February 23, 2016
Thanks to Reid Rumelt for this guest student blog post. Reid explains how the “Allee effect” contributes to understanding the spread of invasive species such as the House Finch in the East.
FeederWatchers delight in the diversity of birds at their feeders and are excited to add a new species to their count list. However, depending where you live, some of the birds you see at your feeders are more recent additions to the local bird community. Over the past 100 years or so, birds like House Sparrows, European Starlings, and House Finches have experienced massive range expansions in North America, moving into areas where they did not historically occur, and are deservedly referred to as “invasive species.” Often when invasive bird species colonize an area, they compete with native bird species for resources such as food and nesting locations. As a result, understanding how invasive bird species spread is an important research topic for ornithologists in North America and worldwide.
To better understand how invasive species spread, scientists from the University of Washington and the University of Utah took a mathematical approach to model the proliferation of the House Finch in eastern North America. The House Finch is native to western North America but was introduced to Long Island in the 1940s and effectively expanded its range to the rest of the eastern United States and southern Canada. Using information on the pattern of House Finch spread obtained from bird banding stations in eastern North America, their model suggests that House Finch populations increase slowly immediately after colonizing an area, then more rapidly as time goes on. The scientists suggest that an initial struggle to find mates in a newly colonized area, called the Allee effect, may have been responsible for this pattern.
While the House Finch invasion has pretty much run its course, today’s high level of international trade and travel means the potential for new bird species to escape and proliferate in North America in the future remains high. The introduction and rapid spread of Eurasian Collared-Doves over the last two decades is a good example. (Read more about Eurasian Collared-Doves on the FeederWatch blog.) Scientists hope that by understanding the population dynamics of invasive species, they can limit their dispersal and concurrent ecological damage. However, despite their best efforts, the birds at your feeder today may be joined by other newer arrivals in the coming decades.
Veit, R. R., & Lewis, M. A. 1996. Dispersal, population growth, and the Allee Effect: Dynamics of the House Finch invasion of eastern North America. The American Naturalist, 148: 255–274.
Reid Rumelt is a senior in Cornell University’s College of Agriculture and Life Sciences. He is passionate about applying his interests in computer science and analytical biology to pressing questions in ecology and conservation. His interests have led to his participation in a number of citizen science initiatives, including eMammal and the Encyclopedia of Life project at the Smithsonian Institution, as well as eBird, Merlin, and the Macaulay Library at the Cornell Lab of Ornithology.