Transcript Substrate

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