The far-reaching ecological effects of genetic fitness in a keystone predator species, grey wolves

Although loss of genetic fitness is known to be severely detrimental to the viability of populations, little is known about how changes in the genetic fitness of keystone species can impact the functioning of communities and ecosystems. Here we assessed how changes in the genetic fitness of a keystone predator, grey wolves, impacted the ecosystem of Isle Royale National Park over 2-decades. The decline and subsequent resurgence of inbreeding in the wolf population led to a rise and then fall in predation rates on moose, the primary prey of wolves and dominant mammalian herbivore in this system. Those changes in predation rate led to large fluctuations in moose abundance which in turn impacted browse rates on balsam fir, the dominant forage for moose during winter and an important species in the forest. Thus, forest dynamics can be traced back to changes in the genetic health of a predator population.

Skeletal and Dental Development Preserve Evidence of Energetic Stress in the Moose of Isle Royale

Food shortages can leave diagnostic, and in the case of the dentition, irreversible changes in mineralized tissue that persist into historical and fossil records. Consequently, developmental defects of tooth enamel might be used to track ungulate population irruption but dental tissue’s capacity for preserving historical population density changes has yet to be investigated in wild populations. We test the ability of enamel defects, mandible and metapodial lengths to track changes in the well-known fluctuating moose population of Isle Royale National Park. Our study demonstrates that 1) a moose density threshold exists on the island above which there is a significant decrease in mandible and metatarsus length and a concomitant increase in enamel hypoplasias, 2) food limitation has a more pronounced effect on male than female skeletal growth, and 3) combined data from tooth enamel hypoplasias and bone lengths reflect the relative density of this ungulate population, and should be broadly applicable to other ungulate osteological samples. Developmental defects in dental enamel were among the highest recorded in a wild population, and even during low-density intervals the population density of Isle Royale moose has been high enough to negatively impact skeletal and dental growth, indicating the comparatively poor health of this century-old ecosystem

Aquatic Macrophytes are Seasonally Important Dietary Resources for Moose

Moose (Alces alces) are generalist herbivores, but are important aquatic-terrestrial ecotone specialists. Aquatic macrophytes are a high-quality food source for moose during summer, but the importance of aquatic food sources to the moose diet is difficult to study. We used stable isotope analysis of carbon and nitrogen from moose hooves and forage (terrestrial plants, aquatic macrophytes, and arboreal lichen) to assess the diet of moose at Isle Royale National Park, Michigan, USA, using Bayesian mixing models. We also evaluated the isotopic variability along chronologies of serially sampled hooves. Overall, our mixing models indicate that 13%–27% of the summer moose diet was aquatic in origin. Among moose that died during winter, body condition was impaired and hoof 15N was higher where aquatic habitats were sparse. Although isotope chronologies preserved in hooves could significantly enhance our understanding of ungulate foraging ecology, interpretation of such chronologies is presently limited by our lack of knowledge pertaining to hoof growth rate and seasonal growth variability related to age and health. Distinct isotopic values among terrestrial plants, aquatic macrophytes, and arboreal lichens indicate that continued methodological advances in stable isotope ecology will lead to more precise estimates of the contribution of aquatic feeding to moose population dynamics and other ungulates.

Aquatic Macrophytes are Seasonally Important Dietary Resources for Moose

Moose (Alces alces) are generalist herbivores but are important aquatic-terrestrial ecotone specialists. Aquatic macrophytes are a high-quality food source for moose during the summer, however their relative importance to moose diet is difficult to study. We used stable isotope analysis of carbon and nitrogen from moose hooves and forage (terrestrial plants, aquatic macrophytes, and arboreal lichen) to estimate the diet of moose at Isle Royale National Park, Michigan, USA, and to evaluate the isotopic variability along chronologies of serially sampled hooves. We hypothesized that aquatic macrophyte consumption and winter body condition (as measured by bone marrow fat content) would be greater at the eastern end of the island where aquatic habitats were most abundant. We were unable to evaluate spatial differences in aquatic macrophyte consumption, but overall, our mixing model results suggest that between 13% and 27% of summer moose diet was from aquatic sources. Among moose that died during winter, body condition was impaired and hoof δ15N (measured at the hairline) was higher at the western end of the island, where aquatic habitats are sparse. Although isotope chronologies preserved in hooves could significantly enhance our understanding of ungulate foraging ecology, interpretation of such chronologies is presently limited by our lack of knowledge pertaining to hoof growth rate and seasonal dynamics in relation to age and health. Significant isotope distinction among terrestrial plants, aquatic macrophytes, and arboreal lichens indicate that continued methodological advances in stable isotope ecology will lead to more precise estimates of the contribution of aquatic feeding to moose population dynamics.

Wolf Listeners: An Introduction to the Acoustemological Politics and Poetics of Isle Royale National Park

Listening to wolf howls as both material object and socially constructed metaphor highlights the contested relationship between nature and culture. The author conducted field research on Isle Royale National Park from 2011 to 2015, from which data he offers a narrative wherein citizen-scientists who listen for the howl literally “lend their ears” to a wolf biologist who has led the longest continuous predator-prey study in the world. The theoretical framework of this essay extends acoustic ecology, first theorized by R. Murray Schafer, to include environmental history and cultural theory, which problematizes definitions of “nature” and “natural.” Ultimately, this introduction describes a nuanced form of participatory, situational environmental music that plays out in the everyday lives of those listening on this remote, roadless island on Lake Superior.