| Lakes are heterogeneous, three-dimensional landscapes, but are rarely appreciated as such. Organisms distribute themselves throughout these aquatic landscapes in a variety of ways, depending on the abiotic (e.g. temperature, oxygen, light) and biotic (e.g. predators, prey) features of the environment. Therefore, change in habitat use by an organism usually reflects temporal variation in the spatial distributions of the physical, chemical, and biological characteristics of lakes, or the constraints they impose on aquatic organisms. Integrating the effects of these changes across multiple scales requires knowledge of the external and internal functions of ecosystems. This task is often hindered by our inability to separate ecological process and pattern from underlying natural variability, especially when comparing the results of small experiments to observations made at larger scales. New development and application of geographic information systems (GIS), remote sensing, computer simulation models, spatial statistics, and sampling techniques has shown how emergent patterns in variability can indicate important spatial features of the landscape. Similar advances in time-series analyses allow us to track dynamic changes in the underlying trends or periodic effects in time-ordered data.; I examined patterns in the spatial and temporal variance within and among several components of aquatic ecosystems. Through a combination of field sampling and quantitative methods, I offered ecological explanations for, and statistical descriptions of temporal and spatial patterns in the variance of observed data. Using ecological data from a variety of different lake ecosystems including relatively pristine Alaskan lakes and others from Washington state that were heavily impacted by human activities, I found that patterns in the spatial or temporal variance of observed data could often be explained by environmental drivers such as the amount of light, lake basin morphology, or the intensity of human disturbance. In all cases, I paid particular attention to the scope of the study and its influence on the results. My results highlight opportunities for ecologists to explicitly consider the role of dynamic changes in the spatial and temporal distribution of organisms in empirical and theoretical studies of aquatic ecosystems. |
