Carrying Capacity

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Carrying Capacity

• Population Growth of Duckweed

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Basics About Population Growth(pages 530-533)

• The environment has a carrying capacity for every
  organism based on the available resources
• If resources are abundant and readily available,
  then a population will show exponential growth

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• During exponential growth the increase in
  population size varies with the number of
  individuals present
• Increase is gradual at first, but rises sharply
  as more individuals become part of the population
• Unlimited resources allow everyone to reproduce!

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Environmental Resistance Factors

• Populations will continue to grow exponentially
  until they come up against limiting factors or
  resistance factors
• Resource limitations
• Food, nutrients, water, sunlight
• Shelter, space
• Competition from other species
• Predation
• Waste accumulation

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Logistic Growth

• In the real world resources are often limiting
• The first part of the growth resembles
  exponential growth
• But over time, the population size levels off in
  logistic growth at a point called the carrying
  capacity

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Carrying Capacity

• The carrying capacity of the environment
  represents the maximum number of individuals of a
  particular species that an area can support
  indefinitely without degrading

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Carrying Capacity

• Natural populations seldom approach carrying
  capacity smoothly
• Or stay at the carrying capacity once reached
• They usually fluctuate around the carrying
  capacity
• Overshooting it or falling below depending on
  resources

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Duckweed Lemna minor

• A small, floating aquatic plant that forms a
  solid cover on the surface of freshwater ponds,
  marshes, lakes and quiet streams
• Very important in the aquatic ecosystem as an
  essential link in the food chain.
• Eaten by fish
• birds (ducks, herons)

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• Shades extensive areas of a pond, reducing algae
  growth
• Good for bioremediation projects
• Ability to take out nitrogen and phosphorus from
  water
• Useful as a water crop
• as a source of food for animals and poultry

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Structure of Duckweed

• Leaves and stems merge in a common structure
  called a frond or thallus
• Has one root
• Fronds have 3 veins
• Air spaces help the plant to float

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Reproduction

• Reproduction is asexual
• Vegetative reproduction
• Unlike the leaves of more ordinary plants, each
  duckweed frond contains buds from which more
  fronds may grow.
• Until they mature, daughter fronds remain attach
  to the parent frond
• Rapidly growing plants can have 3-4 attached
  fronds

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How do Duckweed Survive?

• Autotrophic
• Make their own food through photosynthesis
• Require sunlight
• Require nutrients
• Phosphorous, nitrogen, other minerals
• Need space to grow

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ExperimentPopulation growth in Duckweed

1. Each group will set up TWO flasks
2. Each flask has 100-200 ml pond water
3. Place 2 duckweed plants in one flask
4. Place 15 duckweed plants in the other flask
5. Count all thalli (leaves) greater than 2 mm as
   full grown.
6. Place labeled flasks under the grow lights in
   room 201
7. Record your data twice a week for 3-4 weeks
   (Create your own data table before you leave
   today)

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What kind of population growth do you expect from
the two different Duckweed flasks?

• Exponential growth
• J-shaped growth curve
• Logistic growth
• S-shaped or sigmoidal