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Trophic Relations • Lotic Food Web • Algal-based (previous examples) • Detrital-based – Sources, roles, fates Simplified functional view of food web (Fig. 6.14a) More realistic -- actual pathways of energy flow (Fig. 6.14 b) ENERGY sources • 1) Allochthonous material – external input to stream. Important in most streams … 3 size classes: – CPOM (coarse particulate organic matter), • [CPOM > 1 mm] examples: dead leaves, wood – FPOM (fine particulate organic matter), • [1 mm > FPOM > 0.5 µm], small terrestrial detrital particles and in-stream CPOM breakdown products – DOM (dissolved organic matter), • [DOM < 0.5 µm] • 2) Autochthonous material – produced internally – Algae, Macrophytes ( CPOM detritus, DOM) ENERGY sources • Macroinvertebrates supported by CPOM, FPOM, algae • Fish supported by macroinverts (some algae, detritus) • Microbes supported by DOM (Microbial loop) Terrestrial invertebrates Sources of allochthonous and autochthonous organic matter (see Table 7.1 in text) Both terrestrial and aquatic have CPOM, FPOM, DOM What’s missing from table? Primary production from algae that don’t slough (supports Herbivory) Breakdown of CPOM (leaves) • 3 steps • 1) Leaching (Fig. 5.2) – First 24 hours • 2) Microbial colonization – Fungi + Bacteria add N to the leaf increases palatability – "Peanut Butter on a Cracker” • 3) Detritivore breakdown – Up to 25% loss – FPOM generally low in food quality (C:N) Main factors influencing breakdown rate: • 1) Leaf species (Fig. 6.4, Giller) – Chemical composition • labile compounds: – C = simple sugar – N = protein aquatic macrophytes • refractory material: (break down 3-10 x as fast as many woody plant leaves and sedges/rushes/grasses) – C = cellulose / lignin, – N = tannin – Si = silicon – Generally, more N and less refractory material accelerates breakdown by enhancing microbial growth which attracts shredders high Si tannin wax + tannin • 2) Detritivores – type and abundance – Insecticide treatment on whole stream and response of breakdown of 4 leaf species [Fig. 6.7 (Giller)] • Insects decline, oligochaet worms increase for all leaf packs (6.7a) • Benthic OM on streambed increased (6.7b) • POM transport declines (lack of shredding) (6.7b) • 3) Temperature and pH – Optima for microbes and for macroinvertebrate shredders • 4) Physical abrasion Modeling leaf breakdown Wt (gm) Time (d) Change in mass over time - Board ln(Wt) = loge(Wt) Weight ( g) 100 o o o o o 50 Wt = W i e -kt o o o 0 0 150 300 Exponential decay 450 0 100 4.61 140 50 3.91 482 10 2.30 Time (days) What is "k"? ln(Wt) = ln(Wi) - k(t) For t = 140 days …. ln(50) = ln(100) - k(140) 3.91 = 4.61 - 140k 140k = 0.7; k = 0.005 day-1 k = 0.005 day-1 Ln (Weight ) 5 o 4 o Ln (W t ) = Ln (W i) - kt 3 2 o 1 0 0 150 300 Time (days) 450 CPOM / FPOM • Invertebrate Functional Groups [Table 8.1] Main Trophic Associations • (1) Shredder-CPOM-linkages [Fig. 8.3] – Shredders – Eat ‘conditioned’ leaves • covered with “peanut butter” • A few shredders can digest cellulose – Grow faster when • lots of microbes on leaves • non-refractory leaves – Occur mostly in shaded, headwater streams – Create FPOM • (2) Collector-FPOM-linkages[Fig. 8.5] – Collector-fiterers • Suspension feeders -remove FPOM from water column – Collector-gatherers • Deposit feeders -- collect FPOM from substrate – May eat refractory material in sediment (oligochaets, burrowing mayflies) – May browse on microbial biofilms Sources of FPOM : -Terrestrial -Microbes (use DOM) -Algae (use some DOM) -Shredders (CPOM fragments + feces) -Collector (feces) • (3) Grazer-Periphyton & Piercer-Macrophyte linkages [Fig. 8.8] – Grazers (aka scrapers, herbivores) • Eat attached algae, but may also ingest biofilm, FPOM • Depends on details of forager’s __________? – Piercers (some caddisflies) • Imbibe cell fluids through cell walls of macroalgae/macrophytes • (4) Predator-Prey linkage – Predators • Different modes of predation [Fig. 8.9] Summary of Aquatic insect trophic relations • Functional Groups good general framework, but important exceptions – Ontogeny • Early instars often detritivores – Generalist feeding • Omnivory (eat what goes in mouth) • Seasonal availability – Distinctions among resource types ambiguous • e.g, Algal mats have detritus mixed in. Biofilm has small animals within (remember the “Aufwuchs”!) DOM • Sources – 1) Allochthonous • Groundwater (soil leachate) • leaf leachate – 2) Autochthonous • algal leachate – Quality? • generally low – Fate? • microbial biofilms • (Lock’s model) [Fig. 7.13] • Microbial Food Web – Protozoa and micro-metazoans Large river, Lake water column Stream substrate Linkage of micro-metazoans to higher consumers (macroinvertebrates) is poorly known. Linkage of micro-metazoans to higher consumers (macroinvertebrates) is poorly known. (“Link” or “Sink”?) CPOMshredder biofilm / microbial loop