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...
