Carrying Capacity

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Carrying Capacity

• Population Growth of Duckweed

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ExperimentPopulation growth in Duckweed

• Each group will set up TWO flasks
• Each flask has 200-300 ml pond water
• Place 2 duckweed plants in one flask
• Place 15 duckweed plants in the other flask
• Count all thalli (leaves) greater than 2 mm as
  full grown.
• Place labeled flasks under the grow lights in
  room 201
• Record your data twice a week for 3-4 weeks
  (Create your own data table before you leave
  today)

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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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Importance of Growth Curves

• Managing populations and resources
• Making decisions about when a population needs
• Protection
• Harvesting
• These decisions affect fishing, crab and oyster
  industries
• Managing bear and deer populations in urban areas

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Objectives of Duckweed Lab

• Learn the components of growth curves
• Identify the stages of population growth
• Understand carrying capacity
• Effect of community interactions on population
  growth
• Nutrient overload or depletion
• Effect of population numbers

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Growth Curves

• Lag Phase
• During this phase, the organism prepares to
  grow.  Unseen biochemical changes, cell division
  and differentiation of tissues occur during this
  time.

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• Log or Exponential Phase
• During this phase the plants are growing,
  producing new fronds and dividing rapidly to take
  advantage of fresh medium.

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• Transitional Phase
• During this phase growth slows or the death rate
  increases.  As a result, the initiation of new
  fronds and the senescence and death of old ones
  start to come into equilibrium.  For duckweeds
  this phase typically occurs as nutrients become
  limiting for growth.

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Stationary Phase
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• Stationary Phase
• After this time, birth of new fronds and death of
  old ones is in equilibrium.  New fronds will only
  appear as nutrients are released from the death
  and decay of old fronds.
• 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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• 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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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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The Logistic Growth Curve
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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