Patterns in the structure of Asian and North American desert small mammal communities

Aim We compared assemblages of small mammal communities from three major de sert regions on two continents in the northern hemisphere. Our objective wa s to compare these with respect to three characteristics: (1) species richn ess and representation of trophic groups; (2) the degree to which these ass emblages exhibit nested community structure; and (3) the extent to which co mpetitive interactions appear to influence local community assembly. Location We studied small mammal communities from the deserts of North Amer ica (N = 201 sites) and two regions in Central Asia (the Gobi Desert (N = 9 7 sites) and the Turan Desert Region (N = 36 sites), including the Kara-Kum , Kyzyl-Kum, NE Daghestan, and extreme western Kazakhstan Deserts). Method To provide baseline data we characterized each desert region in term s of alpha, beta, and gamma diversity, and in terms of the distribution of taxa across trophic and locomotory groups. We evaluated nestedness of these communities using the Nestedness Temperature Calculator developed by Atmar & Patterson (1993, 1995), and we evaluated the role of competitive interac tions in community assembly and applied a null model of local assembly unde r varying degrees of competitive interaction (Kelt et al., 1995, 1996). Results All three desert regions have low alpha diversity and high beta div ersity. The total number of species in each region varied, being highest in North America, and lowest in the Turan Desert Region. The deserts studied all present evidence of significant nestedness, but the mechanism underlyin g this structure appears different in North American and Asia. In North Ame rica, simulations strongly implicate interspecific competition as a dominan t mechanism influencing community and assemblage structure. In contrast, da ta from Asian desert rodent communities suggest that these are not strongly influenced by competition; in fact, they have greater numbers of ecologica lly and morphologically similar species than expected. These results appear to reflect strong habitat selection, with positive associations among spec ies that share similar habitat requirements in these communities. Our analy ses support earlier reports suggesting that predation and abiotic forces ma y have greater influences on the assembly and organization of Asian desert rodent communities, whereas interspecific competition dominates assembly pr ocesses in North America. Additionally, we suggest that structuring mechani sms may be very different among the two Asian deserts studied. Gobi assembl ages appear structured by trophic and locomotory strategies. In contrast, T uran Desert Region assemblages appear to be randomly structured with respec t to locomotory strategies. When trophic and locomotory categories are comb ined, however, Turan species are positively and nonrandomly associated. Main conclusions Very different ecological dynamics evidently exist not onl y between these continents, but within them as well. These small mammal fau nas differ greatly in terms of community structure, but also appear to diff er in the underlying mechanisms by which communities are assembled. The und erlying role of history and geography are strongly implicated as central fe atures in understanding the evolution of mammalian faunas in different dese rts of the world.