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Dowling, Thomas E

The extant genetic variation of a population is the legacy of both long-term and recent population dynamics. Most practical methods for estimating effective population size are only able to detect recent effects on genetic variation and do not account for long-term fluctuations in species abundance. The utility of a maximum likelihood estimator of long-term effective population size based upon the coalescent theory of gene genealogies is examined for three endangered Colorado River fishes: humpback chub (Gila cypha), bonytail chub (Gila elegans) and razorback sucker (Xyrauchen texanus). Extant mitochondrial DNA (mtDNA) variation in humpback chub suggests this species has retained its historical equilibrium genetic...
1. The effects of phosphorus enrichment and grazing snails on a benthic microbial community that builds stromatolic oncolites were examined in an experiment at Rio Mesquites, Cuatro Ci´┐Żnegas, Mexico. Chemical analyses of stream water samples indicated that overall atomic ratios of total nitrogen (N) to total phosphorus (P) were approximately 110, indicating a strong potential for P-limitation of microbial growth. 2. Phosphorus enrichment involved addition of 5 ?mol Na2HPO4 L-1 to streamside microcosms receiving intermittent inputs of stream water while grazer manipulation involved removal of the dominant grazer, the snail Mexithauma quadripaludium. After 7 weeks, we examined responses in organic matter content,...
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