Home range ecology of an introduced population of the European wall lizard Podarcis muralis (Lacertilia; Lacertidae) in Cincinnati, Ohio.

INTRODUCTION

Studies of lizard spacing patterns, home range ecology and territoriality have examined the effects of these phenomena on population regulation (Tinkle et al., 1962; Boag, 1973; Tinkle, 1967; Philibosian, 1975), reproductive success (Blair, 1960; Rand, 1965; Tinkle, 1965, 1967; Ferguson et al., 1966; Simon, 1975; Schoener, 1983, 1987; Ruby, 1978), access to limiting resources like food (Blair, 1960; Rand, 1965; Milestead, 1970; Simon, 1975; Krekorian, 1976; Simon and Middendorf, 1980), and adult or offspring survival (Blair, 1960; Rand, 1965; Tinkle, 1967; Fox, 1978, 1983; Fox et al., 1981; Simon and Middendorf, 1980; Ferguson et al., 1983). Rand (1965) hypothesized that, in general, possession of a rigorously defended territory should lend a selective advantage to a male lizard but that the benefits of territorial behavior may not exist in "small populations in unusual habitats" or in "recently occupied areas" (Rand, 1965: 107). The question then arises: what may be expected if preViously advantageous territorial traits become selectively neutral as in the case of Rand's theoretical, small, isolated population? Optimality theorists contend that if behavior, like morphology, is a balance between different selective forces (Ehrman and Parsons, 1976), the relative advantage of territorial behavior might be expected to change over time (Orians, 1961; Owen-Smith, 1977; Wittenburger, 1980; see also reviews in Carpenter, 1958, 1965; Rand, 1965; Stamps, 1977, 1983; Davies and Houston, 1984; Stamps and Eason, 1989) and the degree of territorial behavior actually displayed may change with varying selective pressures of a cost/benefit gambit (Davies and Houston, 1984; Krebs and McCleery, 1984). The advantages of territoriality for lizards include exclusive exploitation of food sources and access of mates (Rand, 1965; Carpenter, 1965; Simon, 1975; Simon and Middendorf, 1980; Schoener, 1983, 1987), familiarity with refuges from predators (Rand, 1965; Simon and Middendorf, 1980; Stamps, 1983), potential niche space availability for offspring' (Brattstrom, 1974; Davies and Houston, 1984), and an overall decrease in intraspecific interference competition (review Kauffmann, 1983). The disadvantages of territorial behavioral include physiological costs in terms of energy expenditure (Rand, 1965; Simon, 1975; Ruby, 1978), a possible decrease in overwintering survival due to expenditure of fat reserves while patrolling and defending an area (Avery, 1970, 1974; Castilla and Bauwens, 1990; see also Claussen et al., 1989), reduced survivorship from increased risks of injury and predation during the active season (for discussion of costs and benefits of territoriality and other related topics, see reviews in: Carpenter 1958, 1965, 1978; Rand, 1965; Brattstrom, 1974; Stamps, 1977, 1983; Ferguson et al., 1983; Kaufmann, 1983; Davies and Houston, 1984). If the associated costs begin to outweigh the benefits of defense of a territory and its resources, optimality theory would predict a decrease in territoriality or a switch to hierarchical dominance relationships characteristic of a "pecking order" (Hunsaker and Burrage, 1969; Rand, 1965; Brattstrom, 1974; Stamps, 1977, 1983; Kaufmann, 1983; Davies and Houston, 1984; Krebs and McCleery, 1984). In many species that are territorial at naturally low densities, dominance hierarchies may form if conditions (experimental laboratory manipulations or obtrusive field enclosure studies) result in an increase in population density (Hunsaker and Burrage, 1969; Brattstrom, 1974). In such instances, crowding and intraspecific aggression become inflated and the benefits of territoriality no longer outweigh the associated costs (see reviews in Carpenter, 1965, 1978; Brattstrom, 1974; Stamps, 1977, 1983; Greenberg, 1978; Jenssen, 1978; Kaufmann, 1983; Davies and Houston, 1984). Moreover, behavior may vary in response to environmental heterogeneity and unpredictability (Simon, 1975; Krekorian, 1976), a fact which prompted Ferguson et al. (1983) to suggest that the most fit individuals of Sceloporus jarrovi should be those who can modify their behavior to respond to fluctuations in food availability and other factors of the biotic environment (see also Simon, 1975; Ruby, 1978; Simon and Middendorf, 1980).

History of Podarcis muralis in Cincinnati, Ohio. - Podarcis muralis is a small oviparous, diurnal, old world lacertid lizard widely distributed throughout much of mainland Europe (Arnold and Burton, 1978). Following a vacation to Northern Italy (Lago di Milan and/or Lago di Como areas) by a Cincinnati resident in the early 1950s, several individuals of this species were released into a single yard on the eastern edge of the city (Vigle, 1977; Hedeen, 1984). Over the past 40 yr, this population has spread throughout much of the city's E side along S-facing hillsides bordering the Ohio river (Conant and Collins, 1991). The success of P. muralis in Cincinnati has been attributed to favorable habitat, a lack of interspecific competition, preadaptation in their original range, and similar seasonality in both northern Italy and Cincinnati (Hedeen, 1984). Described as a human "culture follower" (Gruschwitz and Bohme, 1986: 16), P. muralis is considered "more adventurous and opportunistic" than other closely related lacertids (Arnold and Burton, 1978: 193) and represents the most urban lacertid in Europe (Arnold and Burton, 1978; Gruschwitz and Bohme, 1986). Several years ago a census estimated lizard densities at 1500 individuals/acre in Cincinnati (Kwiat and Gist, 1987). In Cincinnati P. muralis now occurs in clumped distributions with numerous breeding colonies of densely congregated individuals centered around areas of preferred habitat (urban areas such as vacant lots, parks, private gardens and yards). Predominant characteristics of such habitat include S-facing stone containment walls, equipment storage areas with rubbish heaps, building remains, garden walls and rocky hillsides. The frequent association of underbrush and cultivated bushes with the features of preferred habitat mentioned above is particularly important for the …