5.2 Limits to Growth Flashcards
Limiting factor:
a factor that controls the growth og a population
acting sperately or together, limiting factors determine the:
carrying capacity of an environment for a species
limiting factors keep populations between:
extinction and overrunning the planet
density-dependent limiting factors:
opperate strongly only when popunlation density reaches a certain level (doesn’t affect small scatered populations as much)
what are some density-dependent limiting factors
competition, predation, herbivory, parasitism, disease, stress from overcrowding
what does competion do as a limiting factor?
lowers birthrate and increases deathrate because when population becomes croweded individuals compete for resources
Competition between differnet species is a major force behind evolutionary change
How does the predator-prey relationship cycle?
up and down (ex: moose pop grows leading to wolve pop growing, leading to moose pop falling, leading to wolve pop falling, leading to moose pop growing again)
Herbivore effects:
same cycle as predator-prey
humans as predators:
ex: codfish in New England
Parasitism and disease spread more easily in
denser host population
similar cycle of predator-prey
why is stress from overcrowding a limiting factor?
individuals fight if overcrowded causing stress, making them weak to resist disease, kill offspring, and emigrate
density-independent limiting factors:
affect all populations in similar ways regardeless of population size or density
examples of density independent factors
unusual weather (hurricanes, droughts, floods) and natural disasters (wildfires)
population might ‘crash’ after a:
density independent limiting factor occurs (natural disaster, unusual weather)
human activites also cause stress making it hard to:
recover from natural disturbances
how to control introduced species:
herbicides and mechanical removal (expensive and time consuming) better alternatives are natural predators/pests
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what are the 2 categroies of population limiting factors:
density independent and density dependent
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Density independet factors typically involve:
abiotic factors like natural phenomenon (weather events that limit populations)
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Examples of density independent factors
- Extreme heat or cold
- tornadoes
- blizzards (storm atlas reduced population of antelope in western SD)
- hail storms (depleted sharptail grouse poulation in recent years)
- deep snows (decimated pheasant populations in easter SD)
- forest fires (dramaticall decrease nuber of pondersa pines in BH)
- dams on rivers (hover dam on colorado river and humpback chub)
- air/water/land population (long island sound)
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density depedent facotrs are any factor in the environment that depends on
the number of members per unit area (often biotic factors)
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examples of density dependent factors
- predation (coyote and white tailed deer)
- Parasites (diseases introduced by mosquitos on L’iiwee)
- competition (within a species and inter-species competition for resources
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Population Growth Rate (PGR) explains:
how fast a population grows, smaller organism the faster it growws, the larger the slower
in exponential growth there is a slow growth rate called a
lag phase followed by unrestricted growth
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Populations typically go above and below:
carry capacity based on the number of organisms and avaliable resources
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R-strategists (rate strategy) is an
adaptation for living in evironmnts where significant fluctuations (avaliablity of food, extreme changes in temp) in biotic/abiotic factors occur
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describe r-stategists
- typically small with short life spans
- produce many offsprings
- take advantage of short window of opportuity to go through life cycle
- populations controlled by density-ind. factors
- usually insects
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describe k-strategy
- used by large animals with long life spans
- directly related to carry capacity
- few offsprings keeps population in balance wit hresources
- better chances of suriviving to reproductive age because of nurturing recived from adult parents
