A food web is the network of feeding interactions
among species in an ecosystem.
When you think about feeding interactions,
predators and prey are the first thing that spring to mind,
like a cheetah chasing, killing and eating an antelope.
But in fact, there are lots of ways that matter and energy
get transferred from one organism to another:
a calf consuming milk from its mother,
a vulture feeding on a dead fox,
a parasatoid wasp larva living inside and feeding on a caterpillar,
a honey bee gathering nectar and pollen from a sunflower,
and a katydid taking small bites of willow leaves.
There are many ways that the existence of one creature depends on another.
A food chain is one way of representing feeding relationships among several species
with predators eating herbivores that eat plants that draw energy from the sun.
An example is a hawk that eats a rabbit that eats grass.
That's a good start, but it doesn't really let you understand the whole complex ecosystem.
To do that we collect data on the myriad species that co-occur in a habitat
and then figure out who they eat and who eats them.
Each species is usually in many different food chains and those chains weave together to form a network.
That ecological network is called a food web.
Here's an example of an aquatic food web from Little Rock Lake, Wisconsin,
that includes fishes, aquatic insects, zooplankton, algae, plants, and parasites.
The spheres represent different species and the links show the interactions between the species.
There are 92 tacks in this food web with almost a thousand feeding interactions.
This image places species in the food web based on their trophic level.
Trophic is just another word for feeding,Trophic is just another word for feeding,
and trophic level is a measure of how many times energy and matter are transformed
as they work their way up
from species to species up the food web.
Or organisms such as plankton and algae that generate energy from sunlight
have a trophic level of one, and they show up at the bottom of food web.
The species that feed on these, like zooplankton
and aquatic insects, show up in the middle.
Predatory fishes and their parasites show up on the top.
You can use food webs to learn many different things about ecosystems.
For example, we can use food webs from different places
to understand whether a desert food web,
a marine food web
and a tropical forest food web
are organized in similar or different ways.
Our best science suggests that they have fundamentally similar organization,
no matter what the habitat that is examined.
Even food webs from hundreds of millions of years ago
appear to be structured like modern webs.
The species may be very different but their fundamental relationships are not.
We can even use food webs to understand how humans fit into and impact ecosystems
through their roles as hunters, gatherers, fishers, herders and farmers.
We can compare the feeding roles of humans to other species and their food webs
and learn lessons that help us to understand ecological resilience and sustainability.
Developing the science of ecological networks such as food webs
is some of the research we do here at the Santa Fe Institute.