Trophic Relationships

Microbial Food Webs

Microbial Food Webs Bacteria and Fungi Carbon flux evidence shows importance Take up DOM Break down Detritus But they are so small!

How might energy be transferred to fish?

Who Eats Bacteria? Flagellates - 5.0 µm in diameter Food particles are small ~5.0 µM bacterial cell Consumed by protozoans & micro-metazoans Flagellates - 5.0 µm in diameter Ciliates - 25 µm in diameter on average

Microbe Energy Transfer Several trophic transfers within microbial web Energy lost with each transfer: More steps = more loss

Few suspension feeders can capture such small prey: Black fly larvae Asiatic clam Corbicula

Is this the only way to eat microbes?

Energy Transfer Direct ingestion of biofilms! Scraping Ingestion with CPOM Conversion to plankton Scouring Deposit feeders Pass organic matter & microbes through their gut.

Organic microlayer-microbial community on submerged objects in streams

Where is the production? Modest bacterial production in the water column 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?

Microbial Food Webs: H2O column vs. benthos

Microbial Web

Looking and the slide why are bacteria important?

Microbial Web

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 Species are in multiple categories at once More than “usual”

Guilds Guild: Species that consume a common resource and acquire it in a similar fashion Subdivision in feeding roles for inverts and vertebrates Same as functional groups (FFG, Inverts) Guilds assignment easier that typical trophic relationships

Macroinvertebrate functional roles in organic matter processing www.oaa.pdx.edu/CAE/Programs/sti/pratt/feeding/inverts/shredder.html The River Continuum

Feeding roles of invertebrate consumers in running waters 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

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

Collectors Dominant food Feeding mechanisms Decompose fine particulate organic matter (FPOM) Feeding mechanisms Filterers - Detritivores Gatherers – Detritivores www.oaa.pdx.edu/CAE/Programs/sti/pratt/feeding/inverts/collector.html The River Continuum

Representatives Filterers Gatherers Hydropsychidae Simulidae (black flies) Gatherers Elmidae (riffle beetles) Chironomini Baetis Ephemerella Hexagenia A blackfly of the family Simulidae A caddisfly of the family Hydroptilidae www.oaa.pdx.edu/CAE/Programs/sti/pratt/feeding/inverts/collector.html www.oaa.pdx.edu/CAE/Programs/sti/pratt/feeding/inverts/collector.html The River Continuum

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 Boundary layer typically at roughly the height of the upper fan Filtering stance of a black fly larva Filter apparatus: fringe of microtrichia

Scrapers Dominant food Feeding mechanisms Periphyton (attached algae) Material associated with periphyton Feeding mechanisms Graze and scrape mineral and organic surfaces www.oaa.pdx.edu/CAE/Programs/sti/pratt/feeding/inverts/scraper.html The River Continuum

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 www.oaa.pdx.edu/CAE/Programs/sti/pratt/feeding/inverts/scraper.html The River Continuum

Predators Dominant food Living animal tissue Feeding mechanisms Engulfers - Attack prey and ingest whole animals Piercers - Pierce tissues, suck fluids www.oaa.pdx.edu/CAE/Programs/sti/pratt/feeding/inverts/predator.html The River Continuum

Representatives Engulfers Piercers 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 www.oaa.pdx.edu/CAE/Programs/sti/pratt/feeding/inverts/predator.html The River Continuum

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

Ecological roles Macroinvertebrates play a variety of roles in food webs. Benthic macroinvertebrates process organic matter within streams making them important as members of lotic food webs. The functional roles of lotic insects is based on how they obtain food resources. Stream ecologist go beyond the basic ecological roles of herbivores, carnivores, omnivores, and detritivores to reflect the high degree of specialization among stream insects and elucidate a better understanding of stream food webs. These more descriptive functional feeding groups are: Shredders – consume large organic particles (CPOM) and associated bacteria such as leaves that fall into streams. Produce FPOM. 2) Grazers (and scrapers) – forage on benthic surfaces consuming the algae and diatoms found in periphyton. Produce FPOM. Collectors – this largest functional group is divided into gatherers and filterers, both of which feed on FPOM. Filterers obtain food by filtering water with nets or special morphological adaptations. Gatherers collect FPOM in areas where it accumulates, typically in slower flowing depositional areas of a stream. 4) Predators – animals that eat other animals. All are adapted in some way to pursue or stun and capture prey. (Image: Fig. 4.9, p.53 in Allan and Cushing, 2001) Fig. 4.9, p.53 in Allan and Cushing, 2001

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

CPOM conditioning and feeding “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 Amphipod - Gammarus sp. Elm leaves consumed Exp. Design Control (with microbes) + antibiotics + steam sterilization Microbe growth permitted Antibiotics Autoclaved

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 Tensile strength of cloth

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

How do microbes help? Microbial Production Microbial Catalysis Conversion to microbe biomass Microbial Catalysis Changes that render leaves more digestible Partial digestion of substrate by microbes Exoenzymes

Where does the energy come from? The bulk of the energy comes from the leaf So Cummins was not quite on target But microbial action is still critical

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 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

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?

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 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 Similar category Planktivore Midwater specialist on phyto-and zooplankton 3 Seasonally important in large rivers

Trophic guilds of stream fishes for temperate N. America 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

Lotic food webs

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