Jason H. Knouft

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Change in body size within an evolutionary lineage over time has been under investigation since the synthesis of Cope's rule, which suggested that there is a tendency for mammals to evolve larger body size. Data from the fossil record have subsequently been examined for several other taxonomic groups to determine whether they also displayed an evolutionary(More)
Many taxonomic and ecological assemblages of species exhibit a right-skewed body size-frequency distribution when characterized at a regional scale. Although this distribution has been frequently described, factors influencing geographic variation in the distribution are not well understood, nor are mechanisms responsible for distribution shape. In this(More)
Examples of convergent evolution suggest that natural selection can often produce predictable evolutionary outcomes. However, unique histories among species can lead to divergent evolution regardless of their shared selective pressures-and some contend that such historical contingencies produce the dominant features of evolution. A classic example of(More)
Using collections from the years 1892-1999, I determined maximum standard length within each of 1030 populations of riffle-inhabiting darters (Etheostoma spp.) representing five species from 788 sites in Illinois. Each site contained one to four riffle-inhabiting species of Etheostoma. Based on maximum-sized individuals in each collection, I calculated a(More)
Broad-spectrum antimicrobial compounds have recently been identified in the epidermal mucus of fishes and probably serve as a first line of defence against microbial pathogens. Because of the ubiquitous nature of fungi and bacteria in aquatic systems, defence against these pathogens should be required throughout the lifespan of fishes, including the egg(More)
Species distributions are influenced by many processes operating over varying spatial scales. The development of species distribution models (SDMs), also known as ecological niche models, has afforded the opportunity to predict the distributions of diverse taxa across broad geographic areas and identify variables that are potentially important in regulating(More)
Recent advances in ecological niche modeling (ENM) algorithms, in conjunction with increasing availability of geographic information system (GIS) data, allow species' niches to be predicted over broad geographic areas using environmental characteristics associated with point localities for a given species. Consequently, the examination of how niches evolve(More)
Behavioral, genetic, and immune variation within a host population may lead to aggregation of parasites whereby a small proportion of hosts harbor a majority of parasites. In situations where two or more parasite species infect the same host population there is the potential for interaction among parasites that could potentially influence patterns of(More)
Humans are having a profound impact on the geographic distributions of plant populations. In crop species, domestication has been accompanied by the geographic expansion of cultivated populations relative to their wild ancestors. We used a geographical information system (GIS)-based approach to investigate differences in the environmental factors(More)
Covariation between population-mean phenotypes and environmental variables, sometimes termed a "phenotype-environment association" (PEA), can result from phenotypic plasticity, genetic responses to natural selection, or both. PEAs can potentially provide information on the evolutionary dynamics of a particular set of populations, but this requires a full(More)