Building Food Webs
Water Related Services - WP3 | Wessex BESS
Freshwater biologists at Queen Mary University of London have been busy in the laboratory processing the many samples we have collected during the early stages of the project. We are quantifying the food webs of three streams in the Wessex Chalk Area.
To do this, we are using two complementary approaches. Firstly we dissect out the gut of a representative sample of each species of animal found in the stream and identify, measure and count the food items (animal, plant and detritus) found.
We also estimate the biomass of material in the guts using known species-specific relationships between the size of identifiable body parts and mass. Using this information we are constructing a food web with links between consumers and their prey. In addition, the strength of these links (in terms of the the amount of biomass being transferred) is determined so that we can clearly distinguish through which pathways plant and detrital production is being conveyed through the food web.
Our second approach involves accurately measuring the amount of carbon, nitrogen and phosphorus in the tissues of species in the food web. To do this we oven-dry a representative sample of each species, grind the dried material to a fine powder and using a mass spectrophotometer and other chemical techniques, we measure the C, N and P content. Using our estimates of the rate of biomass consumption, we can then quantify the movement of these key elements through the food web and the rate at which they are being recycled within the food web.
Initial results have found that across the three streams, which span a gradient of catchment land-use intensity, there is variation in the range of basal resources consumed, trophic diversity, and extent of niche packing of species.
