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Almoussawi, A., Lenoir, J., Jamoneau, A., Hattab, T., Wasof, S., Gallet-Moron, E., et al. (2019). Forest fragmentation shapes the alpha-gamma relationship in plant diversity. J. Veg. Sci., .
Résumé: Questions Forest fragmentation affects biodiversity locally (alpha diversity) and beyond – at relatively larger scales (gamma diversity) – by increasing dispersal and recruitment limitations. Yet, does an increase in fragmentation affect the relationship between alpha and gamma diversity and what can we learn from it? Location Northern France. Methods We surveyed 116 forest patches across three fragmentation levels: none (continuous forest); intermediate (forest patches connected by hedgerows); and high (isolated forest patches). Plant species richness of both forest specialists and generalists was surveyed at five nested spatial resolutions across each forest patch: 1 m(2); 10 m(2); 100 m(2); 1,000 m(2); and total forest patch area. First, we ran log-ratio models to quantify the alpha-gamma relationship. We did that separately for all possible combinations of fragmentation level (none vs intermediate vs high) x spatial scale (e.g., alpha-1 m(2) vs gamma-10 m(2)) x species type (e.g., alpha-specialists vs gamma-specialists). We then used linear mixed-effects models to analyze the effect of fragmentation level, spatial scale, species type and all two-way interaction terms on the slope coefficient extracted from all log-ratio models. Results We found an interaction effect between fragmentation level and species type, such that forest specialists shifted from a linear (i.e., proportional sampling) to a curvilinear plateau (i.e., community saturation) relationship at low and high fragmentation, respectively, while generalists shifted from a curvilinear to a linear pattern. Conclusions The impact of forest fragmentation on the alpha-gamma relationship supports generalist species persistence over forest specialists, with contrasting mechanisms for these two guilds. As fragmentation increases, forest specialists shift from proportional sampling towards community saturation, thus reducing alpha diversity likely due to dispersal limitation. Contrariwise, generalists shift from community saturation towards proportional sampling, thus increasing alpha diversity likely due to an increase in the edge:core ratio. To ensure long-term conservation of forest specialists, one single large forest patch should be preferred over several small ones.
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Barnagaud, J. - Y., Kissling, W. D., Tsirogiannis, C., Fisikopoulos, V., Villeger, S., Sekercioglu, C. H., et al. (2017). Biogeographical, environmental and anthropogenic determinants of global patterns in bird taxonomic and trait turnover. Glob. Ecol. Biogeogr., 26(10), 1190–1200.
Résumé: AimTo assess contemporary and historical determinants of taxonomic and ecological trait turnover in birds worldwide. We tested whether taxonomic and trait turnover (1) are structured by regional bioclimatic conditions, (2) increase in relationship with topographic heterogeneity and environmental turnover and change according to current and historical environmental conditions, and (3) decrease with human impact. Major TaxaBirds. LocationGlobal. MethodsWe used computationally efficient algorithms to map the taxonomic and trait turnover of 8,040 terrestrial bird assemblages worldwide, based on a grid with 110km x 110 km resolution overlaid on the extent-of-occurrence maps of 7,964 bird species, and nine ecological traits reflecting six key aspects of bird ecology (diet, habitat use, thermal preference, migration, dispersal and body size). We used quantile regression and model selection to quantify the influence of biomes, environment (temperature, precipitation, altitudinal range, net primary productivity, Quaternary temperature and precipitation change) and human impact (human influence index) on bird turnover. ResultsBird taxonomic and trait turnover were highest in the north African deserts and boreal biomes. In the tropics, taxonomic turnover tended to be higher, but trait turnover was lower than in other biomes. Taxonomic and trait turnover exhibited markedly different or even opposing relationships with climatic and topographic gradients, but at their upper quantiles both types of turnover decreased with increasing human influence. Main conclusionsThe influence of regional, environmental and anthropogenic factors differ between bird taxonomic and trait turnover, consistent with an imprint of niche conservatism, environmental filtering and topographic barriers on bird regional assemblages. Human influence on these patterns is pervasive and demonstrates global biotic homogenization at a macroecological scale.
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Baselga, A., & Leprieur, F. (2015). Comparing methods to separate components of beta diversity. Methods Ecol Evol, 6(9), 1069–1079.
