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When we were little, we loved nature shows. One reason was because we didn’t have cable
and it was one of the few things we actually got a TV signal for that didn’t require
you to dance around with the TV antennae for reception. But the other reason was that,
of course, it was cool science. It often showed animals that we couldn’t see in our own
backyard doing some AWESOME things. But then it would be traumatizing when, inevitably,
some predator would walk in and gobble the unsuspecting animal up.
Truly, action scenes with predators and prey are often shown in nature shows because it’s
all part of nature’s food chains. A food chain---starts with a producer. A producer
is an organism that is an autotroph, which means it can make its own food. A plant for
example. The plant is eaten by a primary consumer, this grasshopper. Consumers are heterotrophs,
which means they must feed on other organisms. The primary consumer is eaten by a secondary
consumer, this frog. The secondary consumer is eaten by a tertiary consumer, this snake.
And the food chain can keep going! Notice how the arrows are supposed to point in the
direction of the one doing the eating---which makes sense---because that’s the direction
of the energy flow.
You can also arrange this same food chain into an energy pyramid. The producers at the
base here---in trophic level 1---- actually contain the most energy. What is crazy to
think about is that the primary consumers here---in tropic level 2---actually only store
10% of the energy from the producers. Meaning, let’s say the plants here had 10,000 kilocalories
(that’s an energy unit) of energy. Well the next level here---the primary consumers
in trophic level 2, would only store 1,000 kilocalories of energy. Where did the rest
go? Much of it is lost in heat or undigested. If you go up to the secondary consumers in
trophic level 3, that would be only 100 kilocalories of energy! It’s roughly only 10% of energy
stored each trophic level up.
Back to our food chain. Notice that, like a domino effect, if something is removed ---let’s
say the grasshoppers---you can harm the others because they may not have enough to eat. You
really have to consider the relationships among organisms in a food chain. In fact,
even if you took out the apex predator in this particular food chain---the snake---you
could end up with an excessive population of frogs, so it’s possible the frogs would
suffer from not having enough grasshoppers to support them.
You know, this is actually not a very good model, because in real life, this snake probably
doesn’t just eat frogs. It probably eats rabbits and birds too. Because an ecosystem
doesn’t typically have a single food chain, but instead, it has a food web. A food web
is made up of multiple food chains that interact together. So notice now that we have multiple
food chains here tied in with our original to make a food web
The beauty of a food web is that it shows more interactions among a variety of producers
and various level consumers. It also can show biodiversity. Biodiversity is the variety
of organisms---all types of organisms---living in a given area. The size of the area we are
talking about as well as the climate of the area directly affect the biodiversity that
is present. Biodiversity can contribute to the sustainability of an ecosystem. What I
mean by that is---let’s say there was a decrease in the amount of small birds in this
food web---it is likely it could be harmful to other organisms. However, it is NOT the
only thing that the snakes feed on. They have other options because of the biodiversity.
They also eat rabbits and frogs. Because of the biodiversity, the ecosystem may be more
resilient to changes such as these and possibly recover. However, these changes can still
have detrimental effects, and this is why it is critical to protect ecosystem biodiversity.
High biodiversity has a lot of other benefits---that can include economics---and we’ll need another
video to really touch on all the benefits of high biodiversity.
So if we were to ask you which of our examples here had more biodiversity---our food chain
or our food web---you would definitely want to pick the food web.
One last thing! There are some organisms that we left out of our food webs and food chains,
but they are essential. Decomposers! Decomposers are heterotrophs since they do eat other things…even
if the things they're eating are dead. Decomposers include organisms like bacteria and fungus. Technically if we
were to draw them in…then every arrow would eventually point to them. Well that’s it
for the amoeba sisters and we remind you to stay curious!
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