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
