Olivier, Pieter IgnatiusRolo, VictorVan Aarde, Rudi J.2017-08-102017-08-102017-04-04Olivier PI, Rolo V, van Aarde RJ (2017) Pattern or process? Evaluating the peninsula effect as a determinant of species richness in coastal dune forests. PLoS ONE 12(4): e0173694. https:// DOI.org/ 10.1371/journal.pone.0173694.1932-620310.1371/journal.pone.0173694http://hdl.handle.net/2263/61619S1 Dataset. This file contains the data from the article ªPattern or process? Evaluating the peninsula effect as a determinant of species richness in coastal dune forestsº by Pieter I. Olivier, Victor Rolo, and Rudi J. van Aarde.The peninsula effect predicts that the number of species should decline from the base of a peninsula to the tip. However, evidence for the peninsula effect is ambiguous, as different analytical methods, study taxa, and variations in local habitat or regional climatic conditions influence conclusions on its presence. We address this uncertainty by using two analytical methods to investigate the peninsula effect in three taxa that occupy different trophic levels: trees, millipedes, and birds. We surveyed 81 tree quadrants, 102 millipede transects, and 152 bird points within 150 km of coastal dune forest that resemble a habitat peninsula along the northeast coast of South Africa. We then used spatial (trend surface analyses) and nonspatial regressions (generalized linear mixed models) to test for the presence of the peninsula effect in each of the three taxa. We also used linear mixed models to test if climate (temperature and precipitation) and/or local habitat conditions (water availability associated with topography and landscape structural variables) could explain gradients in species richness. Non-spatial models suggest that the peninsula effect was present in all three taxa. However, spatial models indicated that only bird species richness declined from the peninsula base to the peninsula tip. Millipede species richness increased near the centre of the peninsula, while tree species richness increased near the tip. Local habitat conditions explained species richness patterns of birds and trees, but not of millipedes, regardless of model type. Our study highlights the idiosyncrasies associated with the peninsula effectÐconclusions on the presence of the peninsula effect depend on the analytical methods used and the taxon studied. The peninsula effect might therefore be better suited to describe a species richness pattern where the number of species decline from a broader habitat base to a narrow tip, rather than a process that drives species richness.en© 2017 Olivier et al. This is an open access article distributed under the terms of the Creative Commons Attribution License.BirdsTreesCoastal dune forestsPeninsula effectMillipedesSouth Africa (SA)Article