Ant-mediated seed dispersal in a warmed world

Abstract

Climate change affects communities both directly and indirectly via changes in interspecific interactions. One such interaction that may be altered under climate change is the ant-plant seed dispersal mutualism common in deciduous forests of eastern North America. As climatic warming alters the abundance and activity levels of ants, the potential exists for shifts in rates of ant-mediated seed dispersal. We used an experimental temperature manipulation at two sites in the eastern US (Harvard Forest in Massachusetts and Duke Forest in North Carolina) to examine the potential impacts of climatic warming on overall rates of seed dispersal (using Asarum canadense seeds) as well as species-specific rates of seed dispersal at the Duke Forest site. We also examined the relationship between ant critical thermal maxima (CTmax) and the mean seed removal temperature for each ant species. We found that seed removal rates did not change as a result of experimental warming at either study site, nor were there any changes in species-specific rates of seed dispersal. There was, however, a positive relationship between CTmax and mean seed removal temperature, whereby species with higher CTmax removed more seeds at hotter temperatures. The temperature at which seeds were removed was influenced by experimental warming as well as diurnal and day-to-day fluctuations in temperature. Taken together, our results suggest that while temperature may play a role in regulating seed removal by ants, ant plant seed-dispersal mutualisms may be more robust to climate change than currently assumed.

Reduced dispersal at nonexpanding range margins: A matter of disperser identity

“…This risk may be alleviated by the replacement of the original mutualist with a new one, a role which in our study system granivorous ants may take in the southern range margin of S. clusiana . Moreover, the alternative partners, even if providing less effective services compared to the original ones, are potentially better adapted to higher temperatures and aridity, becoming more effective (Stuble et al, 2014). Even inferior mutualists may thus provide a buffer against climate change‐induced extinction.…”

Asynchrony between ant seed dispersal activity and fruit dehiscence of myrmecochorous plants

“…Experimental warming of ant communities has shown that a 1°C increase in temperature can reduce foraging by ≤50% in some ant species (Pelini et al., ). However, warming of 5.5°C above ambient temperature has no effect on A. rudis foraging (Pelini et al., ; Stuble et al., , ), suggesting that increasingly hot summers may not prevent A. rudis from dispersing seeds released later in the season. Thus, climate change may extend (rather than shift) the period over which seeds can be dispersed by ants in eastern deciduous forests, but much work remains to be done.…”

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“…Behaviorally dominant and abundant genera may remove more seeds at low elevations, while opportunistic genera may remove fewer seeds at high elevation sites. Higher rates of seed removal at lower elevations may also correlate with higher temperatures, which leads to increased activity such as removal rates (Stuble et al 2014). Seed species identity also influenced observed seed removal patterns.…”

“…This gradient extends from desert scrub to subalpine coniferous forest (Brusca and Moore 2013), which is an excellent natural experiment as both plant and arthropod communities tend to change systematically along gradients (Del Toro 2012). Ant-mediated seed dispersal shapes vegetative communities (Zelikova et al 2008) and this important mutualism is potentially resilient to increased temperatures in temperate forests in the eastern U.S. (Stuble et al 2014). However, less is known about the potential breakdown of ant-mediated seed dispersal in a desert to forest mountain gradient due to changes in climate.…”