Predators balance consequences of climate-change induced habitat shifts for range-shifting and resident species

While many species distributions are shifting poleward or up in elevation
in response to a changing climate, others are shifting their habitats
along localized gradients in environmental conditions as abiotic
conditions become more stressful. Whether species are moving across
regional or local environmental gradients in response to climate change,
range-shifting species become embedded in established communities of
competitors and predators. The consequences of these shifts for both
resident and shifting species are often unknown, as it can be difficult to
isolate the effects of multiple species interactions. Using a model system
of insects in high-elevation ponds in the Rocky Mountains of Colorado, we
sought to disentangle the effects of predation and intraguild interactions
on the survival and development of a semi-permanent pond resident
caddisfly Limnephilus externus and the habitat-shifting caddis Asynarchus
nigriculus that is being forced into semi-permanent ponds as temporary
ponds dry too quickly to complete development. We conducted a manipulative
in-situ pond cage experiment in which L. externus and A. nigriculus
caddisfly larvae in single-species treatments and together were exposed to
the presence/absence of predatory Dytiscus diving beetle larvae. This
approach allowed us to isolate the effects of intraguild interactions and
predation on the survival and development of both the resident and
habitat-shifting species. We found that intraguild interactions had strong
negative effects on the resident and habitat-shifting species. Intraguild
interactions reduced the survival of the resident L. externus and
increased the variation in survival of the shifting A. nigriculus.
However, Dytiscus predators reduced these negative effects, stabilizing
the community by increasing L. externus survival and reducing variation in
A. nigriculus survival. We also found that intraguild interactions reduced
L. externus biomass but resulted in increased A. nigriculus development.
A. nigriculus development was also increased by predation. Our results
show that strong intraguild interactions between resident and shifting
species are likely to have negative consequences for both species.
However, the presence of predators reduces these negative consequences of
the habitat shift on both the resident and the shifting.