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Aim: Beta diversity can be partitioned into two components: dissimilarity due to species replacement and dissimilarity due to nestedness (Baselga, 2010, Global Ecology and Biogeography, 19, 134—143). Several contributions have challenged this approach or proposed alternative frameworks. Here, I review the concepts and methods used in these recent contributions, with the aim of clarifying: (1) the rationale behind the partitioning of beta diversity into species replacement and nestedness-resultant dissimilarity, (2) how, based on this rationale, numerators and denominators of indices have to match, and (3) how nestedness and nestedness-resultant dissimilarity are related but different concepts. Innovation: The rationale behind measures of species replacement (turnover) dictates that the number of species that are replaced between sites (numerator of the index) has to be relativized with respect to the total number of species that could potentially be replaced (denominator). However, a recently proposed partition of Jaccard dissimilarity fails to do this. In consequence, this partition underestimates the contribution of species replacement and overestimates the contribution of richness differences to total dissimilarity. I show how Jaccard dissimilarity can be partitioned into meaningful turnover and nestedness components, and extend these new indices to multiple-site situations. Finally the concepts of nestedness and nestedness-resultant dissimilarity are discussed. Main conclusions: Nestedness should be assessed using consistent measures that depend both on paired overlap and matrix filling, e.g. NODF, whereas beta-diversity patterns should be examined using measures that allow the total dissimilarity to be separated into the components of dissimilarity due to species replacement and dissimilarity due to nestedness. In the case of multiple-site dissimilarity patterns, averaged pairwise indices should never be used because the mean of the pairwise values is unable to accurately reflect the multiple-site attributes of dissimilarity.

AIM: The variation in species composition among sites, or beta diversity, can be decomposed into replacement and richness difference. A debate is ongoing in the literature concerning the best ways of computing and interpreting these indices. This paper first reviews the historical development of the formulae for decomposing dissimilarities into replacement, richness difference and nestedness indices. These formulae are presented for species presence–absence and abundance using a unified algebraic framework. The indices decomposing beta play different roles in ecological analysis than do beta‐diversity indices. INNOVATION: Replacement and richness difference indices can be interpreted and related to ecosystem processes. The pairwise index values can be summed across all pairs of sites; these sums form a valid decomposition of total beta diversity into total replacement and total richness difference components. Different communities and study areas can be compared: some may be dominated by replacement, others by richness/abundance difference processes. Within a region, differences among sites measured by these indices can then be analysed and interpreted using explanatory variables or experimental factors. The paper also shows that local contributions of replacement and richness difference to total beta diversity can be computed and mapped. A case study is presented involving fish communities along a river. MAIN CONCLUSIONS: The different forms of indices are based upon the same functional numerators. These indices are complementary; they can help researchers understand different aspects of ecosystem functioning. The methods of analysis used in this paper apply to any of the indices recently proposed. Further work, based on ecological theory and numerical simulations, is required to clarify the precise meaning and domain of application of the different forms. The forms available for presence–absence and quantitative data are both useful because these different data types allow researchers to answer different types of ecological or biogeographic questions.

Aim We explored the range shifts of alien and native birds, the responses of alien and native β‐diversity to abiotic factors, and the effect of native diversity on alien β‐diversity in two time periods. Location Great Britain. Time period 1968–1972, 2007–2011. Taxa studied Breeding birds. Methods We estimated range shifts of alien and native species between the periods 1968–1972 and 2007–2011. Following, β‐diversity of alien and native communities was estimated by Jaccard pairwise index (βtot) and partitioned into richness difference and replacement component for each period. We built abiotic generalized dissimilarity models including abiotic factors for alien and native βtot and their components and a biotic model for aliens including native taxonomic and functional diversity as predictors. Results Most alien and half native species expanded into new regions during the 40‐year period. The native species range shifts did not exhibit a clear pattern along the longitudinal or latitudinal gradient, while alien species tended to move north‐westwards. The richness difference was the dominant component of alien β‐diversity, and the replacement component contributed mostly to native β‐diversity. Alien β‐diversity responded similarly but less strongly than native β‐diversity, to the abiotic gradients. Temperature‐related variables, distance and precipitation were the most important abiotic drivers of native and alien β‐diversity. The biotic model of alien β‐diversity explained more deviance than the abiotic model. Main conclusions Alien species expanded into new regions over the 40 years, with alien β‐diversity driven mostly by species gains. The effect of environmental filtering on alien communities was weaker compared with native communities but was slightly reinforced in the second period compared with the first period, highlighting the role of environmental change in shaping diversity patterns. Native diversity played a key role in driving alien β‐diversity, through biotic interactions or/and by reflecting climatic suitability or niche availability for aliens.

