Foraging by forest ants under experimental climatic warming: a test at two sites

Abstract

Climatic warming is altering the behavior of individuals and the composition of communities. However, recent studies have shown that the impact of warming on ectotherms varies geographically: species at warmer sites where environmental temperatures are closer to their upper critical thermal limits are more likely to be negatively impacted by warming than are species inhabiting relatively cooler sites. We used a large-scale experimental temperature manipulation to warm intact forest ant assemblages in the field and examine the impacts of chronic warming on foraging at a southern (North Carolina) and northern (Massachusetts) site in eastern North America. We examined the influence of temperature on the abundance and recruitment of foragers as well as the number of different species observed foraging. Finally, we examined the relationship between the mean temperature at which a species was found foraging and the critical thermal maximum temperature of that species, relating functional traits to behavior. We found that forager abundance and richness were related to the experimental increase in temperature at the southern site, but not the northern site. Additionally, individual species responded differently to temperature: some species foraged more under warmer conditions, whereas others foraged less. Importantly, these species-specific responses were related to functional traits of species (at least at the Duke Forest site). Species with higher critical thermal maxima had greater forager densities at higher temperatures than did species with lower critical thermal maxima. Our results indicate that while climatic warming may alter patterns of foraging activity in predictable ways, these shifts vary among species and between sites. More southerly sites and species with lower critical thermal maxima are likely to be at greater risk to ongoing climatic warming.

Geographic differences in effects of experimental warming on ant species diversity and community composition

“…In previous studies, we found that worker density of C. lineolata, a species with one of the highest CT max values of those collected in the warming chambers, increased 76% (Diamond et al 2012a) and foraging increased 40% per degree of experimental warming (Stuble et al 2013) at Duke Forest. Using a comparison of historical and current data, we also found that the abundance of C. lineolata doubled over a 35-year period with 2.78C warming at a site in South Carolina, 450 km south of Duke Forest (Resasco et al 2014).…”

“…The slopes have been scaled, but not centered, such that shaded circles always correspond with positive slopes. Data for Protomagnathus americanus are not included in the figure because this species is not represented in Moreau's phylogeny; the results for this species are: slope ¼ 2.3EÀ05, SE ¼ 6.2EÀ05; P ¼ 0.72. v www.esajournals.org may be predictable based on the thermal tolerance (CT max ) of these species (Diamond et al 2012a, Stuble et al 2013. Specifically, the relationships between experimental warming and ant worker densities and foraging were significantly associated with CT max , but only for ants at the southern study site.…”

“…2 and 3) (F 1,18 ¼ .2.8, P ¼ 0.11). Although ants with higher CT max may be more active in higher temperatures (Diamond et al 2012a, Stuble et al 2013, other processes such as thermoregulation (Sunday et al 2014) or changes in nest architecture (Jones and Oldroyd 2007) may allow ant species to persist in the short run in environments that exceed their CT max . In the long run, these acclimations may lead to a reduction in colony size and eventual extirpation (Sinervo 2010).…”

“…Other studies have demonstrated that air temperature can potentially influence ant community structure (Arnan et al 2007, Wittman et al 2010, Lessard et al 2011, diversity (Kaspari et al 2000, Sanders et al 2007, Pelini et al 2011a), colony survival , worker density (Pelini et al 2011a, Diamond et al 2012a, foraging behavior (Ruano et al 2000, Pelini et al 2011a, Stuble et al 2013, and competitive interactions (Cerda et al 1997(Cerda et al , 1998.…”

Interactions in a warmer world: effects of experimental warming, conspecific density, and herbivory on seedling dynamics

“…We did not attempt to sample herbivore populations throughout the experiment because we did not want to alter their potential effects on the seedlings. However, previous work in this system demonstrates that the responses of other insect taxa to warming are often idiosyncratic, with the abundance and activity of some insect taxa responding positively to warming while others respond negatively to warming (Diamond et al 2012, Stuble et al 2013). Another possibility is that generalist herbivores switch from feeding on Q. alba to other species as temperatures increase.…”