Effect of patch occupancy on immigration in the common lizard

1. Colonization is critical to invasion propensity and the viability of fragmented populations. This study evaluates the behavioural and demographic effects of patch occupancy on immigration in the common lizard (Lacerta vivipara). 2. We manipulated connected two-patch systems during one year. Two treatments were contrasted: both patches initially occupied vs. one occupied patch connected to one empty patch. Effects of manipulation were measured on emigration from occupied patches, on settlement in arrival patches and on demographic parameters in residents and immigrants. 3. Settlement probability was not influenced by the presence of conspecifics, but unsettled lizards stayed longer in initially empty than in occupied patches. The relationship between yearlings' body condition and emigration probability was affected by the manipulation, indicating that different yearlings disperse depending upon metapopulation structure. 4. Growth and maturation rate were influenced positively in juveniles colonizing empty patches, whereas there was no difference between immigrants to occupied patches and residents. Faster growth allowed female juvenile immigrants to reproduce earlier during colonization. No effect on growth or reproduction was detected in yearlings and adults. Selective benefits of colonization at the juvenile stage may provide an ultimate explanation for why natal dispersal prevails over breeding dispersal in this species. 5. At the population level, immigration and increased reproductive recruitment led to higher population growth in colonized patches. This may contribute to the species' capacity to develop and maintain a wide geographical distribution.