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The impact of forest harvesting on caribou–moose–wolf interactions decreases along a latitudinal gradient
Abstract
Human activities can impact animal communities by altering species interactions. The influence of forest harvesting on the interaction between threatened boreal caribou, moose, and wolves constitutes a classic example. When conifer forests are logged, clear-cuts are colonized by deciduous vegetation that provides high-quality food for moose. Subsequent changes in wolf distribution alter predation risk for caribou. Given that primary productivity varies along latitudinal gradients, the effects of logging on moose-caribou-wolf interactions could also vary moving northwards. Empirical evidence, however, is lacking and current recommendations for caribou conservation are fixed over space. We assessed whether the impact of logging activities on caribou-moose-wolf interactions varies with latitude. We estimated deciduous vegetation availability from satellite imagery, and followed all three species with GPS collars to evaluate their habitat selection. We found that the availability of deciduous vegetation in logged stands decreased along a 400-km latitudinal gradient. The probability of caribou occurrence remained low in clear-cuts, regardless of deciduous vegetation availability. Moose and wolves increased their selection for clear-cuts as they contained more deciduous vegetation. Accordingly, the relative co-occurrence probability of moose and wolves was strongly associated with clear-cuts at low latitudes, but weakly so at high latitudes. Clear-cuts should therefore attract moose and wolves more strongly to prime boreal caribou habitat at lower latitudes, and caribou predation risk should follow similar geographical patterns. Conservation planning should account for geographical patterns in the risk faced by threatened populations because the effectiveness of strategies developed from average patterns can decrease over space, in consistent manner.
... In general, caribou select mature patches of forest and avoid areas that are recently harvested (Bowman et al. 2010;Chubbs et al. 1993;Courbin et al. 2009;Courtois et al. 2007;DeCesare et al. 2012;Gagné et al. 2016;Rettie and Messier 2000). The avoidance period ranges from 12 years in Ontario mixed-spruce, jack pine forests (Cumming and Beange 1993) to 20 years in Québec balsamfir, white-birch forests and mixed-wood forests in west-central Alberta (Leblond et al. 2016;Peters 2010) to upwards of 40 years in mixed-wood forests in Québec, Alberta, and British Columbia (Gagné et al. 2016;Mumma et al. 2018;Rudolph et al. 2019). ...
... In general, caribou select mature patches of forest and avoid areas that are recently harvested (Bowman et al. 2010;Chubbs et al. 1993;Courbin et al. 2009;Courtois et al. 2007;DeCesare et al. 2012;Gagné et al. 2016;Rettie and Messier 2000). The avoidance period ranges from 12 years in Ontario mixed-spruce, jack pine forests (Cumming and Beange 1993) to 20 years in Québec balsamfir, white-birch forests and mixed-wood forests in west-central Alberta (Leblond et al. 2016;Peters 2010) to upwards of 40 years in mixed-wood forests in Québec, Alberta, and British Columbia (Gagné et al. 2016;Mumma et al. 2018;Rudolph et al. 2019). While some caribou may be more tolerant of harvest blocks if they are adjacent to mature forests, as seen in white birch-balsam fir and black spruce forests in Québec (Hins et al. 2009), there was evidence that the area of avoidance extended beyond the harvest block boundary, with caribou avoiding areas >1 km from recent harvests in coniferous forests in Newfoundland, Ontario, and Alberta (Schaefer and Mahoney 2007;Smith et al. 2000;Vors et al. 2007). ...
... Forest harvesting can provide ecological conditions that increase early-seral forage for moose, deer, and elk, with concurrent increases in the predators of caribou (Gagné et al. 2016;James et al. 2004;Kuzyk et al. 2004). Even in the same stand types, harvested stands have different ecological legacies than wildfires (Best et al. 2024). ...
Ecosystem-based management (EBM) is a landscape-level management and planning process that is common across North America. A primary tenet of EBM is that the area and intensity of anthropogenic disturbance should mimic the historical natural disturbance of the focal ecosystem. Biodiversity should persist, at least at a coarse scale, where anthropogenic disturbance, such as forest harvesting, matches natural disturbance. However, EBM is failing some species, particularly those that are dependent on old forest. Across many areas of Canada, woodland caribou (Rangifer tarandus caribou) are declining because of the direct and indirect effects of habitat loss and fragmentation. This is even though forest management often follows the principles of EBM. We conducted a qualitative comparison of the responses of woodland caribou to wildfire and forest harvesting, considering a broad range of responses, including habitat selection and distribution, forage, movement patterns, and population dynamics. We found that while wildfire and forest harvesting both influence caribou, the negative effects are generally greater following forest harvesting. For example, wildfire and forest harvesting result in the loss of habitat, but caribou are more likely to shift, abandon or contract their range in response to harvest. The literature also suggested a stronger negative population response of caribou to forest harvest when compared to wildfire. This difference could be the result of greater residual forest structure associated with wildfire as well as the extensive resource roads that are necessary for forestry operations. Although there is sound theoretical support for EBM, the practice, as implemented, may not be effective for maintaining the habitat and ultimately populations of woodland caribou.
... First, modifications in climate conditions will directly impact natural disturbance regimes (Boulanger et al., 2014(Boulanger et al., , 2016b, which in turn are likely to alter caribou habitat through changes in age class structure as well as forest composition. For instance, increases in fire activity would promote a higher proportion of regenerating stands and pioneer deciduous species (e.g., birches, aspen) (Tremblay et al., 2018;Boulanger and Puigdevall, 2021), both known to be detrimental to caribou Gagné et al., 2016). Furthermore, changes in temperature and precipitation are likely to alter the growth and regeneration of conifers (Taylor et al., 2017), an important component of caribou habitat (Hins et al., 2009). ...
... Unsurprisingly, our best-supported RSF model confirmed results obtained in previous studies in Québec, which revealed that boreal caribou avoided recently disturbed areas (either by fire or cutblocks) (Leclerc et al., 2012;Leblond et al., 2016b;Lafontaine et al., 2019), deciduous stands (Leclerc et al., 2014;Losier et al., 2015;Lafontaine et al., 2019), large water bodies (Hins et al., 2009;Losier et al., 2015;Gagné et al., 2016) and non-forested polygons (because of post-disturbance regeneration failure; Leclerc et al., 2014), while they selected for wetlands, lichen woodlands and older coniferous stands (Hins et al., 2009;Leblond et al., 2011;Leclerc et al., 2012Leclerc et al., , 2019Gagné et al., 2016). Caribou almost always avoided proximity to roads (Leblond et al., 2011;Leclerc et al., 2012Leclerc et al., , 2014Losier et al., 2015), although this response was mediated by the aboveground tree biomass, with no avoidance observed when roads were found in treeless areas (see Appendix A, Fig. A.1). ...
... Unsurprisingly, our best-supported RSF model confirmed results obtained in previous studies in Québec, which revealed that boreal caribou avoided recently disturbed areas (either by fire or cutblocks) (Leclerc et al., 2012;Leblond et al., 2016b;Lafontaine et al., 2019), deciduous stands (Leclerc et al., 2014;Losier et al., 2015;Lafontaine et al., 2019), large water bodies (Hins et al., 2009;Losier et al., 2015;Gagné et al., 2016) and non-forested polygons (because of post-disturbance regeneration failure; Leclerc et al., 2014), while they selected for wetlands, lichen woodlands and older coniferous stands (Hins et al., 2009;Leblond et al., 2011;Leclerc et al., 2012Leclerc et al., , 2019Gagné et al., 2016). Caribou almost always avoided proximity to roads (Leblond et al., 2011;Leclerc et al., 2012Leclerc et al., , 2014Losier et al., 2015), although this response was mediated by the aboveground tree biomass, with no avoidance observed when roads were found in treeless areas (see Appendix A, Fig. A.1). ...
Many boreal populations of woodland caribou (Rangifer tarandus caribou) have declined in Canada, a trend essentially driven by the increasing footprint of anthropogenic disturbances and the resulting habitat-mediated apparent competition that increases predation pressure. However, the influence of climate change on these ecological processes remains poorly understood. We evaluated how climate change will affect boreal caribou habitat over the 2030–2100 horizon and in a 9.94 Mha study area, using a climate-sensitive simulation ensemble that integrates climate-induced changes in stand dynamics, fire regime, and different levels of commercial timber harvesting. We assessed the relative importance of these three drivers under projections made using different radiative forcing scenarios (RCP 2.6, 4.5, 8.5). Habitat quality was estimated from resource selection functions built with telemetry data collected from 121 caribou between 2004 and 2011 in 7 local populations. At the beginning of our simulations, caribou habitat was already structured along a south-to-north increasing quality gradient. Simulations revealed changes in forest cover that are driven by climate-induced variations in fire regime and scenarios of harvesting levels, resulting in the loss of older coniferous forests and an increase in deciduous stands. These changes induced a generalized decrease in the average habitat quality and in the percentage of high-quality habitat for caribou, and in a northward recession of suitable habitat. Timber harvesting was the most important agent of change for the 2030–2050 horizon, although it was slowly replaced by changes in fire regime until 2100. Our results clearly showed that it is possible to maintain the current average habitat quality for caribou in future scenarios that consider a reduction in harvested volumes, the only lever under our control. This suggests that we still have the capacity to conciliate socioeconomic development and caribou conservation imperatives in the face of climate change, an important issue debated throughout the species distribution range.
... The construction of linear corridors such as roads and trails can also impact caribou, as these features can steepen the functional response of wolves to prey density (i.e., increase prey detection/ hunting efficiency) (21,22). Collectively, such habitat changes alter the spatial dynamics and hence interaction rates of predators and apparent competitors (23,24). Because the main agents of caribou declines are habitat driven, much attention is currently devoted to the role of fire and anthropogenic disturbance in the process. ...
... Covariation between moose density and availability of deciduous (hardwood) vegetation is well established (34). Moose, which are hardwood browsers (24), are most abundant in early to midseral stages of boreal forest succession (35,36) where hardwood trees and deciduous shrubs are generally high in palatable biomass (37). Moose did not alter their overall distribution following the outbreak, as they generally remained most closely associated with forest stands rich in deciduous vegetation. ...
... Prey species with large home ranges and site fidelity, such as boreal caribou (42,43), should be particularly prone to trait-mediated apparent competition. Wolves hunt by targeting areas rich in moose's food, including deciduous or mixed stands and disturbed areas where early-seral vegetation has emerged (23,24,44). Accordingly, we found not only moose that were particularly abundant in areas characterized by a high proportion of SBW cut but also that wolves made selective use of these stands. ...
Significance
Despite the growing recognition that indirect interactions within species networks can determine food web dynamics, empirical evidence remains rare. We demonstrate how the impact of insects on forest structure and composition can reverberate across trophic levels by altering apparent competition in a large-mammal food web subjected to timber extraction. Spruce budworm outbreaks initiated a flush in deciduous vegetation that benefited moose, which translated into apparent competition between moose and boreal caribou through wolf predation. Mortality risk of caribou became indirectly related to patterns of insect and human activities, with the ungulate experiencing higher risk when selecting stands severely infested by budworms and subsequently logged. We expose cascading effects of insect–forest interactions on large-mammal relations in human-altered ecosystems.
... The response of wildlife species to habitat changes is different across ecosystems. Moreover, the ecological factors affecting wildlife will vary according to the different forestry practices used (Gagné et al. 2016, Son et al. 2017. ...
... The clear cutting can affect negatively some species as removing forest cover but also can affect positively other species due to abundant regeneration and the consequent food availability. Gagné et al. (2016) reported that decreased forest cover in a clear-cut area reduced habitat use by caribou Rangifer tarandus, but increased regeneration in the clear-cut area favored habitat use by moose Alces alces. de Bellefeuille et al. (2001) and Thornton et al. (2012) also reported that a clear-cut area could not provide sufficient vegetative cover for snowshoe hare Lepus americanus, which resulted in a decrease in hare abundance. ...
... Hansson (1994) reported that open environments in clear-cut forests made mountain hares Lepus timidus vulnerable to predation and, consequentially, served as a sink habitat for the hare. Gagné et al. (2016) also reported that clear-cutting affected interactions among moose and wolf Canis lupus by increasing habitat use by moose and wolf in clear-cuts and the consequential predation rate for moose. In this study, most mammal species, including herbivores, exhibited positive responses to clear-cut and clear-cut with reserves stands. ...
Forestry practices can lead to changes in wildlife habitat that could have lasting effects on the distribution of species. Hence, the aim of this study was to determine the effects of forestry practices on habitat variables and habitat use by mammals in three different stands (control, clear-cut and clear-cut with reserves) in a Japanese larch Larix kaempferi plantation from April to October in 2016 and 2017. We recorded the presence of field signs for the following six mammal species: Korean hare Lepus coreanus, raccoon dog Nyctereutes procyonoides, Eurasian badger Meles meles, water deer Hydropotes inermis, roe deer Capreolus pygargus and wild boar Sus scrofa. Habitat variables significantly differed among three stands. Field sign (feces, foot prints and feeding signs) abundances of mammals showed significant differences between the control and clear-cut stands. Moreover, field sign abundances of all species were highest in the clear-cut with reserves stand. We calculated the impact of clear-cutting on habitat use by mammals using GLMMs. Both clear-cutting in the models were significant and had positive coefficients on habitat use by Korean hare, raccoon dog, deer and wild boar. In Eurasian badger models, only clear-cutting with reserves show positive impacts on habitat use. Habitat selection by forest edge species such as Korean hare and deer showed dependence on understory structure. Abundant understory in the clear-cut with reserves stand may not only provide vegetative food and cover for herbivores but also small prey species for omnivores and carnivores. The results of our study show that forest understory is one of the most instrumental factors mitigating the effects of clear-cutting on habitat use by mammal and it should, therefore, be given due importance in forestry practices.
... However, we defined the domain of availability as the area both inside and outside (according to movement capacities) of home ranges. Our study thus includes elements of both second-order selection (i.e., outside home ranges) and third-order selection (i.e., within home ranges), as in Boyce et al. (2003), Gagné, Mainguy, andFortin (2016) andLosier et al. (2015). ...
... However, we defined the domain of availability as the area both inside and outside (according to movement capacities) of home ranges. Our study thus includes elements of both second-order selection (i.e., outside home ranges) and third-order selection (i.e., within home ranges), as in Boyce et al. (2003), Gagné, Mainguy, andFortin (2016) andLosier et al. (2015). ...
... These results suggested wolves dynamically select both types of human footprint, which may facilitate wolf predation as road may be used to travel efficiently and encounter prey in cutblock areas. Cutblocks provide early seral forest habitat that provides food for wolf prey (Gagné et al., 2016), and thus may support higher prey densities (Bowman et al., 2010;Peters et al., 2012; Rempel, Elkie, Rodgers, & Gluck, 1997). We also found that F I G U R E 5 Relative selection by wolves of cutblock density (measured at a 1 km 2 scale) as a function of average ecoprovince cutblock density across boreal Canada during the summer (top) and winter (bottom) as modeled using a generalized functional response approach (GFR) wolves selected patches of higher vegetation productivity (i.e., ...
Aim:
The influence of humans on large carnivores, including wolves, is a worldwide conservation concern. In addition, human-caused changes in carnivore density and distribution might have impacts on prey and, indirectly, on vegetation. We therefore tested wolf responses to infrastructure related to natural resource development (i.e., human footprint).
Location:
Our study provides one of the most extensive assessments of how predators like wolves select habitat in response to various degrees of footprint across boreal ecosystems encompassing over a million square kilometers of Canada.
