Laboratory research has contributed greatly to knowledge of how specific genes are involved in the physiological process of organism aging under controlled conditions. However, to better understand the underlying mechanisms of senescence, there is a need to identify not only the genes, but also the environmental factors that influence senescence of organisms in the wild. This project will make use of data from a 40 year study of a population of lesser snow geese in the Arctic and sub-Arctic to examine how changes in the goose population density affect the rate of senescence for these organisms. This research will measure the impact of population density during early development on chances of survival later in life, while controlling for unobserved individual genetic variation using newly developed random-effect and mixture models for survival estimation based on capture-mark-recapture data. Through data analysis and modeling, this project will assess the effect of spatial and temporal variation in age-specific survival on snow goose population dynamics, and predict where the goose population is likely to expand and threaten the local ecosystem. By combining modern statistical methods with a long-term study of uniquely marked individuals, this work will help identify the more general role of population density and environmental conditions during development on patterns of senescence in free-ranging organisms. The population model will help simultaneously elucidate demographic processes regulating the process of invasion of the geese into new habitats over time, and the processes regulating snow geese density after the initial invasion.
High densities of migrating snow geese cause damage to cereal crops in the central United States, transmit diseases such as cholera and influenza to other avian species, and damage Arctic ecosystems which impacts local Native Americans. This research will be conducted on lands used by members of the Cree First Nation for subsistence living. First Nation members are very concerned about the habitat damage that snow geese are creating because it affects other plants and animals that are part of their traditional way of life. Findings from this project could be used to develop novel methods for mitigating the negative impacts of overabundant snow geese on the livelihoods of Native Americans and farmers, as well as Arctic and sub-Arctic species diversity.
Intellectual Merit: Evidence is accumulating that environmentally driven changes in natal conditions can affect the growth, survival, future reproduction and even fitness of both humans and wild organisms. Theories and hypotheses such as the "Thrifty phenotype hypothesis", the "Silver spoon effect", the "Barker hypothesis" or the "Predictive adaptive response hypothesis" are centered around the idea that environmental conditions in early life can generate not only immediate effects, but also effects later in life (e.g. the chance of acquiring a disease). The generalized prediction is that we expect individuals with access to abundant resources during the early part of their life to experience life-long fitness advantages. Vice versa, we expect individuals that experienced resource restrictions or deprivation early in life to pay a cost later in life; if they make it to adulthood. We studied this question in a long-lived herbivore, the lesser snow goose. These birds are at the center of an extreme natural experiment created by their own over-abundance and over-grazing of tundra lowland plants on their breeding grounds. This creates a mosaic of highly degraded to pristine habitats. Some goslings experience severe resource restriction during development while others have access to ample resources. Given the great disparity in resource wealth experienced by developing goslings, snow geese are an especially interesting species for investigating the consequences of natal environmental conditions on survival during the early, middle, and late parts of their life. What we found was surprising. Poor natal conditions led to lower rates of gosling growth and survival through not only the first, but also the second year of their life. This strong force of selection resulted in only the most robust (e.g., small but resilient) individuals making it to old age leading to unexpected lower rates of old-age senescence in the group of individuals that grew up in poor natal environmental conditions. The opposite was observed when natal conditions were of high quality because a greater diversity of individuals made it to old age. This goes against most theoretical concepts mentioned above, but fits nicely with the concept of intra-generational selection whereby frail individuals might exit a population relatively early in life (because of mortality), consequently affecting the composition of a population as individuals proceed through the life cycle. Until now, most studies testing the theories mentioned above either occurred under laboratory conditions on model organisms, or were focused on organisms experiencing semi-domestic environments. This is the first time these questions have been examined in a truly wild species that is overabundant, and through foraging, affects the quality of its habitat where offspring develop. In addition, our results help explain why snow goose populations are so resilient to habitat degradation and continue to grow at unprecedented rates. Broader Impacts: NSF support of this project helped train a post-doctoral researcher and ultimately helped her launch a career in science by securing an assistant professor position. The grant additionally helped train two graduate students, and an REU supplement helped an undergraduate student pursue research for the first time. We also helped train local middle and high school students from Churchill (in northern Manitoba, Canada) in field ecology. The research team also met with Cree and Métis community members each year to discuss research activities and the impacts snow geese are having on the land and other resources they depend upon. Our research shows how long-term ecological data can inform science, public policy, and natural resource management all at once. Our findings are actually used by the U.S. Fish & Wildlife and Canadian Wildlife Services to develop action plans aimed at preventing snow geese from causing further damage to Arctic ecosystems, and hopefully allow habitat conditions to recover such that Arctic biodiversity can be sustainably preserved.
