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

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

3. 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)

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

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

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

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

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

9. Container habitats

11. c. William H. Bond

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

13. Rotifers Flagellates Ciliates Bacteria, fungi

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

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

16. 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)

17. 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)

18. Does energy limit the number of trophic levels?

19. 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).

20. 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

21. 10x increase in energy correlated with < 1 trophic level • Intraguild predation will decrease trophic levels • Covariates?

23. No damselfly larvae below 100 ml capacity

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

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

26. Larva survived Larva missing Bromeliad capacity (ml)

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

29. Effect of habitat complexity on trophic cascades

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

31. 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

32. Experimental design Top trophic level

33. 1 leaf 3 leaves 6 leaves Experimental design Top trophic level X Bromeliad complexity

34. 1 leaf small 3 leaves large 6 leaves Experimental design Top trophic level X Bromeliad complexity X Bromeliad size (Expt. 2 only)

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

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

37. Insects grow more slowly in complex bromeliads

38. 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

39. 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

40. 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

41. 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

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

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

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

45. Alex Reich Bromeliad growth experiment

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

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

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

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

50. 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