Microhabitat and niche separation in species of Ceratiomyxa Carlos Rojas 1 Department of Biological Sciences, University of Arkansas, Fayetteville, Arkansas 72701 Martin Schnittler Botanical Institute and Botanical Garden, Ernst-Moritz-Arndt University Greifswald, Greifswald, Germany Daniella Biffi Department of Biology, Universidad Ricardo Palma, Lima, Peru Steven L. Stephenson Department of Biological Sciences, University of Arkansas, Fayetteville, Arkansas 72701 Abstract: The eumycetozoan genus Ceratiomyxa ap- pears to have a cosmopolitan distribution, although two of the three macroscopic species within the genus have been reported only from tropical regions of the world. In theory these two tropical species might be expected to display more narrow niches than their cosmopolitan counterpart due to their specialization for tropical environments. However ecological data documenting niche separation in eumycetozoans are largely lacking. As part of several investigations carried out in the neotropics the ecology of the three macroscopic species of Ceratiomyxa was studied. The results from in situ measurements of environmental factors associated with their fructifications reveal a clear separation of niches between the two tropical species, which might be an indication of resource partitioning within the genus. As expected in theory the cosmopolitan C. fruticulosa shows the broadest niche of the three species. Moreover the niche overlap value between C. morchella and C. sphaer- osperma along with results from a multivariate CDA analysis seem to indicate that these two species are more specialized than C. fruticulosa. Key words: community ecology, eumycetozoans, neotropics, niche overlap, resource partitioning INTRODUCTION The eumycetozoans are a group of amoeboid protists (Fahrni et al 2003) whose life cycle includes the particular capacity to produce spores and spore- holding structures during reproductive stages (Alex- opoulos et al 1996). The three different taxonomic groups recognized for the eumycetozoans are the myxomycetes (plasmodial slime molds or myxogas- trids), the dictyostelids (cellular slime molds) and the protostelids (Adl et al 2005). Although genus Ceratiomyxa has been considered a protostelid slime mold (Olive 1970), most researchers treat it as a myxomycete (e.g. Tran et al 2006, Stephenson et al 2008). In fact recent molecular analyses suggest that there is strong support showing that the genus is a sister group of the myxomycetes and not of the protostelids (Fiore-Donno et al 2007). Of note, three out of the four species making up the genus have a macroscopic habit and resemble myxomycetes both morphologically and ecologically. Although genus Ceratiomyxa is widely distributed, only the most common species C. fruticulosa has a cosmopolitan distribution. The other two macroscop- ic species appear to be restricted to the tropics (Stephenson et al 2008), where they also seem to be less abundant than C. fruticulosa. A high degree of specialization has been documented in C. sphaeros- perma (Novozhilov et al 2001); however a proper niche analysis for all macroscopic species in the genus has not yet been carried out. In fact there have been few previous studies of this type for any species of eumycetozoans (e.g. Stephenson 1988, Schnittler 2001). The problem inherent in doing such an analysis is that without sufficient ecological informa- tion about the species it is hard to construct an adequate experimental design to evaluate these aspects. In the past most studies involving Ceratiomyxa have had a strictly taxonomic approach (Olive 1970, Olive and Stoianovitch 1979, Scheetz et al 1980), with no real considerations of ecology. However the increas- ing number of biogeographical studies of myxomyce- tes over the past decade (reviewed in Stephenson et al 2004b) has provided evidence that the three macro- scopic species have different geographical distribu- tions, both at the world and at the ecosystem level. The differences in distribution noted for closely related organisms presumably result from differential responses to intrinsic ecological properties such as their ability to colonize particular substrates or utilize different resources available in their immediate environment. When this phenomenon occurs it often is hypothesized that there is a higher niche overlap in species that are closely related phylogenetically (e.g. intrageneric taxa) than in less closely related species (Morin 1999). Unfortunately the effect of biotic Accepted for publication 5 August 2008. 1 Corresponding author. E-mail: crojas@uark.edu Mycologia, 100(6), 2008, pp. 843–850. DOI: 10.3852/07-197 # 2008 by The Mycological Society of America, Lawrence, KS 66044-8897 843