Unit 1, Part 3 Notes - Community Ecology

Unit 10, Part 3 Notes Community Ecology AP Biology Community A group of

species that occur together in a particular geographical area

How do we define a species role within a community? Ecological Niche Total use of and contribution to the biotic

and abiotic resources in its environment (ex: resources it uses, conditions it tolerates, its behaviors, its affect on other organisms) Fundamental vs. realized

niche How is energy transferred within a community? Food Chains vs. Food Webs

Trophic levels Some organisms can fill multiple trophic levels (ex: squid) Low Trophic Efficiency There cannot be consumers beyond the quaternary

consumer level due to low trophic efficiency Reasons for low trophic efficiency 1) Producers use some of the energy they convert into glucose from sunlight during cellular respiration 2) Consumers lose energy from the food they consume during cellular respiration and as waste

3) Not all parts of an organism are consumable and/or digestible Trophic Cascade A drastic increase or decrease in the

number of organisms at one trophic level will greatly affect organisms at other trophic

levels Depicting Low Trophic Efficiency Pyramid of Production/Productivity (aka Pyramid of Energy):

shows the amount of energy stored in the tissues of organisms on each trophic level, where energy is measured in Joules, kilojoules (aka calories),

kilocalories, etc. Pyramid of Biomass: each tier represents the total dry mass (biomass) of all organisms in one trophic level. Most biomass pyramids are bottom heavy

Some aquatic biomass pyramids are inverted (b/c phytoplankton grow, reproduce, and are consumed quickly by zooplankton, so they never reach a large population size or standing crop) Phytoplankton

Zooplankton Pyramid of Numbers: Shows the actual number of organisms at each trophic level

Inverted pyramid of biomass in a forest ecosystem How much energy can photosynthetic producers harvest from sunlight?

Only 1% of visible light from the sun can be captured by produce Gross Primary Productivity (GPP) vs. Net Primary Productivity (NPP) Units of NPP: J/m2/yr or g/m2/yr.

Secondary Productivity / Production NPP: Variation among Ecosystems What are some consequences of food web structure?

Biomagnification Increasing concentration of persistent, toxic substances in organisms at each trophic level

dichlorodiphenyltrichloroe thane (DDT) study by Rachel Carson fragile eggshells in birds increased egg breakage during nesting

Other substances that biomagnify polychlorinated biphenyls (PCBs) used in coolant liquids in the U.S.,

but banned in 1979 Other substances that biomagnify Heavy metals like mercury and cadmium in certain types of seafood

Of particular concern for children and pregnant women How can we determine the stability of a community? High species diversity (biodiversity) in a community less

vulnerable to ecosystem disturbances Factors that affect species diversity = species richness (number of species) and relative abundance (% of the total organisms in the community that are from each species) High species richness and even relative abundance high species diversity

Species richness tends to be higher near the equator (more consistent climate + warm and moist for producers) How do different species interact within a community?

Types of Symbiosis Mutualism, Commensalism, Ammensalism, Parasitism, Predation, Competition Types of Competition: Intraspecific vs. interspecific Competitive Exclusion Principle (when niches

of two species fully overlap, one species will go extinct) Resource Partitioning When species use different parts of a resource to avoid competing directly

More Resource Partitioning Are some species more important than others within a community?

Dominant Species the species that is so abundant that it has the highest biomass of any species in the community In terrestrial ecosystems, dominant species are always

primary producers Removal of a dominant species decreased biodiversity within community American chestnut trees in eastern North American forests

were all killed by a fungus by 1950 seven species of insects killed Keystone Species Not the most abundant species, but they have

an important ecological role Ex: Sea otters in British Columbias coastal kelp forest trapped and killed for fur sea urchins increase kelp decreases and fish that depend on kelp decrease

Another keystone species Prairie dog burrows killed as pests in western grasslands of North America their burrow networks (dog towns) cannot be used for -increasing plant diversity

-turning over soil -increasing the nitrogen content of the soil -allowing deeper water penetration of the soil -homes for other species (ex: black-footed


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