Developed by: Merrick, Richards Updated: August 2003 U1-m4-s1 Trophic Relationships

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s1

Trophic Relationships


Microbial Food Webs


Microbial Food Webs

Bacteria and Fungi Carbon flux evidence shows importance Makes resources available DOM Detritus


How might energy be transferred to fish?


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


Is this the only way to eat microbes?


Energy Transfer

Direct ingestion of biofilms! Scraping Ingestion with CPOM

Conversion to plankton Scouring

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s8Organic microlayer-microbial community on submerged objects 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?


Who eats the bacteria?

Water column Bacterial size: average = 0.5 µm Few suspension feeders able to capture

that size prey:Black fly larvaeAsiatic clam Corbicula

Protozoans most likely grazers Flagellates - 5.0 µm in diameter Ciliates - 25 µm in diameter on average


Who eats the bacteria?

Benthic Associated with microlayers & periphyton

Benthic grazers of attached materialDeposit feeders that pass organic matter & associated microbes through their gut.

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s12Microbial Web


Looking and the slide why are bacteria important?

Developed by: Merrick, Richards Updated: August 2003 U1-m4-s14Microbial Web


Microbial Food Webs: H2O column vs. benthos


Categorization of Trophic Relationships in Streams

How do we normally assign trophic relationships?


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)


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)

Macroinvertebrate functional roles in organic matter processing

A caddisfly of the family Limnephilidae

www.oaa.pdx.edu/CAE/Programs/sti/pratt/feeding/inverts/shredder.html


Collectors Dominant food

Decompose fine particulate organic matter (FPOM) Feeding mechanisms

Filterers - Detritivores Gatherers - Detritivores

Representatives Filterers

• Hydropsychidae • Simulidae (black flies)

Gatherers• Elmidae (riffle beetles)• Chironomini• Baetis• Ephemerella• Hexagenia

Macroinvertebrate functional roles

A blackfly of the family Simulidae

A caddisfly of the family Hydroptilidae

www.oaa.pdx.edu/CAE/Programs/sti/pratt/feeding/inverts/collector.html


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


Predators Dominant food

Living animal tissue Feeding mechanisms

Engulfers - Attack prey and ingest whole animals Piercers - Pierce tissues, suck fluids

Representatives Engulfers

• Anisoptera (dragonflies)• Acroneuria• Corydalus (hellgrammites)

Piercers• Veliidae (water striders)• Corixidae (water boatmen)• Tabanidae (deerflies & horseflies)


A stonefly of the family Perlidae

A “true bug” of the family Notonectidae

www.oaa.pdx.edu/CAE/Programs/sti/pratt/feeding/inverts/predator.html


Ecological roles

Macroinvertebrates play a variety of roles in food webs.

Fig. 4.9, p.53 in Allan and Cushing, 2001


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/filterer-collector

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


Feeding roles of invertebrate consumers in lotic systems

Deposit feeder/ collector-gatherer

FPOM and microbiota, especially bacteria and organic microlayer

Collect surface deposits, browse on amorphous material, burrow in soft sediments

Many Ephemeroptera, Chironomidae and Ceratopogonidae

Grazer Periphyton, especially diatoms; and organic microlayer

Scraping, rasping and browsing adaptations

Several families of Ephemeroptera and 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


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


How would you identify food sources for invertebrate consumers?


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


CPOM Consumers

Shredder-CPOM Linkage Why are invertebrates important to CPOM

breakdown?


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


Who feeds?

Crustaceans Snails Insect Larvae


“Microorganisms on a leaf are like peanut butter on a cracker, with most of the nourishment provided by the peanut butter.”Cummins, 1974


Feeding preference of amphipods

Microbe growth

permitted

Antibiotics

Autoclaved

Amphipod - Gammarus sp.

Elm leaves consumed Exp. Design

Control (with microbes) + antibiotics + steam sterilization


Invertebrate Consumers

Prefer ‘conditioned’ leaves Conditioning by microbial colonization

Preference is for leaves at some peak stage of microbial growth.


How to measure microbial biomass?

ATP Relative N content Softening of leaf discs


Influence of conditioning time of discs of hickory leaves on utilization by Tipula abdominalis.


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


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


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 Highly efficient at processing conditioned leaves at low metabolic cost

Less dependent upon stage of conditioning, probably good at extracting protein, but at high metabolic cost.

Other attributes of feeding ecology

Highly mobile

Polyphagous

Low mobility

Obligate detritivore


Consumers of FPOM


Consumers of FPOM

Collector-FPOM linkage Poorly Understood Where captured?

suspension or substrate Rich sources

Sloughed periphyton Organic microlayers Particles from breakdown of CPOM


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


Collector-FPOM-bacterial linkage modeled for a small stream with a temperate deciduous forest


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


Filtering stance of a black fly larva

Filter apparatus: fringe of microtrichia

Boundary layer typically at roughly

the height of the upper fan


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


Who are they?

Swift Streams Mayflies, Caddisflies, Midges, Crustaceans,

Gastropod Molluscs Slow Currents (fine sediments)

Add oligochaetes and nemotodes


Vertebrates in Lotic Systems


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


Are there morphological features that would tell us what a fish eats?


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


Trophic guilds of stream fishes for temperate N. America

Guild Description Occurrence by species

(%)

Comments for tropical streams

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

Planktivore Midwater specialist on phyto-and zooplankton

3 Seasonally important in large rivers


Trophic guilds of stream fishes for temperate N. America

Guild Description Occurrence by species

(%)

Comments for tropical streams

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)


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


Guilds change as environment changes


Profile of an Amazonian floodplain river, showing main channel, side arms, and extent of flooded forest.


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 U1-m4-s57Lotic food webs


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Developed by: Merrick, Richards Updated: August 2003 U1-m4-s1 Trophic Relationships