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 abiotic and biotic responses. Measurements of these
responses are contained within this dataset. 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 similarly 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.