Lecture 09 Populations

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• Lecture 09Populations

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• What is a population?
• members of a particular species that inhabit a
  particular area
• Various aspects
• Range and distribution
• Size
• Density
• Age structure
• Growth
• Genetic uniqueness ? subpopulations (ecotype)

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• Population growth rate
• Discrete-time
• Geometric growth
• Species which have discrete breeding seasons
• Continuous time
• Exponential growth

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• Geometric Growth
• N(t1) N(t) ? at each interval of time
  population grows by the multiple ?
• Exponential Population growth
• loge? r

Intrinsic rate of increase
Change over time

• Growth rate dN/dt rN

No. of individuals in a population

• The actual rate of population increase is

Birthrate
Deathrate
Net immigration

• r (b d) (i e)

Net emigration
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• Geometric Growth with discrete reproductive
  seasons
• Estimate population at same time in each year
• Mortality of young

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Log population size increasing exponential
against time produces straight line
Slope (at any point) dN/dt rN
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Logistic Population Growth
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Carrying Capacity

• No matter how fast populations grow, they
  eventually reach a limit
• This is imposed by shortages of important
  environmental factors
• Nutrients, water, space, light
• The carrying capacity is the maximum number of
  individuals that an area can support
• It is symbolized by k

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• As resources are depleted, population growth rate
  slows and eventually stops logistic population
  growth.
• Sigmoid (S-shaped) population growth curve.

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rN(1-N/K)
Growth slows as N approaches value of K or as
(1-N/K) approaches 0
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Limits to Population Growth

• Environment limits population growth by altering
  birth and death rates.
• Density-dependent factors
• Disease, Resource competition
• Density-independent factors
• Natural disasters

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• Density-dependent effects
• Competition for resources
• food
• Suitable habitat example nesting sites
• Effects that are dependent on population size and
  act to regulate growth

Reproductive success decreases as population size
increases

• These effects have an increasing effect as
  population size increases

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• Density-independent effects
• Effects that are independent of population size
  but still regulate growth
• Most are aspects of the external environment
• Weather
• Droughts, storms, floods
• Physical disruptions
• Fire, road construction

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• Survivorship and Age structure
• Age structure Proportion of individuals in
  various age classes
• Survivorship is the percentage of an original
  population that survives to a given age
• Involves study development of life table
• Cohort
• Example Cactus finch
• Static
• Example Dall sheep

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• Age Structure Diagrams Visualization of future
  population growth

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• Survivorship curves

• Type I
• Mortality rises in postreproductive years
• Type II
• Mortality constant throughout life
• Type III
• Mortality low after establishment

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r and K Fundamental Contrasts

• Intrinsic Rate of Increase
• Highest in r selected species.
• Competitive Ability
• Highest in K selected species.
• Reproduction
• r Numerous individuals rapidly produced.
• K Fewer larger individuals slowly produced.

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• Where is a species found?
• Range Geographical boundaries a species occupies
• Determined by basic ecological parameters
• No indication of distribution or abundance
• Fundamental niche
• Indication of parts of habitat in which a species
  may be found
• Typically patchy locally aggregated) w/i range
• Realized niche
• Portion of fundamental niche in which species is
  actually found

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• Factors which impact range
• Physiological adaptations
• Available food, nesting sites, etc. factors
  which define suitable habitat
• Predators
• Competition competitive exclusion principle
  to be discussed later
• Chance past climatic and physiological events
• Species could/does survive elsewhere, has not
  been introduced
• Current and past climate influences all these
  things

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• Example
• Range of Canyon Wren
• Distribution
• confined to areas with rock faces, canyons,
  bluffs

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• Fundamental niche
• Indication of parts of habitat in which a species
  may be found
• Typically patchy locally aggregated) w/i range
• Realized niche
• Portion of fundamental niche in which species is
  actually found

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• Patchiness and Subpopulations
• Metapopulations Local Populations (demes) in
  suitable habitat isolated in matrix of unsuitable
  habitat
• Source/Sink Populations source population
  over-reproduces, sink absorbs population
• Landscape Metapopulations linked in matrix of
  varied quality

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• Marmots on Vancouver Island
• Unique species isolated populations in cleared
  areas impacted by fire/forestry practices
• Loss of local populations results in fewer
  stepping stones genetically isolated
  metapopulations
• Loss in genetic diversity
• Movement between populations maintains
  variability within species
• Important to continued viability of species
• From http//www.marmots.org/notes_vim.html

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• Ecotypes
• Sub-populations adapted to particular local
  environments
• Unique genetic make-up?
• Same species
• Common Garden Experiment
• Seed collected from plants of same species
  growing in different environments ?grow in same
  location(s) (p 282)
• Isolation may lead to differentiation into
  different species uniquely adapted to specific
  environments ( see p 200) ? restricted range

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• Size of Populations
• Abundance number of individuals within a
  specified area
• Abundance/area Density
• How do we determine how many individuals there
  are?

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• Estimation of population sizes
• Choice of technique depends on
• motility of target species
• Nature of habitat
• Resources
• Resolution required
• Generally rely on statistical sampling /various
  assumptions
• Examples of techniques
• Capture-mark-recapture
• Christmas Bird Counts
• Aerial surveys
• Acoustic monitoring
• http//www.pwrc.usgs.gov/monmanual/approaches/pops
  ize.htm