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BIOL 208 (March 28, 2014) - Primary Productivity and Energy Flow

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Biology (Biological Sciences)
James Cahill

BIOL 208 – Primary Productivity and Energy Flow (March 28, 2014) • Topics of Focus o Primary production o Trophic dynamics in ecosystems o Top-down controls on production o Biodiversity and ecosystem functioning -------------------------------------------------------------------------------------------------------------------- ----------- • Ecosystems: o Mostly, we have looked at:  Individuals, populations, communities  Interest in abiotic environment based on its effects on organisms…  In turn, organisms influence the environment (eg. succession) o Main components:  Biogeochemistry – raw materials for the ecosystem  Energy – needed to convert raw materials into life forms  Organisms –energy input lets them exist; in turn, they participate in energy flow and nutrient recycling • *“Bags of energy/nutrients” o We will not worry too much about their individual ecology o *Boundaries hard to define  Ex. we have a forest and inside the forest is a stream (an aquatic component)… are they two different systems or one? • They are not independent from each other  *Boundaries are artificial but they “exist” because of legislation • Models of food webs, ecosystem energy, and nutrient cycling o Modelled through - Trophic webs (producers  consumers), compartmental models  *Producers are the first stores of energy (ex. plants) • Consumers have many levels based on what eats what (convert the energy into a different store - flesh)  Compartmental models • There are different pools holding this “energy” o Shows transformation of energy from one component of an ecosystem to another o Trophic classification  Ex. meadow: hawk  fox  hare  grass  *If we look at the amount of energy stored in a system, you will always have a pyramid shape • Total energy is never 100% conserved o Energy is lost with each transformation  Second Law of Thermodynamics (ex. loss of heat) o Ecosystems have two major food chains  Grazing food chains: herbivores feed on living plant biomass  Detrital food chain: source of energy is dead organic matter • Dead things immediately get eaten and lead to respiration  CO2 leaves the system • Ex. earthworms increase decomposition  increase CO2 release into the atmosphere  *These two chains are linked • Ex. the earthworms can now be eaten too • Detritus and waste from grazing chain contributes to detrital chain • Carnivores may not discriminate prey from either chain • Food Chain Length o *Most are short. Reasons:  *Energetic hypothesis • *90% of the total energy at a trophic level is lost in the transfer to the next trophic level • *There just isn’t enough energy to support another viable population passed a certain food chain length because of this loss of energy  Design constraints •
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