WEBVTT 00:00:00.320 --> 00:00:02.968 A food web is the network of feeding interactions 00:00:02.993 --> 00:00:05.039 among species in an ecosystem. 00:00:05.203 --> 00:00:07.056 When you think about feeding interactions, 00:00:07.205 --> 00:00:09.681 predators and prey are the first thing that spring to mind, 00:00:09.720 --> 00:00:12.554 like a cheetah chasing, killing and eating an antelope. 00:00:12.898 --> 00:00:16.014 But in fact, there are lots of ways that matter and energy 00:00:16.039 --> 00:00:18.716 get transferred from one organism to another: 00:00:19.060 --> 00:00:20.997 a calf consuming milk from its mother, 00:00:21.279 --> 00:00:23.240 a vulture feeding on a dead fox, 00:00:23.451 --> 00:00:27.464 a parasatoid wasp larva living inside and feeding on a caterpillar, 00:00:27.723 --> 00:00:30.767 a honey bee gathering nectar and pollen from a sunflower, 00:00:31.031 --> 00:00:34.063 and a katydid taking small bites of willow leaves. 00:00:34.261 --> 00:00:38.544 There are many ways that the existence of one creature depends on another. 00:00:39.269 --> 00:00:44.123 A food chain is one way of representing feeding relationships among several species 00:00:44.279 --> 00:00:48.529 with predators eating herbivores that eat plants that draw energy from the sun. 00:00:48.730 --> 00:00:52.519 An example is a hawk that eats a rabbit that eats grass. 00:00:52.670 --> 00:00:57.789 That's a good start, but it doesn't really let you understand the whole complex ecosystem. 00:00:58.362 --> 00:01:02.990 To do that we collect data on the myriad species that co-occur in a habitat 00:01:03.015 --> 00:01:06.006 and then figure out who they eat and who eats them. 00:01:06.303 --> 00:01:11.996 Each species is usually in many different food chains and those chains weave together to form a network. 00:01:12.254 --> 00:01:14.895 That ecological network is called a food web. 00:01:15.861 --> 00:01:19.447 Here's an example of an aquatic food web from Little Rock Lake, Wisconsin, 00:01:19.472 --> 00:01:25.707 that includes fishes, aquatic insects, zooplankton, algae, plants, and parasites. 00:01:25.944 --> 00:01:30.984 The spheres represent different species and the links show the interactions between the species. 00:01:31.195 --> 00:01:36.573 There are 92 tacks in this food web with almost a thousand feeding interactions. 00:01:37.191 --> 00:01:40.997 This image places species in the food web based on their trophic level. 00:01:41.292 --> 00:01:43.406 Trophic is just another word for feeding,Trophic is just another word for feeding, 00:01:43.446 --> 00:01:48.125 and trophic level is a measure of how many times energy and matter are transformed 00:01:48.150 --> 00:01:49.365 as they work their way up 00:01:49.669 --> 00:01:52.215 from species to species up the food web. 00:01:52.561 --> 00:01:56.211 Or organisms such as plankton and algae that generate energy from sunlight 00:01:56.236 --> 00:02:00.251 have a trophic level of one, and they show up at the bottom of food web. 00:02:00.664 --> 00:02:02.664 The species that feed on these, like zooplankton 00:02:02.689 --> 00:02:05.249 and aquatic insects, show up in the middle. 00:02:06.054 --> 00:02:09.545 Predatory fishes and their parasites show up on the top. 00:02:10.422 --> 00:02:14.875 You can use food webs to learn many different things about ecosystems. 00:02:15.185 --> 00:02:18.802 For example, we can use food webs from different places 00:02:19.091 --> 00:02:21.548 to understand whether a desert food web, 00:02:21.830 --> 00:02:23.080 a marine food web 00:02:23.173 --> 00:02:25.150 and a tropical forest food web 00:02:25.228 --> 00:02:27.540 are organized in similar or different ways. 00:02:27.908 --> 00:02:31.717 Our best science suggests that they have fundamentally similar organization, 00:02:31.742 --> 00:02:34.038 no matter what the habitat that is examined. 00:02:34.521 --> 00:02:37.161 Even food webs from hundreds of millions of years ago 00:02:37.232 --> 00:02:39.776 appear to be structured like modern webs. 00:02:40.097 --> 00:02:44.620 The species may be very different but their fundamental relationships are not. 00:02:45.123 --> 00:02:49.717 We can even use food webs to understand how humans fit into and impact ecosystems 00:02:49.742 --> 00:02:54.818 through their roles as hunters, gatherers, fishers, herders and farmers. 00:02:55.118 --> 00:02:58.946 We can compare the feeding roles of humans to other species and their food webs 00:02:59.126 --> 00:03:03.998 and learn lessons that help us to understand ecological resilience and sustainability. 00:03:04.172 --> 00:03:06.898 Developing the science of ecological networks such as food webs 00:03:06.923 --> 00:03:10.656 is some of the research we do here at the Santa Fe Institute.