Among the Wildflowers

A Life of Science: A Series by New Scientists

In a rapidly changing climate, how does pollinator abundance impact the composition of plant communities?

  

As I trudge up the old mining road towards my field site, I step across a trickle of a stream that had been rushing at the beginning of the summer. Despite being an avid hiker and former college track athlete, I always struggle up this hill of 11,000 feet in the Colorado Rockies. As I round the corner, I am struck by the meadow chock full of wildflowers, a little waterfall and rocky cliffs in the distance. Even further in the distance are the high peaks of the Raggeds Wilderness. At this point in the summer, there are only the tiniest patches of snow up high, and the meadows are lush from recent thunderstorm rains. I recognize how lucky I am to have this meadow blanketed with lupines and sunflowers as my office. Every week, I go through this same cycle. I huff and puff up the hill, and then spend many quiet, productive hours counting flowers and seeds in the wildflower capital of the United States. There isn’t much to complain about.

I dump my backpack in the grass as I get to the top and pull out my yellow Rite in the Rain notebook, pencil, and yarn. The marmots’ warning calls whistle from a distant rock pile. It is late July, and many of the flowers are past their peak, but corn lilies still brush against my shoulders, and the Corydalis and bluebells are waist-high. I find the orange flag that marks the corner of my first plot amidst the lushness, and start my stopwatch for the four-minute pollinator observation: an ant crawls across the dirt, and makes its way up a green stem; a bee the size of my thumb lands on the bluebells. I make tally marks in the bee and ant columns of my notebook.  

Pollinators are essential to many plants’ reproduction, but are not an infinite resource. The study of pollinator behavior has a long history where I work at the Rocky Mountain Biological Laboratory, but pollinator abundance and its effect on plant communities and evolution has been studied less, despite the fact that climate change is driving a decline in pollinator populations worldwide. I want to know how pollinator abundance throughout the season impacts the time at which plants flower, and particularly when and if plants of different species nearby flower in relation to each other, and weekly observations help assess this question.
 

I stay put for four minutes at all four corners of each plot, and record every insect and pollinator that enters. Each corner is unique, and the visitors change from week to week. Usually ants are most common; the fourth plot sometimes has hundreds of the tiny insects within its one square meter of ground. Fat bumblebees are my favorite to watch as they buzz loudly from flower to flower, but they aren’t nearly as common. This week, the biting flies are incessant. They land on my shoulders, legs, and hands as I tried to take notes without flinging my pencil in frustration. They fly into my sunglasses and buzz around my ears. I move through the five plots’ pollinator observations as quickly as I can.

Once I finish four minutes of observation at each corner of the plots, I grab my favorite super simple field tool: yarn. Starting back at the first plot, I tie a short piece around each open flower in the plot, noting the species each time. Every week I use a different color of yarn to track which plants flowered when. This week is electric blue. Throughout the summer, the plots became more and more colorful, and some of the larger plants start to look like overly colorful Christmas trees. As the plants go to seed, I remove the yarn and count the fruits and seeds they produce. After marking the new flowers, I comb through each plot to count seeds and remove the yarn from each wilting flower. As I count seeds, I also come across a handful of plants with the flower cut cleanly from the top. Hungry deer, I imagine, but don’t know for sure.

These three tasks—pollinator observations, flower tagging, and seed counting—may seem unrelated, but when combined, should provide valuable insight into how plant communities are assembled and if evolutionary history plays any role in those patterns.

One of Darwin’s original theories, the Naturalization Hypothesis, proposes that invasive species will be more successful if they are not closely related to species that live in the community they invade. In theory, if they are more distantly related to the native species, they will face less competition and be able to invade more successfully. Like most things in ecology, though, this theory has been found to be widely variable. It’s true for some ecosystems under certain conditions, but broad patterns are difficult to confirm. Scientists use similar ideas about the ability of closely related species to live together to learn more about why biological communities are comprised of their species. Might closely related species do well together because they are similar and can all thrive in a certain habitat? Or do more closely related species compete too much to sustain themselves?

In my research, I am particularly interested in how the timing of flowering of different plants in the community and access to pollinators affects which plants live together. Pollinators are an important resource, and are often attracted to colorful, showy flowers. They might be more likely to visit a patch of flowers with many different species in bloom at once. If more plants flower together, would they all benefit from increased pollinator visits? Similarly, would more closely related species be more likely to flower at similar times?
 

The answers to these questions are important as climate change continues to worsen and impacts plants and their ability to reproduce in innumerable ways. Globally, some plants are moving higher in elevation, some are shifting their flowering timing, and others are employing different strategies to survive new climate challenges. But each individual plant is also part of a community. If certain species are lost, or if new invasive species enter, it will change the dynamics, and potentially affect the way other members of the community live and reproduce. Mountain plant communities are important food sources for animals, as well, and altering their composition could have cascading effects on the plants, insects, and other animals that call these areas home.

With the data I collect this summer, I will create an evolutionary tree with the plant species present in the plots to determine the evolutionary relationships within the community. I’ll be able to see the exact timing for the beginning, middle, and end of flowering for each wildflower, and whether there is overlap between more closely or more distantly related plants. Alongside the flowering timing, counting seeds will highlight the success (or lack thereof) of each plant’s reproduction. And while these data will shine light on the processes assembling Colorado Rocky Mountains wildflower communities, they are important for a broader understanding of plant community ecology, too. If plants flowering together increases pollinator visits and thus seed production, what happens if one of those flowers shifts its range or flowering timing? What if the pollinators shift their timing too, and it doesn’t line up with the plants that need pollination? In the nine months of the year I’m not able to sit amidst the wildflowers, these are the questions I read about, think about, and analyze data to answer.
 

Back in the meadow, I stuff my tangled ball of blue yarn back in my backpack, and make sure I haven’t left any pieces scattered on the ground. I throw my backpack over my shoulder and hike back to my car. As I walk, I can’t help but notice the bright pink-purple fireweed blooming along the path that isn’t in my plots. What insects pollinate this plant? Is it closely related to the others in the plots, or totally different?

With the Rocky Mountain Biological Lab’s remarkable research history, likely someone knows what pollinates the fireweed, and surely someone somewhere has included it in their evolutionary tree. Almost certainly, though, the intersection of timing around flowering, pollination, and evolutionary history hasn’t been fully explored. The relatively simple field work of watching bugs, tying yarn, and counting seeds will combine with evolutionary background information and, I hope, shed light on the current and future state of Rocky Mountains plant communities—and beyond.