Transcript Bio 30 Unit D2 -PopulationsTAR

POPULATIONS
BIOLOGY 30
CHAPTER OUTCOMES
• Describe and apply models that represent population density
and distribution of individuals within populations
• Describe the four main processes that result in population
change and explain how these processes are related
• Analyze population data to determine growth rate and per
capita growth rate
CHAPTER OUTCOMES
• Describe how a population’s biotic potential and the carrying
capacity of its habitat determine its pattern of growth
• Compare r-selected and K-selected reproductive strategies in
terms of life cycles and patterns of population growth
CHAPTER OUTCOMES
• Describe the interactions among population members and
among members of different populations within a community
• Explain how producer-consumer interactions affect
population growth
• Describe defense mechanisms that have evolved within
populations
CHAPTER OUTCOMES
• Understand that symbiosis includes mutual, commensal, and
parasitic relationships
• Distinguish between primary and secondary succession
POPULATION GROWTH
• Quantitative measurements of populations are like snapshots
of moments in time
• Ecologists often rely on a number of measurements over a
long period of time to make inferences about population
growth
• Both the distribution and growth of a population can be
significant when studying populations and communities
POPULATIONS
• Defined by species, location, and time
• Described by
• Habitat – ideal location for breeding and raising young
• Range – movement radius or area or pattern
• Niche – feeding role in the ecosystem web
PATTERNS OF DISTRIBUTION
• habitat can play a role in how populations are distributed
• population distributions can follow one of three general
patterns:
1.Clumped – with the need and availability of food, water, or
shelter
2.Uniform – in competition with adaptation for limited resources
3.Random – with manipulation of environment or relatively fast
evolution for adaptation of a species
POPULATION SIZE AND DENSITY
• population size simply describes the number of organisms in
an area (N) and can change relative to immigration,
emigration, natality, mortality)
• it is often more useful to compare populations by describing
population density (D=N/area or volume)
POPULATION DENSITY FORMULA
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D = N / A where:
D = density of organisms (organisms/unit)
N = # of organisms
A = size of area in units
EXAMPLE:
• Ex: There are 200 lemmings in a 25 ha area. Determine the
population density of the lemmings:
POPULATION CHANGE
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4 factors determine population size:
Natality – birth
Mortality – death
Immigration – incoming
Emigration – exciting
• if all the factors remain the same except for an increase in the
birth rate, population increases
• population change can be calculated in the formula:
• ∆N = (births + immigration) – (deaths + emigration)
• We can also calculate a per capita population growth rate
• cgr = Population Final – Population Initial
Population Initial
• gr= Population Final – Population Initial/Change in Time
POPULATION GROWTH EXAMPLE
• Ex: In a Banks Island Breeding site, 40 cranes were born, and
there were 55 deaths. There was no immigration or emigration
of cranes. The original population was 200. Calculate the
population growth.
BIOTIC POTENTIAL
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biotic potential depends on a number of factors:
Offspring – the maximum number of offspring per birth
Capacity for Survival – the chances of offspring reaching
reproductive age
Procreation – the number of times per year an organism
reproduces
Maturity – the age at which reproduction begins
CARRYING CAPACITY
• Generally, growth in small populations begins slowly and then
the rate of growth increases
• However, the growth must eventually slow because there is a
maximum number of organisms that an ecosystem can
support as far as food, water, and shelter … noting that this is a
dynamic or changing value
GROWTH PHASES
1.
Lag
2.
Log (or Exponential
Growth)
3.
Stationary
4.
Death
S-CURVES
• Many populations exhibit an S-shaped (sigmoidal) growth
curve
• This is also known as a logistic growth pattern
• The population number increases until it reaches the carrying
capacity of the ecosystem
• At this point, the population fluctuates near the carrying
capacity
J-CURVES
• J – shaped curves are representative of quick growth and
then a sharp decline in the population
• this occurs when a population quickly outgrows the carrying
capacity of an ecosystem
• as a result, there is a crash in the population, which is followed
by a relatively stable stationary phase
• these J-curves are most often associated with organisms that
can reproduce very quickly (insects, bacteria, etc.)
