Consequences of migratory coupling of predators and prey when mediated by human actions

Navinder J Singh,Sumanta Bagchi,Per Sandström,Todd Katzner,Birger Hörnfeldt,Frauke Ecke,Martin Jung

doi:10.1111/ddi.13373

Abstract

AbstractAimAnimal migrations influence ecosystem structure, dynamics and persistence of predator and prey populations. The theory of migratory coupling postulates that aggregations of migrant prey can induce large‐scale synchronized movements in predators, and this coupling is consequential for the dynamics of ecological communities. The degree to which humans influence these interactions remains largely unknown. We tested whether creation of large resource pulses by humans such as seasonal herding of reindeer Rangifer tarandus and hunting of moose, Alces alces, can induce migratory coupling with Golden Eagles, Aquila chrysaetos, and whether these lead to demographic consequences for the eagles.LocationFennoscandia.MethodsWe used movement data from 32 tracked Golden Eagles spanning 125 annual migratory cycles over 8 years. We obtained reindeer distribution data through collaboration with reindeer herders based on satellite tracking of reindeer, and moose harvest data from the national hunting statistics for Sweden. We assessed demographic consequences for eagles from ingesting lead from ammunition fragments in moose carcasses through survival estimates and their links with lead concentrations in eagles' blood.ResultsIn spring, eagles migrated hundreds of kilometres to be spatially and temporally coupled with calving reindeer, whereas in autumn, eagles matched their distribution with the location and timing of moose hunt. Juveniles were more likely to couple with reindeer calving, whereas adults were particularly drawn to areas of higher moose harvest. Due to this coupling, eagles ingested lead from spent ammunition in moose offal and carcasses and the resulting lead toxicity increased the risk of mortality by 3.4 times.Main conclusionsWe show how migratory coupling connects landscape processes and that human actions can influence migratory coupling over large spatial scales and increase demographic risks for predators. We provide vital knowledge towards resolving human–wildlife conflicts and the conservation of protected species over a large spatial and temporal scale.

Highlights

Species interact in diverse ways such as predation, parasitism, and symbiotic and competitive interactions (Tylianakis et al, 2008)
We know relatively little about these indirect consequences of human actions on species interactions, distributions, movements and survival
We studied the movements of the Golden Eagle in Fennoscandia (Figure 1)

Summary

Introduction

Species interact in diverse ways such as predation, parasitism, and symbiotic and competitive interactions (Tylianakis et al, 2008). Predators either adjust their migration timing and seasonal distributions to exploit migrant prey aggregations or movements to maximize duration of prey exposure (Furey et al, 2018). Such interactions have traditionally been studied between a single predator species and the distribution of its prey (Wolf and Elk, Fortin et al, 2005; Basking shark and Zooplankton, Sims et al, 2006). Very informative, such an approach does not necessarily account for other simultaneous and potentially important interactions in the ecosystem

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