Nowhere to hide: Effects of linear features on predator–prey dynamics in a large mammal system

Abstract

Abstract1. Rapid landscape alteration associated with human activity is currently challenging the evolved dynamical stability of many predator-prey systems by forcing species to behaviourally respond to novel environmental stimuli.2. In many forested systems, linear features (LFs) such as roads, pipelines and resource exploration lines (i.e. seismic lines) are a ubiquitous form of landscape alteration that have been implicated in altering predator-prey dynamics. One hypothesized effect is that LFs facilitate predator movement into and within prey refugia, thereby increasing predator-prey spatial overlap.3. We evaluated this hypothesis in a large mammal system, focusing on the interactions between boreal woodland caribou (Rangifer tarandus caribou) and their two main predators, wolves (Canis lupus) and black bears (Ursus americanus), during the calving season of caribou. In this system, LFs extend into and occur within peatlands (i.e. bogs and nutrient-poor fens), a habitat type highly used by caribou due to its refugia effects.4. Using resource selection analyses, we found that LFs increased predator selection of peatlands. Female caribou appeared to respond by avoiding LFs and areas with high LF density. However, in our study area, most caribou cannot completely avoid exposure to LFs and variation in female response had demographic effects. In particular, increasing proportional use of LFs by females negatively impacted survival of their neonate calves. 5.Collectively, these results demonstrate how LFs can reduce the efficacy of prey refugia. Mitigating such effects will require limiting or restoring LFs within prey refugia, although the effectiveness of mitigation efforts will depend upon spatial scale, which in turn will be influenced by the life-history traits of predator and prey.

Corridors or risk? Movement along, and use of, linear features varies predictably among large mammal predator and prey species

“…If anthropogenic LFs are associated with risk, we predict that individuals avoid these features and move faster while on them. In our system, we expect to observe these patterns in both ungulate species (caribou and moose), with a magnitude reflecting their respective vulnerability to wolf predation (DeMars & Boutin, ; Mumma et al, ). Lastly, if anthropogenic LFs provide subsidies, as is the expectation for bears, another dominant predator in our system (Dawe, Filicetti, & Nielsen, ; Finnegan, MacNearney, & Pigeon, ; Tigner et al, ), we predict that individuals select these features and move slowly when they are on them.…”

“…Disturbance is linked to woodland caribou declines via an increase in the extent of young seral forest in turn increases the densities of ungulates such as moose Alces alces (Osko, Hiltz, Hudson, & Wasel, ; Schneider & Wasel, ) and therefore the density of wolves Canis lupus , which incidentally prey on caribou (the apparent competition hypothesis; Holt, ). Additionally, predator use of anthropogenic linear features (LFs) such as roads, pipelines, railroads and seismic lines (long narrow cutlines created for oil and gas exploration) increases predator search rates and facilitates access into caribou habitat, thus increasing the likelihood of incidental caribou kills (DeMars & Boutin, ; Dickie, Serrouya, McNay, et al, ; Houle, Fortin, Dussault, Courtois, & Ouellet, ; James & Stuart‐Smith, ). While the influence of human disturbance on behavioural responses by wolves is increasingly well documented, the responses of other key species involved in caribou declines, such as moose, bears and caribou themselves, are less developed (but see Berger, ; DeMars & Boutin, ; Mumma, Gillingham, Johnson, & Parker, ; Serrouya et al, 2017; Tigner, Bayne, & Boutin, ; Vistnes & Nellemann, 2008).…”

“…Additionally, predator use of anthropogenic linear features (LFs) such as roads, pipelines, railroads and seismic lines (long narrow cutlines created for oil and gas exploration) increases predator search rates and facilitates access into caribou habitat, thus increasing the likelihood of incidental caribou kills (DeMars & Boutin, ; Dickie, Serrouya, McNay, et al, ; Houle, Fortin, Dussault, Courtois, & Ouellet, ; James & Stuart‐Smith, ). While the influence of human disturbance on behavioural responses by wolves is increasingly well documented, the responses of other key species involved in caribou declines, such as moose, bears and caribou themselves, are less developed (but see Berger, ; DeMars & Boutin, ; Mumma, Gillingham, Johnson, & Parker, ; Serrouya et al, 2017; Tigner, Bayne, & Boutin, ; Vistnes & Nellemann, 2008). These knowledge gaps and inconsistencies in responses observed across temporal scales of analysis highlight the need to clarify the mechanisms underlying space‐use patterns using high‐resolution data.…”

Logging roads as surrogates for elephant trails: Facilitating social signaling by small forest ungulates despite increasing risks

“…Counterintuitively, we argue that anthropogenic clearings, such as logging roads, can substitute for this functional role of elephants, as evident through our study by the provision of open, dry microhabitats suitable for latrine placement. A caveat is that roads are often cut through the forest in straight lines and anthropogenic linear features are known to upset predator-prey interactions (DeMars & Boutin, 2018). Elephants choose to travel along ridgelines and flat riversides, creating economical contour paths.…”

Potential impacts of climate change on the habitat of boreal woodland caribou

“…Grassland vegetation types and early-seral forests provide less cover for caribou than mature forests, and there is evidence from southern forests that white-tailed deer frequently forage in grasslands near forest edges (Beier and McCullough 1990). High mortality is the limiting factor for many populations of boreal caribou (McLoughlin et al 2003, DeMars and Boutin 2017, Rudolph et al 2017, and increasing predation and disease risk is the primary factor in our projected decrease in overall habitat-quality. High mortality is the limiting factor for many populations of boreal caribou (McLoughlin et al 2003, DeMars and Boutin 2017, Rudolph et al 2017, and increasing predation and disease risk is the primary factor in our projected decrease in overall habitat-quality.…”