As the world grapples with an extinction crisis, it is the large mammals that are most under threat. These threatened species – rhinos, pandas, tigers, polar bears and the like – have a huge influence on their ecosystems. So what will happen to the little animals that are left behind? The past extinctions of fauna can provide us with clues. Thousands of years ago, many large mammals went extinct including the mammoth, the saber toothed cat and the Australian giant wombat. Extinctions occurred at different times, shortly after human occupation occurred on each continent.
In a study I conducted, we found that after the megafauna went extinct, many mammal species remained alive on their own. This weakens connections between species and may make ecosystems more vulnerable. As human activity drives the extinction of modern megafauna, our research provides valuable insights into the potential impact on smaller surviving species.
The animals need each other
The relationships between species large and small are key in the functioning of an ecosystem, making it stable and resilient. Today’s large mammals are relatively smaller than the megafauna of the last ice age. However, they still play an important role in shaping the ecosystem. Just as in the past, modern large mammals can control pests, help disperse seeds, and disperse nutrients (by walking long distances and removing digested vegetation). This benefits humans and other species.
Some large animals also form and make homes for other animals. For example, elephants in Africa push trees to create open grasslands, like their Pleistocene cousins, the Colombian mammoth. This allows other species, such as deer and zebras, to adapt to pasture and share habitats. If the elephants become extinct and stop pushing the trees, the pasture will change and the remaining animals may die or find new habitats. Thus, the loss of interactions between species can make an ecosystem less stable and more vulnerable. If half the species in a community become extinct, then at least three quarters of the possible interactions in the system will die.