What is community ecology? the study of interactions between species and how they influence community structure and function
Ecologists define a community as: species within a particular place that interact or potentially interact
Disturbance: A discrete event that disrupts an ecosystem or commun...
Bio 250 Final Exam Questions and
Correct Answers
What is community ecology? ✅the study of interactions between species and how they
influence community structure and function
Ecologists define a community as: ✅species within a particular place that interact or
potentially interact
Disturbance: ✅A discrete event that disrupts an ecosystem or community
Succession: ✅the repeatable change in community composition through time following
a disturbance
Succession is affected by: ✅self thinning, life history traits
Primary succession: ✅initial establishment of a community
Secondary succession: ✅re-establishment of existing community
What are the 3 models of succession? ✅facilitation, tolerance, inhibition
What is facilitation? ✅When one species opens up niches for other species to grow,
stress-tolerant species make it more habitable
What is inhibition? ✅whoever gets there first survives, inhibits growth of other colonies
What is tolerance? ✅whoever gets there first survives, but has no effect on other
species
What is a climax community? ✅succession progresses towards this, seen as a stable
endpoint
What are allogenic processes? ✅outside influences that effect communities such as
human interventions, immigration by new species, seasonal changes, abiotic
disturbances
What is an example of an allogenic process? ✅human interventions, immigration by
new species, seasonal changes, abiotic disturbances
What do allogenic processes ensure? ✅That a community is almost never in
equilibrium
,Intermediate disturbance hypothesis: ✅species diversity will be greatest when
disturbances are of intermediate frequency, when an intermediate amount of time has
passed after a disturbance, or when the disturbance is of intermediate magnitude
Most species live at ___ amounts of disturbance. ✅intermediate
Direct benefit: ✅from the source to the other thing
Indirect benefit: ✅from the source to another thing and then the other thing
Where does the flow of energy begin? and with who? ✅the first trophic level, primary
producers
What occupies the second trophic level? ✅herbivores
What occupies the third trophic level? ✅predators
What occupies the fourth trophic level? ✅animals that feed directly on predators
Primary consumers only get about ___ of the energy of the producers. ✅10%
What is top-down control? ✅higher trophic level limits the size of the trophic level they
consume
Predation limits ___ and releases pressure on ___. ✅herbivores, vegetation
When a predator is removed, number of herbivores ___ and vegetation ___.
✅increases, decreases
what is a behavioral cascade? ✅where a predator indirectly stimulates primary
production by altering the foraging behavior of its prey
autogenic engineer (indirect): ✅result from the internal architecture of the engineer
itself (corals, trees)
allogenic engineers (indirect): ✅result from the redistribution of living or non-living
materials (beaver dams)
Bottom-up hypothesis: ✅organisms at each trophic level are resource-limited; food-
chain length increases as resource-availability increases
What is an example of the bottom-up hypothesis? ✅crop production increases when
fertilizer (nutrients) are applied
, Even when production is high ___ may limit higher trophic levels because many plants
are low quality food. ✅bottom up control
Productivity hypothesis: ✅more productive ecosystems should have longer food
chains
ex) lakes with higher P concentrations would have longer food chains but that lake size
wouldn't matter
ecosystem size hypothesis: ✅food chain length should increase with ecosystem size
ex) larger lakes would have longer food chains but that P concentration wouldn't matter
productive space hypothesis: ✅food chain length would increase with both phosphorus
concentration and lake size
ex) food chain length would increase with both phosphorus concentration and lake size
Top-down control ✅Energy flow is governed by rates of consumption at the higher
trophic levels which influence abundance at lower trophic levels (Food chain length
determines whether or not herbivores limit plants)
bottom-up control ✅Organisms at each trophic level are resource-limited
(Food-chain length increases as resource-availability increases)
Resistance: ✅ability to withstand a disturbance
Return time: ✅the time required to return to equilibrium after disturbance
(depends on type of disturbance)
Resilience: ✅how closely does the post-recovery community resemble the pre-
disturbance community
High resilience = ✅same species and proportions before/after disturbance
When do alternative stable states occur? ✅occur when more than one type of
community can exist in a particular environment
what is an alternative stable state? ✅a low resilience community may transition into a
very different equilibrium state after a disturbance
Connectance (C) food web formula: ✅links / species ^2
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