Résumé: * Two alternative frameworks have been proposed to partition compositional dissimilarity into replacement and nestedness-resultant component or into replacement and richness-difference components. These are, respectively, the BAS (Baselga 2010, Global Ecology and Biogeography, 19, 134–143) and POD (Podani & Schmera . Oikos, 120, 1625–1638) frameworks. * We conduct a systematic comparison of parallel components in alternative approaches. We test whether the replacement components derived from the BAS and POD frameworks are independent of richness difference. We also evaluate whether previously reported tests of monotonicity between indices and ecological processes are informative to assess the performance of indices. Finally, we illustrate the consequences of differences between the BAS and POD frameworks using the North American freshwater fish fauna as an empirical example. * In the BAS framework, the nestedness-resultant component (βjne or βsne) accounts only for richness differences derived from nested patterns while, in the POD framework, richness-difference dissimilarity (βrich or βrich.s) accounts for all kind of richness differences. Likewise, the replacement components of both alternative methods account for different concepts. Only the replacement component of the BAS framework (βjtu or βsim) is independent of richness difference, while the parallel component in the POD framework (β−3 or β−3.s) is not (i.e. it is mathematically constrained by richness difference). * Therefore, only the BAS framework allows separating (i) the variation in species composition derived from species replacement which is independent of richness difference (i.e. not mathematically constrained by it) and (ii) the variation in species composition derived from nested patterns.
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Bender, M. G., Leprieur, F., Mouillot, D., Kulbicki, M., Parravicini, V., Pie, M. R., et al. (2017). Isolation drives taxonomic and functional nestedness in tropical reef fish faunas. Ecography, 40(3), 425–435.
Résumé: Taxonomic nestedness, the degree to which the taxonomic composition of species-poor assemblages represents a subset of richer sites, commonly occurs in habitat fragments and islands differing in size and isolation from a source pool. However, species are not ecologically equivalent and the extent to which nestedness is observed in terms of functional trait composition of assemblages still remains poorly known. Here, using an extensive database on the functional traits and the distributions of 6316 tropical reef fish species across 169 sites, we assessed the levels of taxonomical vs functional nestedness of reef fish assemblages at the global scale. Functional nestedness was considerably more common than taxonomic nestedness, and generally associated with geographical isolation, where nested subsets are gradually more isolated from surrounding reef areas and from the center of biodiversity. Because a nested pattern in functional composition implies that certain combinations of traits may be represented by few species, we identified these groups of low redundancy that include large herbivore-detritivores and omnivores, small piscivores, and macro-algal herbivores. The identified patterns of nestedness may be an outcome of the interaction between species dispersal capabilities, resource requirements, and gradients of isolation among habitats. The importance of isolation in generating the observed pattern of functional nestedness within biogeographic regions may indicate that disturbance in depauperate and isolated sites can have disproportionate effects on the functional structure of their reef fish assemblages.
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Bonilla-Findji, O., Rochelle-Newall, E., Weinbauer, M. G., Pizay, M. D., Kerros, M. E., & Gattuso, J. P. (2009). Effect of seawater-freshwater cross-transplantations on viral dynamics and bacterial diversity and production. Aquat. Microb. Ecol., 54(1), 1–11.
Résumé: Dilution experiments were carried out to investigate the community composition and the metabolic response of seawater and freshwater bacteria to cross-transplantation, and the effects of nor.-indigenous bacterial hosts on viral dynamics. Changes in viral and bacterial abundance and production, as Well as bacterial respiration, carbon demand and diversity were regularly monitored over a 6 d period. Bacterial production in the transplanted seawater (SB-t) and freshwater (FB-t) bacteria treatments was stimulated up to 256 and 221 %, respectively, compared to controls. The stimulation of bacterial production and carbon demand was accompanied by a decrease in bacterial richness. Net viral production was stimulated by 81% in SB-t and repressed by 75% in FB-t. Transplantation increased the virus-induced mortality of marine bacteria, but decreased it for freshwater bacteria. These results suggest that (1) marine bacteria can readily oxidize freshwater dissolved organic matter, and (2) freshwater viruses might be able to infect marine hosts, thus highlighting their potential role in fueling bacterial growth under resource stress or nutrient-depleted conditions.
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