Network ecology in dynamic landscapes

Abstract

Network ecology is an emerging field that allows researchers to conceptualize and analyse ecological networks and their dynamics. Here, we focus on the dynamics of ecological networks in response to environmental changes. Specifically, we formalize how network topologies constrain the dynamics of ecological systems into a unifying framework in network ecology that we refer to as the 'ecological network dynamics framework'. This framework stresses that the interplay between species interaction networks and the spatial layout of habitat patches is key to identifying which network properties (number and weights of nodes and links) and trade-offs among them are needed to maintain species interactions in dynamic landscapes. We conclude that to be functional, ecological networks should be scaled according to species dispersal abilities in response to landscape heterogeneity. Determining how such effective ecological networks change through space and time can help reveal their complex dynamics in a changing world.

Keywords: ecological network dynamics framework; edge detection; graphlet; motif; multilayer network; spatio-temporal network.

Figure 1.

Example of ecological networks: (a) species as nodes: multipartite network with interactions indicated by directed edges between sets (no edges within a set), and (b) patches as nodes: spatial-temporal network as multilayer network with corresponding supra-adjacency matrix. Each layer is a time; intralayer directed edges indicate dispersal; inter-layer edges indicate dependencies from one layer to another. (Online version in colour.)

Figure 2.

Ecological network dynamics framework: a diagrammatic representation showing that the topology of spatial networks constrains the topology and functions of ecological networks which in turn can modify the topology and functions of the spatial network.

Figure 3.

Example of how to delineate functional spatial ecological networks by scaling the spatial interaction networks (with species as nodes) that occur in spatial networks (with patches as nodes) using species dispersal abilities. (a) First, graphlet templates are used to characterize the species interaction networks (left panel) and then an edge detection algorithm is used to delineate spatial networks. Here, the triangulation-wombling algorithm detects boundaries by determining rates of change among triplets of samples indicated by dashed lines. Low rates of change among triplets indicate homogeneity (i.e. within-patch samples), whereas high rates of change suggest a boundary. (b) These two approaches are combined to compare and integrate scales for the two kinds of networks. Graphlet templates are scaled by species dispersal abilities of both predators (here three predators as indicated by three colours) and prey species (here three species as indicated by three colours). Predator's home range is scaled according to season and food availability. The core areas of the home ranges are indicated as dashed lines while extended home ranges are indicated by solid lines. Then, the edge detection (i.e. triangular template) is also scaled to delineate spatial habitat patches. Integrating the two types of templates (graphlets and spatial triangles) results in the delineation of functional spatial ecological networks at several scales. The functional spatial ecological networks detected correspond to the backbone of species interactions; these persist throughout the landscape although species identities may change (as indicated by colour coding of both predators and prey). These functional spatial ecological networks of possibly different interacting species form a metanetwork, as shown in the lower panel. (Online version in colour.)