From Mesocosms to the Field: The Role and Value of Cage Experiments in Understanding Top-Down Effects in Ecosystems

  • O. J. Schmitz
Part of the Ecological Studies book series (ECOLSTUD, volume 173)


Ecologists routinely use field experiments to gain predictive insights about ecosystem structure and function. However, experiments conducted at a whole ecosystem scale are often too crude to provide the detailed causal understanding needed for prediction. Ecologists instead try to gain such causal understanding by conducting experiments in small-scale enclosures or cages. Enclosure cages offer the fine-scale resolution and control needed to isolate certain combinations of species and derive a detailed understanding of interaction mechanisms among the species. However, the applicability of such insights to predicting whole ecosystem function depends critically on satisfying some key design criteria. These criteria include ensuring that enclosure experiments are conducted in natural field environments, as opposed to artificial laboratory settings; that behaviour of mobile species is not seriously hampered; and that experiments are conducted over time scales that represent species’ natural life cycles. I detail here how enclosure cage experiments can be an effective tool in an endeavour to predict effects of perturbations on whole ecosystem function. I first provide a detailed explanation of the design of enclosure cages used in studies of herbaceous plants and arthropod herbivores and predators. I also provide guidelines for conducting experiments in ways that do not seriously distort the experimental conditions from those of natural environments. I then illustrate how cage experiments lead to predictive insights using an example from my own research on trophic interactions among spider predators, leaf-chewing and sap-feeding insect herbivores and grass and herb plants in a New England meadow ecosystem. I show that fulfilment of critical design criteria can allow one to isolate the dominant predator and herbivore species in this ecosystem and determine the nature and strength of top-down control of plant species composition and biomass production. I then show how predictions about top-down control of plant species diversity and biomass production are tested and confirmed using large-scale, unenclosed field plots that experimentally manipulate both predator and herbivore trophic levels of the meadow ecosystem.


