1. Trophic Relationships

2. Microbial Food Webs

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

4. How might energy be transferred to fish?

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

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

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

8. Is this the only way to eat microbes?

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

10. Organic microlayer-microbial community on submerged objects in streams

11. 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?

12. Microbial Food Webs: H2O column vs. benthos

13. Microbial Web

14. Looking and the slide why are bacteria important?

15. Microbial Web

16. Categorization of Trophic Relationships in Streams
How do we normally assign trophic relationships?

17. Trophic Relationships
Difficult to assign typical categories
Producer, grazer, carnivore, top predator
Trophic level
Species are in multiple categories at once
More than “usual”

18. 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

19. Macroinvertebrate functional roles in organic matter processing
The River Continuum

20. 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

21. 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

22. 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
The River Continuum

23. Collectors Dominant food Feeding mechanisms
Decompose fine particulate organic matter (FPOM)
Feeding mechanisms
Filterers - Detritivores
Gatherers – Detritivores
The River Continuum

24. 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
The River Continuum

25. Black-fly Ecology Extensively studied: pests, carriers of disease
Food size range: 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

26. 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

27. Scrapers Dominant food Feeding mechanisms Periphyton (attached algae)
Material associated with periphyton
Feeding mechanisms
Graze and scrape mineral and organic surfaces
The River Continuum

28. Representatives Helicopsychidae Psephenidae (water pennies)
Thaumaleidae (solitary midges)
Glossosoma
Heptagenia
A dipteran of the family Thaumaleidae
The River Continuum

29. Predators Dominant food Living animal tissue Feeding mechanisms
Engulfers - Attack prey and ingest whole animals
Piercers - Pierce tissues, suck fluids
The River Continuum

30. 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
The River Continuum

31. 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

32. Who are they? Swift Streams
Mayflies, Caddisflies, Midges, Crustaceans, Gastropod Molluscs
Slow Currents (fine sediments)
Add oligochaetes and nemotodes

33. 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

34. CPOM Consumers Shredder-CPOM Linkage
Why are invertebrates important to CPOM breakdown?

35. 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

36. 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

37. Feeding preference of amphipods
Amphipod - Gammarus sp.
Elm leaves consumed
Exp. Design
Control (with microbes)
+ antibiotics
+ steam sterilization
Microbe growth
permitted
Antibiotics
Autoclaved

38. Invertebrate Consumers
Prefer ‘conditioned’ leaves
Conditioning by microbial colonization
Preference is for leaves at some peak stage of microbial growth.

39. How to measure microbial biomass?
ATP
Relative N content
Softening of leaf discs
Tensile strength of cloth

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

41. 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

42. 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

43. 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

44. 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

45. Consumers of FPOM

46. Consumers of FPOM Collector-FPOM linkage Poorly Understood
Where captured?
suspension or substrate
Rich sources
Sloughed periphyton
Organic microlayers
Particles from breakdown of CPOM

47. 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

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

49. Vertebrates in Lotic Systems

50. 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

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

52. 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

53. 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

54. 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)

55. 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

56. Guilds change as environment changes

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

58. 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

59. Lotic food webs

60. Water on the Web
This presentation includes material from Water on the Web (WoW)
WOW 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.
University of Minnesota-Duluth, Duluth, MN
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