Collapse of large herbivores

Some 60% of the 74 largest terrestrial mammals with a body mass of 100 kg or more are threatened with extinction, and the ecological consequences of their decline will be dramatic, scientists warn in a review.

By Karina Toledo

Agência FAPESP – According to a review published recently in the journal Science Advances, 60% of the remaining species of large mammalian herbivores – those with a body mass of 100 kg or more – are threatened with extinction. Almost all the endangered populations are in developing countries.

The review used data from the International Union for the Conservation of Nature (IUCN) and from a group of scientists from several countries led by William Ripple, professor of ecology at Oregon State University in the United States. One of its co-authors was Mauro Galetti, a Brazilian researcher at the Ecology Department of São Paulo State University (UNESP) at Rio Claro, São Paulo State.

“Places like the African savannas are becoming empty landscapes,” Galetti said in an interview with Agência FAPESP. “This isn’t just a matter of ethics or aesthetics. It affects the functioning of natural ecosystems. All these species play important ecological roles, and if they disappear no one will be able to replace them.”

Of the 74 species of terrestrial mammals that compose the group of large herbivores, 71 occur in developing countries and only ten in developed countries. The sole representative of Brazil in the group is the lowland tapir (Tapirus terrestris), which can reach 300 kg and is also threatened with extinction.

According to the review, large herbivores currently occupy only 19% of their historical ranges on average. “This is exemplified by the African elephant (Loxodonta africana), hippopotamus (Hippopotamus amphibius) and black rhinoceros (Diceros bicornis), all of which now occupy just tiny fractions of their historical ranges in Africa. Furthermore, many of these declining species are poorly known scientifically and badly in need of basic ecological research,” the article says.

The tapir’s range has also shrunk in recent years, according to Galetti. Scientists cannot be sure how many tapirs are left in Brazil. “Tapirs were originally found in practically all Brazilian biomes, but today they’ve disappeared in various parts of the Atlantic rainforest. The main reasons are illegal hunting, deforestation, agricultural expansion and roadkill,” Galetti said.

According to the review article, the main threats to large herbivores are hunting, competition with livestock, and land-use changes including habitat loss, human encroachment (such as road building), cultivation and deforestation. Slow reproduction makes large herbivores especially vulnerable to all these hazards.

Illegal hunting for valuable body parts, such as ivory and horns, has driven a dramatic decline in elephant and rhinoceros populations in parts of Africa and southern Asia, reversing decades of conservation efforts, the article says.

Habitat loss is a significant threat above all in Latin America, Africa and Southeast Asia. The causes originate in developed countries, owing mainly to demand for agricultural products and other commodities, according to the authors.

“Southeast Asia has the highest rate of deforestation among tropical regions and, if trends continue, could lose 75% of its original forests and nearly half of its biodiversity by the end of this century,” the article says.

In the case of South America, the defaunation process may have begun 10,000 years ago, coinciding with the arrival of humans on the continent. “There were giant sloths, armadillos as big as a car and other less well-known species, but the region has been transformed into an empty landscape. There’s disagreement in the scientific literature as to whether the main cause is climate or human action. The impact on ecosystems is only just starting to be understood,” Galetti said.

Consequences

By consuming large amounts of vegetation, these mammals help shape the structure of ecosystems, providing services such as nutrient cycling, seed dispersal and fire control, Galetti explained.

“The amount of organic matter recycled by these animals is huge. If they disappear in biomes like the Brazilian or African savannas, the vegetation will grow, wither, and possibly catch fire,” he said.

In Brazil, he added, plant species with large seeds such as the jatobá (Hymenaea courbaril), buriti (Mauritia flexuosa) and bitter coconut (Syagrus oleracea), as well as many others, depend on the tapir for dispersal.

“In addition, tapirs compete for food with several rodents, helping control populations that are hazardous to human health because they transmit diseases such as hantavirus. The tapir is also one of the few animals that serve as prey and help sustain populations of jaguars (Panthera onca), which in turn control various animals that pose a risk to humans,” Galetti said.

Large herbivores are the main source of food for animals such as the lion (Panthera leo), spotted hyena (Crocuta crocuta) and tiger (Panthera tigris), as well as smaller scavengers that feed on carrion, such as the coyote (Canis latrans), fox (Vulpes vulpes), raven (Corvus corax) and eagle (Haliaeetus spp).

The decline of large herbivores also has direct effects on humans, especially with regard to food security in developing regions, the article notes.

“It is estimated that 1 billion people rely on wild meat for subsistence. Wild meat in African forests is expected to decline by more than 80% during the next 50 years. Moreover, charismatic large herbivores are important flagship fauna that draw many tourists to protected areas. A decline of large flagship species translates directly into reduced tourism and thereby a decline in trade balances and employment, particularly in rural parts of the developing world,” the authors say.

Future directions

In the authors’ opinion, efforts to save the remaining large herbivores must include reducing human birth rates, decreasing human consumption of ruminant meat, combating poaching and illegal hunting, expanding protected areas, increasing conservation funding, and mitigating climate change.

The article also urgently recommends more research on the most threatened large herbivores in Southeast Asia, Africa and Latin America, such as the critically endangered tamaraw (Bubalus mindorensis), Visayan warty pig (Sus cebifrons) and walia ibex (Capra walie), as well as the endangered Oliver’s warty pig (Sus oliveri) and others on which fewer than ten scientific articles have been published per species. In Brazil, a previously unknown species of tapir recently described and named Tapirus kabomanii may be critically endangered by hunting and mining in its range in the Amazon biome.

“In particular, more research is needed to understand the various ways that rising human and livestock densities, changing climate, habitat loss and hunting, as well as different combinations of these factors, affect these large herbivores,” the authors say.