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FUNCTIONAL FEEDING GROUP RATIOS AS INDICATORS OF STREAM ATTRIBUTES
GOAL 1:CALCULATION OF THE TOTAL NUMBER OF FUNCTIONAL FEEDING GROUPS PRESENT IN A SAMPLE Step 1: Using the above table of organisms for Saucon Creek: Identify and sum the total number of individual shredders, scrapers, gathering collectors, filtering collectors, and predators within each sample.
GOAL 2:CALCULATION OF THE FUNCTIONAL FEEDING GROUP RATIOS Step 1: Using Table 21.3 (from "Methods in Stream Ecology") (SC# 55) calculate the five functional feeding group ratios needed as indicators of the stream's ecosystem attributes. 1) scrapers to shredders + total collectors = 57/158 = .36 2) shredders to total collectors = 21/158 = .13 3) filtering collectors to gathering collectors = 112/46 = 2.4 4) scrapers + filtering collectors to shredders + gathering collectors = 169/67 = 2.5 5) predators to Total of all other groups = 1/236 = .004 GOAL 3: USE THE FUNCTIONAL FEEDING GROUP RATIOS TO EVALUATE ECOSYSTEM ATTRIBUTES OF STREAM SECTION Step 1: Using Table 21.3 (SC# 55) evaluate the meaning of the ratio number values for the five functional feeding group ratios using the general criteria ratio levels ( in relation to the Saucon Creek stream sample). 1) scrapers to shredders + total collectors = 57/158 = .36 < .75 Stream section is a heterotrophic site. The stream is dependent on allochthonous material, such as leaf litter coming from riparian vegetation outside the stream. An autotrophic site, with a ratio of greater than .75, would be seen where light levels are adequate to support more diatoms (photosynthetic algae) which scrapers consume. 2) shredders to total collectors = 21/158 = .13 < .25 Stream section has a lower than expected shredder association linked to functioning riparian system. This may be explained by rather narrow width and patchy nature of riparian (streamside) vegetation that shades stream but may not provide adequate amounts of leaf litter from upstream sections. 3) filtering collectors to gathering collectors = 112/46 = 2.4 > .50 FPOM (fine particulate organic material) transport greater than normal particulate load in suspension. FPOM may be associated with land-use disturbances that are taking place in the area, although this assessment may be countered by high channel stability rating (see #4 below). FPOM could be supplied by processed organic fragments from leaf litter and soils of riparian zone. Presence of fingernet caddisfly indicates very fine FPOM. 4) scrapers + filtering collectors to shredders + gathering collectors = 169/67 = 2.5 > 0.50 Channel stability high with numerous attachment sites (substrates such as cobbles) available for aquatic insects. 5) predators to total of all other groups = 1/236 = .004 < 0.15 Predator number very low, although value of less than 0.15 tends to indicate normal predator to prey balance. These ratios serve only as indicators of ecosystem attributes. The results for this site may indicate the general influence of the reduction in leaf litter inputs and increased sediment from altered land-use patterns that are taking place in the area. (Source: Saucon Valley High School field data)
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