Above: David Moeller and Allison Shaw at the CBS Conservatory (Photo: Jonathan Pavlica) Below: Lauren Sullivan and Allison Shaw in the field
Living in the Midwest, the odds are good you have, at some point, driven by seemingly endless stretches of corn and soybean fields. These fertile lands were once home to vast expanses of tallgrass prairie, which had deep root systems that stabilized the soil by retaining carbon and preventing erosion. This nutrient-rich soil is the reason crops grow so well in former prairies that have been converted to farm fields. The expanding human population and our need for food production led to a steeo decline in grasslands, which now exist only in small fragments scattered throughout the landscape — some as remnants of prairies and some as restorations. Now, three CBS researchers are investigating a question that has important implications for our remaining prairies: What ability do plants have to disperse among these patches, and how far can they travel?
David Moeller, Allison Shaw, and Lauren Sullivan are using biological sampling, genetic sequencing, and mathematical modeling to track the parentage of flowering prairie plants in an effort to understand how far pollen and seeds can disperse. The outcome of their investigation could bolster state-wide prairie restorations undertaken as part of the Minnesota Prairie Conservation Plan, which is designed to link prairies across the entire latitudinal stretch of western Minnesota. A key component will be to assess how much area to restore and how far apart the fragments can be while still retaining demographic connectivity and genetic diversity. “It’s useful to have some sense of whether the investment is going to work,” says Moeller. “If you’re going to plant purple coneflower, you want to plant it in a fashion that’s amenable to persistence.”
There are two ways that plants disperse — by pollen or by seed. To measure how far seeds can be expected to disperse, Sullivan samples every individual of a target species within a 3.5 hectare area of the Blue Stem Prairie in northwestern Minnesota. She collects tissue and pollen from adult plants, which Moeller then genotypes. Offspring are identified by collecting and growing seeds, then comparing their DNA to records of all possible parents’ DNA. Distances traveled by pollen are quantified by the distance between the ‘father’ and ‘mother’ plant. Pollen dispersal is also a useful surrogate for understanding how far pollinators travel within and between prairie fragments.
Shaw uses those figures to model "dispersal kernels": the distances traveled by the pollen or seed from its source parent plant and the likelihood that a plant will travel that far. “We’ve been looking at how fast populations are growing or spreading and how they’re connected, but we’ve had to make assumptions about how plants are moving,” says Shaw. “We can’t put a tracking collar on pollen or seed, so we had to come up with a different method.”
This method of inferring distances via genotyping (possible only recently due to advances in genetic sequencing) holds promise for future restoration projects. In addition, Sullivan is analyzing plant characteristics that may correlate with dispersal, such as height, life cycle and population density. If certain traits turn out to be good predictors of dispersal, other biologists may be able to estimate dispersal ability based on a plant’s features. “We’re developing tools to estimate similar movement traits across similar species,” says Sullivan. “So anyone who has a prairie anywhere, if you know where other fragments are and what species are in them, you could know how connected those prairies might be to others in the neighborhood.” —Sarah Huebner