Edge effects on lizards and frogs in tropical forest fragments

We investigated whether forest pasture edges affect the distribution of an assemblage of small vertebrate ectotherms in a consistent and predictable m anner. Me describe the abundance and distribution of two species of anoline lizards (Norops) and five species of leaf-litter frogs (Eleutherodactylus) along the edges and in the interiors of nine forest fragments near Las Cru ces, Costa Rica, Over 4 months, we surveyed 44 pairs of plots by visual enc ounter, In each pair of plots, one was immediately adjacent to the pasture and the second was within the forest "interior." Both plots of a pair were searched simultaneously. This block design controlled for the effects of we ather, topography, and searcher ability The distribution of all species was highly variable with respect to edges. Only two species of frogs, Eleuther odactylus podiciferus and E. cruentus, were significantly more abundant in interior plots than in edge plots, although not consistently so. Both speci es of Norops lizards were more abundant along forest edges during the dry s eason. Both Norops species and several Eleutherodactylus species, however, appeared to become more abundant in the forest interior after the onset of the wet season, suggesting a seasonal edge effect. In Norops polylepis, the most abundant anole, rates of ectoparasitism were lower along edges than i n forest interiors. The magnitude of the edge effect on any one species was not influenced by the size of fragments or by the distance of the interior plot from the nearest edge. We believe that edge effects should not be def ined by the distance to which they are detected. Rather, they should be vie wed as highly dynamic in space and time; taxa appear to respond to differen t components of edge effects according to their particular biological requi rements.