COMPARISON OF J & S-CURVES
http://www.emc.maricopa.edu
LIMITING FACTORS IN
POPULATIONS
• if there are a number of substances required for growth, then
the one with the least concentration, or at times, the greatest
concentration, will be the limiting factor for growth
• therefore, the greater an organisms’ range of tolerance for
high and low concentrations of nutrients, the greater its
survival ability and this is usually a K selected species, with poor
recovery. An r-selected species is an indicator species with a
quick drop into a death phase, and yet, often a quick
recovery into a growth phase
• the overall optimum ranges for abiotic factors for each
species is different because each species reacts to each
factor differently
• any abiotic factors that are not affected by population
density are density independent
• such factors include temperature & climate
• factors that are dependent on the population density are
density dependent
• these are factors such as limits to food supply, disease, and
predation and are often termed biotic
• problems involving density-dependent factors are normally
alleviated when a population density returns to lower levels
R AND K SELECTED POPULATIONS
• K-selected populations are:
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Large in body size
Have a long lifespan
Have a long gestation
Have few offspring in a litter
Take care of their young
Long to reach sexual maturity
Have a lower biotic potential/fecundity
• r-selected populations are:
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small in body size
Have a short lifespan
Have a short gestation
Have many offspring in a litter
Do not take care of their young
Short to reach sexual maturity
Have a higher biotic potential/fecundity
INTERACTIONS IN ECOLOGICAL
COMMUNITIES
• An ecological community is a collection of interacting
populations within an area
• In any community, individuals must compete for limited
resources
• The competition between populations is the driving force
behind population dynamics
INTRASPECIFIC AND
INTERSPECIFIC COMPETITION
• Gause’s Principle states that if two populations occupy the
same niche, one of them will be eliminated
• this principle would represent a worst-case scenario in
interspecies competition (the competition between two
different species)
• there also exists intraspecies competition, where members of
the same species compete for resources such as food, space
and mates
PREDATION
• predator and prey populations are often closely tied to one
another (for instance, if a prey population declines, it is likely
that the predator species will as well)
• however, predators are important in ecosystems as they
reduce the number of primary consumers that are feeding on
producers
POPULATIONS OF LYNX & HARES
• in some cases, animals develop camouflage to escape
detection (either by predators or prey)
• other organisms produce physiological adaptations in the
evolution of their DNA and thus their protein production (such
as plant toxins)
• some animals will engage in mimicry, where they will develop
markings similar to those on a poisonous or dangerous animal
• often predators and prey coevolve in an attempt to gain an
upper hand
SYMBIOSIS
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1.
2.
3.
There are 3 types of symbiosis:
Commensalism – where one species gains by the
relationship and the other is unaffected
Parasitism – where one species invades and uses a host to
gain food, water, shelter, and the ability to reproduce, while
the other declines and can die
Mutualism – where both species benefits from the
relationship
SUCCESSION
• succession is the slow, orderly replacement of one community
by another through the development of vegetation
• climax communities are eventually formed through this
process
• a climax community is a stable, mature community
• primary succession occurs where there previously was no
community (on places such as barren volcanic islands)
• secondary succession occurs after the partial or complete
destruction of a community
STEPS IN PRIMARY SUCCESSION
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Bare land is formed.
Pioneer species, such as mosses and grasses that are
relatively hardy move in and decrease soil temperature and
evaporation, while increasing soil fertility.
Small shrubs that tolerate full sunlight move in, stabilizing and
enriching the soil.
Small, fast-growing trees replace the shrubs and deplete the
soil of nutrients and sunlight.
A climax community forms, produced from shade-tolerant
trees which have a high sapling survival rate.
GENERALIZATIONS REGARDING
SUCCESSION
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Species composition changes more rapidly during the
earlier stages of succession.
The total number of species increases dramatically during
the early stages of succession, levels off during the
intermediary phases, and declines as the climax community
is established.
Food webs become more complex and the relationships
more clearly defined as succession proceeds.
Both total biomass and nonliving organic matter increase
during succession and begin to level off during the
establishment of the climax community.