Pollination services decline with distance from natural habitat even in biodiversity-rich areas

摘要

There is considerable evidence for the negative impacts of habitat alteration on pollinators in highly disturbed regions of the world. However, it remains unclear whether these findings reflect a global crisis for crop pollination. Understanding the extent to which world agriculture is endangered by pollinator decline is essential if the economic valuation of nature is to be used to promote conservation. We assess the susceptibility to pollinator limitation of one of the most important tropical and subtropical fruit crops, mango Mangifera indica L., commonly planted in a region of South Africa located between two large biodiversity-rich protected natural areas. We conducted flower visitor surveys, exclusion experiments and spatial analysis of flower visitation and fruit production patterns.3. Our results show that both ants and flower visitors were effective pollinators of mango, the latter significantly declining (in abundance and species richness) with distance to natural habitat while ants were not affected. Neither the absence of pesticides nor the supplementation of flower visitors by using managed honeybees served to offset these negative impacts. Food-web data suggest that maintaining diversity of flower resources within farmland can help maintain pollinator communities. Moreover, models based exclusively on pollinator abundance underestimated the negative effect of distance from natural habitat on production (42% less at 500 m from natural habitat). As soil nutrient levels and water content are regularly measured and corrected in all study sites, these results suggest that pollinator diversity may also be important. Synthesis and applications. This study provides one of the first examples of marked pollination limitation in farms surrounded by well-protected natural habitat. For mango farming to be sustainable, it is essential to limit contiguous growth of farmland and consider practices that restore the complexity of plant-pollinator networks within farms, for example through the creation and maintenance of pollinator-friendly areas. By highlighting the economic gains of adopting pollinator-friendly practices in agriculture, this work contributes to a growing body of studies that reveal that making farmland more suitable for pollinators benefits both agriculture and nature conservation.