Pitcher plants as tiny ecosystems – educational microcosms for IBSE

Kate Whittington, kate.whittington@bgci.org | 25/04/13 | London

 

Sometimes it’s hard to see the bigger picture.

At first glance a lake or pond may seem a simple, tranquil body of water. But we all know that teeming beneath the surface there could be hundreds of organisms, many too small to be seen with the naked eye, and all of which are having some influence on the state of these aquatic ecosystems.

Trying to explain the multitude of inputs, outputs and environmental factors which impact an ecosystem is a complex and difficult task. It can help, therefore, to scale things down and devise some sort of model to observe these concepts.

In order to study “tipping points” – an abrupt shift from one, often favourable state, to another less desirable one - a group of ecologists recently used pitcher plants as tiny model ecosystems.

Each pitcher-shaped leaf of these small carnivorous plants can hold around a quarter of an ounce of rainwater. Each tiny pool of water is home to a multi-level food web of fly larvae and bacteria, which resembles the inner workings of a full-scale water body. Just as with a lake, if the pitcher plant becomes overloaded with nutrients, it can reach a “tipping point”.

In a lake, the presence of excess nutrients (e.g from fertiliser or pollution) would usually lead to a bloom of algal species, which in turn are fed upon by bacteria. The resulting increase in bacteria soon depletes the oxygen levels in the water and leaves the lake murky, green and stagnant.

These researchers simulated this process with the pitcher plants and, after overloading them with organic matter - in this case ground-up wasps – a tipping point was found to occur around 45 hours after the start of feeding. As with a lake, the resident bacteria feeding off of the crushed wasp matter caused oxygen levels to significantly drop.

A single bacterial generation is around 20-60 minutes, whereas fish have generation times of a year or more.  

"We would need to study a lake for 100 years to get the same information we can get from a pitcher plant in less than a week..."

Experiments like this are therefore “like fast-forwarding through a video” says Aaron Ellison - an ecologist at Harvard Forest and co-author of the paper.

So what can we learn about IBSE from these experiments?

Here, we see a common problem faced by scientists and educators – time constraints. Just as scientists don’t always have the time to collect data over several years for problems we need to address now, educators generally have just a few sessions in which to cover certain complex topics. For students, observing results from experiments such as these is vastly more effective (and exciting!) than reading long-term case studies out of textbooks.


Not everyone has a pitcher plant, however, so how about building a terrarium instead?

A terrarium is a sealed transparent container in which a collection of small plants is grown. As with the pitcher plants, they can be used to demonstrate many ecosystem processes such as photosynthesis, respiration and the water cycle. And, rather conveniently, the Fairchild Tropical Botanic Garden, Florida, has developed a handy pdf with all the instructions and activity ideas you need to make your own terrarium.

 


If anyone has any suggestions for similar small-scale experiments which help explain large-scale concepts please share them below. Maybe you have some feedback from your own experiences with these kinds of demonstrations?

 

Photo credits:
1. Pitcher plants at Kew Gardens - by Kate Whittington
2. Terrarium - by Mike Ambs on flickr

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