This video resource offers ringside seats to a territorial battle for dominance between two male koalas.
- Which koala males tend to have the lower-pitched bellows? Why might this be? Why might females prefer to mate with them?
- What is the important role played in a koala community by traveling males?
- Having been chased away by Buster before, why does Jack return to the colony to challenge him again? What has changed since the first encounter? What is the result of their second encounter?
Koalas are generally rather mild-mannered creatures, spending five hours a day eating and the rest of their time dozing in treetops to conserve energy. Like many species, however, koalas live within a social hierarchy in which push occasionally comes to shove. This is most clearly seen in the summer mating season, which—because Australia is in the southern hemisphere where seasons are reversed from North America—occurs between December and March.
A male koala seeking to mate advertises himself with a deep bellow—the deeper the bellow, the larger the male—with females preferring the dominant “alpha males” who tend to be the biggest and strongest around. Alpha status is always subject to challenge by other ambitious males, however, and few stay on top for very long.
The vast majority of face-offs between rival koala males involve a lot of posturing and bellowing—again, the deeper, the more impressive—but occasionally two males actually come to grips, bringing their powerful claws and teeth to bear. Inevitably, one combatant or the other retreats before the fight gets too grisly, with the winner then broadcasting his victory to the colony with yet more deep bellowing.
A male koala’s success in this macho arena does not, however, guarantee that the offspring of local females will be his. For all the hierarchical bluster of male competition, alpha status among koalas is less important than it is for many species. Koalas are essentially solitary animals with little interaction and less loyalty in their relations with each other. Female koalas, for instance, tend to mate with different males every year, and an interesting dimension of koala society is that approximately 50% of all baby koalas—or “joeys”—are not in fact sired by the resident alpha, but rather by solitary “traveling” koalas from other colonies looking for opportunities to mate where they can. These travelers—often young adult males—sneak in behind alphas’ backs to mate with females without bothering to prove their dominance. Sometimes they stay and become alphas themselves, but just as often they move on. In either case, these traveling males provide an important service to the species by helping to maintain diversity within the gene pool; especially as human encroachment has effectively isolated koala populations in evermore crowded habitats throughout southern and eastern Australia, inbreeding has become a real problem, with some of the otherwise healthiest koala populations threatened by it.
Life Science – Content Standard C
As a result of their activities in grades 5-8, all students should develop understanding of
- Diversity and adaptations of organisms
- Biological evolution accounts for the diversity of species developed through gradual processes over many generations. Species acquire many of their unique characteristics through biological adaptation, which involves the selection of naturally occurring variations in populations. Biological adaptations include changes in structures, behaviors, or physiology that enhance survival and reproductive success in a particular environment.
As a result of their activities in grades 9-12, all students should develop understanding of
- Biological evolution
- Species evolve over time. Evolution is the consequence of the interactions of (1) the potential for a species to increase its numbers, (2) the genetic variability of offspring due to mutation and recombination of genes, (3) a finite supply of the resources required for life, and (4) the ensuring selection by the environment of those offspring better able to survive and leave offspring.
- Interdependence of organisms
- Living organisms have the capacity to produce populations of infinite size, but environments and resources are finite. This fundamental tension has profound effects on the interactions between organisms.
- Behavior of organisms
- Organisms have behavioral responses to internal changes and to external stimuli. Responses to external stimuli can result from interactions with the organism’s own species and others, as well as environmental changes; these responses either can be innate or learned. The broad patterns of behavior exhibited by animals have evolved to ensure reproductive success. Animals often live in unpredictable environments, and so their behavior must be flexible enough to deal with uncertainty and change. Plants also respond to stimuli.
- Like other aspects of an organism’s biology, behaviors have evolved through natural selection. Behaviors often have an adaptive logic when viewed in terms of evolutionary principles.