Methods:
We deployed GPS-collars on 172 wolves, monitored movements and used a generalized functional response (GFR) model of resource selection. A functional response in habitat selection occurs when selection varies as a function of the availability of that habitat. GFRs can clarify how human-induced habitat changes are influencing wildlife across large, diverse landscapes.
Results:
Wolves displayed a functional response to footprint. Wolves were more likely to select forest harvest cutblocks in regions with higher cutblock density (i.e., a positive functional response to high-quality habitats for ungulate prey) and to select for higher road density in regions where road density was high (i.e., a positive functional response to human-created travel routes). Wolves were more likely to use cutblocks in habitats with low road densities, and more likely to use roads in habitats with low cutblock densities, except in winter when wolves were more likely to use roads regardless of cutblock density.
Main conclusions:
These interactions suggest that wolves trade-off among human-impacted habitats, and adaptively switch from using roads to facilitate movement (while also risking encounters with humans), to using cutblocks that may have higher ungulate densities. We recommend that conservation managers consider the contextual and interacting effects of footprints when assessing impacts on carnivores. These effects likely have indirect impacts on ecosystems too, including on prey species.
... These movements and predation events were influenced by speciesspecific behavior and the characteristics of the surrounding landscape. Each species exhibited distinct responses to landscape features, such as cuts and roads Gagné et al., 2016), resulting in variations in the types of land cover where the likelihood of predatorprey encounters was highest for each prey species (Courbin et al., 2009. When an individual agent moved, 21 random steps were generated within a buffer surrounding their current position. ...
... Projected increases in fire activity due to CC cumulate with forest harvesting are expected to be important drivers of landscape changes and subsequently in boreal assemblages. The use of a spatially explicit and mechanistic forest model allowed us to simulate changes in forest stand composition, an important driver of bird and beetle occurrences (Cadieux et al., 2019;Mason et al., 2021) and caribou mortality (Courbin et al., 2009;Gagné et al., 2016). In our simulations, a significant proportion of coniferous stands transitioned to deciduousdominated stands after a disturbance. ...
... In both seasons, wolves selected new cutblocks, suggesting better predation opportunities either due to higher prey availability or visibility 53,54 . Forage biomass increases post-harvest due to more solar insolation and nutrients available to plants, subsequently attracting ungulates 12,15,[55][56][57] . However, forage biomass and ungulate use peaks a decade post-harvest 12,55 , and while moose kill-sites were linked to higher proportions of regenerating cutblocks, there was no trend in wolf selection for regenerating blocks. ...
... Forage biomass increases post-harvest due to more solar insolation and nutrients available to plants, subsequently attracting ungulates 12,15,[55][56][57] . However, forage biomass and ungulate use peaks a decade post-harvest 12,55 , and while moose kill-sites were linked to higher proportions of regenerating cutblocks, there was no trend in wolf selection for regenerating blocks. Regenerating cutblocks attract moose for the increased forage biomass and cover 12,14,33 , but increased vegetative cover would reduce prey visibility. ...
Predator search efficiency can be enhanced by anthropogenic landscape change, leading to increased predator–prey encounters and subsequent prey population declines. Logging increases early successional vegetation, providing ungulate forage. This increased forage, however, is accompanied by linear feature networks that increase predator hunting efficiency by facilitating predator movement and increasing prey vulnerability. We used integrated step selection analyses to weigh support for multiple hypotheses representing the combined impact of logging features (cutblocks and linear features) on wolf (Canis lupus) movement and habitat selection in interior British Columbia. Further, we examine the relationship between logging and wolf kill-sites of moose (Alces alces) identified using spatiotemporal wolf location cluster analysis. Wolves selected for linear features, which increased their movement rates. New (0–8 years since harvest) cutblocks were selected by wolves. Moose kill-sites had a higher probability of occurring in areas with higher proportions of new and regenerating (9–24 years since harvest) cutblocks. The combined selection and movement responses by wolves to logging features, coupled with increased moose mortality sites associated with cutblocks, indicate that landscape change increases risk for moose. Cumulative effects of landscape change contribute to moose population declines, stressing the importance of cohesive management and restoration of anthropogenic features.
... Anthropogenic disturbances, such as logging activities, increase habitat loss and fragmentation, which tends to intensify predation rate on caribou by triggering apparent competition (James et al. 2004, Wittmer et al. 2007). Deciduous vegetation invades cutovers few years after logging (Potvin et al. 2005, Gagné et al. 2016, which is the primary food source for moose (Alces americanus, Crête 1989). This increase in vegetation can trigger an increase in moose abundance, followed by a numerical response of the wolf population that can exacerbate predation risk of boreal caribou (Seip 1992, Wittmer et al. 2007). ...
... However, the demographic consequence of maintaining at least 65% of undisturbed habitat varies among populations (Environment Canada 2012, Rudolph et al. 2017 because, for example, the same level of total disturbance can be associated with different compositions (e.g., a landscape with more linear features and fewer cutblocks than another) and that spatial configuration of landscape composition is likely to influence the spatial game of interactions between caribou, wolves, and moose differently . The three species do not react similarly to cuts, roads, and other landscapes features , 2015, Gagné et al. 2016, and those species-specific responses generate spatial patterns in predator-prey co-occurrence (Courbin et al. 2009 and prey mortality (Wittmer et al. 2007, Losier et al. 2015. The caribou-moose-wolf system thus provides an opportunity to use IBMs to inform conservation planning by revealing how different spatial patterns of human disturbances could influence predation rates. ...
Landscape complexity can determine the population dynamics of interacting predators and prey. Yet, management plans are commonly developed from aspatial predictive models. This oversight may result in unexpected outcomes or the loss of opportunities to make spatial interventions that would increase a plan's effectiveness. The management of the threatened woodland caribou (Rangifer tarandus caribou), boreal population, provides an example of such shortcomings when using an aspatial approach. Currently, the most influential management recommendation is to maintain at least 65% of undisturbed forests in areas occupied by caribou populations, regardless of the spatial configuration of the forest cover. Using a spatially explicit individual‐based model (IBM), we evaluated the effects of the spatial configuration of cuts and roads on the mortality of boreal caribou living in sympatry with wolves (Canis lupus) and moose (Alces alces), an apparent competitor. Starting with a real forest landscape, we created forest management scenarios of the specific spatial distribution of cuts (mosaic, small, or large agglomeration) with increasing disturbance levels. We then ran the IBM with simulated agents, representing individuals of the three species, moving according to movement rules determined from radio‐collared individuals. We found that movement responses to land cover types and roads differed among species. For example, caribou and moose generally avoided areas close to roads, contrary to wolves. Those differences influenced the mortality of caribou agents, which not only depended on the levels of disturbance but also depended on the spatial distribution of cuts and roads. After controlling for disturbance level, wolves were more successful when forest management required an extensive road network resulting in relatively high habitat fragmentation. Caribou agents experienced lower mortality in landscapes with low densities of road and disturbance‐related edges. The effect remained much stronger, however, for the level than the spatial configuration of human disturbances. Still, our IBM demonstrated how landscape management could be used to manipulate species interactions, with the intent of either increasing or decreasing predation rates on specific populations, depending on management goals.
... The pathway of habitat alteration leading to increased productivity that favours primary prey and shared predators is complex. Although studies have evaluated individual linkages along this trophic chain [24,26,34,39,40], a more fulsome approach is to track abundance at each trophic level simultaneously. This approach also allows for explicit contrasts among a suite of potential mechanisms. ...
... Factors influencing variation in productivity are complex, many of which will be heavily influenced by natural components such as latitude, elevation and underlying edaphic properties. Nonetheless, we have shown that humans can influence productivity based on the time-series analysis of forest stands regenerating from harvest, with mounting evidence that this process is occurring in the boreal forest [40]. A likely compounding factor that we did not directly estimate in our study is atmospheric CO 2 fertilization, a global phenomenon that is predicted to exacerbate the eutrophication of the boreal forest biome [2]. ...
Changes in primary productivity have the potential to substantially alter food webs, with positive outcomes for some species and negative outcomes for others. Understanding the environmental context and species traits that give rise to these divergent outcomes is a major challenge to the generality of both theoretical and applied ecology. In aquatic systems, nutrient-mediated eutrophication has led to major declines in species diversity, motivating us to seek terrestrial analogues using a large-mammal system across 598 000 km ² of the Canadian boreal forest. These forests are undergoing some of the most rapid rates of land-use change on Earth and are home to declining caribou ( Rangifer tarandus caribou ) populations. Using satellite-derived estimates of primary productivity, coupled with estimates of moose ( Alces alces ) and wolf ( Canis lupus ) abundance, we used path analyses to discriminate among hypotheses explaining how habitat alteration can affect caribou population growth. Hypotheses included food limitation, resource dominance by moose over caribou, and apparent competition with predators shared between moose and caribou. Results support apparent competition and yield estimates of wolf densities (1.8 individuals 1000 km ⁻² ) above which caribou populations decline. Our multi-trophic analysis provides insight into the cascading effects of habitat alteration from forest cutting that destabilize terrestrial predator–prey dynamics. Finally, the path analysis highlights why conservation actions directed at the proximate cause of caribou decline have been more successful in the near term than those directed further along the trophic chain.
... Echoing DeMars et al. (2019), we too question the role of natural disturbance as being a principal factor influencing moose-related DMAC, at least in the absence of other alternate prey such as white-tailed deer or substantive anthropogenic disturbance, both of which were negligible in our study area. Gagné et al. (2016) reported that moose selected for clear-cuts only at low latitudes in their study area in Québec, Canada, where the availability of deciduous vegetation and net primary productivity was higher, suggesting that moose responses to fire, and hence DMAC, may be predicated on the modulating effects of primary productivity. We believe that in the SBS there is a diminished relationship between extent of natural disturbance and how moose respond to it. ...
... The weakening of this link in relation to areas where the hypothesis of DMAC (as a limiting factor for boreal caribou) was initially developed appears to be due to macroecological habitat differences including successional dynamics after fire (Hart et al. 2019). In a broadscale sense, we expect these differences to be underlain by the decline in net primary productivity with increasing latitude in the northern hemisphere (Rosenzweig 1968) and subsequent lack of browse generated for moose after fire (data herein, Gagné et al. 2016). That is, the strength of DMAC in the context of caribou is likely modulated by primary productivity, which we can generally term here as the primary productivity hypothesis of DMAC. ...
The most widely reported threat to boreal and mountain populations of woodland caribou (Rangifer tarandus caribou; caribou) involves habitat‐ or disturbance‐mediated apparent competition (DMAC). With DMAC, natural and anthropogenic disturbances that increase the abundance of deciduous‐browsing cervids (e.g., moose [Alces alces], deer [Odocoileus spp.]) are thought to promote predator (especially wolf [Canis lupus]) numbers, which heightens predation risk to caribou. We know most about the effects of DMAC on caribou where the species is under threat by anthropogenic activities in relatively productive southern boreal and mountain systems. Yet, >60% of extant boreal caribou range in North America consists of northern shield and taiga ecoregions of low productivity where caribou may compete with only 1 ungulate species (moose) in the context of DMAC. In this environment, we know very little of how DMAC acts as a limiting factor to caribou. In Saskatchewan, Canada, from 2014–2018, using a combination of vegetation sampling, aerial surveys, and telemetry data (n = 38 wolves), we searched for evidence of DMAC (trends in data consistent with the hypothesis) in an 87,193‐km2 section of the Western Boreal Shield, a poorly productive but pristine region (0.18% of land cover classed as an anthropogenic feature) with a historically high fire‐return interval (47% of stands aged <40 years). Despite the high levels of disturbance, moose density was relatively low (47 moose/1,000 km2), likely because of the scarcity of deciduous or mixed‐wood stands and low abundance of deciduous browse in the young conifer stands that dominated the landscape. In contrast, boreal caribou density was relatively high for the species (37 caribou/1,000 km2). Wolf density (3.1 wolves/1,000 km2) and pack sizes (urn:x-wiley:0022541X:media:jwmg21982:jwmg21982-math-0001 = 4.0 wolves/pack) were low and resident (established) territories were large (urn:x-wiley:0022541X:media:jwmg21982:jwmg21982-math-0002 = 4,360 km2; 100% minimum convex polygon). The low density of wolves mirrored the low (standardized) ungulate biomass index (UBI; moose + boreal caribou) of the study area (0.36 UBI/km2). We conclude that wolf and hence caribou populations were not responding in accordance with the outcomes generally predicted by DMAC in our study area because the requisite strong, positive response to fire of deciduous‐browse and alternate‐prey abundance was lacking. As a limiting factor to caribou, DMAC is likely modulated at a macroecological scale by factors such as net primary productivity, a corollary to the general hypothesis that we advance here (i.e., primary productivity hypothesis of DMAC). We caution against managing for caribou based on the presumption of DMAC where the mechanism does not apply, which may include much of boreal caribou range in the north. © 2020 The Wildlife Society.
... Human-induced disturbance conflicts with this aspect of their ecology. Timber harvesting returns mature coniferous (softwood) forest stands to an early seral stage that, once invaded by deciduous vegetation, attracts browsing ungulates [12,13]. Local increases in ungulate density can then trigger a numerical response from predator populations, which, in turn, increases predation risk to caribou [14,15]. ...
... Local increases in ungulate density can then trigger a numerical response from predator populations, which, in turn, increases predation risk to caribou [14,15]. Moreover, while wolves (Canis lupus) generally avoid hunting in closed coniferous forests [12,16], they take advantage of linear features such as roads (from forestry and other source) and other corridors (e.g., seismic exploration cut-lines from oil and gas exploration) [17] to venture into forests which diminishes the effectiveness of caribou habitat-selection strategies to avoid predation [18]. The response of predators like wolves to using logging-impacted habitat across boreal caribou range is also non-linear, increasing with prevalence of cutblocks on the landscape [19]. ...
A significant challenge of conservation biology is to preserve species in places where their critical habitat also attracts significant economic interest. The problem is compounded when species distributions occur across large spatial extents. Threatened boreal caribou (Rangifer tarandus caribou) epitomize this problem: their critical habitat encompasses a vast expanse of forest that also supplies much of Canada’s merchantable timber. Boreal caribou were protected under the Canada Species at Risk Act in 2003. We investigated putative drivers of reduced disturbance for caribou habitat since then. Where the cumulative logging footprint slowed within caribou habitat, this has resulted neither from decreases in annual allowable cut of timber nor the creation or expansion of protected areas. Rather, it has fluctuated with the American economy relative to that of Canada. For each CAD, 129 km² of caribou habitat was not disturbed by logging in a given year. Recent population declines have been occurring even though logging typically remained at <70% of allowed levels. Our study raises concerns about how caribou are functionally being conserved under the current application of existing legislation. In this globalized world, the economy of foreign nations is increasingly likely to govern national conservation objectives.
... The positive link between forest productivity and deciduous vegetation during early stages of forest succession (Figs 1 and 4) should therefore have a larger impact on food availability for moose than for caribou. Also, primary productivity influences interaction strengths in plant-prey-predator systems following a combination of non-linear inter-species relationships e.g., numerical and functional responses, and frequency-dependent prey selection by the predator 4,5,43 , and habitat-animal spatial relationships 16,44,45 . In this context, we can consider the typical situation where an increase in deciduous vegetation is followed by an increase in moose abundance that triggers a numerical response by the wolf population. ...
