The Experts below are selected from a list of 606 Experts worldwide ranked by ideXlab platform
Dennis L. Murray - One of the best experts on this subject based on the ideXlab platform.
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broaden your horizon the use of remotely sensed data for modeling populations of forest species at landscape scales
Forest Ecology and Management, 2021Co-Authors: Dennis L. Murray, Paul O Jensen, Arjan J H Meddens, Scott Fisher, Aaron J Wirsing, Daniel H. ThorntonAbstract:Abstract Landscape-scale predictions of species abundance or density are of fundamental importance to conservation and management of ecosystems. Yet, developing these models remains challenging, as they require linking broad-scale population data with habitat characteristics that influence species abundance. Advances in remote sensing technology have resulted in increased availability of spatially continuous, high-resolution data that relate to ecologically important habitat characteristics. In forested systems, Light Detection and Ranging (LiDAR) and Digital Arial Photogrammetry (DAP) are of particular interest owing to their ability to estimate vegetative structure that drives variability in abundance or density of some forest-dependent species. We used an extensive dataset on the density of a keystone boreal forest species, the snowshoe hare (Lepus americanus) in northcentral Washington, USA, to examine which LiDAR- and DAP-derived habitat variables most strongly influence snowshoe hare density, and projected these relationships across the landscape to derive a hare density surface for our 53 km2 study area. We found snowshoe hare density is most influenced by habitat variables related to tree height (a proxy for stand age), horizontal cover, and vertical cover, and our model had high predictive performance on a spatially-independent validation dataset. Hare densities increased as horizontal cover and canopy cover increased, with our highest hare densities occurring in areas with >9% horizontal cover (% of LiDAR returns in 1–4 m height stratum), >65% canopy cover and tree height (a proxy for stand age) of ~5–10 m. To demonstrate the management implications of this work, we show that our landscape-scale model of predicted hare density helps understand habitat use by threatened Canada Lynx (Lynx Canadensis), a primary predator of hare. Our results show how coupling population data with remotely sensed forest structure metrics allows for continuous, large-scale population estimates. Such integration provides an important management tool for examining spatiotemporal changes in populations as boreal ecosystems come under increasing stress from climate and land use change.
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Habitat Loss, Not Fragmentation, Drives Occurrence Patterns of Canada Lynx at the Southern Range Periphery
2016Co-Authors: Megan L Hornseth, Jeff Bowman, Aaron A Walpole, Lyle R Walton, Justina C Ray, Dennis L. MurrayAbstract:Peripheral populations often experience more extreme environmental conditions than those in the centre of a species’ range. Such extreme conditions include habitat loss, defined as a reduction in the amount of suitable habitat, as well as habitat fragmentation, which involves the breaking apart of habitat independent of habitat loss. The ‘threshold hypothesis’ predicts that organisms will be more affected by habitat fragmentation when the amount of habitat on the landscape is scarce (i.e., less than 30%) than when habitat is abundant, implying that habitat fragmentation may compound habitat loss through changes in patch size and configuration. Alternatively, the ‘flexibility hypothesis ’ predicts that individuals may respond to increased habitat disturbance by altering their selection patterns and thereby reducing sensitivity to habitat loss and fragmentation. While the range of Canada Lynx (Lynx Canadensis) has contracted during recent decades, the relative importance of habitat loss and habitat fragmentation on this phenomenon is poorly understood. We used a habitat suitability model for Lynx to identify suitable land cover in Ontario, and contrasted occupancy patterns across landscapes differing in cover, to test the ‘threshold hypothesis ’ and ‘flexibility hypothesis’. When suitable land cover was widely available, Lynx avoided areas with less than 30 % habitat and were unaffected by habitat fragmentation. However, on landscapes with minimal suitable land cover, Lynx occurrence was not related to either habitat loss or habitat fragmentation, indicating support for the ‘flexibility hypothesis’. We conclude that Lynx are broadly affected by habitat loss, and no
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habitat loss not fragmentation drives occurrence patterns of canada Lynx at the southern range periphery
PLOS ONE, 2014Co-Authors: Megan L Hornseth, Jeff Bowman, Aaron A Walpole, Lyle R Walton, Justina C Ray, Mariejosee Fortin, Dennis L. MurrayAbstract:Peripheral populations often experience more extreme environmental conditions than those in the centre of a species' range. Such extreme conditions include habitat loss, defined as a reduction in the amount of suitable habitat, as well as habitat fragmentation, which involves the breaking apart of habitat independent of habitat loss. The ‘threshold hypothesis’ predicts that organisms will be more affected by habitat fragmentation when the amount of habitat on the landscape is scarce (i.e., less than 30%) than when habitat is abundant, implying that habitat fragmentation may compound habitat loss through changes in patch size and configuration. Alternatively, the ‘flexibility hypothesis’ predicts that individuals may respond to increased habitat disturbance by altering their selection patterns and thereby reducing sensitivity to habitat loss and fragmentation. While the range of Canada Lynx (Lynx Canadensis) has contracted during recent decades, the relative importance of habitat loss and habitat fragmentation on this phenomenon is poorly understood. We used a habitat suitability model for Lynx to identify suitable land cover in Ontario, and contrasted occupancy patterns across landscapes differing in cover, to test the ‘threshold hypothesis’ and ‘flexibility hypothesis’. When suitable land cover was widely available, Lynx avoided areas with less than 30% habitat and were unaffected by habitat fragmentation. However, on landscapes with minimal suitable land cover, Lynx occurrence was not related to either habitat loss or habitat fragmentation, indicating support for the ‘flexibility hypothesis’. We conclude that Lynx are broadly affected by habitat loss, and not specifically by habitat fragmentation, although occurrence patterns are flexible and dependent on landscape condition. We suggest that Lynx may alter their habitat selection patterns depending on local conditions, thereby reducing their sensitivity to anthropogenically-driven habitat alteration.
