Whole-Community Facilitation Regulates Biodiversity on Patagonian Rocky Shores

Abstract

BackgroundUnderstanding the factors that generate and maintain biodiversity is a central goal in ecology. While positive species interactions (i.e., facilitation) have historically been underemphasized in ecological research, they are increasingly recognized as playing important roles in the evolution and maintenance of biodiversity. Dominant habitat-forming species (foundation species) buffer environmental conditions and can therefore facilitate myriad associated species. Theory predicts that facilitation will be the dominant community-structuring force under harsh environmental conditions, where organisms depend on shelter for survival and predation is diminished. Wind-swept, arid Patagonian rocky shores are one of the most desiccating intertidal rocky shores ever studied, providing an opportunity to test this theory and elucidate the context-dependency of facilitation.Methodology/Principal FindingsSurveys across 2100 km of southern Argentinean coastline and experimental manipulations both supported theoretical predictions, with 43 out of 46 species in the animal assemblage obligated to living within the matrices of mussels for protection from potentially lethal desiccation stress and predators having no detectable impact on diversity.Conclusions/SignificanceThese results provide the first experimental support of long-standing theoretical predictions and reveal that in extreme climates, maintenance of whole-community diversity can be maintained by positive interactions that ameliorate physical stress. These findings have important conservation implications and emphasize that preserving foundation species should be a priority in remediating the biodiversity consequences of global climate change.

An invasive foundation species enhances multifunctionality in a coastal ecosystem

“…The increase in epifaunal biodiversity is supported by the results of previous investigations (23, 31, 42, 44, 45), although those studies quantified impacts from only a few experimental densities and on smaller spatial scales. Our results are also consistent with a growing body of work demonstrating the importance of positive interactions in ecological communities, especially under conditions of elevated physical stress that dominate degraded coastal habitats targeted for restoration (31,38,46). Furthermore, we note that Gracilaria represents a typical foundation species (sensu ref.…”

“…Furthermore, we note that Gracilaria represents a typical foundation species (sensu ref. 47) because it increases biodiversity through habitat formation and delivers multiple ecosystem functions, analogous to trees in forests (48), salt marshes (38), oyster reefs (8,12), seagrasses (6), mussel beds (46), and many other sessile taxa (1, 9). Our results therefore support the need for an experimental and comprehensive examination of invasive species' effects before ascribing a sign (+ or −) to their overall impact (18,19).…”

Behavioral self-organization underlies the resilience of a coastal ecosystem

“…Mussel beds provide a highly tractable system in which to test the general idea that self-organization can enhance ecosystem persistence. In addition, if this prediction holds, it has direct implications for the management and restoration of mussel beds, which act as a keystone habitat for provisioning of biodiversity (28), as well as being a marine food source.…”

Optimal bioeconomic management of changing marine resources

“…This is important, because such variation exists in real marine systems. For example, strongly competitive systems that exhibit trophic cascades have been observed (Casini et al, 2008), while other systems show strong facilitative interactions (Silliman et al, 2011). These communities may change at vastly different rates.…”

“…This type of obligate facilitation operates, for example, when one species provides habitat for another (e.g., anemones and clownfish (Dunn, 1981), which may be targeted for aquarium trade, or crabs in mussel beds (Silliman et al, 2011)); for other examples, see Bruno et al (2003). In the facilitative model section below, we demonstrate the trade-offs that might be present in these communities.…”