The up-scaling of ecosystem functions in a heterogeneous world

Andrew M Lohrer,Casper Kraan,Judi E Hewitt,Simon F Thrush

doi:10.1038/srep10349

Abstract

Earth is in the midst of a biodiversity crisis that is impacting the functioning of ecosystems and the delivery of valued goods and services. However, the implications of large scale species losses are often inferred from small scale ecosystem functioning experiments with little knowledge of how the dominant drivers of functioning shift across scales. Here, by integrating observational and manipulative experimental field data, we reveal scale-dependent influences on primary productivity in shallow marine habitats, thus demonstrating the scalability of complex ecological relationships contributing to coastal marine ecosystem functioning. Positive effects of key consumers (burrowing urchins, Echinocardium cordatum) on seafloor net primary productivity (NPP) elucidated by short-term, single-site experiments persisted across multiple sites and years. Additional experimentation illustrated how these effects amplified over time, resulting in greater primary producer biomass sediment chlorophyll a content (Chla) in the longer term, depending on climatic context and habitat factors affecting the strengths of mutually reinforcing feedbacks. The remarkable coherence of results from small and large scales is evidence of real-world ecosystem function scalability and ecological self-organisation. This discovery provides greater insights into the range of responses to broad-scale anthropogenic stressors in naturally heterogeneous environmental settings.

Highlights

We predicted that coherent sets of properties would emerge across scales, consistent with the concept of self-organization in ecological systems, as small fast processes mutually reinforce larger slower ones[15,20,21]. We tested this prediction by measuring net primary production (NPP) across a range of environmental conditions encompassing real-world spatial and temporal heterogeneity, and linking these measurements to habitat- and climate-related drivers operating on differing space and time scales
Seafloor light intensity and bottom water temperature were logged throughout the NPP incubations; general weather conditions preceding each Chla sampling event were assessed using 30-day and 7-day cumulative meteorological data; and persistent site-related differences in sediment grain size, organic matter content, macrofaunal communities, and Echinocardium densities were quantified in conjunction with each of the NPP and Chla measurements for use as explanatory variables in multiple regression analyses
Given the amount of environmental heterogeneity represented by our sampling sites and times, we observed a significant positive relationship between Echinocardium density and NPP across space and time scales (Fig. 1A,B), consistent with results from earlier single site experiments[16]

Summary

Introduction

We predicted that coherent sets of properties would emerge across scales, consistent with the concept of self-organization in ecological systems, as small fast processes mutually reinforce larger slower ones[15,20,21]. We tested this prediction by measuring net primary production (NPP) across a range of environmental conditions encompassing real-world spatial and temporal heterogeneity, and linking these measurements to habitat- and climate-related drivers operating on differing space and time scales. Seafloor light intensity and bottom water temperature were logged throughout the NPP incubations; general weather conditions preceding each Chla sampling event were assessed using 30-day and 7-day cumulative meteorological data; and persistent site-related differences in sediment grain size, organic matter content, macrofaunal communities, and Echinocardium densities were quantified in conjunction with each of the NPP and Chla measurements for use as explanatory variables in multiple regression analyses

Objectives

Methods

Results

Conclusion