ch. 54 part 2 Flashcards
dominant species
those that are most abundant or have the highest biomass
how are invasive species usually introduced to a new environment
humans
why do invasive species dominate
they lack natural predators or parasites
keystone species
exert strong control on a community by their ecological roles, or niches
are keystone or dominant species more abundant in the community
dominant
ecosystem engineers (foundation species)
cause physical changes in the environment that affect community structure
- (like beavers and dams)
bottom-up model of community organization
proposes unidirectional influence from lower to higher trophic levels
- present/absence of mineral nutrients (N) control plant (V) numbers, which control herbivore (H) numbers, which control predator (P) numbers
top-down model (trophic cascade model)
proposes that control comes from the trophic level above
- predators limit herbivores, herbivores limit plants, and plants limit nutrient levels
mesopredator release
populations of medium-sized predators rapidly increase in ecosystems after the removal of larger, top carnivores
biomanipulation
deliberate alteration of an ecosystem by adding or removing species, especially predators
what did most ecologists favor decades ago
view that communities are in a state of equilibrium
F. E. Clements
argued that plant communities had only one state of equilibrium, a climax community, controlled by climate
- suggested that biotic interactions caused species in a climax community to function as a superorganism
A. G. Tansley
argued that variation in abiotic conditions created many possible stable communities within a region
H. A. Gleason
viewed communities as a change assemblages of species w/ similar abiotic requirements
disturbance
event that changes a community, removes organisms from it, and alters resource availability
nonequilibrium model
describes communities as constantly changing after disturbance
how do types of disturbances vary
frequency and severity
significant sources of disturbance
storms and fire
high level of disturbance
result of frequent/intense disturbance
- exclude many slow-growing species
low levels of disturbance
result from low frequency or low intensity of disturbance
- allow dominant species to exclude less competitive species
intermediate disturbance hypothesis
moderate levels of disturbance can foster greater diversity than either high or low levels of disturbance
ecological succession
sequence of change sin community composition following a disturbance
primary succession
occurs where no soil exists when succession begins
how may early/later-arriving species be linked?
- early arrivals my facilitate appearance of later species by making environment favorable
- may inhibit establishment of later species
- may have no affect on establishment of later species
serial stages on moraines in Glacier Bay, Alaska
- colonized by pioneering plants
- Dryas stage
- Alder stage
- Spruce stage
what is succession the result of
changes induced by vegetation itself
what do pioneer plants facilitate
later arrivals by increasing soil nitrogen content
secondary succession
begins in an area where soil remains after a disturbance
2 biogeographic factors that affect species diversity of biological communities
- latitude
- area
species richness across globe
- great in tropics
- declines in gradient toward the poles
why may there be greater species richness in tropical environments
more time for speciation and migration to occur
2 main climatic factors correlated with biodiversity in terrestrial communities
- sunlight
- precipitation
evapotranspiration
evaporation of water from soil plus transpiration of water from plants
what is potential evapotranspiration the measure of
potential water loss, assuming water is available
are evapotranspiration and potential evapotranspiration higher in warm/wet conditions or dry/hot conditions
warm and wet conditions of tropics
what does species richness correlate with
both evapotranspiration and potential evapotranspiration
species-area curve
quantifies idea that, all other factors being equal, a larger geographic area has more species
Robert MacArthur and E.O Wilson
developed method for predicting species diversity on islands called island equilibrium model
island equilibrium model
- species richness on islands represents a balance between immigration of new species and extinction of established species
what are immigration and extinction affected by
island size and distance from the mainland
as the number of spices on an island increases…
- immigration decreases
- extinction increases
smaller island
- number of species decreases
- immigration decreases
- extinction increases
larger island
- number of species increases
- immigration increases
- extinction decreases
islands closer to the mainland
- immigration increases
- extinction decreases
islands further from the mainland
- immigration decreases
- extinction increases
equilibriums
rate of immigration is equal to rate of extinction
pathogens
disease-causing microorganisms, viruses, viroids, and prions
- can affect community structure
- can be virulent in new habitat
