The Buzz on Plant-Pollinator Networks

Daniel Song, a third-year doctoral student in biology who studies plant-pollinator networks, is quick to note he’s not the first person to examine correlations between plants and the insects who fertilize them. “For as long as people have been collecting honey, they’ve been understanding pollinators,” he says. However, his distinctive approach to analyzing these networks could have significant implications for conservationists.

Each summer, Song travels to a valley in northern Mongolia, where he spends seven days a week observing which plants are flowering and which insects are landing on them. When he returns to campus each fall, he uses network analysis—a digital tool originally used to study food webs in aquatic environments—to parse the data to see which pollinators are drawn to which plants. He then correlates the physical traits of the plants with their pollinators’ to see what physical characteristics might cause certain insects to choose to pollinate certain flowers. Bigger flowers, for instance, have deeper corolla tubes to get the nectar from, and bigger-bodied insects have longer tongues.

“The thing I’m looking at—and very few people have done this—is when you treat time as an important factor … how does your analysis change?” Song says. Therefore, in addition to considering physical traits, Song looks at temporal traits as well. For example, he considers when certain flowers bloom in relation to which pollinators are emerging, and notes flower size during a particular month vis-à-vis the size of the mouthparts of the insects that are prevalent during that same period.

This new perspective, he says, could give conservationists vital information for saving insect species whose preferred flowers are threatened. “If you need to save a certain bee, for example, and you know it visits a particular flower, you wouldn’t necessarily have to have that flower,” Song says. “You could have another plant that produces the same nectar, has the same color flower and the same corolla depth.” But, he cautions, the substitute plant would also need to bloom at the right time. If it’s not in flower when the bee emerges, “You have a problem,” he says. “It has to be the right flower at the right time.”

Song’s work is part of a National Science Foundation-sponsored collaboration among biologists at Penn, the Academy of Natural Sciences of Drexel University and the National University of Mongolia. The group is examining the ecological and evolutionary effects of climate change and nomadic herding in the remote Lake Hövsgöl region of northern Mongolia. Song is the only member of the group studying plant-insect interaction. He says understanding pollination networks there is crucial because of dramatic changes anticipated in the region. Without conservation measures, Song warns, the dryness of the climate, potential overgrazing due to the decreasingly nomadic nature of its herders, and sharp temperature increases expected due to global warming could transform this fragile region from a grassland to a desert.

Song sees implications for his work far beyond the grasslands of Mongolia, however. He points to his native state of California, which produces a significant portion of America’s fruit. “Fruits are produced by honey bee pollinators,” he says. “The reality we have to face is that honey bees are highly inbred, they’re susceptible to diseases, there are very few species. So what happens if they die? We need an insurance policy. We need to understand in nature how pollination works.”

Visit the PIRE Mongolia website for more information.