Linking spatial variations in life-history traits to environmental conditions across American black bear populations

Spatial variations in food availability may influence life-history traits
of wildlife species, particularly in capital breeding species that store
energy when food is widely available and catabolize it during
energy-intensive reproductive periods. The reproductive success of capital
breeders is thus highly dependent on the accumulation of fat reserves.
Reproductive success may also improve with access to alternative food
resources provided by environments with strong human footprint and
anthropogenic disturbances, but these environments may also increase
mortality risks of wildlife. We performed a systematic review to extract
reproduction and survival traits reported in studies on the American black
bear (Ursus americanus), a capital breeder. Based on 94 studies widely
distributed across North America, we conducted meta-regression analyses to
assess whether interpopulation variation in age at primiparity, litter
size of cubs, annual cub survival, and annual survival of adult females
were associated with environmental conditions, that is, habitat quality,
habitat productivity, and anthropogenic disturbances. We found that mean
age at primiparity decreased from around 5 to 4 years old in areas with
the highest habitat quality and productivity as well as the highest human
population densities compared with those with poor habitat quality and
productivity and low human population densities. Mean litter size
increased by approximately 13% (from 2 to 2.25 cubs per litter) in areas
with the highest compared with the lowest proportion of deciduous forest,
while cub survival increased by about 13% (from 60% to 73%) in areas with
the highest compared with the lowest coverage of agricultural crops. Adult
female survival decreased from 92% to 85% in areas where hunting was
allowed. These results provide new insights into the factors associated
with variations in reproductive success and survival across populations of
a widely distributed species, demonstrating the impact of both natural and
anthropogenic factors. Our study highlights the necessity of considering
the ongoing changes in the distribution and growth of potential food
resources, as well as the growing encroachment of humans into wildlife
habitats, when planning management and conservation actions at the scale
of a species distribution range.