food: Dataset food
In ggcleveland: Implementation of Plots from Cleveland's Visualizing Data Book

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From Cleveland (1993): The food web for the animal species in an ecosystem is a description of who eats whom. A chain is a path through the web. It begins with a species that is eaten by no other, moves to a species that the first species eats, moves next to a species that the second species eats, and so forth until the chain ends at a species that preys on no other. If there are 7 species in the chain then there are 6 links between species, and the length of the chain is 6. The mean chain length of a web is the mean of the lengths of all chains in the web. A two-dimensional ecosystem lies in a flat environment such as a lake bottom or a grassland; movement of species in a third dimension is limited. In a three-dimensional ecosystem, there is considerable movement in three dimensions. One example is a forest canopy; another is a water column in an ocean or lake. A mixed ecosystem is made up of a two-dimensional environment and a three-dimensional environment with enough links between the two to regard it as a single ecosystem. An interesting study reports the mean chain lengths for 113 webs.