The return of large carnivores: Using hunter observation data to understand the role of predators on ungulate populations

Aimee Tallian,Andrés Ordiz,Barbara Zimmermann,Håkan Sand,Camilla Wikenros,Petter Wabakken,Göran Bergqvist,Jonas Kindberg

doi:10.1016/j.gecco.2021.e01587

Abstract

Large carnivores play a key ecological role in nature, yet quantifying the effects of predation at large spatiotemporal scales remains challenging. Wolves and brown bears have recovered in Sweden, where they share the same staple prey, moose. This ecosystem is representative of the Eurasian boreal realm, and makes an interesting case study for exploring the use of hunter-collected observation data to understand the ecological effects of large carnivore recovery in human-dominated ecosystems. We used over 50 million hours of moose observation data collected by “citizen scientists” (i.e., moose hunters) between 2000 and 2017 to evaluate the role of recovering bear and wolf populations on an important ungulate vital rate, calf/cow ratio (the number of observed calves per female in fall). Calf/cow ratios were negatively correlated with both wolf and bear densities, suggesting that summer calf survival decreased via predation. Calf/cow ratios decreased by 7% and 17% in the northern and southern areas where bears and wolves were allopatric, respectively. Where wolves and bears were sympatric, the effect of predator densities was additive; calf/cow ratios decreased by 18%. However, both calf/cow ratios and moose densities declined over the last ~20 years across Sweden, including areas where wolves and bears were absent. While recolonizing large carnivores affected ungulate vital rates in Sweden’s human-dominated landscape, they were likely not the primary driver of long-term moose population trends. Our results reinforce that citizen-collected data are a useful wildlife monitoring tool that help understand ecological processes, including the effects of recovering carnivores on prey populations.

Highlights

The conservation, recovery, and reintroduction of large carnivore populations have become rallying points for conserva tionists around the world
Statistical analysis We evaluated the effect of bear and wolf density on calf/cow ratios in the core large carnivore recovery area (Fig. 1)
Mean calf/cow ratios decreased from 0.65 to 0.63 (β = −0.004; 95% confidence intervals (CI)= −0.004, −0.003, p < 0.001) in the northern area, from 0.70 to 0.60 (β = −0.007; 95% CI= −0.008, −0.006, p < 0.001) in the central area, from 0.77 to 0.62 (β = −0.007; 95% CI= −0.008, −0.006, p < 0.001) in the southern area, and from 0.79 to 0.69 (β = −0.007; 95% CI= −0.007, −0.006, p < 0.001) outside the large carnivore area in southern Sweden (Fig. S7)

Summary

Introduction

The conservation, recovery, and reintroduction of large carnivore populations have become rallying points for conserva tionists around the world. Understanding the long-term effect of recovering carnivore populations on prey population dynamics, when located at the human-wildlife interface, is important for the conservation and management of both large carnivores and their prey, as well as for facilitating human-wildlife coexistence (Jonzen et al, 2013; Carter and Linnell, 2016). Monitoring broad-scale trends in prey population vital rates is expensive and logistically difficult. Long-term and wide-ranging citizen science programs provide a unique opportunity to monitor wildlife populations and trends through time while encouraging stakeholder participation, engagement, and trust (Singh et al, 2014; Cretois et al, 2020). Sweden’s unique hunter observation program has worked with hunters since the mid-1980′s to assist monitoring of moose (Alces alces) (Ericsson and Wallin, 1999) and brown bear (Ursus arctos) populations across the country (Kindberg et al, 2009; Kindberg et al, 2011)

Methods

Results

Discussion

Conclusion