The puzzling patterns of predators

A new study published in Science collated maps showing the ranges of 998 marine species, from sharks to sea snakes, and from mammals and birds to fish. Lead author John Grady from Michigan State University wanted to explore these patterns in diversity and then link them to thermal physiology. In other words, how is it that different animals regulate their body temperature? And does this have anything to do with where they live? The researchers’ findings are interesting: most warm-blooded mammals and birds are most diverse in cooler, temperate seas, whereas there are more species of cold-blooded fish and sharks in tropical waters. Their reasoning for this trend? Cold-blooded fish are often prey and rely on moving fast to avoid predation – their bodies are better able to do this in warm water. In colder seas fish move more sluggishly, which makes them easier prey for the marine mammals that hunt them! The authors of the paper then checked their theory against data that showed where seals and dolphins are most abundant and where in the oceans they feed most. As it turns out, marine mammals eat more as one moves from the equator towards the poles, increasing the amount by a factor of 80.

This is an interesting ecological observation, but what’s the point? Knowing what drives patterns in diversity helps scientists better monitor what may happen when ocean temperatures rise, which will have implications for this delicate balance of predators and prey in the sea.