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ecology
- the study of interactions among living organisms and the interactions with their environment
- the study of the environmental factors and evolutionary forces that influence life histories, distribution and abundance of organisms
- the study of the function and structure of populations, communities, and ecosystems
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organisms
- fundamental unit
- a single living individual of one species
- evolutionary processes work at the individual level
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populations
- consists of all individuals of one species found in a defined area
- longer-lived than an individual organism
- have emergent properties (eg, rates, patterns)
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emergent properties
parameters are not present at lower levels
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species
all individuals in an area that potentially can mate and produce fertile offspring (biological species concept)
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habitat
the place or environment in which the individual or species resides
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linear (arithmetic) growth
- increases at a linear rate over time (eg, 1, 2, 3, 4, 5...)
- not observed in many populations over time
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exponential growth
- the phase in which the population can initially grow at a rapid pace
- in the absence of competitors, disease, weather, preddators
- in the presence of lots of food
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the differential equation creates a j-shaped or exponential curve
- (dt) = change in time
- (dN) = change in population time
- N = initial population size
- r = reproductive rate per individual (growth rate of population)
- ignores immigration and emigration
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r is determined by:
b - d = r
- b = birth rate
- d = death rate
- ignores immigration and emigration
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growth possibilities
- r=0 : no growth (b=d), no change in N
- r<0 : negative growth (b<d), decrease in N
- r>0 : positive growth (b>d), increase in N
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logistic growth
- population size does not continue to increase exponentially, but it tends to level off after a certain population size has been reached
- limits to growth imposed by environment, some resources becoming limiting
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logistic growth equation
- [rate of change in population size over time] = [rate of per capita population growth]x[population density]x[unutilized capacity for population growth]
- K=carrying capacity (constant, maximal, sustainable population size)
- is an S-shaped, sigmoidal graph
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when N = K ......
- dN/dt = 0
- growth rate r = 0
- b = d
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Populations tend to...
...level off or fluctuate around a certain size.
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environmental resistance
factors that limit the exponential growth of a population
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Competition coefficients alpha and beta are used to...
... determine the impact of interspecific competition. Both species compete for the same resources.
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competitive exclusion
if the species compete for long enough, the better competitor can drive the other species into extinction locally
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In any one habitat, two species cannot...
...coexist in the same niche (functional role in a community).
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