Range loss of a threatened grouse species is related to the relative abundance of a mesopredator

Jim‐Lino Kämmerle,Rudi Suchant,Joy Coppes,Simone Ciuti,Ilse Storch

doi:10.1002/ecs2.1934

Abstract

AbstractMammalian generalist mesopredators can reach high densities in forest–farmland mosaic landscapes in the absence of top‐down control. The abundance of generalist mesopredators is a potentially limiting factor for prey populations, especially ground breeding birds such as grouse. High mesopredator abundance has been associated with reduced reproductive success in grouse. There is little evidence, however, on how variation in mesopredator abundance affects grouse population trends while considering other environmental covariates. We make use of range maps spanning two decades (1993–2013) of a locally threatened capercaillie (Tetrao urogallus) population in the Black Forest, Germany, to assess whether range loss of grouse in forest–farmland mosaic landscapes can be explained by a gradient in red fox abundance, while accounting for other potential determinants of grouse range loss. We show that capercaillie range persistence was favored by increasing snow cover, decreasing index of red fox abundance, slightly increasing index for soil quality, and increasing population connectivity. Red fox abundance had the largest relative impact in areas already facing an elevated capercaillie extinction risk due to unsuitable site conditions, dense forests, or lack of connectivity, but the negative effect was compensated under otherwise optimal conditions. This indicates that the relative importance of predator abundance for prey population dynamics is mediated by environmental attributes, emphasizing the threat to remnant populations but also indicating potential for species conservation.

Highlights

IntroductionMammalian mesopredators commonly gain ecological importance when larger predators are lacking in human dominated landscapes (Crooks and Soule 1999, Prugh et al 2009, Ritchie and Johnson 2009, Ripple et al 2013), and their abundance may limit populations of prey (Crooks and Soule 1999, Elmhagen et al 2010, Salo et al 2010, Smith et al 2010)
We found that capercaillie persistence was favored by increasing number of days with snow cover, decreasing predicted red fox abundance, slightly increasing soil quality, and slightly by public forest management regime (Fig. 2 and Appendix S1: Fig. S2)
We found a non-linear effect of mean canopy closure on range persistence that interacted with the predicted fox abundance displaying an optimum around 70% canopy cover at very low to intermediate fox abundance (Table 2, Figs. 2, 3)

Summary

Introduction

Mammalian mesopredators commonly gain ecological importance when larger predators are lacking in human dominated landscapes (Crooks and Soule 1999, Prugh et al 2009, Ritchie and Johnson 2009, Ripple et al 2013), and their abundance may limit populations of prey (Crooks and Soule 1999, Elmhagen et al 2010, Salo et al 2010, Smith et al 2010) Such effects are often found in birds (Brashares et al 2010), because predation by mesopredators can have a significant impact when a large extent of eggs and/or fledglings are lost to predation (Newton 1993, Co^te and Sutherland 1997). There is, little evidence on how variation in predator abundance affects the persistence of bird populations at the landscape scale, while considering how this relationship is influenced by other factors

Methods

Results

Conclusion