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Multitrophic interactions. Interactions across trophic levels, or involving more than two “players”. Multitrophic interactions.
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Multitrophic interactions • Interactions across trophic levels, or involving more than two “players”
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 • Predators, parasites, and diseases keep herbivores rare (top-down regulation). Hairston et al. 1960 Predators Herbivores Plants Hairston, Smith, Slobodkin. 1960. Am Nat 44: 421-425
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 • Top-down and bottom-up both important Hunter and Price 1992. Ecology 73: 724-732
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-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-plant • 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-enemy defended • A trait that defends against herbivores reduces time enemies spend hunting prey on Datura Gassman and Hare, 2005. Oecologia 144:62-71
Plant-herbivore-enemy • 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-enemy • 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-pollinator • Pollinators discriminate based on flower size Strauss and Conner 1996. Am Nat 147:1098-1107.
Impact 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-pollinator • 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-pollinator • Three species (non-myc) increased when myc suppressed, others no significant change
Plant-plant-mychorrizae-pollinator-pollinator • Myc suppression reduced per-stem visit rate… for species with no change in stem number
Plant-plant-mychorrizae-pollinator-pollinator • Change in plant community led to change in pollinator community Flies Small sweat bees Bumble bees Cahill, Elle, Smith, Shore 2008. Ecology 89:1791-1801
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 mutualism • Cladophora adds structure to tide pools, allows for greater total biodiversity when present
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 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 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 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