Climate Dipoles

Climatic Dipoles

Changes in climate often result in the appearance of unusually warm and dry conditions in one part of the world with cold and wet conditions thousands of miles away. These lasting and predictable fluctuations in temperature and rainfall are known as “climatic dipoles” and often emerge across years or decades. A well-known example of this phenomenon is El Nino, where wet conditions across the southern United States are associated with dry conditions to the north. Most ecological studies collect data at local or regional scales. As a result, the continental-scale effects of climatic dipoles on ecological and environmental processes are largely unexplored. Climatic dipoles may provide insight on important phenomena such as animal migrations, agricultural and forest productivity, insect outbreaks, and the emergence of diseases. This study will use long-term observations of bird movements from thousands of citizen scientists, decades of seed production records in trees, and animal population numbers collected throughout the National Ecological Observatory Network (NEON). The project will partner with and guide existing citizen science programs to better predict the effects of climate on animals and plants. Along with collaborators Jalene LaMontagne (DePaul) and Courtenay Strong (Utah), we are organizing “ecoclimatology” workshops to provide training to early-career scientists interested in both climate science as well as ecology.

The research poses a novel framework of methods applied for space-time pattern discovery, used by climate scientists to analyze variability, to identify climate-ecological dipoles across North America. The overarching hypothesis is that many ecological phenomena are entrained at continental scales by dipole modes of climate variability. Specific questions include: 1) do atmospheric circulations and climatic dipoles synchronize seed production in trees (known as masting) and avian irruptions at continental scales?; 2) do unique modes of climate variability affect the population dynamics for multiple taxa (seed-dependent birds, small mammals, and ticks) at disjunct NEON sites and across multiple time lags?; and 3) how might historic and future environmental change influence these climatic-ecological relationships? Analyzing three decades of data from Project FeederWatch and a recently compiled data set of tree masting at hundreds of sites, the research will explore the use of empirical orthogonal functions to understand climate variability impacting plant and animal communities during a time of rapid environmental change. Ecological observatory networks, such as NEON, and citizen science databases are increasingly rich in information. Employing these analytical approaches from climate science will represent a key advance for ecological research.

Masting and Avian Irruptions

Masting in white spruce begins with a heavy crop of green cones that turn brown later in the year. Photo by Jalene LaMontagne.
The late-season brown cones of a masting spruce is concentrated in the upper third of the tree. Photo by Jalene LaMontagneMasting in white spruce begins with a heavy crop of green cones that turn brown later in the year, with the heaviest concentration in the upper third of the tree. Photos by Jalene LaMontagne.

Resources in ecosystems are an important component of biotic interactions, fostering connections within and among trophic levels through exchange of energy and nutrients. Fruiting vegetation plays a critical functional role for both the producers and consumers of the seeding cycle, and the natural ebb and flow of these resources into the food web can both directly and indirectly create or perturb demographic waves in populations.

Masting is a unique phenomenon where plants produce seed at volumes well above the average annual output. It has been documented across many terrestrial taxa that range from graminoids to trees, with some species adhering to predictable cycles while others infrequently and erratically boom and bust. Spatial and temporal synchrony is a unique aspect of this phenomenon that amplifies the impact to ecosystems at both local and geographic scales.

White spruce is an ideal species to investigate drivers of masting events due to the irregular annual cycle of cone volumes. The inconsistent crops also offer the opportunity to examine how this pulsed resource may impact or even influence the movement patterns of irruptive seed-eating birds. Pine siskins (Spinus pinus) and red crossbills (Loxia curvirostra) may experience abrupt changes in their demography during masting years when adults can more successfully produce multiple clutches, ultimately leading to a mass departure of young birds the following year when there is collapse in seed resources across extensive spatial scales. This type of interaction can provide insight into the dynamics of boreal ecosystems, seeking a mechanistic understanding of how constituent species with highly variable resources function in the face of a rapidly changing climate.

Recent related publications

Strong, C., B. Zuckerberg, J. L. Betancourt, and W. D. Koenig. 2015. Climatic dipoles drive two principal modes of North American boreal bird irruption. Proceedings of the National Academy of Sciences, 112(21): E2795-E2802. Link