... Wolves should then increase their focus on moose as they should be more abundant than caribou 44 , especially in a highly productive forest (Fig. 4). The consequence should be a stronger increase in predation rate for moose than for caribou, as can be estimated from the model provided in 44 , with species-specific habitat selection provided in 16 . Moreover, the impact of forest productivity on the demography of boreal caribou depends upon the relationship between forest resilience and productivity. ...
Primary production can determine the outcome of management actions on ecosystem properties, thereby defining sustainable management. Yet human agencies commonly overlook spatio-temporal variations in productivity by recommending fixed resource extraction thresholds. We studied the influence of forest productivity on habitat disturbance levels that boreal caribou – a threatened, late-seral ungulate under top-down control – should be able to withstand. Based on 10 years of boreal caribou monitoring, we found that adult survival and recruitment to populations decreased with landscape disturbance, but increased with forest productivity. This benefit of productivity reflected the net outcome of an increase in resources for apparent competitors and predators of caribou, and a more rapid return to the safety of mature conifer forests. We estimated 3-fold differences in forest harvesting levels that caribou populations could withstand due to variations in forest productivity. The adjustment of ecosystem provisioning services to local forest productivity should provide strong conservation and socio-economic advantages.
... In addition to anthropogenic habitat alteration and climate, deer density is expected to vary depending on landscape context, such as primary productivity (Dawe et al., 2014;Kennedy-Slaney et al., 2018). To account for landscape context, we used the change in the Enhanced Vegetation Index (ΔEVI) as a measure of deciduous vegetation availability (Gagné et al., 2016), which has been found to impact the density of terrestrial herbivores in boreal forests, ...
Anthropogenic habitat alteration and climate change are two well‐known contributors to biodiversity loss through changes to species distribution and abundance; yet, disentangling the effects of these two factors is often hindered by their inherent confound across both space and time. We leveraged a contrast in habitat alteration associated with the jurisdictional boundary between two Canadian provinces to evaluate the relative effects of spatial variation in habitat alteration and climate on white‐tailed deer ( Odocoileus virginianus ) densities. White‐tailed deer are an invading ungulate across much of North America, whose expansion into Canada's boreal forest is implicated in the decline of boreal caribou ( Rangifer tarandus caribou ), a species listed as Threatened in Canada. We estimated white‐tailed deer densities using 300 remote cameras across 12 replicated 50 km ² landscapes over 5 years. White‐tailed deer densities were significantly lower in areas where winter severity was higher. For example, predicted deer densities declined from 1.83 to 0.35 deer/km ² when winter severity increased from the lowest value to the median value. There was a tendency for densities to increase with increasing habitat alteration; however, the magnitude of this effect was approximately half that of climate. Our findings suggest that climate is the primary driver of white‐tailed deer populations; however, understanding the mechanisms underpinning this relationship requires further study of over‐winter survival and fecundity. Long‐term monitoring at the invasion front is needed to evaluate the drivers of abundance over time, particularly given the unpredictability of climate change and increasing prevalence of extreme weather events.
... In Canada, the spatial progression of anthropogenic disturbances over time presents a rather similar northward trend as the one shown by climate-induced shifts in isotherms (Gagné et al., 2016;Parmesan & Yohe, 2003). Anthropogenic disturbances are the most important, well-recognized driver of habitat alteration for boreal caribou populations (Courtois et al., 2007;Lafontaine et al., 2019;Serrouya et al., 2019;Vors & Boyce, 2009); for example, Schaefer (2003) identified forestry as the main driver of northward range recession for caribou in Ontario. ...
The contraction of species range is one of the most significant symptoms of biodiversity loss worldwide. While anthropogenic activities and habitat alteration are major threats for several species, climate change should also be considered. For species at risk, differentiating the effects of human disturbances and climate change on past and current range transformations is an important step towards improved conservation strategies. We paired historical range maps with global atmospheric reanalyses from different sources to assess the potential effects of recent climate change on the observed northward contraction of the range of boreal populations of woodland caribou ( Rangifer tarandus caribou ) in Quebec (Canada) since 1850. We quantified these effects by highlighting the discrepancies between different southern limits of the caribou's range (used as references) observed in the past and reconstitutions obtained through the hindcasting of the climate conditions within which caribou are currently found. Hindcasted southern limits moved ~105 km north over time under all reanalysis datasets, a trend drastically different from the ~620 km reported for observed southern limits since 1850. The differences in latitudinal shift through time between the observed and hindcasted southern limits of distribution suggest that caribou range recession should have been only 17% of what has been observed since 1850 if recent climate change had been the only disturbance driver. This relatively limited impact of climate reinforces the scientific consensus stating that caribou range recession in Quebec is mainly caused by anthropogenic drivers (i.e. logging, development of the road network, agriculture, urbanization) that have modified the structure and composition of the forest over the past 160 years, paving the way for habitat‐mediated apparent competition and overharvesting. Our results also call for a reconsideration of past ranges in models aiming at projecting future distributions, especially for endangered species.
... A parallel study in the same area which used field data (tracks and signs and vegetation cover) found that moose use of seismic lines was linked to the availability of specific forage species and the availability of game trails (Tattersall et al., 2023). It was curious that we found no links between the percent conifer surrounding seismic lines and moose response because moose generally select areas with higher availability of broadleaf trees (Courtois et al., 1998;Gagné et al., 2016;McKay & Finnegan, 2022). It is possible that the scale we measured percent conifer surrounding seismic lines (30 m) was too fine to capture moose response to stand-level tree species. ...
Linear features are pervasive across the boreal forest of Canada, negatively impacting several wildlife species. Understanding how wildlife responds to different types and characteristics of linear features is necessary for coordinated landscape restoration. Currently, linear feature restoration is focused on recovering threatened woodland caribou (Rangifer tarandus) which may have unintended impacts on other boreal species like moose (Alces alces). Understanding how moose respond to different linear features can help ensure restoration is targeted and effective. We used GPS data from seven moose collected between 2008 and 2010 to investigate response to linear features and to determine how moose response was influenced by characteristics of linear features like the surrounding habitat and regeneration. At the landscape scale, moose selected areas closer to seismic lines when they were in areas with lower densities of seismic lines and higher densities of harvest blocks and wild-fires. This response was stronger during winter. Moose selected areas closer to pipelines when they were in areas with lower densities of other linear features, harvest blocks, and wildfires and were indifferent to roads at the population-level. At the fine scale, during winter, moose selected areas closer to seismic lines regardless of vegetation height or the surrounding habitat, but were indifferent to seismic lines during summer, and were indifferent to roads and pipelines during summer and winter. Combined, our results suggest that there are characteristics of seismic lines which make them attractive to moose regardless of the regeneration height on the seismic lines, providing further evidence that effective linear feature restoration will need to address the fact that linear features increase landscape permeability and provide forage for multiple boreal wildlife species. Our results also further illustrate the importance of considering how linear feature restoration efforts focused on caribou may shift the distribution of other boreal wildlife species. Ultimately, conservation efforts for threatened species should recognize that conservation efforts focused on one species may have unintended consequences for interacting species.
... Likewise, while several carnivore species responded negatively to recent clearcuts, others 423 responded positively to them. This is likely due to increased prey availability or hunting 424 success in cleared areas (Gagné et al. 2016, Ausilio et al. 2022). Carnivores in forest 425 harvested using reduced impact logging (RIL), or to a lesser extent partial harvesting, 426 generally showed no difference in use between harvested and unharvested forest. ...
1. Unmodified forests are increasingly rare worldwide, with forestry a major contributor to habitat modification. Extending conservation practices beyond protected areas is important to conserve forest ecosystems.
2. We investigate the response of native mammalian carnivores (both Order Carnivora and Family Dasyuridae) to production forests globally, including harvested native forest and timber plantations. We examine how carnivores recorded in production forests use these forests versus other land uses, particularly native and unharvested forest; how habitat use relates to threatened status, body size, diet, and harvesting method; carnivore responses to habitat features within production forests; and carnivore denning, breeding, and predation behaviour in production forests.
3. We review 294 studies recording 132 carnivore species in production forests. Carnivores generally show higher use of native and unharvested forests and lower use of agricultural land than production forests. Threatened species and large carnivores respond more negatively to production forests than non-threatened species and small carnivores respectively. Hypercarnivores respond more negatively than omnivores to plantations compared to native forest, but there was no difference in the use of harvested and unharvested native forest between these dietary groups.
4. Surprisingly, a high proportion of carnivore species use clearfelled more than unharvested native forest. In forest with partial harvesting or reduced-impact logging, most species show no difference in use between harvested and unharvested forest.
5. Carnivores generally respond positively to habitat features such as riparian areas and coarse woody debris. Several carnivores were recorded denning and breeding in production forests. Production forests often influence the prey availability, hunting success, and diet of carnivores.
6. We show that many carnivores use production forests, and how they respond to production forestry varies with species traits. We recommend that production forests are managed as valuable carnivore habitat, and highlight strategies to enhance the use of these forests by carnivores.
... Indeed, spatial configuration of landscape composition is likely to influence differently the spatial game that wolves play with caribou and moose (Fortin et al., 2015;Vanlandeghem et al., 2021). The three species react differently to landscape features, such as cuts and roads (Fortin et al., , 2015Gagné et al., 2016), which generates differences in the land cover types where each prey species is most likely to encounter a predator (Courbin et al., 2009. Empirical movement rules were determined using SSFs (Appendix S1: Section S2) specific for each species. ...
Abstract Although global change can reshape ecosystems by triggering cascading effects on food webs, indirect interactions remain largely overlooked. Climate‐ and land‐use‐induced changes in landscape cause shifts in vegetation composition, which affect entire food webs. We used simulations of forest dynamics and movements of interacting species, parameterized by empirical observations, to predict the outcomes of global change on a large‐mammal food web in the boreal forest. We demonstrate that climate‐ and land‐use‐induced changes in forest landscapes exacerbate asymmetrical apparent competition between moose and threatened caribou populations through wolf predation. Although increased prey mortalities came from both behavioral and numerical responses, indirect effects from numerical responses had an overwhelming effect. The increase in caribou mortalities was exacerbated by the cumulating effects of land use over the short term and climate change impacts over the long term, with higher impact of land use. Indirect trophic interactions will be key to understanding community dynamics under global change.
... Sex-specific habitat selection can thus create differences in the impact of males and females on ecosystems, a situation that provides opportunities to fine-tune management actions. Nonetheless, habitat selection studies commonly focus on individuals of a single sex (e.g., Boyce et al., 2003;Gagné et al., 2016; or integrate observations from males and females without discrimination (e.g., Chetkiewicz and Boyce, 2009;Matawa et al., 2012). An additional level of complexity comes from density-dependent changes in animal-habitat relationships. ...
Habitat selection models are the basis of an increasing number of conservation and management programs. Decision-makers rely on accurate models to assess animal distribution over space and time, and to recommend suitable actions that can alleviate human-wildlife conflicts. Despite a rapidly growing number of field studies on habitat selection, there remains a paucity of empirical evidence that selection is a density-dependent process that can impact males and females differently. Based on 11 years of monitoring, we demonstrate that the response of African elephants (Loxodonta africana) to land-cover types varied with population size, and that density-dependent adjustments differed between sexes. Specifically, our longitudinal follow-up of GPS-collared elephants revealed that elephants gradually decrease their selection for open woodlands and forests, as the population increased and the availability of palatable browse species decreased. Both sexes – though males more strongly – increased their travel rate together with their relative probability of selection of roads for travel. Also, elephants displayed a density-dependent increase in their selection of infrastructures, a response that was stronger for males than females. The risk of human-elephant conflicts thus increased with population size, with males being particularly prone to be involved in such conflicts. Overall, we provide rare empirical evidence that density-dependence in fine-grain habitat selection can differ between sexes. This information can be critical to accurately forecast potential human-wildlife conflicts, and for taking targeted and effective conservation and management actions.
... Because wolf density generally increases with increasing moose abundance (Bowman et al., 2010;Gagné et al., 2016), SBW outbreaks may intensify predation on caribou. A greater predator density may also be favored by the increase in fruit-bearing species abundances within moderately and severely defoliated stands. ...
Forest logging has contributed to the decline of several woodland caribou populations by causing the fragmentation of mature coniferous stands. Such habitat alterations could be worsened by spruce budworm (SBW) outbreaks. Using 6201 vegetation plots from provincial inventories conducted after the last SBW outbreak (1968–1992) in boreal forests of Québec (Canada), we investigated the influence of SBW‐caused tree defoliation and mortality on understory vegetation layers relevant to woodland caribou and its main predators. We found a positive association between severe outbreaks and the cover of most groups of understory plant species, especially in stands that were dominated by balsam fir before the outbreak, where a high canopy openness particularly benefited relatively fast‐growing deciduous plants. Such increases in early successional vegetation could provide high‐quality forage for moose, which is likely to promote higher wolf densities and increase predation pressure on caribou. SBW outbreaks may thus negatively affect woodland caribou by increasing predation risk, the main factor limiting caribou populations in managed forests. For the near future, we recommend updating the criteria used to define critical caribou habitat to consider the potential impacts of spruce budworm defoliation. Spruce budworm outbreaks affect boreal forest structure and cause an increase in the cover of understory plant species. This could have negative impacts on woodland caribou populations in eastern Canada by increasing the abundance of alternate preys for key caribou predators.
... data availability and resolution, available statistical tools) and the difficulty of observing fine-scale movements and interactions directly. As such, predator-prey overlap has been assessed using readily available telemetry and camera trap data by quantifying co-occurrence (Courbin et al. 2009, Muhly et al. 2011, Gagné et al. 2016, home range or utilization distribution overlap (Courbin et al. 2013), or similarity of habitat use or selection (Basille et al. 2013, Smith et al. 2019a). However, the utility of quantifying spatial overlap to characterize predator-prey interactions is diminished if overlap is not a strong predictor of encounter probability. ...
Predation risk, the probability that a prey animal will be killed by a predator, is fundamental to theoretical and applied ecology. Predation risk varies with animal behavior and environmental conditions, yet attempts to understand predation risk in natural systems often ignore important ecological and environmental complexities, relying instead on proxies for actual risk such as predator–prey spatial overlap. Here we detail the ecological and environmental complexities driving disconnects between three stages of the predation sequence that are often assumed to be tightly linked: spatial overlap, encounters and prey capture. Our review highlights several major sources of variability in natural predator–prey systems that lead to the decoupling of spatial overlap estimates from actual encounter rates (e.g. temporal activity patterns, predator and prey movement capacity, resource limitations) and that affect the probability of prey capture given encounter (e.g. predator hunger levels, temporal, topographic and other environmental influences on capture success). Emerging technologies and statistical methods are facilitating a transition to a more spatiotemporally detailed, mechanistic understanding of predator–prey interactions, allowing for the concurrent examination of multiple stages of the predation sequence in mobile, free‐ranging animals. We describe crucial applications of this new understanding to fundamental and applied ecology, highlighting opportunities to better integrate ecological contingencies into dynamic predator–prey models and to harness a mechanistic understanding of predator–prey interactions to improve targeting and effectiveness of conservation interventions.
... In Québec, Canada, for example, logging reduced moose abundance by nearly 50% in resource-poor, black spruce (Picea mariana) forests (Potvin and Courtois, 2004). More recent research in Québec-examining the potential for logging to exacerbate apparent competition between moose and woodland caribou (Rangifer tarandus caribou)-demonstrated a decrease in the strength of selection by moose for cutblocks along a 400-km latitudinal gradient as a function of lower amounts of deciduous shrub regrowth at higher latitudes (Gagné et al., 2016). ...
