Challenged with new idea that disturbances kept communities from reaching

Challenged with new idea that disturbances kept

This preview shows page 5 - 7 out of 8 pages.

Challenged with new idea that disturbances kept communities from reaching equilibrium Disturbance is an event that changes a community (removes organisms, alters resources; fire, floods, etc.) o Ex. Fire in Yellowstone community destroyed trees start growing again after a year The intermediate disturbance hypothesis suggests that moderate levels of disturbance fosters higher diversity In New Zealand, richness of invertebrate taxa was highest in streams with intermediate intensity of flooding Ecological succession is the sequence of community and ecosystem changes after a disturbance Primary succession: occurs when no soil exists when succession begins Secondary succession: begins in area where soil remains after a disturbance An ecosystem is sum of all organisms living in a given area and the abiotic factors that they interact with Regardless of sizy, dynamics involve 2 main processes:
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o Energy flow (through ecosystems) o Chemical cycling (within and through ecosystems) Energy flow through ecosystems is linear (goes in one direction) Begins as solar energy <1% solar energy trapped by photosynthetic organisms Radiant energy is converted to chemical energy Chemical elements are cycled within and through Producers herbivore carnivore carnivore decomposers nutri ents cycle back to producers Just like energy, matter cannot be created or destroyed This is the law of conversation of mass As a result, we can measure how much of a chemical element recycles through ecosystems Can measure how much carbon, nitrogen, phosphorus is gained or lost over time Easier to trace cycle/flow of matter and energy by grouping species into broad trophic levels Producers (Autotrophs) primary consumers (heterotrophs) secondary tertiary quaternary detritivores/decomposers Primary production is the amount of light energy converted to chemical energy by autotrophs Total photosynthetic production sets spending limit for whole ecosystem’s energy budget Total primary production = ecosystem’s gross primary production (GPP) o Conversion of chemical energy form photosysntehesis per unit time Net primary production (NPP)= GPP – R a (energy used by producers for respiration) o Energy per unit area per time (J/m 2 *yr) or biomass added per unit area per time (g/ m 2 *yr) o NPP is stored chemical energy for consumers; varies between ecosystems Net Ecosystem Production (NEP) measure of total biomass accumulated (producers and consumers) per unit of time NEP = GPP –R T (energy used by producers plus consumers for respiration) Estimated by comparing net flux of CO 2 and O 2 in an ecosystem Useful as indicator of carbon storage or loss over time If more CO 2 enters than leaves, system is storing carbon Release of O 2 indicates system is also storing CO 2 Both light and nutrients limit/control primary production in aquatic ecosystems Depth of light penetration affects 1 st production Nutrients limit primary production more than light Limiting nutrient is element that must be added for production to increase in an area Nitrogen and phosphorus most often limit marine production, but other elements too (ex. Iron)
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