Effects of variable and changing environments on demography : Inferences from a lesser snow goose colony / David T. Iles

Thesis (Ph.D.) -- Utah State University

Includes bibliographical references.

Anthropogenic pressures have caused changes in both the mean and variance of
environmental conditions, with associated effects on the demography of natural
populations. The demographic effects of environmental change can manifest through
direct (i.e., physiological) or indirect pathways (i.e., through shifts in species
interactions). For many populations, environmental change will affect multiple life cycle
stages simultaneously, thereby altering vital rate correlation structures with potentially
important impacts on evolutionary fitness. The effects of environmental change will also
often be habitat-specific, particularly when species interactions modify demographic
sensitivity to climate. As a result, the effects of climate change are likely to vary across a
species range, with important implications for range expansion and population viability.
In chapter 2, I examine the effects of joint vital rate responses to environmental
drivers on the evolution of life histories in variable environments. I show that vital rate
covariation, generated when multiple vital rates respond to a shared environmental driver, can fundamentally alter evolutionary selection pressures. Negative vital rate covariation
promotes the evolution of demographic lability (stronger demographic responsiveness),
while positive covariation promotes buffering (weaker demographic responsiveness),
altering the range of life histories over which the evolution of buffered and labile vital
rates are a predicted evolutionary outcome. By identifying the life histories for which
selection pressures are most sensitive to environmentally-driven vital rate covariation,
this study provides a richer understanding of both life history evolution and the capacity
of species to cope with ongoing changes to contemporary environments.
In chapter 3, I use a long-term study of lesser snow geese to test the hypothesis
that demographic and developmental responses to climate will be weakest in habitats
where resource diversity is greatest. I find support for this hypothesis, and my results
indicate that gosling demography is much more responsive to climate in recently
colonized, freshwater habitats where landscape diversity and gosling diet diversity is low.
These results underscore the potential importance of accounting for biotic interactions
when predicting spatio-temporal responses to climate.
In chapter 4, I quantify the consequences of observed climate change for lesser
snow goose population dynamics across habitats. I find that climate change increases
population growth in all habitats, but that such increases are disproportionately large in
novel inland freshwater habitats. These results suggest that in a warmer and more
variable climate, the breeding range and population growth of lesser snow geese is likely
to increase, counteracting current management efforts to reduce overabundant
populations.