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A food web is the network of feeding interactions

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among species in an ecosystem.

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When you think about feeding interactions,

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predators and prey are the first thing 
that spring to mind,

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like a cheetah chasing, 
killing and eating an antelope.

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But in fact, there are lots of ways 
that matter and energy

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get transferred from one 
organism to another:

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a calf consuming milk from its mother,

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a vulture feeding on a dead fox,

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a parasatoid wasp larva living inside 
and feeding on a caterpillar,

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a honey bee gathering nectar 
and pollen from a sunflower,

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and a katydid taking 
small bites of willow leaves.

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There are many ways that the existence 
of one creature depends on another.

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A food chain is one way of representing 
feeding relationships among several species

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with predators eating herbivores that eat 
plants that draw energy from the sun.

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An example is a hawk 
that eats a rabbit that eats grass.

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That's a good start, but it doesn't really 
let you understand the whole complex ecosystem.

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To do that we collect data 
on the myriad species that co-occur in a habitat

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and then figure out who they eat and who eats them.

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Each species is usually in many different food chains 
and those chains weave together to form a network.

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That ecological network is called a food web.

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Here's an example of an aquatic food web 
from Little Rock Lake, Wisconsin,

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that includes fishes, aquatic insects, 
zooplankton, algae, plants, and parasites.

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The spheres represent different species 
and the links show the interactions between the species.

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There are 92 tacks in this food web 
with almost a thousand feeding interactions.

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This image places species in the food web 
based on their trophic level.

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Trophic is just another word for feeding,Trophic is just another word for feeding,

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and trophic level is a measure of how many times 
energy and matter are transformed

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as they work their way up

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from species to species up the food web.

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Or organisms such as plankton and algae 
that generate energy from sunlight

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have a trophic level of one, and they show up at the bottom of food web.

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The species that feed on these, like zooplankton

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and aquatic insects, show up in the middle.

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Predatory fishes and their parasites 
show up on the top.

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You can use food webs to learn many different things about ecosystems.

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For example, we can use food webs from different places

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to understand whether a desert food web,

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a marine food web

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and a tropical forest food web

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are organized in similar or different ways.

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Our best science suggests that they have 
fundamentally similar organization,

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no matter what the habitat that is examined.

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Even food webs from hundreds of millions of years ago

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appear to be structured like modern webs.

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The species may be very different 
but their fundamental relationships are not.

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We can even use food webs to understand 
how humans fit into and impact ecosystems

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through their roles as hunters, 
gatherers, fishers, herders and farmers.

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We can compare the feeding roles of humans to other species and their food webs

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and learn lessons that help us to understand 
ecological resilience and sustainability.

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Developing the science of ecological networks such as food webs

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is some of the research 
we do here at the Santa Fe Institute.