Edge effects on pollinators, pollination and fruit production in grapefruit plantations bordering Argentinian Yungas forest

CHACOFF, NATACHA & AIZEN, MARCELO

Miami, USA

Congreso; ATBC Geographic and conceptual frontiers of tropical ecology; 2004

Association of Tropical Biology and Conservation

The pollination of flowering plants represents a critical process for both natural and agricultural ecosystems that could be greatly affected by the destruction, degradation, and fragmentation of natural habitats. We estimated abundance and diversity ofpollinators, as well as pollination and reproductive levels in pigmented grapefruit (Citrus paradisi Macf.) plantations bordering subtropical mountain forest in NW Argentina. These variables wcre assessed at increasing distances from the forest edge (0, 10, 100, 500, and 1000 m) in four plantations and over three consecutive years. The total visit frequency, visits by honeybees, visits by other pollinators, and pollinator species richness, all decreased linearly as distance to the forest edge increased. The relative visitation by pollinators other than honeybees declined from 14 to 2% from the forest edge to 1000 m. Pollen loads in the stigma and pollen tubes in the style also decreased monotonically as distance to the forest increased, but no edge effect was found on fruit and seed set. Despite self-compatibility, the studied grapefruit varieties require insect pollination for high yields: open-pollinated flowers set ca. six times morc fruits than either emasculated or bagged flowers. Also, hand-pollinated flowers set nearly twice as many fruit as open-pollinated flowers. This study provides empirical evidence for considering remnants of natural habitats as a source of both native and alien pollinators for agriculture. Although, in general Citrus have been considered as low pollinator-dependent crops, we found that at least in these grapefruit varieties insects play an important role for fruit production. However, in our system a clear negative edge effcct on pollinator abundance and pollination were not strong enough to cause an expected decline in fruit set despite evidence of pollen limitation.