Ecological impact of changes in intrinsic growth rates of species at different trophic levels

Decreased and increased intrinsic growth rate and abundance of a single species can severely and negatively impact other species in the same food web. Here we compare the wider system effects of decreased and increased intrinsic growth rates of species occupying different trophic levels. Specifically, we derive the change in growth rate of a single (focal) species necessary to cause a 90% reduction in the abundance - a quasi-extinction - of another species in model communities. We find that even relatively small changes, negative as well as positive, in the growth rate of the focal species can cause quasi-extinctions of others. Furthermore, the magnitude of change needed to cause a quasi-extinction depends on the trophic level of the perturbed species. The potential ecosystem impact of such 'negative' and 'positive' changes is largely unknown. We argue that such a targeted decrease or increase could be induced by human interference, such as hunting or harvesting, but also by an outbreak or fade-out of an infectious disease. As ecosystems maintain many and diverse infectious agents, these results suggest that these agents may play an important role in the structure and balance of ecosystems.

Automated summary

Decreasing or increasing the intrinsic growth rate and abundance of a species can have severe negative impacts on other species in the same food web. Even small changes in the growth rate of a species can lead to quasi-extinctions of other species. The magnitude of change required for quasi-extinction depends on the trophic level of the affected species. These findings suggest that infectious agents may play a crucial role in the structure and balance of ecosystems.