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Species Are Shrinking

Credit: Romolo Tavani/Adobe

Credit: Romolo Tavani/Adobe

By Martino Malerba

An ingenious experiment has revealed the physiological reasons why many species are becoming smaller in response to global warming, overhunting and overfishing.

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Human-related impacts on natural ecosystems are driving many species to evolve smaller body sizes. This could be because fishing and hunting are disproportionally targeting larger individuals, or because increasing temperatures due to global warming increase the food requirements for species, and this limits their size. These shifts toward smaller size are very common in nature, but we don’t yet know what the consequences are.

What happens when a species evolves to a different size? I have been addressing this question using a technique called “artificial selection”: I evolve species toward smaller and larger sizes and evaluate the physiological and ecological consequences of the size shift.

There are predictable relationships between the size of a species and how it behaves, from small bacteria to giant elephants. Many variables change together with the size of a species: generation time, the number of individuals within a population, how fast they convert food into biomass, the rate at which they divide, their bio-energetic requirements, and so on.

This might indicate that body size is extremely important to the performance of a species in nature, but when multiple variables are correlated it becomes hard to tell what drives what. For example, it might just be that species with short generation times (that also happen to be small) grow faster. How...

The full text of this article can be purchased from Informit.