“Temperature-dependent species interactions shape priority effects and the persistence of unequal competitors”

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Tess Nahanni Grainger, Adam Ivan Rego, and Benjamin Gilbert (Feb 2018)

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Temperature-dependent trophic interactions strengthen priority effects and shift competitive outcomes

Warming strengthens trophic interactions and priority effects

Oleander aphid (Aphis nerii) feeding on common milkweed (Asclepias syriaca).
(Credit: Adam Rego)

‘Priority effects’ occur when an early arriving species alters the long-term make-up of an ecological community. Although common in nature, scientists are only beginning to understand the conditions under which priority effects arise. Tess Grainger and colleagues at the University of Toronto hypothesized that priority effects should be stronger at high temperatures, as warming speeds up growth rates and feeding, allowing early arrivers to more rapidly impact a shared environment. They tackled this prediction using an experiment with two competing aphid species and a shared milkweed host, and demonstrated that warming strengthens priority effects by simultaneously causing a more rapid induction of milkweed defenses and a faster depletion of the plant resource. These changes were matched with a shift in dispersal rates at higher temperature that are likely to influence the timing of species’ arrival at a local plant. This experiment tests emerging theory on the temperature-dependence of trophic interactions, and presents and tests new hypotheses that link temperature, priority effects and dispersal across spatial and temporal scales.


Abstract

The order of species arrival at a site can determine the outcome of competitive interactions when early arrivers alter the environment or deplete shared resources. These priority effects are predicted to be stronger at high temperatures, as higher vital rates caused by warming allows early arrivers to more rapidly impact a shared environment. We tested this prediction using a pair of congeneric aphid species that specialize on milkweed plants. We manipulated temperature and arrival order of the two aphid species, and measured aphid population dynamics and milkweed survival and defensive traits. We found that warming increased the impact of aphids on the quantity and quality of milkweed, which amplified the importance of priority effects by increasing the competitive exclusion of the inferior competitor when it arrived late. Warming also enhanced interspecific differences in dispersal, which could alter relative arrival times at a regional scale. Our experiment provides a first link between temperature-dependent trophic interactions, priority effects and dispersal. This study suggests that the indirect and cascading effects of temperature observed here may be important determinants of diversity in the temporally and spatially complex landscapes that characterize ecological communities.