The unique ecology of human predators

The human predator shares many similarities with other animal predators on this planet.  They are intelligent, they can work either independently or in groups.  They can be strategic, cunning, and postulate on possible future outcomes of actions and events.  Despite such similarities, the human predator is very different from any other currently living on Earth.  At a population of over 7.3 billion, humans can be found across the whole planet.  They have harnessed the power of other animals to help their survival.  A highly adaptable animal and a generalist feeder, they exploit a range of different prey.  They have gone beyond simple tool use, creating technology capable of killing thousands of animals in one go (and technology that can potentially wipe out a significant number of humans too).  They have developed fuel to allow them to travel vast distances, and societal systems to maximise the efficiency of exploitation.  We are not just predators, we are “super predators”.

Evolutionary biologist Thomas Reimchen (University of Victoria) has spent many years studying stickleback fish predation.  Many different species like to feed on stickleback but the work Thomas has done found that stickleback predators typically target juveniles, and never take more than 2% of the population in his study area on Haida Gwaii each year.  In contrast, Thomas noted that fishers on Haida Gwaii took much more than 2% of the salmon… and they took mostly adults.  It’s a pattern many of us will have seen.  We take lots, and we take a lot of big individuals.  In this new paper Thomas, alongside Chris Darimont - Hakai-Raincoast professor at the University of Victoria, and science director for the Raincoast Conservation Foundation and colleagues explore just how different our exploitation rates are from other predators.

The paper does not make for happy reading.  We are acutely aware of both historical and in some cases continued extreme exploitation of marine fishes.  The paper calculates that overall we exploit marine fish populations at 14 times the rate of other marine predators.  The problem goes a little deeper than high exploitation rates.  As with the stickleback observations, non-human predators target significantly less adults than do their human counterparts.  The team also noticed a difference in fishing exploitation between the Atlantic and Pacific Oceans, with Atlantic fishers exploiting 2.9 times more than their Pacific counterparts.  As for the land, humans exploited 9 times more than non-human predators.  Hunting preferences came to light too.  Human predators exploited mesocarnivores (such as foxes, martens civets, skunks) at rates 4.3 times higher than non-human predators.  Large carnivores were exploited 9.2 times more.  As for herbivores… human and non-human predators exploited them at similar rates.

"Our impacts are as extreme as our behaviour and the planet bears the burden of our predatory dominance" Chris Darimont explained to his university press release office.  The burdens we place are many.  Because we target adults, we are removing individuals at a reproductive age.  Less reproduction means less offspring, and less offspring means smaller populations.  We also don’t necessarily kill for food.  Trophy hunting, or removing competition for resources, and at times for protection is also on the list of why the human-predator takes its prey.

The authors briefly list some of the consequences of our super-predation.  “Despite contributions from the ‘sustainable exploitation’ paradigm, contemporary humans can rapidly drive prey declines, degrade ecosystems, and impose evolutionary change in prey. Owing to long-term coevolutionary relationships that generally limit exploitation rates, especially on adult prey, these are extreme outcomes that nonhuman predators seldom impose” .

The team call for a transformation of “humanity’s own design: cultural, economic, and institutional changes as pronounced and widespread as those that provided the advantages humans developed over prey and competitors”.  In short, if we truly want to obtain sustainable use, we need to put limits on ourselves, and we need to find ways to mimic those non-human predators we so love to hunt.

The original paper

The paper was published in the journal Science.  Unfortunately it is behind a paywall, but if you have access to the journal or fancy paying for a copy you can find it here

Image: Chris has a history of working with coastal wolves in British Columbia.  Here, a British Columbia coastal wolf is hunting salmon.  The image was taken by Guillaume Mazille and kindly offered for media use with the team’s publication.