Forestry activities are globally widespread and can have a large positive or negative influence on wildlife. Wildlife responses to forestry cutblocks (defined areas where trees were harvested) vary as a function of forest succession, which differs across systems. Across their distribution, moose (Alces alces) and forestry are often closely associated. Moose are predicted to select for cutblocks because of greater browse quantity in early successional vegetation, but moose responses to cutblocks are inconsistent across studies. Our objective was to compare moose spatial responses to cutblocks as a function of year since cut between study areas (Prince George South [PGS] and Bonaparte [BP]) while considering differences in vegetation composition and regrowth to better inform forestry planning in British Columbia, Canada. We characterized cutblocks by dominant tree species as a proxy for vegetation composition and estimated the normalized burn ratio (NBR) from multispectral satellite imagery as an index of vegetation regrowth (i.e., structure). We then examined the use of cutblocks by moose dependent upon vegetation composition and NBR using generalized additive mixed effects models. Next, we used locations of collared moose and nearby available locations to examine moose responses as a function of year since cut and used those responses to group cutblocks into age classes, which were incorporated into resource selection functions (RSF) to compare moose responses between study areas. Vegetation composition differed between study areas, and although cutblocks in both study areas followed similar regrowth trajectories, NBRs for cutblocks > 13 years post-logging in PGS exceeded those in BP. Moose demonstrated greater use of locations within cutblocks with intermediate NBRs and dominanted by spruce (Picea engelmannii × glauca) versus Douglas fir (Pseudotsuga menziesii var. glauca). Moose responses as a function of year since cut varied seasonally, but across seasons, moose tended to avoid new cutblocks (1–8 years), select for regenerating cutblocks (9–24 years), and avoid older cutblocks (25–40 years). In both study areas, RSFs revealed that moose avoided new cutblocks, but moose in PGS were more likely to select for regenerating cutblocks in comparison to BP. Our analyses suggest that the use of cutblocks by moose is a function of year since cut, vegetation composition, and vegetation regrowth, likely resulting from differences in browse quantity and lateral cover. To maintain stable moose populations, managers should consider vegetation composition and regrowth during forestry planning, and future research should focus on identifying region-specific forestry thresholds for moose.
... Although moose resource selection has been studied extensively, those studies are limited to specific foci. Anderson et al. (2018) focused on the role of elevation, and Gagné et al. (2016) focused on moose-caribou (Rangifer tarandus caribou)wolf (Canis lupus) movement along an elevational gradient. Courbin et al. (2014) modeled individual behavior and movement relative to nodes in a planar network. ...
Since 2010, several moose (Alces alces) populations have declined across North America. These declines are believed to be broadly related to climate and landscape change. At the western reaches of moose continental range, in the interior of British Columbia, Canada, wildlife managers have reported widespread declines of moose populations. Disturbances to forests from a mountain pine beetle (Dendroctonum ponderosae) outbreak and associated salvage logging infrastructure in British Columbia are suspected as a mechanism manifested in moose behavior and habitat selection. We examined seasonal differences in moose habitat selection in response to landscape change from mountain pine beetle salvage logging infrastructure: dense road networks and large intensive forest harvest cutblocks. We used 157,447 global positioning system locations from 83 adult female moose from 2012 to 2016 on the Bonaparte Plateau at the southern edge of the Interior Plateau of central British Columbia to test whether increased forage availability, landscape features associated with increased mortality risk, or the cumulative effects of salvage logging best explain female moose distribution using resource selection functions in an information‐theoretic framework. We tested these hypotheses across biological seasons, defined using a cluster analysis framework. The cumulative effects of forage availability and risk best predicted resource selection of female moose in all seasons; however, the covariates included in the cumulative models varied between seasons. The top forage availability model better explained moose habitat use than the top risk model in all seasons, except for the calving and fall seasons where the top risk model (distance to road) better predicted moose space use. Selection of habitat that provides forage in winter, spring, and summer suggests that moose seasonally trade predation risk for the benefits of foraging in early seral vegetation communities in highly disturbed landscapes. Our results identified the need for intensive landscape‐scale management to stem moose population declines. Additional research is needed on predator densities, space use, and calf survival in relation to salvage logging infrastructure. © 2020 The Wildlife Society. Female moose are selecting intensively logged areas and their populations are declining within them. Equally intensive landscape management through restoration and deactivations of aspects of salvage logging (i.e., roads) and landscape scale restoration is necessary to stem these declines.
... In combination with anthropogenic land use, these changes are altering the composition and structure of boreal forests around the world and testing the resilience of this ecosystem and its inhabiting people (Gauthier et al., 2015). Since the persistence of large mammals is a useful indicator for effective principal threats to persistence of forest-dwelling boreal caribou include habitat loss and increased predation, the latter likely facilitated by road building (Dickie et al., 2017), forest harvesting and other activities that create early seral habitat beneficial for competitive ungulate species (Gagné et al., 2016). The increase in abundance of competitive species thereby increases caribou mortality by higher consequent abundance of wolves and other predators (Festa-Bianchet et al., 2011), that is, apparent competition (Holt, 1977). ...
Understanding how conservation of woodland caribou, an at-risk species for which large undisturbed areas are often proposed to maintain viable populations, can contribute to conservation of boreal biodiversity is an important consideration for an ecosystem warming at twice the global average and experiencing rapid resource development. We assess the focal or 'umbrella' value of the boreal population of woodland caribou for conservation of mammalian and avian richness (n = 432) in the boreal region of Canada by (i) evaluating co-occurrence of caribou distribution with that of boreal mammals (n = 102), birds (n = 330), at-risk mammals (n = 11) and at-risk birds (n = 47); and (ii) conducting systematic conservation planning using MARXAN software to identify minimum representative and complementary reserve networks, comprised of planning units deemed large enough (10,000 km 2) for persistence of terrestrial wildlife, both at the extent of boreal caribou distribution and the entire boreal region. While boreal caribou overlap with the range of 90% of boreal birds and mammals, area-efficient networks representative of boreal diversity focus on species-rich areas south of caribou distribution and other areas that contain relatively small-ranged species. A similar pattern occurs when the MARXAN analysis focused only on caribou distribution, i.e. representative networks are preferentially located on southern herd ranges. However, this situation differs markedly to include large areas within the distribution of caribou if anthropogenic footprint on the landscape is considered as a constraint on reserve design. Efforts to sustain boreal caribou offer considerable opportunities to conserve diversity of co-occurring mammals and birds, including areas of the relatively more disturbed caribou southern ranges that have irreplaceable value in an efficient and representative pan-boreal network of reserves. The high focal value of boreal caribou for animal diversity should be considered when making decisions and policy choices about how to best allocate conservation efforts across its extensive distribution.
... Previous studies focusing on trophic cascades in terrestrial ecosystems have often been carried out in boreal ecosystems with limited land-use change (Ripple & Beschta 2012;Lyly et al. 2015Lyly et al. , 2016. As the impact of predators on prey populations depends to a large extent on the productivity of the landscape, which determines the growth rates and abundance of prey populations (Elmhagen et al. 2010), human management regimes and human-mediated food subsidies may, in particular, be expected to interact with the impact of mammalian or avian predators on prey populations (Gagn e et al. 2016). Therefore, the functional role of predators could be modified under varying levels of resource conditions. ...
... The impact of carnivores on prey populations depends to a large extent on the productivity of the landscape, which determines the growth rates and abundance of prey populations [85]. Thus, human management regimes, and humanmediated food subsidies in particular, could be expected to interact with the impact of carnivores on prey populations [86]. The current recolonization of large carnivores in Europe occurs along large-scale gradients in productivity, human density and land-use intensity ( figure 3). ...
Large carnivores are frequently presented as saviours of biodiversity and ecosystem functioning through their creation of trophic cascades, an idea largely based on studies coming primarily out of relatively natural landscapes. However, in large parts of the world, particularly in Europe, large carnivores live in and are returning to strongly human-modified ecosystems. At present, we lack a coherent framework to predict the effects of large carnivores in these anthropogenic landscapes. We review how human actions influence the ecological roles of large carnivores by affecting their density or behavior or those of mesopredators or prey species. We argue that the potential for density-mediated trophic cascades in anthropogenic landscapes is limited to unproductive areas where even low carnivore numbers may impact prey densities or to the limited parts of the landscape where carnivores are allowed to reach ecologically functional densities. The potential for behaviourally mediated trophic cascades may be larger and more widespread, because even low carnivore densities affect prey behaviour. We conclude that predator–prey interactions in anthropogenic landscapes will be highly context-dependent and human actions will often attenuate the ecological effects of large carnivores. We highlight the knowledge gaps and outline a new research avenue to study the role of carnivores in anthropogenic landscapes.
Woodland caribou ( Rangifer tarandus caribou ) are declining across much of their distribution in Canada in response to habitat alteration, leading to unsustainable predation, particularly by wolves ( Canis lupus ). Habitat alteration can benefit the primary prey species of wolves (moose [ Alces alces ] and deer [ Odocoileus spp.]) by creating early seral conditions that contain more of their preferred food types. This increase in primary prey populations results in elevated wolf abundance and heightened predation pressure on caribou. In response to the elevated wolf populations and the risks to caribou, managers have reduced wolf abundance in key areas. Ecological theory suggests that reducing wolf abundance would release moose from the top‐down effects of wolf predation, potentially allowing moose populations to grow. Elevated moose abundance thus has the potential to cause wolf populations to rebound quickly each year following reductions, suggesting a possible link between moose abundance and the number of wolves killed for caribou conservation. To test this idea we used a unique management situation in British Columbia and Alberta, Canada, where lethal wolf removals were annually conducted across specific southern mountain caribou population ranges and, in some places, moose populations were concurrently reduced via liberalized hunting. We used indices of moose abundance and wolf removal data to test the hypothesis that reducing moose populations to a historical abundance target by hunting leads to fewer wolves killed for caribou conservation. After controlling for habitat quality, wolves removed per km ² was 3.2 times lower in areas with reduced moose density ( = 1.55 wolves/1,000 km ² ± 0.33 [SE]) than in those without reduced moose density ( = 5.02 wolves/1,000 km ² ± 0.52). However, the average number of wolves removed per year decreased under both conditions. After 9 years, there was a 35% reduction in the predicted difference in the annual removal between areas with and without moose reduction. Our results suggest that policies that do not reduce or stabilize moose abundance will result in the removal of more wolves to increase caribou abundance. Like wolf reductions, moose reductions can also be controversial and affect local harvesters. Thus, understanding the consequences of actions that support caribou recovery is essential to supporting evidence‐based policy discussions.
Unmodified forests are increasingly rare worldwide, with forestry a major contributor to habitat modification. Extending conservation practices beyond protected areas is important to conserve forest ecosystems.
We investigate the response of native mammalian carnivores (both Order Carnivora and Family Dasyuridae) to production forests globally, including harvested native forest and timber plantations. We examine how carnivores recorded in production forests use these forests versus other land uses, particularly native and/or unharvested forest; how habitat use relates to threatened status, body size, diet and harvesting method; carnivore responses to habitat features within production forests; and carnivore denning, breeding and predation behaviour in production forests.
We review 294 studies recording 132 carnivore species in production forests. Carnivores generally show higher use of unharvested native forests and lower use of agricultural land than production forests. Threatened species and large carnivores respond more negatively to production forests than non‐threatened species and small carnivores respectively. Hypercarnivores respond more negatively than omnivores to plantations compared to native forest, with no difference in the use of harvested and unharvested native forest between these dietary groups.
Notably, a high proportion of carnivore species use clearfelled more than unharvested native forest. In forest with partial harvesting or reduced‐impact logging, most species show no difference in use between harvested and unharvested forest.
Carnivores generally respond positively to habitat features such as riparian areas and coarse woody debris. Several carnivores were recorded denning and breeding in production forests. Production forests often influence the prey availability, hunting success and diet of carnivores.
We show that many carnivores use production forests, and how they respond to production forestry varies with species traits and conservation status. We recommend that production forests are managed as valuable carnivore habitat, and highlight strategies to enhance the use of these forests by carnivores.
Moose are an iconic symbol of northern forests. In many jurisdictions, the management of moose has focused on regulating harvest with less emphasis on understanding moose–habitat relationships. We reviewed the literature and summarised the effects of forest harvest and management on the ecology of moose. Greater than 50 years of scientific studies document both positive and negative effects of forest harvest and associated activities such as silviculture and road building. Moose require spatially adjacent patches of younger plant communities for forage and older forests for thermal and security cover. Extensive and rapid forest harvest can result in the prevalence of young forest with a corresponding reduction in the fitness of moose populations. A warming climate likely will exacerbate the negative effects associated with the broad-scale removal of forest cover. Resource roads can create edge habitat that may serve as forage, but those features result in increased hunting and collisions with vehicles and facilitate the movement of predators. Post-harvest silviculture, including the application of herbicides, can create stand conditions that provide very little or low-quality forage. The ecological and societal benefits of moose are dependent on forest management that provides a mix of old and young forest, employs silviculture that retains adequate cover and forage plants, and minimises the development of roads.
As global conservation actions become more urgent, informed decision-making requires robust analyses of the costs and benefits of policy options, based on available evidence. Recovery planning for threatened or endangered species must assume a cause-and-effect relationship between proposed management interventions and population responses. However, a significant portion of current knowledge about threatened or endangered species is derived from observational studies because experiments that fully meet random and controlled design criteria are largely infeasible or unethical. Large-scale field experiments are becoming more common, yet the greater uncertainty generated by what remain fundamentally observational studies can lead researchers to weak inferences about causal mechanisms, creating debate and confusion among decision-makers, planners and stakeholders. This has been an acute problem facing conservationists and governments as they struggle with the successful recovery of species in decline. In other domains where experimental evidence is difficult to collect, causal modelling has been adopted to identify causal relationships from observational data, based on a set of strong assumptions and identification rules. In Canada, significant and ongoing efforts have had limited success in reversing the population decline of woodland caribou (Rangifer tarandus caribou). We examine the scientific framework for woodland caribou recovery efforts through the lens of causal modelling, highlighting feasible steps that could be taken to improve the rigour of causal inferences.
Woodland caribou is a Threatened or Endangered subspecies across much of Canada. In many cases, these caribou are declining because of human‐mediated predation in the form of apparent competition. Provincial and federal agencies have employed a number of conservation actions to arrest the decline, but insufficient time and limited replication make it difficult to test the efficacy of those activities. We built a three‐species population model that served as a tool to integrate current knowledge, explore uncertainties, and assess activities focused on the recovery of caribou. We applied the model to interconnected populations of caribou, moose, and wolves at two locations in Canada (Chinchaga [British Columbia], Charlevoix [Québec]) and explored the efficacy of conservation actions unique to each population: predator control, restoration of linear features, reduction of habitat for moose, supplementation, maternal pens, and predator exclosures. Results confirmed that caribou at these two locations faced different recovery challenges, dictated by specific population dynamics and threats. Wolf predation, enhanced by seismic lines and resource roads, was responsible for the decline of the simulated Chinchaga population. The most cost‐effective recovery actions for that population were long‐term lethal wolf control (λ1–50 = 1.014, 170,767/caribou), and the aggressive restoration of linear features (λ1–50 = 1.002, 148,473/caribou). Short‐term population supplementation provided only a temporary increase in abundance (λ1–50 = 0.994, $62,143/caribou). The model was limited by ecological and data uncertainties, but served as an effective platform for representing and testing our understanding of the complex interspecific interactions that underlie the recovery of woodland caribou.
