Behmer et al. 10.1073/pnas.0711870105.
Fig. 3. Geometric framework. (a) Protein--carbohydrate intake target for a hypothetical consumer, plus two hypothetical foods (represented as trajectories, or rails) that vary in their protein--carbohydrate content. If the distribution of nutrients in our two hypothetical foods is homogeneous, a bite from the 2:1 food (the orange dashed line) will result in the consumption of twice as much protein as carbohydrate, whereas a bite from the 1:3 food (the blue dashed line) will lead to three times as much carbohydrate as protein being ingested. Our hypothetical animal can reach its intake target (the blend of protein and carbohydrate that leads to optimal growth) by switching between the two foods and eating slightly more of the 2:1 food. Arrows running parallel to the two rails represent individual meals, and length of the arrow indicates meal size. (b and c) Intake targets for seven hypothetical coexisting species that have similar intake targets (the null model). (b) Absolute amounts of protein and carbohydrate eaten by each of the seven species are similar. (c) In contrast, the seven species differ in absolute amounts eaten, but the ratio of protein to carbohydrate eaten is similar (the seven species occupy an identical slice, or wedge, of protein--carbohydrate nutrient space). (d) Nutrient space for grass- and forb-feeding grasshoppers. The nutrient space provided by grass is defined as the area between the two maroon dashed lines, and the nutrient space provided by forbs (which tend to be richer in protein) is defined by the area between the two green dashed lines. The two data points represent the mean (±SEM) protein--carbohydrate intake targets for two grasshopper species (the circle is the grass-feeding grasshopper Locusta migratoria, and the square is the mixture-feeding Schistocerca gregaria (data from ref. 1). A mixture-feeding grasshopper has access to a greater area of nutrient space because it eats both grasses and forbs.
1. Raubenheimer D, Simpson SJ (2003) J Exp Biol 206:1669-1681.