Whitebark Pine, Population Density, and Home-Range Size of Grizzly Bears in the Greater Yellowstone Ecosystem

Bjornlie, Daniel D.; Manen, Frank T. van; Ebinger, Michael R.; Haroldson, Mark A.; Thompson, Daniel J.; Costello, Cecily M.

doi:10.1371/journal.pone.0088160

Cited by 55 publications

(33 citation statements)

References 36 publications

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“…Our study findings corroborate those of Bjornlie et al (), who reported evidence of an inverse relationship between home‐range size and the index of grizzly bear population density; they did not observe a relationship between home‐range size and availability of live whitebark pine stands. Combined, these studies provide evidence that grizzly bear density may become an increasingly important factor to consider for management of the grizzly bear population in the GYE.…”

Section: Management Implicationssupporting

confidence: 92%

“…These cells were not solvable in terms of correlations and were excluded. Of the remaining cells ( n = 250), we detected little correlation between the rate of change of the cumulative capture index and that of the density index: the distribution of correlation coefficients for these 250 cells approached a normal distribution with a mean near 0 (

\overset{x}{true} = 0.07; σ = 0.28

; Bjornlie et al ). The second caveat is that the initial and ending years from 1975 to 2012 underestimated density relative to the middle years of this period.…”

Section: Methodsmentioning

confidence: 83%

“…If bears were responding to a decline in carrying capacity, however, we would have expected home‐range size and movements to have increased (McLoughlin et al ), bears to have relied on lower‐energy food resources (McLellan ), and body condition to have declined as a consequence (Rode et al , Robbins et al , Zedrosser et al ). To date, there is little support for these conditions in the Yellowstone Ecosystem: female home ranges have decreased in size and are less variable in areas with greater bear densities (Bjornlie et al ), daily movement rates and daily activity radii have not changed for either sex during fall (Costello et al ), bears continue to use high‐quality foods (Fortin et al ), and body mass has not declined (Schwartz et al ). As we discussed previously, percent body fat among adult females has not declined since the early 2000s (IGBST , Schwartz et al ) and, regardless, this effect would be consistent with either interference or exploitation competition and would not explain the changes in vital rates that occurred much earlier than the declines in foods.…”

Section: Discussionmentioning

confidence: 99%

“…We ended the period for validation in 2006 because of the aforementioned time lag for sampling bears. For the 1998–2006 period, the mean density index was positively correlated with mean log‐transformed counts of bear groups/hour/1,000 km 2 within BOAs ( r = 0.725, P < 0.001, n = 28; Bjornlie et al ). Assuming that changes in observation rates over time are a product of the number of bears in BOAs, these results support the efficacy of the index to track relative changes in bear density.…”

Section: Methodsmentioning

confidence: 97%

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Density dependence, whitebark pine, and vital rates of grizzly bears

et al. 2015

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Understanding factors influencing changes in population trajectory is important for effective wildlife management, particularly for populations of conservation concern. Annual population growth of the grizzly bear (Ursus arctos) population in the Greater Yellowstone Ecosystem, USA has slowed from 4.2–7.6% during 1983–2001 to 0.3–2.2% during 2002–2011. Substantial changes in availability of a key food source and bear population density have occurred. Whitebark pine (Pinus albicaulis), the seeds of which are a valuable but variable fall food for grizzly bears, has experienced substantial mortality primarily due to a mountain pine beetle (Dendroctonus ponderosae) outbreak that started in the early 2000s. Positive growth rates of grizzly bears have resulted in populations reaching high densities in some areas and have contributed to continued range expansion. We tested research hypotheses to examine if changes in vital rates detected during the past decade were more associated with whitebark pine decline or, alternatively, increasing grizzly bear density. We focused our assessment on known‐fate data to estimate survival of cubs‐of‐the‐year (cubs), yearlings, and independent bears (≥2 yrs), and reproductive transition of females from having no offspring to having cubs. We used spatially and temporally explicit indices for grizzly bear density and whitebark pine mortality as individual covariates. Models indicated moderate support for an increase in survival of independent male bears over 1983–2012, whereas independent female survival did not change. Cub survival, yearling survival, and reproductive transition from no offspring to cubs all changed during the 30‐year study period, with lower rates evident during the last 10–15 years. Cub survival and reproductive transition were negatively associated with an index of grizzly bear density, indicating greater declines where bear densities were higher. Our analyses did not support a similar relationship for the index of whitebark pine mortality. The results of our study support the interpretation that slowing of population growth during the last decade was associated more with increasing grizzly bear density than the decline in whitebark pine. Grizzly bear density and its potential effect on vital rates and population trajectory warrant consideration for management of the grizzly bear population in the Greater Yellowstone Ecosystem. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

