Community structure of macroinvertebrates, bryophytes and fish in boreal streams : patterns from local to regional scales, with conservation implications

Abstract

Voitaisiinko luonnonsuojelualueiden valinnassa käyttää nykyistä helpompia menetelmiä? Tällainen voisi olla esimerkiksi ns. ilmentäjälajien käyttö niiden valinnassa, jos eri eliöyhteisöjen rakenteet olisivat yhteneviä sekä paikallisessa että laajemmassa, esimerkiksi jokisysteemien yli ulottuvassa mittakaavassa. Riku Paavolan väitöskirjassa tarkastellaan tätä kysymystä pohjoisissa virtavesissä makroskooppisten pohjaeläinten, vesisammalten ja kalojen avulla. Aihetta on sisävesissä tutkittu maailmanlaajuisestikin erittäin vähän, eikä yhtä seikkaperäisiä nimenomaan virtavesissä tehtyjä tutkimuksia ole lainkaan olemassa.

The alarming lack of information about the habitat requirements, biogeographical patterns and degree of concordance in community patterns of freshwater species seriously obstructs the implementation of conservation and monitoring programs. In addition to providing information on the basic community patterns of stream macroinvertebrates, bryophytes and fish, the major aims of this thesis were (1) to investigate the degree of concordance among patterns in community structure and species richness of the three taxonomic groups, (2) examine how patterns in concordance relate to spatial scale, and (3) assess the implications of concordance for stream conservation. Patterns in environmental characteristics and macroinvertebrate assemblages of boreal headwater streams were rather congruent with ecoregional delineations, but showed weaker correspondence with a finer classification at the level of subecoregions, implying that an ecoregional framework holds promise for a successful implementation of stream management programs. At a local scale, macroinvertebrate communities correlated mainly with stream size, acidity, and water colour, while bryophytes were mainly related to nutrient levels and in-stream habitat complexity, and fish communites to oxygen levels, depth and substratum size. At the scale of ecoregions, spatial coordinates, acidity and depth were important for all three taxonomic groups. Community concordance among macroinvertebrates, bryophytes, and fish was strong when viewed across drainage systems, but weak or variable at the scale of single river systems. Strong concordance at broad spatial scales was caused by the three groups responding largely to the same set of environmental cues, whereas weak concordance at the scale of individual river systems was attributed to each group correlating with distinctively different environmental gradients. Communities of headwater streams were less concordant than those of medium sized streams. Species richness patterns among macroinvertebrates, bryophytes and fish were significantly concordant, but the relationships had a low predictive power. These results show that surrogate measures may be of limited value in stream biodiversity inventories. Overall, there may be no cost-effective shortcuts for extensive inventories of lotic biodiversity, incorporating a wide array of taxonomic groups with differing sizes and ecologies.