Chapter 53:Community ecology
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what is a community?
- interacting species, usually living within a defined area
- ex.2 species interacting
interactions among species have two main outcomes:
- 1.they affect thr distribution and abundance of the inetracting species
- 2.they are agents of natural selection
occurs when individuals use the same resoruces, resulting in lower fitness(-/-)
when two species interact in a way that confers fitness to both (+/+)
occurs when one species but the other species is unaffected (+/0)..The least studied
One organism eats another, increasing the predators fitness but decreases the prey(+/-)
animal eats plant. (+/-)
- competition that occurs between memebers of the same species
- -Occurs when the niches of two species overlap
- occurs when individuals from different species use the same limiting resources
- ex. the barnacles>>>>Chthamalus(high tidal area); Balanus(low tidal area); Balanus outcompetes Chthamalus from coming down
the range of resources that the species is abe to use or the range of conditions it can tolerate
Competitive exclusion principle
Not possible for species with the same niche to coexist
one species suffers a much greater fitness decline than the other species does
each of the interacting species experiences a roughly equal decrease in fitness
- the combination of resources or areas used or conditions tolerated in the absence of predators
- -always larger larger than the realized
the portion of resoruces or areas used or conditions tolerated when competition occurs
Niche differentiaition(resource partitioning)
- an evolutionary change in resource use, caused by competition.
- ex.if 2 species compete over a resource(middle part), then overtime they would grow apart so they would not be competing(no more middle part would remain in the ven diagram)
- the change that occurs in species traits, and that allows individuals to exploit different resources
- Ex. Galapagos Finches
when harmful species resemble each other
when non-harmful species resemble harmful species
defensive traits that are produced only in response to the presence of a predator
any event that removes biomass from a comunnity
when a disturbance removes the soil and its organism. Ex.Glaciers, floods, volcanic eruptions
- when a disturbance removes some or all organism but leaves the soil intact.
what are early successional communties dominated by?
early successional communties are dominated by species that are short-lived and small in stature
What are late successional communites dominated by?
Late successional communities are dominated by species that tend to be long-lived, large and good competitiors for light and nutrients
tend to have "weedy" life histories. adapted for growth in distrubed soils
early species makes condtions more favorable for the next species. Shade/nutrients
existing species do not affect how the new species establishes
one species inhibits the establishment of another
how many species are present in a given community
- incorporates the number of species in an area and also their relative abundance
- -(How common or how rare compared to other species) Eveness
species richeness should be higher on
1.larger islands2.nearshore islands
Intermediate distrubance hypothesis:
the region with a moderate type, frequency, and severity of disturbance should have high species richness and diversity
What is niche differentiation?
-the evolution of traits that reduce niche overlap and competiton
why are inducible defenses advantageous?
-they make efficient use of resources, because they are produced only when needed
Species diversity is correlated with
- 3.island size
What is net primary productivity?
-the amount of energy that is stored in standing biomass per year
herbivore populations are kept at relatively low levels by predation and disease
plant matter is low in nitrogen or defended by chemicals that are toxic to herbivores
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