A model is proposed to account for the level of diversity supported by any ecological community. If we begin with a hypothetical increase in the stability of the physical environment, the following consequences ensue. With greater environmental stability less energy is required for regulatory activities, that is, those which counter the challenges offered by the environment. Therefore, more energy is allocated for net productivity, that is, growth and reproduction. With increased net productivity, larger populations are supported. Larger populations provide more opportunities for the formation of interspecific associations; they also maintain greater genetic variety. Animals in more productive communities are more sedentary so that the species tends to be broken into many semi-isolated populations. As a result, speciation is favored with the interspecies associations providing the new adaptive opportunities. Plants which are pollinated by animals would be in the same situation. The new species tend to be ...

The Ecological Regulation of Species Diversity

We examine patterns of community richness among intestinal parasitic helminth communities in fishes, herptiles, birds and mammals with respect to the comparative number of component species in a host population. We show that terrestrial hosts have, on average, fewer component species than aquatic hosts. We also show that the mean number of component species in aquatic hosts increases from fishes through herptiles to birds before declining slightly in mammals. For terrestrial hosts, the mean number of component species increases from herptiles, through birds, reaching a maximum in mammals. We conclude that: (i) habitat of the host is more important in determining community richness than is host phylogeny; (ii) the phenomenon of ‘host capture’ may be largely responsible for increased species richness in some host groups; (iii) aquatic birds harbour the richest intestinal helminth communities; and (iv) as we interpret them, our data refute the time hypothesis, which would predict that fishes as the oldest lifestyle should have the richest helminth communities.

Ecological versus phylogenetic determinants of helminth parasite community richness

Fleas are one of the most interesting and fascinating taxa of ectoparasites All species in this relatively small order are obligatory haematophagous (blood-feeding) parasites of higher vertebrates This book examines how functional, ecological and evolutionary patterns and processes of host-parasite relationships are realized in this particular system As such it provides an in-depth case study of a host-parasite system, demonstrating how fleas can be used as a model taxon for testing ecological and evolutionary hypotheses The book moves from basic descriptive aspects, to functional issues and finally to evolutionary explanations It extracts several general principles that apply equally well to other host-parasite systems, so it appeals not only to flea biologists but also to 'mainstream' parasitologists and ecologists

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Functional and Evolutionary Ecology of Fleas: A Model for Ecological Parasitology

Examples of the apparently stochastic nature of freshwater fish helminth communities illustrating the erratic and unpredictable occurrence and distribution of many species are provided for six species of fish from several localities throughout Britain. By focussing on parasite colonization strategies two categories of helminths are recognized: autogenic species which mature in fish and allogenic species which mature in vertebrates other than fish and have a greater colonization potential and ability. Three groups of fish are distinguished: salmonids, in which helminth communities are generally dominated by autogenic species which are also responsible for most of the similarity within and between localities; cyprinids, in which they are dominated by allogenic species which are also responsible for most of the similarity within and between localities; and anguillids, whose helminth communities exhibit intermediate features with neither category consistently dominating nor providing a clear pattern of similarity. Recognition and appreciation of the different colonization strategies of autogenic and allogenic helminths in respect of host vagility and ability to cross land or sea barriers and break down habitat isolation, and their period of residence in a locality, whether transient or permanent, provides an understanding of, and explanation for, the observed patchy spatial distribution of many helminths. Comparison with other parts of the world indicates that colonization is a major determinant of helminth community structure.

Patterns in helminth communities in freshwater fish in Great Britain: alternative strategies for colonization

The ciliate Ichthyophthirius multifiliis is an important pathogen of freshwater teleosts occurring in both temperate and tropical regions throughout the world. The disease, ichthyophthiriosis, accounts for significant economic losses to the aquaculture industry, including the ornamental fish trade, and epizootics in wild fish populations can result in mass kills. This review attempts to provide a comprehensive overview of the biology of the parasite, covering the free-living and parasitic stages in the life cycle, host-parasite interactions, and the immune response of host and immune evasion strategies by the parasite. Emphasis on the immunological aspects of infection within the fish host, including molecular studies of i-antigens, reflects the current interest in this subject area and the quest to develop a recombinant vaccine against the disease. The current status of methods for the control of ichthyophthiriosis is discussed, together with new approaches in combating this important disease.

V. A. Dogelʹ

Papers

Parasitology of fishes.