Evolution

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One of the most powerful means plant and animal species have for avoiding extinction during climate change is the ability to evolve in ways that enable them to deal with the change. Several studies have demonstrated the abilities of numerous plants and animals to do just that.

Working in the Swiss Alps, Stocklin et al. (2009) studied the consequences of the highly structured alpine landscape for evolutionary processes in four different plants (Epilobium fleischeri, Geum reptans, Campanula thyrsoides, and Poa alpina), testing for whether genetic diversity within their populations was related to altitude and land use, while seeking to determine whether genetic differentiation among populations was related more to different land use or to geographic distances. In pursuit of these goals, the three Swiss scientists determined that within-population genetic diversity of the four species was high and mostly not related to altitude and population size, while genetic differentiation among populations was pronounced and strongly increased with distance, implying “considerable genetic drift among populations of alpine plants.”

Based on these findings and the observations of others, Stocklin et al. write, “phenotypic plasticity is particularly pronounced in alpine plants,” and “because of the high heterogeneity of the alpine landscape, the pronounced capacity of a single genotype to exhibit variable phenotypes is a clear advantage for the persistence and survival of alpine plants.” Hence they conclude, “the evolutionary potential to respond to global change is mostly intact in alpine plants, even at high altitude.” This result makes it much easier to understand why—even in the face of significant twentieth-century global warming—no species of plants have been observed to have been “pushed off the planet” in alpine regions. This has been shown to be the case in several pertinent studies, including Walther et al. (2005), Kullman (2007), Holzinger et al. (2008), Randin et al. (2009), and Erschbamer et al. (2009).

Describing another approach to the subject, Franks and Weis (2009) note a “rigorous way to determine if evolution has occurred in a natural population is to collect propagules before and after an environmental change and raise them under common conditions.” They state “this approach was used previously to show that Brassica rapa [a self-incompatible weedy winter annual] evolved drought escape through earlier flowering following a series of recent dry years in Southern California, and that early flowering results in higher fitness under drought conditions (Franks et al., 2007).” They also note “a related study showed that multiple phenological traits and their interactions evolved in response to the drought (Franks and Weis, 2008).”

Working with the same pre- and post-drought collection lines from their earlier experiment (Franks et al., 2007), the two researchers estimated the amount of assortative mating within, and the degree of phenological isolation between, two B. rapa populations. Their results indicated “climate change can alter plant phenology, which can change patterns of assortative mating within populations,” and “this assortative mating can directly change genotype frequencies and can also increase the rate of evolution by interacting with selection.” In addition, they demonstrated “climatically driven changes in phenology can potentially influence gene flow among populations due to changes in overlap in flowering schedules,” and “these changes in gene flow can also influence both the rate and pattern of evolutionary change.”

Given these findings, the two scientists conclude “the high degree of interdependence of flowering time, assortative mating, selection and gene flow make predicting evolutionary responses to changes in climate particularly complex and challenging.” This great degree of complexity suggests that among the multiplicity of outcomes, there is a good chance one or more will be just what the plants need to respond successfully to the climate change that elicited the outcomes.

Finally, Kuparinen et al. (2010) note “climate change is predicted to increase average air surface temperatures by several degrees in this century,” and “species exposed to changes in the environmental conditions may first show plastic phenotypic responses (e.g. Rehfeldt et al., 2002); but, in the long term, rapid climate change raises the question how quickly species can evolutionarily adapt to future climates in their habitats.” Against this backdrop, therefore, the authors investigated “the adaptation of Scots pine (Pinus sylvestris) and Silver birch (Betula pendula) to climate change induced prolongation of the thermal growing season,” using “quantitative genetic individual-based simulations to disentangle the relative roles of mortality, dispersal ability and maturation age for the speed of adaptation.”

The three scientists state their simulations predict “after 100 years of climate change, the genotypic growth period length of both species will lag more than 50% behind the climatically determined optimum,” but “this lag is reduced by increased mortality of established trees,” in conformity with the prior suggestion of Savolainen et al. (2004) and Kramer et al. (2008) that “the persistence of maladapted old trees preventing the establishment of seedlings better adapted to a changed environment” is not helpful to their long-term survival.

In addition, and in light of the fact that Kuparinen et al.’s findings suggest, as they put it, “adaptation might be sped up if mortality factors such as storms, fires, or insect outbreaks get more common in the future,” it could actually turn out to be a positive thing—in this particular instance, at least, and for these specific species—if some of the envisioned negative consequences of global warming were ever to become a reality.

References

Erschbamer, B., Kiebacher, T., Mallaun, M., and Unterluggauer, P. 2009. Short-term signals of climate change along an altitudinal gradient in the South Alps. Plant Ecology 202: 79–89.

Franks, S.J., Sim, S., and Weis, A.E. 2007. Rapid evolution of flowering time by an annual plant in response to a climate fluctuation. Proceedings of the National Academy of Sciences USA 104: 1278–1282.

Franks, S.J. and Weis, A.E. 2008. A change in climate causes rapid evolution of multiple life-history traits and their interactions in an annual plant. Journal of Evolutionary Biology 21: 1321–1334.

Franks, S.J. and Weis, A.E. 2009. Climate change alters reproductive isolation and potential gene flow in an annual plant. Evolutionary Applications 2: 481–488.

Holzinger, B., Hulber, K., Camenisch, M., and Grabherr, G. 2008. Changes in plant species richness over the last century in the eastern Swiss Alps: elevational gradient, bedrock effects and migration rates. Plant Ecology 195: 179–196.

Kramer, K., Bulteveld, J., Forstreuter, M., Geburek, T., Leonardi, S., Menozzi, P., Povillon, F., Scherlhaas, M.J., Teissier du Cros, E., Vendramin, G.G., and van der Werf, D.C. 2008. Bridging the gap between ecophysiological and genetic knowledge to assess the adaptive potential of European beech. Ecological Modelling 216: 333–353.

Kullman, L. 2007. Long-term geobotanical observations of climate change impacts in the Scandes of West-Central Sweden. Nordic Journal of Botany 24: 445–467.

Kuparinen, A., Savolainen, O., and Schurr, F.M. 2010. Increased mortality can promote evolutionary adaptation of forest trees to climate change. Forest Ecology and Management 259: 1003–1008.

Randin, C.F., Engler, R., Normand, S., Zappa, M., Zimmermann, N.E., Pearman, P.B., Vittoz, P., Thuiller, W., and Guisan, A. 2009. Climate change and plant distribution: local models predict high-elevation persistence. Global Change Biology 15: 1557–1569.

Rehfeldt, G.R., Tchebakova, N.M., Parfenova, Y.I., Wykoff, W.R., Kuzmina, N.A., and Milyutin, L.I. 2002. Intraspecific responses to climate change in Pinus sylvestris. Global Change Biology 8: 912–929.

Savolainen, O., Bokma, F., Garcia-Gil, R., Komulainen, P., and Repo, T. 2004. Genetic variation in cessation of growth and frost hardiness and consequences for adaptation of Pinus sylvestris to climatic changes. Forest Ecology and Management 197: 79–89.

Stocklin, J., Kuss, P., and Pluess, A.R. 2009. Genetic diversity, phenotypic variation and local adaptation in the alpine landscape: case studies with alpine plant species. Botanica Helvetica 119: 125–133.

Walther, G.-R., Beissner, S., and Burga, C.A. 2005. Trends in the upward shift of alpine plants. Journal of Vegetation Science 16: 541–548.


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