Spatial and behavioural consequences of a density manipulation in the common lizard

Density has been assumed to be a determinant factor of population regulation in the common lizard (Lacerta vivipara), as in most reptiles. This assumption was tested by experimentally decreasing and increasing the density of two wild populations from Mont Lozere (Massif Central, France). The behavioural modifications induced by the experiment are reported here. Spacing behaviour, habitat use, level of aggression and level of activity were studied in both populations during two to three years following the manipulation. The density manipulation affected all the variables studied, but most of the differences due to the site vanished two years after the beginning of the experiment. Space use (home range size and co-occurrence) and time of activity were deeply modified, most probably because of an increase of competition level. According to their age and sex, individuals reacted differently. On the site with increased density, yearlings were more often excluded from the potential foraging sites and the size of their home range was also reduced. Adult females began to be active later in the day, whereas adult males increased their home range overlap. These results are highly consistent with those obtained on demography (Massot et al., 1992). Due to density manipulation, such a home range size adjustment with a temporal separation of activity between age and sex classes shows that common lizard populations are able to respond to density change by behavioural modifications.