Food Webs

Food webs (aka trophic webs) illustrate the trophic (feeding) relationships in an ecological community. They are important tools for the study of biotic interactions that determine energy flows between organisms. These patterns profoundly affect species composition and richness, ecosystem stability and productivity, and the evolutionary trajectories of interacting species.

EOL Food Web Diagrams

EOL food web diagrams focus on the feeding relationships of a particular species. Each diagram shows the focal species along with species it feeds on (prey), species that feed on it (predators) and other species that feed on the same prey (potential competitors). Species are represented by circles (nodes), and arrows represent the transfer of energy (via food) from one species to another. When you hover over a node, the species name, its role in the current food web, and a thumbnail will be displayed to the right of the diagram. You can click on the name above the thumbnail to go to the EOL page for the species and learn more about it. You can also drag nodes around to make it easier to view relationships in different parts of the diagram. If you click on a node, the diagram will reload and center on the selected species showing its predators, prey, and competitors. You can use this feature to explore the trophic relationships of a series of species that are connected through links in their food webs.

Food web diagrams are displayed in the data tabs of EOL species pages if relevant data are available. To see a diagram, navigate to the data tab of a given species page, then select “eats” or “eaten by” from the “filter by attribute” menu. If the food web is large, it may take a few seconds to load. The data records that are used to build the food web for a given species are listed below the diagram. However, note that the data listing does not update as you move around the graph. You will remain in the data tab of the species that served as the starting point of your food web exploration until you navigate to another species page using the link above the thumbnail next to the food web diagram.

The diagrams are derived from the open source prototype created by Sungeun An.

Data Sources & Data Quality

EOL food webs are based on data supplied by Global Biotic Interaction (GloBI), a project that aggregates and integrates interaction data from diverse sources. Data are harvested from the scientific literature (books and journal articles), scientific databases, specimens from natural history collections, text mining and citizen science projects. Most GloBI data are supplied by the scientific community and will be of good quality. But neither GloBI nor EOL curates individual data records, so errors may occur. This caveat applies particularly to data originating from text mining and citizen projects, but even records derived from the peer-reviewed scientific literature may be subject to errors in interpretation or transcription. You can explore the provenance of interaction records in the data listed below the food web of a given species. Click on the caret below each data record to reveal the source of the record along with other available metadata.

A few things to keep in mind when interpreting the food web diagrams:
  • Most EOL food webs will not be complete representations of all trophic relationships of a given species. The completeness of each food web will depend on data availability and technical constraints (see Data Selection below).
  • Food webs are based on very general interaction types (eats, eaten by), and there is often more to the story. For example, you may be surprised to find a record of a crayfish eating an otter, until you realize that it is based on an account of a crayfish scavenging on an otter carcass. Similarly confusing records may state that a sparrow eats a horse (it eats horse manure), a water beetle eats a toad (it eats the toad’s eggs) or that a mosquito eats a bird (it eats the bird’s blood). You may find clues to some of these mysteries in the metadata of individual data records. For example, the life stage of the organism may be specified in some cases. But often you will have to go back to the original source to understand the full depth of an interaction record.
  • The terms predator, prey, and competitor are used loosely and in a very general sense in these diagrams. Most people would not consider a mosquito to be a “predator” of its victims. Plants are not usually seen as the “prey” of the species that feed on them, especially if the plant parts that are eaten are nectar or pollen. Also, not all species feeding on another species are necessarily competitors. If they feed at different times in the species life cycle or consume different parts of the organism, their resource needs may not actually overlap.

Data Selection

While GloBI supplies data for a variety of interaction types (eats|flowers visited by|has host|host of|infects|interacts with|is eaten by|is infected by|is parasitized by|is pollinated by|is preyed on by|is spread by|is killed by|is symbiont of|kills|parasitizes|pollinates|preys on|spreads|visits flowers of), only data for the “eats” and “is eaten by” interaction types are used in the EOL food web diagrams. Also, to qualify for inclusion in the diagrams, the data have to represent interactions between species. More general interaction records of the form “Rufous Hummingbird eats insects” are not included. To ensure usability of the graphs, we impose a constraint on the number of nodes that can be included. This means that some of the available interaction data may be omitted for organisms with complex food webs. In these cases, nodes are selected arbitrarily from the available data, and reloading the food web for a given species may result in a slightly different selection of predators, prey, or competitors.

Explore Food Webs

Here are some examples of rich food webs that can serve as starting points for the exploration of food webs on EOL:

Reptiles & Amphibians
Marine Invertebrates

Further Reading