A new research suggests that changes in animal size depend on two key ecological factors: Competition for resources between species and the risk of extinction due to the environment.
- The study was published January 18 in the journal Communications Biology.
Key points
- A team of researchers challenge an existing theory, known as Cope’s Rule, for why animals change size throughout their evolution.
- Cope’s rule suggests there is a tendency for many animal groups to evolve larger body sizes over thousands and millions of years.
- But the new study suggest Cope’s rule had clear exceptions. Reptiles, for instance, shrank from the size of giant dinosaurs to hand-sized geckos and sparrows.
- First, animals increase in size over time. The researchers found that animals grow bigger due to less competition between species when, for instance, food is abundant. During the Jurassic period, when dinosaurs grew to massive proportions.
- Second, the model found that some animals get bigger and then become extinct. Dinosaurs and woolly mammoths, for instance, grew to meet competitive demands, then went extinct due to environmental catastrophes or being out-competed by other species.
- Third, the model found the opposite of Cope’s rule: that species shrink over time. This happens when competition is high and there is a degree of overlap in habitat and the use of resources. For example, small horses that lived in Alaska during the Ice Age rapidly shrank due to changes in climate and vegetation.
- Polar bears have shrunk to two-thirds of their previous size in the past 30 years alone. And it’s not just polar bears — many species of birds, amphibians, and mammals have become smaller over the past century.
- Scientists think it’s because animals are rapidly adapting to the changing climate.
