Morphological diversity and community organization of desert anurans Christopher M. Schalk * , Carmen G. Monta ~ na 1 , Laura Springer 2 Biodiversity Research and Teaching Collections, Department of Wildlife and Fisheries Sciences, Texas A&M University, College Station, TX, USA article info Article history: Received 11 December 2014 Received in revised form 20 May 2015 Accepted 29 June 2015 Available online xxx Keywords: Amphibian Assembly rules Community structure Ecomorphology Environmental filtering Null model abstract Morphological approaches have been used extensively to understand assembly rules (species in- teractions, environmental filtering, and neutral processes) that structure ecological communities. Desert anurans cope with limited water by either being restricted to permanent water or becoming more fossorial, which should be reflected in their morphology. We examined morphological diversity of 16 frog species across six habitat types within the Chihuahuan Desert to investigate the relationship between species richness and morphological space. We measured 13 morphological traits associated with loco- motion, habitat use, and feeding. Principal components analysis separated species into three ecomor- phological groups: fossorial, terrestrial, and semi-aquatic species. Morphological diversity was analyzed and compared against a null model and revealed nonrandom community structure. The total assemblage morphospace increased in relation to species richness, though this relationship was not significant. Species were significantly packed within the morphospace exhibiting high morphological similarity while being less evenly dispersed, with increasing species richness, indicative of a response to an environmental gradient. Given the highly xeric nature of the Chihuahuan Desert, our results support the assumption that environmental filtering, rather than interspecific interactions, shapes assemblages' structure by favoring species with similar traits to co-occur more often within a given habitat type than expected by chance. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Ecological communities are structured as the result of the interaction between local and regional processes as well as biogeographical constraints (Ricklefs, 1987; Ricklefs and Schluter, 1993). Regional processes, such as abiotic factors, and the con- straints set by historical biogeography tend to exert stronger in- fluence at broad spatial scales, whereas local processes such as habitat heterogeneity, species interactions, and productivity exert greater influence on community structure at smaller spatial scales (Ricklefs and Schluter, 1993; Monta~ na et al., 2014). The roles these processes have in structuring a community can be inferred by studying the structure of species assemblages and the functional organization of species in relation to one another (Mouillot et al., 2007). In particular, functional organization on a trait-based approach has emerged as an important aspect to understanding community assembly rules and community functioning (Adler et al., 2013). Many processes influence patterns of species richness and community structure at each spatial scale, but three main assembly rules have been proposed to explain these patterns: species in- teractions, environmental filtering, and neutral processes (Mouchet et al., 2013). Species richness and community structure can be influenced by biotic interactions via the principles of limiting similarity (MacArthur and Levins, 1967) and competitive exclusion (Hardin, 1960), with the underlying assumptions being that species are in competition with one another, that each niche is occupied by the competitively dominant species and that species possessing similar functional traits are unable to co-occur. Coexistence is promoted by assemblages of species possessing characteristics (i.e., functional traits) that are more dissimilar in relation to one another via complementarity or trait overdispersion. With the process of environmental filtering, abiotic factors sort species possessing * Corresponding author. E-mail address: cschalk@tamu.edu (C.M. Schalk). 1 Present Address: Department of Applied Ecology, North Carolina State Univer- sity, Raleigh, NC, USA. 2 Present Address: Department of Biology, Stephen F. Austin State University, Nacogdoches, TX, USA. Contents lists available at ScienceDirect Journal of Arid Environments journal homepage: www.elsevier.com/locate/jaridenv http://dx.doi.org/10.1016/j.jaridenv.2015.06.019 0140-1963/© 2015 Elsevier Ltd. All rights reserved. Journal of Arid Environments 122 (2015) 132e140