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influence of adrenocorticotrophin hormone challenge and external factors age sex and body region on hair cortisol concentration in canada Lynx Lynx Canadensis
General and Comparative Endocrinology, 2013Co-Authors: C V Terwissen, Gabriela F Mastromonaco, Dennis L. MurrayAbstract:Abstract Land use changes are a significant factor influencing the decline of felid populations. However, additional research is needed to better understand how these factors influence populations in the wild. Hormone analysis can provide valuable information on the basic physiology and overall health of an animal, and enzyme immunoassays (EIA) are generally used for hair hormone analysis but must first be validated for the substrate of choice and species of interest. To date, hormone assays from hair have not been validated for Felidae, despite that the method holds considerable promise for non-invasive sampling of free-ranging animals. We sought to: (1) evaluate whether increased adrenocorticotrophin hormone (ACTH) during the period of hair growth results in elevated hair cortisol; (2) validate the enzyme immunoassay used; and (3) identify any variations in hair cortisol between age, sex and body regions, using Canada Lynx. We quantified hair cortisol concentrations in captive animals through an ACTH challenge and collected samples from legally harvested Lynx to compare variability between body regions. An EIA was validated for the analysis of hair cortisol. Lynx (n = 3) had a qualitative increase in hair cortisol concentration following an ACTH challenge in captive animals (20 IU/kg of body weight weekly for 5 weeks), thereby supporting the use of an EIA to quantify cortisol values in hair. Based on our analysis of sampled Lynx pelts, we found that hair cortisol did not vary between age and sex, but varied within the foot/leg region to a greater extent than between individuals. We recommend that future studies identify a standardized location for hair cortisol sampling.
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Reconsidering the Specialist-Generalist Paradigm in Niche Breadth Dynamics: Resource Gradient Selection by Canada Lynx and Bobcat
PloS one, 2012Co-Authors: Michael J. L. Peers, Daniel H. Thornton, Dennis L. MurrayAbstract:The long-standing view in ecology is that disparity in overall resource selection is the basis for identifying niche breadth patterns, with species having narrow selection being classified “specialists” and those with broader selection being “generalists”. The standard model of niche breadth characterizes generalists and specialists as having comparable levels of overall total resource exploitation, with specialists exploiting resources at a higher level of performance over a narrower range of conditions. This view has gone largely unchallenged. An alternate model predicts total resource use being lower for the specialized species with both peaking at a comparable level of performance over a particular resource gradient. To reconcile the niche breadth paradigm we contrasted both models by developing range-wide species distribution models for Canada Lynx, Lynx Canadensis, and bobcat, Lynx rufus. Using a suite of environmental factors to define each species’ niche, we determined that Canada Lynx demonstrated higher total performance over a restricted set of variables, specifically those related to snow and altitude, while bobcat had higher total performance across most variables. Unlike predictions generated by the standard model, bobcat level of exploitation was not compromised by the trade-off with peak performance, and Canada Lynx were not restricted to exploiting a narrower range of conditions. Instead, the emergent pattern was that specialist species have a higher total resource utilization and peak performance value within a smaller number of resources or environmental axes than generalists. Our results also indicate that relative differences in niche breadth are strongly dependent on the variable under consideration, implying that the appropriate model describing niche breadth dynamics between specialists and generalists may be more complex than either the traditional heuristic or our modified version. Our results demonstrate a need to re-evaluate traditional, but largely untested, assumptions regarding resource utilization in species with broad and narrow niches.
Michael J. L. Peers - One of the best experts on this subject based on the ideXlab platform.
