Residents in Texas and Louisiana might find it hard to believe that warming winters are a concern in the wake of recent storms, but a new review warns that a general trend of higher temperatures is likely to bring increasing numbers of tropical animals to the region. The phenomenon is called tropicalization, an ecological process that sees temperate ecosystems flushed with poleward-moving tropical animals and botanical species who can thrive in a climate that was once too cool.
The researchers on the review (published in the journal Global Change Biology) wanted to examine how cold snaps in tropical-temperate transition zones limit the range of certain organisms. These species are ones for whom freezing temperatures would be harmful (see: raining iguanas) or even fatal, sometimes on a large scale. Cold weather is, therefore, an effective deterrent – but when these cold events become few and far between, it can foster population increase as tropical animals increase their range, causing a shift within native ecosystems. This makes the tropical-temperate transition zones a key area for observation, as it’s here we will begin to see changes in the typical flora and fauna of the environment.
"For the vast majority of organisms, if they freeze, they die," said co-author on the paper Caroline Williams of the University of California, Berkeley, in a statement. "Cold snaps like the recent one in Texas might not happen for 30 or 50 or even 100 years, and then you see these widespread mortality events where tropical species that have been creeping northward are suddenly knocked back. But as the return times become longer and longer for these extreme cold events, it enables tropical species to get more and more of a foothold, and even maybe for populations to adapt in situ to allow them to tolerate more cold extremes in the future."
To wildlife enthusiasts, the prospect of turtles and manatees finding their way to water systems on your doorstep might be hugely exciting, but snakes such as the predatory Burmese python – which can grow to five meters (16 feet) – might be less so. Even if you’re reptiles’ biggest fan, the introduction of effective predators can be devastating for native ecosystems and the wildlife that sits within them.
It’s therefore important that we keep tabs on which animals are the most likely to develop wanderlust and relocate to more northern climes. And it’s not just the lives of animals that are a stake, as the researchers warn disease-carrying insects could follow suit in seeking out northern populations to feed on. This has the potential to bring illnesses like the Zika virus and dengue (both transmitted by the Aedes aegypti mosquito) to areas of the globe that aren’t accustomed to tackling such health threats.
"Quite a few mosquito species are expanding northward, as well as a lot of forestry pests: bark beetles, the southern mountain pine beetle," continued Williams. "In our study, we were really focusing on that boundary in the U.S. where we get that quick tropical-temperate transition. Changes in winter conditions are one of the major, if not the major, drivers of shifting distributions."