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Section: Management Implicationssupporting

confidence: 92%

\overset{x}{true} = 0.07; σ = 0.28

; Bjornlie et al ). The second caveat is that the initial and ending years from 1975 to 2012 underestimated density relative to the middle years of this period.…”

Section: Methodsmentioning

confidence: 83%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 97%

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Density dependence, whitebark pine, and vital rates of grizzly bears

et al. 2015

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“…Grizzly bears are a known predator of elk calves and may strongly influence calf recruitment (Barber‐Meyer et al , Griffin et al ); thus, we developed an index of grizzly bear density. We estimated the index using procedures developed by the Interagency Grizzly Bear Study Team (IGBST; see Bjornlie et al for in‐depth description). The index is derived from capture and telemetry locations of known‐age individuals ≥2 years old in conjunction with survival records to back‐ and forecast lifetime home ranges.…”

Section: Methodsmentioning

confidence: 99%

Influences of supplemental feeding on winter elk calf:cow ratios in the southern Greater Yellowstone Ecosystem

Foley¹,

Cross

Christianson

et al. 2015

Jour. Wild. Mgmt.

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Several elk herds in the Greater Yellowstone Ecosystem are fed during winter to alleviate interactions with livestock, reduce damage to stored crops, and to manage for high elk numbers. The effects of supplemental feeding on ungulate population dynamics has rarely been examined, despite the fact that supplemental feeding is partially justified as necessary for maintaining or enhancing population growth rates. We used linear regression to assess how the presence of feedgrounds, snowpack, summer rainfall, indices of grizzly bear density and wolves per elk, elk population trend counts, brucellosis seroprevalence, and survey date were correlated with midwinter calf:cow ratios, a metric correlated with population growth, from 1983-2010 from 12 ecologically similar elk herd units (7 fed and 5 unfed) in Wyoming, USA. Our statistical approach allowed for rigorous tests of the hypotheses that supplemental feeding had positive effects on calf: cow ratios and reduced sensitivity of calf:cow ratios to bottom-up limitation relative to top-down limitation from native predators. Calf:cow ratios generally declined across all herd units over the study period and varied widely among units with feedgrounds. We found no evidence that the presence of feedgrounds had positive effects on midwinter calf:cow ratios in Wyoming. Further, fed elk showed stronger correlations with environmental factors, whereas calf:cow ratios for unfed elk showed stronger correlations with predator indices. Although we found no consistent association between winter feeding and higher calf:cow ratios, we did not assess late winter mortality and differences in human offtake between fed and unfed regions, which remain a priority for future research. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

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Of wolves and bears: Seasonal drivers of interference and exploitation competition between apex predators

Tallian

Ordiz

Metz

et al. 2022

Ecological Monographs

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Competition between apex predators can alter the strength of top-down forcing, yet we know little about the behavioral mechanisms that drive competition in multipredator ecosystems. Interactions between predators can be synergistic (facilitative) or antagonistic (inhibitive), both of which are widespread in nature, vary in strength between species and across space and time, and affect predation patterns and predator-prey dynamics. Recent research has suggested that gray wolf (Canis lupus) kill rates decrease where they are sympatric with brown bears (Ursus arctos), however, the mechanisms behind this pattern remain unknown. We used data from two long-term research projects in Scandinavia (Europe) and Yellowstone National Park (North America) to test the role of interference and exploitation competition from bears on wolf predatory behavior, where altered wolf handling and search time of prey in the presence of bears are indicative of interference and exploitation competition, respectively. Our results suggest the mechanisms driving competition between bears and wolves were dependent on the season and study system. During spring in Scandinavia, interference competition was the primary mechanism driving decreased kill rates for wolves sympatric with bears; handling

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Whitebark Pine, Population Density, and Home-Range Size of Grizzly Bears in the Greater Yellowstone Ecosystem

Cited by 55 publications

References 36 publications

Density dependence, whitebark pine, and vital rates of grizzly bears

Density dependence, whitebark pine, and vital rates of grizzly bears

Influences of supplemental feeding on winter elk calf:cow ratios in the southern Greater Yellowstone Ecosystem

Of wolves and bears: Seasonal drivers of interference and exploitation competition between apex predators

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