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Climate change increases predation risk for a keystone species of the boreal forest
Nature Climate Change, 2020Co-Authors: Michael J. L. Peers, Thomas S Jung, Rudy Boonstra, Yasmine N. Majchrzak, Allyson K. Menzies, Emily K. Studd, Guillaume Bastille-rousseau, Murray Humphries, Alice J. Kenney, Charles J. KrebsAbstract:Canada Lynx ( Lynx Canadensis ) and snowshoe hares ( Lepus americanus ) form a keystone predator–prey cycle that has large impacts on the North American boreal forest vertebrate community. Snowshoe hares and Lynx are both well-suited for snowy winters, but climate change-associated shifts in snow conditions could lower hare survival and alter cyclic dynamics. Using detailed monitoring of snowshoe hare cause-specific mortality, behaviour and prevailing weather, we demonstrate that hare mortality risk is strongly influenced by variation in snow conditions. Although predation risk from Lynx was largely unaffected by snow conditions, coyote ( Canis latrans ) predation increased in shallow snow. Maximum snow depth in our study area has decreased 33% over the last two decades and predictions based on prolonged shallow snow indicate that future hare survival could resemble that seen during population declines. Our results indicate that climate change could disrupt cyclic dynamics in the boreal forest. Monitoring of snowshoe hare ( Lepus americanus ) cause-specific mortality and behaviour reveals increased risk of predation from coyote ( Canis latrans ) in shallow snow. This could disrupt the keystone Canada Lynx ( Lynx Canadensis )–hare predator–prey cycle in North American boreal forests.
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prey availability and ambient temperature influence carrion persistence in the boreal forest
Journal of Animal Ecology, 2020Co-Authors: Michael J. L. Peers, Charles J. Krebs, Rudy Boonstra, Yasmine N. Majchrzak, Allyson K. Menzies, Emily K. Studd, Alice J. Kenney, Sean M Konkolics, Clayton T Lamb, April Robin MartinigAbstract:Scavenging by vertebrates can have important impacts on food web stability and persistence, and can alter the distribution of nutrients throughout the landscape. However, scavenging communities have been understudied in most regions around the globe, and we lack understanding of the biotic drivers of vertebrate scavenging dynamics. In this paper, we examined how changes in prey density and carrion biomass caused by population cycles of a primary prey species, the snowshoe hare Lepus americanus, influence scavenging communities in the northern boreal forest. We further examined the impact of habitat and temperature on scavenging dynamics. We monitored the persistence time, time until first scavenger, and number of species scavenging experimentally-placed hare carcasses over four consecutive years in the southwestern Yukon. We simultaneously monitored hare density and carrion biomass to examine their influence relative to temperature, habitat, and seasonal effects. For the primary scavengers, we developed species-specific scavenging models to determine variation on the effects of these factors across species, and determine which species may be driving temporal patterns in the entire community. We found that the efficiency of the scavenging community was affected by hare density, with carcass persistence decreasing when snowshoe hare densities declined, mainly due to increased scavenging rates by Canada Lynx Lynx Canadensis. However, prey density did not influence the number of species scavenging a given carcass, suggesting prey abundance affects carrion recycling but not necessarily the number of connections in the food web. In addition, scavenging rates increased in warmer temperatures, and there were strong seasonal effects on the richness of the vertebrate scavenging community. Our results demonstrate that vertebrate scavenging communities are sensitive to changes in species' demography and environmental change, and that future assessments of food web dynamics should consider links established through scavenging.
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error in trapper reported sex of Lynx Lynx Canadensis and wolverine gulo gulo implications for analyses of harvest records
European Journal of Wildlife Research, 2020Co-Authors: Thomas S Jung, Stan Boutin, Michael J. L. Peers, Piia M. Kukka, Rudy Boonstra, Fiona K A Schmiegelow, Yasmine N. MajchrzakAbstract:Monitoring trends in the abundance of furbearers may be challenging, particularly at the spatio-temporal scales relevant for management. As such, wildlife managers often rely on harvest records to identify broad-scale harvest patterns and trends. Yet, the reliability of harvest records is often unknown. Analyses of harvest records to determine quotas and assess sustainability need to account for error rates when they are > 0. We evaluated the accuracy of trapper-reported sex of Lynx (Lynx Canadensis; n = 185) and wolverine (Gulo gulo; n = 467)—two meso-carnivores commonly targeted by fur trappers in northwestern Canada and Alaska—by comparing that to sex determined via necropsies of the same carcasses. Overall error rates differed significantly between wolverine (5%) and Lynx (13%). Error rates were sex-biased for wolverine, but not Lynx. Body size did not affect error rates for either species. Our data demonstrated species- and sex-specific error rates in the sex reported in harvest records. Error rates for wolverine (5%) were likely trivial for determining harvest sustainability because sex-based bias was small, given that overall accuracy was high. While error rates were greater for Lynx (13%), there was no sex-based bias in trapper-reported sex. Because accuracy was lower for Lynx, managers should exercise caution when using trapper-reported sex to conduct population analyses or assess harvest sustainability. Managers should be particularly interested in error rates of harvested species that exhibit relatively little sexual size dimorphism and lack obvious genitalia, similar to Lynx. We recommend assessing error in trapper-reported sex prior to analysis of harvest records, as well as ongoing education with trappers to increase their ability to reliably determine the sex of animals they harvest.
