Abstract
Inherent in climate change experiments is the assumption that
researchers seek to understand the impacts of contemporary climate
change and not the impacts of changes in the abiotic environment that
are not predicted to occur. In general, climate warming is expected to
be asymmetrical, with a mean increase in temperature that is driven more
by warming at night rather than during the day. However, climate warming
experiments tend to disproportionately increase daytime temperatures. If
day and night warming have different effects on ecosystems, the mismatch
in timing may produce misleading inference about the effects of climate
change. To better understand how the timing of warming affects species
and their interactions, we examined a food chain of lady beetles, aphids
and host plants within environmental chambers programmed to simulate
four w treatments (ambient, constant warming, day warming, and night
warming). Our results show that the timing of warming influences
predators and their interactions with prey in several ways. In
plant-only treatments, all warming treatments increased plant
above-ground biomass. When aphids were added, the positive direct effect
of warming on plants disappeared, and night-warming indirectly reduced
plant biomass more than the day- and constant-warming treatments.
Although our feeding trial experiments found that lady beetles in
day-warming treatments consumed the most aphids in a 24 hour period,
predators generated a trophic cascade in only the night warming
treatment. Our results contributes to mounting evidence predators can
mediate the effects of climate warming and that these predators are
affected by day and night warming differently.