Trophic Relations

1. Trophic Relations

2. I. Background Trophic relationships describe the flow of energy through a system The concept of a feeding guild Distinguishes among feeding roles using Types of food consumed How food was consumed If several species share a common food resource & procure food in a similar manner, then they are considered to be in the same feeding guild Useful in aquatic systems

3. I. Background Why feeding guilds? Standard trophic categories for marine & terrestrial systems (Lindeman 1942) do not provide much information

4. C. Why feeding guilds? Inverts often polyphagous rather than monophagous --omnivores Inverts--gut contents difficult to distinguish Most fish eat inverts, so little difference if consider only trophic levels Lots of diet overlap Microbial portion of food webs (detrital) needs to be considered�importance in flowing water has been underestimated

5. II. Food sources, food webs & energy transfer�general concepts

6. A. Food sources: a review Palatability & nutritional value of thought to depend on C:N ratio with lower ratio better Animal>algae>FPOM>CPOM (leaves) >CPOM (wood)

7. B. Food webs Link consumers with resources for a given community Can be based on trophic structure or feeding guilds Can be qualitative (shows just the links) or quantitative (shows links + the amount of energy transferred)

8. 4. Qualitative web

9. 5. Quantitative web

10. 6. Energy flow Energy flows through system On average about 10% (?) of the energy in one trophic level (or feeding guild) is transferred to the next higher level Much energy is lost as heat Energy needed for growth, reproduction & maintenance

11. 6. Energy flow Assimilation�the portion of the food energy content consumed that is actually metabolized (some passes right through)

12. 7. Quantitative food web�in depth Allochthonous material�from outside the system Autochthonous material�energy produced within the system

13. 7. Quantitative food web�in depth

14. 7. Quantitative food web�in depth

15. 7. Quantitative food web�in depth

16. III. Stream trophic relations Microbial food web�the microbial loop Take DOM and FPOM & converts it into bacterial biomass which is then used by protozoans and then by invertebrates & nutrients can be recycled Evidence for importance comes from lakes found too little algal productivity to support the increases in algal biomass important in oligotrophic lakes

17. 3. Microbial loop in lakes

18. 4. Microbial loop in streams Benthic bacteria more abundant & active than suspended ones Metazoan consumers of benthic bacteria & protists�copepods, oligochaetes, rotifers, nematodes How much of the microbial loop is transferred to macroinvertebrate assemblage? If protists need to eat bacteria first, then consumers eat protists, there will be too many transfers and not much energy left Some bacteria are consumed directly (e.g., oliogochaetes)

19. B. Invertebrate consumers

20. 1. Shredders Use CPOM as wood or leaves Crustaceans (amphipods, isopods, crayfish) & insect larvae (craneflies, some caddisflies, some stoneflies)

21. 1. Shredders Different feeding mechanisms Radula of snails very effective at scraping soft tissue Crayfish eat all material by engulfing Most CPOM consumers prefer conditioned leaves (colonized by bacteria & fungi) Microbes add tissue & excretory products Make CPOM more digestible Only snails, crustaceans & oligochaetes have cellulase, most insects don�t

22. 2. Collector-filterers Suspension feeders FPOM in the water column Most have morphological adaptations for filtering Blackflies (family Simulidae) paired cephalic fans

23. 2. Collector-filterers Caddisflies in the family Hydropsychidae Spin nets & capture particles passively Different species have different mesh sizes Longitudinal distribution of species from those that spin large mesh in headwaters to those that spin fine mesh in large rivers

24. 3. Collector-gatherers Deposit feeders on FPOM Mechanisms less diverse or less well known Generalists Many organisms Some �bulk feed� eating lots of refractory material (e.g., Hexagenia limbata, a mayfly, can consume 100% of its dry mass in a day)

25. 3. Collector-gatherers

26. 4. Grazer-scrapers Eat periphyton Traditional view have specialized mouth parts (e.g., snail radula, some caddisfly mouthparts) Recent evidence suggests they may use more diverse feeding

27. 5. Predators Eat other animals True predators either engulf prey whole (e.g., odonates, stoneflies) or pierce prey and suck out contents (hemipterans) Many are occasional predators

28. C. Limitations of functional feeding groups Change in diet with age Change in diet with food availability

29. D. River continuum Attempt to construct a synthetic framework to describe the function of lotic ecosystems from source to mouth Physical characteristics change from headwaters to mouth Original idea for temperate woodland streams & tied to stream order

30. D. River continuum

31. Tests Often functional groups do not fit P:R ratio often fit Importance as a general organizing principle Why don�t functional groups fit? Anything that �Resets� the stream Input of tributaries Input of groundwater D. River continuum

32. D. River continuum

33. E. Vertebrate consumers-fish Fish thought to be the most important, but others are being studied now Number of attempts to construct feeding guilds for fish Problems similar to those of invertebrates

34. E. Vertebrate consumers-fish

35. E. Vertebrate consumers-fish Trends in temperate streams Benthic invertebrate feeders most numerous Surface and water column feeders are also numerous Planktivores & large predators sparse Downstream trends Planktivores absent from headwater Piscivores increase downstream

36. E. Vertebrate consumers-fish Trends in tropical streams Risky business, extensions is tentative Allochthonous inputs greater in the tropics because of extensive flood plains, thus greater role for mud & detritus feeders Greater diversity of food resources (e.g., seeds, fruits, terrestrial vertebrates) Specialized morphological feeding adaptations

37. E. Vertebrate consumers-fish Specialized adaptations Visual pigments �Short-wave-shifted� species had visual pigments in the short wave range, works in shallow areas, diurnal feeding from surface in shallow water �long-wave-shifted� species had visual pigments in the long wave range, works in deep areas, nocturnal or turbid water feeders (e.g., catfishes)

38. 3. Specialized adaptations Body shape Deep, flat bodies associated with slower water habitats (e.g., blue gill) Bullet shaped bodies associated with faster water habitats (e.g., trout) Gut morphology Ventral mouths�more food from bottom Terminal or anterior mouths�food from water column

39. 3. Specialized adaptations Others Fishes that dwell near bottom have reduced swim bladders Mud feeders have longest relative gut length

40. F. Other vertebrate consumers All higher vertebrates are represented in lotic food webs Largest impact probably from fish-eating snakes, birds & crocodiles Salamander�carnivore of invertebrates, other amphibians & fish, can get large (e.g., hellbender)

41. F. Other vertebrate consumers Birds�feed on fish & invertebrates 11 orders (e.g., ducks, great blue heron) In Panama armored catfish don�t go into the shallows because of birds; these fish scrape algae & distribution of algae inversely mirrors the distribution of fish Mammals Shrews, racoons, bears occasional feeders Otters fully aquatic