Original article Niche analysis and conservation of the orchids of east Macedonia (NE Greece) Spyros Tsiftsis a , Ioannis Tsiripidis a, *, Vassiliki Karagiannakidou a , Dimitrios Alifragis b a Department of Botany, School of Biology, Aristotle University of Thessaloniki, GR-54124 Thessaloniki, Greece b Department of Forestry and Natural Environment, Aristotle University of Thessaloniki, GR-54124 Thessaloniki, Greece article info Article history: Received 23 May 2007 Accepted 28 August 2007 Published online 22 October 2007 Keywords: Conservation Orchidaceae Outlying Mean Index Specialists Generalists abstract The orchid family is one of the largest in the flowering plant kingdom and includes a lot of rare, threatened or endangered species. The determination of plant species niche is consid- ered fundamental for their conservation. Two parameters closely related with species niche are niche marginality and breadth. The first parameter is a measure of how typical or atyp- ical a species niche is within an area, while the second is a measure of species tolerance. This study deals with niche analysis of the orchids of east Macedonia (NE Greece). Factors that are known to determine species distribution on a regional scale, such as altitude, aspect, habitat type, bedrock type and soil properties (acidity, organic matter, and phosphorus content) were used as explanatory variables. Geographical coordinates were also employed in order to explore spatial patterns in orchid distribution. Niche analysis was carried out using the Outlying Mean Index (OMI) analysis. Out of the total data of 55 taxa that were analyzed, 41 had a significant marginal niche compared with the average niche of the study area. Alti- tude, soil acidity and certain habitat types were found to be the most important factors in determining orchid distribution. Five different species groups were distinguished on the basis of their ecological preferences and niche breadth. Species niche marginality and breadth, the amplitude of their geographical distribution, the size of their populations and the rareness and conservation status of their habitats were taken into account in order to set conservation priorities for the orchids in the study area. The above characteristics com- bined with intuitive criteria (e.g. geographical distribution, endemicity) for the species with a small number of occurrences could form a sound basis for setting conservation priorities. ª 2007 Elsevier Masson SAS. All rights reserved. 1. Introduction Species’ distributions, as well as changes in these distribution patterns, are influenced by several factors (Hampe, 2004). Among these factors, macroclimate together with evolution- ary and migration history determine species distribution on broad geographical scales (Summerhayes, 1969; Currie, 1991; Huntley et al., 1995; Knollova ´ and Chytry ´ , 2004; Pearson et al., 2004; Tsiripidis et al., 2007). On a regional scale, factors such as the physical and the chemical properties of the soil, the distribution of suitable plant communities, physiographi- cal factors as well as disturbance regimes determine the dis- tribution of species (Bailey et al., 2002; Knollova ´ and Chytry ´, 2004; Tsiripidis et al., 2007). Niche theory (Hutchinson, 1957) is mainly concerned with the interactions between species, trade-offs in the utilization of resources among coexisting species and the range of environmental conditions in which a species can occur. An ecological niche as defined by * Corresponding author. Tel.: þ30 2310 998584; fax: þ30 2310 998295. E-mail address: tsiripid@bio.auth.gr (I. Tsiripidis). available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/actoec 1146-609X/$ – see front matter ª 2007 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.actao.2007.08.001 acta oecologica 33 (2008) 27–35