Rear Mirror: Lizard Extinctions?

Source: CO2 Science

Reference
Chamaille-Jammes, S., Massot, M., Aragon, P. and Clobert, J. 2006. Global warming and positive fitness response in mountain populations of common lizards Lacerta vivipara. Global Change Biology 12: 392-402.

Background
Many are the predictions of species extinctions arising from warming-induced changes in the characteristics of regions to which the species are endemic. See our major report – The Specter of Species Extinction: Will Global Warming Decimate Earth’s Biosphere? – for many examples of the concept, as well as a multitude of evidences that reveal it to be wholly unrealistic. Then, read on to discover another such example.

What was done
The authors studied four unconnected populations of the common lizard (Lacerta vivipara), a small live-bearing lacertid that lives in peat bogs and heath lands scattered across Europe and Asia, concentrating on a small region near the top of Mont Lozere in southeast France, at the southern limit of the species’ range. More specifically, from 1984 to 2001 they monitored a number of life-history traits of the populations, including body size, reproduction characteristics and survival rates, during which time local air temperatures rose by approximately 2.2°C.

What was learned
Individual body size dramatically increased in all four lizard populations over the 18-year study period, with snout-vent length expanding by roughly 28%. This increase in body size occurred in all age classes and, in the words of Chamaille-Jammes et al., “appeared related to a concomitant increase in temperature experienced during the first month of life (August).” As a result, they found that ‘adult female body size increased markedly, and, as fecundity is strongly dependent on female body size, clutch size and total reproductive output also increased.” In addition, for a population where capture-recapture data were available, they learned that “adult survival was positively related to May temperature.”

What it means
In summing up their findings, the French researchers say that since all fitness components investigated responded positively to the increase in temperature, “it might be concluded that the common lizard has been advantaged by the shift in temperature.” This finding, in their words, stands in stark contrast to the “habitat-based prediction that these populations located close to mountain tops on the southern margin of the species range should be unable to cope with the alteration of their habitat.” Hence, they conclude that “to achieve a better prediction of a species persistence, one will probably need to combine both habitat and individual-based approaches,” noting, however, that individual responses, such as those documented in their study (which were all positive), represent “the ultimate driver of a species response to climate change.”

Reviewed 14 June 2006