On the Diversity of Reptile and Amphibian Species in a Bornean Rain Forest

Abstract

Intensive collecting carried out over an entire year in 20 square miles of lowland rain forest in Borneo yielded 72 species of amphibians and reptiles considered to be regular inhabitants of the forest floor. Thirty-eight of these species, plus 12 that are "refugees" in the sense that they do not live primarily in this habitat, were collected in 402 quadrats randomly distributed over the forest floor. The average species diversity per individual was H' = 4.26 ± 0.21 bits, using Pielou's (1966a) method for estimating H' and its standard error from individual quadrats. This much diversity is equivalent to 28.3 hypothetical "equilibrium" species having relative abundances distributed according to the "broken stick" model of MacArthur (1957, 1960). The ratio of 28.3 to 84 (72 regular plus 12 refugee species) gives an "equitability" value (Lloyd and Ghelardi, 1964) of E = 0.34. Treating frogs, lizards, and "snakes" separately, we obtain diversity values of 3.30, 3.10, and 2.86 and equitability values of 0.47, 0.67, and 0.28 for the three groups, respectively. Although an equitability of E = 0.34 is well above the "ecological minimum" of E = 0.17 that would characterize 84 species having a lognormal distribution (Preston, 1962), it is surprisingly far below the "ecological maximum" of E = 1.0 that one would expect from the "equilibrium" community of a rain forest-a community rich in species, presumably having relatively constant, equable, predictable conditions for life. This leads us to re-examine the assumption that the rain forest floor environment is relatively constant and predictable. In respect of temperature it certainly is, but not so with rainfall. There is no dry season, but the spacing of heavy rainfalls (more than 1 inch in 24 hr) has an essentially random pattern. Rains of this intensity cause raging floods in the small streams in which many of the frog species breed. Conceivably this might often result in catastrophic mortality. The endless disturbance of intense rains may therefore prevent the community from achieving the theoretical equilibrium. Specimens obtained by general collecting were combined with those caught in the quadrats to form a total forest floor collection for this area of rain forest. Applying Pielou's (1967) method for partitioning diversity by taxonomic hierarchy, only a small part of the total species diversity (0.72 out of 4.65) is attributable to congeneric species living in the same habitat. This holds true also when frogs, lizards, and snakes are considered separately.