Transcript Microbial Food Webs

Trophic Relationships
Developed by: Merrick, Richards
Updated: August 2003
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Microbial Food Webs
Developed by: Merrick, Richards
Updated: August 2003
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Microbial Food Webs
 Bacteria and Fungi
 Carbon flux evidence shows importance
 Makes resources available
 DOM
 Detritus
Developed by: Merrick, Richards
Updated: August 2003
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How might energy be transferred to fish?
Developed by: Merrick, Richards
Updated: August 2003
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Energy Transfer
 Microbes consumed by protozoans & micro-
metazoans
 Food particles are small (~5.0 µM bacterial cell)
 Several trophic transfers within microbial web
 Energy lost with each transfer:
 typical models transfer 10% between levels
 90% lost as entropy to system
 More steps = more loss
Developed by: Merrick, Richards
Updated: August 2003
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Is this the only way to eat microbes?
Developed by: Merrick, Richards
Updated: August 2003
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Energy Transfer
 Direct ingestion of biofilms!
 Scraping
 Ingestion with CPOM
 Conversion to plankton
 Scouring
Developed by: Merrick, Richards
Updated: August 2003
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Organic microlayer-microbial
community
onAugust
submerged
objects
Developed by: Merrick, Richards
Updated:
2003
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in streams
Where is the production?
 Bacterial production in the water column is
modest
 Benthic bacteria dominate community respiration
 We don’t know enough . . .
 Looking for a good research topic:
 The importance of bacterial and fungal metabolism
to Carbon cycling in lotic ecosystems?
Developed by: Merrick, Richards
Updated: August 2003
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Who eats the bacteria?
 Water column
 Bacterial size: average = 0.5 µm
 Few suspension feeders able to capture
that size prey:
 Black fly larvae
 Asiatic clam Corbicula
 Protozoans most likely grazers
 Flagellates - 5.0 µm in diameter
 Ciliates - 25 µm in diameter on average
Developed by: Merrick, Richards
Updated: August 2003
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Who eats the bacteria?
 Benthic
 Associated with microlayers & periphyton
 Benthic grazers of attached material
 Deposit feeders that pass organic matter &
associated microbes through their gut.
Developed by: Merrick, Richards
Updated: August 2003
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Microbial Web
Developed by: Merrick, Richards
Updated: August 2003
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Looking and the slide why are bacteria
important?
Developed by: Merrick, Richards
Updated: August 2003
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Microbial Web
Developed by: Merrick, Richards
Updated: August 2003
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Microbial Food Webs:
H2O column vs. benthos
Developed by: Merrick, Richards
Updated: August 2003
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Categorization of Trophic Relationships in
Streams
 How do we normally assign trophic
relationships?
Developed by: Merrick, Richards
Updated: August 2003
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Trophic Relationships
 Difficult to assign typical categories
 Producer, grazer, carnivore, top predator
 Trophic level
 Assignment to guilds is easier
 Guild = species that consume a common resource and
acquire it in a similar fashion
 Provides subdivision in feeding roles for both inverts and
vertebrates
 Same as functional groups (FFG, Inverts)
Developed by: Merrick, Richards
Updated: August 2003
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Macroinvertebrate functional roles in
organic matter processing
 Shredders
 Dominant food
 Vascular macrophyte tissue
 Coarse particulate organic material (CPOM)
 Wood

Feeding mechanisms
 Herbivores - Chew and mine live macrophytes
 Detritivores - Chew on CPOM

Representatives
 Scathophagidae (dung flies)
 Tipulidae (crane flies)
A caddisfly of the
family Limnephilidae
www.oaa.pdx.edu/CAE/Programs/sti/pratt/feeding/inverts/shredder.html
Developed by: Merrick, Richards
Updated: August 2003
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Macroinvertebrate functional roles
 Collectors
 Dominant food
 Decompose fine particulate organic matter (FPOM)
 Feeding mechanisms
 Filterers - Detritivores
 Gatherers - Detritivores
 Representatives
 Filterers
• Hydropsychidae
• Simulidae (black flies)
A blackfly of the
family Simulidae
 Gatherers
•
•
•
•
•
Elmidae (riffle beetles)
Chironomini
Baetis
Ephemerella
Hexagenia
A caddisfly of the
family Hydroptilidae
www.oaa.pdx.edu/CAE/Programs/sti/pratt/feeding/inverts/collector.html
Developed by: Merrick, Richards
Updated: August 2003
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Macroinvertebrate functional roles
 Scrapers
 Dominant food
 Periphyton (attached algae)
 Material associated with periphyton

