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Characteristics of a Population. Population - individuals inhabiting the same area at the same time Population Dynamics: Population change due to Population Size - number of individuals Population Density - population size in a certain space at a given time

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Characteristics of a Population

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characteristics of a population
Characteristics of a Population
  • Population - individuals inhabiting the same area at the same time
  • Population Dynamics: Population change due to
    • Population Size - number of individuals
    • Population Density - population size in a certain space at a given time
    • Population Dispersion - spatial pattern in habitat
    • Age Structure - proportion of individuals in each age group in population
population size
Population Size
  • Natality
    • Number of individuals added through reproduction
  • Mortality
    • Number of individuals removed through death
population density
Population Density
  • Population Density (or ecological population density) is the amount of individuals in a population per unit habitat area
    • Some species exist in high densities - Mice
    • Some species exist in low densities - Mountain lions
  • Density depends upon
    • social/population structure
    • mating relationships
    • time of year
population dispersion
Population Dispersion

Population dispersion is the spatial pattern of distribution

There are three main classifications

Clumped: individuals are

lumped into groups

population dispersion1

Uniform: Individuals are regularly spaced in the environment

Random: Individuals are randomly dispersed in the environment tips/2002/clover611.htm

Population Dispersion

age structure
Age Structure
  • The age structure of a population is usually shown graphically
  • The population is usually divided up into prereproductives, reproductives and postreproductives
  • The age structure of a population dictates whether is will grow, shrink, or stay the same size
population growth
Population Growth
  • Population growth depends upon
    • birth rates
    • death rates
    • immigration rates (into area)
    • emigration rates (exit area)

Pop = Pop0 + (b + i) - (d + e)

population growth1
Population Growth
  • Populations show two types of growth
    • Exponential
      • J-shaped curve
      • Growth is independent of population density
    • Logistic
      • S-shaped curve
      • Growth is not independent of population density
population dynamics and carrying capacity
Population Dynamics and Carrying Capacity
  • Basic Concept: Over a long period of time, populations of species in an ecosystem are usually in a state of equilibrium (balance between births and deaths)
carrying capacity k
Carrying Capacity (K)
  • Exponential curve is not realistic due to carrying capacity of area
  • Carrying capacity is maximum number of individuals a habitat can support over a given period of time due to environmental resistance (sustainability)
logistic growth
Logistic Growth
  • Because of Environmental Resistance, population growth decreases as density reaches carrying capacity
  • Graph of individuals vs. time yields an S-curved growth curve
  • Reproductive time lag causes population overshoot
  • Population will not be steady curve due to resources (prey) and predators
density dependent limiting factor
Density Dependent Limiting Factor
  • Only affects a population when it reaches a certain density (size).
  • Competition
    • Fighting for resources
  • Predation
    • Increase of predators in an area will limit the growth of prey
  • Disease
    • High densities make it easier for parasites and diseases to find a host and spread.
  • Parasitism
    • More animals for the parasites…more parasites that are there to harm the host
  • Crowding
    • Over-crowding can cause a depletion of resources, disease and stress
  • Stress
    • Makes organisms weak and prone to diseases
density independent factors
Density Independent Factors
  • Affect a population no matter what the density is
    • Natural disasters
      • Droughts, floods, tornadoes, fires, hurricanes…they don’t care how many organisms are in an area
    • Temperature
      • Determines which organisms can survive
    • Sunlight
      • Can only penetrate up to 30 m of water.
  • Human Activities
    • Habitat destruction, hunting, pollution…
  • Physical Characteristics
    • adaptations
  • Behaviors
    • Migration, societies, feeding areas…
reproductive strategies
Reproductive Strategies
  • Goal of every species is to produce as many offspring as possible
  • Each individual has a limited amount of energy to put towards life and reproduction
  • This leads to a trade-off of long life or high reproductive rate
conservation biology
Conservation Biology
  • Careful and sensible use of natural resources by humans
  • Originated in 1970s to deal with problems in maintaining earth's biodiversity
  • Dedicated to protecting ecosystems and to finding practical ways to prevent premature extinctions of species
conservation biology1
Conservation Biology
  • Three Principles
    • Biodiversity and ecological integrity are useful and necessary to all life on earth and should not be reduced by human actions
    • Humans should not cause or hasten the premature extinction of populations and species or disrupt vital ecological processes
    • Best way to preserve earth’s biodiversity and ecological integrity is to protect intact ecosystems that provide sufficient habitat
habitat fragmentation
Habitat Fragmentation
  • Process by which human activity breaks natural ecosystems into smaller and smaller pieces of land
  • Greatest impact on populations of species that require large areas of continuous habitat
  • Also called habitat islands

1949 1964

Habitat fragmentation in northern Alberta

1982 1991

human impacts
Human Impacts
  • Fragmentation and degrading habitat
  • Simplifying natural ecosystems
  • Strengthening some populations of pest species and disease-causing bacteria by overuse of pesticides
  • Elimination of some predators
human impacts1
Human Impacts
  • Deliberately or accidentally introducing new species
  • Overharvesting potentially renewable resources
  • Interfering with the normal chemical cycling and energy flows in ecosystem