Showing papers by "Jonathan B. Losos published in 1992"

The Evolution of Convergent Structure in Caribbean Anolis Communities

Abstract: Just as the factors responsible for the origin of an adaptation may not be responsible for its maintenance, the processes currently operating in a community may not have been important in assembling the community. Consequently, historical and ecological studies must be integrated to understand why communities are structured as they are. Examples from Caribbean Anolis assemblages indicate the unique ecological insight a historical perspective can provide. In the Lesser Antilles, phylogenetic analysis indicates that character displacement probably has occurred, but perhaps only once, and that patterns of size dissimilarity across islands result from ecological size assortment subsequent to the evolutionary change in size

Reproductive Biology and Diets of Goannas (Reptilia: Varanidae) from Australia

Abstract: Aspects of the reproductive biology and diets of nine species of Varanus from the seasonal tropics and temperate zones of Australia were examined by dissection of 386 preserved museum specimens. We investigated whether morphological and habitat diversity in the varanids was expressed in reproductive and dietary diversity. Most species from seasonal tropical areas had enlarged testes in the dry season (June-October) and females with oviductal eggs were collected at the end of the dry season and the beginning of the wet season (September-January). However, three species seemed to be exceptions to this trend, with an extended reproductive season (V. storr), or reproductive activity in the late wet season (V. semiremex and V. kingorum). A diversity of reproductive seasons for varanids from seasonal tropical regions in Australia was also found in a review of the literature. Temperate zone species had enlarged testes in spring (September-November) and laid eggs in spring or late summer. Clutch sizes ranged from 1-7 eggs. Regression slopes of maternal SVL and clutch size seemed to be higher for the smaller-bodied species compared to the larger-bodied species, but sample sizes were too low to compare them statistically. A review of reproductive data on Australian varanids suggested that some large-bodied species (e.g., V. varius) had relatively small clutch sizes. Most species had generalized diets with lizards and orthopterans being the most important prey. Large-bodied species such as V. giganteus and V. glebopalma tended to eat larger prey items, and specialized on vertebrate prey. Varanus semiremex ate mostly aquatic prey. Diets were relatively similar for most species but appear to be influenced by body size and habitat.

A critical comparison of the taxon-cycle and character-displacement models for size evolution of Anolis lizards in the lesser Antilles

Abstract: revealed an interesting pattern: on most islands with only one species, that species is of intermediate size, but two-species islands usually contain both a large and a small species (Schoener, 1970; Table 1). The evolution of large and small size has often been interpreted as an example of character displacement (e.g., Schoener, 1988b; Williams 1972; Losos, 1990). Roughgarden and associates (e.g., Roughgarden et al., 1987; Roughgarden and Pacala, 1989; Rummel and Roughgarden 1985a) have proposed an alternative hypothesis; they argue that a taxon cycle is operating in the northern Lesser Antilles in which a larger species invades an island occupied by an intermediate-sized species, and both evolve smaller size until the former species is intermediate in size and the latter species is extinct (Fig. 1). Roughgarden and Pacala (1989) reviewed the pertinent data and concluded that the available evidence overwhelmingly favors the taxon-cycle model. Here I argue that much of this evidence is either inconclusive, incorrect, or more consistent with the character-displacement model.