A new study has explained the low number of lions in Eastern and Southern Africa by looking at the relationship between predators and available prey.
While one may happen to believe that doubling the number of prey means that the number of predators will also double, a team of researchers from various universities have proven that that’s not the case. In fact, an ecosystem full of prey will only have a fairly small number of predators.
The study started when Ian Hatton, a PhD student from McGill University, first started studying lions and various prey, in protected parks from Eastern and Southern Africa. He noticed an unusually low number of lions for the abundance of gazelles and Zebras that were running around.
PhD Hatton recruited some colleagues to help him with the project and further investigation revealed that this was a common pattern. Areas full of prey did not host a large number of predators. While they did have a few more predators than the areas with smaller numbers of prey, the increase was not at all proportional.
PhD Hatton gave a statement informing that “When you double your prey, you also increase your predators, but not to the same extent. Instead they grow at a much diminished rate in comparison to prey”.
What’s more, the researchers found that this pattern is not only limited to the lion – prey relationship, but all predator – prey relationships. And it’s not limited to carnivores either. The same held true when they looked at the relationship between herbivores and their food.
The findings baffled the team as Kevin McCann, study co-author and field expert from Guelph University, the Department of Integrated Biology, gave a statement of his own saying that “We kept being astonished. This is just an amazing pattern”.
The researchers explained that this pattern is caused by prey reproduction rates. It turns out that prey reproduces at much slower rates in crowded areas. As a consequence, the prey’s population mostly consists of healthy adult individuals that are much harder to catch and kill than younger or older individuals.
Younger and older individuals are generally weaker or slower, and make for easier meals.
This relationship points at the fact that every species on the planet influences all others. Tremendous changes have been noticed in environments where a species had either died out or has just been reintroduced. It’s not just the population of the reintroduced animal that changes, but all of the other populations in the environment also change.
One noticeable example is the wolves being reintroduced in Yellowstone National Park. Their presence caused more berries to grow, which in turn affected the population if the bears.
The intricacy of this relationship, has led PhD Hatton to conclude that “The cell, the tissue, the body, the community: Those are all levels of organization in ecology-speak”. He believes that there are processes that recur and recapitulate across different levels.
The findings were published earlier this week, on Thursday (September 3, 2015), in the journal Science.