Spatial variation of benthic macroinvertebrate biodiversity in boreal streams : biogeographic context and conservation implications

Heino, Jani Spatial variation of benthic macroinvertebrate biodiversity in boreal streams Biogeographic context and conservation implications Jyvaskyla: University of Jyvaskyla, 2002, 43 p. (Jyvaskyla Studies in Biological and Environmental Science, ISSN 1456-9701; 116) ISBN 951-39-1349-X Yhteenveto: Pohjaelainyhteisojen monimuotoisuuden spatiaalinen vaihtelu pohjoisissa virtavesissa eliomaantieteellinen yhteys seka merkitys jokivesien suojelulle Biodiversity patterns of most lotic animal and plant groups remain poorly known, which hinders the implementation of effective conservation, monitoring, and restoration programs. The major aims of this thesis were (i) to examine spatial variation in macroinvertebrate assemblage structure and diversity across natural environmental gradients, and (ii) to assess the utility of such information as the basis of stream conservation programs. Stream environmental characteristics and macroinvertebrate assemblage structure exhibited a clear, yet variable correspondence with regional delineations. The northernmost arctic-alpine and north boreal streams showed the highest degree of correspondence with ecoregion delineations, whereas streams of the southernmost hemiboreal ecoregion showed an opposite pattern. These findings were further supported by direct ordination analyses, showing that latitude was the best predictor of variation in macroinvertebrate assemblage structure across headwater streams. Such patterns were likely related to the fact that the distributions of ectothermic organisms, such as aquatic insects, are largely controlled by temperature. Latitudinal patterns in assemblage structure were further accentuated by geographical gradients in stream environmental conditions. However, there was no clear latitudinal gradient in local macroinvertebrate diversity. Local richness of macroinvertebrates showed a positive linear relationship with regional richness, though there was considerable within-region variation in local diversity accounted for by local environmental factors. These results suggest that the determination of macroinvertebrate diversity in streams constitutes a complex series of processes, which probably act differently on different ecological and taxonomic groups. Dissecting macroinvertebrate assemblages into taxonomic subgroups yielded additional insights into the biodiversity patterns in headwater streams. Although some pairwise comparisons of taxon richness and turnover diversity among mayflies, stoneflies, caddisflies, and chironomid midges were statistically significant, the correlations were overall low. It thus appears that no single group of stream insects can be used as an effective indicator of biodiversity in other taxa. By contrast, high degrees of congruence in provincial biodiversity were found among macrophytes, dragonflies, aquatic beetles, and fish. Patterns of decreasing species richness with latitudinal and altitudinal gradients were parallelled by variation in large-scale climatic conditions. There was, however, an exception to the general pattern: stoneflies showed an opposite pattern to those of the other groups in that their species richness was positively related to province altitude. Based on the main results of this thesis, stream conservation and bioassessment programs would benefit from regional stratification. Such spatial stratifications could, for instance, guarantee that (i) the conservation of lotic ecosystems is conducted within biogeographically and ecologically meaningful frameworks, and that (ii) predictive models for stream bioassessment are more robust and accurate than those generated for larger, more heterogeneous areas.