Spatiotemporal dynamics of complex ecological networks: Power-law scaling and implications for conservation planning

Christopher Wright

doi:10.1038/npre.2008.2532.2

Abstract

AbstractSpatial constraints on the topology of complex networks are just beginning to be appreciated, both theoretically and in concrete examples like the Internet and global air transportation network. Ecological networks, composed of habitat patches connected by species dispersal, are intrinsically spatial and show promise as a tool for conservation planning; but while habitat-loss effects on ecological networks have been simulated, such effects have not been directly measured in ecological networks varying over time. In this study, I used satellite remote sensing to study ecological networks composed of wetland habitat in the Prairie Pothole Region (PPR) of North America. I find power-law scaling of important topological properties as a function of dispersal ability and as wetland density varies with climate. Prairie wetland networks are 'meso-worlds' with mean topological distance increasing faster with network size than small-world networks, but slower than regular lattices. While similar dynamics have been shown in random spatial networks, these results emphasize the importance of processes determining locations of nodes in a spatial network, with possible implications in other areas like wireless communication networks or disease transmission networks. Wetland networks establish a climate envelope for landscape connectivity in the PPR, and I show that wetland-dependent species face a 'crisis of connectivity' with climate change. The global biodiversity crisis requires that conservation planners act quickly over large areas using limited resources; a network-based approach to coarse-filter conservation planning in dynamic landscapes should be broadly applicable to this problem.

Highlights

The Prairie Pothole Region (PPR) spans approximately 800,000 km[2] of glaciated prairies from Alberta, Canada to northern Iowa in the United States (SI Fig. 1), containing tens of millions of closed-basin, depressional wetlands and encompassing the most productive waterfowl habitat in North
Wetland networks (Fig. 1b) were extracted from water bodies identified in a time series of Landsat Thematic Mapper (TM) imagery from eastern North Dakota, U.S.A17
At the 500 m dispersal scale, links were established between all neighboring wetlands separated by no more than 500 m; at the 1000 m scale all wetlands within 1000 m of one another were connected, and so on at the 1500 m scale. These distances are representative of annual dispersal by a number of wetland-dependent bird, amphibian, and plant species resident in the PPR18-21

Summary

Introduction

The PPR spans approximately 800,000 km[2] of glaciated prairies from Alberta, Canada to northern Iowa in the United States (SI Fig. 1), containing tens of millions of closed-basin, depressional wetlands and encompassing the most productive waterfowl habitat in North. Euclidean distances between water bodies were calculated on a centroid-to-centroid basis and wetland networks were constructed at three dispersal scales; 500 m, 1000 m, and 1500 m (Fig. 1b). I found exponential node degree distributions (SI Fig. 2, SI Table 2) and power-law distributions of cluster size (SI Fig. 3, SI Table 3) across all networks.

Results

Conclusion