Dominance–diversity relationships in ant communities differ with invasion

Arnan X., Andersen A.N., Gibb H., Parr C.L., Sanders N.J., Dunn R.R., Angulo E., Baccaro F.B., Bishop T.R., Boulay R., Castracani C., Cerdá X., Toro I.D., Delsinne T., Donoso D.A., Elten E.K., Fayle T.M., Fitzpatrick M.C., Gómez C., Grasso D.A., Grossman B.F., Guénard B., Gunawardene N., Heterick B., Hoffmann B.D., Janda M., Jenkins C.N., Klimes P., Lach L., Laeger T., Leponce M., Lucky A., Majer J., Menke S., Mezger D., Mori A., Moses J., Munyai T.C., Paknia O., Pfeiffer M., Philpott S.M., Souza J.L.P., Tista M., Vasconcelos H.L., Retana J. (2018) Dominance–diversity relationships in ant communities differ with invasion. Global Change Biology. 24: 4614-4625.
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Doi: 10.1111/gcb.14331

Resum:

The relationship between levels of dominance and species richness is highly contentious, especially in ant communities. The dominance-impoverishment rule states that high levels of dominance only occur in species-poor communities, but there appear to be many cases of high levels of dominance in highly diverse communities. The extent to which dominant species limit local richness through competitive exclusion remains unclear, but such exclusion appears more apparent for non-native rather than native dominant species. Here we perform the first global analysis of the relationship between behavioral dominance and species richness. We used data from 1,293 local assemblages of ground-dwelling ants distributed across five continents to document the generality of the dominance-impoverishment rule, and to identify the biotic and abiotic conditions under which it does and does not apply. We found that the behavioral dominance–diversity relationship varies greatly, and depends on whether dominant species are native or non-native, whether dominance is considered as occurrence or relative abundance, and on variation in mean annual temperature. There were declines in diversity with increasing dominance in invaded communities, but diversity increased with increasing dominance in native communities. These patterns occur along the global temperature gradient. However, positive and negative relationships are strongest in the hottest sites. We also found that climate regulates the degree of behavioral dominance, but differently from how it shapes species richness. Our findings imply that, despite strong competitive interactions among ants, competitive exclusion is not a major driver of local richness in native ant communities. Although the dominance-impoverishment rule applies to invaded communities, we propose an alternative dominance-diversification rule for native communities. © 2018 John Wiley & Sons Ltd

Llegeix més

Increased anthropogenic disturbance and aridity reduce phylogenetic and functional diversity of ant communities in Caatinga dry forest

Arnan X., Arcoverde G.B., Pie M.R., Ribeiro-Neto J.D., Leal I.R. (2018) Increased anthropogenic disturbance and aridity reduce phylogenetic and functional diversity of ant communities in Caatinga dry forest. Science of the Total Environment. 631-632: 429-438.
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Doi: 10.1016/j.scitotenv.2018.03.037

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Anthropogenic disturbance and climate change are major threats to biodiversity. The Brazilian Caatinga is the world's largest and most diverse type of seasonally dry tropical forest. It is also one of the most threatened, but remains poorly studied. Here, we analyzed the individual and combined effects of anthropogenic disturbance (three types: livestock grazing, wood extraction, and miscellaneous use of forest resources) and increasing aridity on taxonomic, phylogenetic and functional ant diversity in the Caatinga. We found no aridity and disturbance effects on taxonomic diversity. In spite of this, functional diversity, and to a lesser extent phylogenetic diversity, decreased with increased levels of disturbance and aridity. These effects depended on disturbance type: livestock grazing and miscellaneous resource use, but not wood extraction, deterministically filtered both components of diversity. Interestingly, disturbance and aridity interacted to shape biodiversity responses. While aridity sometimes intensified the negative effects of disturbance, the greatest declines in biodiversity were in the wettest areas. Our results imply that anthropogenic disturbance and aridity interact in complex ways to endanger biodiversity in seasonally dry tropical forests. Given global climate change, neotropical semi-arid areas are habitats of concern, and our findings suggest Caatinga conservation policies must prioritize protection of the wettest areas, where biodiversity loss stands to be the greatest. Given the major ecological relevance of ants, declines in both ant phylogenetic and functional diversity might have downstream effects on ecosystem processes, insect populations, and plant populations. © 2018 Elsevier B.V.

