Here’s another contribution from my PhD student, Salvador Herrando-Pérez (see his previous ConservationBytes.com post on micro-evolution here).
Once upon a time at the produce section of a supermarket, a little girl confided to me that she had no idea that little plants could grow on carrots. This sympathetic scene portrays the split between the food we consume and the environments that produce it.
Mediterraneans love their cuisine. In fact, we are fairly proud of all our food. Yet how many of us associate a juicy tomato in our multicoloured salads, the smoothness of a escalibada (grilled veggies) bathed in virgin olive oil, the afternoon’s delicious expresso among friends and colleagues, or the last Christmas’ crunchy nougat shared with our beloved, with an insect that one given day pollinates a flower whose fertilized ovary will reach our dining room in the form of a sweet, infusion, fruit, sauce, soup or veggie.
Biodiversity fuels this relationship between insects and food. A study led by Alexandra Klein on highland coffee (Coffea arabica) from Sulawesi (Indonesia) demonstrates this concept well1. The German team showed that the amount of coffee beans produced in 24 agro-forestry sites increased with the number of bee species visiting the flowers (Fig. 1).
Figure 1. Percentage of highland coffee flowers yielding ripe beans in relation to number of bee species pollinating 24 agro-forestry sites in Sulawesi (Indonesia), according to Klein et al. (2003). Overall, a total of seven social and 22 solitary bee species were recorded. Coffee fruit set (and harvest) increases with closeness to the Lore Lindu National Park (habitat cue for social bee species), and (graph not shown) with solar illumination and botanic diversity (habitat cue for solitary bees).
Among others, three entwined mechanisms can explain this pattern. Firstly, coffee yield peaks across sites as they get closer to the forests of Lore-Lindu National Park – this facilitates daily access of social bees to crops from their nests within neighbouring forests [CJAB's note - see previous post on the role of ruderal vegetation in promoting pollinator diversity and increasing crop yields]. Secondly, in agro-forestry schemes, coffee plantations are often grown under the shade of secondary forests (Fig. 2) – the enhanced botanic heterogeneity procures suitable nesting and sheltering habitat (ground, fallen trees, etc.) for many species of solitary bees. Finally, bee species can select flowers at a given plant height and be active only for certain times of the day2; thus, different species can complement their pollination function and maximize the number of pollinated flowers per day. In terms of production, farmers want coffee flowers to receive as many bee visits per unit time as possible because they wither only two days after blossoming.
Pollination is indeed a classical example of an ‘ecosystem service’. This concept was conceived in the 1970s to argue that species extinctions impact ecosystem functions which provide services to humans in so far as they contribute to our welfare3. One of the key takes from Klein and colleagues’ work1 is that farmers targeting coffee or many other products reliant on animal pollination (75 % of leading food crops)4 can benefit from management scenarios that guarantee the coexistence of cultivated land with native habitats and pollinators. Over the last decade, we have started assigning monetary value to ecosystem services to internalize them in political and economic agendas. The core question remains: if restoring pollination (and the services it renders) is more expensive than preventing its destruction, will business and policy makers invest in conservation to save money in the long run?
Figure 2. Agro-forestry farm in Nueva Alemania (Chiapas, Mexico) where coffee plants and their white flowers thrive among rain forests (Courtesy of Shalene Jha)13. In this type of managed systems, bees can provide several valuable ecosystem services including pollination, honey and wax.
Pollination services are worth 153 billion euros (~20 euros per person worldwide) and its deterioration could cause up to 30-40% loss in production and a considerable inflation of prices5. Hence, the bee’s buzz is in on our plates and in our pockets. Recent studies indicate that the total area of pollination-dependent crops has increased by 70% from the 1960s6 and occupies today 12 times the surface of Spain. Many are intensive (heavily chemically protected) monocultures, e.g., California almonds (1/3 of the world’s consumption), where farmers are forced to rent hives to provision enough pollination.
However, thousands of hives are destroyed every year by invasive species, mites, diseases and the colony collapse disorder – a mysterious syndrome whereby bees abandon their hives from one day to the next7. As a result, preoccupation about the conservation of bee populations8,9 and contrasting views addressing a possible global pollination crisis10 have conflated. Had such pollination crisis not been reached, if the health of pollinators and their natural habitats continues to be jeopardized (for which strong evidence exists)11,12 and pollination-dependent agriculture keeps expanding (as current trends and predictions support)4,6, then bees, butterflies, flies, wasps and the remaining workers in the pollen-carrier guild might fail sooner or later to keep replacing (at no cost to us) the fruits and vegetables we harvest from the supermarket – magically, so to speak.
1Klein, A. M., Steffan-Dewenter, I. & Tscharntke, T. Fruit set of highland coffee increases with the diversity of pollinating bees. Proceedings of the Royal Society London: B 270, 955-961, doi:10.1098/rspb.2002.2306 (2003).
2Hoehn, P., Tscharntke, T., Tylianakis, J. M. & Steffan-Dewenter, I. Functional group diversity of bee pollinators increases crop yield. Proceedings of the Royal Society London: B 275, 2283-2291, doi:10.1098/rspb.2008.0405 (2008).
3Ehrlich, P. R. & Mooney, H. A. Extinction, substitution, and ecosystem services. BioScience 33, 248-254, doi:10.2307/1309037 (1983)
4Winfree, R. Pollinator-dependent crops: an increasingly risky business. Current Biology 18, R968-R969, doi:10.1016/j.cub.2008.09.010 (2008).
5Gallai, N., Salles, J. M., Settele, J. & Vaissiere, B. E. Economic valuation of the vulnerability of world agriculture confronted with pollinator decline. Ecological Economics 68, 810-821, doi:10.1016/j.ecolecon.2008.06.014 (2009).
6Aizen, M. A., Garibaldi, L. A., Cunningham, S. A. & Klein, A. M. Long-term global trends in crop yield and production reveal no current pollination shortage but increasing pollinator dependency. Current Biology 18, 1572-1575, doi:10.1016/j.cub.2008.08.066 (2008).
7Oldroyd, B. P. What’s killing American honey bees? PLoS Biology. 5, 1195-1199, doi:10.1371/journal.pbio.0050168 (2007).
8Kearns, C. A., Inouye, D. W. & Waser, N. M. Endangered mutualisms: the conservation of plant-pollinator interactions. Annual Reviews of Ecology and Systematics 29, 83-112 doi:10.1146/annurev.ecolsys.29.1.83 (1998).
9Grünewald, B. Is pollination at risk? Current threats to and conservation of bees. Gaia 19, 61-67 (2010).
10Ghazoul, J. Buzziness as usual? Questioning the global pollination crisis. Trends in Ecology and Evolution 20, 367-373, doi:10.1016/j.tree.2005.04.026 (2005).
11Winfree, R., Aguilar, R., Vázquez, D. P., LeBuhn, G. & Aizen, M. A. A meta-analysis of bees’ responses to anthropogenic disturbance. Ecology 90, 2068-2076 doi:10.1890/08-1245.1 (2009).
12Potts, S. G. et al. Global pollinator declines: trends, impacts and drivers. Trends in Ecology and Evolution 25, 345-353, doi:10.1016/j.tree.2010.01.007 (2010).
13Jha, S. & Dick, C. W. Shade coffee farms promote genetic diversity of native trees. Current Biology 18, R1126-R1128, doi:10.1016/j.cub.2008.11.017 (2008).