Small mammals, big personalities

            The seed dispersal habits of small mammals have long been known to have a significant bearing on the health and growth of forests. Now a doctoral student at the University of Maine has found that the various personalities of those small mammals also determines whether seeds germinate and grow.

            “People are generally willing to accept that dogs and cats have personalities because they can see behaviors that consistently differ among individuals of the same species. The

Recording a mouse personality (Holland Haverkamp)

same is true of mice,” said Allison Brehm, who conducted a study of how the personalities of small mammals affect forest structure. “Some are consistently more active or bolder than others, and we wanted to know whether small mammal personality influences seed predation and seed dispersal.”

            She captured 648 mice, voles and shrews and put them through a series of behavioral tests that determined their timidness, docility and anxiety. Then she released them into forests undergoing three silviculture treatments, dispersed seeds of various sizes nearby, and watched what happened.

            “We know small mammals have personalities; we know they play a role in seed dispersal; but the main question was whether all individuals contribute in the same way or are some individuals playing an especially important role and does personality predict their decisions in terms of seed dispersal,” Brehm said. “We wanted to see if personality influenced their selection of seed size, dispersal of seeds, the probability of them consuming the seeds, and if it influenced where they cached the seeds.”

            And she found that in almost every case it did.

            For instance, Brehm found that mice that were especially active when compared to others were more likely to remove seeds from where they were found and consume the seeds rather than cache them. She also found that bold voles dispersed seeds farther than timid ones, perhaps because they are more willing to risk attack by predators while carrying seeds a greater distance. More docile voles, however, tended to store seeds in locations that were more optimal for germination, like close to a fallen log.

            She also discovered that the distribution of small mammal personalities differed by silviculture treatment. She captured few timid mice in even-aged forests, for example, but equal numbers of bold and timid mice in an unmanaged 100-year old forest.

            “It may be that the even-aged forest is a riskier environment to live in, so it pays off to be a bolder individual, since there may be fewer resources available and bolder individuals are better competitors,” Brehm said.

            The study suggests that it may be worthwhile to promote the diversity of personalities within small mammal populations as a way of helping to conserve ecosystems. How exactly to do that is uncertain.

            “Promoting behavioral diversity is probably best done by promoting diversity in the environment,” said Brehm. “Diverse environments will lead to a greater diversity of personality types that can survive there.”

This article first appeared in the winter 2020 issue of Northern Woodlands magazine.