_10.jpg)
Welcome to Pocket Science: an overview of recent research by Husker scientists and engineers. For those who want to quickly learn the “What”, “So what” and “Now what” of Husker research.
What?
For more than 100,000 years, the proliferation and migration of humans around the world has been followed by the disappearance of large mammals – mammoths, mastodons, ground sloths and many other species – which were probably hunted until extinction. And the pace of these extinctions has accelerated dramatically, with large mammal species disappearing between 10 and 100 times faster since then. Homo sapiens came to dominate the planet.
These large-bodied species, many of which have evolved within specific ecosystems over millions of years, have played multiple roles critical to the identity and functioning of those ecosystems. By consuming massive amounts of leafy vegetation and traversing large swaths of a landscape, for example, tall species recycle essential nutrients to support more vegetation and support other smaller herbivores, which in turn support the carnivores that feed on them.
So what?
A growing body of evidence suggests that even mid-sized mammal species may struggle to fill the ecological niches left when their gigantic peers disappear. But the effects of ongoing extinctions can take decades to fully manifest – time that conservationists and the remaining species they seek to protect may not have. To better understand the potential consequences of modern extinctions, Felisa Smith of the University of New Mexico, Kate Lyons of Nebraska and their colleagues turned to the past. The team focused on the past 20,000 years, when human dispersal across North America triggered the extinction of more than 65 species of large mammals on the continent.
Smith, Lyons and their colleagues specifically analyzed the molars and other fossils of more than 2,000 mammals in an area of Texas known to have suffered numerous extinctions. Analyzing concentrations of a particular carbon atom, carbon-13, helped the team determine whether a fossilized specimen was a grazer that primarily consumed cool-season trees, shrubs and grasses, a grazer that ate mostly tropical and subtropical grasses, or both. These fossils, alongside existing knowledge of the species, also allowed the team to estimate the size of living mammal specimens before or after the onset of extinctions.
The research team found that extinctions of large species left “missing pieces” in the ecosystem that the remaining small plant eaters did not fill. The disappearance of mammoth, horse and bison species, for example, opened up the possibility for medium-sized herbivores to consume the leafier vegetation of extinct grazers and, in turn, grow to larger sizes themselves. . But the researchers found little evidence for this. Instead, the ecosystem transformed from one with a wide range of body sizes, as found in contemporary African savannas, to one in which many herbivores of similar size generally competed for the same types of vegetation.
In contrast, the extinction of the community’s top predators, especially its saber-toothed cats, led the largest remaining carnivore, the jaguar, to shift from a general diet to a more specialized diet that consisted primarily of the remnant energy-rich grazers previously hunted by sabertooth. The cougar, meanwhile, exploded in numbers as it expanded its menu to prey abandoned by the jaguar.
Now what?
Emerging research indicates that less complex and more homogeneous ecosystems — the very type that the Texas community became after the extinction of its largest plant-eating mammals — may be less resilient to climate change, human encroachment and environmental influences. other challenges. From this perspective alone, the team said, the study underscores the importance of maintaining biodiversity and protecting massive keystone mammal species that are, increasingly evidently, irreplaceable.
