All species harbour genetic variation, enabling populations to evolve to match their local environmental conditions, or to adapt when those conditions change. Rapid evolutionary change might therefore be critical for the persistence of some populations faced with climate and other environmental changes. However “rapid" evolution is still a slow process relative to the duration of most research projects, making it difficult to directly observe in the wild. To tackle this, we study spatial patterns of adaptation across the geographic range of native species, and those arising during the spread of non-native species, to help us to understand when evolution might “rescue” populations faced with environmental change.
climate adaptation during biological invasions
The changes in climate that non-native species experience as they spread in their new ranges are analogous to the changes in climate that native populations of those same species will experience over time with climate change. Invasions therefore provide a useful model system to study the pace, limits and ecological consequences of rapid adaptation to changing climate.
Our work has shown that the Eurasian species prickly lettuce (Lactuca serriola) has evolved earlier flowering phenology after introduction to arid parts of its non-native range. Despite undergoing rapid evolution and climatic niche expansion relative to the source region (Europe), the total variation in phenology observed in the non-native range, as well as the climate niche, does not exceed that found in the native range as a whole. This suggest that Lactuca can adapt rapidly to different climates that are within the climatic niche of the species, but hits a constraint to adaptation that occurs at the niche, or distribution, boundary. In this case, we might not expect evolution to “resuce” populations that already occur at the arid range edge following climate change.
We are also interested in the consequences that climate adaptation might have on the wider community. In a field experiment, we showed how the evolution of earlier flowering phenology could have made it increasingly difficult for native Californian annual plants to coexist with non-native Lactuca.
adaptation at species range margins
Distribution limits can emerge when populations are no longer able to adapt to environmental conditions beyond the range margin. Therefore, understanding why adaptation fails at range margins, and geographical patterns of adaptation more generally, can provide insight into the processes that might constrain or promote evolutionary rescue when environments change.
In her PhD project at ETH Zurich, Aud Halbritter studied patterns of distribution and adaptation in range edge and range centre populations of native plants across latitudinal gradients in Scandinavia and elevation gradients in Switzerland. Her results suggested that adaptation is more likely to arise at high elevation range edges, which is potentially related to higher levels of gene flow from range-centre populations.
Alexander, J.M., Levine, J.M. (2019) Earlier phenology of a nonnative plant increases impacts on native competitors. Proceedings of the National Academy of Sciences, 116, 6199–6204. [DOI]
Halbritter, A.H., Fior, S., Keller, I., Billeter, R., Edwards, P., Holderegger, R., Karrenberg, S., Pluess, A.R., Widmer, A., Alexander, J.M. (2018) Trait differentiation and adaptation of plants along elevation gradients. Journal of Evolutionary Biology, 31, 784–800. [DOI]
Halbritter, A., Billeter, R., Edwards, P.J., Alexander, J.M. (2015). Local adaptation at range edges: comparing elevation and latitudinal gradients. Journal of Evolutionary Biology [DOI]
Moran, E., Alexander, J.M. (2014) Evolutionary responses to global change: lessons from invasive species. Ecology Letters, 17, 637–649. [DOI]
Keller, I., Alexander, J.M., Holderegger, R., Edwards, P.J. (2013) Widespread phenotypic and genetic divergence along altitudinal gradients in animals. Journal of Evolutionary Biology, 26, 2527–2543. [DOI]
Alexander, J.M. (2013) Evolution under changing climates: climatic niche stasis despite rapid evolution in a non-native plant. Proceedings of the Royal Society B, 280 (1767). [DOI]
Halbritter, A., Alexander, J.M., Edwards, P.J., Billeter, R. (2013) How comparable are species distributions along elevational and latitudinal temperature gradients? Global Ecology and Biogeography, 22, 1228–1237.[DOI]
Alexander, J.M., van Kleunen, M., Ghezzi, R., Edwards, P.J. (2012). Different genetic clines in response to temperature across the native and introduced ranges of a global plant invader. Journal of Ecology, 100, 771–781. [DOI]
Alexander, J.M., Edwards, P.J. (2010). Limits to the niche and range margins of alien species. Oikos, 119, 1377–1386. [DOI]
Alexander, J.M. (2010). Genetic differences in the elevational limits of native and introduced Lactuca serriola populations. Journal of Biogeography, 37, 1951–1961. [DOI]