Herbivores, animals whose diets revolve around plants, are supposedly facing the highest risk of extinction, a new study suggests.
The research team, led by Utah State University Assistant Professor Trisha Atwood of the Watershed Sciences, inquired past the existing extinction-risk paradigm that poses predators to be the more at-risk species. In their study, they set out to examine whether herbivores are actually at a higher risk of extinction.
Comparing Diets Of Mammals, Birds, and Reptiles
The Utah State University-led research team combed through the dietary patterns across the three taxonomic groups--mammals, birds, and reptiles. Generating a database, they categorized the data according to trophic groups predator, herbivore, and omnivore and diets of 22,166 species of mammals, birds, and reptiles as assessed by the International Union for Conservation of Nature (IUCN).
After examining the data, the research team has arrived at an estimated extinction risk of 18 percent across the IUCN threatened species. It was achieved by dividing the number of threatened species over the total number of species in the study. In this slice of the data, herbivores were the most at-risk at around 25 percent of plant-eating species appearing in the IUCN threatened species list. This is equivalent to some 300 herbivores facing risks of extinction.
The share of herbivores at risk of extinction is significantly higher than omnivores and predators, with eight percent more herbivores in the threatened list compared to omnivores and 10 percent compared to predators.
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From these numbers, herbivorous reptiles like tortoises and some species of iguana face the highest risk among their ranks. The research pointed out that more than half--roughly 52 percent--of the generally cold-blooded plant-eaters are already threatened.
To eliminate any possibility of trophic biases, researchers also looked into other factors such as the extinction risk patterns in relation to geographic regions. They studied the proportion of threatened species for the thirteen land regions and five major marine regions as classified by the IUCN.
Again, herbivores were highlighted for possessing risks higher than the background extinction risk. They found these elevated risks in at least one taxonomic class in 85 percent of land regions and up to 80 percent of marine regions.
Throwing Off a Long-Accepted Preconception
Aside from the evidence presented in the Utah State University-led study, pieces of historical evidence were also posited in the study. It highlighted that human activities had played an active part in previous instances that led to the disproportionate extinction of herbivores, starting at least from the late Pleistocene period some 11,000 to 50,000 years ago. Historical data on herbivore-dominated extinction events provide additional insight, as patterns offer researchers data on future iterations of similar events.
"The results were somewhat shocking," Atwood said. She added that humanity's "highly publicized and fraught relationship with predatory animals" has created the unfounded preconception that predators are more at risk of extinction.
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Utilizing evidence-based science serves humankind in creating informed decisions for preservation efforts and related policy. This study, which identifies which kinds of animals are actually facing increased risks of extinction.
"Documenting a pattern in extinctions is only the first step towards curbing the loss of species," Atwood added.
To have an idea how Africa's megaherbivores went to extinction, watch the video from the University of Utah below:
