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Lecture 24

BIOSC 0160 Lecture 24: Biology 2 Lecture 3.7: Ecosystem Ecology

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University of Pittsburgh
Biological Sciences
BIOSC 0160

Biology Week 15 41317 Lecture 3.7 Species Richness: total number of species in a community Relative abundance: proportion each species contributes to the total number of individuals of all species in the community (p i ni) Shannon diversity index: H = (sum from 1 to n) (i)(lni) Keystone species: have a disproportionate (much larger) impact on the abundance of other species their presence is critical for the survival of other species Disturbance: strong, shortlived disruption to a community that changes the abundance and distribution of biotic and abiotic components of the environment (ex. Forest fires, floods, etc.) characterized by type, frequency, and severity Succession: the gradual colonization of a habitat after a disturbance, usually by a series of species Facilitation: earlyarriving species make conditions more favorable for the arrival of later species Inhibition: presence of one species inhibits the establishment of another species Primary producer = autotroph = organism that can synthesize its own food from inorganic sources o In most ecosystems (all biotic and abiotic factors), this will be photosynthetic organisms GPP (gross primary production) = total carbon fixed by primary producers NPP (net primary production) = energy used for growth and reproduction o NPP = GPP respiration Remaining energy is either lost or metabolized for energy in mitochondria (respiration) Consumers: eat living organisms Decomposers: detritivores = obtain energy from feeding on the remains of other organisms (eat dead organisms) Organisms that consume energy from the same type of source occupy the same trophic level Brown food webs: most of the components of the food web are not living (ex. Forests) Green food webs: primary producers are living Biomass and energy declines at each trophic level only about 10 of available biomass if transferred from one trophic level to the next Energy budget: o Maintenance is energy lost as heat o Growth and reproduction are energy converted into mass (this is all thats available for the next level) o Excretion is energy that is passed without conversion Trophic cascade: when you remove or add a keystone species, it results in a huge array of effects; occurs when changes in topdown control affect populations 23 links away in food web (otters: topdown control on sea urchins) o When the species is higher up in the food web, it has a larger effect Reintroduction of wolves in yellowstone changed the abiotic conditions as well
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