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Protistology Biodiversity Patterns in Protozoan Communities: Linking

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Protistology Biodiversity Patterns in Protozoan Communities: Linking Protistology Protistology 5 (4), 268–280 (2008) Biodiversity patterns in protozoan communities: linking processes and scales 1 Yuri Mazei Department of Zoology and Ecology, V.G. Belinsky State Pedagogical University, Penza, Russia Summary One of the general questions in ecology is how patterns of species diversity change across spa- tial scales. In this study additive partitioning methodology, which allows estimating relative contributions of alpha and beta diversity components to total diversity, was applied to data on protozoan (heterotrophic flagellates and testate amoebae) communities from sphagnum bogs collected from a nested design consisting of five hierarchical levels. It allowed evaluating addi- tive diversity partitioning on four spatial scales: 1) the Russian plain vs. ecoregions, 2) ecore- gions vs. ecosystems, 3) ecosystems vs. sites, and 4) sites vs. samples. A significant percentage of total species richness was attributed to beta diversity between ecoregions and among ecosys- tems (different bogs) within ecoregions. Protozoan communities seem to be alpha-dominant at the broadest spatial scale and beta-dominant at finer scales. A switch in relative dominance from beta to alpha diversity with increasing spatial scale suggests scale transitions in ecological processes. This pattern is likely to be a result of different processes operating at different scales. At fine scales protozoan species interact directly, and niche partitioning is the strongest deter- minant of diversity, which results in differences between local communities. At broader spatial scales, where processes such as dispersal and colonization–extinction dynamics structure the communities, these interactions are probably not evident. Keywords: biodiversity patterns, additive biodiversity partitioning, alpha-diversity, beta-di- versity, gamma-diversity, scale, microbial ecology, protozoa, heterotrophic flagellates, testate amoebae Introduction and evolutionary change in shaping the structure of ecological communities (Green et al., 2004). A central goal of ecology is to understand how Although spatial patterns have been documented biodiversity is generated and maintained. Spatial in many studies of plant and animal diversity, such patterns of species diversity provide information patterns are not as well documented in microbial about the mechanisms that regulate biodiversity at species, i.e. those of Bacteria, Archaea, and micro- different scales (Levin, 1992; Gaston and Blackburn, scopic Eukarya (Green and Bohannan, 2006). This 2000; Hillebrand and Blenckner, 2002; Brown et al., is a serious omission given that microorganisms 2002). For instance, these patterns can offer valuable could comprise much of the biodiversity on Earth clues to the relative influence of dispersal limitation, (Foissner, 1999; Torsvik et al., 2002) and have crucial environmental heterogeneity, and environmental roles in biogeochemical cycling and ecosystem func- 1 Materials presented on the V European Congress of Protistology (July 23–27, 2007, St. Petersburg, Russia). © 2008 by Russia, Protistology Protistology • 269 tioning (Gilbert et al., 1998; Morin and McGrady- scales of analysis it is often expressed as indices that Steed, 2004). weigh both the richness and equitability (evenness There are some reasons for our lack of understand- of abundance across species) of a sample. Moreover, ing of the scaling of microbial diversity. Conceptually, some authors, in order to distinguish and underline it is assumed that microbes are different biologically certain spatial scale, have adopted the term species from other forms of life so that their biodiversity density for the number of species sampled in a stan- scales in a fundamentally different way (Azovsky, dardized sample unit, e.g. per unit area (Whittaker, 1996, 2000, 2002; Finlay et al., 1996, 1996a, 1999, 1975; Lomolino, 2001). Others have used this proto- 2004; Fenchel et al., 1997; Finlay, 1998, 2002; Finlay col, i.e. holding area constant, but retain the terms and Esteban, 1998; Finlay and Clarke, 1999; Finlay diversity or richness rather than density (O'Brien, and Fenchel, 1999, 2004; Hillebrandt and Azovsky, 1993; Fraser, 1998). 