Widths and compositions of diets

Consumers can be classified as either monophagous (feeding on a single prey type), oligophagous (few prey types) or polyphagous (many prey types). An equally useful distinction is

... as illustrated by desert interactions food quality rather than quantity can be of paramount importance range and classification of diet widths

Figure 9.13 (a) The quality of food measured as percentage crude protein available to (o) and eaten by (•) wildebeest in the Serengeti during 1971. Despite selection ('eaten' > 'available'), the quality of food eaten fell during the dry season below the level necessary for the maintenance of nitrogen balance (5-6% of crude protein). (b) The fat content of the bone marrow of the live male population (o) and those found dead from natural causes (•). Vertical lines, where present, show 95% confidence limits. (After Sinclair, 1975.)

Figure 9.13 (a) The quality of food measured as percentage crude protein available to (o) and eaten by (•) wildebeest in the Serengeti during 1971. Despite selection ('eaten' > 'available'), the quality of food eaten fell during the dry season below the level necessary for the maintenance of nitrogen balance (5-6% of crude protein). (b) The fat content of the bone marrow of the live male population (o) and those found dead from natural causes (•). Vertical lines, where present, show 95% confidence limits. (After Sinclair, 1975.)

between specialists (broadly, monophages and oligophages) and generalists (polyphages). Herbivores, parasitoids and true predators can all provide examples of monophagous, oligophagous and polyphagous species. But the distribution of diet widths differs amongst the various types of consumer. True predators with specialized diets do exist (for instance the snail kite Rostrahamus socia-bilis feeds almost entirely on snails of the genus Pomacea), but most true predators have relatively broad diets. Parasitoids, on the other hand, are typically specialized and may even be monophagous. Herbivores are well represented in all categories, but whilst grazing and 'predatory' herbivores typically have broad diets, 'parasitic' herbivores are very often highly specialized. For instance, Janzen (1980) examined 110 species of beetle that feed as larvae inside the seeds of dicotyledonous plants in Costa Rica ('parasitizing' them) and found that 83 attacked only one plant species, 14 attacked only two, nine attacked three, two attacked four, one attacked six and one attacked eight of the 975 plants in the area.

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