Over the past decade, declines of Canadian populations of boreal caribou (Rangifer tarandus caribou) have received considerable attention from scientists, government agencies, environmental nongovernmental organizations, Indigenous communities, and the forest industry. Boreal caribou (also known as boreal woodland caribou) was listed as a threatened species in Canada when the Species at Risk Act came into force in June 2003. Many boreal caribou populations have been shown to be decreasing, in some cases precipitously, and empirical evidence from adult survival and calf recruitment surveys indicates that the cumulative effect of habitat disturbance, including that which results from industrial development, is a key driver in the decline. Yet, as scientific understanding of the decline has become clearer, and agreement among scientists and governments about habitat management requirements has increased, campaigns of denial have intensified in the public sphere. In this paper, we examine parallels with climate change rhetoric prolific in the 2000s and show that willful ignorance disguised as skepticism has resulted in public uncertainty despite robust scientific evidence. We show how these strategies of manufactured uncertainty used in climate change denial campaigns have seeped into wildlife management debates, with pernicious results. In this case, it has successfully delayed efforts to effectively address the decline of boreal caribou, which is protected under federal, provincial, and territorial legislation, and inhibited meaningful dialogue about socially acceptable conservation solutions. © 2018 The Wildlife Society.
Trophic interactions in multiprey systems can be largely determined by prey distributions. Yet, classic predator-prey models assume spatially homogeneous interactions between predators and prey. We developed a spatially informed theory that predicts how habitat heterogeneity alters the landscape-scale distribution of mortality risk of prey from predation, and hence the nature of predator interactions in multiprey systems. The theoretical model is a spatially explicit, multiprey functional response in which species-specific advection-diffusion models account for the response of individual prey to habitat edges. The model demonstrates that distinct responses of alternative prey species can alter the consequences of conspecific aggregation, from increasing safety to increasing predation risk. Observations of threatened boreal caribou, moose and grey wolf interacting over 378 181 km(2) of human-managed boreal forest support this principle. This empirically supported theory demonstrates how distinct responses of apparent competitors to landscape heterogeneity, including to human disturbances, can reverse density dependence in fitness correlates.
© 2015 The Author(s).
Ecological theory predicts that the intensity of antipredator responses is dependent upon the spatiotemporal context of predation risk (the risk allocation hypothesis). However, most studies to date have been conducted over small spatial extents, and did not fully take into account gradual responses to predator proximity. We simultaneously collected spatially explicit data on predator and prey to investigate acute responses of a threatened forest ungulate, the boreal caribou (Rangifer tarandus), to the spatiotemporal dynamics of wolf (Canis lupus) distribution during spring. Movement analysis of GPS-collared individuals from both species revealed high plasticity in habitat-selection decisions of caribou. Female caribou avoided open areas and deciduous forests and moved relatively fast and toward foraging areas when wolves were closer than 2.5 km. Caribou also avoided food-rich areas only when wolves were within 1 km. Our results bridge the gap between long-term perceived risk and immediate flight responses by revealing dynamic antipredator tactics in response to predator proximity.
Modern ecological research often involves the comparison of the usage of habitat types or food items to the availability of those resources to the animal. Widely used methods of determining preference from measurements of usage and availability depend critically on the array of components that the researcher, often with a degree of arbitrariness, deems available to the animal. This paper proposes a new method, based on ranks of components by usage and by availability. A virtue of the rank procedure is that it provides comparable results whether a questionable component is included or excluded from consideration. Statistical tests of significance are given for the method. The paper also offers a hierarchical ordering of selection processes. This hierarchy resolves certain inconsistencies among studies of selection and is compatible with the analytic technique offered in this paper.
Habitat connectivity influences the distribution dynamics of animals. Connec-
tivity can therefore shape trophic interactions, but little empirical evidence is available, especially for large mammals. In forest ecosystems, logging alters functional connectivity among habitat patches, and such activities can affect the spatial game between large herbivores and their predators. We used graph theory to evaluate how harvesting-induced changes in habitat connectivity influence patch choice and residency time of GPS-collared caribou (Rangifer tarandus caribou) and moose (Alces alces) in winter in the boreal forest. We then investigated the predator–prey game by assessing how GPS-collared wolves (Canis lupus) adjusted their movements to changes in landscape properties and in the networks of their prey species. We built prey habitat networks using minimum planar graphs organized around species-specific, highly selected habitat patches (i.e., network nodes). We found that spatial dynamics of large herbivores were influenced not only by the intrinsic quality of habitat patches, but also by the connectivity of those network nodes. Caribou and moose selected nodes that were connected by a high number of links, and moose also spent relatively more time in those nodes. By limiting node accessibility, human disturbances influenced travel decisions. Caribou and moose avoided nodes that were surrounded by a high proportion of cuts and roads, but once within these nodes, moose stayed longer than in other nodes. Caribou selectively moved among nodes with low distance costs, and their residency time increased with distance costs required to reach the nodes. Wolves selected their prey’s nodes, where vegetation consumed by caribou and moose was highly abundant. Furthermore, wolves discriminated among those nodes by selecting the most connected ones. In fact, selection by wolves was stronger for their prey’s nodes than for the prey’s utilization distribution per se, a difference that increased with the level of human disturbance. Considering the difficulty of keeping track of highly mobile prey, predators may benefit by targeting not only their prey’s resource patches, but also the most highly connected patches. Matrix quality and connectivity are therefore key elements shaping the predator–prey spatial game in human-altered landscapes because of their impact on the spatial dynamics of the interacting species.
AimGlobal patterns in primary productivity in natural ecosystems are important for interpreting ecological processes and patterns of biodiversity. Net primary productivity (NPP) on land has long been thought to be greatest in tropical forests and to decrease towards the poles. However, it has recently been claimed that the NPP of mid-latitude forests is as great as, or even greater than, that of tropical forests and that ecologically relevant productivity peaks at mid-latitudes. Here we evaluate these hypotheses by testing for relationships between latitude and productivity using a range of forest productivity datasets.LocationGlobal.Methods
We apply ordinary least squares regression and t-test analyses to published latitude–productivity data for forests, specifically updated to include an expanded dataset for the previously data-poor tropics, and we evaluate the relationship between the primary productivity of forests and modelled vascular plant species richness.ResultsContrary to the recent claims, we found strong support for a negative relationship between latitude and annual NPP of forests with all datasets, and NPP was significantly greater in tropical forests than in temperate forests. Vascular plant richness was positively correlated with NPP.Main conclusionsNPP of forests increases towards the equator. Given that species richness also increases towards the equator, and that vascular plant richness correlates with NPP, these results are consistent with recent meta-analyses showing that the relationships between productivity and species richness of both plants and animals in natural ecosystems are predominantly positive. These results are congruent with ecological theories that predict a positive relationship between species richness and productivity, and they indicate that there is no need to explain peaked richness–productivity relationships over broad spatial extents, since they do not appear to exist.
The hypothesis that the regular multiannual population oscillations of boreal and arctic small rodents (voles and lemmings) are driven by predation is as old as the scientific study of rodent cycles itself. Subsequently, for several decades, the predation hypothesis fell into disrepute, possibly because the views about predation and rodent dy-namics were too simplistic. Here we review the work that has been done on the predation hypothesis primarily in Fennoscandia over the past decade. Models of predator–prey interaction have been constructed for the least weasel (Mustela nivalis) and the field vole (Microtus agrestis), which are considered to be the key specialist predator and the key prey species in the multispecies communities in the boreal forest region in Fennoscandia. The basic model has been parameterized with independent field data, and it predicts well the main features of the observed dynamics. An extension of the model also including generalist and nomadic avian predators predicts correctly the well-documented and striking geographic gradient in rodent oscillations in Fennoscandia, with the amplitude and cycle period decreasing from north to south. These geographic changes are attributed to the observed latitudinal change in the density of generalist and nomadic predators, which are expected to have a stabilizing effect on rodent dynamics. We review the other observational, modeling, and experimental results bearing on the predation hypothesis and conclude that it accounts well for the broad patterns in rodent oscillations in Fennoscandia. We discuss the application of the predation hypothesis to other regions in the northern hemisphere. The predation hypothesis does not make predictions about multiannual and latitudinal changes in body size, behavior, and demography of ro-dents, which may have some population-dynamic consequences. With the current evidence, however, we consider it unlikely that the phenotypic and genotypic composition of pop-ulations would be instrumental for generating the broad patterns in rodent oscillations. of predator–prey interaction; mus-telid; population oscillation of small rodents; predation hypothesis for population cycles; predator– prey theory; predators, specialists vs. generalists; rodent cycle.
Understory regeneration within canopy gaps in old-growth boreal forests may provide suitable habitat for wildlife typically associated with early-seral stages, leading to an increase in their abundance in late succession. We surveyed a chronosequence of postfire (17–265 years) and postharvest (3–63 years) stands in Canada’s eastern boreal forest to determine whether snowshoe hares (Lepus americanus Erxleben, 1777) followed a bimodal abundance distribution with stand age that reflects changes in food and cover during postdisturbance succession. A strong peak in relative hare abundance occurred during the first 80 years of succession, with highest faecal pellet densities observed between 40 and 50 years after disturbance. Changes in hare abundance during this period were similar among fire- and clearcut-origin stands and closely tracked changes in lateral cover and vertical cover. Pellet density increased again in stands >180 years. Variation in hare abundance during late succession was partially mediated by gap dynamics, with highest pellet densities in stands occupied by an intermediate proportion of mortality-origin canopy gaps. Hares thus undergo rapid changes in abundance during early succession followed by a much longer period of subtle changes in density as stands develop old-growth structure. Shifting forest age-class distribution induced by forest management could therefore significantly alter regional spatiotemporal dynamics of snowshoe hares.
Mountain caribou are an endangered ecotype of woodland caribou (Rangifer tarandus caribou) that historically occurred throughout the high snowfall regions of southeast British Columbia and the northwestern United States. The decline in caribou is thought to be due to apparent competition where increases in early-seral conditions stimulate a numerical response in primary ungulate prey and their predators and these incidentally kill an unsustainable number of caribou. Based on the known location of death of 207 radio collared animals, we tested hypotheses pertaining to relationships between landscape composition and predator-specific mortality of mountain caribou at 2 ecologically based spatial scales. Relative to landscape conditions within subpopulation boundaries (level 1) or within home ranges (level 2), caribou were at greater risk of predation at low elevations particularly within otherwise complex terrain (i.e., valleys) with more variation in overstory canopy closure and greater road densities. Caribou vulnerability to bears was also positively related to the variation in overstory age. Cougar predation was not related to roads or terrain complexity but occurred more often in landscapes with warmer aspects and greater proportions of stands of <120 years. Wolf predation occurred primarily at low elevations at the broader scale and in association with roads at the finer scale. Our results indicate that caribou vulnerability to predation was a function of both static (e.g., terrain) and dynamic (e.g., overstory conditions) factors, but we did not find evidence that localized habitat fragmentation due to forest harvest influenced predation on caribou. This result is not inconsistent with the apparent competition hypothesis but suggests that habitat change largely functions at broader spatial scales involving landscapes that can be beyond those occupied by caribou, including the winter ranges of primary ungulate prey. These changes and the season-dependent dispersion of other ungulates and their predators may largely influence mortality risk to mountain caribou. Although roads and forest fragmentation are interrelated, roads may further contribute to caribou predation by increasing the efficiency of movement of some predators and thereby increasing encounter rates with caribou.
Predation has long been implicated as a major selective force in the evolution of several morphological and behavioral characteristics of animals. The importance of predation during evolutionary time is clear, but growing evidence suggests that animals also have the ability to assess and behaviorally influence their risk of being preyed upon in ecological time (i.e., during their lifetime). We develop an abstraction of the predation process in which several components of predation risk are identified. A review of the literature indicates that an animal's ability to assess and behaviorally control one or more of these components strongly influences decision making in feeding animals, as well as in animals deciding when and how to escape predators, when and how to be social, or even, for fishes, when and how to breathe air. This review also reveals that such decision making reflects apparent trade-offs between the risk of predation and the benefits to be gained from engaging in a given activity. Despite this body of evidence, several areas in the study of animal behavior have received little or no attention from a predation perspective. We identify several such areas, the most important of which is that dealing with animal reproduction. Much work also remains regarding the precise nature of the risk of predation and how it is actually perceived by animals, and the extent to which they can behaviorally control their risk of predation. Mathematical models will likely play a major role in future work, and we suggest that modelers strive to consider the potential complexity in behavioral responses to predation risk. Overall, since virtually every animal is potential prey for others, research that seriously considers the influence of predation risk will provide significant insight into the nature of animal behavior.
Population increases of primary prey can negatively impact alternate prey populations via demographic and behavioural responses of a shared predator through apparent competition. Seasonal variation in prey selection patterns by predators also can affect secondary and incidental prey by reducing spatial separation. Global warming and landscape changes in Alberta's bitumen sands have resulted in prey enrichment, which is changing the large mammal predator–prey system and causing declines in woodland caribou Rangifer tarandus caribou populations. We assessed seasonal patterns of prey use and spatial selection by wolves Canis lupus in two woodland caribou ranges in northeastern Alberta, Canada, that have undergone prey enrichment following recent white-tailed deer Odocoileus virginianus invasion. We determined whether risk of predation for caribou (incidental prey) and the proportion of wolf-caused-caribou mortalities varied with season. We found that wolves showed seasonal variation in primary prey use, with deer and beaver Castor canadensis being the most common prey items in wolf diet in winter and summer, respectively. These seasonal dietary patterns were reflected in seasonal wolf spatial resource selection and resulted in contrasting spatial relationships between wolves and caribou. During winter, wolf selection for areas used by deer maintained strong spatial separation between wolves and caribou, whereas wolf selection for areas used by beaver in summer increased the overlap with caribou. Changing patterns in wolf resource selection were reflected by caribou mortality patterns, with 76.2% of 42 adult female caribou mortalities occurring in summer. Understanding seasonal patterns of predation following prey enrichment in a multiprey system is essential when assessing the effect of predation on an incidental prey species. Our results support the conclusion that wolves are proximately responsible for woodland caribou population declines throughout much of their range.
Habitat selection strategies translate into movement tactics, which reckon with the predator–prey spatial game. Strategic habitat selection analysis can therefore illuminate behavioural games. Cover types at potential encounter sites (i.e. intersections between movement paths of predator and prey) can be compared with cover types available (i) within the area of home‐range‐overlap ( HRO ) between predator and prey; and (ii) along the path ( MP ) of each species. Unlike the HRO scale, cover‐type availability at MP scale differs between interacting species due to species‐specific movement decisions. Scale differences in selection could therefore inform on divergences in fitness rewarding actions between predators and prey.
We used this framework to evaluate the spatial game between GPS ‐collared wolves ( C anis lupus ) versus caribou ( R angifer tarandus ), and wolf versus moose ( A lces alces ).
Changes in cover‐type availability between HRO and MP revealed differences in how each species fine‐tuned its movements to habitat features. In contrast to caribou, wolves increased their encounter rate with regenerating cuts along their paths ( MP ) relative to the HRO level. As a consequence, wolves were less likely to cross caribou paths in areas with higher percentage of regenerating cuts than expected based on the availability along their paths, whereas caribou had a higher risk of intersecting wolf paths by crossing these areas, relative to random expectation along their paths. Unlike for caribou, availability of mixed and deciduous areas decreased from HRO to MP level for wolves and moose. Overall, wolves displayed stronger similarities in movement decisions with moose than with caribou, thereby revealing the focus of wolves on moose.