Changes in the biodiversity of aquatic environments over time and space due to human activities are a topic of theoretical and conservational interest in ecology. Thus, variation in taxonomic beta diversity of the planktonic ciliates community was investigated along a temporal and spatial gradient in two subsystems of a Neotropical floodplain, one impacted by dams (Paraná) and the other free of them along its course (Ivinhema). For the spatial analysis, the Paraná subsystem did not show a significant decrease in beta diversity, presenting a pattern like that observed for the Ivinhema subsystem. Therefore, biotic homogenization was not observed for the ciliate's community downstream of the dams. It was noted that there was a fluctuation in the relevance of the components of beta diversity, regardless of the subsystem analyzed. For the temporal analysis there was a significant change in species composition from the first to the last year investigated, essentially for the subsystem impacted by dams, and that this was determined mainly by species loss. Although spatial beta diversity remained high without a clear process of biotic homogenization, dams promoted remarkable changes in ciliate species composition over the years mainly by continuous loss of species.

Aim: In urbanized areas, exotic invasions, native extinctions, and the alteration of habitats and natural processes drive homogenization, which is a form of biotic impoverishment This study examines whether urbanization and flooding induce homogenization of herbaceous communities in riparian forests and quantifies the relationships between taxonomic and functional β-diversity. Location: Montreal, Quebec, Canada. Methods: Inventories were conducted in 56 riparian forests. Taxonomic and functional p-diversity were calculated as between-site similarities in species or trait composition for three levels of urbanization and flooding. Differences among the disturbance levels were compared using tests for homogeneity in multivariate dispersions. We quantified the correlation between local species richness, exotic proportion, taxonomic and functional β-diversity. We also partitioned taxonomic p-diversity into species turnover and richness difference. Results: Urbanization led to taxonomic and functional differentiation, while increased flooding led to taxonomic and functional homogenization. We found a significant correlation between taxonomic and functional p-diversity. Changes in β-diversity were associated with species and trait turnover among both urbanization and flood levels, and with changes in species richness. Differentiation was associated with low species richness, and homogenization with high species richness. Exotic invasions tended to favour differentiation, but only at a low urbanization level. Main Conclusions: The effect of urbanization on plant diversity in riparian forests was twofold: first, it directly induced taxonomic and functional differentiation through its effect on species loss and turnover (higher β-diversity at high urbanization level); second, differentiation was indirectly favoured through the reduction in flooding (higher β-diversity at low flood level). Taxonomic and functional p-diversity followed similar patterns, likely because species invasions and extinctions are not random, but are related to species traits. Our results underline the need to move our focus from exotic species to the true underlying factors of biodiversity loss and homogenization, notably land use changes and human disturbances.

We studied β diversity of grasses in a subtropical grassland over 60 years in South Africa. We examined the effects of burning and mowing on 132 large plots. We sought to determine the effects of burning and mowing, and mowing frequency, on the replacement of species and the species richness. We conducted the study at Ukulinga, research farm of the University of KwaZulu‐Natal, Pietermaritzburg, South Africa (29°24′E, 30°24′S) from 1950–2010. Plots were burned annually, biennially, triennially, and a control (unburned). Plots were mowed in spring, late summer, spring plus late summer, and a control (unmowed). We calculated β diversity, with a focus on replacement and richness differences. We also used distance‐based redundancy analyses to examine the relative effects of replacement and richness differences on mowing and burning. We used beta regressions to test for the effect of soil depth and its interactions with mowing and burning. There was no significant change in grass beta diversity until 1995. Thereafter, there were changes in β diversity that demonstrated the primary effects of summer mowing frequency. There was no significant effect of richness differences but a strong effect of replacement post‐1995. There was a significant interaction between mowing frequency and soil depth in one of the analyses. Changes in grassland composition took a long time to manifest themselves and were unapparent prior to 1988. However, there was a change in sampling strategy prior to 1988, from point hits to nearest plants, that may also have influenced the rates of changes in replacement and richness differences. Using β‐diversity indices, we found that mowing was more important than burning that burning frequency was unimportant, and there was a significant interaction effect between mowing and soil depth in one of the analyses. We studied β diversity of grasses in a subtropical grassland over 60 years with different burning and mowing frequencies. Changes in grassland composition took a long time to manifest themselves. We found that summer mowing was the primary driver and that there was a significant interaction effect between mowing and soil depth.

We carried out a literature review to investigate the taxonomic and functional β diversity of zooplankton and its species replacement (β repl ) and richness difference (β rich ) components in Brazilian rivers. In addition, the taxonomic (LCBD-t) and functional ecological uniqueness (LCBD-f) were also measured. We tested the following hypotheses: (i) The β repl component is the main driver of taxonomic β diversity, while β rich is most important for functional β diversity, due to functional simplification; (ii) Sites with lower taxonomic and functional richness are the ones that most contribute to LCBD. Contrary to expectations, β rich drove the taxonomic and functional β diversity. This may have occurred due to environmental constraints and geographic distance, thus causing a loss or gain of species and traits between hydrographic regions. For just two regions, the sites with the lowest functional richness were the ones that most contributed to LCBD-f. This reinforces that sites with lower richness can support species that perform unique functions in the ecosystem. As studies involving zooplankton from lotic systems are still limited in Brazil, we suggest that future research should consider the patterns of β diversity in these dynamic, diverse, and threatened aquatic ecosystems.

