The Influence of Adult and Larval Food Habits on Population Size of Neotropical Ground-Feeding Drosophila

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Abstract
The influence of feeding and breeding habits upon population size was investigated in 73 species of neotropical forest-dwelling Drosophilidae. Three classes of ground feeders are defined according to fruit preferences and attractability to traps baited with cultivated fruits. Class A species prefer small drier fallen fruits and blossoms both for adult feeding and larval breeding and enter traps to a limited degree. Class B species use fleshy fruits in addition to these, and enter traps to a moderate extent. Class C species use chiefly fleshy fruits for breeding, and show a strong inclination to enter traps. As a consequence of their feeding and breeding habits, class A species undergo population expansions, where such occur, in the wet season when their fruits and blossoms suffer less from desiccation. Class B and some class C species undergo expansions in the dry season since they are able to use fleshy fruits. Some class C species exhibit nonseasonal fluctuations. The range of mean sizes of minimal population samples of class A and B species collected by net sweeping is similar to that of class C species collected by trapping. Because they utilize fleshy fruits for breeding, most class B and C species are collected in expanded populations far oftener than class A species. Larval development of different species of ground-feeding Drosophila, including members of the same species group or even of the same sibling set, generally occurs almost synchronously, although successional development has been observed. Since the number of species netted from a given fruit greatly exceeds the number of species bred from a limited volume of the fruit, a type of interference between species during ovi-position has been inferred.

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