Predators as Agents of Selection and Diversification

Predation is ubiquitous in nature and can be an important component of both ecological and evolutionary interactions. One of the most striking features of predators is how often they cause evolutionary diversification in natural systems. Here, we review several ways that this can occur, exploring empirical evidence and suggesting promising areas for future work. We also introduce several papers recently accepted in Diversity that demonstrate just how important and varied predation can be as an agent of natural selection. We conclude that there is still much to be done in this field, especially in areas where multiple predator species prey upon common prey, in certain taxonomic groups where we still know very little, and in an overall effort to actually quantify mortality rates and the strength of natural selection in the wild.

Pest suppression by ant biodiversity is modified by pest biodiversity

Agroecosystems are often complex ecosystems with diverse food webs. Changes in food web complexity may have important context-dependent consequences for pest control strategies. The success of predator introductions to suppress pests may depend on the diversity of pests. For crops with diverse pest assemblages, it is hypothesized that diverse predator communities are needed to suppress diverse pest assemblages below damaging levels. In this study, we compare the ability of ant predator monocultures and polycultures to suppress single- and diverse- (three species) pest assemblages in a coffee foodweb. We use a factorial experiment that compared treatments of predator and pest diversity to understand the impact of pest diversity on multiple predator effects. We show that predator polycultures enhanced pest risk relative to predator monocultures significantly more in the diverse-pest treatment relative to in the single-pest treatments for two of three pest species. Further, we show that pest diversity significantly reduced pest risk in all predator treatments except for the predator polyculture treatment. These results suggest that pest diversity may reduce the efficiency of single predator species at suppressing pest damage, but do not limit multiple predator species. This in turn leads to stronger effects of predator diversity with greater pest diversity. These results highlight the need to consider foodweb complexity, such as pest diversity, when designing and implementing biology control programs.

Pest suppression by ant biodiversity is modified by pest biodiversity

Agroecosystems are often complex ecosystems with diverse food webs. Changes in food web complexity may have important context-dependent consequences for pest control strategies. The success of predator introductions to suppress pests may depend on the diversity of pests. For crops with diverse pest assemblages, it is hypothesized that diverse predator communities are needed to suppress diverse pest assemblages below damaging levels. In this study, we compare the ability of ant predator monocultures and polycultures to suppress single- and diverse- (three species) pest assemblages in a coffee foodweb. We use a factorial experiment that compared treatments of predator and pest diversity to understand the impact of pest diversity on multiple predator effects. We show that predator polycultures enhanced pest risk relative to predator monocultures significantly more in the diverse-pest treatment relative to in the single-pest treatments for two of three pest species. Further, we show that pest diversity significantly reduced pest risk in all predator treatments except for the predator polyculture treatment. These results suggest that pest diversity may reduce the efficiency of single predator species at suppressing pest damage, but do not limit multiple predator species. This in turn leads to stronger effects of predator diversity with greater pest diversity. These results highlight the need to consider foodweb complexity, such as pest diversity, when designing and implementing biology control programs.

Effects of multiple predator species on green treefrog (Hyla cinerea) tadpoles

Prey species that occur across a range of habitats may be exposed to variable communities of multiple predator species across habitats. Predicting the combined effects of multiple predators can be complex. Many experiments evaluating the effects of multiple predators on prey confound either variation in predator density with predator identity or variation in relative predator frequency with overall predation rates. We develop a new experimental design of factorial predator combinations that maintains a constant expected predation rate, under the null hypothesis of additive predator effects. We implement this design to evaluate the combined effects of three predator species (bass, aeshnid and libellulid odonate naiads) on mortality rate of a prey species, Hyla cinerea (Schneider, 1799) tadpoles, that occurs across a range of aquatic habitats. Two predator treatments (libellulid and aeshnid + libellulid) resulted in lower tadpole mortality than any of the other predator treatments. Variation in tadpole mortality across treatments was not related to coarse variation in microhabitat use, but was likely due to intraguild predation, which occurred in all predator treatments. Hyla cinerea tadpoles have constant, low survival values when exposed to many different combinations of predator species, and predation rate probably increases linearly with predator density.