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Fish in Lakes. Lake Food Chain. Generally represent the end of the food chain in most lakes Only a small fraction of the energy fixed in the system makes it to this level. Lake Food Chain. Important group because of effects they can have on all other levels of living things in lakes.
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Lake Food Chain • Generally represent the end of the food chain in most lakes • Only a small fraction of the energy fixed in the system makes it to this level
Lake Food Chain • Important group because of effects they can have on all other levels of living things in lakes
Feeding Categories • Piscivores - feed on fish • Basses, pikes, walleye
Feeding Categories • Planktivores - feed on phytoplankton, zooplankton • Visual particulate feeders or strainers • Young of many species, clupeids like alewife
Feeding Categories • Benthivores - pick materials off bottom • Macroinvertebrates, algae, plants, detritus • Suckers
Feeding Categories • Omnivores - feed on everything • Carp, gizzard shad (planktivore tendencies)
Trophic Control • Each trophic group is important, but piscivores & omnivores have more overall control on the entire system
Trophic Control • Strong populations of piscivores can keep other fish types in check and keep system “balanced” • Top-down control
Out of Control! • In absence of predators, other fish types can dominate, affect other lake components • Planktivores - shad • Benthivores - stunted bluegill
The Carp Cascade • Feeding activities of carp can modify littoral substrate and muddy the water • Macrophytes cannot grow • Muddy water - reduced transparency, reduced phytoplankton, reduced zooplankton, etc.
The Bottom Line • Presence or absence of a single species may have significant impact on the functioning of the entire lake
Fish Productivity • Varies greatly among different fishes • Fishes feeding nearer the base of the food chain (herbivores) are more productive than predatory forms
Fish Productivity • The younger the fish population (mean age), the more productive it is • Young fish, greater % of food intake to growth • Older fish, greater % of food intake to maintenance
Fish Productivity • In temperate zone lakes, production of fish limited mostly to spring, summer, autumn • Considerably lower than in tropical lakes
Fish Productivity • Tropics: 100s of g/m2/year • Temperate lakes: 1-20 g/m2/year • Temperate streams: ~50 g/m2/year