All over the warming globe, plant and animal species are moving up…northward and to higher elevations, that is…in order to find cooler temperatures. Evidence from the largest-scale migration study ever conducted shows that this trend is accelerating.
Previous studies of plant and animal migrations have offered indications that something — perhaps rising temperatures — was driving species northward and/or to higher altitudes. But these studies were isolated and doubts remained as to the true trigger of these movements and migrations.
But now comes evidence from the largest-scale analysis to date that such northward, migratory expansions and accelerating movements up-slope (i.e., to cooler/higher elevations) are largely attributable to warming and climate forcings.
The study, led by conservation biologist Chris D. Thomas of the University of York (England), “puts to bed” the question of whether these shifts in flora and fauna ranges and altitudes are due to climate change. According to Thomas, as quoted in a recent Washington Post article (see link below), “There isn’t any obvious alternative explanation for why species should be moving poleward in studies around the world.”
The new meta-analysis incorporated data from over 50 papers and included altitude data on 23 plant and animal groups and latitude data (i.e., range shifts northward) from 31 groups. One of the more general findings of the study, which analyzed species migrations in Europe, North America, Chile and Malaysia, was that greater warming in any given region was strongly correlated to farther, northward migration (to cooler climes).
Despite expected variations in such shifts from species to species, the study revealed a clear trend: uphill migration, on average, was 36 feet per decade (11.0 meters) and migration away from the equator was 10 miles (16.9 km) per decade. These rates of migration are 2 to 3 times greater than findings from the last major migration study, conducted in 2003, indicting a likely acceleration trend.
While some plant and animal species thrive in warming temperatures (which can open new zones to colonize), many plant and animal species are adapted to ecological niches that fall within a relatively narrow temperature range. As temperatures rise, these species’ survival often depends upon moving to cooler locales, such as higher-up mountain slopes. This of course, brings the migrating species into contact with the already established (in that niche) species. This can result in co-existence (a new, stable ecological web), or a reshuffling of the web. Amongst similar species (such as with moths, birds), the result is often increased competition over food sources and/or the up-slope-migrating species driving out the previously established one.
In some cases, such as with certain species of butterfly in the Sierra Nevada mountains, the pushed-out species has nowhere to move to, and its existence becomes imperiled. Another example of accelerating migration is the North American pika (a mountain-dwelling rodent) which has shown a ten-fold increase in its up-slope migration (per decade) just in the past 20 years or so.
The researchers also note the variation in migratory ranges between individual species and suggest that multiple factors may be at work in these responses.
Quoting from the paper’s abstract:
“The distances moved by species are greatest in studies showing the highest levels of warming [emphasis added] with average latitudinal shifts being generally sufficient to track temperature changes. However, individual species vary greatly in their rates of change, suggesting that the range shift of each species depends on multiple internal species traits and external drivers of change. Rapid average shifts derive from a wide diversity of responses by individual species.”
The researchers also sought to determine how far a given species of plant or animal in a given region had to migrate in order to find the same or cooler temperature. Surprisingly, the average distance turned out to be between 50 and 60 km to attain a 0.5° C cooler temp, which is quite far considering that often these regions are populated by humans. More surprisingly, there was no difference in movement rate noted across taxonomic groups; plants and insects move equally fast, and birds and mammals move equally fast.
Exceptions do exist; some bird species, like the Cirl bunting, actually have migrated to warmer regions, proving that at least a few animal species are more flexible in their adaptive responses to changing climate conditions.
One other puzzling outcome of this meta-analysis was a slower rate of migration up-slope than was anticipated. Since one need migrate a shorter distance up-slope in order to encounter cooler temperatures (about 100 meters for a 0.5° C drop), it was theorized that higher elevation movements would occur faster. Their findings did not support this hypothesis. One explanation is that the given animal population is in fact moving laterally on the mountain face, possibly due to being “squeezed” by higher-up species and/or to achieve a more northerly-facing direction (which receives less sunlight).
Many biologist are concerned that some species will not be able to move (adapt) quickly enough, or simply run out of room to migrate to. The ultimate effects of this ecological reshuffling are unknown and still a matter of intense study.
And, there is an additional threat here to human health: the World Health Organization and Centers for Disease Control have issued warnings in the past that pathogen carrying insects (such as mosquitoes carrying malaria, dengue fever, etc.) will also expand their ranges in response to steady, global warming.
As an example, the return of dengue fever carrying mosquitoes to Key West Florida in 2009 — after an absence of more than 75 years — has been blamed partly on warming-induced insect migration (and partly on a decline in the bat population).
The study, Rapid Range Shifts of Species Associated with High Levels of Climate Warming (Chen et al) was published in the August 19 edition of the journal Science.
Some source material for this post came from the Washington Post article: Plants and animals migrating upward as climate change by Brian Vastag, and, the Science Now article In Warming World, Critters Run to the Hills by Sara Reardon.
Top photo: (Parnassian Butterfly) Heather Dwyer / UC Davis
Second photo: (American pika) Justin.Johnsen; CC – By -SA 3.0
Third photo: (Cirl bunting) Paco Gómez from Castellón, Spain; CC – By – SA 3.0
Fourth photo: USDA