Perturbed partners: opposite responses of plant and animal mutualist guilds to inundation disturbances

Abstract

Mutualists have been suggested to play an important role in the assembly of many plant and animal communities, but it is not clear how this depends on environmental factors. Do, for instance, natural disturbances increase or decrease the role of mutualism? We focused on entire guilds of mutualists, studying seed-dispersing ants and ant-dispersed plants along gradients of inundation disturbances. We first studied how abundance and richness of the mutualists, relative to non-mutualists, change along 35 small-scale gradients of inundation disturbances. We found that at disturbed sites, mutualistic plant species, those that reproduce by seeds dispersed by ants, increased in abundance and in consequences in richness, relative to other herbaceous plants. In contrast, we found that among the epigeic arthropods the abundance of mutualists declined, even more so than other arthropods. Correspondingly, distributions of plant and animal mutualists became increasingly discordant at disturbed sites: most plant mutualists were spatially separated from most animal mutualists. We finally found that high abundances of plant mutualists did not translate into a high nutrition service rendered to ants: at disturbed sites, many of the plants of ant-dispersed species did not produce seeds, which coincided with a decline in seed dispersal by ants and a changing searching behavior of the ants. Overall, the small-scale natural disturbances we studied were correlated to a major change in the assembly of mutualist guilds. However, the correlation was often opposite between interacting plant and animal mutualist guilds and may thus reduce the potential interaction between them.

Floodplain ants show a stronger response to an extensive flood than to variations in fallen‐timber load

“…This is consistent with the increases in abundance and richness of ants reported following a similar flood in Barmah Forest upstream of our experimental plots (Ballinger et al 2007). This observation runs counter to studies on floodplains elsewhere, where there was either no change (Ellis et al 2001;Meeson et al 2002) or decreased abundances of ants (Prinzing et al 2007) after flooding. This discrepancy could be a result of contrasting flood durations, with the floods on the Murray River floodplain lasting several months while the other floods were for about 1 week.…”

Understanding the impact of flooding on trait‐displacements and shifts in assemblage structure of predatory arthropods on river banks

“…However, spatially restricted disturbance can be important to facilitate the occurrence of specialized species that are able to react rapidly upon changing environment conditions (Bonn, Hagen & Wohlgemuth-von Reiche 2002;Rothenbücher & Schaefer 2006). Observed patterns may, however, vary considerably according to the taxonomic group and with the spatial scale of study (Pollock, Naiman & Hanley 1998;Prinzing et al . 2007;Sanders et al .…”

Life history variation across a riverine landscape: intermediate levels of disturbance favor sexual reproduction in the ant‐dispersed herbRanunculus ficaria

“…Large‐scale climatic disturbance events such as inundation have become increasingly frequent and powerful worldwide (Groisman et al 2005). Such impacts may accelerate the role of disturbance mosaics across landscapes, shift the balance between species, and influence the assembly of species communities (Prinzing et al 2007, Schaefer et al 2008). Moreover, the disturbance mosaic across a landscape may also shift the ecological costs and benefits of different life‐history traits within a given species.…”