Effects of Natal Dispersal and Density-Dependence on Connectivity Patterns and Population Dynamics in a Migratory Network

Caz M Taylor

doi:10.3389/fevo.2019.00354

Abstract

Migratory species can be visualized as spatial networks with nodes representing regions and the populations that seasonally occupy them and links between seasonal subpopulations representing migratory connectivity. Connectivity is often regarded as a static property of a migratory network and visualized to evaluate the vulnerability of migratory populations to changes in specific regions. However if the network itself is a dynamical system, its connectivity can be an output of the system that may be changed by perturbations to the network. I constructed a regulated, tripartite network population model with breeding, winter, and migration route nodes that also includes natal dispersal and in which connectivity goes to a dynamical equilibrium. I investigated how natal dispersal as well as the relative regulation in different seasons affects connectivity patterns and the responses of the network population to simulated habitat loss. I found that when the population is primarily regulated by availability of habitat in only one season and natal dispersal was geographically constrained, connectivity patterns were unsymmetrical with weak (diffuse) connectivity from the non-regulating to regulating season and stronger connectivity in the other direction. Less-constrained natal dispersal always resulted in weak connectivity throughout. The overall magnitude of declines caused by habitat loss was determined by relative regulation and generally was not affected by natal dispersal although it was possible, with high natal dispersal, for loss of low-quality nodes in a non-regulating season to cause increases in network population size since the low-quality nodes were acting as an ecological trap. Although we expect that localness (i.e., the extent to which declines resulting from local winter habitat loss was concentrated in a small breeding area versus spread across a larger area) should be predicted by connectivity, localness was in fact hugely variable and affected by both regulation and natal dispersal and generally quite difficult to predict from the connectivity pattern. In summary, the complexity of the system meant that visualization of a network by itself, without knowledge of the underlying processes causing connectivity patterns, often does not provide a good indication of the vulnerability of the network or individual node populations to habitat loss.

Highlights

In recent years, a great deal of research has used various tracking technologies to determine the migratory connectivity, i.e., the connections between breeding and non-breeding locations (Webster et al, 2002) of species of migratory animals, birds
When density-dependent regulation was skewed toward one season, this caused an asymmetry in connectivity but only when there was no or low natal dispersal
Unoccupied nodes, which only occurred in networks with no or low natal dispersal and in seasons where regulation was relatively weak, tended to be lower quality than occupied nodes but occupancy depended on the location of the node within the network

Summary

Introduction

A great deal of research has used various tracking technologies to determine the migratory connectivity, i.e., the connections between breeding and non-breeding locations (Webster et al, 2002) of species of migratory animals, birds. I explore how natal dispersal (with serial residency) and the strength of density-dependent population regulation during breeding and non-breeding seasons affect connectivity and the consequences of local winter habitat loss.

Results

Conclusion