Complementary influences of co-occurring physical ecosystem engineers on species richness: insights from a Patagonian rocky shore

Abstract

Structural modification of the environment by physical ecosystem engineers often allows for the occurrence of species that are not able to establish in unengineered habitats, thus leading to increased species richness at the landscape-level (i.e., areas encompassing engineered and unengineered habitats). Unlike previous studies that focused on the contribution of a single engineering species to landscape-level species richness, this study evaluates whether co-occurring engineers—i.e., intertidal mussels (primarily Perumytilus purpuratus) and rock boring bivalves (Lithophaga patagonica)—contribute to landscape-level species richness in a similar or complementary way. Our results show that both mussel and L. patagonica patches harbor a substantial number of invertebrate species in addition to those occurring in the unenegineered rock substrate. However, the distinctive habitat patches created by each engineer add exclusive subsets of species to the study area, which implies that mussel and L. patagonica patches contribute complementarily to overall species richness in our intertidal landscape. Here we postulate that complementary engineering effects on landscape-level species richness will occur when the engineered patches structurally differ from each other and, thus, vary in their relative ability to modulate two or more abiotic conditions and/or resources that prevent species establishment in the unengineered state. In spite of its inherently small spatial scale (500 m), our study highlights the potential for complementary engineering impacts at the larger scales that are usually implied in biodiversity conservation and management (tens to hundreds of kilometers) and outlines a simple conceptual basis and approach to address them.