Structural Complexity, Movement Bias and Metapopulation Extinction Risk in Dendritic Ecological Networks

Ecologists are increasingly interested in how habitat configuration influences metapopulation processes. Spatial complexity in metacommunities can be separated into three main components: size (i.e. number of habitat patches), spatial arrangement of habitat patches (network topology), and diversity of habitat patch types. Much attention has been paid to lattice-type networks, such as patch-based metapopulations, while interest is building on understanding ecological networks of alternative geometries, such as dendritic networks. Examples of these dendritic ecological networks (DENs) include some increasingly threatened ecological systems, such as caves and streams. The restrictive architecture of dendritic ecological networks may have overriding implications for species persistence, thus understanding general principles in these networks is needed. I discuss how the number and spatial arrangement of habitat patches influence metapopulation extinction risk in two DENs with differing size and topology. While the number of habitat patches is proportional to metapopulation persistence, this relationship is mediated by both the network geometry and the dispersal pathways utilized in navigating the network.  Larger networks, especially those with greater topological complexity, generally had lower extinction risk than smaller and less complex networks, though dispersal bias and magnitude affected the shape of this relationship.