Equal and Opposite Effects of Floral Offer and Spatial Distribution on Fruit Production and Predispersal Seed Predation in Xanthosoma daguense (Araceae)¹

Abstract

Inflorescences of the terrestrial aroid Xanthosoma daguense in the Andes of Colombia are visited by Dinastinae and Nitidulidae beetles. Plants produce one inflorescence at a time, which is pollinated during the first night of opening. Dynastine beetles act as pollinators, whereas Nitidulids lay eggs in the inflorescence and the larvae damage the seeds. We explored the effects of floral offer and distance among inflorescences on the number of pollinator visits, fruit production, and predispersal seed predation. Number of Dynastine visits per inflorescence tended to increase with increasing distances among inflorescences, but fruit predation increased when inflorescences were more clumped. Both pollinator visitation rates and predispersal seed predation were low at high floral offer. Fruit set increased when inflorescences were visited by two or more Dynastines, but the proportion of fruits damaged by Nitidulid larvae was equivalent to the increase in fruit production due to more Dinastine visits. The net result was a similar number of undamaged fruits in all infructescences produced, independent of the number of Dinastine visits. Our results revealed that both pollinators and predators responded to the number of available inflorescences and their spatial distribution, but they had opposing effects on the infructescences. Thus, our study suggests that the interaction of two ecological processes, pollination and predispersal seed predation, may cancel each other's effects under natural conditions.

Geographic Variation and Succession of Arthropod Communities in Inflorescences and Infructescences of Xanthosoma (Araceae)1

“…The spathe tube also has a very important function during the specialized nocturnal pollination by dynastine beetles typical of Xanthosoma (García‐Robledo et al 2004, García‐Robledo et al 2005). In the species under consideration in this study, the flowering process lasts for only two nights.…”

Restoration of Plant–Pollinator Interactions: Pollination Neighborhood and Asymmetric Pollen Flow Between Restored Habitats in a Beetle‐Pollinated Aroid

“…I recorded the spatial distribution of all reproductive plants within each restoration strategy ( N natural regeneration = 127 and N ash plantation = 361). Xanthosoma daguense densities in each habitat were calculated as the number of reproductive plants divided by the area of the smallest polygon containing all the reproductive plants (polygon in secondary forest = 10,000 m 2 , polygon in ash plantation = 15,000 m 2 ) (García‐Robledo et al 2005 a ).…”

“…Pollinators of X. daguense tend to fly to the closest inflorescence available (García‐Robledo et al 2004; 2005 a ). Therefore, the distribution of pollen flow distances is highly leptokurtic.…”

“…The understorey of secondary forests and ash plantations was colonized by the native aroid Xanthosoma daguense Engl, a terrestrial herb circa 1.5 m tall (García‐Robledo et al 2004; 2005 a , 2005 b ). This species flowers throughout the year, with a peak between May and early July.…”

“…1b). Because beetles move every night only between two inflorescences, it is possible to track pollinator movements and pollen flow with high accuracy (Young 1988; García‐Robledo 2004; García‐Robledo et al 2005 a ).…”