Unexpected life history traits in a very dense population of dice snakes

A population of dice snakes (Natrix tessellata) monitored since 2008 in a small island (18 ha, 850 m a.s.l., FYR of Macedonia) revealed unforeseen patterns for snakes living in temperate climates. More than 5000 individuals have been marked and the density is one of the highest ever recorded (>500 resident snakes per hectare). Reproductive and mortality rates are elevated, suggesting a high population turnover. These traits evoke a tropical rather than a temperate-climate ophidian demographic system. The population is highly polymorphic, three colour morphs (dotted, grey, and black) are observed in both sexes and each morph is represented by large numbers of individuals. This polymorphism pattern was not previously documented in snakes. Data obtained for other life history traits (e.g. body size, size at maturity, clutch size, diet, predation) markedly diverged in comparison to available information. Overall, our results reinforce the notion that the strong inter-population variability (often mediated by phenotypic plasticity) of snakes should be taken into account over large geographic scales; otherwise attempts to derive general patterns may well be strongly biased.