Ecological models of environmental change

21 Jul 2016. NUS researchers develop a new theory which captures the dramatic fluctuations in species population abundances often observed in nature.

Species in ecosystems worldwide exhibit striking changes in population abundances over time. For example, in Panama, the tropical tree species Inga marginata nearly doubled its population from 2005 to 2010. How do such dynamic upheavals emerge?

Prof Ryan CHISHOLM and Dr Tak FUNG, both from the Department of Biological Sciences in NUS, together with researchers from the Forest Research Institute Malaysia (FRIM) and the University of Illinois postulated that this intriguing pattern is caused by species being regularly buffeted by a multitude of random environmental factors. The research team verified their hypothesis by applying a mathematical model to decadal census data from two tropical forests.

In recent decades, the “Unified Neutral Theory of Biodiversity” has emerged as a simple, elegant explanation of patterns observed in nature. This leading theory posits that species are ecologically the same, with species diversity being maintained by a balance between random events that act on individual organisms – dispersal, birth and death. This theory produces accurate “static” snapshots of nature, but it greatly underestimates changes over time, such as the big increase in the population abundance of Inga marginata in Panama. The challenge is to develop a theory that captures both the static patterns and dynamic fluctuations.

Inspired by observations of species being subjected to environmental forces such as fires and floods, the research team developed a new mathematical model that incorporates random environmental events, which affect all individuals of a species, in addition to random events which act on individuals. The environmental variation was found to be crucial in allowing the model to produce the observed dynamic and static patterns of biodiversity in two tropical forests, located in Panama and Peninsular Malaysia. This model can be used as a basis for studying the effects of future environmental change on biodiversity, which is particularly important for conservation and sustainable management.

Presently, the new model represents the effects of random environmental events indirectly via changes in species population abundances. This can be expanded to incorporate a more explicit representation of the processes by which such events affect species population abundances, especially given the recent availability of large datasets on climatic and other environmental variables. The model could also be applied to other ecosystems (e.g., coral reefs) to further test the generality of the underlying mechanisms.

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Figure shows a scene of a wildfire, which is a common environmental disturbance in tropical forests. [Source: Wikimedia Commons].



Fung T, O’Dwyer JP, Rahman KA, Fletcher CD, Chisholm RA. “Reproducing static and dynamic biodiversity patterns in tropical forests: the critical role of environmental variance.” Ecology. 97 (2016) 1207-1217.