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Reconsidering the Specialist-Generalist Paradigm in Niche Breadth Dynamics: Resource Gradient Selection by Canada Lynx and Bobcat
PloS one, 2012Co-Authors: Michael J. L. Peers, Daniel H. Thornton, Dennis L. MurrayAbstract:The long-standing view in ecology is that disparity in overall resource selection is the basis for identifying niche breadth patterns, with species having narrow selection being classified “specialists” and those with broader selection being “generalists”. The standard model of niche breadth characterizes generalists and specialists as having comparable levels of overall total resource exploitation, with specialists exploiting resources at a higher level of performance over a narrower range of conditions. This view has gone largely unchallenged. An alternate model predicts total resource use being lower for the specialized species with both peaking at a comparable level of performance over a particular resource gradient. To reconcile the niche breadth paradigm we contrasted both models by developing range-wide species distribution models for Canada Lynx, Lynx Canadensis, and bobcat, Lynx rufus. Using a suite of environmental factors to define each species’ niche, we determined that Canada Lynx demonstrated higher total performance over a restricted set of variables, specifically those related to snow and altitude, while bobcat had higher total performance across most variables. Unlike predictions generated by the standard model, bobcat level of exploitation was not compromised by the trade-off with peak performance, and Canada Lynx were not restricted to exploiting a narrower range of conditions. Instead, the emergent pattern was that specialist species have a higher total resource utilization and peak performance value within a smaller number of resources or environmental axes than generalists. Our results also indicate that relative differences in niche breadth are strongly dependent on the variable under consideration, implying that the appropriate model describing niche breadth dynamics between specialists and generalists may be more complex than either the traditional heuristic or our modified version. Our results demonstrate a need to re-evaluate traditional, but largely untested, assumptions regarding resource utilization in species with broad and narrow niches.
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Reconsidering the specialist-generalist paradigm in niche breadth dynamics: resource gradient selection by Canada Lynx and Bobcat
2012Co-Authors: Michael J. L. Peers, Daniel H. Thornton, Dennis L. MurrayAbstract:The long-standing view in ecology is that disparity in overall resource selection is the basis for identifying niche breadth patterns, with species having narrow selection being classified ‘‘specialists’ ’ and those with broader selection being ‘‘generalists’’. The standard model of niche breadth characterizes generalists and specialists as having comparable levels of overall total resource exploitation, with specialists exploiting resources at a higher level of performance over a narrower range of conditions. This view has gone largely unchallenged. An alternate model predicts total resource use being lower for the specialized species with both peaking at a comparable level of performance over a particular resource gradient. To reconcile the niche breadth paradigm we contrasted both models by developing range-wide species distribution models for Canada Lynx, Lynx Canadensis, and bobcat, Lynx rufus. Using a suite of environmental factors to define each species ’ niche, we determined that Canada Lynx demonstrated higher total performance over a restricted set of variables, specifically those related to snow and altitude, while bobcat had higher total performance across most variables. Unlike predictions generated by the standard model, bobcat level of exploitation was not compromised by the trade-off with peak performance, and Canada Lynx were not restricted to exploiting a narrower range of conditions. Instead, the emergent pattern was that specialist species have a higher total resource utilization and peak performance value within a smaller number of resources or environmental axes than generalists. Our results also indicate that relative differences in nich
Charles J. Krebs - One of the best experts on this subject based on the ideXlab platform.
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Climate change increases predation risk for a keystone species of the boreal forest
Nature Climate Change, 2020Co-Authors: Michael J. L. Peers, Thomas S Jung, Rudy Boonstra, Yasmine N. Majchrzak, Allyson K. Menzies, Emily K. Studd, Guillaume Bastille-rousseau, Murray Humphries, Alice J. Kenney, Charles J. KrebsAbstract:Canada Lynx ( Lynx Canadensis ) and snowshoe hares ( Lepus americanus ) form a keystone predator–prey cycle that has large impacts on the North American boreal forest vertebrate community. Snowshoe hares and Lynx are both well-suited for snowy winters, but climate change-associated shifts in snow conditions could lower hare survival and alter cyclic dynamics. Using detailed monitoring of snowshoe hare cause-specific mortality, behaviour and prevailing weather, we demonstrate that hare mortality risk is strongly influenced by variation in snow conditions. Although predation risk from Lynx was largely unaffected by snow conditions, coyote ( Canis latrans ) predation increased in shallow snow. Maximum snow depth in our study area has decreased 33% over the last two decades and predictions based on prolonged shallow snow indicate that future hare survival could resemble that seen during population declines. Our results indicate that climate change could disrupt cyclic dynamics in the boreal forest. Monitoring of snowshoe hare ( Lepus americanus ) cause-specific mortality and behaviour reveals increased risk of predation from coyote ( Canis latrans ) in shallow snow. This could disrupt the keystone Canada Lynx ( Lynx Canadensis )–hare predator–prey cycle in North American boreal forests.
