Description

Student Introduction: Some biological attributes of organisms scale proportionately with body size; for a given type of organism the relationship between a physical or physiological attribute and body size is the same regardless of the organism's size. Often, however, this relationship changes relative to the size of the organism. For example, metabolic rate increases with body mass, but increases less than one would expect if the relationship were simply proportional. On the other hand, skeleton weight increases with body mass more than expected based on simple proportionality. Similar relationships are found in plants: tree diameter increases with height, but at a greater-than-proportional rate. These are examples of allometric relationships, in which the scaling relationship between some biological attribute and body size is dependent on the organism's size.

The distribution of species with different feeding modes among body size classes is shown below for the herbivorous insect fauna of India (graph redrawn from Novotny & Wilson, 1997 [data from Distant, 1906-18, in Novotny & Wilson]). For each body size class (indexed by body length) the graph shows the percentage of species in that size class that feed on xylem, phloem, or mesophyll cells.

Note that there are no xylem feeders in the two smallest size classes.

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