Posted by: oikosasa | March 4, 2013

When to stay and when to go – how porpoises make their decisions

How do animals decide how to forage? In the new Early View paper “How a simple adaptive foraging strategy can lead to emergent home ranges and increased food intake” Jacob Nabe-Nielsen and colleagues demonstrate that it only requires a few simple behavioural rules to produce most of the complex movement patterns observed for harbour porpoises.

What is it that makes an animal stay within more or less the same area for weeks or months before eventually moving to a new place? Surely it must have been feeding in the area, but how does it decide when it is time to leave? One of the central questions in behavioural ecology is whether animals have evolved many different kinds of behaviour, where each behavioural response is fine-tuned to a particular condition that the animals encounter in nature, or if a few simple mechanisms are sufficient to enable them to respond optimally in a wide range of conditions.

Porpoise in a pound net

The simulated harbour porpoise movements closely corresponded to those of satellite-tracked animals.

Porpoise release after tagging

The harbour porpoise (Phocoena phocoena) is an example of an animal species that displays very complex movement patterns. Porpoises often stay within relatively well-defined areas, or home ranges, where they presumably prey on various species of small fish before moving to new areas. In order to investigate whether a few different cognitive mechanisms could be sufficient to generate this complex behaviour, we developed a simulation model that included only two different kinds of behaviour. In the model the food was distributed in minute, scattered patches. Animals that had recently found plenty of food moved at random, much like cows that walk at their own pace in a field with lots of fresh green grass. Animals that had not been able to find food for some time became increasingly attracted to the patches where they had found food in the past. We let the animals’ ability to find their way back to previously visited food patches be governed by a spatial memory. It turned out that the combination of these two kinds of behaviour enabled home ranges to emerge, and when the animals’ memory about previously visited foraging sites decayed at a particular rate the model was able to produce movement patterns that closely resembled those observed for satellite-tracked porpoises in Danish waters. The right balance between the two kinds of behaviour also allowed animals to maximise their food intake. This suggests that it could be selectively advantageous for animals to base their decision on how to forage on a few, simple behavioural mechanisms.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s


%d bloggers like this: