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Miniature worlds: Bromeliad food webs as a model system for ecology

Miniature worlds: Bromeliad food webs as a model system for ecology. Diane Srivastava. The idea of the archetype If we have a precise knowledge of that which constitutes the typical structure of each of these groups, we shall have, so far, an exhaustive knowledge of the Animal Kingdom.

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Miniature worlds: Bromeliad food webs as a model system for ecology

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  1. Miniature worlds: Bromeliad food webs as a model system for ecology Diane Srivastava

  2. The idea of the archetype If we have a precise knowledge of that which constitutes the typical structure of each of these groups, we shall have, so far, an exhaustive knowledge of the Animal Kingdom. - T.H. Huxley (1869)

  3. Easily manipulated • Many replicates possible • Quick response time

  4. ? • Easily manipulated • Many replicates possible • Quick response time

  5. Real ecosystem, co-evolved species! • Difficult to manipulate • Low replication • Slow response time

  6. ? General ecological principles • Real ecosystem, co-evolved species! • Difficult to manipulate • Low replication • Slow response time

  7. ? “Replication vs. realism” -David Schindler

  8. Container habitats

  9. c. William H. Bond

  10. Bromeliad food web Intermediate predators Microbial Food web c. William H. Bond Bacteria, fungi Detritus

  11. Rotifers Flagellates Ciliates Bacteria, fungi

  12. Why bromeliads are useful systems • Discrete, simple food webs • Number of trophic levels (with M. Melnychuk, J. Ware)

  13. Why bromeliads are useful systems • Discrete, simple food webs • Stable manipulations of community structure • Effect of habitat complexity on trophic cascades

  14. Why bromeliads are useful systems • Discrete, simple food webs • Stable manipulations of community structure • Scale of population dynamics differs with taxa • Extinction cascades (with T. Bell)

  15. Why bromeliads are useful systems • Discrete, simple food webs • Stable manipulations of community structure • Scale of population dynamics differs with taxa • Similar habitat occurs over broad geographic range • Biogeographical comparisons (B. Richardson) • Contained ecosystem for nutrient budgets • Insects and bromeliad growth? (A. Reich, J. Ngai)

  16. Does energy limit the number of trophic levels?

  17. Theory: Energy is lost in the transfer between trophic levels (about 10% transfer efficiency). If energy is limiting, trophic diversity will be a logarithmic function of basal energy (every 10x increase in energy can support one more trophic level).

  18. Problem: Theory: Energy is lost in the transfer between trophic levels (about 10% transfer efficiency). If energy is limiting, trophic diversity will be a logarithmic function of basal energy (every 10x increase in energy can support one more trophic level). Difficult to quantify basal energy, number of trophic levels

  19. 10x increase in energy correlated with < 1 trophic level • Intraguild predation will decrease trophic levels • Covariates?

  20. No damselfly larvae below 100 ml capacity

  21. Damselflies present Damselflies absent 1997 2000 Bromeliad capacity (ml)

  22. Damselflies present Damselflies absent 1997 Prey available (g per M. modesta larva) 2000 Bromeliad capacity (ml)

  23. Larva survived Larva missing Bromeliad capacity (ml)

  24. Larva survived Larva missing Growth rate, corrected for initial mass (g day-1) Bromeliad capacity (ml)

  25. Effect of habitat complexity on trophic cascades

  26. Theory: Trophic cascades occur when there are strong linear trophic links. Habitat complexity may increase predator search time, or increase prey survival (refuges)

  27. Problems: Theory: Trophic cascades occur when there are strong linear trophic links. Habitat complexity may increase predator search time, or increase prey survival (refuges) Manipulating habitat complexity, isolating effects on predators and prey

  28. Experimental design Top trophic level

  29. 1 leaf 3 leaves 6 leaves Experimental design Top trophic level X Bromeliad complexity

  30. 1 leaf small 3 leaves large 6 leaves Experimental design Top trophic level X Bromeliad complexity X Bromeliad size (Expt. 2 only)

  31. Expt. 1 = = Predation x complexity or complexity2 P<0.05

  32. Expt. 1 = = Predation x complexity P<0.0001

  33. Insects grow more slowly in complex bromeliads

  34. Effect of predator diminishes with complexity…and size Predator x Complexity: P<0.05 Detrital processing: No predator - Predator 1 3 6 Complexity Larger bromeliads also have reduced foraging efficiency Detrital processing: Small - Large 1 3 6 Complexity

  35. Effect of predator diminishes with complexity…and size Detrital processing: No predator - Predator 1 3 6 Complexity Larger bromeliads also have reduced foraging efficiency Detrital processing: Small - Large 1 3 6 Complexity

  36. Effect of predator diminishes with complexity…and size Predator x Size: P<0.05 Detrital processing: No predator - Predator 1 3 6 Complexity Larger bromeliads also have reduced foraging efficiency Detrital processing: Small - Large 1 3 6 Complexity

  37. Effect of predator diminishes with complexity…and size Predator x Size: P<0.05 Detrital processing: No predator - Predator 1 3 6 Complexity Larger bromeliads also have reduced foraging efficiency No predator: Size effect P=0.01 Predator: NO Size effect: P=0.88 Detrital processing: Small - Large 1 3 6 Complexity

  38. Increased bromeliad complexity - Decreased detritivore efficiency Direct effect Effect on detrital processing

  39. Increased bromeliad complexity Higher trophic level present Trophic effect - Decreased detritivore efficiency Direct effect + Decreased predator efficiency Effect on detrital processing

  40. Increased bromeliad size Higher trophic level present Trophic effect - Decreased detritivore efficiency Direct effect + Decreased predator efficiency Effect on detrital processing

  41. Alex Reich Bromeliad growth experiment

  42. What happens to food webs and ecosystems when species go extinct?

  43. Theory: • Declining species diversity will cause: • Loss of species at lower trophic levels (extinction cascades) • Reduction in ecosystem functions

  44. Theory: • Declining species diversity will cause: • Loss of species at lower trophic levels (extinction cascades) • Reduction in ecosystem functions • Manipulating animal diversity! Problem:

  45. Experimental design extinction Top predator response (cascade) extinction Detritivores Ciliates Detritus response (function)

  46. Detritivore communities Red chironomid (R) Yellow chironomid (Y) Tipulid (T) Helodid (H) • 1 species (4 community types): THRY • 2 species (6 community types): THTRTYHRHYRY • 4 species (1 community type): THRY

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