Evolution of Fruiting Strategies Among Fleshy-Fruited Plant Species of Eastern Kansas

• Published in: Ecology (Durham) 1982-01, Vol.63 (5), p.1422-1431
• Main Author: Stapanian, Martin A.
• Format: Article
• Language: English
• Subjects: Aves; Aviculture; Birds; Breeding seasons; Caterpillars; Fruiting; Fruits; Plants; Standard deviation; Summer; Winter
• ISSN: 0012-9658; 1939-9170
• DOI: 10.2307/1938869

Seed dispersal of fleshy-fruited plants by birds in Kansas riparian forests was investigated from an energetic point of view. Energy invested in fruit represents a reward to birds, but to plants it is a cost that is necessary to attract birds to eat the fruit and disperse the seeds. Seed volume (proportional to seed energy) in fruit represents a cost to birds in terms of digestive processing and mass carried, but a benefit to plants in terms of offspring dispersed. Increasing the fleshy energy per fruit would make the fruit more attractive to birds, but this would result in a decrease in the number of seeds a plant can make for a given reproductive energy budget. None of the birds in the study are fruit @'specialists@'; their preferred food is insects. An energetic model is presented: it hypothesizes that plants species fruiting when a preferred food (caterpillars) is abundant should have a high ratio of fleshy energy: seed energy: those fruiting when caterpillars are less abundant should have a lower ratio of fleshy energy: seed energy. This hypothesis was supported from phenology and calorimetry data for 16 species of fleshy-fruited plants. Frugivorous birds were found to be most numerous but very unpredictable in fall (migration season), moderately numerous and fairly unpredictable in winter, and least numerous but very predictable in their breeding season. The trade-offs among fruiting season of plants and the energetic cost of fruit, the number of interspecific competitors, the energy and nutritional requirements of birds, and the predictability of birds as a resource over time are discussed.