Niche Dynamics and Organization of Waterfowl Guilds in Variable Environments

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Abstract
Factors influencing the diversity of coexisting ducks in the prairie—pothole region of North America were investigated. Thirty—five years of census data and data on breeding—habitat use for each of two guilds (diving and dabbling ducks) from aspen—parkland and mixed—prairie habitats were analyzed to investigate the means by which species were accommodated in diverse assemblages. There was a regular increase in the temporal variability of breeding habitats of each guild in this order: parkland divers < parkland puddle ducks < grassland divers < grassland puddle ducks. A positive relationship between a multivariate measure of niche separation derived from discriminant function analysis and species diversity, suggesting competitively induced adjustments to niche parameters, was found only for parkland diving ducks. Species diversity was better correlated with total niche space for guilds occupying more variable breeding habitats. Niche separation and species diversity were never inversely related, suggesting that competition for limited resources in evolutionary time sets the limits to species' similarity in resource use, but the importance of competition as a factor influencing community structure in ecological time depends on environmental variability. Evidence that duck populations may be in long—term equilibria with resource levels in breeding areas is presented.