O. Gy. Dely szerk.: Vertebrata Hungarica 22. (Budapest, 1984)

Korsós, Z.: Comparative niche analysis of two sympatric lizard species (Lacerta viridis and Lacerta agilis) 5-14. o.

VERTEBRATA HUNGARICA TOM. XXII. 1984 p. 5-14 Comparative niche analysis of two sympatric lizard species (Lacerta viridis and Lacerta agilis) By Z. KORSÓS (Received November 21, 1983) Abstract: A capture-mark-recapture investigation on two sympatric populations of Lacerta viridis and L. agilis has been carried out for a period of two years. Niche segregation has been studied from three main points of view: microhabitat, daily activity pattern and food selection. SCHOENER's measure of niche overlap was used in clarifying the roles of various factors. Food niche breadths of the two species has been described by an analysis of resource utilization curves. The following approximately equal in weight three factors are considered to be of greatest importance in the ecological segregation: 1. microclimatic and activity pattern differences, 2. prey taxa, and 3. prey size. Coexistence of two closely related species populations may be preserved in the same blotope (in sensu UDVARDY 1959) for a long time only by niche segregation. Populations can reduce competition by partitioning the environmental resource set and by adapting to the conditional factors which regulate the utilization of these resources. In such a way similar species can live together permanently. Ecological studies on niche segregation are important not only for the knowledge of species coevolution but also in trying to save the endangered species from extinction. In the present study I analyse the niche relations of sympatric Lacerta viridis and L. agilis populations. The first part of the results of the two-year investigation included a clarification of dispersion patterns, a morphometrical analysis and a preliminary comparison of niche dimensions (KORSÓS 1982). The purpose of the following part Is to answer questions such as: Which are the niche factors principally responsible for the coexistence of the two lizard populations? What survival values do these populations occupy? To what extent do they overlap? How long can their coexistence be preserved? Niche segregation has been studied from three main points of view (PIANKA 1973): habitat, time and food. Some authors (e.g. WEATHERLEY 1963) consider food segregation to be of such great Importance that they think niche to be identical with the animals' functional status in the food web. Habitat partitioning is one of the most frequent studies of niche (SCHOENER 1968, ROSE 1976). Within it many variables can be selected (e.g. vegetational structure, temperature, soil types, etc.), partitioning of which among different species is usually measured (PIANKA & PIANKA 1976, SIMON 1976, SIMON & MIDDENDORF 1976). Although every species has its own habitat (UDVARDY 1959), in the case of these sympatric lizard species it is more correct to talk about mi-