An initial assessment of how variation in the susceptibility of species to local extinction alters the effect of predator biodiversity on prey suppression

Background/Question/Methods

Anthropogenic activity is causing our planet’s biodiversity to decline at an alarming rate and it is essential to understand how this loss affects the functioning and stability of natural systems if society is interested in conserving or restoring ecosystems and species.  There is much evidence to suggest that important ecosystem processes, like primary productivity, varies with the number of plant species present and an increasing amount of work suggests that a change a number of predator species present can also have an important effect on the ability of predators to suppress their prey.  Nearly all of the existing studies, however, have examined the effects of species loss that result from random patterns of species loss.  Species loss in nature, however, is not random and more effort needs to be directed toward understanding how different non-random patterns of species loss affect ecological processes.  I conducted an experiment in artificial ponds to examine how non-random patterns of species loss from a guild of predatory insects found in temporary ponds affects the ability of the predators to suppress population size of their prey, tadpoles of the squirrel treefrog.

Results/Conclusions

Preliminary analyses indicate that fewer prey survive when more predator species are present than when fewer species are present.  The effects of predator species loss on prey suppression depended on whether predator species remaining in the foodweb numerically increased in abundance to compensate for the lost species.  On average, the effect of predator species loss on prey suppression was greater when numerical compensation of remaining predators did not occur.  The effect of species loss on prey suppression occurred also depended on the pattern of predator species loss.  The preferential loss of numerically less common predator species caused a greater reduction in the ability of the predator assemblage to suppress prey then a pattern of species loss that retains comparable phylogenetic diversity in the predator assemblage.  Changes in species richness that are associated with the loss of a particular phylogenetic lineage from a foodweb caused the greatest reduction in the ability of the predator assemblage to suppress prey.  The results reported here demonstrate the importance of predator species richness for suppressing prey population size but the extent to which prey suppression is reduced depends on the particular pattern (i.e., which species are more predisposed to local extinction) of species loss.