Reading group: towards unification

This is the second instalment of our fortnightly reading group blog series. This time, our group was led by Skip Woolley and we discussed the paper Towards a unification of unified theories of biodiversity by McGill 2010.

This is an interesting paper that identifies different community ecology theories that are generated by inherently different mechanisms, but in turn, generate very similar community ecology patterns. These patterns are: species-area relationships, a hollow shaped abundance curve (RAD) and distance-decay relationships (Fig. 1).


Figure 1. Intrinsic patterns in community ecology. a) Species-area relationship; b) Rank abundance distributions; and c) Distance-decay relationships.

A case is put forward by McGill (and others) that this generality can be used to unify these theories and establish a set of rules that are applicable to all these approaches and thus, can be taken as generality.

McGill settles on the rules:

  1. Individuals within a species are clumped together
  2. Abundance between species follows a hollow shaped curve
  3. Species are treated as independent and are placed without regard to other species.

As a group, we liked the summation of these approaches and the respective patterns they produce. Lending us to accept certain mathematical forms, the rules are shared in common across these approaches and thus can be taken as generality. Similar concepts have been applied to other fields of science and the concept has previously been discussed amongst our reading group (The common patterns of nature by Frank 2009).

We did feel that the unification of these theories was a slight stretch, and that a way forward would be to test under which conditions these rules stand up? For example, a number of our reading group participants are involved in modelling joint species distributions, so we felt that the assumption of species independence was not a requirement to generate the patterns. Given this, what would be the bare number of rules required to generate these patterns? One way to do this would be to start with a set of necessary starting conditions (for example, species interactions from a food web) and assess which patterns arise from these interactions.

We also felt a more interesting question was: what drives these patterns? Along these lines of reasoning, we discussed the idea that these patterns could be viewed as null models and further investigation via theoretical or empirical studies could help highlight deviations from these expected patterns. As a whole, we felt that understanding the cases where these rules breakdown would help us understand their underlying mechanisms. In this vein, McGill touches on a need to understand processes that drive richness and abundance patterns at the end of the paper. A better understanding on the processes that shape these patterns will help theoretical ecologists more accurately investigate the relationships between these theories, and have the added benefit of assisting applied ecologists in their efforts to manage biodiversity.

Until next time.

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