A recent international study claims that the dwindling numbers of several species of large predators, such as killer whales, lions, wolves, sharks and elephant-like megaherbivores, may be “humankind’s most pervasive influence on the natural world.”
The revelation is in contrast to the notion that top-tier consumers only affect the species they directly consume. In fact, the report claims that loss of these apex consumers has “far-reaching effects” on diverse ecosystem processes.
The report “Trophic Downgrading of Planet Earth,” a result of research conducted by 24 scientists, was recently published in the journal Science. It claims that the planet is currently in the midst of a mass extinction event characterized by the loss of “apex consumers in particular.”
Although mass extinction events have long been part of earth’s history of biodiversity, this report claims that this extinction event is caused largely by humans.
Thomas Schoener, a co-author of the report and a professor at UC Davis, explained the human contribution to the declining population of these predators.
“The loss of producers (plants etc.) can leave the rest of the food web precarious,” he said.
Schoener said that the loss of much of the earth’s flora was due to human-induced stressors and pointed out that tigers in India now number about 2,000 – down from 40,000 a century ago.
James Estes, co-author and a professor of biology at UC Santa Cruz added, “There are two main [causes] – direct persecution because of concerns over personal safety, wildlife, stock depredation; and habitat fragmentation, since most large apex consumers require large areas of habitat to maintain viable populations.”
The report states that apex consumers play a huge role in “top-down forcing,” a trickle-down effect of peak consumers which affects species ranked lower on the food chain, such as insects and plants, and ultimately the related ecosystem processes.
The report states that, “responses to the loss or addition of a species may require years or decades to become evident.”
The authors caution that “[we] often cannot unequivocally see the effects of large apex consumers until after they have been lost from an ecosystem.”
The report, which reviews a large body of steadily growing empirical data, describes several examples of perturbed trophic cascades and ecosystems, some of them affecting human beings in unprecedented ways.
In the 1800s, introduction of rinderpest in East Africa led to the loss of the megaherbivores wildebeest and buffalo. This resulted in increased plant biomass, thus fueling wildfires in the dry season. Wildfires cost billions of dollars every year in damages.
Eventually, rinderpest was eliminated from the region in the 1960s and the herbivore populations flourished, with fewer wildfires.
Nowhere is the impact of the loss of these consumers more conspicuous than on the Scottish island of Rùm. The island lost its wolf population 250 – 500 years ago resulting in an increased number of herbivores. The once forested island now stands treeless.
“I think this gives conservation a new momentum with regard to apex consumers. Such animals are now realized to have major ecological environmental impacts,” Dr. Schoener said.
Indeed, the magnitude of the report’s impact on conservation efforts across the globe can only be imagined.
“In order to realize the myriad influences of large apex consumers, conservation areas must be very large,” Dr. Estes said.
He later predicted a shift in the scale at which conservation must be attempted.
SASHA SHARMA can be reached at science@theaggie.org.
Human population growth has increased to almost 78 millions a year and they are having longer life too. Every one needs food & space too. So the deforestation is occuring and seems to be the root cause of other problems