Figure 43.6 Climate Warming Stresses Spiny Lizards
It is thought that climate change is going to result in a wave of species extinctions over the next century. Sinervo et al. (2010) examined the effect of climate change on lizards, including Sceloporus serrifer. The researchers hypothesized that higher daytime temperatures would result in a reduction of hours per day that the lizards would remain active, thus reducing the amount of time available for foraging. Using thermal models that record operative temperatures, the researchers compared conditions for S. serrifer at four sites in the Yucatan region of Mexico. Sceloporus serrifer was present at all four sites in 1975; when this study was conducted in 2008, S. serrifer populations were extant at only two of the sites, whereas they were extinct at the other two sites. Across the four sites, the researchers compared the maximum air temperature and the number of hours when the body temperature of the thermal model exceeded 31°C, the temperature at which the lizards are known to retreat into their burrows and, thus, stop foraging. Sinervo and colleagues determined that for each degree of increase in the maximum air temperature, the lizards would reduce their activity by 0.75 hours. Thus, as temperatures increase, the lizards spend less time foraging, which will then decrease growth and fecundity, resulting in an increased risk of extinction. Their data certainly support this conclusion; the two sites where the lizards are extinct had considerably more hours during which the lizards would be inactive in comparison to the two sites where S. serrifer is still extant. The researchers estimated that, since 1975, 4% of worldwide lizard populations have gone extinct. They further estimated that, because of climate change, 20% of lizard species will be extinct worldwide by 2080. Unfortunately, lizards are not the only organisms in danger of climate change-related extinction. There are also concerns about many other plants and animals (for example, see Thomas et al., 2004 and commentary by Pounds and Puschendorf, 2004).
Original Paper
Sinervo, B. et al. 2010. Erosion of Lizard Diversity by Climate Change and Altered Thermal Niches. Science 32: 894–899.
http://dx.doi.org/10.1126/science.1184695
[Note: Be sure to check out the supporting online material and podcast interview]
Links
Huey, R. B., J. B. Losos, and C. Moritz. 2010. Are Lizards Toast? Science 328: 832–833.
http://dx.doi.org/10.1126/science.1190374
AAAS: News: Science: As Global Temperatures Rise, the World’s Lizards Are Disappearing
http://www.aaas.org/news/releases/2010/0513sp_lizard.shtml
University of California-Santa Cruz: The lab of Dr. Barry Sinervo
http://bio.research.ucsc.edu/~barrylab/
Lemonick, M. D. 2010. Study: Global Warming Is Driving Lizards to Extinction. TIME, May 13, 2010.
http://www.time.com/time/health/article/0,8599,1989115,00.html
Camill, P. 2010. Global Change: An Overview. Nature Education Knowledge 2(1):49.
http://www.nature.com/scitable/knowledge/library/global-change-an-overview-13255365
Kearns, C. 2010. Conservation of Biodiversity. Nature Education Knowledge 1(9):7.
http://www.nature.com/scitable/knowledge/library/conservation-of-biodiversity-13235087
Mott, C. L. 2010. Environmental Constraints to the Geographic Expansion of Plant and Animal Species. Nature Education Knowledge 1(9):72.
http://www.nature.com/scitable/knowledge/library/environmental-constraints-to-the-geographic-expansion-of-13236052
Pounds, J. A. and R. Puschendorf. 2004. Ecology: Clouded futures. Nature 427: 107–109.
http://dx.doi.org/10.1038/427107a
Thomas, C. D. et al. 2004. Extinction risk from climate change. Nature 427: 145–148.
http://dx.doi.org/10.1038/nature02121
Figure 43.11 Corridors Can Rescue Some Populations
Fragmentation of formerly extensive habitat divides species that are restricted to that habitat into subpopulations that are isolated from one another. The unsuitable habitats that surround occupied habitat patches are thought to be barriers that prevent animals from moving among them. Many studies have demonstrated that habitat destruction and fragmentation due to human activities are major contributing causes of species extinction. To test the hypothesis that even small barriers to dispersal may reduce the number of species in a habitat patch, Gonzalez and Chaneton conducted two sets of experiments using a habitat consisting of moss growing on rocks as a model ecosystem. They trimmed the moss growing on the rocks to form distinct habitat patches. They then counted the number of small arthropods (primarily springtails and mites) living in the patches over time.
