Inter-relationships between type, size and colour of fruits and dispersal in southern African trees

Abstract

The indigenous angiosperm tree flora (1,340 species) of southern Africa was analysed for type, size and colour of fruits and class of biotic dispersal agent (consumer). Species producing fleshy (drupes and berries) and dry (pods, capsules and nuts) fruits account for 52% and 47%, respectively, of the flora. The flora contains about 2.5 times as many berry-producing as drupe-producing species. Based on a log-linear model, fruit type, consumer and fruit size are dependent statistically on each other, whereas fruit colour depends on both fruit size and consumer type acting independently of each other. Drupes and berries are consumed by birds and mammals, with berries being favoured by both birds and mammals. At least 23% (307 species) of the flora apparently depends predominantly on birds for seed dispersal. Drupes and berries favoured by birds tend to be small and brightly coloured (red or black), whereas those eaten mainly by mammals tend to be large and dull (yellow or green). Relatively few fleshy fruits are brown. Pods, capsules and nuts tend to be brown or green. Birds apparently tend to avoid eating green fruits. The notion that green coloration has evolved to enhance crypsis and/or to signal unpalatability in unripe fruit to reduce premature exploitation is questioned. Green as a cryptic colour is incompatible with the demonstrated mammalian selection of this colour, while to function aposematically a stronger contrast colour may be required.