Seasonality is a fundamental component of the earth’s climate. Seasonality, and other forms of environmental variation, can play a major role in regulating biodiversity. Many places have such pronounced variability in seasonal conditions that they can favor entirely different communities and food webs during different parts of each year. Mediterranean streams are a prime example of this, often with complete community turnover (i.e. complete change in assemblages) between wet and dry seasons. Annual plants in deserts often share the same space between different seasons, with some species growing during winter-spring rains and others during summer rains. There are also many other adaptations that organisms have to capitalize on seasonality, such as migration, egg dormancy, and shifting food sources.
In a recent paper in Ecology, we show that understanding the role of seasonality is not complete without and understanding of how predictable the fluctuations are over time. For instance, for a habitat to support regularly repeating distinct communities between seasons from year to year, the seasonal fluctuations need to be repeatable over time. We developed a framework to quantify these aspects using a combination of wavelet analysis and information theory and tested this on rainfall data from sites at similar latitudes around the world, as well as stream invertebrate data from three locations spanning a seasonality-predictability gradient. As predicted, highly predictable seasonal environments (i.e. Mediterranean) promoted the highest level of temporal turnover in communities, with strong oscillations between community types between seasons. By contrast, unpredictable and aseasonal environments (i.e. New Zealand) led to communities that fluctuated somewhat randomly.
We hope that this quantitative framework will spark renewed interest in the role of seasonality in shaping temporal patterns in biodiversity, and open the door to new research examining the role of environmental predictability in conjunction with seasonality. Considering both aspects together will hopefully allow for a better prediction and management of biodiversity under global change. While mostly focused on seasonal timescales, the framework we presented can also provide tools for examining linkages between temporal fluctuations in the environment and biodiversity at a range of spatial and temporal scales. Go check it out.
Tonkin, J. D., M. T. Bogan, N. Bonada, B. Rios-Touma, and D. A. Lytle. 2017. Seasonality and predictability shape temporal species diversity. Ecology DOI:10.1002/ecy.1761.