Our study reveals how differences in fine‐scale movement tactics between species create asymmetric relative encounter probabilities between predators and prey, given their paths. Increase in relative risk of encounter for prey and decrease for predators associated with specific cover types emerging from HRO to MP scale analysis can disclose potential weaknesses in current movement tactics involved the predator–prey game, such as caribou use of cutovers in summer–autumn. In turn, these weaknesses can inform on subsequent changes in habitat selection tactics that might arise due to evolutionary forces.
Apparent competition is an indirect interaction between 2 or more prey species through a shared predator, and it is increasingly recognized as a mechanism of the decline and extinction of many species. Through case studies, we evaluated the effectiveness of 4 management strategies for species affected by apparent competition: predator control, reduction in the abundances of alternate prey, simultaneous control of predators and alternate prey, and no active management of predators or alternate prey. Solely reducing predator abundances rapidly increased abundances of alternate and rare prey, but observed increases are likely short-lived due to fast increases in predator abundance following the cessation of control efforts. Substantial reductions of an abundant alternate prey resulted in increased predation on endangered huemul (Hippocamelus bisulcus) deer in Chilean Patagonia, which highlights potential risks associated with solely reducing alternate prey species. Simultaneous removal of predators and alternate prey increased survival of island foxes (Urocyon littoralis) in California (U.S.A.) above a threshold required for population recovery. In the absence of active management, populations of rare woodland caribou (Rangifer tarandus caribou) continued to decline in British Columbia, Canada. On the basis of the cases we examined, we suggest the simultaneous control of predators and alternate prey is the management strategy most likely to increase abundances and probabilities of persistence of rare prey over the long term. Knowing the mechanisms driving changes in species' abundances before implementing any management intervention is critical. We suggest scientists can best contribute to the conservation of species affected by apparent competition by clearly communicating the biological and demographic forces at play to policy makers responsible for the implementation of proposed management actions.
It has been long established that the richness of vascular plant species and many animal taxa decreases with increasing latitude, a pattern that very generally follows declines in actual and potential evapotranspiration, solar radiation, temperature, and thus, total productivity. Using county-level data on vascular plants from the United States (3000 counties in the conterminous 48 states), we used the Akaike Information Criterion (AIC) to evaluate competing models predicting native and nonnative plant species density (number of species per square kilometer in a county) from various combinations of biotic variables (e.g., native bird species density, vegetation carbon, normalized difference vegetation in-dex), environmental/topographic variables (elevation, variation in elevation, the number of land cover classes in the county, radiation, mean precipitation, actual evapotranspiration, and potential evapotranspiration), and human variables (human population density, crop-land, and percentage of disturbed lands in a county). We found no evidence of a latitudinal gradient for the density of native plant species and a significant, slightly positive latitudinal gradient for the density of nonnative plant species. We found stronger evidence of a sig-nificant, positive productivity gradient (vegetation carbon) for the density of native plant species and nonnative plant species. We found much stronger significant relationships when biotic, environmental/topographic, and human variables were used to predict native plant species density and nonnative plant species density. Biotic variables generally had far greater influence in multivariate models than human or environmental/topographic variables. Later, we found that the best, single, positive predictor of the density of nonnative plant species in a county was the density of native plant species in a county. While further study is needed, it may be that, while humans facilitate the initial establishment invasions of non-native plant species, the spread and subsequent distributions of nonnative species are con-trolled largely by biotic and environmental factors.
We investigated whether woodland caribou (Rangifer tarandus caribou) would remain in a 2772km² area in eastern Quebec where the forest management plan included the preservation of large forest blocks (35182km²) linked with>400 m wide corridors and where cuts were amalgamated in large zones. To evaluate changes in caribou abundance and habitat selection, we conducted five aerial surveys and followed by telemetry 13 to 22 female caribou each year, from March 1998 to March 2005. Caribou numbers declined by 59% between 1999 and 2001 but gradually recovered to initial abundance. Female survival increased from 73.3% in 1999 to 87.3%93.4% in 2004 and 2005. Caribou selected protected blocks, used corridors in proportion to their availability, and avoided logged areas. They preferred closed conifer stands without terrestrial lichens and open conifer stands with or without terrestrial lichens throughout the study. Open habitats (clearcuts and burns), regenerating sites, mixed and deciduous stands, and water bodies were avoided. The main zones used by caribou gradually shifted towards the southwest of the study area, likely as a result of disturbance and habitat loss due to logging of mature conifers in the east. We conclude that caribou numbers were maintained within the managed area as a result of the presence of protected blocks and uncut continuous forest.
Habitat alteration by humans may change the supply of food and cover for wild ungulates, but few studies have examined how these resources are utilised over time by individuals of different sex and reproductive status. We examined circadian and seasonal variation in habitat utilisation within a moose Alces alces population in central Norway. Our study area covers forests and open habitats, both influenced by human alterations (e.g. forestry and agriculture). We expected moose to select habitats with good forage and cover in all seasons, but to select open foraging habitats mainly during night-time. Moose selected good foraging habitats, such as young forest stands and cultivated land during night, whereas the utilisation of older forest stands providing cover increased during daytime. This circadian pattern changed throughout the year, seemingly related to variation in hours of daylight and provision of forage. Young forest stands provided higher density of preferred food plants compared to older stands and were highly selected from spring until autumn. Relative to young forest, the selection for older forest stands increased towards winter, likely due to provision of higher plant quality late in the growing season, and to reduced accumulation of movement-impeding snow during winter. Selection of cultivated land varied among seasons, being highest when crop biomass was high. We also found some indications of state-dependent habitat selection as reproducing females avoided open, food rich areas in the first months after their calves were born, whereas males and females without young selected these areas in spring and summer. Our results clearly show that moose exploit the variations in cover and food caused by forestry and agriculture. This is particularly relevant for moose in Norway as current changes in forestry practice lead to a reduction in young, food-rich forest stands, possibly aggravating the already declining body conditions and recruitment rates of moose.
The functional response of a predator to changing prey density is an important determinant of stability of predator–prey systems. We show how Manly's selection indices can be used to distinguish between hyperbolic and sigmoidal models of a predator functional response to primary prey density in the presence of alternative prey. Specifically, an inverse relationship between prey density and preference for that prey results in a hyperbolic func-tional response while a positive relationship can yield either a hyperbolic or sigmoidal func-tional response, depending on the form and relative magnitudes of the density-dependent preference model, attack rate, and handling time. As an example, we examine wolf (Canis lupus) functional response to moose (Alces alces) density in the presence of caribou (Rangifer tarandus). The use of selection indices to evaluate the form of the functional response has significant advantages over previous attempts to fit Holling's functional response curves to killing-rate data directly, including increased sensitivity, use of relatively easily collected data, and consideration of other explanatory factors (e.g., weather, seasons, productivity).
Experimental evidence of trophic cascades initiated by large vertebrate pred-ators is rare in terrestrial ecosystems. A serendipitous natural experiment provided an opportunity to test the trophic cascade hypothesis for wolves (Canis lupus) in Banff National Park, Canada. The first wolf pack recolonized the Bow Valley of Banff National Park in 1986. High human activity partially excluded wolves from one area of the Bow Valley (low-wolf area), whereas wolves made full use of an adjacent area (high-wolf area). We investigated the effects of differential wolf predation between these two areas on elk (Cervus elaphus) population density, adult female survival, and calf recruitment; aspen (Populus tremuloides) recruitment and browse intensity; willow (Salix spp.) production, browsing intensity, and net growth; beaver (Castor canadensis) density; and riparian songbird di-versity, evenness, and abundance. We compared effects of recolonizing wolves on these response variables using the log response ratio between the low-wolf and high-wolf treat-ments. Elk population density diverged over time in the two treatments, such that elk were an order of magnitude more numerous in the low-wolf area compared to the high-wolf area at the end of the study. Annual survival of adult female elk was 62% in the high-wolf area vs. 89% in the low-wolf area. Annual recruitment of calves was 15% in the high-wolf area vs. 27% without wolves. Wolf exclusion decreased aspen recruitment, willow production, and increased willow and aspen browsing intensity. Beaver lodge density was negatively correlated to elk density, and elk herbivory had an indirect negative effect on riparian songbird diversity and abundance. These alternating patterns across trophic levels support the wolf-caused trophic cascade hypothesis. Human activity strongly mediated these cascade effects, through a depressing effect on habitat use by wolves. Thus, conservation strategies based on the trophic importance of large carnivores have increased support in terrestrial ecosystems.
American black bears (Ursus americanus) and brown bears (U. arctos) can be important predators on neonatal ungulates. They prey less commonly on adult ungulates. Bear predation appears to be additive at low ungulate densities and may become compensatory as prey density approaches carrying capacity, K. As such, black and brown bear predation can limit, but generally does not regulate, ungulate populations. Maternal and neonatal physical condition, birth synchrony, and birth mass may predispose neonates to predation or other mortality factors. Though black and brown bear predation is an important proximate cause of ungulate neonatal mortality, habitat quality and quantity are important ultimate factors influencing this dynamic. Manipulating bear populations to enhance ungulate populations may be successful in the short-term if predation is additive, but long-term success has not been demonstrated.
Introduced species can compete with, prey upon or transmit disease to native forms, resulting in devastation of indigenous communities. A more subtle but equally severe effect of exotic species is as a supplemental food source for predators that allows them to increase in abundance and then overexploit native prey species. Here we show that the introduction of feral pigs (Sus scrofa) to the California Channel Islands has sustained an unnaturally large breeding population of golden eagles (Aquila chrysaetos), a native predator. The resulting increase in predation on the island fox (Urocyon littoralis) has caused the near extirpation of three subspecies of this endemic carnivore. Foxes evolved on the islands over the past 20,000 years, pigs were introduced in the 1850s and golden eagles, historically, were only transient visitors. Although these three species have been sympatric for the past 150 years, this predator-prey interaction is a recent phenomenon, occurring within the last decade. We hypothesize that this interaction ultimately stems from human-induced perturbations to the island, mainland and surrounding marine environments.
To address the central question of how climate change influences tree growth within the context of global warming, we used dendroclimatological analysis to understand the reactions of four major boreal tree species –Populus tremuloides, Betula papyrifera, Picea mariana, and Pinus banksiana– to climatic variations along a broad latitudinal gradient from 46 to 54°N in the eastern Canadian boreal forest. Tree-ring chronologies from 34 forested stands distributed at a 1° interval were built, transformed into principal components (PCs), and analyzed through bootstrapped correlation analysis over the period 1950–2003 to identify climate factors limiting the radial growth and the detailed radial growth–climate association along the gradient. All species taken together, previous summer temperature (negative influences), and current January and March–April temperatures (positive influences) showed the most consistent relationships with radial growth across the gradient. Combined with the identified species/site-specific climate factors, our study suggested that moisture conditions during the year before radial growth played a dominant role in positively regulating P. tremuloides growth, whereas January temperature and growing season moisture conditions positively impacted growth of B. papyrifera. Both P. mariana and P. banksiana were positively affected by the current-year winter and spring or whole growing season temperatures over the entire range of our corridor. Owing to the impacts of different climate factors on growth, these boreal species showed inconsistent responsiveness to recent warming at the transition zone, where B. papyrifera, P. mariana, and P. banksiana would be the most responsive species, whereas P. tremuloides might be the least. Under continued warming, B. papyrifera stands located north of 49°N, P. tremuloides at northern latitudes, and P. mariana and P. banksiana stands located north of 47°N might benefit from warming winter and spring temperatures to enhance their radial growth in the coming decades, whereas other southern stands might be decreasing in radial growth.
Various management plans have been developed to mitigate the effects of human activities on threatened woodland caribou (Rangifer tarandus caribou) populations. Most plans do not account for the behavior of wolves (Canis lupus), their main predator. The success of caribou recovery plans may nonetheless depend on how landscape management shapes wolf-caribou
interactions. We evaluated the species-specific responses of caribou and wolves to a management plan in Québec, and assessed
its impact on the probability of wolf-caribou co-occurrence. Landscape management consisted of the protection of large forest
blocks, and the spatial aggregation of cutblocks. Based on telemetry data, we modeled animal-habitat spatial relationships
with resource selection functions, and then estimate the relative probability of wolf-caribou co-occurrence. We found that
caribou selected mature conifer forests with lichen. Wolves selected mixed and deciduous stands. Caribou avoided roads and
cutblocks, while wolves selected them, which resulted in a relatively low probability of co-occurrence in harvested areas.
Concurrent habitat selection by the two species was such that the highest probability of wolf-caribou co-occurrence took place
in protected forest blocks (PB) from December to May. For efficient mitigation measures, the location of PBs should be selected
while accounting for differences in habitat selection between wolf and caribou. The blocks should include mature conifer forests
with lichen, minimize the abundance of mixed and deciduous stands, and be far from roads and cutblocks. Consideration of predator
behavior can improve suitability of landscape management plans for the long-term persistence of threatened prey populations
under top-down control.
Forest harvesting involves the creation of roads and cutblocks, both of which can influence animal habitat use. We evaluated
the cumulative effects of forestry on habitat selection by six packs of gray wolf (Canis lupus) widely distributed in Quebec’s boreal forest. Resource selection functions were used to evaluate cumulative effects at two
levels. First, we studied how the response of wolves to roads and cutblocks varied within their home range (HR level) as a
function of the local abundance of these habitat features. Second, we assessed whether differences in the response to roads
and cutblocks observed among packs (inter-HR level) could be explained by variations in their average abundance among individual
home ranges. At the HR level, we found that cumulative effects shaped habitat selection of wolves, and the nature of the effects
varied during the year. For example, we detected a decrease in the selection of roads following an increase in local road
density during the rendez-vous and the nomadic periods, but not during the denning period. At the inter-HR level, we found
a functional response to logging activity only during the denning period. Packs with home ranges characterized by a larger
proportion of recent cutblocks selected these cutblocks more strongly. We conclude that cumulative effects of logging activities
occur at multiple levels, and these effects can have profound effects on habitat use by wolves, thereby influencing spatial
predator–prey dynamics. Wildlife conservation and management in boreal ecosystems should thus account for cumulative impacts
of anthropogenic features on animal distribution.
