Myrmecological News 20 15-23 Online Earlier, for print 2014 * This paper is dedicated to the memory of Elisabeth K.V. Kalko, to honour her dedication as an outstanding scientist and mentor. Niche-based processes and temporal variation of environment drive beta diversity of ants (Hymenoptera: Formicidae) in dryland ecosystems of Iran * Omid PAKNIA & Martin PFEIFFER Abstract Clarifying the mechanisms that determine diversity in communities is a key task in biodiversity conservation. Niche differentiation, dispersal limitation, and stochastic processes are possible causes of variation in community composition, or beta diversity. In this study we quantified variation in ant assemblages related to environmental and spatial factors. We used pitfall traps to sample ant assemblages across a ca. 1200 km transect through arid and semi-arid heterogeneous environments of Iran. We then applied these data to canonical analysis to disentangle the relative importance of environ- mental and spatial processes. A total of 69 species / morphospecies were collected along the North-South transect. Cataglyphis was the most speciose genus with 12 species, followed by Messor and Monomorium with ten and seven species, respectively. Our parsimonious environmental and spatial models jointly explained 62% of the variation in community composition of ants. Community composition was primarily controlled by environmental factors (45%). Vari- ation in ant species composition was driven by the amount of precipitation and also by its occurrence patterns. A large number of species were highly localized to a certain habitat. The overall findings suggest that mechanisms linked to environmental filtering and niche-based processes may be regulating beta diversity on ants in the Persian semi-deserts and deserts. Environmental factors appear also to control ant dispersal. Future conservation studies on insects should carefully take the temporal pattern of precipitation into account. Key words: Beta diversity, contemporary climate, dispersal, Iran, PCNM analysis, variation partitioning. Myrmecol. News 20: 15-23 (online xxx 2014) ISSN 1994-4136 (print), ISSN 1997-3500 (online) Received 18 April 2013; revision received 16 September 2013; accepted 25 October 2013 Subject Editor: Nicholas J. Gotelli Omid Paknia (contact author), University of Ulm, Institute for Experimental Ecology, Albert Einstein Allee 11, D-89069 Ulm, Germany; present address: Institute of Animal Ecology and Cell Biology, TiHo Hannover, D-30559 Hannover, Germany. E-mail: omid.paknia@ecolevol.de; omid.paknia@gmail.com Martin Pfeiffer University of Ulm, Institute for Experimental Ecology, Albert Einstein Allee 11, D-89069 Ulm, Germany; pre- sent address: National University of Mongolia, Department of Ecology, Baga toiruu 47, Ulaanbaatar 210646, Mongolia. Introduction Ant community ecologists have historically focused much of their efforts on studying factors and mechanisms related to variation in alpha diversity (e.g., SANDERS & al. 2003, DUNN & al. 2009, RYDER WILKIE & al. 2009). As a re- sult, we have a better knowledge about the drivers of alpha diversity than we do about beta diversity. Beta diversity in this context means variation in species composition among sites (ANDERSON & al. 2011). Beta diversity and the fac- tors that contribute to its variation have foundational roles in general ecological theory (e.g., RICKLEFS 1987) and key implications for effective conservation management (e.g., JOST & al. 2010, PAKNIA & PFEIFFER 2011a). A large body of studies, conducted on other organisms, has demons- trated that beta diversity is a niche-based process (e.g., BRAY & CURTIS 1957, JANKOWSKI & al. 2009). More spe- cifically, beta diversity is simultaneously regulated by ex- trinsic factors related to environmental conditions and geo- graphy such as climate variables and geographical posi- tion and by intrinsic features related to species' traits such as body size (see SOININEN & al. 2007 for a review). An alternative theory proposes that beta diversity is the result of spatial processes. The neutral view of community com- position postulates that all species in local communities are effectively equivalent. Regarding the changes in com- munity composition, this latter view grants primacy to spa- tial factors, namely dispersal limitation (HUBBELL 2001). Limited dispersal among local communities will tend to cause community similarity to be inversely associated with spatial distance. Consequently, one major prediction of this theory is a smooth decay in community similarity with dis- tance due to dispersal limitation of species. It is unlikely that ecological communities are strictly niche-based or strictly dispersal-based. Aspects of both processes likely operate simultaneously (see SIEPIELSKI & al. 2010). The important question is how the relative weights of these two processes differ in their contribution to com- munity assembly. Regarding the ants, quantifying the rela- tive contributions of environmental conditions and spatial factors to species composition can help to improve our un- derstanding of the drivers of ant beta diversity. A growing body of literature has evaluated the relative importance of these two driving forces by comparing the