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BIOC50H3 (15)
Chapter 20

chapter 20 book notes

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University of Toronto Scarborough
Biological Sciences
Marc Cadotte

Chapter 20 Ecology Trophic interactions: by their feeding (their ecological roles are determined by what they eat and by what eats them). Organisms can be grouped into trophic levels. Trophic levels = feeding category and is based on the number of feeding steps by which it is separated from autotrophs. The first trophic level consists of autotrophs and detritus (primary procurers that generate chemical energy from sunlight or inorganic chemical compounds, and also generates most of the dead organic matter in an ecosystem). The second trophic level is composed of herbivores that consume the autotroph biomass as well as detritivores that consume the dead organic matter. The remaining trophic levels (third and up) contain carnivores that consume the animals at the trophic level below them. Most ecosystems have 4 or fewer tropic levels. Some organisms dont fit into trophic levels such as opportunistic feeders and omnivores. Coyotes are opportunistic feeders and consume vegetation, mice, and other carnivores. All organisms are either consumed or end up as detritus. Most of the energy flow is through detritus as most of the biomass is not consumed. Detritus usually comes from plants within a terrestrial ecosystem. Detritus from aquatic ecosystems usually comes from terrestrial matter (external to the aquatic environment). External energy inputs to an ecosystem is called allochthonous inputs (plant leaves, stems, wood, dissolved organic matter that fall in from adjacent terrestrial ecosystems or flow in via ground water). Autochthonous energy: energy produced by autotrophs within the system. Fig 20.4: B.) Most of the studies, more than 50% of NPP end up as detritus. C.) These trends are stronger for terrestrial ecosystems than for aquatic ecosystems. In most of the studies, only a small proportion of NPP is consumed by herbivores. Energy between trophic levels is lost. Plants lose their energy by cellular respiration. Energy flow between trophic levels can be depicted using energy or biomass pyramids. Trophic pyramid shoes us how energy flows through the ecosystem. In terrestrial ecosystems, energy and biomass pyramids are usually similar because biomass is typically closely associated with energy production. In aquatic ecosystems, the high consumption rate and the relatively short life spans of the primary producers (phytoplankton) result in an unusual situation in which the biomass pyramid is inverted relative to the energy pyramid. Fig 20.5 C.) Inverted pyramids are more common as autotroph biomass decreases. Ratios above 1 indicate inverted pyramids. Inverted pyramids in aquatic ecosystems are more common in nutrient-poor waters with low autotrophic biomass. Energy flow between trophic levels differs amount ecosystem types. www.notesolution.com
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