Scholars reveal the changing nature of U.S. cities

Cities are not all the same, or at least their evolution isn’t, according to new research from the University of Colorado Boulder.

These findings, out this week in Nature Communications Earth and Environment and Earth System Science Data, buck the historical view that most cities in the United States developed in similar ways. Using a century’s worth of urban spatial data, the researchers found a long history of urban size (how big a place is) “decoupling” from urban form (the shape and structure of a city), leading to cities not all evolving the same—or even close.

The researchers hope that by providing this look at the past with this unique data set, they’ll be able to glimpse the future, including the impact of population growth on cities or how cities might develop in response to environmental factors like sea level rise or wildfire risk.

“We can learn so much more about our cities about and urban development if we know how to exploit these kinds of new data, and I think this really confirms our approach,” said Stefan Leyk, a geography professor at CU Boulder and one of the authors on the papers.

“It’s not just the volume of data that you take and throw into a washing machine. It’s really the knowing how to make use of the data, how to integrate them, how to get the right and meaningful things out there.”

Its projected that by 2050, more than two-thirds of humans will live in urban areas. What those urban areas will look like, however, is unclear, given limited knowledge of the history of urban areas, broadly speaking, prior to the 1970s.

This work and previous research, however, hopes to fill that gap by studying property-level data from the property management company, Zillow, through a property-share agreement.

This massive dataset, called the Zillow Transaction and Assessment Dataset or ZTRAX, contains about 374 million data records that include the built year of existing buildings going back over 100 years. Previously, the researchers then used these data to create the Historical Settlement Data Compilation for the United States (HISDAC-US), a set of unique time series data set that’s freely available for anyone to use.

For this new research, which were funded by the National Science Foundation, the Institute of Behavioral Sciences and Earth Lab, the researchers applied statistical methods and data mining algorithms to the data, trying to glean all available information on the nature of settlement development, particularly for metropolitan statistical areas, or high-density geographic regions.

What they found is that not only were they able to learn more about how to measure urban size, shape and structure (or form), including the number of built-up locations and their structures, they were also able to see very clear trends in the evolution of these distinct categories of urban development.

“We can learn so much more about our cities about and urban development if we know how to exploit these kinds of new data.”

Stefan Leyk, a geography professor at CU Boulder and one of the authors on the papers

In particular, the researchers found that urban form and urban size do not develop the same as previously thought. While size generally moves in a single direction, especially in large cities, form can ebb and flow depending on constraints, such as the geography of places as well as environmental and technological factors.

“This (the categorization) is something that is really novel about that paper because this could not be done prior to that because these data were just not available,” said Johannes Uhl, the lead author of the paper and a research associate at CU Boulder.

It’s remarkable, according to the researchers, that the two articles are being published by different high-impact journals on the same day. While the Nature Communications Earth and Environment piece discusses the substantive application of the data, the Earth System Science Data discusses the data themselves, the methods to create them, and the limitations with them.

“There’s so much potential in this current data revolution, as we call it,” Leyk commented. “The growth of so-called data journals is a good trend because it’s becoming more and more systematic to publish formal descriptions of the data, to learn where the data can be found, and to inform the community what kind of publications are based on these data products. So, I like this trend and we try and make use of it.”

This research, however, is still far from finished. Next, the researchers hope to further examine the categories, and, in particular, the different groups of cities that emerged in the process of this research to hopefully determine a classification system for urban evolution, while also applying the data approach to more rural settings.

“The findings are interesting, but they can of course be expanded into greater detail,” Uhl said.

The researchers are also working with other researchers in different fields across the university to explore the applications of these data on topics as far reaching as urban fuel models for nuclear war scenarios, the exposure of the built environment to wildfire risk, and settlement vulnerability from sea level rise.

“The context is a little different in each of these fields, but really interesting,” Leyk said. “You realize how important that kind of new data, new information, can become for so many unexpected topics.”

Republished with permission from the Colorado Arts and Sciences Magazine

New grant to study life-and-death trait of chickadees

Spatial cognition—how space is perceived and remembered—is an incredibly important trait that can determine life or death for chickadees, yet not much is known about it or how it developed. A new grant awarded to the University of Colorado Boulder and the University of Nevada Reno, though, aims to provide some insight.

This $2.7 million National Science Foundation grant will allow researchers from both institutions to build off existing research to examine the genetic underpinnings of spatial cognition—and the role natural selection may play on the trait—in mountain chickadees in both the Sierra Nevada and the Rocky Mountains.

Beyond just chickadees, though, this new grant will also allow the researchers to study natural selection on a complex behavioral trait, an incredibly difficult task that could potentially expand the ways natural selection is studied broadly, while also shedding light on how it relates to a changing climate.