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A framework for deriving measures of chronic anthropogenic disturbance: Surrogate, direct, single and multi-metric indices in Brazilian Caatinga

Arnan X., Leal I.R., Tabarelli M., Andrade J.F., Barros M.F., Câmara T., Jamelli D., Knoechelmann C.M., Menezes T.G.C., Menezes A.G.S., Oliveira F.M.P., de Paula A.S., Pereira S.C., Rito K.F., Sfair J.C., Siqueira F.F.S., Souza D.G., Specht M.J., Vieira L.A., Arcoverde G.B., Andersen A.N. (2018) A framework for deriving measures of chronic anthropogenic disturbance: Surrogate, direct, single and multi-metric indices in Brazilian Caatinga. Ecological Indicators. 94: 274-282.
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Doi: 10.1016/j.ecolind.2018.07.001

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The development of multi-metric indices of chronic anthropogenic disturbance (CAD) from disparate disturbance indicators represents a major challenge for understanding the impacts of CAD on biodiversity, especially in tropical dry areas where livelihoods of local populations are highly dependent on natural resources. We present a conceptual framework for deriving variably integrated, multi-metric measures of CAD from disparate disturbance indicators. Our framework has three steps: (1) identifying the main sources of CAD in the target region, and quantifying them using data of varying levels of spatial and intensity precision; (2) classifying the sources of disturbance into general disturbance pressures, and deriving an index for each; and (3) combining the individual disturbance pressure indices into a fully integrated index that characterizes the overall level of CAD. We apply this framework to Catimbau National Park in the Brazilian Caatinga, using 12 primary data sources to derive disturbance pressure indices relating to livestock, wood extraction and people pressure. The meaningfulness of pressure and overall CAD indices were validated by reference to variation in ant communities. Our analysis revealed notable findings. First, indirect measures from the geographic and socio-ecological context were poorly correlated with direct, field-based measurements, and were therefore of questionable reliability. Second, the three main disturbance pressures were largely independent of each other, which points to complex patterns of resource use by local communities. Third, different weightings of component disturbance pressure indices had little influence on the Global index, making our Global CAD index somewhat insensitive to assessments of the relative importance of different disturbance pressures. Finally, our results caution against a reliance on multivariate ordination to derive integrated indices of disturbance from disparate data sources. Our multi-scale integration of disturbance data can facilitate the analysis of the resource use effects on biodiversity, contributing to effective conservation management and sustainable livelihood development. © 2018 Elsevier Ltd

Llegeix més

Guidelines and considerations for designing field experiments simulating precipitation extremes in forest ecosystems

Asbjornsen H., Campbell J.L., Jennings K.A., Vadeboncoeur M.A., McIntire C., Templer P.H., Phillips R.P., Bauerle T.L., Dietze M.C., Frey S.D., Groffman P.M., Guerrieri R., Hanson P.J., Kelsey E.P., Knapp A.K., McDowell N.G., Meir P., Novick K.A., Ollinger S.V., Pockman W.T., Schaberg P.G., Wullschleger S.D., Smith M.D., Rustad L.E. (2018) Guidelines and considerations for designing field experiments simulating precipitation extremes in forest ecosystems. Methods in Ecology and Evolution. 9: 2310-2325.
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Doi: 10.1111/2041-210X.13094

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Precipitation regimes are changing in response to climate change, yet understanding of how forest ecosystems respond to extreme droughts and pluvials remains incomplete. As future precipitation extremes will likely fall outside the range of historical variability, precipitation manipulation experiments (PMEs) are critical to advancing knowledge about potential ecosystem responses. However, few PMEs have been conducted in forests compared to short-statured ecosystems, and forest PMEs have unique design requirements and constraints. Moreover, past forest PMEs have lacked coordination, limiting cross-site comparisons. Here, we review and synthesize approaches, challenges, and opportunities for conducting PMEs in forests, with the goal of guiding design decisions, while maximizing the potential for coordination. We reviewed 63 forest PMEs at 70 sites world-wide. Workshops, meetings, and communications with experimentalists were used to generate and build consensus around approaches for addressing the key challenges and enhancing coordination. Past forest PMEs employed a variety of study designs related to treatment level, replication, plot and infrastructure characteristics, and measurement approaches. Important considerations for establishing new forest PMEs include: selecting appropriate treatment levels to reach ecological thresholds; balancing cost, logistical complexity, and effectiveness in infrastructure design; and preventing unintended water subsidies. Response variables in forest PMEs were organized into three broad tiers reflecting increasing complexity and resource intensiveness, with the first tier representing a recommended core set of common measurements. Differences in site conditions combined with unique research questions of experimentalists necessitate careful adaptation of guidelines for forest PMEs to balance local objectives with coordination among experiments. We advocate adoption of a common framework for coordinating forest PME design to enhance cross-site comparability and advance fundamental knowledge about the response and sensitivity of diverse forest ecosystems to precipitation extremes. © 2018 The Authors. Methods in Ecology and Evolution © 2018 British Ecological Society

Llegeix més

Xylem hydraulic safety and construction costs determine tropical tree growth

B. Eller, C., de V. Barros, F., R.L. Bittencourt, P., Rowland, L., Mencuccini, M., S. Oliveira, R. (2018) Xylem hydraulic safety and construction costs determine tropical tree growth. Plant Cell and Environment. 41: 548-562.
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Doi: 10.1111/pce.13106

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Experimental evidence of the quantitative relationship between the prokaryote ingestion rate and the food vacuole content in mixotrophic phytoflagellates

Ballen-Segura M., Catalan J., Felip M. (2018) Experimental evidence of the quantitative relationship between the prokaryote ingestion rate and the food vacuole content in mixotrophic phytoflagellates. Environmental Microbiology Reports. 10: 704-710.
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Doi: 10.1111/1758-2229.12696

