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Multitrophic interactions. Interactions across trophic levels, or involving more than two “players”. Multitrophic interactions.

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multitrophic interactions
Multitrophic interactions
  • Interactions across trophic levels, or involving more than two “players”
multitrophic interactions2
Multitrophic interactions
  • Interactions in real communities include all interactions discussed so far (competition, herbivory, predation, pollination) plus others (decomposers, mutualistic and antagonistic fungi, predators and parasitoids)
  • How does the outcome of one interaction affect the outcome of another?
why the world is green
Why the world is green
  • Predators, parasites, and diseases keep herbivores rare (top-down regulation). Hairston et al. 1960




Hairston, Smith, Slobodkin. 1960. Am Nat 44: 421-425

why the world is green part 2
Why the world is green, part 2
  • Plants are fundamentally poor food (bottom-up regulation) Southwood 1973.
  • Herbivores are “between the devil [predators] and the deep blue sea [inedible food]” Lawton and McNeill 1979.
playing chutes and ladders
Playing Chutes and Ladders
  • Top-down and bottom-up both important

Hunter and Price 1992. Ecology 73: 724-732

trophic cascades do not include all interactions
Trophic cascades do not include all interactions

De Deyn and Van Der Putten, 2005. TREE 20 (11) 625-633

predator prey plant
  • Reintroduction of wolves to Yellowstone leads to aspen recovery—through both predation and fear
  • Recovery primarily in riparian areas with downed logs (predation risk higher)

Ripple and Beschta 2007. Biological Conservation 138:514-519

fish dragonfly pollinator plant predator predator prey plant
  • Fish eat dragonfly larvae; dragonflies eat pollinators like bees and flies

Knight et al. 2005. Nature 437:880-883

fish dragonfly pollinator plant
  • Fewer dragonfly larvae in and adults near pods with fish (for three size categories)

Knight et al. 2005. Nature 437:880-883

fish dragonfly pollinator plant11
  • Visit rate higher near ponds with fish; plants near these ponds had lower pollen limitation

Knight et al. 2005. Nature 437:880-883

plant herbivore enemy
  • Scale insects perform differently on different citrus cultivars; performance of scale affects size and sex ratio of offspring of parasitoid wasp

Hare and Luck, 1991. Ecology. 72: 1576-1585

plant herbivore enemy13


  • A trait that defends against herbivores reduces time enemies spend hunting prey on Datura

Gassman and Hare, 2005. Oecologia 144:62-71

plant herbivore enemy14
  • Herbivore survival depends on both plant defenses and enemies

Gassman and Hare, 2005. Oecologia 144:62-71

plant plant enemy
  • Dodder (Cuscuta) in salt marsh changed competitive relationships
plant plant enemy16
  • Herbivore damage may increase when competitors (that protect the herbivore) are present

J. Facelli, unpublished

plant herbivore pollinator
  • Flower size smaller in plants damaged manually or by herbivores

Strauss 1997. Ecology 78:1640-1645

plant herbivore pollinator18
  • Pollinators discriminate based on flower size

Strauss and Conner 1996. Am Nat 147:1098-1107.

plant host herbivore pollinator


  • Castilleja (indian paintbrush) is a hemiparasite
  • Experimentally grown on lupine hosts that either do or do not produce chemical defense (alkaloid)
plant host herbivore pollinator20
  • Alkaloids from host plant reduce herbivory, increase pollinator visits in Castilleja

% plants visited

Adler 2000. Am Nat 156:92-99

plant mychorrizae pollinator
  • Smaller flower size, reduced visitation in fireweed without AM fungi (compared to plants with AM fungi)

Wolfe et al 2005. Ecology Letters 8:218-223

plant plant mychorrizae pollinator pollinator
  • Suppression of mychorrizae in rough fescue grassland changed # flowering stems per plot in a species-specific manner

Cahill, Elle, Smith, Shore 2008. Ecology 89:1791-1801

plant plant mychorrizae pollinator pollinator23
  • Three species (non-myc) increased when myc suppressed, others no significant change
plant plant mychorrizae pollinator pollinator24
  • Myc suppression reduced per-stem visit rate… for species with no change in stem number
plant plant mychorrizae pollinator pollinator25
  • Change in plant community led to change in pollinator community



sweat bees

Bumble bees

Cahill, Elle, Smith, Shore 2008. Ecology 89:1791-1801

whole community mutualism
Whole community mutualism
  • Tide pools are low N areas, only slow-growing seaweeds usually grow there
  • Fast-growing Cladophora, when associated with invertebrates, can grow even in N-limited tide pools

(ostracods, nematodes,

polychaetes, etc)

Bracken et al 2007. Ecology 88(9):2211-2219

whole community mutualism27
Whole community mutualism
  • Cladophora adds structure to tide pools, allows for greater total biodiversity when present
ecosystem level effects
Ecosystem-level effects
  • Poplar species hybridize; grow along rivers
  • Genetic variation among parent species (Populus fremontii and P. angustifolia) and their hybrids in leaf tannin content

Many papers by Tom Whitham and others

ecosystem level effects29
Ecosystem-level effects
  • Variation in tannins affects:
    • Population densities of endophytic fungi, aquatic invertebrates, herbivorous insects, insectivorous birds
    • Decomposition rate of leaves, N mineralization in the soil
ecosystem level effects30
Ecosystem-level effects
  • Experimental planting of poplars:
    • Selective felling by beavers (avoid trees high in tannin)
    • Change in relative frequency of high-tannin trees: beavers select for more tannins!
multitrophic interactions31
Multitrophic interactions
  • Some multitrophic effects can be predicted from pairwise interaction effects and trophic cascades
  • Thus far, no emerging theory; we are working towards integrating mutualism, competition into models of trophic cascades to allow for better prediction