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BIOC50H3 (15)
Chapter 20

chapter 20 book notes

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Department
Biological Sciences
Course Code
BIOC50H3
Professor
Marc Cadotte

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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.
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Fig 20.6: positive relationship between net primary production and the amount of biomass
consumed by herbivores. This suggests that herbivores production is limited by the amount
of food available. The amount of autotroph biomass consumed is significantly higher in
aquatic ecosystems than in terrestrial ecosystems. To explain the lower proportion of
autotroph biomass consumed in terrestrial ecosystems, hypotheses were made. 1.)
Population growth of herbivores is constrained by predation, keeping population sizes below
their potential carrying capacities. Predator removal experiments support this hypothesis
in some ecosystems by demonstrating that significant increases in prey populations follow
removal of their predators. 2.) Defences against herbivores (including secondary compounds
and structural defences) lower the amount of consumption of some autotrophs. Plants of
resource-poor environments (desert and tundra) tend to be more strongly defended against
herbivory than plants from resource-rich environments. This greater allocation to defence
may explain why the proportion of plant biomass consumed is lower in resource-poor
environments. 3.) Terrestrial plants contain nutrient-poor structural materials such as
stems and wood, which are typically absent in aquatic autotrophs. The chemical
composition of phytoplankton makes them more nutritious for herbivores than terrestrial
plants. Herbivores typically have high requirements for nutrients such as N and P to meet
their demands for structural growth, metabolism, and protein synthesis.
The efficiency of energy transfer (= efficiency output of energy per unit of energy input)
varies among consumers. Biomass that isnt ingested or assimilated enters the pool of
detritus.
Consumption efficiency = proportion of the available biomass that is ingested by consumers.
Higher in aquatic ecosystems than terrestrial. Higher for carnivores than herbivores.
Assimilation efficiency = proportion of the ingested biomass that consumers assimilate by
digestion. Food that is ingested but not assimilated is lost as SHIT to the environment,
entering the pool of detritus. Determined by the quality of food (chemical composition) and
the physiology of the consumer. Quality of food available to herbivores and detritivores is
generally lower than that of the food available to the carnivores. Plants are composed of
complex molecules (lignin, cellulose, humic acids) and are not easily digested, plants also
have low concentrations of N and P. Animals on the other hand have a carbon: nutrient
ratio that is usually very similar to that of the animal consuming them and are assimilated
more readily.
Production efficiency = proportion of assimilated biomass used to produce new consumer
biomass. Strongly related to the thermal physiology and size of the consumer. Endotherms
allocate much of their assimilated food to metabolic production of heat, and therefore have
less energy left over to allocate to growth and preproduction than ectotherms.
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Description
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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