Kristin Davis Uncovers Nuanced Songbird Population Responses Between North America & Europe
Our ability to predict how any given species will respond to the environmental changes that are happening in our world - like extreme temperatures and drought - hinges on a fundamental ecological assumption: the niche conservatism hypothesis. This hypothesis posits that a species' ecological niche, or the set of environmental conditions where individuals can survive and reproduce, remains stable over space and time. But is that assumption too simplistic?
Modeling Abundance Data Reveals Niche Differences Within Conserved Boundaries
Kristin Davis, DSE postdoctoral researcher, is the lead author on a new paper in Diversity and Distributions that challenges the niche conservatism hypothesis. The study explored whether two songbirds, the European starling (Sturnus vulgaris) and the house sparrow (Passer domesticus), exhibited niche conservatism between their native distributions in Europe and their non-native distributions in North America.
Species Studied
Left: European starling (Becky Matsubara). Right: house sparrow (Imran Shah).
Kristin synthesized over 400,000 observations of these species collected over 22 years (between 1997–2018) across 28 countries in North America and Europe. To test for niche conservatism, she and her collaborators analyzed these data using two approaches:
🐦An ordination analysis where the abundance data was reduced to presence / absence to quantify change in niche shape and boundaries between the continents, which is the standard approach for quantifying species’ niches, and
🐦Generalized linear mixed effects models to quantify whether the species’ abundance varied with climate and land cover variables representing the species’ habitat (e.g. grassland, urban areas) differently across continents.
The team’s ordination analysis based on niche shape / position indicated that both species’ ecological niches remained stable during this time period between Europe and North America, thus exhibiting niche conservatism. Interestingly, however, abundance models revealed differences in how the species responded to temperature and land cover between the continents, which suggests a lack of niche conservatism. For example, house sparrow abundance increased more with grassland in its native distribution in Europe versus its non-native distribution in North America. In addition, the abundance data revealed that European starlings and house sparrows occupied wetter areas in Europe, but did not occupy similarly wet areas in North America - a phenomenon known as “niche unfilling.”
Bridging Continents and Data Availability
This research, which formed a core part of Kristin’s dissertation, was a complex undertaking that built from the incredible effort of volunteers, scientists, and governments that have sustained long-running continental bird monitoring programs. Kristin collaborated with international scientists and / or monitoring program coordinators from the Pan-European Common Bird Monitoring Scheme (PECBMS), which was the source of the European bird data in the study - particularly Dr. Henning Heldbjerg (Aarhus University, Denmark) and Dr. Henrik Smith (Lund University, Sweden), who provided expertise on the species in their native range, and Dr. Anna Gamero (research officer, Czech Society for Ornithology), who provided expertise on the PECBMS data.
Receiving access to the European bird abundance data was a testament to international collaboration, with national coordinators from roughly 25 European countries generously giving permission to use their data. The study also relied on data from the North American Breeding Bird Survey, a long-term effort in which volunteers collect and U.S. federal scientists process and make publicly available annual data on bird abundance across North America. Compiling and modeling the data for this study required careful work to account for differences in sampling design and monitoring protocols across countries, which strengthened Kristin’s data science skills and enabled the comparison of species’ abundance responses across entire continents.
Expanding Future Modeling Efforts Under Global Environmental Change
Kristin’s research demonstrates the limits of solely investigating species’ niche boundaries, and provides a critical framework for future models aimed at assessing invasion risk or sensitivity to ongoing global change.
“To improve assessments and predictions of species’ invasion risk or sensitivity to global environmental change, I hope to see the study of niche conservatism continue to expand to explore changes at both the edges of and within niche boundaries,” Kristin said.
