Enhancements to population monitoring of Yellowstone grizzly bears

Evidence for density‐dependent effects on body composition of a large omnivore in a changing Greater Yellowstone Ecosystem

“…As dispersal of bears continues into more human-dominated areas, conflicts and mortality may intensify. Monitoring data support this, with demography primarily driven by intrinsic, density-dependent factors within the core area and anthropogenic factors (i.e., human-caused mortality) on the periphery of occupied range(van Manen et al, 2016;van Manen & Haroldson, 2017). We observed these patterns under legal protection of the species for almost five decades.…”

“…Because of different land ownership and management practices, the history of population dynamic processes varies within the study area: Yellowstone National Park is the core strictly protected area where grizzly bears have always been present at relatively higher densities. Conversely, the presence of grizzly bears outside the national park was reduced until conservation measures were implemented and densities began to increase in adjacent areas starting in the mid-1980s, and peripheral areas of the ecosystem were re-occupied only in the last two decades (Figure 2) (van Manen & Haroldson, 2017). Therefore, we controlled for spatial heterogeneity of population dynamic histories by using estimates of local density, as described under the covariates subsection below.…”

“…The conservation status of the GYE grizzly bear population markedly improved from 1970s to present, driven by concerted management efforts that resulted in relatively high survival rates for several decades (Schwartz et al, 2006). More specifically, the grizzly bear population increased from perhaps fewer than 250 to around 1000 individuals (van Manen et al, 2022; Figure 1a), and the occupied range expanded (Figure 2). Population growth has slowed since the early 2000s in the presence of density‐dependent effects, primarily due to lower immature (<2 years old) survival rates, with intraspecific killing by male bears playing a likely role, as well as lower fecundity of females (van Manen et al, 2016).…”

“…(a) Standardized (left y ‐axis) and estimated (right y ‐axis) count of female grizzly bears with cubs‐of‐the‐year and 95% confidence interval (1997–2020) based on annual population monitoring (van Manen et al, 2022). (b) Standardized temporal trends (1990–2020) of high‐calorie food sources for grizzly bears in the Greater Yellowstone Ecosystem, specifically bison (dark yellow line), elk (dark red line), cutthroat trout (dark blue line), and whitebark pine (dark green line).…”

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

“…Bears have been observed at over half of all adult-ungulate wolf kills during summer in Yellowstone, where multiple bears often compete simultaneously for access (Stahler et al, 2020). Second, the number of brown bears present at a carcass increases with carcass size (van Manen et al, 2017), which may create a competitive tipping point for which it is advantageous for wolves to defend, or vie for access to, smaller kills, but not larger ones. In other words, multiple bears may be able to fully usurp a carcass from wolves, causing them to abandon their kill sooner than they would have otherwise.…”