Conceptual framework for the analysis of riparian influences on fish and invertebrate assemblages

The paper questions the usefulness of the static concept of the habitat as a templet in analyses of the influence of the riparian environment on the dynamics of riverine fish assemblages. Studies on the effect of deforestation on the water quality and invertebrate assemblages in upland streams in mid-Wales found that changes in the nature of the riparian habitat caused by logging had relatively few unambiguous effects. A 22 years study of the population dynamics of a short-lived species, Gasterosteus aculeatus, inhabitating a backwater of a small river in west Wales, found that population characteristics were relatively stable although the study included periods of record drought and irregular episodes of flooding. The literature relating riparian characteristics to fish assemblages also illustrates the weakness of the the static 'habitat as templet' model. A more dynamic concept is required. Life histories can be viewed as sampling devices through which the habitats available can be explored and utilised by fish. Models should direct attention to the extent to which the biological characteristics of species based on the phenotypes of individuals in the species populations define the interactions between the riparian environment and the riverine invertebrate and fish assemblages. The emphasis needs to shift to quantitative effects of riparian influences on the movement, growth, mortality and reproduction of individuals in riverine populations.