Structure and functioning of ecological entities across levels of biological organization

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Environmental variation influences ecological structure and function across multiple levels of biological organization and spatio-temporal scales. The physical environment affects properties of individual organisms, such as their growth and metabolic rates, and how they disperse, feed, and interact with other individuals. Because those individual properties influence higher levels of organization, environmental effects on individuals should propagate upwards and be expressed as functional differences at the population, community, and ecosystem levels. Accordingly, understanding and predicting ecological responses to the physical environment ideally requires a multilevel approach that combines observations and experiments conducted across organizational levels and spatio-temporal scales. Recent work in freshwater systems has shown that changes in ecosystem and food web structure are predictably linked to individual-level traits, such as body size and foraging mode. These traits are related to the movement scales of consumers at different trophic levels, and thus to the consumers' potential to feed on a broad range of resources and spatially couple distinct habitats. Furthermore, theory and observations show that consumer responses to resource variation between habitats may change predictably along natural environmental gradients, and that these differential consumer responses may have a profound influence on higher-level processes such as habitat coupling and trophic subsidies. The main goal of the proposed research is to examine the processes driving the spatial distribution of fish species in two adjacent macrohabitats, a large fluvial lake and its fringing floodplain. Special emphasis will be placed on understanding context-dependent responses, i.e., the interactive effects of functional traits and environmental gradients on key ecological processes, and their implications for structure and function across organizational levels, from the individual to the ecosystem. Identifying patterns that connect properties of individuals to those of higher levels of organization can yield insights into general processes and mechanisms that are applicable beyond a specific study system. This knowledge is useful to understand current human impacts and predict and manage future changes such as increasing water turbidity and temperature trends arising from changing land use and climate patterns. It also represents a step towards theory-based biomonitoring that incorporates scientific knowledge on interactions within trophic webs to capture functional relationships and their role in sustaining ecosystem function. For example, managers may be interested in whether the movements of large predators typically targeted by fisheries are critical to sustaining floodplain connectivity and production subsidies between macrohabitats.