Testing Generalities in the Shape of Patch Occupancy Frequency Distributions

Abstract

Abstract. Bimodal patch occupancy frequency distributions regularly appear in studies of a variety of taxa at a variety of spatial scales. Metapopulation models associated with the core-satellite hypothesis and a strong rescue effect predict the occurrence of this bimodality. However, there have been numerous other explanations, both artifactual and biological, of bimodality in patch occupancy frequency distributions. One approach to a better understanding of the phenomenon is to conduct studies on a variety of taxa and spatial scales. Here we examine patterns of patch occupancy frequency distributions for plants, dung beetles, and birds at four spatial scales in sand forest and mixed woodland in Tembe Elephant Park and Sileza Nature Reserve in South Africa. We then examine the predictions of each alternative mechanism proposed to explain bimodality with respect to the patterns found in this study. The incidence of bimodality was high. Little evidence was found for any of the artifactual or nonmetapopulation-based explanations of bimodality. Although there were no between-taxon differences in the shape of occupancy distributions, there was a clear trend of decreasing frequency of bimodality with an increase in the size of the area examined. The general shape of range-size frequency distributions in combination with an area effect is suggested as a mechanism underlying this pattern. Metapopulation dynamics associated with a strong rescue effect could also not be excluded as a possible mechanism playing a role in generating the bimodality found at the patch scale.

Marine ecosystem engineering by the alien ascidian Pyura praeputialis on a mid-intertidal rocky shore

“…For instance, Collins & Glenn (1997) demonstrated that such patterns depend on the aerial extent of the study (i.e. distance scaling; see van Rensburg et al 2000 for changes in species frequency distribution between patch types). This may also apply to patterns in species frequency distribution when comparing engineered and non-engineered habitats (hereafter referred to as habitat scaling).…”

A typing error in Tokeshi's test of bimodality

“…Unfortunately, at least three recent studies (Guo et al ., 2000;Van Rensburg et al ., 2000;Perelman et al ., 2001) have referred to the incorrect equation in Collins & Glenn (1997). Applying the correct equation to the data of Van Rensburg et al .…”

A spatial and temporal analysis of Sand Forest tree assemblages in Maputaland, South Africa

“…Sand Forest is part of the Tropical Dry Forest group, which is found in Maputaland (Licuati Sand Forest) and in some parts of the Kruger National Park in South Africa (Nwambyia Sand Forest) (Mucina & Rutherford 2006). The conservation of forests in South Africa is difficult because their distribution is patchy, and therefore large networks of interconnected patches are needed to conserve their species diversity and dynamics (Midgley et al 1990;Everard et al 1994;Everard et al 1995;Low & Rebelo 1998;Van Rensburg et al 2000b;Lawes et al 2004).…”

“…The phytogeographic affinities and similarities of Sand Forest with Afromontane and Coastal forests (Van Rensburg et al 1999;Matthews et al 2001) suggest that Sand Forest may be a relict of previous climatic conditions . Many authors agree that under the current climatic conditions, Sand Forest may be transformed into woodlands (Van Rensburg et al 1999;Van Rensburg et al 2000b;Botes et al 2006;.…”