Figure 2.

Assumptions and their implications when extending the population-level notion of logistic growth to species-level logistic growth. Left: phylogenetic/single-clade approach. (a) Simple scaling up of population level logistic growth makes some assumptions that are unrealistic when viewing evolution in deep time. (b) Relaxing the assumption of a fixed carrying capacity renders the phylogenetic approach more reasonable, and allows for a role for diversity dependence even if non-equilibrial processes dominate. Right: whole biota approach. (c) This approach makes some simple assumptions that are valid on short timescales. (d) To use the approach on longer timescales, it is necessary to include speciation as a relevant process. (e) Palaeontologists have co-opted the whole biota island biogeography approach, where the whole Earth is viewed as an island. In addition, they have used it hierarchically. In both approaches, the use of a logistic formulation becomes more reasonable once one incorporates the idea that the carrying capacity might change through time.