AIM: Our aim was to determine the relative contribution of species replacement and richness differences to overall beta diversity in Macaronesian spiders, the influence of several biogeographical drivers in shaping such dissimilarity patterns, and how these change according to the dispersal ability of spiders. LOCATION: Four Macaronesian archipelagos: the Azores, Madeira, Selvagens and the Canary Islands. METHODS: Each spider species was assigned to a group relative to its ballooning propensity (frequent, occasional or rare), used as a surrogate of dispersal ability, based on its family membership. Beta diversity was decomposed for each group, by disentangling all compositional differences (overall beta diversity, βₜₒₜₐₗ) into two components, species replacement (βᵣₑₚₗ) and species richness differences (βᵣᵢcₕ). The effects of island area, environmental heterogeneity, geological age, distance to mainland and inter‐island distances on βᵣₑₚₗ and βᵣᵢcₕ were tested by partial Mantel tests and hierarchical partitioning of variation for each mobility group. RESULTS: The archipelagos studied had similar intra‐archipelagic richness differences, but species replacement was lower within the Azores for the three groups of spiders. The variation in community composition among the archipelagos was determined by species replacement for frequently ballooning spiders, while richness differences dominated for less mobile spiders. Island area was more important for species with higher mobility, while less mobile species were mostly affected by the distance to mainland and inter‐island distances. Environmental heterogeneity had an effect, mostly on richness differences, across the three spider groups. Time had only a weak effect on species replacement for less mobile species. MAIN CONCLUSIONS: The partition of βₜₒₜₐₗ into βᵣₑₚₗ and βᵣᵢcₕ identified different causes of beta‐diversity patterns as driven by the dispersal ability of spiders. Dispersal‐limited species responded more strongly to isolation than more mobile species. In contrast, the latter were influenced more by island area. Thus our findings emphasize the importance of interspecific traits and dispersal limitation for structuring species assemblages on islands.

Aim: Gradients in climate and land use occur simultaneously in many of the Earth's ecosystems and thus collectively impact most ecological communities. Albeit climate and land use have potentially interacting effects on ecological communities that may exacerbate or ameliorate their individual effects, little is known about the effect of the climate-land use interaction on community composition. A better understanding of the interaction between climate and land use is essential to predict the impacts of environmental change on ecological communities. Location: Mt Kilimanjaro, Tanzania. Methods: We quantified the community composition of bird species and feeding guilds on 64 study plots of 13 different habitat types along an elevational gradient from 870 to 4550 m a.s.l. We partitioned the variation in pairwise beta-diversity (βcc) of birds and its two additive components, abundance differences (βabu) and replacement (β₋₃), among the effects of temperature, land-use intensity and their interaction. Results: Temperature and land use had synergistic effects on beta-diversity (βcc) of birds; that is, the combination of high temperature and high land-use intensity led to higher beta-diversity than expected from the sum of both individual effects. While temperature explained more of the variation in abundance differences (βabu), land use explained more of the variation in the replacement of individuals between species and feeding guilds (β₋₃), indicating that different processes drove avian beta-diversity along the temperature and land-use gradients. Main Conclusions: Our results challenge previous studies that investigated the effects of climate and land use in isolation because disregarding their synergistic interaction underestimates the joint effect of climate and land use on biodiversity. A consideration of the synergy between climate and land use is essential for adequate predictions of the impact of global change on biodiversity.

QUESTION: The spread of alien species has been changing the diversity of plant communities all over the world, perhaps most notably in urban habitats. It has been shown that alien species with different residence times have different impacts on the β‐diversity of urban plant communities: archaeophytes tend to contribute to homogenization, while neophytes tend to increase differentiation among sites. However, it has not been determined whether these processes result from changes in species turnover or from differences in species richness. Here, we use an additive partitioning framework to disentangle the contribution of species turnover and richness difference to β‐diversity patterns in invaded urban plant communities. LOCATION: Thirty‐two cities in ten countries of Central Europe and Benelux. METHODS: We analysed the effects of alien species on β‐diversity of urban plant communities separately for archaeophytes and neophytes to assess whether the observed patterns differ between these two groups of species with different residence times in the invaded region. We used additive as well as non‐additive measures of species turnover and richness difference. For this purpose, we proposed a new index that complements the recently proposed Podani‐Schmera index of richness difference. RESULTS: We confirmed the results of earlier studies that neophytes tend to differentiate the urban plant communities, while archaeophytes tend to homogenize, although in some specific habitats they can also contribute to differentiation. The observed changes in β‐diversity were related to the turnover component of β‐diversity in most cases, especially for neophytes. In contrast, the richness difference component was not significantly different between neophytes and native species. The trends for archaeophytes were less consistent, but in most habitats their turnover and richness difference were not significantly different from native species. CONCLUSIONS: Changes in β‐diversity of urban plant communities induced by the establishment of alien species reflect mainly species turnover, whereas the richness difference component has small effects restricted to certain habitats only.