Comparing Model Projections with Observations: Lizards
Chamaille-Jammes et al. (2006) studied four discontinuous subpopulations 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 several life-history traits of the subpopulations, including body size, reproduction characteristics, and survival rates, while local air temperatures rose by approximately 2.2°C. They found individual body size increased dramatically in all four lizard populations over the 18-year study period, with snout-vent length expanding by roughly 28 percent. This increase in body size occurred in all age classes and, as they describe it, “appeared related to a concomitant increase in temperature experienced during the first month of life (August).” As a result, they found “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 “adult survival was positively related to May temperature.”
Since all fitness components investigated responded positively to the increase in temperature, the French researchers stated, “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.” They concluded, “to achieve a better prediction of a species persistence, one will probably need to combine both habitat and individual-based approaches.” Furthermore, they note individual responses, such as those documented in their study (which were all positive), represent “the ultimate driver of a species response to climate change.”
In providing some background for their study of montane rainforest lizards, Bell et al. (2010) note tropical species long have been considered to be “especially sensitive to climatic fluctuations because their narrow thermal tolerances and elevational ranges can restrict their ability to persist in, or disperse across, alternate habitats.” NASA’s James Hansen expressed this concept much more bluntly on 21 November 2006—when accepting the World Wildlife Fund’s Duke of Edinburgh Conservation Medal at St. James Palace in London—by declaring, “species living on the biologically diverse slopes leading to mountains will be pushed off the planet” as the planet warms, opining—as we have already noted he also did before the U.S. House of Representatives—that there will simply be no place else for them to go.
In an empirical test of this idea, Bell et al. compared “responses to historical climate fluctuation in a montane specialist skink, Lampropholis robertsi, and its more broadly distributed congener, L. coggeri, both endemic to rainforests of northeast Australia,” by combining “spatial modeling of potential distributions under representative palaeoclimates, multi-locus phylogeography and analyses of phenotypic variation.” This work revealed, in the words of the seven scientists, that “both species exhibit pronounced phylogeographic structuring for mitochondrial and nuclear genes, attesting to low dispersal and high persistence across multiple isolated regions.” Referring specifically to L. robertsi, the researchers state their evidence demonstrates “persistence and isolation” of most populations of the montane species “throughout the strong climate oscillations of the late Pleistocene, and likely extending back to the Pliocene.”
Noting many of the isolated refugia they studied “are particularly rich in narrowly endemic species,” Bell et al. state this characteristic has been attributed to “their relative stability during recent episodes of climate change (Williams and Pearson, 1997; Yeates et al., 2002; Graham et al., 2006; VanDerWal et al., 2009).” Furthermore, they indicate these observations “support the general hypothesis that isolated tropical montane regions harbor high levels of narrow-range taxa because of their resilience to past climate change,” citing Fjeldsa and Lovett (1997) and Jetz et al. (2004). Thus, they write, “at first sight, species such as L. robertsi would seem especially prone to local extinction and loss of considerable genetic diversity with any further warming; yet, these populations and those of other high-montane endemic species (Cophixalus frogs; Hoskin, 2004) have evidently persisted through past warming events.”
Bell, R.C., Parra, J.L., Tonione, M., Hoskin, C.J., Mackenzie, J.B., Williams, S.E., and Moritz, C. 2010. Patterns of persistence and isolation indicate resilience to climate change in montane rainforest lizards. Molecular Ecology 19: 2531–2544.
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.
Fjeldsa, J. and Lovett, J.C. 1997. Biodiversity and environmental stability. Biodiversity and Conservation 6: 315–323.
Graham, C.H., Moritz, C., and Williams, S.E. 2006. Habitat history improves prediction of biodiversity in rainforest fauna. Proceedings of the National Academy of Sciences, USA 103: 632–636.
Hoskin, C.J. 2004. Australian microhylid frogs (Cophixalus and Austrochaperina): phylogeny, taxonomy, calls, distributions and breeding biology. Australian Journal of Zoology 52: 237–269.
Jetz, W., Rahbek, C., and Colwell, R.K. 2004. The coincidence of rarity and richness and the potential signature of history in centers of endemism. Ecology Letters 7: 1180–1191.
VanDerWal, J., Shoo, L.P., and Williams, S.E. 2009. New approaches to understanding late Quaternary climate fluctuations and refugial dynamics in Australian wet tropical rain forests. Journal of Biogeography 36: 291–301.
Williams, S.E. and Pearson, R.G. 1997. Historical rainforest contractions, localized extinctions and patterns of vertebrate endemism in the rainforests of Australia’s wet tropics. Proceedings of the Royal Society of London Series B - Biological Sciences 264: 709–716.
Yeates, D.K., Bouchard, P., and Monteith, G.B. 2002. Patterns and levels of endemism in the Australian wet tropics rainforest: evidence from flightless insects. Invertebrate Systematics 16: 605–661.