Diversity and abundance

We use experimentation and observation to address questions related to the roles of abiotic and biotic factors in variation in diversity and abundance through space and time. This work has focused mainly on tundra plant community composition and dynamics at a long-term study site near Kangerlussuaq, Greenland, where we have been running an herbivore exclusion and warming experiment since 2003.

Additionally, we are interested in the roles of abiotic (i.e., climatic) and biotic (i.e., density dependent) factors in the population dynamics of large herbivores, especially caribou and muskoxen. We also use large data sets to examine response diversity in the population dynamics of large herbivores to climatic variation across species’ distributions.

Representative recent publications:

Large herbivore diversity slows sea ice–associated decline in arctic tundra diversity, 2023, Science 380 (6651), 1282-1287

Large herbivores facilitate the persistence of rare taxa under tundra warming, 2022, Scientific Reports 12, 1292

Contrasting dynamical responses of sympatric caribou and muskoxen to winter weather and earlier spring green-up in the Arctic, 2021, Food Webs 27, e00196

Phenology and life history variation

We combine experimentation, observation, and analytical modeling to investigate species-specific and community-level patterns of variation in phenology. Much of this work, also conducted at the long-term study site near Kangerlussuaq, Greenland, focuses mainly on factors influencing the timing of expression of life history traits related to seasonal growth onset and flowering in tundra plants; timing of migratory arrival and offspring production by caribou; and phenological interactions between plants and large herbivores, including both caribou and muskoxen. Additional recent work on this topic has focused on critically endangered Sierra Nevada bighorn sheep in California.

Representative recent publications:

Fine-scale landscape phenology revealed through time-lapse imagery: implications for conservation and management of an endangered migratory herbivore, 2023, Remote Sensing in Ecology and Conservation 1 (10.1002/rse2.331)

Demographic consequences of phenological shifts in response to climate change, 2021, Annual Review of Ecology, Evolution, and Systematics 52, 221-245

The nature of time in ecology

In ecology, time is traditionally treated as a niche axis along which organisms avoid competition and exploitation. My most recent work, deriving from a long-standing interest in phenology, is focused on the development and application of conceptual models that promote an understanding of the role of time in the evolution of life history strategies related to growth, maintenance, and offspring production.

Representative recent publications:

Weak coupling between energetic status and the timing of reproduction in an Arctic ungulate. Scientific Reports, 2024.

Seasonal timing on a cyclical Earth: Towards a theoretical framework for the evolution of phenology, 2022, PLoS Biology 20 (12), e3001952

Time in Ecology – a Theoretical Framework, 2019, Princeton University Press

From Chapter 9, “The more general role of time in ecology”, Time in Ecology (2019).