Mechanisms underpinning the impact of climate change on natural populations: May 2016 blog entry

12 May 2016

This project was funded by the CCI Collaborative Fund and active from September 2011 – August 2012. It reviewed the scientific literature to quantify the evidence for different potential climate change impact mechanisms and appraise their relative importance. Meta-analyses was conducted to consider how their relative importance varies between taxa, habitats and regions. For further information, please visit the project page on the CCI website.

The following blog is written by James Pearce-Higgins, Director of Science, BTO (Project Lead).

Identifying how climate change affects species’ populations

There is an urgent need to identify the mechanisms which underpin the impact of climate change impacts on biodiversity, to document observed impacts, to improve future assessments of species’ vulnerability to climate change and to inform adaptive conservation management. This CCI-funded project has produced two key publications (Ockendon et al. 2014 Global Change BiologyPearce-Higgins et al. 2015 Proceedings of the Royal Society London, Series B) documenting the importance of biotic mechanisms in driving species’ responses to climate change, and showing that the links between climate and species’ populations vary geographically (Fig.1).

We used a systematic review approach to identify 146 published studies of the impacts of variation in temperature and precipitation upon populations of wild species. The majority were from temperate latitudes of Europe and North America, and two thirds of species covered were either birds or mammals. Although we only considered studies that spanned a minimum of 20 years, study duration had a strong positive effect upon the probability of a study detecting a significant relationship between a climatic variable and population change. This emphasises the value of long-term biological monitoring data, and shows how studies spanning decades are required to fully document the impacts of climate change.

The review of mechanisms found significantly greater support for indirect, biotic mechanisms than direct, abiotic mechanisms as mediators of the impact of climate on populations (Ockendon et al. 2014). Thus, it is likely to be changes in the abundance of predators or prey that will cause long-term population changes in other species. These biotic effects were most important in affecting populations of species from higher trophic levels, whilst populations of primary consumers responded equally to biotic and abiotic mechanisms (Fig.2).

The response of populations to climatic variables varied geographically (Pearce-Higgins et al. 2015). Temperature tended to have a greater overall impact on populations than precipitation, although the effects of increased precipitation varied strongly with latitude, being most positive at low latitudes. These findings match those previously found for birds (Pearce-Higgins & Green 2014). Thus, in line with macroecological theory, populations in the tropics appear most affected by changes in rainfall patterns, whereas at higher latitudes, it is likely to be warming that is most important.

This study has two further implications. Firstly, we identified a general lack of data from the tropics whilst also suggesting that the processes linking species’ populations to climate in the tropics are likely to differ from those at higher latitudes, where most studies have been undertaken. Uncertainty is compounded by the fact that precipitation is the key climatic component driving tropical systems, but is much more difficult for climatologists to predict than temperature. Our limited understanding about the impacts of climate change in the tropics highlights an urgent requirement for long-term monitoring of even relatively common and widespread species to be undertaken in these regions. These studies should ideally focus on keystone species and groups, and collect data across a range of trophic levels.

Secondly, we found significant differences in population responses to climatic variables between studies with evidence of a significant climatic trend through time, and those without. Biotic mechanisms were more frequently supported in studies where there was evidence climate change, and that in such studies, the effects of temperature were more negative, and the effects of precipitation, more positive. In other words, climate change is already disrupting ecosystems by affecting interactions between species and altering the response of populations to climatic variables. 

 

Fig. 1 Fitted regression line between study duration and the probability of a particular test linking temporal variation in a climate variable to temporal variation in a species population parameter being significant. From Pearce-Higgins et al. (2015).
Fig. 2 Although populations of high latitude species can be cold-limited, there is evidence that habitat specialists, such as this golden plover, may be detrimentally affected by warming through biotic mechanisms (Pearce-Higgins et al. 2010).

References

Ockendon, N., Baker, D.J., Carr, J.A., White, E.C., Almond, R.E.A., Amano, T., Bertram, E., Bradbury, R.B., Bradley, C., Butchart, S.H.M., Doswald, N., Foden, W., Gill, D.J.C., Green, R.E., Sutherland, W.J., Tanner, E.V.J. & Pearce-Higgins, J.W. (2014) Mechanisms underpinning climatic impacts on natural populations: altered species interactions are more important than direct effects. Global Change Biology 20: 2221-2229

Pearce-Higgins, J.W., Dennis, P., Whittingham, M.J. & Yalden, D.W. (2010) Impacts of climate on prey abundance account for fluctuations in a population of a northern wader at the southern edge of its range. Global Change Biology 16: 12-23.

Pearce-Higgins, J.W. & Green, R.E. (2014) Birds and Climate Change: Impacts and Conservation Responses. Cambridge University Press, Cambridge.

Pearce-Higgins, J.W., Ockendon, N., Baker, D.J., Carr, J., White, E.C., Almond, R.E.A., Amano, T., Bertram, E., Bradbury, R.B., Bradley, C., Butchart, S.H.M., Doswald, N., Foden, W., Gill, D.J.C., Green, R.E., Sutherland, W.J. & Tanner, E.V.J. (2015) Geographical variation in species’ population responses to changes in temperature and precipitation. Proceedings Royal Society, Series B. 282: 20151561