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An intensive sampling study, undertaken in a natural sandflat population of an estuarine neogastropod, Ilyanassa obsoleta, revealed a marked degree of spatial heterogeneity for a number of important characteristics. Growth rate could be inferred by observing changes in size—classes over time, but the inequitable spatial distribution of size—classes renders size/frequency analysis impractical and of dubious predictive value for this population. Overall parasitism rate in this population is high, generally increases exponentially with increasing age, and creates a relatively narrow reproductive fenestra temporalis by apparently permanent sexual impairment of infected snails. In fact, the strong influence of parasites on behavior and physiology of snails may necessitate distinguishing between apparent and functional individuals, with regard to their role in estuarine benthic communities. However, incidence of both parasitism and parasite species is highly variable in space. Nearly half of all samples taken departed significantly from the overall sex ratio, indicating that distribution of sexes is also heterogeneous. Since there is little predictive relationship between specific samples and overall population trends, it is likely that differentiating between trends that are truly temporal and those that are in reality spatial is difficult at best. Moreover, high spatial heterogeneity in the field has implications for the interpretation of laboratory studies as well as those done in the field and indicates that generalizations about the biology and ecology of this species gleaned from small, albeit random, samples should be viewed with caution.
Curtis et al. (Mon,) studied this question.