Monday, March 23, 2020

A family tradition of ecology--now with isotopes!

Nick Smith Herman, Evan Swarth, Brendan O'Connor, San Jacinto Mountains, 2009

In 1908, Southern California was still a fairly wild place. Los Angeles was a growing new city with only a few automobiles relative to today. Caltech wasn’t even “Caltech” then. Noted California ecologist Joseph Grinnell had just taken a job as the first director of UC Berkeley’s Museum of Vertebrate Zoology (MVZ). He’d completed a study of the birds and mammals in the San Bernardino Mountains, east of LA. His first formal field trip for MVZ was with my husband’s grandfather Harry S. Swarth—who I wrote about on last week’s blog. They spent the summer examining and collecting specimens of birds, mammals, and reptiles in the San Jacinto Mountains, which form a barrier between the coastal zone of Southern California and the Mojave Desert to the south and east.

Their 230-page report was published in 1913. The two authors were following the work of C. Hart Merriam, a noted ecologist, who developed the concept of life zones in Arizona and Northern California in the late 1800s. The botanist Harvey Monroe Hall studied the plants in the San Jacinto Mountains in 1902. He described his work in terms of life zones that are based on the types of plants growing there. In the San Jacinto Mountains, there are four life zones: the Lower Sonoran (an arid lower elevation vegetation type), the Upper Sonoran (slightly higher elevation plants), Transition, and Boreal (high elevation species) zones. In the San Jacinto region, the mountains soar to 10,800 feet with a sharp elevational gradient on the east side, and a more gradual uplift to the west.
Evan, Jim Patton, curator of mammals MVZ, and Nick, 2008

Swarth and Grinnell’s field trip started out with hauling gear in wagons transitioning to pack animals when they reached steep slopes with no roads. There were few established trails. They collected (i.e., they shot and stuffed) birds from 169 species. In 1908, mist netting—the way in which birds are trapped today—didn’t exist. So, ornithologists needed to be sharpshooters. We have Harry’s small gauge shotguns that he filled with sand for the smaller birds and fine metal shot for larger species like crows or ravens. That summer they collected about 1,700 specimens that are housed still today at UC Berkeley’s MVZ.
Marilyn and Chris at MVZ, 2009

One hundred years later, scientists at the San Diego Natural History Museum (SDNHM) started a retrospective field campaign to cover the same territory that Grinnell and Swarth had studied in 1908. Phil Unitt, the curator of birds at the SDNHM, and my husband Chris Swarth were in contact in early 2008 regarding a diary that Harry Swarth had written as a 17-year old. Phil mentioned he was planning a San Jacinto Resurvey for the coming summer. Chris shared the story with me, and we were excited to plan a 100-year Swarth re-involvement in the re-survey—of course this time with a stable isotope twist!

I had started to work with Smithsonian’s Gary Graves and postdoc Seth Newsome on isotopes in bird feathers, mostly hydrogen isotopes to study avian migration, but we typically checked our work using carbon and nitrogen isotopes. My son Evan Swarth (age 17) was beginning his senior year of high school in September 2008, and he was looking to amp up his resume before applying for college. A field trip of Swarths was planned! Chris, Evan, and his buddy Nick Smith-Herman, flew out to Berkeley in June 2008 and toured MVZ seeing the specimens collected by his great grandfather 100 years earlier. They drove south to the San Jacinto Mountains joining Phil and his colleagues on their first trip.

Although just a high school student, Evan had participated in many of my field trips to Belize, Australia, and within the United States since the age of three. He knew how to sample plants and animals, keep a field notebook, and label sample bags making sure his records were accurate. Nick’s parents are physicians, not outdoor folks, so this was all new to him. That summer, they camped with the SDNHM folks for two weeks helping trap mammals with biologist Scott Tremor, help man the mist nests with Phil and his colleague Lori Hargrove, and survey plants with numerous museum botanists. They also collected insects, preserved plants, and brought back feathers all for stable isotope analyses!
The field team, 2009

Phil is a trim man wearing jeans in the field and while working at the museum. He was usually the first to arise, wolfed a granola bar, then was off for the day. The rest of us woke up slowly, made coffee, and prepared a hearty breakfast and packed a lunch. Phil was patient with the interns, interjecting his conversation with a sage, “Uh-huh!” when asked a question. In the museum he works in a windowless room with Lori, a recent UC Riverside PhD. Lori always has a little smile and is Phil’s counterpoint in many ways. They make an excellent team, both of them detail oriented with Phil as a consummate writer and Lori, a recent knowledge of ecology. Their colleague Scott Tremor, the curator of mammals, was used to working with younger folks and interacted easily with the interns. They loved waking early to check the mammal traps with him. Scott had a good sense of humor, a deep laugh, and a commanding voice.
Scott Tremor and Nick, 2009

When Evan’s senior year started, he had a half time schedule, so planned 4 hours of research in the afternoon. His buddy Brendan O’Connor talked his way into the lab as well. Having two funny, slapstick, young kids in the lab gave the place a different, youthful energy. They played loud hip-hop and rap music on the sound system and treated the sophisticated instruments with bravado that wasn’t necessarily warranted. Evan worked on the San Jacinto project, while Seth hired Brendan to help him weigh out the thousands of samples he had. This was the first science experience for Brendan, an active, often hyperactive, guy we called the “Water Buffalo.” Seth had high expectations for Brendan, who might be seen goofing off on any given day. As a mom, I was used to such behavior, but Seth was a sterner taskmaster.  It wasn’t uncommon for Seth to “fire” Brendan once a week. I would “rehire” him immediately. It was a learning experience for both of them.
Brendan running the mass spec, 2009

In 2009, I flew out to San Diego with Evan, Nick, and Brendan. Evan and Brendan had learned how to prep samples, load up the instruments, and run the isotope mass specs as high school students. They mastered Excel spreadsheets and prepared PowerPoint, giving lectures to the Lab and community nature groups. Now it was their turn to see the real thing—and learn what this project was all about.

