Food Webs and Energy Pyramids: Bedrocks of Biodiversity

Captions are on! TO turn off, click the CC button at bottom right. Follow the amoebas on Twitter (@amoebasisters) and Facebook! 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! Follow the amoebas on Twitter (@amoebasisters) and Facebook!

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