Comunities and ecosystems represent aggregates of lower-level orders of
organization - generally, individual species, and populations of those
species. There is considerable research in the Department, primarily
concerned with analysis and understanding of the dynamics of populations,
and how these dynamics might vary within and among species.
The following highlights just a
few of the
several
'population' research projects currently active in the Department (for a
more complete
listing, click here. Alternatively, consult web
pages of the people
associated with research in this
area):
Snow goose
grazing dynamics | Snow goose grazing dynamics - Snow Geese are a colonially nesting species, with extremely strong natal philopatry amongst females, with strong tradition in their use of nesting and feeding areas. Such breeding and foraging patterns reflects, to a significant degree, a strongly synergistic relationship between herbivorous geese and their principal salt-marsh food plants. Under moderate grazing pressure, there is a positive feedback between grazing intensity and fecal nitrogen deposition and both net above-ground primary production and nitrogen content of food plants. In general, grazing pressure over the course of the breeding season reduces both above-ground forage and the capacity of vegetation to show compensatory growth following grazing. However, the size of the LPB population has nearly doubled in the last 15 years, and high-intensity grazing and early-season grubbing by increased numbers of geese has significantly reduced the annual standing crop of food available at LPB since the beginning of the study. This has had significant long-term negative impacts on both the plants, and the geese. This rapid deterioration of conditions over a comparatively short time span, and the seasonal variation in food supply, creates a behavioral conflict: at the one extreme, birds can remain philopatric to specific nesting or feeding areas, regardless of predictable or unpredictable changes in environmental conditions. | | | 
swan project | Atlantic Flyway Tundra Swan Project - Tundra Swans are a long-lived species with relatively low annual recruitment. Since swans breed in remote areas, little is known about their breeding ecology and distribution. In addition, the species is hunted in North Carolina, Virginia, North Dakota, South Dakota, and Montana. Harvest management would be more effective if more was known about their vital rates, migratory patterns, and distribution. Objectives of this study include: to determine the breeding range and migration stopover locations of the Eastern Population (EP) of Tundra Swans, as well as patterns of movement between these areas; to determine fidelity and possible sub-population affiliations of Tundra Swans to Atlantic Flyway wintering locations within years and between subsequent years; to increase precision of survival rate estimates for EP swans; and to determine extent and nature of winter movements of Tundra Swans in relation to habitat use and human disturbance. What makes this project unique is it’s scale and size: hundreds of birds have been marked over most of their Eastern wintering areas, providing a fairly representative sample of the Eastern Population. | | | 
Harvest of
structured
populations | Optimal harvest of structured populations - Population dynamics are in simplest terms governed by the balance between realized fecundity and recruitment, and mortality (or permanent emigration). For harvested species, this poses the potentially complex problem of determining the harvest practice which, by some criterion, is determined to be "optimal". Optimality decisions are generally derived with reference to the conditions under which population growth is maintained at some sustained equilibrium, either naturally, or through the harvest itself. The calculation of the optimal harvest conditions are often complex, especially where harvesting is variable with respect to time. Many analyses of optimal harvesting assume no age-structure, and continuous time. However, for many populations, this assumption of no age- or stage-structure, and continuous time, is clearly unrealistic. Failure to account for this can contribute significantly to sources of uncertainty, which affects our ability to successfully manage the resource. Preliminary analysis indicates failing to adequately account for structure in the harvested population can lead to unpredictable results in some cases. This result also has significant implications for biodiversity and management of resources, since it allows a flexible framework to assess the relative importance of individuals of a particular age or stage, and in a particular location, to a complex structured system. This is increasingly important in assessing viability of populations in fragmented landscapes. | | |
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