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- biological richness of a community occupying a particular habitat
- understood as having two components: richness and evenness.
richness of diversity.
number of species.
evenness of diversity.
statistical distribution of relative abundances.
diversity of one restricted area within a habitat.
one that move s across a landscape across different terrains and habitats, alpha diversity changes.
narrow niches means...
less shared resource use.
broader niches mean...
more shared resource use.
example of narrow niche.
A. cybotes (Jarabacoa)
example of broad niche.
A. marmoratus ferreus (Marie Galante)
- discrete event in time that disrupts population, community or ecosystem structure and changes resources or physical environment
- -abrupt, catastrophicchanges in physical conditions that cause massive removals of organisms.
Intermediate distrubance hypothesis -Joseph Connell.
species diversity will be highest in communities that experience intermediate levels of distrubances
examples of disturbances.
turbidity flows on continental shelves, ice scours in shallow bays, wave attering rocky shores, unusually low tides on coral reefs...
favors dominance of a few weedy species with fast life cycles
favors dominance of a few competitively dominant species.
enough time for wide variety of organisms to colonize; not enough for competitive exclusion to be completed.
intermediate disturbance hypothesis base on...
realization that intermediate stages tend to be more diverse cuz consist of older individuals from early stages and young individuals from later starges.
more or less orderly series of species replacement following a severe disturbance.
order of species is fixed and thus certain.
order is variable, and thus occurrence of a particular sequence probabilistic
assemblage of species at a given successional stage.
final sere, capable of replacing itself indefinitely
primary succession (terrestrial communities)
process that occurs on newly exposed geological substrate (little to no organic activity in substrate)
secondary succession (terrestrial)
process that occurs when disturbance removes a community without destroying the soil
first species to colonize an open area after disturbance
...until removed by disturbance.
- three established theories.
- 1. facilitation
- 2. tolerance
- 3. inhibition
- -successional stages seens as developmental stage for super organism, climax is maturity.
- -"early" succession species only organisms capable of colonizing initial conditions following disturbance and able to modify physical environment to favor young of "lates" and disfavor own young
- -chain of "altruistic" replacements, succession id deterministic
example of facilitation.
alder-spruce succesion on glacial till.
- based on "competitive exclusion principla"
- -young of all species can colonize initials conditions, but "earlies' usually do so cuz have adaptations for rapid colonization. young of "lates" more tolerant of low resource levels.
- -succession proceeds, competition increases cuz resources diminish.
- -succession: a chain of competitive exclusions "lates" win, tolerant of low resource levels cuz use resources more efficiently
- -is stochastic.
example of tolerance.
tropical rainforest tress, with later stages tolerant of low light.
- primacy of predation and adaptive trade-offs.
- -"earlies" allocate to reproduction and vegetative growth, and good colonizers and competitors.
- -"lates" allocate more resources to resist predation/herbivory and physical stresses
- -as succession proceeds, predation becomes intense as consumers populations increase. less defend "earlies" removed, "lates" survive to become numerous
- -succesion is stochastic
example of inhibtion.
- blouder field algae
- -algal succession in tertidal boulder fields.
- -climax of red alga: Gigartina after 2 yrs after disturbance.
under all three theories, "earlies" always replaced by lates. how do they persist?
continuing local disturbance and cryptic stages of early succession species within climax assemblage.