GEOGRAPHIC RANGE, LIFE HISTORY PATTERNS, AND BODY SIZE IN A GUILD OF CORAL‐DWELLING MANTIS SHRIMPS

The extent of geographic distribution, or "geographic range" is an important attribute of a species, since evolutionary rates appear to be related to size of the geographic range. Environmental changes and catastrophies are more likely to occur on a local than regional scale (see Endean, 1976; Connell, 1978). Thus, some populations or broadly distributed species usually persist in spite of local environmental changes, whereas species with narrow ranges have a higher probability of extinction. Indeed, Jackson (1974) and Hansen (1978) found that widespread species of tropical bivalves and volutid gastropods, respectively, persist longer in the fossil record than species with narrower distributions. In addition to suffering high extinction rates, volutids with narrow ranges also undergo species multiplication (Hansen, 1978). Furthermore, the extent of the geographic range is related to several ecological characteristics of the organism. Size of the geographic range increases with body size and tendency toward predation in some groups of mammals (Van Valen, 1973). Rocky shore fishes have more limited dispersal and narrower distributions than species from sandy bottoms in the Eastern Pacific (Rosenblatt, 1963). High intertidal gastropods generally show narrower latitudinal ranges and greater endemism than species restricted to low intertidal areas (Kay, 1967; Vermeij, 1972), and in some cases intertidal mollusks on exposed rock surfaces show greater endemism than species occupying relatively homogeneous habitats beneath rocks (Vermeij and Porter, 1971; Vermeij, 1972). Using data from a study on salt marsh bivalves, Vermeij (1972) showed that most deep-burrowing species have wider ranges than shallow-burrowing species; and McAlester and Rhoads (1967) observed that deeper burrows are found in more species of bivalves living in shallow than in deep water. Tropical infaunal bivalves living from intertidal areas to one meter below low water level have broader geographic ranges than species living in deeper water (<100 m; Jackson, 1974). Jackson suggests that bivalves living in shallow, relatively discontinuous environments suffer more frequent perturbations and may have greater dispersal ability than the species occurring in deeper habitats. Marine species with dispersing larvae usually occupy larger geographic ranges than species with nondispersing young (e.g., Thorson, 1950; Scheltema, 1971, 1977, 1978; Shuto, 1974; Hansen, 1978). Also, larval dispersal has been related to evolutionary rates. The amount of larval exchange in five species of trans-Atlantic gastropods is inversely correlated with amount of morphological divergence among populations of these species (Scheltema, 1977). Volutid gastropods with dispersing larvae and wider geographic ranges have lower evolutionary rates than volutids with nonplanktonic larvae and narrower ranges (Hansen, 1978). In prosobranch gastropods, the mean longevity in the fossil record for species in families with long-lived larvae is greater than that for the overall prosobranch fossil assemblage (Schletema, 1978). The average species longevity in a group of proso-branch gastropods with nonpelagic development (and restricted geographic distribution) is less than the average species longevity for species in families with pe-