KeywordsCutblocks-Cumulative effects-Habitat selection-Forestry-Mixed effects logistic regression-Predators-Roads-Resource selection functions-Wolves
1.The selection for particular habitat patches can vary as a function of local and regional levels of anthropogenic disturbance. Although such functional responses can better reveal habitat loss for species of precarious status faced with dwindling resources, they remain rarely used in conservation planning. We show that functional responses can occur at multiple levels, even as nested hierarchies, and that they can explain the plasticity in habitat selection observed in threatened forest-dwelling caribou Rangifer tarandus caribou, within and among home-ranges. 2.Twenty-seven caribou were followed with global positioning system collars between 2005 and 2010. Generalized linear mixed models served as the basis from which we built multi-level functional responses characterizing how caribou alter their selection for closed-canopy conifer forests, depending upon the availability of these forests and the amount of cutovers and roads. 3.Caribou increased their selection for closed-canopy conifer forests in areas of their home-range that were comprised of a high proportion of recent cutovers during calving and summer and of high closed-canopy conifer forests during winter. Also, caribou that were established in highly disturbed areas displayed an overall stronger selection for conifer forests. These individuals further adjusted their selection for conifer forests in areas of their home-ranges that were largely comprised of recent cutovers. This concurrent response to local and global anthropogenic disturbances provides evidence of nested-hierarchical functional responses. 4.Synthesis and applications. Reliable characterization of disturbance effects on animals is necessary for conservation planning. Multi-level functional responses can accurately describe animal distribution, and we provided a framework for modelling these responses. Our multi-level functional responses indicate that fixing habitat requirements based on patterns of habitat selection for the average amount of disturbance can be misleading because it overlooks plasticity in the response of animals to habitat heterogeneity. For example, selection of closed-canopy conifer forests by caribou generally became stronger with increasing disturbance levels. Anthropogenic disturbance thus could not only lead to the functional loss of residual habitat, but it can also increase the 'relative value' of residual patches. Our study provides a tool for more thorough assessments of spatial variation in the attractiveness of resource patches and, presumably, in the fitness benefits. © 2012 The Authors. Journal of Applied Ecology
In northeastern Alberta, Canada, continued expansion of the oil and gas industry along with timber harvesting has raised concerns that the resulting environmental changes may negatively affect the woodland caribou (Rangifer tarandus caribou) population in this region. Caribou are a threatened species in Alberta, and populations in northeastern Alberta appear to be stable or slightly decreasing. The spatial distribution of caribou in relation to alternative prey (commonly moose [Alces alces]) has been hypothesized to affect the level of wolf (Canis lupus) predation on caribou populations. We monitored radiomarked caribou, moose, and wolves between 1993 and 1997, and we found that selection of fen/bog complexes by caribou and selection of well-drained habitats by moose and wolves resulted in spatial separation. This spatial separation in turn reduced wolf predation pressure on caribou but did not provide a total refuge from wolves. Any management activities that increase the density of moose and wolves or increase access of wolves into fen/bog complexes will likely reduce the refuge effect provided by large fen/bog complexes.
With the intensification of human activities, preserving animal populations is a contemporary challenge of critical importance. In this context, the umbrella species concept is appealing because preserving a single species should result in the protection of multiple co-occurring species. Practitioners, though, face the task of having to find suitable umbrellas to develop single-species management guidelines. In North America, boreal forests must be managed to facilitate the recovery of the threatened boreal caribou (Rangifer tarandus). Yet, the effect of caribou conservation on co-occurring animal species remains poorly documented. We tested if boreal caribou can constitute an effective umbrella for boreal fauna. Birds, small mammals, and insects were sampled along gradients of post-harvest and post-fire forest succession. Predictive models of occupancy were developed from the responses of 95 species to characteristics of forest stands and their surroundings. We then assessed the similarity of species occupancy expected between simulated harvested landscapes and a 90 000-km2 uncut landscape. Managed landscapes were simulated based on three levels of disturbance, two timber-harvest rotation cycles, and dispersed or aggregated cut-blocks. We found that management guidelines that were more likely to maintain caribou populations should also better preserve animal assemblages. Relative to fragmentation or harvest cycle, we detected a stronger effect of habitat loss on species assemblages. Disturbing 22%, 35%, and 45% of the landscape should result, respectively, in 80%, 60%, and 40% probability for caribou populations to be sustainable; in turn, this should result in regional species assemblages with Jaccard similarity indices of 0.86, 0.79, and 0.74, respectively, relative to the uncut landscape. Our study thus demonstrates the value of single-species management for animal conservation. Our quantitative approach allows for the evaluation of management guidelines prior to implementation, thereby providing a tool for establishing suitable compromises between economic and environmental sustainability of human activities.
Functional responses in habitat selection occur when individuals adjust their selection of habitat features as a function of the availability of those features. Functional responses in habitat selection are generally assumed to be fitness‐rewarding tactics and are used to guide conservation actions. Fitness consequences of functional responses, however, have rarely been evaluated.
Eighty‐three caribou were followed with GPS collars to establish the link between functional responses in habitat selection and adult female survival, a strong fitness correlate for caribou. We measured how caribou avoidance of mixed/deciduous stands and 6‐ to 20‐year‐old clear‐cuts varied with the proportion of 6‐ to 20‐year‐old clear‐cuts within their 100% minimal convex polygon ( MCP ), and if these functional responses were linked to survival. Mixed/deciduous stands and 6‐ to 20‐year‐old clear‐cuts are risky for caribou because they are selected by moose, thereby attracting wolves and increasing predation risk for caribou.
Caribou avoided mixed/deciduous stands, especially when 6‐ to 20‐year‐old clear‐cuts comprised a large proportion of their MCP , but this functional response did not differ between caribou that died and those that survived. When the proportion of 6‐to 20‐year‐old clear‐cuts in the MCP was low, caribou generally had low odds of occurring near 6‐ to 20‐year‐old clear‐cuts. However, when the proportion of clear‐cuts in the MCP was relatively high, caribou that strongly increased their odds of being near 6‐ to 20‐year‐old clear‐cuts were generally those that died.
Synthesis and applications . Assessing the fitness consequences of how animals respond to habitat disturbances is central to wildlife conservation. We demonstrate that distinct functional responses in habitat selection involve different mortality risks and that population dynamics should depend on the frequency of the different tactics observed within populations. Individuals that persistently select riskier areas should be important drivers of population decline. Caribou mortality could be reduced by decreasing the appeal of 6‐ to 20‐year‐old clear‐cuts for moose by removing deciduous vegetation through cleaning, which should reduce the selection of wolves for these stands. Removing deciduous vegetation should be especially effective in areas where those clear‐cuts comprise a large proportion of the landscape, because this is where a subset of the caribou population experiences high mortality rates by selecting 6‐ to 20‐year‐old clear‐cuts.
Winter aerial surveys of moose (Alces alces) were completed on 14 landscapes (10– 256 km 2) formed of aggregated black spruce (Picea mariana) clear-cuts logged 3–9 years ago in southcentral Québec. Moose were present in 8 landscapes (11 yards) and had a mean density of 0.20 moose/10 km 2 , which was 50% of the density observed in the same hunting zone with a similar forest composition. Based on previous work, effects of variability in hunting pressure and time since cutting were assumed not to influence distribution and abundance of moose. Browse density did not increase with age of cuts. Moose density was not related to the size of the clear-cut landscapes or the proportion of residual forest (18–40%) within each landscape (P = 0.14). Moose yards were not located close to uncut forest surrounding the landscapes and did not have a greater proportion of residual forest than clear-cut landscapes. Moose yards had a denser shrub layer and more browse available than random sites selected in the same landscapes. The presence of moose in large clear-cut black spruce landscapes is related to vegetation characteristics and not the spatial pattern of the forest. The authors propose two strategies to maintain moose populations and moose hunting activity in this type of forest after harvesting. RÉSUMÉ: Nous avons réalisé l'inventaire aérien hivernal de l'orignal (Alces alces) dans 14 paysages formés de grandes coupes totales agglomérées (10–256 km 2) effectuées au cours des 3 à 9 dernières années au centre-sud du Québec. La forêt d'origine était dominée par l'épinette noire (Picea mariana). La présence de l'orignal a été confirmée dans 8 paysages (11 ravages), pour une densité moyenne de 0,20 orignal/10 km 2 , soit 50% de celle retrouvée dans cette zone de chasse ayant le même type de forêt. D'après un travail antérieur, nous assumons que la variation de la pression de chasse et le nombre d'années après coupe n'ont pas influencé la distribution et l'abondance de l'orignal. La taille des paysages de coupe totale ou la proportion de forêt résiduelle (18–40%) à l'intérieur de ceux-ci n'a pas influencé la densité (P = 0,14). Les ravages d'orignaux n'étaient pas situés à proximité de la forêt intacte autour des paysages de coupe et ne contenaient pas davantage de forêt résiduelle que les paysages de coupe. Cependant, les ravages d'orignaux avaient une strate arbustive plus dense et une disponibilité de brout plus grande que des sites aléatoires choisis dans les mêmes paysages. La présence de l'orignal dans des paysages formés de grandes coupes totales en pessière noire est davantage reliée aux caractéristiques de la végétation qu'à la configuration spatiale de la mosaïque forestière. Nous proposons deux stratégies pour favoriser après coupe le maintien de l'orignal et de l'activité de chasse dans ce type de forêt.
1. The selection for particular habitat patches can vary as a function of local and regional levels of anthropogenic disturbance. Although such functional responses can better reveal habitat loss for species of precarious status faced with dwindling resources, they remain rarely used in conservation planning. We show that functional responses can occur at multiple levels, even as nested hierarchies, and that they can explain the plasticity in habitat selection observed in threatened forest-dwelling caribou Rangifer tarandus caribou, within and among home-ranges.
2. Twenty-seven caribou were followed with global positioning system collars between 2005 and 2010. Generalized linear mixed models served as the basis from which we built multi-level functional responses characterizing how caribou alter their selection for closed-canopy conifer forests, depending upon the availability of these forests and the amount of cutovers and roads.
3. Caribou increased their selection for closed-canopy conifer forests in areas of their home-range that were comprised of a high proportion of recent cutovers during calving and summer and of high closed-canopy conifer forests during winter. Also, caribou that were established in highly disturbed areas displayed an overall stronger selection for conifer forests. These individuals further adjusted their selection for conifer forests in areas of their home-ranges that were largely comprised of recent cutovers. This concurrent response to local and global anthropogenic disturbances provides evidence of nested-hierarchical functional responses.
4. Synthesis and applications. Reliable characterization of disturbance effects on animals is necessary for conservation planning. Multi-level functional responses can accurately describe animal distribution, and we provided a framework for modelling these responses. Our multi-level functional responses indicate that fixing habitat requirements based on patterns of habitat selection for the average amount of disturbance can be misleading because it overlooks plasticity in the response of animals to habitat heterogeneity. For example, selection of closed-canopy conifer forests by caribou generally became stronger with increasing disturbance levels. Anthropogenic disturbance thus could not only lead to the functional loss of residual habitat, but it can also increase the ‘relative value’ of residual patches. Our study provides a tool for more thorough assessments of spatial variation in the attractiveness of resource patches and, presumably, in the fitness benefits.
Actual evapotranspiration (AE) is shown to be a highly significant predictor of the net annual above-ground productivity in mature terrestrial plant communities. Communities included ranged from deserts and tundra to tropical forests. It is hypothesized that the relationship of AE to productivity is due to the fact that AE measures the simultaneous availability of water and solar energy, the most important rate-limiting resources in photosynthesis. 27 references, 1 figure, 1 table.
Predators impact prey populations not only by consuming individuals, but also by altering their behaviours. These nonlethal effects can influence food web properties as much as lethal effects. The mechanisms of nonlethal effects include chronic and temporary anti‐predator behaviours, the nature of which depends on the spatial dynamics of predators and the range over which prey perceive risk.
The relation between chronic and ephemeral responses to risk determines predator–prey interactions, with consequences that can ripple across the food web. Nonetheless, few studies have quantified the spatio‐temporal scales over which prey respond to predation threat, and how this response varies with habitat features.
We evaluated the reaction of radio‐collared caribou and moose to the passage of radio‐collared wolves, by considering changes in movement characteristics during winter and summer. We used an optimization algorithm to identify the rate at which the impact of prior passage of wolves decreases over time and with the predator's distance.
The spatial and temporal scales of anti‐predator responses varied with prey species and season. Caribou and moose displayed four types of behaviour following the passage of wolves: lack of response, increased selection of safe land cover types, decreased selection of risky cover types and increased selection of food‐rich forest stands. For example, moose increased their avoidance of open conifer stands with lichen in summer, which are selected by wolves in this season. Also in winter, caribou increased their selection of conifer stands with lichen for nearly 10 days following a wolf's passage. This stronger selection for food‐rich patches could indicate that the recent passage of wolves informs caribou on the current predator distribution and reveals the rate at which this information become less reliable over time.
Caribou and moose used anti‐predator responses that combine both long‐ and short‐term behavioural adjustments. The spatial game between wolves and their prey involves complex and nonlinear mechanisms that vary between species and seasons. A comprehensive assessment of risk effects on ecosystem dynamics thus requires the characterization of chronic and temporary anti‐predator behaviours.
Summary • Understanding animal–habitat relationships is central to the development of strategies for wildlife management and conservation. The availability of habitat attributes often changes along latitudinal and longitudinal axes, and animals may respond to those changes by adjusting their selection. We evaluated whether landscape selection by forest-dwelling woodland caribou Rangifer tarandus caribou varied along geographical gradients in habitat attributes. • Centroids (n = 422) of track networks made by caribou in winter were recorded during aerial surveys conducted over 161 920 km2 of boreal forest in Québec, Canada. Autologistic models were estimated by comparing the characteristics of landscapes (201 km2) centred on each centroid to an equal number of randomly located landscapes, with an autocovariate controlling for the non-independence among caribou locations. • The availability of habitat attributes varied along longitudinal and latitudinal gradients, and caribou altered their landscape selection with respect to those gradients. • Information Theory provided substantial support for only one model. The model revealed that the probability of occurrence of caribou increased with the abundance of conifer forests over most of the study region, but this positive response gradually became negative towards the southern portion of the region. The association between caribou and lichens changed from being negative west of the study region to being positive in the eastern part. Availability of landscapes dominated by lichen decreased from west to east. Finally, caribou generally displayed an aversion to areas with high road density, a negative association that became positive in the southern part of the study region. • Synthesis and applications. Under current legislation in Canada, the critical habitat of woodland caribou must be defined, and then protected. Our autoregressive models can help to identify landscapes to prioritize conservation efforts. The probability of occurrence of caribou was related to different landscape characteristics across their range, which implies that the typical habitat of woodland caribou differs spatially. Such behavioural plasticity could be problematic for defining critical habitat, but we showed that spatial variation in landscape selection was organized along geographical gradients. Our study illustrates how geographical trends in habitat selection can guide management and conservation decisions.
