Data from: Predators drive community reorganization during experimental range shifts

1. Increased global temperatures caused by climate change are causing
species to shift their ranges and colonize new sites, creating novel
assemblages that have historically not interacted. Species interactions
play a central role in the response of ecosystems to climate change, but
the role of trophic interactions in facilitating or preventing range
expansions are largely unknown. 2. The goal of our study was to understand
how predators influence the ability of range-shifting prey to successfully
establish in newly available habitat following climate warming. We
hypothesized that fish predation facilitates the establishment of
colonizing zooplankton populations, because fish preferentially consume
larger species that would otherwise competitively exclude smaller bodied
colonists. 3. We conducted a mesocosm experiment with zooplankton
communities and their fish predators from lakes of the Sierra Nevada
Mountains in California, USA. We tested the effect of fish predation on
the establishment and persistence of a zooplankton community when
introduced in the presence of higher- and lower-elevation communities at
two experimental temperatures in field mesocosms. 4. We found that
predators reduce the abundance of larger bodied residents from the alpine
and facilitate the establishment of new lower-elevation species. In
addition, fish predation and warming independently reduced the average
body size of zooplankton by up to 30%. This reduction in body size offset
the direct effect of warming induced increases in population growth rates,
leading to no net change in zooplankton biomass or trophic cascade
strength. 5. We found support for a shift to smaller species with climate
change through two mechanisms: 1) the direct effects of warming on
developmental rates and, 2) size-selective predation that altered the
identity of species’ that could colonize new higher elevation habitat. Our
results suggest that predators can amplify the rate of range shifts by
consuming larger bodied residents and facilitating the establishment of
new species. However, the effects of climate warming were dampened by
reducing the average body size of community members, leading to no net
change in ecosystem function, despite higher growth rates. This work
suggests that trophic interactions play a role in the reorganization of
regional communities under climate warming.