One third of mammals can't flee climate change, new estimate finds

The study looks into whether mammals will be able to spread to new, more suitable habitats fast enough to avoid being threatened by climate change.

Luca Santini, a biologist from Sapienza University Rome, is trying to answer some of the many unknowns surrounding climate change and the impact it will have on the environment. He and his team built a predictive model to estimate how quickly mammals can spread from their native habitats and whether they will be able to outpace the rate of climate change. We talked to him to find out why his estimate is likely to be conservative, and what we can do to mitigate the negative effects climate change could have on animals.

ResearchGate: What makes your model of animal spread in the case of climate change different from existing models?

Santini: The novelty of our model is the idea behind it. Models for predicting the spread rate of a species already exist, but are mostly used to explore theoretical questions, as we lack sufficient information to model real species. In our study we generated virtual species that resembled real species in their biological characteristics, and estimated their population spread rate. The analytical framework we used let us make the best use of the little knowledge we have about species biology to predict variables that generally can’t be collected in the field (for example, how quickly animal populations can spread), and to understand how these correlate with biological variables we do have data for (such as species’ body mass).

RG: You say that close to 30% of species are projected to be unable to spread faster than future climate change. What does this mean for these animals?

Santini: If the climate changes at a rate that is faster than a species’ ability to disperse into new areas then they can lose part of their geographic distribution, thus increasing their extinction risk. Our estimate suggests that a large proportion of species might be threatened by climate change because of their limited ability to colonize new environments. It is likely, however, that our estimate is optimistic. For example, the velocity at which species colonize new environments also depends on habitat loss, species interactions, and several other factors that we have not taken into account and that might increase the estimate.

It is also worth noting that mammals are, on average, good dispersers when compared with many other groups of animals, so the overall proportion of animal species that will be negatively affected by climate change might be much higher.

RG: Do these figures match those found in other studies?

Santini: Yes, in the last 10-15 years several studies using different methodologies and focusing on different threats of climate change have reached similar conclusions.

RG: Is there any way to reduce the threat these animals face?

Santini: Firstly, slowing down climate change by reducing greenhouse gas emissions would certainly help. Also, the ability of a species to spread to a new area depends on landscape permeability to animal movement (i.e. landscape connectivity). Enhancing connectivity by reducing landscape fragmentation and implementing a well connected system of protected areas can increase species chances to adapt to changing conditions. Some scientists have suggested a form of “assisted colonization”, whereby animals with poor dispersal abilities are moved into new areas, however this tactic is very controversial.

RG: What kind of animals do you predict will be most at risk? In which environments?

Santini: The species that will be most affected by range loss are those characterized by poor dispersal abilities and slow biological life cycles. Additionally, species that are in areas in which the climate is shifting more rapidly, such as flooded grasslands and savannas, deserts, and mangroves, are projected to be particularly threatened. However, in our study we only considered one of the factors that make species vulnerable to climate change, for example, species that depends on particular habitats (e.g. forests specialists) might be particularly threatened because of their aversion to move into different habitats. Similarly, species might not be able to colonize new areas because of the lack of prey species, or because of the competition with other species.

RG: What were the limitations of your study?

Santini: Population spread is an extremely complex process, and the models that we used had several simplifications due to a lack of knowledge about certain aspects of species movement behavior. For example, we may know approximately how far the animals move linearly, but we do not know how tortuous their path is, or how often they die while attempting to disperse. Also, we were interested in estimating species’ ability to spread given their biology and did not consider how their ability to spread is affected by habitat heterogeneity, fragmentation, or loss.

Image credit Diana Robinson.