Friday, January 4, 2013

An insular, high elevation population of the semi-aquatic dice snake in Macedonia

The dice snake and its distribution.
The semi-aquatic dice snake (Natrix tessellata) ranges from Italy to China, an east-west axis of more than 5500 km and it uses a very wide variety of habitats. Current ecological information on this species is limited to the most western parts of the species’ range, notably Italy, Switzerland, and Germany. Preliminary reports from other areas  suggest that this species might be polytypic. A study in press and online in early view (Ajtic et al) investigates how its ecological situation may influence its life history adaptations.  The authors examine a very dense population of dice snakes on Golem Grad, an 18 ha  island  situated in a high altitude lake (850 m above sea level) where the species environment is quiet divergent from other study sites in Western Europe. Island life deeply influences a wide range of life history traits, particularly diet, predation, and density dependent processes. The Golem Grad population exhibits a set of unusual characteristics in this high population density, insular environment.

The authors marked more than 5000 individuals and produced estimates of more than 500 snakes per hectare, one of the highest ever recorded for snakes. Reproductive and mortality rates are elevated, suggesting a high population turnover. These traits evoke a tropical rather than a temperate-climate demographic pattern. The Golem Grad population is highly polymorphic, three color morphs (spotted, grey, and black) are observed in both sexes and each morph is represented by large numbers of individuals.  Data obtained for other life history traits ( body size, size at maturity, clutch size, diet, predation) suggest this population is quite diverged in comparison to other populations. Overall,the results reinforce the idea that the inter-population variability  of snakes should be taken into account over large geographic scales; otherwise attempts to derive general patterns may well be strongly biased.

R. Ajtića, L. Tomović, B. Sterijovskid, J. Crnobrnja-Isailović, S. Djordjević, M. Djurakić, A. Golubović, A. Simović, D. Arsovski, M. Andjelković, M. Krstić, G. Šukalo,  S. Gvozdenovićh, A. Aïdam, C. L. Michel, J-M. Ballouard, X Bonnet. 2013. Unexpected life history traits in a very dense population of dice snakes. Zoologischer Anzeiger - A Journal of Comparative Zoology

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