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)

Terrestrial invertebrates 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 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 (Fig. 5.2) 1) Leaching 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 refractory material: C = cellulose / lignin, N = tannin Si = silicon Generally, more N and less refractory material accelerates breakdown by enhancing microbial growth which attracts shredders aquatic macrophytes (break down 3-10 x as fast as many woody plant leaves and sedges/rushes/grasses) high Si tannin wax + tannin

2) Detritivores 3) Temperature and pH 4) Physical abrasion 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

Change in mass over time - Board Modeling leaf breakdown Time (d) Wt (gm) ln(Wt) = loge(Wt) 100 4.61 140 50 3.91 482 10 2.30 Change in mass over time - Board Exponential decay 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

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 [Fig. 8.9] Predators Different modes of predation

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 2) Autochthonous Quality? Fate? Groundwater (soil leachate) leaf leachate 2) Autochthonous algal leachate Quality? generally low Fate? microbial biofilms (Lock’s model) [Fig. 7.13]

Large river, Lake water column 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.

biofilm / microbial loop Linkage of micro-metazoans to higher consumers (macroinvertebrates) is poorly known. (“Link” or “Sink”?) CPOM-shredder biofilm / microbial loop