Quickly migrating species can keep track of climate change by migrating along the optimum of their climate zone habitat. Paradoxically these species increase the pressure on slower dispersers, increasing their extinction risk. Overall, adding such complex interspecies interaction to models increases the biodiversity loss predictions as the result of climate change.

Graph shows that adding the interaction of slowly and quickly migrating species in response to climate change, increases the overall time lag (of population average) compared to the geographically shifting temperature gradient – and therefore the overall extinction risk associated with this warming.

This we learn from a very interesting publication in Proceedings of the Royal Society B from 2012, by three biologists: Mark Urban of the University of Connecticut, and Josh Tewksbury and Kimberly Sheldon of the University of Washington.

Quick dispersing species increase extinction of slow dispersers

All across the globe ecologists are documenting that species have already begun to migrate in response to climate change – usually in a poleward direction, looking to stay in the preferred (cooler) climate zones. This happens on land, but also in the oceans, where challenges for climate-migrating species are equally hard, perhaps the most for Arctic and Antarctic species – that more than any other have no where else to go.

Sometimes migratory routes are blocked. Clear examples are mountain species that simply run out of mountain while migrating uphill (again to a cooler climate zone) – or endemic island species, that have to cross seas or oceans in search of another suited habitat. In search of a ‘new habitat’ temperature is of course only one parameter, precipitation being an important other, just like for instance soil type, intensified human landscapes (cities, roads, agriculture) and… ecosystem interaction. As you migrate, you’d hope that your food sources migrate along – and that you don’t fall prey to a predator you did not co-evolve with.

In other words, interspecies balance is crucial for survival – but of course also very hard to model and predict. If however you try, like the group of Mark Urban did, results are that net ecological damage increases, we read in the publication:

“Variation in dispersal among species—ubiquitous in nature—resulted in the most dramatic biodiversity losses. The species that face the greatest extinction risks might not be limited to those that disperse less than climate change absolutely requires, but also apply to those that disperse poorly relative to their warm-adapted competitors.”

The researchers describe two (previously unaccounted for) mechanisms through which species interaction might increase the biodiversity loss of climate change: firstly general competition during the ‘low-fitness’ general migration period, leading to reduced species abundances.

In addition “competition creates asymmetries in species’ abundances by decreasing abundances in those species that randomly have more similar thermal optima. Climate change deepens these asymmetries, which can lead to extinctions.” In models this species competition increases the lag in climate tracking by up to 1.2 degrees Celsius (as shown in above graph).

“Because species interact and differ in dispersal ability, we might be vastly underestimating climate change impacts on biodiversity. This means that current predictions underlying biodiversity threats used by governments and conservation organizations could be conservative.”

Improving predictions of climate change-induced biodiversity loss

The authors think existing climate-induced biodiversity loss predictions that do not account for complex species interaction may gravely underestimate extinction risk. This includes IPCC AR4 biodiversity loss forecasts that the study refers to. (Unlike its 2013-2014 successor this report (dating from 2007) did present quantitative global projections for biodiversity loss, expressed on a temperature gradient – a thing that is of course ideal for policy makers and the wider public to come to terms with ecological climate urgency.)

“We challenge ecologists to incorporate species interactions and dispersal differences into future predictions of biodiversity under climate change, and we suggest that conservation biologists should consider concentrating protection efforts on those species that disperse poorly and interact strongly.”

© Rolf Schuttenhelm | www.bitsofscience.org