Carrying Capacity

1. Carrying Capacity Population Growth of Duckweed

2. 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

3. 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!

4. 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

5. 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

6. 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

7. 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

8. 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)

9. 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

10. 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

11. 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

12. How do Duckweed Survive? Autotrophic Make their own food through photosynthesis Require sunlight Require nutrients Phosphorous, nitrogen, other minerals Need space to grow

13. Experiment:Population growth in Duckweed Each group will set up TWO flasks Each flask has 100-200 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)

14. 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