Species recovery is often impeded by inadequate knowledge on mechanisms of community interactions that cause and exacerbate species endangerment. Caribou and wild reindeer Rangifer tarandus are declining in many regions of their circumpolar range likely because of human-induced landscape changes. In general, their niche specialization enables Rangifer to survive in nutrient-poor habitats spatially separated from other ungulates and their shared predators. Research has indicated that shifts in primary prey distribution following human landscape alteration may result in spatial overlap with Rangifer. We studied overlap relationships of woodland caribou R. t. caribou and moose Alces alces, quantified by their differential use of environmental resources, and evaluated the role of human landscape alteration in spatial sepa-ration in south-western Canada. Anthropogenic conversion of old-growth forests to early seral stands is hypothesized to decrease the spatial separation between caribou and moose, the dominant prey for wolves Canis lupus, contributing to increased caribou mortality. Redundancy analysis (RDA) was first used to examine coarse scale resource separation across our study area. Second, at a finer spatial scale, we used logistic regression to compare resource-and spatial separa-tion of sympatric pairs of 17 moose and 17 caribou. Finally, we tested if the frequency of predator-caused caribou mor-talities was higher in regions with higher moose resource use. Although environmental resource separation was strong at the coarser scale, we observed substantial spatial overlap ( 50%) at the finer scale. In summer we reported a signifi-cant positive relationship between spatial overlap of moose and caribou and the degree of human landscape alteration. Most importantly, locations of caribou mortalities corresponded with areas of high resource use by moose in summer. Thus, consistent with the spatial separation hypothesis, our research suggests that early successional forest stages may decrease spatial separation between caribou and moose, resulting in increased mortality risk for threatened caribou. Over the last century humans have significantly impacted the global environment, leading to dramatic changes in species distributions and increased extinction rates well above natural background levels (Chapin et al. 2011). Ecosystem functions and processes are commonly influ-enced by interactions among species and human-induced changes of systems such as competition and trophic inter-actions can have wide-ranging ecosystem effects. Direct (e.g. habitat loss or over-exploitation) and indirect (e.g. changes in community interactions) mechanisms often act concurrently and their combination can drive vulner-able populations towards extinction (Brook et al. 2008). Therefore, conservation biologists need to understand the mechanisms leading to population declines, and complex interactions among those mechanisms to manage and con-serve species. Unfortunately, how human landscape altera-tion can affect spatial overlap of species and their use of resources, and thus competitive interactions, often remains unstudied in many systems. For example, interactions of
Applications of logistic regression in a used-unused design in wildlife habitat studies often suffer from asymmetry of errors: used resource units (landscape locations) are known with certainty, whereas unused resource units might be observed to be used with greater sampling intensity. More appropriate might be to use logistic regression to estimate a resource selection function (RSF) tied to a use-availability design based on independent samples drawn from used and available resource units. We review the theoretical motivation for RSFs and show that sample ''contamination'' and the exponential form commonly assumed for the RSF are not concerns, contrary to recent statements by Keating and Cherry (2004; Use and interpretation of logistic regression in habitat-selection studies. Journal of Wildlife Management 68:774-789). To do this, we re-derive the use-availability likelihood and show that it can be maximized by logistic regression software. We then consider 2 case studies that illustrate our findings. For our first case study, we fit both RSFs and resource selection probability functions (RSPF) to point count data for 4 bird species with varying levels of occurrence among sample blocks. Drawing on our new derivation of the likelihood, we sample available resource units with replacement and assume overlapping distributions of used and available resource units. Irrespective of overlap, we observed approximate proportionality between predictions of a RSF and RSPF. For our second case study, we evaluate the classic use- availability design suggested by Manly et al. (2002), where availability is sampled without replacement, and we systematically introduce contamination to a sample of available units applied to RSFs for woodland caribou (Rangifer tarandus caribou). Although contamination appeared to reduce the magnitude of one RSF beta coefficient, change in magnitude exceeded sampling variation only when .20% of the available units were confirmed caribou use locations (i.e., contaminated). These empirically based simulations suggest that previously recommended sampling designs are robust to contamination. We conclude with a new validation method for evaluating predictive performance of a RSF and for assessing if the model deviates from being proportional to the probability of use of a resource unit. (JOURNAL OF WILDLIFE MANAGEMENT 70(2):347-357; 2006)
In northeastern Alberta, Canada, continued expansion of the oil and gas industry along with timber harvesting has raised concerns that the resulting environmental changes may negatively affect the woodland caribou (Rangifer tarandus caribou) population in this region. Caribou are a threatened species in Alberta, and populations in northeastern Alberta appear to be stable or slightly decreasing. The spatial distribution of caribou in relation to alternative prey (commonly moose [Alces alces]) has been hypothesized to affect the level of wolf (Canis lupus) predation on caribou populations. We monitored radiomarked caribou, moose, and wolves between 1993 and 1997, and we found that selection of fen/bog complexes by caribou and selection of well-drained habitats by moose and wolves resulted in spatial separation. This spatial separation in turn reduced wolf predation pressure on caribou but did not provide a total refuge from wolves. Any management activities that increase the density of moose and wolves or increase access of wolves into fen/bog complexes will likely reduce the refuge effect provided by large fen/bog complexes.
American black bears (Ursus americanus) and brown bears (U. arctos) can be important predators on neonatal ungulates. They prey less commonly on adult ungulates. Bear predation appears to be additive at low ungulate densities and may become compensatory as prey density approaches carrying capacity, K. As such, black and brown bear predation can limit, but generally does not regulate, ungulate populations. Maternal and neonatal physical condition, birth synchrony, and birth mass may predispose neonates to predation or other mortality factors. Though black and brown bear predation is an important proximate cause of ungulate neonatal mortality, habitat quality and quantity are important ultimate factors influencing this dynamic. Manipulating bear populations to enhance ungulate populations may be successful in the short-term if predation is additive, but long-term success has not been demonstrated.
Logging negatively affects the threatened forest-dwelling caribou (Rangifer tarandus caribou) through its positive effects on large predator populations. As recruitment is a key component of caribou population growth rate, we assessed calving rates of females and calf survival rates during the most critical period for calf survival, the calving period. We also identified causes of calf mortality and investigated the influence of predation risk, food availability, and human disturbance on habitat selection of females during the calving period at both the home-range and forest stand scales. We hypothesized that caribou should display habitat selection patterns to reduce predation risk at both scales. Using telemetry, we followed 22 females and their calves from 2004 to 2007 in a highly managed study area in Québec, Canada. Most females (78.5 ± 0.05 [SE]) gave birth each year, but only 46.3 ± 8.0% of the calves survived during the first 50 days following birth, and 57.3 ± 14.9% of them died from black bear (Ursus americanus) predation. At the home-range scale, caribou selected calving areas located at upper slope positions and avoided high road density areas. Surprisingly, they also selected the forested habitat type having the lowest lateral cover (mixed and deciduous stands) while avoiding the highest cover (regenerating conifer stands). At the forest stand scale, caribou selected areas located at relatively high elevations and with a lower basal area of black spruce trees. The selection of upper slope positions likely favored spatial segregation between calving females and wolves (Canis lupus) but not black bear. Our results suggest that calving females used areas from which they could visually detect approaching predators. While wolf avoidance appeared to be effective in a highly managed landscape, caribou did not appear to have adjusted their predator avoidance strategy to the recent increase in black bear abundance, who have benefited from increased food abundance. This situation requires focused attention from wildlife managers as logging activities are progressing towards the north within the core of forest-dwelling caribou range. © 2011 The Wildlife Society.
Predation is a fundamental ecological and evolutionary process that varies in space, and the avoidance of predation risk is of central importance in foraging theory. While there has been a recent growth of approaches to spatially model predation risk, these approaches lack an adequate mechanistic framework that can be applied to real landscapes. In this paper we show how predation risk can be decomposed into encounter and attack stages, and modeled spatially using resource selection functions (RSF) and resource selection probability functions (RSPF). We use this approach to compare the effects of landscape attributes on the relative probability of encounter, the conditional probability of death given encounter, and overall wolf and elk resource selection to test whether predation risk is simply equivalent to location of the predator. We then combine the probability of encounter and conditional probability of death into a spatially explicit function of predation risk following Lima and Dill's reformulation of Holling's functional response. We illustrate this approach in a wolf–elk system in and adjacent to Banff National Park, Alberta, Canada. In this system we found that the odds of elk being encountered by wolves was 1.3 times higher in pine forest and 4.1 times less in grasslands than other habitats. The relative odds of being killed in pine forests, given an encounter, increased by 1.2. Other habitats, such as grasslands, afforded elk reduced odds (4.1 times less) of being encountered and subsequently killed (1.4 times less) by wolves. Our approach illustrates that predation risk is not necessarily equivalent to just where predators are found. We show that landscape attributes can render prey more or less susceptible to predation and effects of landscape features can differ between the encounter and attack stages of predation. We conclude by suggesting applications of our approach to model predator–prey dynamics using spatial predation risk functions in theoretical and applied settings.
One expected response to climate warming in the Arctic is an increase in the abundance and extent of shrubs in tundra areas. Repeat photography shows that there has been an increase in shrub cover over the past 50 years in northern Alaska. Using 202 pairs of old and new oblique aerial photographs, we have found that across this region spanning 620 km east to west and 350 km north to south, alder, willow, and dwarf birch have been increasing, with the change most easily detected on hill slopes and valley bottoms. Plot and remote sensing studies from the same region using the normalized difference vegetation index are consistent with the photographic results and indicate that the smaller shrubs between valleys are also increasing. In Canada, Scandinavia, and parts of Russia, there is both plot and remote sensing evidence for shrub expansion. Combined with the Alaskan results, the evidence suggests that a pan-Arctic vegetation transition is underway. If continued, this transition will alter the fundamental architecture and function of this ecosystem with important ramifications for the climate, the biota, and humans.
In this paper, we present a new approach, based on a mixed model procedure, to quantify the tree-ring-based growth-climate relationship of trembling aspen along a latitudinal gradient from 46 to 54 °N in eastern Canada. This approach allows breaking down the growth response into general intersite and local climatic responses, and analyzing variations of absolute ring width as well as interannual variations in tree growth. The final model also integrates nonclimatic variables such as soil characteristics and the occurrence of insect outbreaks into the growth predictions. Tree level random effects on growth were important as intercepts but were nonsignificant for the climatic variables, indicating that a single climate–growth relationship was justified in our case. The response of tree growth to climate showed, however, a strong dependence on the spatial scale at which the analysis was performed. Intersite variations in tree growth were mostly dependent on variations in the thermal heat sum, a variable that showed low interannual and high intersite variation. When variation for a single site was analyzed, other variables showed up to be important while the heat sum was unimportant. Finally, future growth under six different climate change scenarios was simulated in order to study the potential impact of climate change. Results suggest only moderate growth increases in the northern portion of the gradient and a growth decrease in the southern portion under future climatic conditions.
Resource selection functions (RSF) have contributed to the conservation of species negatively affected by human activities. Despite these applications, two assumptions frequent many studies: the assumption of independence among groups in social species, and that selection is proportional to resource availability. This latter case is known as a functional response in resource selection, and may be especially important in human–wildlife relationships where there is a fitness cost of proximity to humans.
Recent advances in generalized linear mixed models offer new ways to account for resource selection in social species and functional responses by accommodating correlations within hierarchical groups with random intercepts, and functional responses with random coefficients.
We illustrate the application of mixed‐effects RSF models using a case study of resource selection by individual wolves Canis lupus living in packs as a function of human activity.
In areas of low human activity, wolf resource selection was independent of proximity to humans. As human activity increased, wolves displayed a functional response selecting areas closer to human activity. With increasing human activity, however, wolves displayed spatio‐temporal avoidance of human activity during daylight. This could lead to behaviourally induced trophic cascades mediated by wolf avoidance of human activity, and fits within the framework of attractive sink habitats.
Accounting for the hierarchical social structure of wolves clearly showed that the response of wolves to human disturbance was strongly correlated, but different, within packs, and that the correlation was strongest during winter and weakest during summer.
Syntheses and applications . Failure to consider the social structure of wolves and the functional response to human activity would result in mistaken conclusions about wolf–human relationships. Our approach provides a unifying framework to understand the contradictory results of previous studies of wolf–human relationships and a template for future studies to evaluate effects of increasing human activity on wildlife.
1. Caribou and reindeer Rangifer tarandus are declining across North America and Scandinavia in part from wolf Canis lupus ‐mediated apparent competition with more abundant ungulate prey species. While caribou generally persist in areas with low wolf density, wolf packs that overlap caribou ranges could trigger caribou declines. Moreover, anthropogenic linear features such as roads, trails and seismic lines are hypothesized to increase predation risk for caribou, yet few studies have examined the mechanistic effects of linear features or spatial overlap on wolf–caribou encounter rates and predation risk.
2. We used (a) time‐to‐event models of wolf–caribou encounters estimated from concurrent global positioning system (GPS) radio‐collar data from wolves and caribou and (b) wolf resource selection models of travel locations, to determine the potential influence of wolf–caribou spatial overlap, linear features, elevation and season on encounter rates. Analyses were based on data from 35 adult female caribou and 37 male and female wolves from 11 wolf packs from Banff and Jasper National Parks, Canada, from 2002 until 2010.
3. Wolf–caribou encounter rates increased with high wolf–caribou overlap, proximity to linear features and lower elevations. Wolves strongly selected low elevations, especially during winter and spring. Selection for linear features as travel routes increased with elevation.
4. Caribou risk of encounter was highest during the summer and autumn when wolves spent the most time at high elevations. Most wolf‐caused mortalities ( n = 12) occurred during spring and summer.
5. Synthesis and applications . The presence of anthropogenic linear features and the amount of time wolves spend in caribou range could be equally as important as wolf density when prioritizing caribou recovery actions such as wolf or primary prey reductions or re‐introductions. The use of GPS locations and time‐to‐event modelling offers a powerful tool for evaluating factors affecting predation risk of threatened and endangered species.
Habitat alteration caused by forest harvesting seems to contribute to the decline of forest-dwelling caribou, an ecotype of woodland caribou (Rangifer tarandus caribou) inhabiting the boreal ecosystem. To serve as basework to the establishment of conservation measures for the species, we have studied the hierarchical habitat selection of forest-dwelling caribou in a boreal landscape of Québec strongly impacted by logging. Fifteen females were surveyed by GPS telemetry between April 2004 and March 2006. Home ranges showed a high proportion of 90–120 year-old forests, a low proportion of regenerating forests (20–40 years old) and a tendency to include a greater proportion of 6–20 year-old clearcuts in relation to their availability in the study area. At the home range scale, selection patterns differed between periods, possibly reflecting specific requirements linked to caribou life cycle. Caribou selected open lichen woodlands throughout the year while mature closed forests (≥50 years) were selected uniquely during summer. The 6–20 year-old clearcuts were avoided during calving, in summer and during the rutting period but were selected during spring. Our results indicate that mature forest and open lichen woodlands are highly selected forest cover types by caribou at both spatial scales. Although clearcuts were generally avoided at the home range scale, such avoidance was not observed at the larger scale, the search for 90–120 year-old forests being hampered by a uniform distribution of clearcuts. An a posteriori landscape analysis highlighted the spatial association between 6–20 year-old clearcuts and 90–120 year-old forests, an association that can be explained by the current regulations used in Québec. Our results underline the importance of pursuing research concerning the impact of such an exploitation regime on the long-term maintenance of the forest caribou in the boreal landscape.
We evaluated the initial 12 months of vegetation index product availability from the Moderate Resolution Imaging Spectroradiometer (MODIS) on board the Earth Observing System-Terra platform. Two MODIS vegetation indices (VI), the normalized difference vegetation index (NDVI) and enhanced vegetation index (EVI), are produced at 1-km and 500-m resolutions and 16-day compositing periods. This paper presents an initial analysis of the MODIS NDVI and EVI performance from both radiometric and biophysical perspectives. We utilize a combination of site-intensive and regionally extensive approaches to demonstrate the performance and validity of the two indices. Our results showed a good correspondence between airborne-measured, top-of-canopy reflectances and VI values with those from the MODIS sensor at four intensively measured test sites representing semi-arid grass/shrub, savanna, and tropical forest biomes. Simultaneously derived field biophysical measures also demonstrated the scientific utility of the MODIS VI. Multitemporal profiles of the MODIS VIs over numerous biome types in North and South America well represented their seasonal phenologies. Comparisons of the MODIS-NDVI with the NOAA-14, 1-km AVHRR-NDVI temporal profiles showed that the MODIS-based index performed with higher fidelity. The dynamic range of the MODIS VIs are presented and their sensitivities in discriminating vegetation differences are evaluated in sparse and dense vegetation areas. We found the NDVI to asymptotically saturate in high biomass regions such as in the Amazon while the EVI remained sensitive to canopy variations.