Deleting species from model food webs

In natural biological communities the disappearance of one species can have knock‐on effects causing extinction of further species from the food web. To investigate these effects we used an evolutionary model to assemble many independent simulated food webs, and studied their dynamical behaviour when one species was deleted. On average, only 2.1% of the remaining species went extinct as a result of the deletion. However, the probability of extinction of predators and indirect predators (more than one link up the chain) of the deleted species was several times larger than for an average species. The model allows predators to adapt their choice of prey in response to changing frequencies of the prey. It was found that the larger the proportion of the deleted species in the predator's diet, the greater its probability of extinction. The probability of extinction of prey of the deleted species was also significantly higher than for an average species. This is due to increased competition between prey species after removal of their predator. The effect was largest for prey species that formed an intermediate fraction of the diet of the deleted species. The number of further extinctions increased significantly with the number of links in the food web to the deleted species prior to deletion, and was also correlated with the bottom‐up and top‐down keystone species indices. We also considered which properties of the web as a whole influenced its robustness to species deletion. This revealed a significant correlation between ecosystem redundancy and deletion stability, but no clear relationship with complexity.