Poster, 5th International conference of the International Biogeography Society, Irakleio, Crete, Greece: 07.01.2011 - 11.01.2011
I will I) demonstrate limitations of distance-decay studies and II) show a possible application. The relationship between geographic distance and similarity in species composition is regularly used as a measure of species turnover and beta diversity. Distance-decay analyses are applied, cited and compared over several spatial scales. In addition different sized plots (like islands or states) are regularly used within such analyses, implicitly assuming that the distance-decay relation is independent from plot size. I use an artificial one dimensional "landscape" to show that the slope and goodness of fit measure R2 of the distance-decay relationship is influenced by plot size and extent of the study. A comparison between different studies must thus be done with caution or be restricted to those cases where sampling scale and pattern is constant. I illustrate such an example by comparing the distance-decay relation of an area dominated by agriculture in southern Germany with a nearby semi-natural military training area that is not exposed to agricultural use. While distance decay is still present in the semi-natural area, no distance decay was found in the agricultural area in close proximity. It is likely that the human disturbance regimes in the agricultural landscape dominates over niche processes as a driver of beta-diversity.