Unexpected effect of climate change on body size for many different species

Assistant Professor David Bickford from the Department of Biological Sciences at the NUS Faculty of Science, and his collaborator Dr Jennifer Sheridan, have in a recent study, provided compelling evidence from scientific literature that climate change has an unexpected effect on body size for many different species all over the world.

The researchers found that increasing temperatures have had far-reaching effects on the body size of a wide array of species, from plants to top predators. Many organisms are already getting smaller and many more are likely to shrink as a result of continued climate warming. This trend is evident in numerous studies and has a firm theoretical foundation following fundamental ecological and metabolic rules that also enable scientists to test hypotheses about exactly how and why so many species are getting smaller, which ones might get even smaller in the future, and how it will affect society. The study by Bickford and Sheridan has been published online in Nature Climate Change.

Bickford is a lead scientist at the Evolutionary Ecology and Conservation Lab in the NUS Department of Biological Sciences, and a faculty member in the University Scholars Programme at NUS. Sheridan embarked on this study while she was a post-doctoral research fellow at the Lab.

On the uniqueness of this study, Bickford said: "We have summarised the data and provided a review of what has been shown to be occurring over the past few decades, as well as similar trends from fossil record that also demonstrate a cohesive trend. We have also provided the theories that explain the data, a set of reasonable ecological and metabolic rules that help explain why we see this repeat trend of species getting smaller. Many studies are corroborating this general trend, and as more studies come out saying the same thing, we need to understand why this trend is happening and what it will mean for society."

He added: "This is a very different frame of reference, scientifically. It implies that we are changing the planet's climate enough to have an effect on most species and we do not fully understand what will happen when species get smaller."

The effects of shrinking organisms will be varied and difficult to predict. The researchers pointed out that the main problem is not necessarily the shrinking itself, but the differential responses of species -- some are shrinking while others do not appear to be affected in the same manner. Why this is not universal is problematic because it has the potential to upset ecosystems and food webs more as organisms do not change together or in a similar way. Nonetheless, reduced size of individuals due to climate change will have repercussions across many food webs and potentially synergistic negative effects on biodiversity. Smaller plants mean fewer resources for consumers, which can lead to smaller body size and/or smaller populations of consumers. Ultimately, decreasing organism size could result in loss of biodiversity and effects that would not be beneficial to society, for example, crop harvests getting smaller or ecosystem services being compromised or limited.