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prey availability and ambient temperature influence carrion persistence in the boreal forest
Journal of Animal Ecology, 2020Co-Authors: Michael J. L. Peers, Charles J. Krebs, Rudy Boonstra, Yasmine N. Majchrzak, Allyson K. Menzies, Emily K. Studd, Alice J. Kenney, Sean M Konkolics, Clayton T Lamb, April Robin MartinigAbstract:Scavenging by vertebrates can have important impacts on food web stability and persistence, and can alter the distribution of nutrients throughout the landscape. However, scavenging communities have been understudied in most regions around the globe, and we lack understanding of the biotic drivers of vertebrate scavenging dynamics. In this paper, we examined how changes in prey density and carrion biomass caused by population cycles of a primary prey species, the snowshoe hare Lepus americanus, influence scavenging communities in the northern boreal forest. We further examined the impact of habitat and temperature on scavenging dynamics. We monitored the persistence time, time until first scavenger, and number of species scavenging experimentally-placed hare carcasses over four consecutive years in the southwestern Yukon. We simultaneously monitored hare density and carrion biomass to examine their influence relative to temperature, habitat, and seasonal effects. For the primary scavengers, we developed species-specific scavenging models to determine variation on the effects of these factors across species, and determine which species may be driving temporal patterns in the entire community. We found that the efficiency of the scavenging community was affected by hare density, with carcass persistence decreasing when snowshoe hare densities declined, mainly due to increased scavenging rates by Canada Lynx Lynx Canadensis. However, prey density did not influence the number of species scavenging a given carcass, suggesting prey abundance affects carrion recycling but not necessarily the number of connections in the food web. In addition, scavenging rates increased in warmer temperatures, and there were strong seasonal effects on the richness of the vertebrate scavenging community. Our results demonstrate that vertebrate scavenging communities are sensitive to changes in species' demography and environmental change, and that future assessments of food web dynamics should consider links established through scavenging.
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Synchrony in the snowshoe hare (Lepus americanus) cycle in northwestern North America, 1970–2012
2014Co-Authors: Can J. Zool, Charles J. Krebs, Downloaded Keith, B Mather, Library Geophysical Inst/iarc, Knut Kiell, John Bryant, Frank Doyle, Carol Mcintyre, Donna DifolcoAbstract:Abstract: Snowshoe hares (Lepus americanus Erxleben, 1777) fluctuate in 9–10 year cycles throughout much of their North American range. Regional synchrony has been assumed to be the rule for these cycles, so that hare populations in virtually all of northwestern North America have been assumed to be in phase. We gathered qualitative and quantitative data on hare numbers and fur returns of Canada Lynx (Lynx Canadensis Kerr, 1792) in the boreal forest regions of Alaska, Yukon, Northwest Territories, and northern British Columbia to describe synchrony in the time window of 1970–2012. Broad-scale synchrony in Lynx fur returns was strong from 1970 to about 1995 but then seemed to break down in different parts of this region. Hare populations at 20 sites in Alaska, the Yukon, and Northwest Territories showed peak populations that lagged by 1–4 years during the 1990s and 2000s cycles. The simplest hypothesis to explain these patterns of asynchrony in hare cycles is the movement of predators from British Columbia north into the Yukon and then east into the Northwest Territories and west into Alaska. A traveling wave of these cycles is clearly seen in the Lynx fur returns from western Canada and Alaska from 1970 to 2009. One consequence of a failure of synchrony is that hare predators like Canada Lynx and Great-horned Owls (Bubo virginianus (Gmelin, 1788)) can move from one adjacent area to the next within this region and survive long enough to prolong low densities in hare populations that have declined earlier
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linking climate change to population cycles of hares and Lynx
Global Change Biology, 2013Co-Authors: Chuan Yan, Charles J. Krebs, Nils Chr. Stenseth, Zhibin ZhangAbstract:The classic 10-year population cycle of snowshoe hares (Lepus americanus, Erxleben 1777) and Canada Lynx (Lynx Canadensis, Kerr 1792) in the boreal forests of North America has drawn much attention from both population and community ecologists worldwide; however, the ecological mechanisms driving the 10-year cyclic dynamic pattern are not fully revealed yet. In this study, by the use of historic fur harvest data, we constructed a series of generalized additive models to study the effects of density dependence, predation, and climate (both global climate indices of North Atlantic Oscillation index (NAO), Southern Oscillation index (SOI) and northern hemispheric temperature (NHT) and local weather data including temperature, rainfall, and snow). We identified several key pathways from global and local climate to Lynx with various time lags: rainfall shows a negative, and snow shows a positive effect on Lynx; NHT and NAO negatively affect Lynx through their positive effect on rainfall and negative effect on snow; SOI positively affects Lynx through its negative effect on rainfall. Direct or delayed density dependency effects, the prey effect of hare on Lynx and a 2-year delayed negative effect of Lynx on hare (defined as asymmetric predation) were found. The simulated population dynamics is well fitted to the observed long-term fluctuations of hare and Lynx populations. Through simulation, we find density dependency and asymmetric predation, only producing damped oscillation, are necessary but not sufficient factors in causing the observed 10-year cycles; while extrinsic climate factors are important in producing and modifying the sustained cycles. Two recent population declines of Lynx (1940–1955 and after 1980) were likely caused by ongoing climate warming indirectly. Our results provide an alternative explanation to the mechanism of the 10-year cycles, and there is a need for further investigation on links between disappearance of population cycles and global warming in hare–Lynx system.