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The verification that many phytoflagellates ingest prokaryotes has changed the view of the microbial loop in aquatic ecosystems. Still, progress is limited because the phagotrophic activity is difficult to quantify in natural assemblages. Linking the food vacuole content in protist with the ingestion rate of prokaryotes would provide a crucial step forward. In this study, using the catalysed reporter deposition – fluorescence in situ hybridization protocol (CARD-FISH), which allows the visualization of labelled prokaryotes inside protists without relying on incubation procedures, we experimentally relate the food vacuole content of prokaryotes (Vc) to the population-averaged ingestion rates (Ir) estimated using bacteria-size fluorescent microspheres. The two variables relate according to the equation Ir = 7.52 Vc 0.9, which indicates a prokaryote half-life of about 6 min in the protist vacuole. Five mixotrophic flagellate species from natural and culture populations were evaluated seven times during 24 h; they provided a broad range of average vacuole content (0.01 to 2.02 prokaryote protist−1) and ingestion rates (0.18 to 23 prokaryote protist−1 h−1). Consequently, the relationship found can be applied to quantify the mixotrophy activity in a large variety of field and experimental studies. © 2018 Society for Applied Microbiology and John Wiley & Sons Ltd

Llegeix més

Assessing ecosystem isoprene emissions by hyperspectral remote sensing

Balzarolo M., Peñuelas J., Filella I., Portillo-Estrada M., Ceulemans R. (2018) Assessing ecosystem isoprene emissions by hyperspectral remote sensing. Remote Sensing. 10: 0-0.
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Doi: 10.3390/rs10071086

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This study examined the relationship between foliar isoprene emissions, light use efficiency and photochemical reflectance index (PRI) throughout the canopy profile and explored the contribution of xanthophyll cycle pigments versus other carotenoid pigments to the isoprene/PRI relationship. Foliar isoprene emissions within the canopy profile were measured in a high-density poplar plantation in Flanders (Belgium) during the 2016 growing season. The results confirmed that PRI was a promising estimator of isoprene emissions at canopy level. Interestingly, xanthophyll cycle pigments contributed more to isoprene biosynthesis than chlorophyll and drove the isoprene/PRI relationship. The simple independent pigment index and novel defined indices, such as the hyperspectral isoprene index and simple hyperspectral isoprene index, showed promising results and could be suitable estimators of isoprene emissions due to their strong relationship with the xanthophyll pool. © 2018 by the authors.

Llegeix més

Multi-temporal influence of vegetation on soil respiration in a droughtaffected forest

Barba, J., Lloret, F., Poyatos, R., Molowny-Horas, R., Yuste, J.C. (2018) Multi-temporal influence of vegetation on soil respiration in a droughtaffected forest. IForest. 11: 189-198.
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Doi: 10.3832/ifor2448-011

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Loss of pollinators: evidences, causes and consequences [Pérdida de polinizadores: Evidencias, causas y consecuencias]

Bartomeus I., Bosch J. (2018) Loss of pollinators: evidences, causes and consequences [Pérdida de polinizadores: Evidencias, causas y consecuencias]. Ecosistemas. 27: 1-2.
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Doi: 10.7818/ECOS.1542

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[No abstract available]

Llegeix més

Trophic transfer from aquatic to terrestrial ecosystems: a test of the biogeochemical niche hypothesis

Bartrons M., Sardans J., Hoekman D., Peñuelas J. (2018) Trophic transfer from aquatic to terrestrial ecosystems: a test of the biogeochemical niche hypothesis. Ecosphere. 9: 0-0.
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Doi: 10.1002/ecs2.2338

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Matter and energy flow across ecosystem boundaries. Transfers from terrestrial to aquatic ecosystems are frequent and have been widely studied, but the flow of matter from aquatic to terrestrial ecosystems is less known. Large numbers of midges emerge from some lakes in northern Iceland and fly to land. These lakes differ in their levels of eutrophication due to different intensities of geothermal warming and nutrient inputs. In the context of this material transfer from an aquatic to a terrestrial ecosystem, we investigated the relationships between the deposition of midges and the elemental composition and stoichiometry of organisms in low-productivity terrestrial ecosystems. We analyzed several terrestrial food webs in northeastern Iceland with similar food web compositions of terrestrial arthropods but different inputs of midges and analyzed the stoichiometric composition of the different trophic groups. Elemental composition differed among trophic groups and taxa much more than within each trophic group or taxa across the midge deposition gradient. Specifically, the change in N concentration was significant in plants (up to 70% increase in the site with maximum input) but not in predators, which had a more homeostatic elemental composition. These results thus show (1) a significant movement of matter and nutrients from an aquatic to a terrestrial habitat via the emergence of aquatic insects and the deposition of insect carcasses, (2) a larger impact on the elemental composition of plants than arthropods, and (3) support for the biogeochemical niche hypothesis, which predicts that different species should have a specific elemental composition, stoichiometry, and allocation as a consequence of their particular metabolism, physiology, and structure. © 2018 The Authors.

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