Defining and classifying migratory habitats as sources and sinks: The migratory pathway approach

Abstract

Abstract1. Understanding and conserving migratory species requires a method for characterizing the seasonal flow of animals among habitats. Source-sink theory describes the metapopulation dynamics of species by classifying habitats as population sources (i.e. net contributors) or sinks (i.e. net substractors). Migratory species may have non-breeding habitats important to the species (e.g. overwintering or stopover habitats) that traditional source-sink theory would classify as sinks because these habitats produce no individuals. Conversely, existing migratory network models can evaluate the relative contribution of non-breeding nodes, but these models make an equilibrium assumption that is difficult to meet when examining real migratory populations.2. We extend a pathway-based metric allowing breeding habitats, non-breeding habitats and migratory pathways connecting these habitats to be classified as sources or sinks. Rather than being based on whether place-or season-specific births exceed deaths, our approach quantifies the total demographic contribution from a node or migratory pathway over a flexibly defined yet limited time period across an organism's life cycle. As such, it provides a snapshot of a migratory system and therefore does not require assumptions associated with equilibrium dynamics.3. We first develop a generalizable mathematical notation and then demonstrate how the metric may be used with two case studies: the common loon (Gavia immer) and Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri). These examples highlight how stressors can impact stopover and wintering habitats (loons) and habitat management targeting migratory pathways can improve population status (trout). Synthesis and applications.Each of the two case studies presented describes how effects at one location are felt by populations in another through the seasonal flow of individuals. The contribution metric we present should be helpful in allocating regulatory and management attention to times and locations most critical to migratory species persistence.

Beyond Site-Specific Criteria: Conservation of Migratory Birds and Their Habitats from a Network Perspective

“…Millions of birds are being watched, tracked, or ringed each year, providing a large number of occurrence and movement data (Supplementary Text S3). Meanwhile, a growing body of models and algorithms have been introduced to measure the structure of bird migration networks and site contributions to their connectivity [12,19,[21][22][23]. Combining the abundant observations for bird movements with these scientific approaches may be harnessed to quantitatively identify keystone sites in a site network for bird migration.…”

“…This can also be the case in a bird movement network, because birds may establish new movement pathways or make use of novel sites to compensate when a favored site is disturbed, or when new sites are added to the network [62,63]. Spatially explicit individual-based models [64,65] and other theoretical modelling frameworks for migratory populations regarding migration flows [15,21,22,66,67] can improve understanding of a species' resilience and its decision rules for habitat selection. These theoretical approaches can be used to quantify the importance of site groups by their contribution to set a conservation target, accounting for focal changes in all the sites in a network [68,69], and may ultimately improve the accuracy of simulations for dynamics in movement networks [70].…”

Ecosystem service flows from a migratory species: Spatial subsidies of the northern pintail

“…1). We used the model to calculate C r , a metric developed to estimate the per-capita contribution for each region over each season (i.e., wintering and breeding) within a migratory network (Wiederholt et al in press;Erickson et al 2018; Appendix S1). The per-capita contribution of a region is defined as the number of individuals in the entire population after one annual cycle that are generated from each individual that occupied the region, pathway, or transition at some stage of the year.…”

Population recovery, seasonal site fidelity, and daily activity of pirarucu (Arapaima spp.) in an Amazonian floodplain mosaic

“…These movement patterns can play a critical role in two pathways within community‐based management schemes. Firstly, migrant individuals can boost colonisation rates of neighbouring lakes through source–sink dynamics (Erickson et al., ), increasing the economic value of protected area (PA) mosaics, if neighbouring villages in unprotected landscapes also benefit from lake protection. Replenishing wider stocks and delivering important social outcomes for disenfranchised communities makes this a powerful conservation tool, particularly when applied outside PAs (Campos‐Silva & Peres, ).…”