Feeding mechanisms
 Graze and scrape mineral and organic surfaces

Representatives
 Helicopsychidae
 Psephenidae (water pennies)
 Thaumaleidae (solitary midges)
 Glossosoma
 Heptagenia
A dipteran of the
family Thaumaleidae
www.oaa.pdx.edu/CAE/Programs/sti/pratt/feeding/inverts/scraper.html
Developed by: Merrick, Richards
Updated: August 2003
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Macroinvertebrate functional roles
 Predators
 Dominant food
 Living animal tissue

Feeding mechanisms
 Engulfers - Attack prey and ingest whole animals
 Piercers - Pierce tissues, suck fluids

A stonefly of the
family Perlidae
Representatives
 Engulfers
• Anisoptera (dragonflies)
• Acroneuria
• Corydalus (hellgrammites)
 Piercers
• Veliidae (water striders)
• Corixidae (water boatmen)
• Tabanidae (deerflies & horseflies)
A “true bug” of the
family Notonectidae
www.oaa.pdx.edu/CAE/Programs/sti/pratt/feeding/inverts/predator.html
Developed by: Merrick, Richards
Updated: August 2003
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Ecological roles
 Macroinvertebrates play a variety of roles in
food webs.
Fig. 4.9, p.53 in Allan and Cushing, 2001
Developed by: Merrick, Richards
Updated: August 2003
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Feeding roles of invertebrate consumers in running waters
Feeding Role
Food Resource
Feeding Mechanism
Examples
Shredder
Non-woody CPOM:
leaves & associated
microbiota
Chewing and mining
Several families of
Trichoptera,
Plecoptera,
Crustacea: some
Diptera, snails
Shredder/gouger
Woody CPOM and
microbiota, especially
fungi
As above
Occasional taxa
among Dipter,
Coleoptera,
Tricoptera
Suspension
feeder/filterercollector
FPOM and
microbiota, bacteria &
sloughed periphyton
Collect particles using
setae, specialized
filtering apparatus or
nets and secretions
Net-spinning
Trichoptera,
Simuliidae and some
Diptera; some
Ephemeroptera
Developed by: Merrick, Richards
Updated: August 2003
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Feeding roles of invertebrate consumers in lotic systems
Deposit feeder/
collector-gatherer
FPOM and
microbiota, especially
bacteria and organic
microlayer
Grazer
Periphyton, especially Scraping, rasping and Several families of
diatoms; and organic browsing adaptations Ephemeroptera and
microlayer
Trichoptera; some
Diptera, Lepidoptera,
and Coleoptera
Predator
Macrophytes
Piercing
Hydroptilid caddis
larvae
Animal prey
Biting and piercing
Odonata,
Megaloptera, some
Plecoptera,
Tricoptera, Diptera
and Coleoptera
Developed by: Merrick, Richards
Collect surface
deposits, browse on
amorphous material,
burrow in soft
sediments
Many
Ephemeroptera,
Chironomidae and
Ceratopogonidae
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Which FFG/Guild?
 Can be hard to determine
 Food resources don’t separate cleanly
 Leaf enriched w/ fungi supports algae & biofilm
 However, classifications can be helpful
 Changes based upon river characteristics
Developed by: Merrick, Richards
Updated: August 2003
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How would you identify food
sources for invertebrate
consumers?
Developed by: Merrick, Richards
Updated: August 2003
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Identifying food sources for
invertebrate consumers?
 Gut analysis
 Diatom frustules easy to ID
 Food of “soft” tissues turns to mush
 Stable Carbon & Nitrogen Isotopic Analysis
 Isotopic ratios reflect the food source
 13C/12C ratio
 In an animal’s tissue = record of recent feeding history
 Reflects assimilation, not just ingestion.
 Link or sink?
 Zebra mussels
Developed by: Merrick, Richards
Updated: August 2003
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CPOM Consumers
 Shredder-CPOM Linkage
 Why are invertebrates important to CPOM
breakdown?
Developed by: Merrick, Richards
Updated: August 2003
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Small Stream Model:
Links between CPOM, fungi & bacteria
 Model for a small stream
within a temperate
deciduous forest
 CPOM -> FPOM
 Physical abrasion
 Microbial activity
 Invertebrate shredders
 DOM release
 Chemical leaching
 Microbial excretion &
respiration
 Much C enters detrital
pools as feces and
fragments
Developed by: Merrick, Richards
Updated: August 2003
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Who feeds?
 Crustaceans
 Snails
 Insect Larvae
Developed by: Merrick, Richards
Updated: August 2003
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“Microorganisms on a leaf are like peanut
butter on a cracker, with most of the
nourishment provided by the peanut
butter.”
Cummins, 1974
Developed by: Merrick, Richards
Updated: August 2003