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synchrony in the snowshoe hare lepus americanus cycle in northwestern north america 1970 2012
Canadian Journal of Zoology, 2013Co-Authors: Charles J. Krebs, Knut Kielland, Mark Odonoghue, John P Bryant, Frank I Doyle, Carol L Mcintyre, Donna Difolco, Nathan Berg, Suzanne Carriere, Rudy BoonstraAbstract:Snowshoe hares (Lepus americanus Erxleben, 1777) fluctuate in 9-10 year cycles throughout much of their North American range. Regional synchrony has been assumed to be the rule for these cycles, so that hare populations in virtually all of northwestern North America have been assumed to be in phase. We gathered qualitative and quantitative data on hare numbers and fur returns of Canada Lynx (Lynx Canadensis Kerr, 1792) in the boreal forest regions of Alaska, Yukon, Northwest Territories, and northern British Columbia to describe synchrony in the time window of 1970-2012. Broad-scale synchrony in Lynx fur returns was strong from 1970 to about 1995 but then seemed to break down in different parts of this region. Hare populations at 20 sites in Alaska, the Yukon, and Northwest Territories showed peak populations that lagged by 1-4 years during the 1990s and 2000s cycles. The simplest hypothesis to explain these patterns of asynchrony in hare cycles is the movement of predators from British Columbia north into the Yukon and then east into the Northwest Territories and west into Alaska. A traveling wave of these cycles is clearly seen in the Lynx fur returns from western Canada and Alaska from 1970 to 2009. One consequence of a failure of synchrony is that hare predators like Canada Lynx and Great-horned Owls (Bubo virginianus (Gmelin, 1788)) can move from one adjacent area to the next within this region and survive long enough to prolong low densities in hare populations that have declined earlier.
Daniel H. Thornton - One of the best experts on this subject based on the ideXlab platform.
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broaden your horizon the use of remotely sensed data for modeling populations of forest species at landscape scales
Forest Ecology and Management, 2021Co-Authors: Dennis L. Murray, Paul O Jensen, Arjan J H Meddens, Scott Fisher, Aaron J Wirsing, Daniel H. ThorntonAbstract:Abstract Landscape-scale predictions of species abundance or density are of fundamental importance to conservation and management of ecosystems. Yet, developing these models remains challenging, as they require linking broad-scale population data with habitat characteristics that influence species abundance. Advances in remote sensing technology have resulted in increased availability of spatially continuous, high-resolution data that relate to ecologically important habitat characteristics. In forested systems, Light Detection and Ranging (LiDAR) and Digital Arial Photogrammetry (DAP) are of particular interest owing to their ability to estimate vegetative structure that drives variability in abundance or density of some forest-dependent species. We used an extensive dataset on the density of a keystone boreal forest species, the snowshoe hare (Lepus americanus) in northcentral Washington, USA, to examine which LiDAR- and DAP-derived habitat variables most strongly influence snowshoe hare density, and projected these relationships across the landscape to derive a hare density surface for our 53 km2 study area. We found snowshoe hare density is most influenced by habitat variables related to tree height (a proxy for stand age), horizontal cover, and vertical cover, and our model had high predictive performance on a spatially-independent validation dataset. Hare densities increased as horizontal cover and canopy cover increased, with our highest hare densities occurring in areas with >9% horizontal cover (% of LiDAR returns in 1–4 m height stratum), >65% canopy cover and tree height (a proxy for stand age) of ~5–10 m. To demonstrate the management implications of this work, we show that our landscape-scale model of predicted hare density helps understand habitat use by threatened Canada Lynx (Lynx Canadensis), a primary predator of hare. Our results show how coupling population data with remotely sensed forest structure metrics allows for continuous, large-scale population estimates. Such integration provides an important management tool for examining spatiotemporal changes in populations as boreal ecosystems come under increasing stress from climate and land use change.
