The only thing we have to fear is lack of fear itself, says new research in predator ecology. According to researchers from the University of Western Ontario, as published in Nature Communications last Tuesday, fear of predators can be enough to produce a cascade of changes in ecosystem structure, even when there are no predators around (Suraci et al., 2016). These findings shed some interesting new light onto the role that top predators play in an ecosystem, and may even provide us with insight towards how we can repair habitats suffering from a shortage of these long-persecuted, yet ecologically crucial, creatures.
In the Gulf Islands of British Columbia, raccoons have become a downright menace. With humans having locally eradicated all of their natural predators (cougars, wolves, and black bears), these secondary “mesopredators” have run amok, to the detriment of local bird, fish, and crab species. By playing recordings of predator sounds through speakers placed around the islands, and using non-predator sounds as a control, the researchers sought to determine if they could transform the species composition of the island ecosystems by merely convincing the raccoons that predators were near. Sure enough, the introduction of predator sounds led to significant rebounds in the prey populations previously ravaged by the overzealous raccoons, as well as corresponding declines in the populations of species consumed by those prey, in turn. Thus, by harnessing the raccoons’ instinctive fear of predators, the experimenters were able to directly manipulate multiple levels of the Gulf Islands’ ecosystem structure.
Due to their position at the top of the food chain, apex predators can exert profound effects on their respective ecosystems: keeping prey populations down, and all other species impacted by said prey in balance, as a result. Unfortunately, from as far back as the Pleistocene, apex predators have also been a major target of hunting activity, due to the danger they present to humans and livestock. Loss of these species often gives rise to surges in mesopredator populations, which can have serious destabilizing effects on the ecosystem as a whole (Prugh et al., 2009). For this reason, the restoration of predator species has become an issue of great concern to modern conservation. That the fear of predation, in and of itself, may have the power to manifest changes in ecosystem function is not a new concept (Laundré et al., 2001), but this groundbreaking study marks the first true experimental confirmation of this theory.
Before we may claim the ability to reform disturbed ecosystems with only the power of sound, however, some key issues remain to be resolved. For starters, this experiment took place over the course of only one month. It is impressive that such a significant recovery was achieved over such a relatively short timeframe, but without any actual danger of predation accompanying the artificial predator noise, these sounds may lose their threatening nature over time, and the reversal of any effects they may have produced on a given ecosystem would be likely to follow. Additionally, the researchers were merely able to partially reverse some of the trends plaguing an already heavily-disrupted ecosystem. To actually return the ecosystem of the Gulf Islands to its original state, such as it was before the loss of its native predator species, we will surely need more than a few strategically-placed speakers.
Nevertheless, these findings still certainly represent a significant step along the way to determining how best to heal the lasting effects of mankind’s unfortunate predator-killing habit.
Suraci, J. P., Clinchy, M., Dill, L. M., Roberts, D., & Zanette, L. Y. (2016). Fear of large carnivores causes a trophic cascade. Nature Communications 7, 10698, doi: 10.1038/ncomms10698.
Laundré, J. W., Hernández, L. & Altendorf, K. B. (2001). Wolves, elk, and bison: reestablishing the ‘landscape of fear’ in Yellowstone National Park, U.S.A. Can. J. Zool. 79, 1401-1409, doi: 10.1139/z01-094.
Prugh, L. R., Stoner, C. J., Epps, C. W., Bean, W. T., Ripple, W. J., Laliberte, A. S., & Brashares, J. S. (2009). The Rise of the Mesopredator. Bioscence 59 (9), 779-791, doi: 10.1525/BIO.2009.59.9.9.