Madagascar has over 10,000 endemic plant species but few range shift studies that predict where species will move under climate change. Credit: Jeff Gibbs

Many species are expected to experience range shifts under climate change. How the dynamics of these range shifts play out will depend, in part, on the connectivity of the land- or seascape through which individuals are moving. Because of this, studies that examine how connectivity affects range expansions and contractions can make the choice between different climate adaptation strategies easier.

A recent study on range shifts focuses on endangered plant species in Madagascar, a biodiversity hotspot under threat from high rates of deforestation, degradation, and habitat fragmentation. Range shifts for 87 vulnerable species were modeled under three scenarios: a climate-only scenario that assumes current trends continue, a combined climate and land cover change scenario, and a connectivity scenario based on least-cost path.

The resulting species distributions show that land cover change and habitat connectivity will likely limit the number of species that experience range contractions, compared with the climate-only scenario. However, even when connectivity is considered, many species are still predicted to experience range contractions. This makes incorporating connectivity into range shift predictions even more important in order to not under- or overestimate species ability to reach safe areas. Climate adaptation strategies should thus focus on conserving not only protected areas, but also the corridors that connect them.

Trichogramma spp. Credit: Victor Fursov

A related study looks specifically at range expansions, which can occur in one of two ways: either “pulled” expansions, where low-density edge populations provide the front pull for species advance, or “pushed” expansions, where high-density populations behind the front push the expansion forward. The difficulty in empirically testing these types of expansions means that creativity is needed to learn more about them. In this case, parasitoid wasps (Trichogramma brassicae) were placed in replicated experimental “landscapes” in the lab to determine how altering connectivity affects the pushed vs. pulled status of expansions.

These experiments, combined with simulations that looked at expansion velocity and genetic diversity, showed that reduced connectivity leads to pushed dynamics. The complexity of the response, however, highlights the fact that much more information is needed to understand how the impact of pushed experiments depends on underlying causal mechanisms.  Regardless, using the pushed-pulled framework is one more strategy that may better predict range expansions, especially under changing landscape connectivity.

Climate adaptation strategies have varied a lot over time. A recent literature review of over 500 wildlife publications that focused on climate adaptation revealed over 2,300 management recommendations.  Choosing which recommendations to follow can be made easier with a better understanding of how habitat connectivity impacts species distributions and population dynamics.

Resources

Dahirel, M., Bertin, A., Haond, M., Blin, A., Lombaert, E., Calcagno, V., Fellous, S., Mailleret, L., Malausa, T. and Vercken, E. 2021. Shifts from pulled to pushed range expansions caused by reduction of landscape connectivity. Oikos 130(5): 708-724.

Yesuf, G.U., Brown, K.A., Walford, N.S., Rakotoarisoa, S.E. and Rufino, M.C. 2021. Predicting range shifts for critically endangered plants: Is habitat connectivity irrelevant or necessary? Biological Conservation 256: 109033.

Connectivity across both space and time is important to facilitate range shifts (May 2020)

Managing range shifts under climate change across new habitats and borders (September 2019)

Range expansion and the need for both high- and low- quality habitat (August 2019)