Global Variability of Degree Distribution in Marine Food Webs

Abstract

Aim

In complex networks, the degree distribution varies and provides an insight into the general structure of the system. For example, it may show scale-free characteristics of the network, indicating higher vulnerability against non-random disturbances. However, investigating its spatio-temporal variability, degree distribution in marine food webs remains an unresolved issue. In this paper, we focus on describing the global variability of degree distribution in marine food webs.

Location

Global.

Methods

We studied 105 marine food webs. By Kolmogorov–Smirnov test, and kernel density estimation, we determined the degree distribution of each food web, described its spatio-temporal pattern and quantified the correlation between relevant parameters as a function of the scale-free property of the degree distribution.

Results

Marine food webs around the globe did not strictly exhibit scale-free characteristics in most regions, and only below 5% of the food webs entered the “strongest fit” level of the scale-free network. We also find food webs in the polar regions indicate relatively high goodness-of-fit to scale-free networks. The upwelling ecosystem related to ocean currents is prone to form a scale-free web, which exhibits periodic scale-free characteristics. The ecosystem types with relatively ‘low fit’ levels were mainly concentrated in the ecosystems heavily influenced by human activities.

Main Conclusions

This research will enhance the research in terms of (a) classifying degree distribution in marine food webs; (b) revealing the variability in the spatial pattern of particular distributions, for example, the scale-free characteristics and (c) exploring the distribution of in-degree in space, quantifying the proportion of generalist and specialist species, as a potential indicator of adaptive potential of ecosystems. This research contributes to our understanding of the scale-free features of marine food webs globally. It also offers a real systems-based conservation approach to assess the spatial heterogeneity of the structural vulnerability of marine ecosystems.