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Updated May 23, 2008.
Predictive Mapping of Ecosystem Flux and Food Web Interactions Through Space and Time
Topography exerts first order controls on environments, and therefore species performance and ecological interactions down drainage networks. In river networks, environmental conditions (habitat structure, temperature, disturbance, and solar radiation) change downstream in a partially predictable fashion. The physiological and behavioral responses of organisms affect their population dynamics and roles in food webs and ecosystems. Our map-based approach investigates spatially-explicit shifts in ecosystem regimes. Understanding the causes for these shifts should inform efforts to forecast organism and ecosystem responses to climate, land-use, and biotic change.
Areas Under Investigation
1. Predictive mapping of key biotic populations: relationships to habitats.
2. Understanding linkages among solutes, soil production and microbial community.
3. Upscaling transport laws and biotic processes.
4. Linking food webs and channel networks, including dynamic response.
Current Research
We have made several advances toward ecological prediction based on topography, remote sensing, and network structure. We can now pinpoint the drainage area threshold for a number of ecological "regime shifts" at the Angelo Coast Range Reserve (ACRR) field site:
1. The 2 km2 threshold at which algae grazing armored caddisflies (invulnerable to fish and other predators) start suppressing accrual of their algal food.
2. The 10 km2 threshold at which this algal carbon also becomes available to the predator supporting chains in river food webs.
3. The 17 km2 threshold at which bat foraging mode on emerging aquatic insects switches to the more effective surface skimming mode.
4. The 100 km2 threshold at which biological nitrogen fixation starts to enrich fluxes of available nitrogen to the river water column and attached benthic biofilms.
We have identified a major potential contributor of fixed nitrogen in these mainstem reaches—a family of epiphytic diatoms with cyanobacterial endosymbionts, which can be monitored over large scales photogrammetrically because of the distinctive rusty color they impart to algal proliferations. Furthermore, we have successfully used dimensional analysis and scaling relationships to upscale algae abundance and ecosystem metabolism, to quantify denitrification potential, and to compute the abundance of an important free-living cyanobacterial nitrogen fixer. Within this large scale topographic framework, we have documented that most denitrification in channels occurs in hot spots, which make up a small fraction of stream reaches. Field and laboratory studies have been launched to reveal the mechanisms controlling these hot spots in aquatic environments.
NCED commitment to long-term support of field research has born fruit this past year in two major results. Plots in a meadow at the ACCR with simulated elevated rainfall (now in its eighth year of experimentation) show that the responses of individual species are reversed through community level interactions—challenging the predictability of environmental response to anticipated climate change. In contrast, the soil microbial community in these experimental plots has remained unchanged, responding only to unusual weather events. Scouring floods cause considerable mortality, but they rejuvenate river food webs that support the growth of predators who are then dynamically linked to the abundances of algae and invertebrate prey lower in the food chain. These findings call for dam releases to "stir" gravelbeds of rivers to enhance their food production for fish.
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