Delphinids: Spotted, Striped, and Spinning Dolphins

Pantropical spotted dolphin

The closest relatives of the common and bottlenose dolphins, which are perhaps the most familiar species to the western public, are those in the genus Stenella. Or at least, that might be true, because there has been a lot of confusion about the genus over the years.

It was first created in 1866 as a subgenus within Steno, the "narrow-beaked" dolphins, and contained just one species. It became a full genus in 1934,and by the end of the 20th century was agreed to contain five species - all of which had, in fact, been named before 1866. Since then, our understanding of genetics has greatly improved, and it has become clear that these various species cannot be so neatly arranged on a family tree as we might like.

Hanging Out with Other Species

Spinner dolphin

Animals interact with members of other species in a range of different ways. Most obvious, perhaps, are predator-prey relationships, but not all interactions necessarily have to have the potential for violence. Often, we find members of different species living side by side because they simply happen to like the same habitat, or one species may steal the burrows of another rather than making the effort to dig their own. But there are also some more organised relationships, where two or more relatively large mammalian species actively congregate together for some sort of mutual benefit.

We commonly see this in herd animal, especially where one species is relatively rare within a given region. So long as they don't irritate the other species too much, it may be to the benefit of the rarer one to join the herd of the more common species, gaining the advantage from large herd sizes that it cannot achieve on its own. Aside from grazing herd animals, other social animals that often congregate with other, related, species, include examples among both primates and cetaceans. (Examples from other groups of mammal are rarer, but have been reported).

Broadly speaking, there are three different reasons why animals might want to actively hang out with members of another species. There is no particular why two or more of these reasons cannot be true at once, and disentangling them can take a fair amount of observation. Let's take a look at one recent study as an example.