Brendan, in particular, was extraordinarily enthused. When we drove past some unusual plants, he shouted, “We could measure their isotopes and find out what they’re eating!” [Note: this just works for animals. Plants don’t “eat” things.]
Taquitz Valley, California

We joined the field team hiking up the west side to Tahquitz Valley to around 8,000 feet elevation. Our heavier gear was packed up by horses and mules. At that time, I could backpack my gear for the trip all by myself.  I concentrated on collecting plants; the lads did the animal sampling. Chris joined us a few days later. It was a fun family trip. Phil, Lori, Scott, and Brad Hollingsworth the herpetologist, worked with the students patiently.

The SDNHM team was interested in determining whether an endangered species of flying squirrel was still living in the region. A ladder was propped up on a lodgepole pine where there was a suspected squirrel nest.

Nick climbed up, looked in, and said, “I see something. Do we have a vial?”

Evan answered, “We have a vial!” and quickly labeled and sent up a 50 milliliter plastic tube to sample bits and pieces of a possible flying squirrel nest for DNA analysis.

They had become budding field biologists! We measured the stable isotope compositions of everything we collected.

Later in the summer, Chris and I made a special trip to MVZ and subsampled feathers from about 185 birds that Swarth and Grinnell had collected in 1908. Our goal was to compare the two time periods.
Phil Unitt and Hannah Moore, at the mist nest, 2010

The next school year, Hannah Moore, then a high school senior and a neighborhood buddy of Evan’s, joined the lab as that year’s intern—hiring interns during the school year was now something that I did on a yearly basis. The following summer, 2010, she joined Evan and Nick as well as my daughter Dana in that summer’s trip to Round Valley another boreal zone site. They reached this high altitude area starting on the tram near Palm Springs. Dana was a natural at skinning bird samples, having watched her dad do this all her life. Hannah was an experienced hiker, but never had participated in a scientific field trip. The rigorous hours and rough conditions were a test for her, but she persisted.
Scott Tremor, Dana Swarth, and Phil, prepping specimens, 2010

The following summer, Collin Black, a buddy of Evan’s at the University of Connecticut, was the intern. Collin, then a goofy, leggy guy who was a good student, but had very little practical experience, knuckled down and measured hundreds of isotope samples that summer. 2011 was Evan and Nick’s fourth trip. They learned to shoot the shotguns, trapped rattlesnakes, and carried out the Swarth Family tradition in fieldwork.

We’ve measured almost 500 feather samples, hundreds of insects, and nearly a thousand plants. In addition to the modern plant samples, the interns sampled plants from a plant collection from 1908 housed at the Smithsonian Institution. Unfortunately, no insects were collected in 1908.

Collin Black and rodent, 2011
What did we find? It goes without saying that the influx of people has caused massive environmental change in the world, and in particular in southern California. The concentration of carbon dioxide has increased dramatically, and its isotope signature has changed by a known, measurable amount. We can see this change when we compare the carbon isotope signatures between early 1900s plants with ones collected a hundred years later. Nitrogen pollution from automobiles in the LA Basin travels far—we can detect this in the nitrogen isotope signals in plants sampled on the western San Jacinto region in 2008-2012. I expected these changes, but really what the SDNHM team was more interested in was whether the fauna had moved in response to a hotter, drier climate, changed their habitat or diet, or altered their behavior because of human intrusion.

We began our work sampling every specimen collected in the field. With time, we refined our investigation to 14 species that are resident birds—ones that spend their lives within the San Jacinto Mountains for the most part. In that way, we would be interpreting local isotope signals—not isotope signals synthesized a distance away. We are comparing the 1908 and the 2008-2012 specimens using simple and more complex statistical methods.

Phil and Lori tested the original hypothesis that birds would move into higher elevations in response to warming due to climate change. They found that things are not that simple. In any serious scientific endeavor, that’s generally true. Some species moved up, some moved down. Some species increased in abundance—some disappeared. Some were no longer found where they were seen in 1908, but were found in other sites. In comparison, the SDNHM study was conducted over several years and during many seasons, whereas Grinnell and Swarth’s study took place in one summer only.

Stable isotopes have provided some insight into whether the diets of these species have changed over time and whether or not they are feeding at the same position on the food web. Many of the birds rely on insects when they are feeding young or making new feathers (called molting). We found that species considered to be secondary consumers, those eating insects, are feeding lower on the food chain then they were a hundred years ago. The greatest changes in food chains seem to be on the lower life zones—the Lower and Upper Sonoran, which makes some sense since these are the most heavily impacted by humans. We’re now working through the higher order statistics to determine finer scale changes.

This 12-year project is now coming to the point where a manuscript will be prepared with all of the data on the birds and a summary of our findings for insects and plants. It ain’t easy to pull together a study that long in the making, but I think we’ve learned more in the past decade of how to use statistics to get more out of our analytical data. Stay tuned for a complete manuscript.

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