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The Role of Climate Variability in Duck Population Ecology



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Climate change is having profound impacts on animal populations globally, and is expected to become a stronger stressor in future, influencing abundance and persistence of many species. In northern hemisphere bird populations, local weather and climate cycles play important roles via effects on components of individual fitness (i.e., survival and reproductive success), and thus annual fluctuations in population sizes. I used congruent long-term data for duck populations, individuals, and climatic variables to test hypotheses about the relative roles of climate and other factors in population dynamics, variation in vital rates, and timing of breeding. Where possible I used interspecific comparisons to evaluate whether responses were mediated by life-history traits. First, I examined annual variation in the timing, length, and productivity of growing seasons on duck population growth rates in North American boreal forest, 1982-2013. I found limited evidence that spring phenology, growing season length or productivity influenced annual population growth rates, and effects were not always in the direction predicted based on species-specific timing of breeding. Second, I evaluated impacts and potential synchronizing forces of shared trends in temperature and precipitation on widely separated populations of ecologically equivalent duck species in North America and western Europe, 1976-2011. Several duck species-pairs shared increasing time trends but growth rates were not synchronized among years. This pattern of shared trends but no annual synchrony was mirrored in climate variables recorded over the major breeding areas on each continent. Third, at the individual-level, I found that ducklings of a late-breeding species, lesser scaup (Aythya affinis), had slower growth rates when hatched late relative to their cohort but I detected no effect of spring phenology. Hatch date effects did not carryover to influence postfledging survival. In contrast, a negative effect of conspecific density on prefledging growth seemed to carryover to influence postfledging survival, and possibly first-year breeding probability. Fourth, examining breeding dates of individually marked females, I found that early-nesting species tracked spring phenology, while late-nesting species did not. Yet, annual variation in the timing of breeding in late-nesting species suggests that females respond to other unmeasured cues not related to spring phenology. Collectively, results indicate that individual ducks are resilient to annual fluctuations in climatic drivers, so populations respond more strongly to sustained long-term trends in climate cycles. Species I studied have varying capacity to respond to annual phenological cues, but it may be that density dependence in vital rates mediates adverse environmental effects that occur in only one season. Therefore, climate trends that impact per capita resource availability (e.g., wetland area, food quality and quantity) may be the primary concern for conservationists assuming that annual climatic fluctuations remain within the range observed during my study periods. Experimental studies that manipulate environmental variables may be necessary to gain further insights into how ducks will respond to climate change predicted in this century.



Anatidae, population ecology, demography, climate, climate variability



Doctor of Philosophy (Ph.D.)






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