For elk reintroduced in the Missouri Ozarks, love is in the air

Habitat loss and overhunting decimated local elk populations in the 1800s. Now, researchers are finding new ways to return them to their native land. Featured image source: https://www.flickr.com/photos/8398907@N02/23105761300

Reference: Pero, E.M., Chitwood, M.C., Hildreth, A.M., Berkman, L.K., Keller, B.J., Sumners, J.A., Hansen, L.P., Isabelle, J.L., Eggert, L.S., Titus, C.L. and Millspaugh, J.J. (2022), Acclimation of elk mating system following restoration to the Missouri Ozarks, U.S.A.. Restoration Ecology. Accepted Author Manuscript. https://doi.org/10.1111/rec.13623

Love will keep us together

Restoration managers have much to consider when bringing a population back from the brink. One strategy to restore populations is to move individuals from healthier areas to habitats where the abundance has dwindled. This strategy, known to conservation biologists as translocation, can kickstart mating patterns in the wild that make local populations more resilient and less reliant on captive breeding programs. However, there are countless variables that could go wrong when trying to a restore a population to resilient numbers, from unexpected severe weather to pollution to the stress of navigating a new environment.

The greatest risk of failure comes during acclimation, the initial period after the reintroduction where the transplants learn to adapt to their environment and the new social relationships between members of their own species. While predation and human interaction are common pitfalls to a successful translocation, the complex social hierarchies found in many species are an additional unknown that can jeopardize restoration efforts in the long term. These relationships aren’t well understood for many species, but a recent project published in Restoration Ecology uncovered insights into the social lives of one of North America’s most charismatic animals: the elk.

One is the loneliest number

To understand how reintroduction might influence the elk mating scene, researchers introduced 106 young males into the Missouri Ozarks, an area with an existing but small elk population. Elk are polygynous, meaning they are likely to have multiple partners throughout the year and do not mate for life. Populations of polygynous animals tend to have unbalanced reproductive success, meaning a small number of males outcompete all the others in a bid to bed the females.

Such is the case with elk, where “prime age” sires dominate the dating scene and are far more likely to reproduce. These elk are larger and stronger, which gives them an edge against their younger rivals when sparring over a potential mate. Since elk social structure tends to favor the more mature sires, it was unclear how an influx of young males would change mating patterns throughout the population. The restoration “tactic” taken by the researchers, then, was to create an environment that favored the youth and see how the social structure changed over time as new generations were born and the age structure stabilized.

            Most wildlife restoration efforts hinge on the survival and fertility of the initial population of introduced organisms, since a population won’t take hold if they cannot thrive or pass on their genes. In this study, the young elk not only survived, but even reproduced at a rate higher than expected at first. The sudden increase in young males created an environment where the old sires simply could not compete with every young buck looking for a mate, leading to a decrease in polygyny as the prime age sires lost their monopoly of the females. This situation could be ideal for preserving genetic diversity, since more individuals from the introduced population were able to mate and thus contribute to the gene pool. This contribution is an imperative part of restoration efforts; if new individuals cannot pass on their genes, the population will still have low genetic diversity over time.

Ain’t nothing like the real thing, baby

The initial disruptions to the status quo did not last forever, however. Four years after releasing the young elk, polygyny returned to typical levels and the age structure of prime sires became more variable. Both effects were expected: as the population density increased, males grew older, and new calves were born, the competitive environment in which polygyny thrives returned. The new “prime age” sires came from both local and introduced populations, indicating long-term success in establishing a more robust gene pool.

These results indicate a successful restoration of the elk population, and they provide useful insight into how age and sex intertwine in conservation efforts. The conclusion that established social dynamics win out in the long run even when an introduction intentionally favors a specific age group is optimistic, as it gives some hope that translocation efforts can be optimized for both the short-term survival of the animals moved and the long-term health of the gene pool. In this case, favoring translocation of young elk ensured the population would be robust without permanently changing the social structure. This success story provides hope for future restoration efforts, brightening the future of one of North America’s most charismatic animals.

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