Predation alters community structure through multiple trophic cascades

Predation plays a crucial role in shaping community structure and can initiate trophic cascades that alter abundances across adjacent trophic levels. Intraspecific variation among predators could lead to varying levels of top-down control with implications for trophic cascade strength. In this experiment, we manipulated body size variation in populations of predatory mole salamanders (Ambystoma talpoideum) within mesocosms and monitored a suite of biotic responses. We predicted that predator populations with increased body size variation would have limited top-down control due to weaker interactions with greater numbers of prey species. Conversely, we predicted that populations with similar sized predators would have strong control over fewer prey species, leading to trophic cascades. Salamander presence affected nearly every parameter measured, suppressing some populations (e.g. invertebrate predators) and facilitating others (e.g. invertebrate collectors), triggering multiple trophic cascades across several trophic channels, including both 'green' and 'brown' pathways. However, only a few invertebrate taxa responded to variation in predator body size, and in nearly all these instances, those taxa responded more strongly to treatments with increased body size variation than to treatments with similarly sized predators. In contrast to our hypothesis, predator size variation may promote individual dietary specialization of differently sized predators, resulting in strong control of focal prey. These results demonstrate that predators can have pervasive and multichannel effects on all trophic levels within communities, regardless of size structure and that increased body size variation can lead to stronger top-down control.