Duckweed (Lemna sp) and its ecology

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

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

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

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

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

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.

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

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

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.

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

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.

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.

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.

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