Trophic compensation reinforces resistance: herbivory absorbs the increasing effects of multiple disturbances

Abstract

Disturbance often results in small changes in community structure, but the probability of transitioning to contrasting states increases when multiple disturbances combine. Nevertheless, we have limited insights into the mechanisms that stabilise communities, particularly how perturbations can be absorbed without restructuring (i.e. resistance). Here, we expand the concept of compensatory dynamics to include countervailing mechanisms that absorb disturbances through trophic interactions. By definition, 'compensation' occurs if a specific disturbance stimulates a proportional countervailing response that eliminates its otherwise unchecked effect. We show that the compounding effects of disturbances from local to global scales (i.e. local canopy-loss, eutrophication, ocean acidification) increasingly promote the expansion of weedy species, but that this response is countered by a proportional increase in grazing. Finally, we explore the relatively unrecognised role of compensatory effects, which are likely to maintain the resistance of communities to disturbance more deeply than current thinking allows.

Global patterns of kelp forest change over the past half-century

“…Many kelp forest ecosystems are naturally highly variable on both seasonal and interannual time scales, and over small spatial scales (42)(43)(44), reflecting a high reactivity to environmental drivers and variation in their capacity to resist (45) and recover from both small-and large-scale disturbances (46,47). This wide temporal variation contrasts with other marine foundation species such as seagrasses (48,49) and corals (50), which tend to hold space for many years and take decades to recover from disturbance.…”

Twenty-first century climate change and submerged aquatic vegetation in a temperate estuary: the case of Chesapeake Bay

“…Conversely, Martínez-Crego, Olivé, and Santos (2014) found no impact of CO 2 enrichment on grazing rates on Zostera noltii grown in mesocosms, despite some impacts of acidification and fertilization on plant nutrient levels. However, these and other authors did find that grazers can have an important positive impact by protecting seagrass communities when they preferentially consume epiphytes and fleshy seaweeds, which threaten to overgrow slower growing seagrass under high CO 2 conditions (Reynolds, Paul, and Emmett 2014;Martínez-Crego, Olivé, and Santos 2014;Baggini et al 2015;Ghedini, Russell, and Connell 2015).…”

“…The ability of ecological communities to resist and/or adapt to future climate change is linked to their species and genetic diversity. In fact, community diversity, overall species richness, mixed assemblages of different plant species, genetic diversity within populations, and presence and diversity of grazer functional groups are all positively associated with resistance to climate stress (e.g., Reusch et al 2005;Ghedini, Russell, and Connell 2015). For SAV communities, genetic and species diversity improves SAV survival and the maintenance of ecosystem services in seagrass meadows (Duarte 2000;Ehlers, Worm, and Reusch 2008;Hughes, Best, and Stachowicz 2010;Reynolds, McGlathery, and Waycott 2012;Gustafsson, Boström, and Unsworth 2013;Duffy et al 2015) and freshwater SAV beds Ritchie 2001, 2002;Engelhardt, Lloyd, and Neel 2014).…”

Ocean acidification affects competition for space: projections of community structure using cellular automata

“…It seems therefore that ocean acidification could increase bottom-up forcing, with effects on algae working up the food web, as well as decrease trophic forcing as we have found in our study. On the other hand, trophic interactions may play an increasingly important role in buffering effects of environmental disturbances that may propagate up the food web [57]. The structuring role of trophic interactions in the future ocean may then depend on several factors in the face of climate change [58], including the continued absence of phenological shifts in macroalgae and grazers, minimal direct negative effects of acidification on grazers, and the relative importance of bottom-up versus top-down trophic control in different coastal systems.…”