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Feeding preference of amphipods
 Amphipod -
Gammarus sp.
 Elm leaves consumed
 Exp. Design
Microbe growth
permitted
 Control (with microbes)
 + antibiotics
 + steam sterilization
Antibiotics
Autoclaved
Developed by: Merrick, Richards
Updated: August 2003
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Invertebrate Consumers
 Prefer ‘conditioned’ leaves
 Conditioning by microbial colonization
 Preference is for leaves at some peak stage of
microbial growth.
Developed by: Merrick, Richards
Updated: August 2003
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How to measure microbial biomass?
 ATP
 Relative N content
 Softening of leaf discs
Developed by: Merrick, Richards
Updated: August 2003
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Influence of conditioning
time of discs of hickory
leaves on utilization by
Tipula abdominalis.
Developed by: Merrick, Richards
Updated: August 2003
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How do microbes help?
 Microbial Production
 Conversion to microbe biomass
 Microbial Catalysis
 Changes that render leaves more digestible
 Partial digestion of substrate by microbes
 Exoenzymes
 The bulk of the energy comes from the leaf
 So Cummins was not quite on target
Developed by: Merrick, Richards
Updated: August 2003
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Leaf digestion by inverts?
 Where is the cellulase?
 Found in some mollusks, crustaceans and
annelids
 Aquatic insects generally lack
 Some have endosymbionts
 Tipula (Crane Fly)
 Primary source is microbial: bacteria & fungi
 Exoenzymes
Developed by: Merrick, Richards
Updated: August 2003
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Contrasting feeding strategies of 2 CPOM detritivores
Gammarus fossarum
Tipula abdominalis
Feeding mechanism
Scrapes at leaf surfaces
Chews entire leaf
Gut pH & digestive
biochemistry
Anterior gut slightly acid
Fore & midgut highly alkaline (up
to 11.6)
Its own enzymes and fungal
exoenzymes attack leaf
carbohydrates
Result is high proteolytic activity
but inactivation of fungal
exoenzymes thus little activity
toward leaf carbohydrates
Posterior gut is alkaline, would
digest microbial proteins and some
leaf proteins
Efficiency
Other attributes of
feeding ecology
Highly efficient at processing
conditioned leaves at low metabolic
cost
Highly mobile
Polyphagous
Developed by: Merrick, Richards
Less dependent upon stage of
conditioning, probably good at
extracting protein, but at high
metabolic cost.
Low mobility
Obligate detritivore
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Consumers of FPOM
Developed by: Merrick, Richards
Updated: August 2003
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Consumers of FPOM
 Collector-FPOM linkage
 Poorly Understood
 Where captured?
 suspension or substrate
 Rich sources
 Sloughed periphyton
 Organic microlayers
 Particles from breakdown of CPOM
Developed by: Merrick, Richards
Updated: August 2003
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Suspension Feeding Ecology
 Many suspension feeders at lake outlets
 Densities decrease downstream
 Blackflies 15X more abundant at outflow vs. 2 km downstream
 Tricopteran net size dependent upon flow
 Fine mesh more efficient but creates more drag
 High flow => larger mesh size
 Feeding on CPOM by one invertebrate makes
more food available to FPOM consumers
 32P labeled alder leaves: more label transferred to suspension feeders
(of FPOM) in the presence of a shredder
Developed by: Merrick, Richards
Updated: August 2003
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Collector-FPOM-bacterial linkage modeled
for a small stream with a temperate
deciduous forest
Developed by: Merrick, Richards
Updated: August 2003
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Black-fly Ecology
 Extensively studied: pests, carriers of disease
 Food size range: 1 - 350 µm
 May be reared on a bacterial suspension
 May manipulate flow vortices to enhance
feeding
 Not limited to suspension feeding
 Scraping substrate using mandibles and labrum
 May deposit feed on FPOM
 May ingest animal prey
Developed by: Merrick, Richards
Updated: August 2003
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Boundary layer typically at roughly
the height of the upper fan
Filtering
stance of a
black fly
larva
Filter apparatus: fringe of microtrichia
Developed by: Merrick, Richards
Updated: August 2003
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Deposit feeders
 Least well understood guild
 Some taxa shift opportunistically between this
and shredding or collecting of FPOM
