RECONCILING LANDSCAPE AND LOCAL VIEWS OF AQUATIC COMMUNITIES - LESSONS FROM MICHIGAN TROUT STREAMS

1. Rapidly advancing geographical information systems (GIS) technologi es are forcing a careful evaluation of the roles and biases of landsca pe and traditional site-based perspectives on assessments of aquatic c ommunities. Viewing the world at very different scales can lead to see ming contradictions about the nature of specific ecological systems. I n the case of Michigan trout streams, landscape analyses suggest a pre dictable community shaped by large-scale patterns in hydrology and geo logy. Most site-based studies, however, suggest these communities are highly variable in structure over time, and are strongly shaped by sit e-specific physical and biological dynamics. As the real world is comp rised of processes operating both at local and landscape scales, an an alytical framework for integrating these paradigms is desirable. 2. De composition of variances by factorial ANOVA into time, space and time- space interaction terms can provide a conceptual and analytical model for integrating processes operating at landscape and local scales. Usi ng this approach, long-term data sets were examined for three insects and two fishes common in Michigan trout streams. Each taxon had a uniq ue variance structure, and the observed variance structure was highly dependent upon sample size. 3. Both spatially extensive designs with l ittle sampling over time (typical of many GIS studies) and temporally extensive designs with little or no spatial sampling (typical of popul ation and community studies), are biased in terms of their view of the relative importance of local and landscape factors. The necessary, bu t in many cases costly, solution is to develop and analyse data sets t hat are both spatially and temporally extensive.