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
ferret)
