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.

Turning to the probably most Important distinctive factor, the food, we can establish that though L. agllts has a broader prey spectrum, yet its trophic diversity (i.e., selectivity) is smaller (SIMPSON'S formula has greater value at lower diversity!). It consumes more food categories (47) and makes little distinction among them. L. viridis is much more specialized in the quality of food, a notion which is supported by the low overlap value (18.5 %). Average prey size is also a considerable factor (35.2 %) as a consequence of the different body sizes of the species. Head measurements are generally accepted to be In good correlation with food size (SCHOENER 1968, SCHOENER & GORMAN 1968). On the basis of ROUGHGARDEN'

s theory (1974), the total niche width of a population Is equal to the variance of the probability density function of resource utilization, regarding in this case only food size as a niche dimension. Total niche width includes two components: the within phenotype component equals the variance of the resource utilization function of the individual, and the between phenotype component which is the same for the whole population. The former gives Information on whether the population is composed of food generalists or specialists, and from the latter we can obtain evidence of the intensity of intrapopulatlon (interphenotypic) competition. According to the data (see Results), In the L. viridis population a strong interphenotypic competition dominates (small BPC variance). That may be connected with the elaborate social organization (frequent interactions, hierarchical fights) of green lizard population (WEBER 1957), Sand lizards show no such features (SCHULZ 1972). From the analysis of niche segregation I have concluded that the three main dividing dimensions (habitat, time, food) of PIANKA (1973) are characters of unequal weight. Hence the factors affecting the resource partitioning of the populations were abstracted along the following three axes: 1. microhabltat (soil and air temperatures, light Intensity, structure of vegetation) and activity periods; 2. food quality; 3. food size. The allocation of food to two axes is justified by its Important separating effect, indicated by the smallest overlap values: 18.5 and 35.2 %, respectively. The reduction of the other factors to one axis Is also logical; thus their overlap value, calculated on the basis of a discriminant analysis, is only 39.7 %. Connexion of the apparently Independent dimensions (habitat and activity periods) in the first axis is not surprising. PIANKA' s distinction inplles in reality a grave conflict. Time itself must not be taken as a niche dimension or environmental factor, because it is Impossible to conceive a population tolerance aspect which Is in direct complementary relation with time. Time is, similarly to chance, an inherent character of all environmental variables by virtue of their dynamical changes. Thus activity period may only be explained as a response of the population to some kinds of environmental factors. Air and soil temperatures are of this sort, and their dynamics Is followed by the frequency distribution of active lizards as a population reply. Environmental factors, ordinated along three main axes as detailed above, reduce to the minimal the overlap between the realized niches of the two populations. These realized niche volumes are not simply parts of the n-dlmensional hyperspace, but actually Its subspaces, because the seven factors observed in this study do not represent all the relevant conditions which may affect the populations. REFERENCES ARNOLD, E.N., J.A. BURTON &D.W. OVENDEN (1978): A field guide to the reptiles and amphibians of Britain and Europe. - Collins, London, pp. 272. CRUCE, M. (1970): The seasonal and diurnal activity cycle in the lizard Lacerta taurica. - Studil Cere. Biol. Acad. R.P.R., Ser. Zool., 22j 467-472 (in Roumanian). DIXON, W.J. (ed.) (1981): BMDP Statistical software. - Univ.Calif.Press, Berkeley, X+725 pp. KORSÓS, Z. (1982): Field observations on two lizard populations (Lacerta viridis and L. agilis). Vertebr.hung., 21: 185-194. LEVINS, R. (1968): Evolution in changing environment. - Princeton Univ. Press, pp. 117. MAGUIRE, B. Jr. (1973): Niche response structure and the analytical potentials of its relationship to the habitat. - Am. Nat., 107: 213-246. OTIS, D.L., K.P. BURNHAM, C.C. WHITE &D.R. ANDERSON (1978): Statistical Inference from capture data on closed animal populations. - Wildl. Monogr., 62; 1-135. OUBOTER, P.E. (1981): The ecology of the island-lizard Podarcls slcula salfii: Correlation of microdistribution with vegetation coverage, thermal environment and food size. - AmphibiaReptilia, 2\ 243-257.