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Recent low levels of differentiation in the native Bombus ephippiatus (Hymenoptera: Apidae) along two Neotropical mountain-ranges in Guatemala
Landaverde González, Patricia ; Baltz, Lucie M. (coaut.) ; Escobedo Kenefic, Natalia (coaut.) ; Mérida Rivas, Jorge Alfredo (coaut.) ; Paxton, Robert J. (coaut.) ; Husemann, Martin (coaut.) ;
Contenido en: Biodiversity and Conservation Vol. 27, no. 13 (November 2018), p. 3513-3531 ISSN: 1572-9710
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Resumen en: Inglés |
Resumen en inglés

Recent anthropogenic fragmentation has led to population differentiation threatening viability of many species, including species specialized on mountainous ecosystems. Bombus ephippiatus, a widespread species mostly found in mountains in the Neotropics, seems to use the highlands as island, and deforested lowland areas may represent barriers to their dispersal, leading to isolation and potentially loss of genetic diversity. Yet, lack of knowledge of its population structure does not allow adequate management and conservation. To fill this knowledge gap, we assessed the population structure and inferred dispersion of B. ephippiatus in two mountain-ranges in Guatemala (Volcanic Chain and Sierra de las Minas). This region is characterized by high topographic variation and considerable deforestation strain. We analyzed the effects of elevation and land-use on genetic differentiation of B. ephippiatus populations and inferred its demography in the region. Our results suggest that B. ephippiatus is able to disperse long distances across most landscape types, reflected by its high genetic diversity, high effective population size, considerable gene flow, low population differentiation, as well as the lack of isolation by distance. Hence, B. ephippiatus may be a resilient species for the provision of pollination services. However, we detected a subtle divergence of B. ephippiatus into two clusters, of which Sierra de las Minas has been identified as a regional hotspot of genetic and species endemism. Yet, differentiation is very recent and hence likely caused by lowland deforestation. The combined effects of current forest cover and elevation partially explain the observed subtle patterns of differentiation suggesting that the maintenance of suitable habitat is crucial to ensure population connectivity of this keystone pollinator.

Resumen en: Inglés |
Resumen en inglés

1. Traditional tropical agriculture often entails a form of slash-and-burn land management that may adversely affect ecosystem services such as pollination, which are required for successful crop yields. The Yucatán Peninsula of Mexico has a >4000 year history of traditional slash-and-burn agriculture, termed ‘milpa’. Hot ‘Habanero’ chilli is a major pollinator-dependent crop that nowadays is often grown in monoculture within the milpa system. 2. We studied 37 local farmers’ chilli fields (sites) to evaluate the effects of landscape composition on bee communities. At 11 of these sites, we undertook experimental pollination treatments to quantify the pollination of chilli. We further explored the relationships between landscape composition, bee communities and pollination service provision to chilli. 3. Bee species richness, particularly species of the family Apidae, was positively related to the amount of forest cover. Species diversity decreased with increasing proportion of crop land surrounding each sampling site. Sweat bees of the genus Lasioglossum were the most abundant bee taxon in chilli fields and, in contrast to other bee species, increased in abundance with the proportion of fallow land, gardens and pastures which are an integral part of the milpa system. 4. There was an average pollination shortfall of 21% for chilli across all sites; yet the shortfall was unrelated to the proportion of land covered by crops. Rather, chilli pollination was positively related to the abundance of Lasioglossum bees, probably an important pollinator of chilli, as well indirectly to the proportion of fallow land, gardens and pastures that promote Lasioglossum abundance.

5. Synthesis and applications. Current, low-intensity traditional slash-and-burn (milpa) agriculture provides Lasioglossum spp. pollinators for successful chilli production; fallow land, gardens and pasture therefore need to be valued as important habitats for these and related ground-nesting bee species. However, the negative impact of agriculture on total bee species diversity highlights how agricultural intensification is likely to reduce pollination services to crops, including chilli. Indeed, natural forest cover is vital in tropical Yucat an to maintain a rich assemblage of bee species and the provision of pollination services for diverse crops and wild flowers.