and K. Grigulis. 2007. Functionaldiversity — at the crossroads between ecosystem functioning and environmental filters. In: J.G. Canadell, D. Pataki and L. Pitelka (eds),
Terrestrial Ecosystems in a Changing World
. Springer-Verlag, Berlin
Authors:J. Podani, C. Ricotta, J.G. Pausas, and D. Schmera
A new approach to the measurement of functional diversity based on two-state nominal traits is developed from the florula diversity concept of P. Juhász-Nagy. For evaluating functional diversity of an assemblage, first a traits by species matrix is compiled. Various information theory functions are used to examine structural properties in this matrix, including the frequency distribution of trait combinations. The method is illustrated by actual examples, the first from plant communities prone to fire in Spain, and the second from running water invertebrate assemblages in Hungary. The results suggest that of the various functions used the standardized joint entropy, termed combinatorial functional evenness supplies most meaningful results. In plant communities, high fire recurrence decreased combinatorial functional evenness, while this measure for freshwater assemblages was uncorrelated with stream width and negatively correlated with the degree of human impact. Stream width is negatively correlated with the number of manifested functional combinations. In both case studies, combinatorial functional evenness has an inverse relationship to species richness — i.e., fewer species have a larger chance to produce equiprobable functional combinations.
The functional diversity of native mesorhizobial genotypes nodulating chickpea was assessed using two chickpea cultivars under pot culture conditions. The symbiotic effectiveness ratio of the mesorhizobial genotypes showed the existence of wide functional diversity among the isolates in Haryana soils. Mesorhizobial isolates belonging to the third genotype (MG III) were more efficient than the other genotypes. The majority of the isolates (94%) had intermediate effectiveness and only a very small percentage (2%) were ineffective, while 4–6% of the isolates were highly effective with a symbiotic ratio > 4.0. These included CP2381A, CP741, CP1423 and CP2437. Among all the isolates, strain CP2381A was the most efficient isolate for both cvs HC1 and HC5. The symbiotic ratio of the shoot N contents varied for both the cultivars after inoculation with mesorhizobial isolates from different districts. The most efficient chickpea mesorhizobial isolates were found to be present in soils from the Bhiwani district followed by that from RDS Farm, Hisar, but isolates from Mahendragarh, Fatehabad and Jhajjar were less efficient.
Due to its nonlinearity with respect to species addition, some applications of the Rao quadratic diversity are meaningful only if they are first transformed into their equivalent number of species, which is the theoretical species richness of a maximally distinct and perfectly even community with the same diversity as the original community. In this paper, relaxing the requirement of maximal distinction among species, we generalize the notion of the equivalent number of species for the Rao diversity to partially distinct species. The biological meaning of this proposal is illustrated with one dedicated case study in sand dune communities in Italy. According to our results, the proposed approach proved appropriate for comparing the functional diversity of different plant communities with varying levels of environmental constraints.
In community ecology, randomization tests with problem specific test statistics (e.g., nestedness, functional diversity, etc.) are often applied. Researchers in such studies may want not only to detect the significant departure from randomness, but also to measure the effect size (i.e., the magnitude of this departure). Measuring the effect size is necessary, for instance, when the roles of different assembly forces (e.g., environmental filtering, competition) are compared among sites. The standard method is to calculate standardized effect size (SES), i.e., to compute the departure from the mean of random communities divided by their standard deviations. Standardized effect size is a useful measure if the test statistic (e.g., nestedness index, phylogenetic or functional diversity) in the random communities follows a symmetric distribution. In this paper, I would like to call attention to the fact that SES may give us misleading information if the distribution is asymmetric (skewed). For symmetric distribution median and mean values are equal (i.e., SES = 0 indicates p = 0.5). However, this condition does not hold for skewed distributions. For symmetric distributions departure from the mean shows the extremity of the value, regardless of the sign of departure, while in asymmetric distributions the same deviation can be highly probable and extremely improbable, depending on its sign. To avoid these problems, I recommend checking symmetry of null-distribution before calculating the SES value. If the distribution is skewed, I recommend either log-transformation of the test statistic, or using probit-transformed p-value as effect size measure.
Authors:W. Qi, X. Zhou, M. Ma, J. M. H. Knops, W. Li, and G. Du
Despite a long history of alpine meadows studies, uncertainty remains about the importance of environmental factors in structuring their assembly. We examined the functional and phylogenetic structure of 170 alpine Tibetan meadow communities in relation to elevation, soil moisture and shade. Functional community structure was estimated with both communityweighted mean (CWM) trait values for specific leaf area (SLA), plant height and seed mass and functional diversity (Rao’s quadratic index) for their traits individually and in combination (multivariate functional diversity). We found that shade induced by woody plants significantly increased the phylogenetic diversity and functional diversity of SLA of co-occurring species, suggesting that woody plants behave as “ecosystem engineers” creating a different environment that allows the existence of shade tolerant species and thereby facilitates the coexistence of plant species with different light resource acquisition strategies. We also found evidence for a clear decrease in phylogenetic diversity, CWM and functional diversity related to plant height in the two extreme, both the dry and wet, soil moisture conditions. This indicates that both drought and excess moisture may act as environmental filters selecting species with close phylogenetic relationships and similar height. Moreover, we detected significant decreases in both CWM and functional diversity for seed mass along elevational gradients, suggesting that low net primary productivity (NPP) limits seed size. Finally, because of different individual trait responses to environmental factors, the multivariate functional diversity did not change across environmental gradients. This lack of multivariate response supports the hypothesis that multiple processes, such as environmental filtering, competition and facilitation, may operate simultaneously and exert opposing effects on community assembly along different niche (e.g., water use, light acquisition) axes, resulting in no overall functional community structure change. This contrast between individual and multivariate trait patterns highlights the importance of examining individual traits linked with different ecological processes to better understand the mechanisms of community assembly.