Native bees mediate long-distance pollen dispersal in a shade coffee landscape mosaic

Abstract

Coffee farms are often embedded within a mosaic of agriculture and forest fragments in the world's most biologically diverse tropical regions. Although shade coffee farms can potentially support native pollinator communities, the degree to which these pollinators facilitate gene flow for native trees is unknown. We examined the role of native bees as vectors of gene flow for a reproductively specialized native tree, Miconia affinis, in a shade coffee and remnant forest landscape mosaic. We demonstrate extensive crosshabitat gene flow by native bees, with pollination events spanning more than 1,800 m. Pollen was carried twice as far within shade coffee habitat as in nearby forest, and trees growing within shade coffee farms received pollen from a far greater number of sires than trees within remnant forest. The study shows that shade coffee habitats support specialized native pollinators that enhance the fecundity and genetic diversity of remnant native trees.A n estimated 13 million ha of tropical forest are destroyed every year (1) by the expansion of crops, pasture, and logging (1, 2). In deforested tropical regions, one of the most widely cultivated and economically valuable crops is coffee. Often grown adjacent to remnant forest patches, coffee covers over 11 million ha of land within many of the world's most biodiverse regions (3, 4). Intensively farmed "sun" coffee supports little native vegetation and can create an inhospitable matrix that isolates plant and animal populations living within forest fragments (3, 5). Alternatively, coffee grown under a canopy of overstory trees in the traditional "shade-grown style" can preserve ecological processes and provide farmers with ecosystem services (4, 5). For example, shade coffee farms serve as a habitat for migratory birds and nonmigratory bats, both of which provide farmers with pest control (6-8). Tropical animals living within shade coffee farms may also facilitate seed dispersal for native trees, thus providing opportunities for the maintenance of shade trees and future reforestation (9).However, pollination mutualisms may be particularly vulnerable to habitat alteration, however, and many tropical tree species are self-incompatible and dependent on animal pollinators for reproduction and gene flow (reviewed in 10, 11-14). Although some agricultural landscapes provide suitable habitat for pollinators (15-17), many agricultural practices negatively impact native pollinator communities (18)(19)(20). Agricultural landscapes can also have high densities of exotic honey bees (Apis mellifera scutellata), which may not provide pollinator services for reproductively specialized native plants (21, reviewed in ref. 22). Exotic honey bees can maintain gene flow in altered habitats for plants with unspecialized flowers and abundant nectar and/or pollen, even if a subset of the native pollinators is lost (reviewed in ref. 12; e.g., refs. 23, 24). However, loss of the native pollinators of reproductively specialized plants can lead to reduced genetic diversity and inbre...

The pollen dispersal kernel and mating system of an insect-pollinated tropical palm, Oenocarpus bataua

“…Similarly, the dispersal kernel we generated for O. bataua using the spatially-explicit NEIGHBOURHOOD model was best described by a Weibull distribution with high probability of dispersal at intermediate distances, and a very rapid decline in dispersal probability with increasing distance. The preponderance of intermediate distance pollination events and overall pollen movement we observed is qualitatively similar to that documented in recent studies (for example, Bittencourt and Sebbenn (2007); de Lacerda et al (2008); Jha and Dick (2010); Zhou and Chen (2010); Fuchs and Hamrick (2011)), suggesting a non-leptokurtic pattern of realized pollination events may not be uncommon, especially amongst tropical species. Dispersal kernel modelling estimates the frequency distribution of dispersal distances of propagules from an individual source tree (Oddou-Muratorio et al, 2005), in contrast to the population-level patterns of pollen receipt detected via paternity analysis.…”

Genetic connectivity and diversity in inselberg populations of Acacia woodmaniorum, a rare endemic of the Yilgarn Craton banded iron formations

“…Generalist insects including native and introduced bees are known to routinely fly distances of several kilometres, especially among fragmented habitat (Dick, 2001;Jha and Dick, 2010;Hagler et al, 2011) and may directly facilitate pollen dispersal when traversing intervening unsuitable habitat among populations. Pollen dispersal over a distance of 1.6 km has also been recorded previously for A. saligna, a common widespread species of the more mesic areas of south west WA, using direct paternity analysis methods (Millar et al, 2008.…”

Mating system and early viability resistance to habitat fragmentation in a bird-pollinated eucalypt

“…The average pollen dispersal distances estimated here, for both intact and lower density landscape contexts, are at the upper end of the range in comparison to other studies on Eucalyptus species using similar indirect methods (remnant Eucalyptus stand: 324-493 m, Sampson and Byrne, 2008;87-149 m, Mimura et al, 2009;25-64 m, Field et al, 2011;fragmented Eucalyptus stand: 69-833 m, Mimura et al, 2009). An increase in average pollination distance in a lower density compared with higher density and more intact habitat context is perhaps to be expected for tree species with labile pollinators (for example, birds: Mimura et al, 2009;mobile insects: Dick, 2001;White et al, 2002;Jha and Dick, 2010). More detailed analysis of pollen flow using direct parentage analysis would certainly be a fruitful line of enquiry to better understand gene flow dynamics in the fragmented landscape we studied here, including understanding the direction of gene flow between isolated trees and fragments.…”