally increases with habitat openness in large mammalia n herbivores, be it within species or across a given taxonomic family when considering the typical habitat and herd size of each species. Th is correlation is often considered to be the adaptive outcome of selec tive pressures arising from predation and from the intraspecific compe tition that communal foraging may entail. However, the increase of gro up size with habitat openness, when it occurs within a given species, might be the simple consequence of the instability of groupings and of the increasing possibility of perceiving congeners with environment o penness. This is shown in the present paper through the outcomes of a simple model for group fusion and splitting-up, which assumes that the individuals behave independently of habitat openness. Some possible e volutionary consequences of the phenomenon are discussed. The spontane ous increase of group size with environment openness might in particul ar have initiated the evolutionary trend to large body sizes in the he rbivore species which colonized open spaces. (C) 1995 Academic Press L imited