A new study published today (Monday 28 May) in the journal Nature Climate Change provides insights into why and how species are moving around the globe in response to climate warming.
Turning up the heat is opening up areas for animals that were previously too cold, leading to the expansion of species towards the poles. However, in the hottest areas of a species range, marine and terrestrial animals seem to be responding differently.
Ocean warming is causing marine species to retreat to cooler water near the poles at both ends of their normal range spectrum. But on land so far, species are staying put at the warm end of their range even though temperatures are rising.
A research team from Simon Fraser University in Canada, Deakin University and the Institute for Marine and Antarctic Studies (IMAS) at the University of Tasmania hit the library to understand how temperature constrains the cold pole-ward and warm equator-ward range boundaries of animals and how each boundary is shifting with climate warming.
The team, led by Dr Jennifer Sunday of Simon Fraser University, first gathered published data from a century of experiments that involved heating and cooling animals to find the point at which they cease functioning. The authors found the hot and cold limits for 169 cold-blooded animals, including snails, crustaceans, dragonflies, beetles, frogs, lizards and fishes.
They then examined their maps to find the upper and lower latitudes of each species’ geographic footprint. They lined up the data for each species to compare where it lived to its temperature limits.
The team found a good match in the ocean - the footprint of marine animals closely conformed to the temperature that they could potentially occupy.
However, they were surprised to find a mismatch between where land animals are found and where they could live. Most terrestrial species can cope with more tropical temperatures but are not found there. In other words, warm temperatures aren’t limiting terrestrial species from living closer to the equator.
Why are the warm boundaries of land species less sensitive to warming?
“We think it’s a combination of three things’’ explains Dr Amanda Bates, co-author from IMAS. “A species niche isn’t just set by temperature. On land where water is key, species may be hindered more by dryness, rather than being too hot at this range boundary.
“Second, it could be rare heat waves that are actually setting boundaries on where species can live. Finally, as Darwin pointed out more than 150 years ago, there are more species and much more ecological competition toward the tropics, which may be enough to exclude some species from living in the warmer end of their potential real estate.”
The authors call for research to better understand how climate change will affect animals, especially those on land where predicting responses to warming may be particularly difficult.
They conclude by pointing out that while chaotic species combinations may be bad news for animals on land, entire assemblages of species are likely to shift in the ocean, meaning that we can make predictions about how marine species redistribute in the face of climate change.