Giant mammals such as saber-toothed tigers and mammoths occupied important positions in the food web during their lifetime. But between 50,000 and 10,000 years ago, giant predators and herbivores died out in most parts of the world – be it due to climate changes or human influences. A study has now reconstructed how their disappearance affected the remaining species and also shows what further species losses could mean for ecosystems.
The living creatures in an ecosystem are connected to one another through complex food webs. The herbivores form the food basis for carnivores, which themselves may fall victim to other carnivores. If a species dies out, it also affects all the species associated with it: if an important prey species is missing, the carnivores that depend on it find less food and have to switch to other prey. If a carnivore species disappears, the prey may proliferate excessively. Both events can trigger serious changes to the respective ecosystem and influence its stability in the long term.
Predator-prey relationships
A team led by Chia Hsieh from Michigan State University in East Lansing has now reconstructed how the disappearance of large mammals that once played an important role in their respective ecosystems has affected food webs. To do this, the researchers collected data on predator-prey relationships from more than 440 modern mammal species at 389 locations in tropical and subtropical regions of America, Africa and Asia.
“Our results show striking differences between the continents,” reports the research team. Many large mammals have survived in Africa to this day, from colossal herbivores such as elephants and buffaloes to large predators such as lions and leopards. Here the predators feed on a wide range of different prey. This ensures a stable, highly interconnected food web.
Gaps in the food web
“In contrast, the Neotropical food webs in South and Central America bear clear traces of the extinction of megafauna,” explain Chia Hsieh and her colleagues. Huge deer once formed an important base of the food web here. When they died out around 12,000 years ago, they were missing as prey for predators such as saber-toothed tigers and giant wolves, which also eventually disappeared. Today, most of South America’s predators are significantly smaller. Unlike in Africa, they are usually limited to a narrow range of prey species and, according to the study, their prey is also more vulnerable to ecological changes. With the extinction of most large mammals, food webs have become flatter, with individual species connected to fewer other species.
According to the researchers, Asia occupies a kind of intermediate position. Due to habitat loss, both predator and prey populations have shrunk. Today’s large predators such as tigers eat both herbivores and smaller carnivores such as red foxes. Overall, however, their nutritional niche is very small. The study suggests that this development is due not only to today’s environmental conditions, but also to past extinction events.
Many of the world’s large mammals that have survived to this day are now threatened with extinction. According to Hsieh and her colleagues, their study can help understand the potential long-term impacts that a disappearance of these species could bring. “By examining the past, we can also try to understand what awaits us in the future,” Hsieh said.
Source: Chia Hsieh (Michigan State University, East Lansing, USA) et al., Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.2519938123