Aside from being hunted by MN dentists: Why are there less lions?

Curious as to why there weren’t more lions and other predators at dozens of wildlife parks in eastern and southern Africa, McGill University PhD student Ian Hatton set out to discover the reasons behind this phenomenon – and came up with some rather startling revelations.

The lack of predators, Hatton and his colleagues learned, had nothing to do with human hunters, and prey was bountiful enough to be able to support a larger lion population. In reality, the team found that even as the quantity of prey increased significantly, the amount of food produced for predators failed to keep pace, causing their populations to only increase slightly.

The discovery suggests that ecosystems possess a previously unrecognized level of structure and function, the study authors explained in a statement. Furthermore, while biologists already knew that regular, mathematical laws governed body functions, this study is the first to suggest that the same types of laws could also exist and govern ecosystems all over the world.

Van Savage, an associate professor of biomathematics at UCLA who was not involved in the study, called the findings “compelling and mysterious… because it is rare to find such strong, systematic patterns in biology, especially at such a large scale as an ecosystem.” The research was published in the September 4 online edition of the journal Science.

Reduced herbivore reproduction rates limits carnivore abundance

In a statement, Hatton explained that the discovery happened by chance during vacations spent at national parks while he was a high school student in Zimbabwe. After beginning his PhD studies at McGill, he returned there to compare communities of African animals in protected ecosystems to investigate the relationship between carnivore numbers and available prey.

He gathered as much animal census data as possible, and when he and his fellow investigators started analyzing the numbers, they found a regular but unexpected pattern: in each park, there appeared to be a consistent but complex predator to prey relationship, and that surprisingly, the number of predators did not directly correspond to the size of the herbivore populations.

Previously, Hatton said, “the assumption has been that when there is a lot more prey, you’d expect correspondingly more predators.” However, as he looked at their figures, he discovered that the ratio of predators to their prey was “greatly reduced” in the lushest ecosystems all over the world, and that the increased crowding resulted in a reduced rate of reproduction amongst prey species, which in turn limited the abundance of their predators.

“These results are striking because they indicate that the quantity of harvestable predators, for example, commercial fisheries that feed on marine prey, increase little despite large increases in prey,” Dr. Just Cebrian, a professor in marine sciences at the University of South Alabama and a senior marine scientist at Dauphin Island Sea Lab said in a statement emailed to redOrbit.

“Clearly more productive ecosystems are inefficient when it comes to transferring energy up the food chain,” he continued, adding that the authors of the paper “generalize this for all ecosystems on Earth and quantify the inefficient rate at which energy is transferred up the food chain.”

—–

Feature Image: When they started looking at the relation between predators and prey in a range of ecosystems around the world, McGill researchers discovered a predator-prey power law that seems to be consistent across a range of ecosystems. (Credit: Amoury Laporte)