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.
According to the woody vegetational categories (KORSOS 1982) the lizards are distributed as in Fig. 2. There is a mild tendency of L. viridis to occur at higher values (i.e. in denser and loftier woods and shrubs) with greater relative frequency, nevertheless the calculated overlap between the two species has been found as high as 74.1 %. Testing the distributions of woody vegeta tion and capture points of lizards I found no significant interrelationship between them = 21.84 p>30 %). Fig. 2. Relative frequency distributions of lizards according to ligneous vegetational categories Examination of changes in the number of lizards observed and in the average wind velocity data together was aimed at the differences in activities of the two species on variously windy days . The data and the correlation matrix (Table 2) show that the lizards were active (catchable) independently of the velocity of the wind. Table 2. Correlation matrix of changes in lizard activities and wind velocity data Lacerta viridis Lacerta agilis wind velocity Lacerta viridis 1 Lacerta agilis 0.4953 1 wind velocity 0.0656 0.1640 1 In addition to the above treated spatial niche segregation there is another possibility for durable coexistence of two populations: temporal resource partitioning (PIANKA 1973). This niche dimension actually means periods of foraging or other activities. The overlap of utilization functions of limited environmental resources may be reduced to a high degree with the temporal separation of utilizations (e.g. diurnal and nocturnal foraging strategies). However, neither of the sympatric populations of L. viridis and L. agilis can realize nocturnal activity because of the substantial fall of temperature during the nights in the temperate zone, but they can effectively reduce competition by shifting their diurnal foraging periods. It was possible to compile a spring and a summer activity diagram from the pooled data of the two-year investigation (Fig. 3). The overlap between the spring activity periods is 69 %. In this aspect the one-peak activity of the sand lizard and its earlier appearance in the morning are remarkable. The green lizard begins its foraging afterwards with a little fluctuation at high noon,