2001; Fenchel and Finlay, 2004, 2005). On the other Species richness is the simplest and the most hand, some of the recent research has challenged this frequently used diversity measure. However, spe- conception, providing evidence of microbial ende- cies-richness assessments are notoriously sensitive mism (Whittaker et al., 2003; Foissner, 2004, 2006; to scale, due to the species–area relationship (Palmer Mitchell and Meisterfeld, 2005), and also of a spatial and White, 1994; Veech, 2000), and to sampling ef- patterning of microbial biodiversity (Chernov, 1993; fort, due to the difficulty of obtaining complete spe- Wilkinson, 1994, 2001; Green et al., 2004; Noguez et cies lists (Palmer, 1995). The two problems are closely al., 2005; Bell et al., 2005; Smith et al., 2005) that is related: the number of the species observed generally similar qualitatively to that of plants and animals. increases with the number of individuals sampled, So, the question remains open. A reasoning that and the number of individuals increases with the could reconcile different views is that, since process- size of the sampling unit (Lu et al., 2007). Thus, an es that produce biological diversities operate differ- important starting point in analyzing spatial pat- ently and at different rates according to the position terns in richness is to control the area: a step that is of the biological phenomena along the scales of space very often ignored or fudged in analysis, especially at and time, many theories and paradigms are prob- coarser scales (Whittaker et al., 2001). ably more complementary than conflicting (Blondel, In order to consider scale in assessment of species 1987). diversity, Whittaker (1960, 1975) proposed scale-de- Here, I aimed to reveal spatial scaling of biodi- pendent species diversity terms. First, he designat- versity patterns in different types of protozoan com- ed inventory diversity, or simply richness, assessed munities from different biotopes using original data at four scales: (1) point scale (2) alpha (3) gamma collected within the European part of Russia. To dis- (landscape), and (4) epsilon (regional). Secondly, he cover the way in which total species diversity is parti- described a separate phenomenon, compositional tioned into the alpha and beta components on differ- turnover. This he termed differentiation diversity, ent spatial scales, the additive partitioning methodol- identifying three scales: (1) internal beta or pattern ogy was applied (Lande, 1996; Loreau, 2000; Wagner diversity, lying between the inventory scales of point et al., 2000; Gering, Crist, 2002; Veech et al., 2002; Lu and alpha; (2) beta diversity, between alpha and et al., 2007). This approach allows linking biodiver- gamma scales, and (3) geographical differentiation sity patterns with scales and processes operating at or delta diversity, between gamma and epsilon scales. different scales (Whittaker et al., 2001). He thus subdivided diversity into seven categories in total. However, this scheme has not been widely ad- Background opted because of a limited number of scales. Most of the authors currently referring to the framework fol- Species diversity and scale low, in practice, the version proposed by Cody (1975). There is a general agreement over the terms alpha and Measuring species diversity is critical for eco- beta in the two schemes. However, Cody’s gamma logical research and biodiversity conservation. In scale was intended to apply to the inventory diversity the ecological literature, many measures have been (species richness) of a whole landscape. Others ad- proposed to assess species diversity based on data opted his scheme, but generally took gamma diversi- on presence or abundance of species (Pielou, 1975; ty to refer to areas of different scales, perhaps because Magurran, 1988). Accordingly, a lot of terms have Whittaker initially set no upper bound to the term. arose. The term species richness is used for the num- What actual spatial scales do the terms alpha, ber of species in a sample. Species diversity is com- beta, gamma translate to? Given that different taxa monly used interchangeably for richness, but at local of terrestrial and aquatic creatures differ by many or- 270 • Yuri Mazei ders of magnitude in body size, it is evident that the spatial scales at which alpha, beta and gamma should be operationalized can vary between taxa (Burkovsky et al., 1994; Azovsky, 2000, 2002; Whittaker et al., 2001). The precise scale chosen is often a matter of convenience relating to the scale at which species have been mapped (Linder, 1991). I favor (in the same way as O'Brien et al., 2000 and Whittaker et al., 2001) the use of the more intuitive (and intentionally im- precise) terms local-scale (micro-scale), landscape- scale (meso-scale), regional-scale (macro-scale), and geographical-scale (mega-scale). However, the dis- tinction made by Whittaker (1977) between inven- tory and differentiation diversity is an important and useful one, as is the recognition that each of these concepts can be applied at different scales of analy- sis. Additive diversity partitioning Although the hierarchical concept of diversity has a strong conceptual meaning for ecologists, it has lacked until recently the mathematical proper- Fig. 1. Theadditivepartitioningoftotaldiversityintoalphaand ties to make it useful in empirical or experimental beta components
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