Carnivory in the Bromeliad Brocchinia reducta, with a Cost/Benefit Model for the General Restriction of Carnivorous Plants to Sunny, Moist, Nutrient-Poor Habitats

Brocchinia reducta is the first documented case of carnivory in the Bromeliaceae. Its erect leaves form a yellowish cylinder with a cuticular lubricant on its inner surface, impound fluid that emits a nectarlike fragrance, and bear trichomes capable of absorbing amino acids from this fluid in which numerous insects, mainly ants, drown. Trichome absorptivity and aspects of trichome structure appear unique in the primitive subfamily Pitcairnioideae. We present the first rigorous definition of carnivory in plants, and discuss its implications for the identification of cases of carnivory and protocarnivory in bromeliads. A cost/benefit model for the evolution of carnivory is developed to analyze why carnivorous plants are restricted mainly to sunny, moist, nutrient-poor sites and seasons, and why carnivory is rare in epiphytes and other bromeliads. The relative advantages of carnivory and ant-fed myrmecophily are discussed in terms of this model, and predictions made regarding the nature of the ant-plant mutualism in understory myrmecophytes.