TRADE-OFFS RELATED TO ECOSYSTEM ENGINEERING: A CASE STUDY ON STIFFNESS OF EMERGING MACROPHYTES

TLDR

Ecosystem engineering, the biologically mediated alteration of abiotic conditions, can profoundly influence ecosystems, yet the costs and benefits of the traits that enable such engineering remain largely unexplored. The authors compared two intertidal plant species—Spartina anglica and Zostera noltii—to investigate how differences in shoot stiffness affect their capacity to modify hydrodynamic energy. By measuring hydrodynamic forces on the shoots of these species, which experience similar currents and waves, the study quantified how each species’ physical structure alters energy dissipation. The results reveal a trade‑off: stiff leaves dissipate hydrodynamic energy roughly three times more than flexible leaves but also incur higher drag, demonstrating that the ability to engineer the environment is directly linked to the cost of resisting flow.

Abstract

Biologically mediated modifications of the abiotic environment, also called ecosystem engineering, can significantly affect a broad range of ecosystems. Nevertheless, remarkably little work has focused on the costs and benefits that ecosystem engineers obtain from traits that underlie their ecosystem engineering capacity. We addressed this topic by comparing two autogenic engineers, which vary in the degree in which they affect their abiotic environment via their physical structure. That is, we compared two plant species from the intertidal coastal zone (Spartina anglica and Zostera noltii), whose shoots are exposed to similar currents and waves, but differ in the extent that they modify their environment via reduction of hydrodynamic energy. Our results indicate that there can be trade-offs related to the traits that underlies autogenic ecosystem engineering capacity. Dissipation of hydrodynamic forces from waves was roughly a factor of three higher in vegetation with stiff leaves compared to those with flexible leaves. Drag was highest and most sensitive to hydrodynamic forces in stiff vegetation that does not bend with the flow. Thus, shoot stiffness determines both the capacity to reduce hydrodynamic energy (i.e., proxy for ecosystem engineering capacity) and the drag that needs to be resisted (i.e., proxy for associated costs). Our study underlines the importance of insight in the trade-offs involved in ecosystem engineering as a first step toward understanding the adaptive nature of ecosystem engineering.