Ecological factors affecting midcontinent light goose recruitment
Ross, Megan V 1992-
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A full understanding of population dynamics requires knowledge about the relative contributions of both adult survival and recruitment to population growth rate. Avian life cycles consist of a number of reproductive stages leading to recruitment, each of which is highly susceptible to annual variability in environmental conditions. The purpose of my research was to identify key ecological factors associated with a long-term decline in the per capita gosling production of Ross’s geese (Chen rossii) and lesser snow geese (Chen caerulescens caerulescens) using historical data collected from 1992-2014 at Karrak Lake, Nunavut. I evaluated effects of (i) nutritional deficiencies of pre-breeding female Ross’s geese and lesser snow geese stemming from density-dependence following large increases in nesting population size and (ii) phenological mismatch between peak gosling hatch and peak forage quality, inferred from measurements of NDVI on brood-rearing areas. Annual gosling production (i.e., proportional composition of young during brood-rearing) was reduced for both species when the mass of nutrient reserves for pre-breeding females arriving to nest were lighter. Mismatch between peak gosling hatch and peak forage quality was also related to decreases in gosling production, while delays in nest initiation negatively affected clutch size and nest success (i.e., ≥ 1 egg hatched). Vegetation phenology was significantly earlier in years with warmer spring (i.e., 25 May – 30 June) surface air temperatures. Additionally, increased mismatch over the course of the 23-year study period apparently resulted from advancing vegetation phenology without a contemporaneous advance in goose breeding phenology. I did not find evidence of a direct effect of annual nesting population size on colony gosling production. Given an absence of information on the pre-fledging stage of the life cycle for geese originating from Karrak Lake, I studied the effect of conditions experienced during early life on the growth and survival of goslings. Time constraints due to strong seasonality at arctic-nesting grounds highlight the importance of foraging conditions (i.e., quality, quantity, availability) for offspring during brood-rearing. I found that an increase in the number of nesting geese was associated with a reduction in gosling survival for both Ross’s geese and snow geese. There was weak evidence that snow goose gosling body size was negatively related to breeding population size at the colony, while no effect was detected for Ross’s geese. Increasing mismatch between the seasonal peak in vegetation quality and timing of hatch was negatively related to both gosling size and survival probability; suggestive of nutritional stress. My results lend support to the notion that both global (i.e., climate change) and local (i.e., foraging/habitat conditions) phenomena may result in reduced offspring production and success, and alludes to the possibility of an eventual decline in recruitment into the breeding cohort.
DegreeMaster of Science (M.Sc.)
CommitteeMorrissey, Christy A; Clark, Robert G; Wei, Yangdou D; Clark, Douglas A
Copyright DateJune 2017