Cage Experiment Enclosure Experiment Feeding Guild Herb Biomass Spider Predator 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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  1. Abrams PA (1984) Foraging time optimization and interactions in food webs. Am Nat 124: 80–96CrossRefGoogle Scholar
  2. Abrams PA (1992) Predators that benefit prey and prey that harm predators: unusual effects of interacting foraging adaptations.Am Nat 140: 573–600Google Scholar
  3. Abrams PA (1995) Implications of dynamically-variable traits for identifying, classifying, and measuring direct and indirect effects in ecological communities. Am Nat 146: 112–134CrossRefGoogle Scholar
  4. Beckerman AP, Uriarte M, Schmitz OJ (1997) Experimental evidence for a behavior-mediated trophic cascade in a terrestrial food chain. Proc Natl Acad Sci USA 94: 10735–10738CrossRefPubMedPubMedCentralGoogle Scholar
  5. Belovsky GE, Slade JB (1993) The role of vertebrate and invertebrate predators in a grasshopper community. Oikos 68: 193–201CrossRefGoogle Scholar
  6. Belovsky GE, Slade JB (1995) Dynamics of some Montana grasshopper populations: relationships among weather, food abundance and interspecific competition. Oecologia 101: 383–396CrossRefGoogle Scholar
  7. Carpenter SR (1996) Microcosm experiments have limited relevance for community and ecosystem ecology. Ecology 77: 677–680CrossRefGoogle Scholar
  8. Carpenter SR (1999) Microcosm experiments have limited relevance for community and ecosystem ecology: reply. Ecology 80: 1085–1088CrossRefGoogle Scholar
  9. Carpenter SR, Kitchell JF, Hodgson JR (1986) Cascading trophic interactions and lake productivity. Bioscience 35: 634–639CrossRefGoogle Scholar
  10. Chase J (1996) Abiotic controls of trophic cascades in a simple grassland food chain. Oikos 77: 495–506CrossRefGoogle Scholar
  11. Drake GG, Leadley PW, Arp WJ, Nassiry D, Curtiss PS (1989). An open-top chamber for field studies of elevated atmospheric CO2 concentration on saltmarsh vegetation. Funct Ecol 3: 363–371CrossRefGoogle Scholar
  12. Finke DL, Denno RF (2002) Intraguild predation diminished in complex-structured vegetation: implications for prey suppression. Ecology 83: 643–652CrossRefGoogle Scholar
  13. Fisher SG (1997) Creativity, idea generation and the functional morphology of streams. J N Am Benth Soc 16: 305–318CrossRefGoogle Scholar
  14. Foelix RF (1996) The biology of spiders. Harvard University Press, Cambridge, MAGoogle Scholar
  15. Hairston NG (1990) Ecological experiments: purpose, design and execution. Cambridge University Press, CambridgeGoogle Scholar
  16. Hairston NG, Smith FE, Slobodkin LB (1960) Community structure, population control, and competition.Am Nat 94: 421–425CrossRefGoogle Scholar
  17. Hunter MD, Price PW (1992) Playing chutes and ladders — heterogeneity and the relative roles of bottom-up and top-down forces in natural communities. Ecology 73:724–732Google Scholar
  18. Leibold MA (1989) Resource edibility and the effects of predators and productivity on the outcome of trophic interactions.Am Nat 134: 922–949Google Scholar
  19. Leibold MA (1996) A graphical model of keystone predators in food webs: trophic regulation, of abundance, incidence, and diversity patterns in communities. Am Nat 147: 784–812CrossRefGoogle Scholar
  20. Levin SA (1998) Ecosystems and the biosphere as complex adaptive systems. Ecosystems 1: 431–436CrossRefGoogle Scholar
  21. Lima SL, Dill LM (1990) Behavioral decisions made under the risk of predation. Can J Zool 68: 619–640CrossRefGoogle Scholar
  22. MacNally R (2000) Modeling confinement experiments in community ecology: differential mobility among competitors. Ecol Model 129: 65–85CrossRefGoogle Scholar
  23. Mangel M, Clark CW (1986) Towards a unified foraging theory. Ecology 67: 1127–1138CrossRefGoogle Scholar
  24. Oksanen L, Fretwell SD, Arruda J, Niemela P(1981) Exploitation ecosystems in gradients of primary productivity.Am Nat 118: 240–262CrossRefGoogle Scholar
  25. Ovadia O, Schmitz OJ (2002) Linking individuals with ecosystems: experimentally identifying the relevant organizational scale for predicting trophic abundances. Proc Natl Acad Sci USA 99: 12927–12931CrossRefPubMedPubMedCentralGoogle Scholar
  26. Ovadia O, Schmitz OJ (2004) Weather variation and trophic interaction strength: sorting the signal from the noise. Oecologia (in press)Google Scholar
  27. Paine RT (1966) Food web complexity and species diversity.Am Nat 100: 65–73Google Scholar
  28. Paine RT (1988) Food webs: road maps of interaction or grist for theoretical development? Ecology 69: 1648–1654CrossRefGoogle Scholar
  29. Polis GA, Strong DR (1996) Food web complexity and community dynamics. Am Nat 147: 813–846CrossRefGoogle Scholar
  30. Power ME (1992) Top-down and bottom-up forces in food webs–do plants have primacy? Ecology 73: 733–746CrossRefGoogle Scholar
  31. Raffaelli D, Moller H (2000) Manipulative field experiments in animal ecology: do they promise more than they can deliver? Adv Ecol Res 30: 299–337CrossRefGoogle Scholar
  32. Ritchie ME, Tilman D (1992) Interspecific competition among grasshoppers and their effect on plant abundance in experimental field environments. Oecologia 89: 524–532CrossRefGoogle Scholar
  33. Root RB (1996) Herbivore pressure on goldenrods (Solidago altissima): its variation and cumulative effects. Ecology 77: 1074–1087CrossRefGoogle Scholar
  34. Rosenzweig ML (1973) Exploitation in three trophic levels.Am Nat 107: 275–294Google Scholar
  35. Rothley KD, Schmitz OJ, Cohon JL (1997) Foraging to balance conflicting demands: novel insights from grasshoppers under predation risk. Behav Ecol 8:551–559CrossRefGoogle Scholar
  36. Schmitz OJ (1993) Trophic exploitation in grassland food webs: simple models and a field experiment. Oecologia 93: 327–335CrossRefGoogle Scholar
  37. Schmitz OJ (1994) Resource edibility and trophic exploitation in an old-field food web. Proc Natl Acad Sci USA 91: 5364–5367CrossRefPubMedPubMedCentralGoogle Scholar
  38. Schmitz OJ (1998) Direct and indirect effects of predation and predation risk in old-field interaction webs.Am Nat 151: 327–342Google Scholar
  39. Schmitz OJ (2000) Combining field experiments with individual-based modeling to identify the dynamically-relevant organizational scale in a field system. Oikos 89: 471–484CrossRefGoogle Scholar
  40. Schmitz OJ (2003) Top predator control of plant diversity and productivity in an old-field ecosystem. Ecol Lett 6: 156–163CrossRefGoogle Scholar
  41. Schmitz OJ, Suttle KB (2001) Effects of top predator species on direct and indirect interactions in a food web. Ecology 82: 2072–2081CrossRefGoogle Scholar
  42. Schmitz OJ, Beckerman AP, O’Brien KM (1997) Behaviorally mediated trophic cascades: effects of predation risk on food web interactions. Ecology 78: 1388–1399CrossRefGoogle Scholar
  43. Schmitz OJ, Hambäck PA, Beckerman AP (2000). Trophic cascades in terrestrial systems: a review of the effects of top carnivore removals on plants.Am Nat 155: 141–153Google Scholar
  44. Sih A (1980) Optimal behavior: can foragers balance two conflicting demands? Science 210: 1041–1043CrossRefPubMedGoogle Scholar
  45. Skelly DK (2002) Experimental venue and estimation of interaction strength. Ecology 83: 2097–2101CrossRefGoogle Scholar
  46. Sokol-Hessner L, Schmitz OJ (2002) Aggregate effects of multiple predator species on a shared prey. Ecology 83: 2367–2372CrossRefGoogle Scholar
  47. Tilman D, Reich PB, Knops J, Wedin D, Mielke T, Lehman C (2001) Diversity and productivity in a long-term grassland experiment. Science 294: 843–845CrossRefPubMedGoogle Scholar
  48. Uriarte M, Schmitz OJ (1998) Trophic control across a natural productivity gradient with sap-feeding herbivores. Oikos 82: 552–560CrossRefGoogle Scholar
  49. Werner EE (1998) Ecological experiments and a research program in community ecology. In: Resetarits WJ, Bernardo J (eds) Experimental ecology: issues and perspectives. Oxford University Press, OxfordGoogle Scholar
  50. Wilsey BJ, Potvin C (2000) Biodiversity and ecosystem functioning: importance of species evenness in an old field. Ecology 81: 887–892CrossRefGoogle Scholar
  51. Wise DH (1993) Spiders in ecological webs. Cambridge University Press, CambridgeCrossRefGoogle Scholar
  52. Yodzis P (1995) Food webs and perturbation experiments: theory and practice. In: Polis GA, Winemiller KO (eds) Food webs: integration of patterns and dynamics. Chapman and Hall, New YorkGoogle Scholar

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© Springer-Verlag Berlin Heidelberg 2008

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  • O. J. Schmitz

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