New research suggests that individual behaviours within animal species may serve evolutionary purposes and constitute more than just “noise” in the data


While most pet owners will confirm that there are personality differences in animals, just as there are in people, scientific research into animal behaviour has not always taken the existence of such differences seriously. Generally, researchers used to consider variation in individual behavior within a species as “noise” in their data and for the most part ignored it.

That attitude may be changing, however. According to an article in the journal Science, entitled “The Power of Personality”, scientists may be coming around to the idea that personality differences within a species not only exist, but may play a role in evolution or survival of the species.

The article reports the example of one animal study that looked at the behaviour of a certain type of salamander. Researchers observed that some of the salamanders tended to hide when fish that preyed on them were in the vicinity, while others did not. Initial hypotheses were that the risk-taking salamanders would be eaten, and thus be removed from the species by natural selection. However, further observation showed that the bolder salamanders were in fact better hunters, which allowed them to grow and reproduce faster, and gave them an evolutionary advantage in small bodies of water that were apt to dry up and cut short the life cycles of the slower growing, more timid individuals.

Other studies have supported the idea that different personalities will favour or disadvantage individuals in a species, depending on the environment.  A German study of a bird called the European tit, for example, showed that the success of aggressive or timid individuals varied depending on the density of the populations within which the birds had to compete.  While it was commonly assumed that more aggressive individuals would prevail, this turned out to be the case only when populations were low. When bird populations were dense, researchers found that the aggressive individuals got into more fights, which resulted in them dying off more quickly and reproducing less than the docile individuals. However, when populations were lower, the aggressive birds were more likely to out-compete their gentler counterparts, and thus be the dominant individuals.

Another study, involving stickleback fish, showed that personality difference may also play a role in evolution by helping to divide a species into separate populations that eventually differentiate and produce separate gene pools.  Researchers looking at the fish observed that bold individuals tended to form groups and live as schools, whereas the more shy fish, unable to compete for food in the group, moved out of the group and lived alone. However, the shy fish thrived outside the group, because remaining still was an effective anti-predator defense. The bold fish, in contrast, became targets for predators attracted to the large schools, or were easily picked off when isolated.

Similarly, a study looking at lizard behaviour found that while some individuals were social by nature and tended to congregate in groups, others were loners or wanderers.  Some wandered so far that they ended up in a different habitat entirely, a result that could spur the evolution of behavioral, physiological, or even morphological changes that differentiate the wandering lizards from the less adventurous individuals in the species.

Even spiders, it seems, have personalities. A study looking at a species of small, brown North American spider found that differences in personality among spiders in the colony were essential to the survival of the colony.  Researchers noted that roles within the colony were differentiated according to whether individual spiders were aggressive or non-aggressive.  Spiders were classified according to how long they stayed curled up after being frightened by a puff of air.  After observation, it appeared that those who tended to stay curled longer were typically also the ones responsible for tending young and fixing cobwebs. On the other hand, spiders that tended to uncurl more quickly had the role of attacking prey and fending off intruders. Researchers further found that having a healthy mix of the two was essential to the survival of the colony. Colonies where the mix of personalities was not adapted to the environment in which the spiders lived were likely to die off.

These studies suggest that it may be worthwhile for scientists interested in animal behaviour and evolutionary adaptations to reconsider the old view on the role of personality in the animal kingdom.




Written By: Linda Jensen

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