Animals pollinate 80% of flowering plants, and this ecosystem service has an estimated economic value to humans of $120-200 billion annually.1 Despite their great value, there is a continuing worldwide decline in the abundance and number of species of pollinators, and 1200 wild vertebrate pollinators are at risk of extinction.2 These declines threaten humans by negatively impacting food production through loss of pollination of agricultural crops3 but the problem also extends to pollination of natural vegetation. For humans living in tropical areas, the strong dependence on forest products for subsistence living makes animal pollination of economically important forest trees an essential ecosystem service.4 Yet these areas are also heavily threatened by forest fragmentation, which has been linked to pollinator declines, and pollen limitation appears to be a primary contributor to the reduced reproductive success for plants in forest fragments.5 In this era of increasing human driven fragmentation of landscapes, there is an urgent need to understand the influence of landscape level variables that affect plant-pollinator interactions. This information is essential for land managers to make appropriate decisions about the landscape features and land area requirements necessary to maintain pollinator services.
Bats are important pollinators in the tropics, with the capacity to move pollen far across the landscape. Due to this capacity, there is an untested assumption that pollinating bats help maintain connectivity among fragmented plant populations. Although some bat species have been known to travel long distances to forage6, and cross pastures and forest fragments during foraging trips7, studies of bat-pollinated trees suggest that plant reproductive success may be compromised in disturbed habitats due to less frequent visits by bat pollinators.8 Other studies suggest the degree to which forest fragmentation reduces pollinator visitation and plant reproductive success varies among bat and plants species9, illustrating a need to evaluate whether pollination by bats is affected by landscape change. In particular, it is critical that we understand the extent to which ecological and genetic processes of plant populations are jeopardized by this landscape change.
Recent studies in landscape ecology have examined the role of the landscape matrix (the heterogeneous mix of landscape types surrounding the patch of interest) in patterns of organism abundance and movement, and found significant effects of the matrix on these measures.10 My research will address the effects of the landscape matrix on contemporary pollen-mediated gene flow in a bat-pollinated tropical tree species, Crescentia, alata. I will use a landscape genetics framework to examine the following questions about connectivity among sites surrounded by a continuous forest matrix, and sites surrounded by a matrix of pasture, clear cut and forest fragments:
1) Are trees in different landscape types connected by pollen-mediated gene flow differently?
2) Does landscape matrix in different landscape types affect the relative abundance and diversity of bat pollinators?
3) Do bats found in different landscape types visit floral species differently?
1Millennium Ecosystem Assessment (2005) Ecosystems and human well-being: Synthesis. Reid WV, ed. Washington (DC): Island Press. 137 p.
2Allen-Wardell G. et al. (1998) The potential consequences of pollinator declines on the conservation of biodiversity and stability of food crop yields. Conservation Biology 12: 8–17.
3Kremen C, Williams NM, Thorp RW. (2002) Crop pollination from native bees at risk from agricultural intensification. PNAS 99:16812-16816.
4Ashworth L, Quesada M, et al. (2009) Pollinator dependent food production in a mega-inhabited country: the case of Mexico. Biological Conservation 142: 1050–1057.
5Aguilar R, Ashworth L, Galetto L, Aizen MA. (2006) Plant reproductive susceptibility to habitat fragmentation: review and synthesis through a meta-analysis. Ecology Letters 9(8): 968-980.
6Horner MA, Fleming TH, Sahle CT. (1998) Foraging behaviour and energetics of a nectar-feeding bat, Leptonycteris curasoae (Chiroptera: Phyllostomidae). Journal of Zoology 244: 575-586.
7Law BS, Lean M. (1999) Common blossom bats (Syconycteris australis) as pollinators in a fragmented Australian tropical rainforest. Biological Conservation 91: 201–212.
8Quesada M, Stoner KE, et al. (2003) Effects of habitat disruption on the activity of nectarivorous bats (Chiroptera: Phyllostomidae) in a dry tropical forest: implications for the reproductive success of the neotropical tree Ceiba grandiflora. Oecologia 135: 400-406.
9Quesada M, Stoner KE, et al. (2004) Effects of Forest Fragmentation on Pollinator Activity and Consequences for Plant Reproductive Success and Mating Patterns in Bat-pollinated Bombacaceous Trees. Biotropica 36(2): 131–138.
10Ricketts TH. (2001) The Matrix Matters: Effective Isolation in Fragmented Landscapes. American Naturalist 158(1): 87-99.
Left: A Leptonycteris yerbabuenae bat covered in orange pollen. Right: Bats are attracted to the flowers of the Crescentia alata tree.