Top Predators More Crucial to Ecosystems, Threatened by Humans

A new study published in the journal Science highlights the critical role that apex predators play in food chains and suggests that their general decline is disrupting ecosystems worldwide. 

The implications are ubiquitous and grave, explains lead author of the the study, James Estes, a marine ecologist and evolutionary biologist at the University of California Santa Cruz.  “The loss of apex consumers is arguably humankind’s most pervasive influence on the natural world.”

Funded by the National Science Foundation, an international team of scientists brought together data collected from various terrestrial, freshwater, and marine ecosystems to study the impact of top predators on food chains. 

Their findings stress the significance of humans’ detrimental impact on the environment.  Hunting, overfishing, and the fragmentation of natural habitats has decimated populations of top predators, triggering “trophic cascades” in various ecosystems. 

Trophic cascades are ecological phenomenons catalyzed by the loss of apex consumers, causing a top-down effect that magnifies consequences at lower levels of the food chain. 

Such effects are, “far-reaching and often [have] surprising consequences, including changes in vegetation, wildfire frequency, infectious diseases, invasive species, water quality and nutrient cycles.” 

DiscoveryNews writer Jessica Marshall noted in her report that, “large top predators (and some top plant-eaters) keep systems in balance in ways that control human disease, wildfires, carbon emissions and more, while benefiting agriculture, water resources and forestry, among others.

“We deplete them at our peril,” she added, a poignant admonition, given the significance of the consequences in examples cited by the study’s authors. 

For example, the collapse of sea otter populations in coastal ecosystems witnessed a corollary demise of populations of mussels and other fish.  Indirectly, these marine lifeforms were affected by the sea otters, as this apex consumer kept sea urchin populations in check.  Sea urchin numbers – in the absence of their natural predators – proliferated, and consequently overgrazed kelp forests, which are essential to providing a habitat for mussels and other fish.  These ecosystems have since recovered, but serve as a illustration of the significance of apex predators to food chains and entire ecosystems. 

In Yellowstone National Park, the elimination of the wolf population allowed for the explosion of the elk population.  Grazing freely in the absence of their predators, the abundance of elk hampered the growth of aspen and willow along the beds of rivers and streams.  These shaded streams were home to beavers, songbirds, and fish, whose numbers dwindled in the absence of the trees.  Although these ecosystems were ubiquitously disrupted, they have since recovered with the reintroduction of the wolf population to Yellowstone. 

In estuarine ecosystems, the collapse of shark populations allowed for the outbreak of cow-nosed rays and the subsequent demise of their natural prey: shellfish. 

Marshall highlights yet another compelling case: “In…Africa, the researchers point to rinderpest, a viral disease also known as ‘cattle plague,’ which decimated populations of wildebeest and buffalo. Without these large herbivores, vegetation overgrew the area, turning grasslands into shrublands and leading to more frequent, more intense wildfires.”

Rinderpest has since been eradicated, wildebeest levels were subsequently stabilized, and the natural landscape has been restored. 

Some such examples suggest that remedial solutions may be effective.  “The world can be fixed in many cases. I think that’s the good news,” said Estes.  One caveat: a remedy is not always available. 

The study suggests that more attention should be paid instead to conserving big predator populations – wolves, bears, sharks, sea otters – particularly as their decline is the most pronounced of the world’s apex consumers. 

Estes explained, “To the extent that conservation aims to restore functional ecosystems, the reestablishment of large animals and their ecological effects is fundamental.” 

Photo credit:  flickr.com/photos/tambako/3559257456/

 

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