The Ultimate Mesopredator

The idea of the apex predator has banged around popular culture long enough that almost everybody knows what it means. It refers to animals at the top of the food chain like killer whales, great white sharks, lions, tigers, and bears (oh my!). The term mesopredator, however, is rarely seen outside of scientific literature. Nonetheless, this label refers to animals such as raccoons, baboons, and stingrays. These carnivorous or omnivorous animals occupy the middle of the food chain hunting those at the bottom and being hunted by those at the top.

Sector Murcielago, Guanacaste, Costa Rica 2008. Don't worry, the grill was not on.
Sector Murcielago, Guanacaste, Costa Rica 2008. Don’t worry, the grill was not on.

 

As anyone on the mailing list for any environmental charity knows, apex predators are declining around the world. (The findings of Burgess et al. 2014 suggest that great white sharks in California may be an exception to this trend). While the decline of apex predators certainly results in a loss for biodiversity, it has led to extreme gains by mesopredators.

 

In their dramatically titled review “The Rise of the Mesopredator”, Prugh et al. (2009) introduce the concept of mesopredator release. This refers to the explosion of mesopredator populations that occurs once apex predators have been removed from an ecosystem. This can, in turn, lead to population collapses of the mesopredators’ prey. Humans may attempt to address this problem by culling mesopredators, but the high fertility rates of these species (Palomares et al. 1995) may reduce culling programs to ecological whack-a-mole.

 

Truthfully, controlling mesopredators may be difficult because of their ecological similarity to our own species. While humans currently occupy the top of the food chain, we had to fight our way to it. Once our ancestors learned to cooperate, use fire, throw rocks, and set traps they were able to drive their predators as well as much of their prey to extinction or increasingly small refuge habitat.

 

In spite of our newfound ecological dominance we still behave like mesopredators. We remain omnivorous and abundant (7 billion strong) and our numbers are increasing at a rate of roughly 80 million per year (http://www.worldometers.info/world-population/#growthrate). We may even be the most abundant mammalian mesopredator on the planet, although we will probably never know for sure because rats are difficult to census. Furthermore, I think we can claim the title of ‘Ultimate Mesopredator’ because the rise of our species paved the way for all the rest.

 

While humans celebrate the ascension of our own species, many of us are less than thrilled that other mesopredators came along for the ride. Rats are notorious plague vectors, baboons raid crops, and misunderstandings between humans and stingrays became infamous with the death of Steve Irwin. It is difficult for humans to control populations of these species, but apex predators seem to be quite good at it (Prugh et al. 2009). This means that any effort to reduce the negative impacts of mesopredator release will require allowing surviving apex predator species to go the way of the great white shark rather than the saber-toothed tiger. Obviously, this strategy will be somewhat scary to the Ultimate Mesopredator, but Steve Irwin would approve.

 

Sources:

Burgess GH, Bruce BD, Caillet GM, Goldman KJ, Grubbs RD, Lowe CG, MacNeill MA, Mollet HF, Weng KC, O’Sullivan JB. 2014. A Re-Evaluation of the Size of the White Shark (Charcharodon carcharias) Population off California, USA. PLoS One 9(6). Burgess at al. 2014

Palomares F, Gaona P, Ferreras P, Delibes M. 1995. Positive Effects on Game Species of Top Predators by Controlling Smaller Predator Populations: An Example with Lynx, Mongooses, and Rabbits. Conservation Biology 9, 295-305 Palomares et al. 1995

Prugh LR, Stoner CJ, Epps CW, Bean WT, Ripple WJ, Laliberte AS, Brashares JS. 2009. The Rise of the Mesopredator. Bioscience 59(9), 779-791. the rise of the mesopredator

http://www.worldometers.info/world-population/#growthrate

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