“Even documenting natural selection on relatively simple traits like coat color in the wild is difficult, and behaviors are harder to pin down for a lot of reasons,” said Scott Taylor, an assistant professor at CU Boulder and the new director of the Mountain Research Station, who is one of the lead investigators on the grant.

“Especially things like spatial cognition, for a long time, people thought that it’s all environmental or its all learned and there’s no genetic basis. But our preliminary data show that there is likely some genetic basis for the trait, and this grant will explore our preliminary findings in more depth.”

Chickadees do not migrate like some other bird species, which means that they have to survive the winter. To do that, chickadees, which have long been known for their spatial memory, rely on food reserves or caches that they’ve hidden throughout the season as a consistent source of food.

“The reason they (chickadees) have such great memory abilities is that they use spatial learning and memory to find these caches. If they fail to find them during critical times of need in the winter, they are likely to die, so having good spatial cognition is critical for their survival,” said Vladimir Pravosudov, a professor at the University of Nevada Reno and the other lead investigator.

Pravosudov used that behavior to his advantage to study their spatial cognition. He created a spatial array, or a group of sensors designed to test spatial learning in memory in wild chickadees in their natural environment. Each array consists of eight “smart” feeders equipped with Radio Frequency Identification (RFID) technology allowing him and his lab to control which bird can get food at each feeder.

All chickadees were also banded with unique passive integrated transponder tags, which are then detected by the RFID board in each smart feeder when any bird lands on the feeder perch with the embedded RFID antenna. That board can then grant access to the food within the feeder, making it possible to assign each bird to a single feeder within the array.
The researchers then measured spatial learning and memory by looking at how many errors the individual birds make as they become familiar with the spatial location of their rewarding feeder.

While Pravosudov’s lab was collecting these data, Taylor, who studies the genetic underpinning of speciation within chickadee populations, was invited to give a talk at the University of Nevada Reno. What initially began as a simple conversation of the genetics underlying spatial cognition between the two labs became a “well, maybe,” and they decided to give it a try through a pilot study looking at the highest and lowest performing individuals.

“It’s usually hard to measure traits in wild populations and relate those to natural selection. … This research expands the kinds of ways we can explore how natural selection operates in nature and then, ultimately, shapes the variation that we’re fascinated by.”

Scott Taylor, Assistant professor at cu boulder, lead researcher

Their initial findings, which are in a forthcoming paper, suggest that genetics is at play. This fits with Pravosudov’s recent findings that provide strong evidence that this complex behavioral trait is acted upon by natural selection. In other words, chickadees with better spatial cognition are more likely to survive their first winter of life and thus reproduce come spring.

“This was a critical finding, as it has long been hypothesized that differences in cognition between populations and species evolve via natural selection, but the only previous evidence available was indirect, based on comparative studies,” said Pravosudov.
And Taylor agrees:

“It’s usually hard to measure traits in wild populations and relate those to natural selection,” he said. “This research expands the kinds of ways we can explore how natural selection operates in nature and then, ultimately, shapes the variation that we’re fascinated by.”
This National Science Foundation grant, which was recently funded, allows both labs to expand the study to even more chickadees both in the Sierra Nevada mountains—where the initial research was conducted—and at the Mountain Research Station, where more smart feeders will be installed.

While Taylor’s lab begins a genomic analysis of samples previously collected over seven years by Pravosudov’s lab to see if they can pinpoint the most important regions of the genome related to variation in spatial cognition in chickadees, Pravosudov’s lab will continue gathering results with the smart feeder arrays.

The new data, beyond just allowing the researchers to understand natural selection’s role broadly speaking, will also allow the researchers to look at the impacts of yearly variation in winter, with some years getting more snow than others.

Considering consistent trends in climate warming, the researchers think this study might provide insight into how such warming affects cognition and genetic variation within chickadees.

“This study provides a rather unique opportunity to investigate how variation in winter climate, which is likely the main driver of natural selection on spatial cognition in food-caching birds, can affect the strength of selection, cognitive abilities, as well as genetic variation underlying these abilities across different montane environments over multiple years,” said Pravosudov.

Beyond just collecting and analyzing the data, Pravosudov and Taylor also plan on conducting public outreach related to the research by establishing the feeders in easily visible areas and creating materials aimed at K–12 audiences talking about the trait and why it’s important. The grant will also allow them to bring on additional research opportunities for undergraduates, graduate students and postdocs.

“I think this grant is going to help our research expand in a new and exciting direction,” said Taylor.

Republished with permission from the Colorado Arts and Sciences Magazine.