Authors:Y. Zhang, K. Ma, M. Anand, W. Ye, and B. Fu
Alpha, beta, and gamma diversity are three fundamental biodiversity components in ecology, but most studies focus only on the scale issues of the alpha or gamma diversity component. The beta diversity component, which incorporates both alpha and gamma diversity components, is ideal for studying scale issues of diversity. We explore the scale dependency of beta diversity and scale relationship, both theoretically as well as by application to actual data sets. Our results showed that a power law exists for beta diversity-area (spatial grain or spatial extent) relationships, and that the parameters of the power law are dependent on the grain and extent for which the data are defined. Coarse grain size generates a steeper slope (scaling exponent z) with lower values of intercept (c), while a larger extent results in a reverse trend in both parameters. We also found that, for a given grain (with varying extent) or a given extent (with varying grain) the two parameters are themselves related by power laws. These findings are important because they are the first to simultaneously relate the various components of scale and diversity in a unified manner.
Plant community types and botanical composition of herbaceous and woody plants in the Borana lowlands were investigated by multivariate methods (TWINSPAN and DCA) based on 125 plots of size 20 m × 20 m sampled from three districts across different functional land use units. By TWINSPAN, eight plant communities were identified: (i) Acacia drepanolobium-Pennisetum mezianum, (ii) Bidens hildebrandtii-Chrysopogon aucheri, (iii) Chrysopogon aucheri-Commiphora africana, (iv) Cenchrus ciliaris-Chrysopogon aucheri, (v) Acacia bussei-Pennisetum mezianum, (vi) Commiphora erythraea-Sansevieria ehrenbergii, (vii) Acacia melliphera-Setaria verticillata, and (viii) Heterpogon contortus-Hildebrandtia obcordata. Characteristic species at the different levels of TWINSPAN divisions were identified. The Chrysopogon aucheri-Commiphora africana community had the highest beta (3.37) and gamma (131) diversity, whereas the Heterpogon contortus-Hldebrandtia obcordata community had the smallest beta (0.35) and gamma (23) diversity. The frequency of plant communities was positively and strongly correlated with beta and gamma diversity.
Authors:R. E. Lorenzón, A. H. Beltzer, P. M. Peltzer, A. L. Ronchi-Virgolini, M. Tittarelli, and P. Olguin
We studied spatial changes in species composition (i.e., beta diversity) of local assemblages of birds along ∼450 km of the Middle Paraná River, an extensive fluvial system of South America. Point counts were used to survey birds at 60 plots located in shrub swamps and marshes of the floodplain within four sites (15 plots per site). Two sites were surrounded by each of the two upland ecoregions. Beta diversity of bird assemblages was high and was more important than alpha diversity in shaping regional diversity (i.e., gamma diversity) of the fluvial system. Compositional changes were related to species turnover among plots, while nestedness dissimilarity was not important for shaping diversity patterns. Variation-partitioning analysis showed that local conditions (i.e., landscape composition within a radius of 200 m from the center of each plot) accounted for more spatial variation in assemblage composition than did location along the fluvial system. Adjacent upland ecoregions did not account for spatial changes in bird composition within the fluvial system. In conclusion, environmental heterogeneity created by flood pulses is an important factor for sustaining regional diversity of birds within the fluvial system through effects on beta diversity.
Authors:M. Zeidler, M. Duchoslav, M. Banaš, and M. Lešková
Dwarf pine (Pinus mugo) is a successful pioneer tree, but also an invader of the subalpine belt in Central-European mountains. In the Hrubý Jeseník Mts. (Czech Republic), dwarf pine was introduced at the end of the 19th century by humans into alpine communities. To analyse the influence of non-native woody species on species diversity, vegetation composition and the ecological bioindication of invaded alpine communities, three habitats (non-invaded alpine grasslands, gaps of alpine grasslands within dwarf pine stands and closed dwarf pine stands) were compared at two localities (Keprník, Tabulové kameny) using the space-for-time substitution approach. Plant species composition was assessed by means of phytosociological relevés, and bioindication by means of Ellenberg indicator values. At both localities, both beta and gamma diversity were lower, and species composition more uniform in dwarf pine plantations in contrast to the gaps within and alpine grasslands outside of dwarf pine stands. At Keprník, alpha diversity was lower in the dwarf-pine plantation than outside of it, while at Tabulové kameny no significant differences were found. This is probably due to the somewhat different spatial structure of the dwarf pine stands and the different timing of dwarf pine introduction at these localities. Bioindication showed that dwarf-pine stands were drier, more shaded and had a higher soil fertility than alpine grasslands. Dwarf pine colonisation of alpine grasslands causes the extinction of many endangered plant species, complicating conservation goals. Because of the limited size of alpine areas, changes caused by dwarf pine in medium-high mountains might be more significant than in mountains with large alpine forest-free areas.
Authors:A. Chiarucci, G. Bacaro, D. Rocchini, and L. Fattorini
Crist, T.O. and J.A. Veech. 2006. Additive partitioning of rarefaction curves and species-area relationship: unifying alpha-, beta-and gamma-diversity with sample size and habitat area.