Occupancy frequency distribution

In macroecology and community ecology, an occupancy frequency distribution (OFD) is the distribution of the numbers of species occupying different numbers of areas.^[1] It was first reported in 1918 by the Danish botanist Christen C. Raunkiær in his study on plant communities. The OFD is also known as the species-range size distribution in literature.^[2][3]

Bimodality

A typical form of OFD is a

Other factors that have been proposed to be able to affect the shape of OFD include the degree of habitat heterogeneity,[10]^[11] species specificity,^[12] landscape productivity,^[13] position in the geographic range,^[14] species dispersal ability^[15] and the extinction–colonization dynamics.^[16]

Mechanisms

Three basic models have been proposed to explain the bimodality found in occupancy frequency distributions.

Sampling results

Random sampling of individuals from either

Core-satellite hypothesis

Bimodality may be generated by colonization-extinction metapopulation dynamics associated with a strong rescue effect.^[16][18] This model is appropriate to explain the range structure of a community that is influenced by metapopulation processes, such as dispersal and local extinction.^[19] However, it is not robust because the shape of the occupancy frequency distribution generated by this model is highly sensitive to species immigration and extinction parameters.^[7][20] The metapopulation model does also not explain scale dependence in the occupancy frequency distribution.

Occupancy probability transition

The third model that describes bimodality in the occupancy frequency distribution is based on the scaling pattern of occupancy under a self-similar assumption of species distributions (called the occupancy probability transition [OPT] model).^[21][22] The OPT model is based on Harte et al.'s bisection scheme^[23] (although not on their probability rule) and the recursion probability of occupancy at different scales. The OPT model has been shown to support two empirical observations:^[21]

1. That bimodality is prevalent in interspecific occupancy frequency distributions.
2. that the number of satellite species in the distribution increases towards finer scales.

The OPT model demonstrates that the sample grain of a study, sampling adequacy, and the distribution of species saturation coefficients (a measure of the fractal dimensionality of a species distribution) in a community are together largely able to explain the patterns commonly found in empirical occupancy distributions.

• Rank abundance curve

References