Seasonality in ecology: Progress and prospects in theory

Seasonality is an important feature of essentially all natural systems but the consequences of seasonality have been vastly underappreciated. Early work emphasized the role of seasonality in driving cyclic population dynamics, but the consequences of seasonality for ecological processes are far broader. In ecological systems, seasonality may include variations in temperature, precipitation, or other processes. Seasonality is typically not explicitly included in either empirical or theoretical studies. However, many aspects of ecological dynamics can only be understood when seasonality is included, ranging from the oscillations in the incidence of childhood diseases to the coexistence of species. Further, studies of phenology and global climate change only make sense in the context of seasonal dynamics. Our goal is to outline what is now known about seasonality and to set the stage for future efforts. We review the effects of seasonality on ecological systems in both laboratory and field settings. We then discuss approaches for incorporating seasonality in mathematical models, including Floquet theory. We argue, however, that these tools are still limited in scope and more approaches need to be developed. We demonstrate the range of impacts of seasonality on ecological systems and show the necessity of incorporating seasonality to understand ecological dynamics.