Browsing by Author "McFadden, Roger Timothy"
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Item Hybridization and introgression of toads of the Bufo americanus group(1970) McFadden, Roger Timothy; Jameson, David L.; Aumann, Glenn David; Kimball, Aubrey P.Toads in the Bufo americanus group are capable of extensive interbreeding. In the laboratory hybridization frequently results in viable sexually mature offspring. The complex of toads found in eastern Texas and western Louisiana is remarkably heterogeneous suggesting either extremely close phylogenetic relationships among the toads, or wide-spread hybridization and introgression. Morphological and biochemical characters of individual toads sampled from this complex were examined. Blood proteins were analysed by acrylamide gel disc electrophoresis and the morphological characters by multiple-group discriminant analysis. Analysis of the electrophoretic banding patterns over a wide range of protein systems by cluster analysis failed to reveal meaningful differences between species or populations. Discriminant analysis showed significant overlap between populations indicating that successful hybridization is occurring. Isolation mechanisms appear to be inoperative. The breakdown of these isolating mechanisms appear to be contributing to the removal of reproductive separation between the populations and the formation of a heterogeneous interbreeding complex.Item Structure and seasonality in an arthropod community(1978) McFadden, Roger Timothy; Jameson, David L.; Aumann, Glenn David; Bryant, Edwin H.; Brady, David W.This study explores the relationship between species composition and the structure of an arthropod community in an open field, and attempts to determine the factors which account for changes in species composition and abundance. The numerical response of the arthropods to seasonal change is examined by factor analysis and compared with compositional changes reflected in the heterogeneity of the community. Seasonality in the insect community is exhibited by complex patterns of temporal niche diversification involving all trophic levels. Primary seasonal components revolve around distinctions between summer and winter species based on resource availability and utilization patterns. Summer and winter species are characterized by their responses to qualitatively different properties of the environment: winter species respond to temperature variability while summer species respond to average temperatures. The evidence suggests that the heterogeneity of the community is closely associated with events occuring in the vegetation. In general, more complex vegetation structure is reflected in an increase in the heterogeneity of the insects.