Warmer Climate, Shrinking Species?

Research indicates rising global temperatures may result in smaller plant and animal species. (Photo credit: Evgeny Dubinchuk/Fotolia)

Plants and animals are already beginning to change their behavior due to a warmer climate. Animals are beginning to migrate earlier, plants have changed their flowering periods, and many plants and animals have shifted their distribution away from the equator and closer to the cooler north and south poles. Recent research indicates that these modified behaviors are not the only change that species will undergo if the climate continues to warm as expected. These studies show that plant and animals may actually shrink in size as the climate continues to change.

Jennifer Sheridan, a professor of conservation biology at the University of Alabama, and David Bickford, a professor of environmental science at the National University of Singapore collaborated together on an article published in the journal Nature Climate Change. In the article, the scientists evaluated data from the fossil record, as well as modern-day studies to hypothesize what might happen if plant and animal sizes shrink due to a warming climate.

Their studies of the fossil record indicate that animals such as beetles, spiders, and pocket gophers significantly shrank in size during the Paleocene-Eocene Thermal Maximum, which occurred around 55.8 million years ago. Modern-day observations indicate that over the last 100 years, a variety of plant and animal species have decreased in size as average global temperatures have increased.

In addition to synthesizing data from the fossil record and current literature, the scientists also conducted two experiments. In one experiment, the scientists exposed ocean-dwelling creatures such as scallops, oysters, and scallops to conditions mimicking ocean water with increasing levels of acidity. As the acidity of the water increased, the marine animals ability to form their shells decreased, leading to an overall decrease in size. In a second experiment in which plants were grown under controlled climate conditions, the scientists found that for every 2 degrees that the temperature was increased, fruit size decreased by 3 to 17 percent. Similarly, when a variety of animals, including fish, beetles, marine invertebrates, and salamanders were exposed to increasing temperatures, they decreased in size, too. Fish, in particular, decreased between 6 and 22 percent in size.

ome species of salamanders are decreasing in size due to increased temperatures. (Photo credit: Carsten Meyer/Fotolia)

Research published in the journal The American Naturalist corroborates this data. This study focused on ectotherms, also known as cold-blooded animals, and how increased temperatures affect their growth rate and development. Experiments conducted with copepods, which are tiny aquatic crustaceans, showed that when exposed to warmer temperatures, the copepods go through their life stages at a quicker pace, meaning they reach adulthood at a smaller size than normal. This observation held true for a range of copepod species.

Why are species shrinking? Scientists point to a few explanations. Smaller plant size is linked to warmer and drier conditions and scarce water supplies. In addition, drought conditions often lead to forest fires, which diminish the amount of nitrogen, a nutrient necessary for plant growth, in the soil. These smaller plants in turn provide less of a satisfying meal for the herbivores that eat them. If the herbivores are unable to eat enough of their plant food source, or cannot find a replacement plant to eat, they will likely be unable to grow to their full size. Smaller herbivores in turn require predators to find more prey to eat to maintain their body size, or they too, will shrink in size.

Though not much is yet known about how worldwide food webs will be affected by a potential decrease in size across species, scientists hypothesize that changes in one species could have a ripple-effect on other species within their food web. They also foresee some species not feeling any affects due to a changing climate, which could also lead to imbalances within a food web, as some species thrive while others decline. Though computer models can help to show how shrinking species size may affect ecosystems in the future, only time will tell the actual impact these changes. As described above, current research indicates that shrinking species size could have a significant impact, though more research is necessary.

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