Whole-Community Facilitation Regulates Biodiversity on Patagonian Rocky Shores

Brian R Silliman,Andrew H Altieri,Mark D Bertness,Fernando J Hidalgo,Maria V Reyna,Caitlin M Crain,John N Griffin,M Cielo Bazterrica,Steve Vollmer

doi:10.1371/journal.pone.0024502

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.

Highlights

Biodiversity and the critical services it provides are under global siege from human impacts [1,2,3,4]
Typical rocky shore consumers that forage on bare rock and overtop mussel beds such as seastars, chitons, crabs, and shell-drilling snails were only found within the mussel matrix (Fig. 2, 3), while only 2 limpet species, and an invasive barnacle, occurred in significant numbers outside of mussel beds (Fig. 3)
Our surveys across 15u of latitude of wind-swept Patagonia rocky shorelines revealed a striking example of whole-community facilitation

Summary

Introduction

Biodiversity and the critical services it provides are under global siege from human impacts [1,2,3,4]. Habitat destruction, over-harvesting, pollution, and species introductions are leading anthropogenic forces driving declines in species populations, diversity and ecosystem services [1,5,6,7,8] Recognition of these growing threats to biodiversity has sparked added attention to both elucidating the key biological and physical factors that structure local species richness and evenness [9,10], and the context-dependency of their relative impacts. Refined understanding of these issues will be critical for predicting how biodiversity will be impacted by an increasingly variable and changing environment and the potentially compounding effects of losing key diversity-regulating species interactions [11,12]. 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 contextdependency of facilitation

Methods

Results

Conclusion