Transient Population Dynamics and Population Momentum in Vertebrates
Type of DegreeDissertation
Forestry and Wildlife Sciences
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Maintenance of sustainable wildlife populations is one of the primary purposes of wildlife management. Thus, it is important to monitor and manage population growth and size over time. Population structure (i.e., age, stage, or size distribution) can affect both population size and growth over time; however, the effects of population structure on vertebrate population dynamics are poorly studied. Here, I examine and compare the effects of population structure on short- (i.e., transient) and long-term (i.e., asymptotic) population dynamics across selected vertebrate taxa. A general formula for relating sensitivity of transient population growth rate to changes in life history parameters was developed. Using this tool and others, I found that variation in transient growth rates and their sensitivities to changes in life history parameters were largely dependent upon a population’s initial net reproductive value. Furthermore, transient population dynamics of long-lived, slow reproducing species were more variable and different than asymptotic dynamics when compared to short-lived, fast reproducing species. Management actions have strong potential to change population structure, which can produce strong residual effects on population size, commonly known as population momentum. I examined management actions targeted at halting the growth or decline of hypothetical populations and measured the effects of instantaneous changes in fertility or survival on short-term transient dynamics and population momentum. Population momentum following changes in fertility actually reduced population size in growing populations and increased population size in declining populations. Changes in survival rarely reversed the direction of short-term population growth, and resulting population momentum was generally in the direction of historical population growth. Because population momentum has not been well studied across vertebrates, novel formulas and hypotheses relating the dynamics of population momentum to life history parameters were developed. Using algebra, calculus and computer simulation, I compared the dynamical relationship between life history and population momentum across a variety of bird, mammal, turtle, lizard, snake, and bony fish life histories. Population momentum was related to age at maturity within each taxon, and was largest in late maturing bony fishes. Lastly, I provide examples that illustrate how studies of population momentum can be used to better understand life histories, source-sink metapopulation dynamics, and management actions.