 Common in early instars - switch to more
specialized guilds later
 Many “bulk-feed” from 1 - many X body weight to
get enough nutrition from sediments
 Seem to have fewer morphological modifications
Developed by: Merrick, Richards
Updated: August 2003
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Who are they?
 Swift Streams
 Mayflies, Caddisflies, Midges, Crustaceans,
Gastropod Molluscs
 Slow Currents (fine sediments)
 Add oligochaetes and nemotodes
Developed by: Merrick, Richards
Updated: August 2003
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Vertebrates in Lotic Systems
Developed by: Merrick, Richards
Updated: August 2003
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Feeding Ecology of Riverine
Fishes
 Fish are the principle vertebrates in streams. Others?
 Most stream fishes
invertivores > piscivores > herbivores
 North America: 55 / 700 species are herbivores
Developed by: Merrick, Richards
Updated: August 2003
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Are there morphological features that
would tell us what a fish eats?
Developed by: Merrick, Richards
Updated: August 2003
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Feeding Ecology of Riverine
Fishes
 You are what you eat?
 Form follows function
 You can tell what a fish (mostly) eats by
 Specialization of dentition
 Jaw shape
 Body form
 Alimentary tract
 Many fish are flexible in feeding habits
 Some change feeding habits during life cycle
Developed by: Merrick, Richards
Updated: August 2003
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Trophic guilds of stream fishes for temperate N. America
Guild
Description
Piscivore
Primarily fish, some
Large inverts
16
May consume part or
specialize on whole
Benthic
invertebrate feeder
Primarily immature
insects
33
Most common in small
to mid-order streams
Surface & H2O
column feeder
Consumes surface prey
(terrestrial) & drift (zoops
& inverts of benthic
origin)
11
Diverse surface foods
in forested
headwaters and
during seasonal flood
Generalized
invertebrate feeder
Feeds at all depths
11
Similar category
Midwater specialist on
phyto-and
zooplankton
Developed
by: Merrick, Richards
3
Planktivore
Occurrence Comments for tropical
by species streams
(%)
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Updated: Augustin
2003
Trophic guilds of stream fishes for temperate N. America
Guild
Description
Herbivore detritivor
Bottom feeder ingesting
periphyton and detritus:
includes mud feeders
with long intestinal tracts
7
Herbivory may be
subdivided into
micro- and
macrophytes, and
detritus feeders
separated from
mud feeders
Omnivore
Ingests a wide range of
foods: plant, animal,
detritus
6
Similar category
Parasite
Ectoparasite (e.g.
lampreys)
3
Ectoparasite (e.g.
candirú catfishes)
Developed by: Merrick, Richards
Occurrence
by species
(%)
Comments for
tropical streams
Updated: August 2003
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Multiple Jobs
 Many fish are “flexible” feeders
 Must use the same care here as FFGs But,
morphology does follow function
 Incredible specialization
 Nut eaters
 Fin/Eye/Scale eaters
Developed by: Merrick, Richards
Updated: August 2003
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Guilds change as environment changes
Developed by: Merrick, Richards
Updated: August 2003
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Profile of an Amazonian floodplain river, showing
main channel, side arms, and extent of flooded
forest.
Developed by: Merrick, Richards
Updated: August 2003
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Abundance of 3 fish feeding
guilds in small forested
streams in Panama
(a) Cichlasoma & Pimelodus:
generalized invertivores
(b) Brycon: detritivore when small,
omnivore when larger
(c) catfish feeding on periphyton
Developed by: Merrick, Richards
Updated: August 2003
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Lotic food webs
Developed by: Merrick, Richards
Updated: August 2003
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Water on the Web
 This presentation includes material from Water
on the Web (WoW)
• WOW. 2004. Water on the Web - Monitoring Minnesota
Lakes on the Internet and Training Water Science
Technicians for the Future - A National On-line Curriculum
using Advanced Technologies and Real-Time Data.
• http://WaterOntheWeb.org).
• University of Minnesota-Duluth, Duluth, MN 55812.
• Authors: Munson, BH, Axler, R, Hagley C, Host G,
Merrick G, Richards C.
 I would also like to thank Dr. Jewett-Smith for
her contributions to this presentation
Developed by: Merrick, Richards
Updated: August 2003
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