Listen to part of a lectures in an animal behavior class.

P: OK, yesterday, we talked about how the different behaviors help animals adapt in response to competitors. We looked at how moving to another location and becoming geographically isolated from other members of the species often explains how a group of animals eventually evolves into a different species. Now, what do we call this process? Dan?

S: Speciation. P: Good, speciation. Explain what we said about that, OK? S: Eventually, the isolated group becomes a distinct species that will no longer interbreed with members of the species it became isolated from.

P: Exactly. Now, some scientists argue that speciation can only occur if there's a geographical barrier, that behavioral differences alone won't cause two groups of animals to become two different species over time, and it's true that it can be hard to prove that behavioral differences are the cause of speciation. I mean, if a small group of animals starts behaving differently from the larger group, they might physically isolate themselves, move to another location. So we could argue that it was the geography that actually caused the speciation.

But to limit ourselves to only one possible explanation for speciation, it's a bit of an oversimplification. There are many complicated reasons species evolve. Let's look at an example where speciation due to behavioral differences might be happening. We're going to talk about killer whales, specifically killer whales found off the western coast of Canada.

Researchers have found that in this region, the species has divided behaviorally into two separate types that don't interact. They call these two types: transients and residents. Transients move a much greater distance along the Pacific Coast looking for food than residents do. Residents, as their name suggests, live in one general location. Resident killer whales eat fish such as salmon, but transients eat seals.

Now, let's assume that transients and residents both developed from a single kind of killer whale that had one specialized diet, whichever diet that was, fish or seal, the whales were all competing for that food. It's easy to imagine that if competition for that food got tough, any members of the species who evolved an ability to live on alternative food sources would improve their chances for survival. That's what we think might've happened here.

But it's the diet of their prey that I want you to consider now. Seals and salmon both have basically the same diet. They feed on smaller fish. Let's look at this chart. This chart represents a food web, a possible model for how residents and transients interact. There are still some unknowns, but the layout here is a logical guess based on what we know about the diets of the animals involved. So even if the residents and transients don't directly interact with each other, their prey share the same diet, so there is still a connection there.

S: But I don't understand if the seals and salmon are directly competing for the same food, isn't that going to have a negative effect on all the animals involved?

P: That's a good question. Think about it, by eating salmon, resident killer whales reduce competition for smaller fish. Without as many salmon eating the smaller fish, the seals have more food, so the seal population increases. Then the transient whales benefit because they have more seals to eat. But the reverse is also true. When the transients eat more seals, there are more fish for the salmon, so the residents have more salmon to eat.

Now, we've noticed other behavioral differences among these two types of killer whales. For instance, residents usually travel in much larger groups than transients. Any ideas why?

S: Well, I guess seals are probably harder to catch than salmon. P: OK...

S: I mean, if seals know that the transients are around, they could just go on land for a little while, right? So maybe a smaller group of transient whales are less likely to be noticed by the seals, but the residents, they don't have to avoid notice by staying in small groups, because, well, salmon probably don't have much chance of escaping them anyway.

P: Right. It's important to understand the relationships in this food web because the resident killer whale population in the area we've been discussing is now listed as endangered. And knowing how resident killer whales interact with their environment and the other killer whales around them will provide valuable insights into how to save the resident killer whales.