1. Duckweed (Lemna sp) and its ecology

2. Typical duckweed habitat:
Stream or pond where water movement is slow
Lots of detritus – dead plants and organic waste.
Shade but ....
Sufficient light for photosynthesis
Warmth – not hot; not cold
Water containing abundant minerals, especially phosphorous and nitrogen
These are mostly ABIOTIC FACTORS

3. What other organisms live with duckweed?
Algae and other water plants
Snails, mud worms, larvae, etc
Larvae in the water & insects above
Fish
Frogs and toads
Birds – some insectivores, some seed eaters, some predators
These are BIOTIC FACTORS

4. Some aspects of the ecological niche of duckweed
Aquatic photosynthesisers, so act as a carbon sink and an oxygen releaser
Source of food for herbivorous fish, snails and may-fly larvae
Float on the surface, so provide shade and cooling for water and life beneath
Remove excess nutrients like nitrates and phosphates from the water – make water habitable
Provide hiding and breeding places for fish, insects and micro-organisms

5. Typical duckweed food chain:
Energy loss
Flow of energy
Solar energy
Owls
Frogs
Mayfly larvae
Nutrient cycling
Duckweed

6. The right words in the right places!
Producer (autotroph)
Primary consumer
Secondary consumer
Tertiary consumer
First trophic level
Second trophic level
Third trophic level
Fourth trophic level
Herbivore
Omnivore
Top carnivore
Owls
Frogs
Mayfly larvae
Duckweed

7. In reality, it is much, much more complex – FOOD WEBS
In reality, it is much, much more complex – FOOD WEBS. But all the same principles apply.

8. Energy flows through food chains but the available energy becomes less as it moves through each trophic level. Why?

9. The loss of available energy leads to the concept of ENERGY PYRAMIDS

10. The role of the decomposers?
The decomposers are a bunch of worms and larvae, insects, fungi and bacteria which live off and digest dead animals and plants at the bottom of the duckweed pond. They recycle nutrients and make them available again. Without decomposers, there’s no food chain.

11. Decomposers play a HUGE role
Decomposers play a HUGE role! The duckweed (producers) need them to provide their nutrients.

12. REMINDER OF THE DYNAMICS OF ENERGY AND NUTRIENTS IN ECOSYSTEMS.
Energy flows into an ecosystem from the sun and less and less becomes available as it passes through the food chains.
REMINDER OF THE DYNAMICS OF ENERGY AND NUTRIENTS IN ECOSYSTEMS.
Nutrients cycle within an ecosystem. Organisms die and are decomposed, so their nutrients are recycled for the producers to take up again.

13. This makes our duckweed pond a quite amazing place of energy flow and nutrient recycling.
The pond may well be stinky because there is so much decomposition going on but that is good news for the duckweed.

15. The possibilities of duckweed:
Produces more protein per square meter than soybeans.
Produces more starch per square meter than corn. Biofuel?
Help in the fight against global warming.
Easier to harvest than algae or other aquatic plants.
Can be used to feed fish, poultry and cattle. Your pet dog! Even you!
Can purify and concentrate nutrients from wastewater (sewage effluent).
Provides food for wildlife – highly productive base to the food chain.

16. Perhaps we should be taking the humble duckweed much more seriously!