Arctic greening and bird nest predation risk across tundra ecotones

Abstract

Alarming global-scale declines of birds numbers are occurring under changing climate 1 and species belonging to alpine and arctic tundra are particularly affected 2,3. Increased nest predation appears to be involved 4 , but the mechanisms linking predation to climate change remain to be shown. Here we test the prediction from food web theory that increased primary productivity (greening of tundra) in a warming arctic leads to higher nest predation risk in tundra ecosystems. Exploiting landscape-scale, spatial heterogeneity in primary productivity across alpine tundra ecotones supplied with experimental nests in sub-arctic Scandinavia, we found that predation risk indeed increased with primary productivity. The productivity-predation risk relationship was independent of simultaneous effects of rodent population dynamics and vegetation cover at nest sites. Predation risk also increased steeply with altitude, implying that species at the high-altitude end of alpine tundra ecotones are particularly vulnerable. Our study contributes to an improved understanding of how climate change may affect arctic-alpine ecosystems and threaten endemic biodiversity through a trophic cascade. Main Text Biota belonging to the globe's coldest biomes-alpine and arctic tundra-are expected to be disproportionally exposed to global warming 3,5. Indeed, declines in abundance and distribution ranges of arctic-alpine bird species have been reported 1,2,6-9. Although, these declines are consistent with recent climate change, the ecological mechanisms involved are mostly unknown. Unravelling such mechanisms will yield improved predictive models of future changes as well as better basis for implementing effective management actions 10,11. Birds are often subjected to strong food web interactions, of which predation has pervasive impacts on population dynamics and extinction risk 12. Eggs and nestlings are bird life stages particularly vulnerable to predation 13. Hence, factors determining nest predation have been the targets of a large number of studies. Yet, how climate change may affect nest predation has been claimed to be a remaining frontier 14. Alpine and arctic birds place their nests on the ground, sometimes in tundra landscapes with sparse vegetation cover. Hence, their nests can be expected to be particularly vulnerable to predation since they are often very exposed (i.e. visible because of little cover) and easily accessible to predator species that are present. Alpine and arctic tundra are also the biomes where climate warming is most profound 3,5 and a critical question is how this influence nest predation risk. A new study has shown that nest predation in arctic waders has increased steeply concurrent with recent climate warming 4 , but without providing evidence for the ecological mechanisms that may be involved. The most fundamental response of tundra ecosystems to climate warming is increased plant biomass-the tundra is greening 15,16. While increased vegetation cover could yield lower exposure of bird nests to predators 13 , f...

End‐user involvement to improve predictions and management of populations with complex dynamics and multiple drivers

“…Finally, it should be noted that Ptarmigan (both Rock Ptarmigan and Willow Ptarmigan) are presently declining together with a host of other ground‐nesting bird species in alpine and Arctic ecosystems (Lehikoinen et al 2014, Lehikoinen et al 2019). This trend points toward drivers of change that are not exclusively linked to species‐specific traits or management, but rather to general changes in the ecosystem such a climate‐warming‐induced increased primary productivity (greening) and increased nest predation rates (Kubelka et al 2018, Ims et al 2019). This may also explain the declining trend in the Willow Ptarmigan population that was not accounted for by any of the predictors included in our model.…”

“…Considerations are further complicated by uncertainty about whether the population is in a transient state or at its natural attractor (Hastings et al 2018), that itself may be moving due to climate change. Furthermore, the community and continent‐wide decline in ground‐nesting birds (Lehikoinen et al 2014, Lehikoinen et al 2019) also urge for consideration of general drivers of change in alpine‐Arctic ecosystems (Ims et al 2019).…”

Accounting for food web dynamics when assessing the impact of mesopredator control on declining prey populations

“…While we conclude that the red fox culling action had a clear positive effect by curbing the population decline seen in most places in Finnmark (Henden, Ims, et al., 2020), it did not lead to a population increase. A likely reason is that several other generalist predators like corvids exert increased impacts on alpine‐arctic birds in a warming climate (Ims et al., 2019). An important challenge for future studies is to obtain direct estimates of how populations of red fox and other members of arctic predator communities are impacted by climate change and management interventions.…”

“…Increased nest predation from mesopredators has become a genuine concern regarding the conservation of many bird populations (Côté & Sutherland, 1997; Crooks & Soule, 1999; Kubelka et al., 2018; Marolla et al., 2019; Roos et al., 2018). Increased nest predation appears presently to be particularly acute in the Arctic (Ims et al., 2019; Kubelka et al., 2018), although no studies have so far been able to attribute this to any particular mesopredator species.…”

Scavenger community structure along an environmental gradient from boreal forest to alpine tundra in Scandinavia

“…Climate change might have direct impact on some species, while others might be more affected by changes in carrion availability. Carrion availability from wild and domestic ungulates is to a great extent affected by management practices (Henden et al., 2014; Selås & Vik, 2006), possibly strengthening ecosystem disturbance caused by changes in climatic conditions (Ims et al., 2019). Management should take both factors into account, and we encourage further studies of the underlying mechanisms driving observed patterns of scavenger occurrence at baits, as these might be important to understand and predict ongoing ecosystem changes.…”