Biology
Predator-Mediated Coexistence in Sympatric Ungulate Communities
Quick fact
In the Serengeti, wildebeest, zebra, and Thomson's gazelle coexist partly because lions and hyenas preferentially hunt the most abundant species, preventing any one from outcompeting the others.
Why this is interesting
Imagine a savanna with dozens of antelope species coexisting, even though they all eat grass. How can this be? Surely competition should eliminate all but the best? The answer lies in the sharp teeth and keen eyes of predators.
Read the full explanation
Understanding Predator-Mediated Coexistence in Sympatric Ungulate Communities
Picture a field with several types of grazing animals, each with a slightly different preference for which plants to eat. If resources are limited, the species that is most efficient at converting grass into offspring should eventually dominate, driving others to extinction. This is the competitive exclusion principle. However, in reality, many ungulate species share the same habitat. One key solution is predation. Predators like lions don't eat every species equally; they often target the most common prey, which is easier to find and catch. By removing individuals from the dominant species, predators keep its population from reaching the level where it would outcompete others. This 'keeps the peace' among prey species, allowing several to thrive. It's like a schoolteacher who frequently interrupts the class bully, preventing the bully from hogging all the attention and letting quieter students participate.
A deeper explanation
The mechanism behind predator-mediated coexistence relies on predators acting as agents of density-dependent mortality. When a prey species becomes abundant, it becomes a more profitable target for predators due to increased encounter rates. Predators may also exhibit prey switching, focusing on whichever prey is currently most common. This creates a negative feedback loop: as prey A's population grows, predation pressure on A intensifies, slowing its growth and reducing its competitive advantage over prey B. Meanwhile, prey B, being less numerous, experiences lower predation, allowing its population to persist. This stabilizes the community by preventing any single species from reaching competitive dominance. Moreover, predators can create spatial refuges where competitively inferior species survive in areas that predators avoid, further enabling coexistence. This top-down control complements bottom-up factors like food availability, painting a complete picture of community regulation. Understanding this mechanism is crucial for conservation, as removing top predators can trigger a cascade of competitive exclusions, leading to biodiversity loss.