Predators maintain ecosystem resilience: A quantitative evaluation of the tropic role of predation using foodweb models

Background/Question/Methods   In the past decades, biodiversity has experienced a major decline all over the planet, and increasing numbers of animal and plant species are at risk of extinction. The loss of top-predators and the resulting trophic cascades are now well documented, and numerous case study report and analyze these changes in different ecosystems. What is less known though is what are the effects of these predatory losses, and how it can affect important ecosystem function such as stability. We did a meta-analysis to quantify cascading effects and their effects on stability over a wide range of marine, freshwater and terrestrial ecosystems. We used 50 ecosystem models that employ real estimates of parameters and are validated for their ecological reliability. We simulated the loss of the top-predator in each foodweb, and then quantified the resilience with and without these top-predators. The models were also used to quantify the cascading effects and compare the over different types of ecosystems. We then synthesize the evidence for the importance of top-predators in maintaining the structure and stabilizing functions of marine, freshwater, and terrestrial ecosystems.

Results/Conclusions   The eradication of the top-predators in each foodweb have led to trophic cascades that are different depending on the habitat. In each ecosystem though, the simulated resilience significantly decreased when the top-predator was eradicated, compared to initial simulations. These results suggest that top-down control is not uniformly strong in ecosystems, but is always important enough to maintain the structure of ecosystems and protect their resilience. Considering that top-predators are often the first trophic levels to be hardly affected by overexploitation, pollution and other anthropogenic factors, this represents an alarming testimony of how fragile most ecosystems of the world are. The presence of top-predators is often thought to be a sign of a healthy system. Our results are in line with this idea, and provide an explanation on why efforts towards their protection are so important to preserve ecosystem integrity, and continue to benefit from the many services they can offer.