1. 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 b)

2. 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)

3. 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

4. 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)

5. 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)

6. 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

7. 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

8. 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 = k
140k = 0.7;
k = day-1
k = day-1

9. CPOM / FPOM
Invertebrate Functional Groups [Table 8.1]

10. 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

11. (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)

12. (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

13. (4) Predator-Prey linkage [Fig. 8.9]
Predators
Different modes of predation

14. 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”!)

15. 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]

16. 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.

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