Document: MEL-3-92-4

Multiple mechanism effects on the shape of patch-occupancy frequency distributions: Implications for their use as community descriptors.

MCGEOCH, M.A.*

University of Pretoria, Pretoria, 0002, South Africa ¹

Abstract:
A variety of both artifactual and biological mechanisms have been proposed to be responsible for the shape of empirically derived patch-occupancy frequency distributions. Although it is over 80 years since occupancy distributions were first constructed, the debate on the role of artifactual versus biological, as well as scaling, mechanisms in shaping them has not been adequately resolved. The combined effects of mechanisms underlying the shape of occupancy distributions have also never been addressed. Here, new hypotheses are proposed that address the interaction of mechanisms, and that involve assemblage, rather than species, characteristics. Although all new and previously proposed mechanisms need further testing, spatial scale and position were identified as the primary determinants of observed patterns in the shape of occupancy distributions. The combination and identity of mechanisms underlying the shape of occupancy distributions change with changes in these parameters. For example, rare species properties, environmental heterogeneity, range size distributions and position within the assemblage range are all likely to contribute across a range of spatial scales. In contrast, metapopulation dynamics will only play a role at semi-closed system scales. Approaches and tests to compensate for artifactual effects, and to separate the effects of potential mechanisms on the shape of occupancy distributions are suggested. However, the non-independence of many mechanisms makes the usefulness of occupancy distributions as descriptors of community distribution patterns questionable.

Keywords: species distributions, spatial scaling, core-satellite hypothesis, sampling artefacts, metapopulation dynamics

This abstract is being presented at: 11:30 AM in session:
Oral Session #39: Theoretical Ecology.