Competition between brown bears and grey wolves

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Different apex predators may share the same resources in a given environment. For instance, the grey wolf and the brown bear are predators of ungulates in North America and Europe. Bears usually dominate scavenged prey, which motivates the common assumption that wolves have to hunt more in the presence of bears to compensate the loss of resources. Tallian et al. evaluated a long dataset to understand how the presence of bears affects the killing rate of wolves and found , unexpectedly, that the time between consecutive kills made by wolves increased in the presence of bears, in both sites. The authors suggest some mechanisms to explain this:

• bears reduce densities of neonate ungulates (i.e. exploitative competition)
• wolves take longer between kills by attacking larger preys or by feeding on usurped kills under bears' presence (i.e. interference competition and/or kleptoparasitism)

© Stan Tekiela

Propose and analyze a simple mathematical model to describe the coupled dynamics of populations of wolves and bears, taking into account the possibility of quite distinct details about their interaction.

• Be careful about the distinctions between kill rate, consumption rate and population growth rate.
• Consider the difference, in this system, between exploitative and interference competition. How can bears increase the feeding rate of wolves? Do bears affect the handling time of wolves?
• Are there only negative effects of bears on wolves’ kills, or are positive effects possible? In that case, what would be the consequence for the populations dynamics?
• The authors suggest that the presence of both predators possibly impact prey less than the sum of their individual impacts. Does your model confirm that possibility under some circumstances?

Competition between apex predators? Brown bears decrease wolf kill rate on two continents. Tallian et al. 2017. Proceedings of the Royal Society B: Biological Sciences. 284: 20162368.http://rspb.royalsocietypublishing.org/content/royprsb/284/1848/20162368.full.pdf