This week we turned our discussion to the topic of ecological niches. That is, we discussed the variety of ways that a species’ ecological niche could be defined from its environmental tolerances, to the species interactions, to an n-dimensional hypervolume. We also discussed the concept of an “empty niche” and its role in speciation and invasion.
For our classic paper we read “Concluding Remarks” by G.E. Hutchinson,1 which he wrote to summarize the new ideas and thoughts from a recent Symposium on populations and demography. Hutchinson describes his quantitative approach to understanding niche theory, as pulling out the metaphorical vacuum cleaner to synthesize the “irrelevant litter” that has accumulated around niche theory. He starts by arguing that the applicability (or lack of) to human demography is not a reflection of a flaw in the theory, but instead demonstrates that we are not considering it on the right time scale or asking the right questions. He then uses an example of amphipods that don’t exist in seemingly suitable habitat to argue that the “suitable habitat” is based on our understanding and perception of the environment, which differs considerably from that of an amphipod species. Our discussion of this long-winded paper ultimately led us to consider how variation in space/time can contribute significantly to the maintenance of species diversity.
We turned next to discuss the Sahney et al.2 and the concept of the empty niche contributing to the explosion of biodiversity with the expansion of species to terrestrial environments. Sahney used body size, diet and habitat to explore the potential modes of life that species could fill. The modes of life in some ways are similar to Hutchinson’s n-dimensional cube with 3 specific dimensions. In this case, Sahney argued that when species moved from sea to land there were countless niches waiting to be filled, which contributed to the rapid speciation and expansion of tetrapods. They also suggested that 64% of the terrestrial “modes of life” have yet to be filled and that tetrapod diversity may continue to increase as those modes are filled. While this suggestion will ultimately be difficult to verify, it seems plausible that empty niches may still play a vital role in understanding biodiversity.
Understanding the role of empty niche space can also help us better understand the vulnerability of systems to invasion. Recent anthropogenic disturbances to environments have led to major disruptions to ecosystems through both the extirpation of existing species and the introduction of novel players. These disruptions can lead to unexpected consequences like invader meltdown and community collapse. For that reason taking into account the amount of empty niche space in a habitat may help inform management decisions.
References:
- Hutchinson, G. E. Concluding Remarks. 117, 1937–1938 (1975).
- Sahney, S., Benton, M. J. & Ferry, P. A. Links between global taxonomic diversity , ecological diversity and the expansion of vertebrates on land. Biol. Lett. 6, 544–547 (2010).