Scientists have developed a new conceptual framework to understand how some of the major threats to biodiversity combine and interact.

Climate Change and Environment

Climate change and the fragmentation of natural habitats are two of the greatest threats to biodiversity today. Yet despite a lot of research into these impacts, there is still a fundamental knowledge gap in understanding and predicting their combined effects. In the FRAGCLIM project, which was funded by the European Research Council, a team of scientists led by José Montoya (website in French), research director at the National Centre for Scientific Research (CNRS) in France, developed a new theory on the ecological consequences of these global threats on complex biological communities, which they tested in a series of experiments. “Our new theory helps with forecasting the effects of warming and fragmentation on multispecies communities and ecosystem functioning,” says Montoya, FRAGCLIM project coordinator.

Developing a new theory

The new theoretical framework conceived in the FRAGCLIM project aims to predict the combined effects of climatic warming and habitat fragmentation on biodiversity, dynamics within a community and the impacts on the functioning of ecosystems. It enables simple and accurate predictions of the effects of warming on community structure and stability, identifies which biological parameters are most sensitive to warming, and tests previously contradictory experimental results. The team also developed a new food web model that explores the stability of ecosystems in the face of habitat loss.

Experimental testing

Some of the predictions of this new theory were tested in a mesocosm experiment – a controlled outdoor experiment that aims to mimic conditions in the natural world – and in a series of laboratory experiments. In the lab, the team investigated the impact of warming on the interaction and dynamics between several algae species and zooplankton that feeds on them, in incubators ranging from 14 to almost 40 degrees. The mesocosms contained over 2 000 litres of water, filled with a complex community of phytoplankton and zooplankton sourced from surrounding lakes. “We manipulated warming and fragmentation, such that we had 48 mesocosms in total, divided into three sets of four tanks corresponding to four experimental treatments,” Montoya explains. The experiments ran for three years, and the scientists measured diversity and abundance of species and trophic levels – the position of organisms in a food web – along with daily measures of a number of ecosystem functions, in particular carbon sequestration and release.

Results and future

The project revealed a number of novel, sometimes counter-intuitive, potential outcomes. “More generally, we developed a new conceptual framework to understand and predict the eco-evolutionary consequences of habitat warming, fragmentation, and their interaction, on multispecies systems,” adds Montoya. “We demonstrated how warming, and fragmentation can individually alter selective pressures, as well as the size, structure and connectivity of populations, interacting species and more complex communities.” The project led to several major studies. One published in ‘PNAS’ in 2021 was a breakthrough in the area of climate change effects on the importance of biodiversity for ecosystem functioning, finding that in more fluctuating environments, biodiversity is more important for ecosystem functioning than in constant environments. Another publication soon to be submitted explores the combined effect of warming and fragmentation on ecosystems. “We show that fragmentation has larger effects than warming on phytoplankton biodiversity across spatial scales, challenging prevailing wisdom,” says Montoya.

Keywords

FRAGCLIM, climate change, habitat fragmentation, biodiversity, combine, effect, warming, ecosystems