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Reconsidering the Specialist-Generalist Paradigm in Niche Breadth Dynamics: Resource Gradient Selection by Canada Lynx and Bobcat
PloS one, 2012Co-Authors: Michael J. L. Peers, Daniel H. Thornton, Dennis L. MurrayAbstract:The long-standing view in ecology is that disparity in overall resource selection is the basis for identifying niche breadth patterns, with species having narrow selection being classified “specialists” and those with broader selection being “generalists”. The standard model of niche breadth characterizes generalists and specialists as having comparable levels of overall total resource exploitation, with specialists exploiting resources at a higher level of performance over a narrower range of conditions. This view has gone largely unchallenged. An alternate model predicts total resource use being lower for the specialized species with both peaking at a comparable level of performance over a particular resource gradient. To reconcile the niche breadth paradigm we contrasted both models by developing range-wide species distribution models for Canada Lynx, Lynx Canadensis, and bobcat, Lynx rufus. Using a suite of environmental factors to define each species’ niche, we determined that Canada Lynx demonstrated higher total performance over a restricted set of variables, specifically those related to snow and altitude, while bobcat had higher total performance across most variables. Unlike predictions generated by the standard model, bobcat level of exploitation was not compromised by the trade-off with peak performance, and Canada Lynx were not restricted to exploiting a narrower range of conditions. Instead, the emergent pattern was that specialist species have a higher total resource utilization and peak performance value within a smaller number of resources or environmental axes than generalists. Our results also indicate that relative differences in niche breadth are strongly dependent on the variable under consideration, implying that the appropriate model describing niche breadth dynamics between specialists and generalists may be more complex than either the traditional heuristic or our modified version. Our results demonstrate a need to re-evaluate traditional, but largely untested, assumptions regarding resource utilization in species with broad and narrow niches.
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Reconsidering the specialist-generalist paradigm in niche breadth dynamics: resource gradient selection by Canada Lynx and Bobcat
2012Co-Authors: Michael J. L. Peers, Daniel H. Thornton, Dennis L. MurrayAbstract:The long-standing view in ecology is that disparity in overall resource selection is the basis for identifying niche breadth patterns, with species having narrow selection being classified ‘‘specialists’ ’ and those with broader selection being ‘‘generalists’’. The standard model of niche breadth characterizes generalists and specialists as having comparable levels of overall total resource exploitation, with specialists exploiting resources at a higher level of performance over a narrower range of conditions. This view has gone largely unchallenged. An alternate model predicts total resource use being lower for the specialized species with both peaking at a comparable level of performance over a particular resource gradient. To reconcile the niche breadth paradigm we contrasted both models by developing range-wide species distribution models for Canada Lynx, Lynx Canadensis, and bobcat, Lynx rufus. Using a suite of environmental factors to define each species ’ niche, we determined that Canada Lynx demonstrated higher total performance over a restricted set of variables, specifically those related to snow and altitude, while bobcat had higher total performance across most variables. Unlike predictions generated by the standard model, bobcat level of exploitation was not compromised by the trade-off with peak performance, and Canada Lynx were not restricted to exploiting a narrower range of conditions. Instead, the emergent pattern was that specialist species have a higher total resource utilization and peak performance value within a smaller number of resources or environmental axes than generalists. Our results also indicate that relative differences in nich
Jeff Bowman - One of the best experts on this subject based on the ideXlab platform.
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fine scale habitat selection by sympatric canada Lynx and bobcat
Ecology and Evolution, 2020Co-Authors: Samantha J Morin, Robby R. Marrotte, Jeff Bowman, Mariejosee FortinAbstract:The Canada Lynx (Lynx Canadensis) and the bobcat (Lynx rufus) are closely related species with overlap at their range peripheries, but the factors that limit each species and the interactions between them are not well understood. Habitat selection is a hierarchical process, in which selection at higher orders (geographic range, home range) may constrain selection at lower orders (within the home range). Habitat selection at a very fine scale within the home range has been less studied for both Lynx and bobcat compared to selection at broader spatiotemporal scales. To compare this fourth-order habitat selection by the two species in an area of sympatry, we tracked Lynx and bobcat during the winters of 2017 and 2018 on the north shore of Lake Huron, Ontario. We found that both Lynx and bobcat selected shallower snow, higher snowshoe hare abundance, and higher amounts of coniferous forest at the fourth order. However, the two species were spatially segregated at the second order, and Lynx were found in areas with deeper snow, more snowshoe hare, and more coniferous forest. Taken together, our findings demonstrate that the Lynx and bobcat select different resources at the second order, assorting along an environmental gradient in the study area, and that competition is unlikely to be occurring between the two species at finer scales.
