quantitative ecology chap 12
TRANSCRIPT
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CHAPTER 12
Quantitative ecology
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Quantitative ecology
Outline
Population ecology
Population dispersion
Biotic potential
Factors influencing population growth
Life history patterns
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Population ecology
population consists of the individuals of a species that
occur together at one place at one time
three important aspects of population
i. the range throughout which a population occurs
ii. dispersion of individuals within that range
iii. size of the population attains
Population distributions
most species have relatively limited geographic range
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Population dispersion
Randomly spaced
not common in nature
individuals do not interact strongly one another
Uniformly spaced
always results from competition for resources
in animals, it occurs because individuals tend to
defend their territories which provide them resources
among plants, results of competition for the sunlight,
nutrients or water
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Population dispersion
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Biotic potential
to understand populations, we must consider how they
grow and factors in nature limit population growth
The exponential growth model
the actual rate of population increase
r= (b-d) + (i-e) r= difference between the birthrate (b) and death rate (d)e= movement out of area and i= movement into area
movement of individuals have a major impact onpopulation growth rates
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Biotic potential
biotic potential = rate at which a population of a given
species will increases when no
limits are placed on its rate of
growthdN/dt = riN, N = num. of individuals in population,
dN/dt = rate of change in its num. over time
ri = innate capacity for growth
innate capacity of growth of any population isexponential
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Biotic potential
Carrying capacity
how rapidly population grows, they will reach limit
imposed by several factors such as space, light, water..
carrying capacity,K = maximum number ofindividuals that environment can support
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Biotic potential
Logistic growth model
as population reaches its carrying capacity, its rate of
growth slows greatly because lack of resources
dN/dt = rN(K-N/K)
as N increases, the fraction by r is multiplied becomes
smaller, and the rate population increases decline
in many cases, real population display trendscorresponding to a logistic growth curve
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Models of population growth
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Population growth is limited by the
environment
population dynamics - study of factors that affectgrowth, stability and decline of population known
population undergo three distinct phase
i. growthii. stability
iii. decline
population growth occurs when resources exceed thenumber of individuals able to use them
reproduction is rapid and death rates are low, increasein population size
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Population growth is limited by the
environment
population stability is always the longest phase,
growing population outstrips its available resources,
decline occurs because decrease in the individuals
number in a population, lead to extinctionFactors influencing population growth
as long resources available, almost all populations will
ten to grow exponential affect by birth rate and death rate
intrinsic rate = birth rate death rate
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The influence of population density
density-dependent = population size affect populationgrowth rate
when population approach their carrying capacity,
competition can be severe, increased risk of mortalityand decrease birthrate
predators tend to focus on particularly common prey,increased rates of mortality as population increase
high population led to accumulation of toxic wastes
behavioral changes also affect population growth rates,results from hormonal actions
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The influence of population density
crowded populations may led to decreased in
population growth rate because of emigration factor
in some cases, growth rate increase with increase
population size (Allee effect) individuals are difficult finding mates in population
that are too sparsely distributed, some species rely on
large groups to deter predator
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The influence of population density
Density-independent effects
rate of growth of a population at any instant is limited
by something other that the size of population
factors such as extremely cold winter, drought, storms,volcanic eruptions may affects populations
when such events occurs, population extremely
decrease and will increase rapidly when environmentback to normal
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The influence of population density
Survivorship curves
survivorship is defined as the percentage of an originalpopulation that survives to a given age
Type I
- flat at early and middle life and drops suddenlyas death rate increases among the elderly
- associated with species such as humans and otherlarge mammals that produce few offspring that
are well cared for.Type II
- intermediate, mortality more constant over lifespans, can be seen in Hydra and the grey
squirrels
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The influence of population density
Type III
- very high death rates for the young, followed bylower death rates
- often associated with organisms, such as oysters,that produce very many offspring but
provide little or no care.
some invertebrates show a "stair-stepped" curve withbrief periods of high mortality during molts, followed
by periods of lower mortality when the exoskeleton ishard.
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Survivorship curves
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Life history patterns
the logistic population model predicts two main lifehistory patterns.
most populations cannot be characterized as either r-orK-strategists; they have intermediate characteristics.
r-Selectiona. species that undergo selection to maximize their
rate of natural increase
b. often opportunistic species, tend to be colonizers.
c. strategy for continued existence is based onindividuals having the following traits: (small size,short life span, mature fast, produce manyoffspring, engage in little caring of offspring)
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Life history patterns
d. such populations usually exhibit a survivorshipcurve similar to type III.
e. thus, they rely on rapid dispersal to newunoccupied environments.
K-Selectiona. species that hold their populations fairly constant
near the carrying capacity
b. such populations are equilibrium species, tend to
be specialists rather than colonizers, and maybecome extinct when their evolved way of life isdisrupted (grizzly bear, Florida panther, etc.).
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Life history patterns
c. overall strategy for continued existence is based onhaving the following traits: (large size, long lifespan, slow to mature, produce few offspring,expend considerable energy in care)
d. such populations usually have a survivorshipcurve similar to type I.
e. thus, they rely on competitive superiority tosecure limited resources.
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Life history patterns
Population pyramids
at the beginning of twentieth century, humanpopulation grow rapidly
different countries shows different growth rate (eg.Mexico grow rapidly)
rate which population can be expected to grow in thefuture can be represent by population pyramids
human population pyramid displays the age population
by sex, female in most region have longer lifeexpectancy than male
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Population pyramids
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