Six General Ecosystem Properties are more Intense in Biogeochemical Cycling Networks than Food Webs

TL;DR

This study compares biogeochemical cycling and food web ecosystem networks, finding that biogeochemical networks exhibit more intense general properties, emphasizing the role of recycling and indirect interactions in ecosystem functioning.

Contribution

It demonstrates that biogeochemical cycling networks display stronger ecosystem properties than food webs, highlighting the importance of recycling and indirect effects in ecosystem network analysis.

Findings

Five properties occurred in all BGC models

Network mutualism occurred in 86% of BGC models

Properties were significantly greater in BGC networks

Abstract

Network analysis has revealed whole-network properties hypothesized to be general characteristics of ecosystems including pathway proliferation, and network non-locality, homogenization, amplification, mutualism, and synergism. Collectively these properties characterize the impact of indirect interactions among ecosystem elements. While ecosystem networks generally trace a thermodynamically conserved unit through the system, there appear to be several model classes. For example, trophic (TRO) networks are built upon a food web, usually follow energy or carbon, and are the most abundant in the literature. Biogeochemical cycling (BGC) networks trace nutrients like nitrogen or phosphorus and tend to have more recycling than TRO. We tested (1) the hypothesized generality of the properties in BGC networks and (2) that they tend to be more strongly expressed in BGC networks than in the TRO networks due to increased recycling. We compared the properties in 22 BGC and 57 TRO ecosystem networks from the literature using enaR. The results generally support the hypotheses. First, five of the properties occurred in all 22 BGC models, while network mutualism occurred in 86% of the models. Further, these results were generally robust to a $\pm$50% uncertainty in the model parameters. Second, the mean network statistics for the six properties were statistically significantly greater in the BGC models than the TRO models. These results (1) confirm the general presence of these properties in ecosystem networks, (2) highlight the significance of model types in determining property intensities, (3) reinforce the importance of recycling, and (4) provide a set of indicator benchmarks for future systems comparisons. Further, this work highlights how indirect effects distributed by network connectivity can transform whole-ecosystem functioning, and adds to the growing domain of network ecology.