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Multi-species genetic connectivity in a terrestrial habitat network
Movement Ecology, 2017Co-Authors: Robby R. Marrotte, Michael G.c. Brown, Melanie B. Prentice, Kimberley Y. Morris, Chad Cordes, Jeff Bowman, Paul J WilsonAbstract:Background: Habitat fragmentation reduces genetic connectivity for multiple species, yet conservation efforts tend to rely heavily on single-species connectivity estimates to inform land-use planning. Such conservation activities may benefit from multi-species connectivity estimates, which provide a simple and practical means to mitigate the effects of habitat fragmentation for a larger number of species. To test the validity of a multi-species connectivity model, we used neutral microsatellite genetic datasets of Canada Lynx (Lynx Canadensis), American marten (Martes americana), fisher (Pekania pennanti), and southern flying squirrel (Glaucomys volans) to evaluate multi-species genetic connectivity across Ontario, Canada. Results: We used linear models to compare node-based estimates of genetic connectivity for each species to point-based estimates of landscape connectivity (current density) derived from circuit theory. To our knowledge, we are the first to evaluate current density as a measure of genetic connectivity. Our results depended on landscape context: habitat amount was more important than current density in explaining multi-species genetic connectivity in the northern part of our study area, where habitat was abundant and fragmentation was low. In the south however, where fragmentation was prevalent, genetic connectivity was correlated with current density. Contrary to our expectations however, locations with a high probability of movement as reflected by high current density were negatively associated with gene flow. Subsequent analyses of circuit theory outputs showed that high current density was also associated with high effective resistance, underscoring that the presence of pinch points is not necessarily indicative of gene flow. Conclusions: Overall, our study appears to provide support for the hypothesis that landscape pattern is important when habitat amount is low. We also conclude that while current density is proportional to the probability of movement per unit area, this does not imply increased gene flow, since high current density tends to be a result of neighbouring pixels with high cost of movement (e.g., low habitat amount). In other words, pinch points with high current density appear to constrict gene flow.
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Habitat Loss, Not Fragmentation, Drives Occurrence Patterns of Canada Lynx at the Southern Range Periphery
2016Co-Authors: Megan L Hornseth, Jeff Bowman, Aaron A Walpole, Lyle R Walton, Justina C Ray, Dennis L. MurrayAbstract:Peripheral populations often experience more extreme environmental conditions than those in the centre of a species’ range. Such extreme conditions include habitat loss, defined as a reduction in the amount of suitable habitat, as well as habitat fragmentation, which involves the breaking apart of habitat independent of habitat loss. The ‘threshold hypothesis’ predicts that organisms will be more affected by habitat fragmentation when the amount of habitat on the landscape is scarce (i.e., less than 30%) than when habitat is abundant, implying that habitat fragmentation may compound habitat loss through changes in patch size and configuration. Alternatively, the ‘flexibility hypothesis ’ predicts that individuals may respond to increased habitat disturbance by altering their selection patterns and thereby reducing sensitivity to habitat loss and fragmentation. While the range of Canada Lynx (Lynx Canadensis) has contracted during recent decades, the relative importance of habitat loss and habitat fragmentation on this phenomenon is poorly understood. We used a habitat suitability model for Lynx to identify suitable land cover in Ontario, and contrasted occupancy patterns across landscapes differing in cover, to test the ‘threshold hypothesis ’ and ‘flexibility hypothesis’. When suitable land cover was widely available, Lynx avoided areas with less than 30 % habitat and were unaffected by habitat fragmentation. However, on landscapes with minimal suitable land cover, Lynx occurrence was not related to either habitat loss or habitat fragmentation, indicating support for the ‘flexibility hypothesis’. We conclude that Lynx are broadly affected by habitat loss, and no
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habitat loss not fragmentation drives occurrence patterns of canada Lynx at the southern range periphery
PLOS ONE, 2014Co-Authors: Megan L Hornseth, Jeff Bowman, Aaron A Walpole, Lyle R Walton, Justina C Ray, Mariejosee Fortin, Dennis L. MurrayAbstract:Peripheral populations often experience more extreme environmental conditions than those in the centre of a species' range. Such extreme conditions include habitat loss, defined as a reduction in the amount of suitable habitat, as well as habitat fragmentation, which involves the breaking apart of habitat independent of habitat loss. The ‘threshold hypothesis’ predicts that organisms will be more affected by habitat fragmentation when the amount of habitat on the landscape is scarce (i.e., less than 30%) than when habitat is abundant, implying that habitat fragmentation may compound habitat loss through changes in patch size and configuration. Alternatively, the ‘flexibility hypothesis’ predicts that individuals may respond to increased habitat disturbance by altering their selection patterns and thereby reducing sensitivity to habitat loss and fragmentation. While the range of Canada Lynx (Lynx Canadensis) has contracted during recent decades, the relative importance of habitat loss and habitat fragmentation on this phenomenon is poorly understood. We used a habitat suitability model for Lynx to identify suitable land cover in Ontario, and contrasted occupancy patterns across landscapes differing in cover, to test the ‘threshold hypothesis’ and ‘flexibility hypothesis’. When suitable land cover was widely available, Lynx avoided areas with less than 30% habitat and were unaffected by habitat fragmentation. However, on landscapes with minimal suitable land cover, Lynx occurrence was not related to either habitat loss or habitat fragmentation, indicating support for the ‘flexibility hypothesis’. We conclude that Lynx are broadly affected by habitat loss, and not specifically by habitat fragmentation, although occurrence patterns are flexible and dependent on landscape condition. We suggest that Lynx may alter their habitat selection patterns depending on local conditions, thereby reducing their sensitivity to anthropogenically-driven habitat alteration.
