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

Christopher Wright

doi:10.1038/npre.2008.2532.1

Abstract

AbstractSpatial constraints on the topology of complex networks are just beginning to be appreciated, both theoretically^1-3^ and in concrete examples like the Internet^4^ and global air transportation network^5^. 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^6-8^. 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^9^, but slower than regular lattices^10^. While similar dynamics have been shown in random spatial networks^1,3^, 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^11^ or disease transmission networks^12^. 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^13,14^; 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