Ecosystem engineering structures facilitate ecological resilience: A coral reef model
Pak‐Yin Cheung, Yoko Nozawa, Takeshi Miki
Abstract
Abstract Ecosystem engineers are organisms that affect ecosystem state by modifying the physical habitats in which biological interactions occur. Such engineering effect depends on both the engineers for environmental transformation and the persistency of engineered structures, but the distinction has rarely been considered. Here, we examined their relative effect on ecosystem in terms of ecological resilience. We used a mathematical model of a coral reef that incorporates reciprocal facilitation between corals and herbivores. Coral skeletons create physical habitats and promote habitat complexity, allowing more herbivore grazing on macroalgae, which opens further space for coral colonization. By quantifying resilience in form of its basin of attraction, we found that resilience declined much rapidly with the loss of habitat complexity (engineered structures) than from the loss of either corals (engineers) or herbivores, under the substantial pressures of fishing and eutrophication. This model outcome is in accordance with observed empirical patterns. It arises due to two characteristics of habitat complexity: slow temporal changes and habitat provisioning. Habitat complexity can persist even when corals are lost, facilitating the recovery of herbivores and, in turn, of corals. Our model suggests that, as the persistency of engineered structures increases, their influence on ecosystem dynamics increases and becomes independent from that of ecosystem engineer. Identifying such a distinction and its context are vital to preserving ecosystem resilience and to better avoid catastrophic shifts.