Panel Discussion 1

Douglas Smith - Yellowstone National Park, USA

David Mech - USGS, USA

Topic: Do wolves control their own numbers? 

In 1967 Doug Pimlott published that wolf density would not compress any more than 1 wolf/10 square miles which led to the conclusion that wolves self-regulate. Later, this was referred to as ‘protected rearing space’ a behavior partly in response to the possibility of infanticide by conspecifics. L. David Mech wrote on the subject in 1970 in his landmark book The Wolf: Ecology and Behavior of and Endangered Species and agreed with this conclusion. Then in 1983, Lloyd Keith and later his student Todd Fuller, re-evaluated this idea and found that wolf density was correlated with ungulate biomass a finding Mech agreed with. In this research 25 unexploited, in other words wolf populations that were not impacted by humans, wolf populations were used to test this relationship and the correlation was 72% and a linear relationship. However, others using different analytical procedures found at higher prey densities the relationship was not linear but curva-linear, or wolf density could have been higher based on food but was not. 

More research followed, including Mech’s, and a consensus formed about the linear relationship with the most recent evidence from Yellowstone National Park. These finding were interesting because in 1997 Jerry Wolff published a paper on mammal population regulation and defined the terms ‘intrinsic’ vs ‘extrinsic’ regulation. In short, intrinsically regulated species are territorial and protective of young from attack from conspecifics which acts to space individuals preventing higher densities even if food was available. Territoriality was also used to sequester food and was responsive to food abundance. Extrinsically regulated species are those regulated by food and are non-territorial. Wolves are classically territorial so therefore are the only mammalian species described in his paper that would be territorial and extrinsically regulated. D.W. Smith and others in a book on Yellowstone wolves discussed this debate in the context of wolf vital rates: birth, death, immigration and emigration concluding that framing the argument in a population biology context may be revealing. They also stated more work and collaboration were needed. Mech responded to this chapter by indicating a need to discuss these findings in greater detail.

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Acknowledging that there are few places left where wolf numbers are not limited by humans, the underpinning factors behind wolf population regulation is still worthwhile to understand. Thus, Doug and Dave will openly discuss in a public forum intrinsic vs. extrinsic control of wolf populations, or do wolves self-regulate, a topic of great importance to the public and management decisions (e.g., killing wolves is not necessary as they ‘self-regulate’).