Population dynamics and Productivity of McCown's Longspur at Matador, Saskatchewan
Felske, Brian Edward
Organisms at the carnivore-omnivore level of an ecosystem, such as birds, do not represent a significant amount of biomass because of the inefficiency of energy transfer through the trophic levels of a natural system. Relative to that which is stored by the autotrophs, secondary consumer energy fixed as production is minimal. Nevertheless, secondary producers do represent a flow of energy and exert a regulatory effect on the system through the act of consuming. Generally, the productivity of an organism can be regulated through one or more causal pathways as outlined by Watt (1968). Natality, the birth rate, is determined by the fecundity and fertility of the species. Those organisms which are born are then subjected to mortality as a result of predation and other causes. Individuals which escape mortality produce biomass through increment during growth usually at a rate specific to the species. Individual characteristics of a species or group of organisms may add some specific means of productivity such as the moult and growth of new feathers in birds. These causal pathways can all be ultimately regulated by the food energy available to the parent generation during reproduction and to the offspring during growth. Lack (1968) in his concluding statement on bird population theory, repeats that the availability of food for the young and to lesser extent that available to the female combined with the risks of predation are the most important factors in determining the course of the evolution of breeding habits in birds. This study was designed to grossly assess the production aspects of the life history of McCown's Longspur (Rhynchophanes mccownii Baird) as a secondary producer in the Matador grassland ecosystem and to determine the factors which affect the causal patterns of production described above. Within these terms of reference, habitat preference, density, standing crop and biomass components of the adult population were studied. The moult and rate of production of new feathers together with the effect on body components were also considered. The major source of productivity through reproduction and growth of offspring was quantified together with the effects of natality, mortality, growth rate and the availability and source of food energy.