In the first experiment, which they initiated in 1995, the control patches were 50 cm2, and the experimental patches included a set of four circular patches of 20 cm2 each. The researchers examined the response to fragmentation over a period of one year by counting the number of arthropods in each patch. The results showed that isolation resulted in a drastic reduction in species richness in the experimental patches, with 40 percent of species becoming extinct within one year. Thus, populations in small, isolated patches were more likely to become extinct than those in larger patches.
In the second experiment, Gonzalez and Chaneton again used a control or “mainland” patch, but this time they included three different sets of test patches: four unconnected patches, four circular patches connected by 7-cm corridors to the “mainland" patch, and four circular patches with “mainland” corridors that were interrupted by small barriers only 10 mm wide. After three and six months they counted the arthropods in the different patches. In patches connected by 7-cm corridors, only 14 percent of species had become extinct after six months, whereas around 40 percent of species had become extinct after six months in patches disrupted by tiny barriers and in the totally isolated patches. These findings suggest that even a small barrier between patches is sufficient to increase the rate of extinction and decrease species richness. By comparison, corridors allowed arthropods to move between various habitat patches and the “mainland”, thereby reducing extinction rates of local populations.
To assess some of the longer-term effects of imposing barriers to dispersal, an experiment such as that conducted by Sharon Collinge is needed. Collinge (2000) performed a three-year field experiment in which she studied the effect of habitat fragmentation and corridors on insect species living in a native grassland habitat. Specifically, she tested the hypothesis that corridors influence patterns of population loss, rates of recolonization, and insect movements among habitat patches. Her results indicated that corridors do not necessarily protect against species loss, although species richness was slightly higher in patches with corridors than those without corridors. Further, her results indicated that corridors had the strongest positive effect under dry environmental conditions. Overall, Collinge concluded that corridors do have the potential to promote species dispersal of organisms between habitat patches, but that any positive effects from corridors depends on species characteristics, landscape context, and patch size, as well as environmental variation.
Original Paper
Gonzalez, A., and E. J. Chaneton. 2002. Heterotroph species extinction, abundance and biomass dynamics in an experimentally fragmented microecosystem. Journal of Animal Ecology 71: 594–602.
http://dx.doi.org/10.1046/j.1365-2656.2002.00625.x
Links
Collinge, S. K. 2000. Effects of grassland fragmentation on insect species loss, colonization, and movement patterns. Ecology 81: 2211–2226.
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CCYQFjAB&url=http%3A%2F%2Fwww.collingelab.com%2Fwp-content%2Fuploads%2F2011%2F09%2FCollinge_S.K._2000..pdf&ei=mGstVJCSOoaZyASI2YHYCA&usg=AFQjCNGkgFO-UJUD_Lwv60U6hbgA3fUsqQ&bvm=bv.76477589,d.aWw
Collinge, S. 2010. Spatial Ecology and Conservation. Nature Education Knowledge 1(8):69.
http://www.nature.com/scitable/knowledge/library/spatial-ecology-and-conservation-13900969
McGill University: Department of Biology: Gonzalez Lab
http://biology.mcgill.ca/faculty/gonzalez/
University of Colorado: The Collinge Lab Web Page: Research: Insect responses to grassland loss and fragmentation
http://www.colorado.edu/eeb/EEBprojects/CollingeLab/research/insect.html
University of Connecticut: Kent Holsinger: Habitat Fragmentation
http://darwin.eeb.uconn.edu/eeb310/lecture-notes/fragmentation/fragmentation.html
Science Daily: Hummingbird 'Tag' Suggests Fragmentation May Be Part Of Pollination Crisis
http://www.sciencedaily.com/releases/2009/02/090209223515.htm