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.LinkDoi: 10.1111/gcb.14331
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
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.LinkDoi: 10.1016/j.scitotenv.2018.03.037
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.
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.LinkDoi: 10.1016/j.ecolind.2018.07.001
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
Câmara T., Leal I.R., Blüthgen N., Oliveira F.M.P., Queiroz R.T., Arnan X. (2018) Effects of chronic anthropogenic disturbance and rainfall on the specialization of ant-plant mutualistic networks in the Caatinga, a Brazilian dry forest. Journal of Animal Ecology. : 0-0.LinkDoi: 10.1111/1365-2656.12820
Anthropogenic disturbance and climate change might negatively affect the ecosystem services provided by mutualistic networks. However, the effects of such forces remain poorly characterized. They may be especially important in dry forests, which (1) experience chronic anthropogenic disturbances (CADs) as human populations exploit forest resources, and (2) are predicted to face a 22% decline in rainfall under climate change. In this study, we investigated the separate and combined effects of CADs and rainfall levels on the specialization of mutualistic networks in the Caatinga, a seasonally dry tropical forest typical of north-eastern Brazil. More specifically, we examined interactions between plants bearing extrafloral nectaries (EFNs) and ants. We analysed whether differences in network specialization could arise from environmentally mediated variation in the species composition, namely via the replacement of specialist by generalist species. We characterized these ant-plant networks in 15 plots (20 × 20 m) that varied in CAD intensity and mean annual rainfall. We quantified CAD intensity by calculating three indices related to the main sources of disturbance in the Caatinga: livestock grazing (LG), wood extraction (WE) and miscellaneous resource use (MU). We determined the degree of ant-plant network specialization using four metrics: generality, vulnerability, interaction evenness and H2'. Our results indicate that CADs differentially influenced network specialization: we observed positive, negative, and neutral responses along LG, MU and WE gradients, respectively. The pattern was most pronounced with LG. Rainfall also shaped network specialization, markedly increasing it. While LG and rainfall were associated with changes in network species composition, this trend was not related to the degree of species specialization. This result suggests that shifts in network specialization might be related to changes in species behaviour, not species composition. Our study highlights the vulnerability of such dry forest ant-plant networks to climate change. Moreover, dry forests experience highly heterogeneous anthropogenic disturbances, creating a geographic mosaic of selective forces that may shape the co-evolution of interactions between ants and EFN-bearing plants. © 2018 British Ecological Society.
Flo, V., Bosch, J., Arnan, X., Primante, C., Martín González, A.M., Barril-Graells, H., Rodrigo, A. (2018) Yearly fluctuations of flower landscape in a Mediterranean scrubland: Consequences for floral resource availability. PLoS ONE. 13: 0-0.LinkDoi: 10.1371/journal.pone.0191268
Gibb H., Sanders N.J., Dunn R.R., Arnan X., Vasconcelos H.L., Donoso D.A., Andersen A.N., Silva R.R., Bishop T.R., Gomez C., Grossman B.F., Yusah K.M., Luke S.H., Pacheco R., Pearce-Duvet J., Retana J., Tista M., Parr C.L. (2018) Habitat disturbance selects against both small and large species across varying climates. Ecography. 41: 1184-1193.LinkDoi: 10.1111/ecog.03244
Global extinction drivers, including habitat disturbance and climate change, are thought to affect larger species more than smaller species. However, it is unclear if such drivers interact to affect assemblage body size distributions. We asked how these two key global change drivers differentially affect the interspecific size distributions of ants, one of the most abundant and ubiquitous animal groups on earth. We also asked whether there is evidence of synergistic interactions and whether effects are related to species’ trophic roles. We generated a global dataset on ant body size from 333 local ant assemblages collected by the authors across a broad range of climates and in disturbed and undisturbed habitats. We used head length (range: 0.22–4.55 mm) as a surrogate of body size and classified species to trophic groups. We used generalized linear models to test whether body size distributions changed with climate and disturbance, independent of species richness. Our analysis yielded three key results: 1) climate and disturbance showed independent associations with body size; 2) assemblages included more small species in warmer climates and fewer large species in wet climates; and 3) both the largest and smallest species were absent from disturbed ecosystems, with predators most affected in both cases. Our results indicate that temperature, precipitation and disturbance have differing effects on the body size distributions of local communities, with no evidence of synergistic interactions. Further, both large and small predators may be vulnerable to global change, particularly through habitat disturbance. © 2017 The Authors
Leal I.R., Ribeiro-Neto J.D., Arnan X., Oliveira F.M.P., Arcoverde G.B., Feitosa R.M., Andersen A.N. (2018) Ants of the Caatinga: Diversity, biogeography, and functional responses to anthropogenic disturbance and climate change. Caatinga: The Largest Tropical Dry Forest Region in South America. : 65-95.LinkDoi: 10.1007/978-3-319-68339-3_3
Despite the outstanding diversity and ecological relevance of ants in most terrestrial ecosystems, current knowledge of the ants of the Caatinga is still incipient. This chapter offers an overview covering the diversity, taxonomy, biogeography, and functional composition of the Caatinga ant fauna, and a synthesis on ant response to chronic anthropogenic disturbance and increased aridity. We compiled a database consisting of 572 presence-absence ant records and 276 ant species from 37 localities in the Caatinga. As expected, most of the Caatinga has not been intensively sampled for ants, with the intensive sampling that has been conducted revealing high rates of species turnover across localities. Most ant species recorded in the Caatinga are widely distributed in other biomes, especially in Cerrado, and few species can be considered endemic to the Caatinga. Thus, the Caatinga ant fauna appears to represent an impoverished subset of the Cerrado's fauna. Such a reduced endemism and the occurrence of a highly depauperate ant fauna at a regional level contrast to the diversity patterns exhibited by the Caatinga flora and other faunal groups. Significant changes in ant taxonomic and functional composition in response to human disturbance are observed, with a predictable winner-loser replacement. Disturbance winners consist of generalist species exhibiting wide environmental tolerances and those inhabiting open habitats (Opportunists and Dominant Dolichoderinae). Highly specialized species are disturbance losers (Specialist predators). Aridity also affects both species occurrence and functional-group composition of local assemblages. Since several ant species and functional groups are sensitive to increasing disturbance and aridity, ant-mediated ecological services are already threatened in the Caatinga biota. © Springer International Publishing AG 2017.
Osorio-Canadas S., Arnan X., Bassols E., Vicens N., Bosch J. (2018) Seasonal dynamics in a Cavity-Nesting beewasp community: Shifts in composition, functional diversity and host-parasitoid network structure. PLoS ONE. 13: 0-0.LinkDoi: 10.1371/journal.pone.0205854
Ecological communities are composed of species that interact with each other forming complex interaction networks. Although interaction networks have been usually treated as static entities, interactions show high levels of temporal variation, mainly due to temporal species turnover. Changes in taxonomic composition are likely to bring about changes in functional trait composition. Because functional traits influence the likelihood that two species interact, temporal changes in functional composition and structure may ultimately affect interaction network structure. Here, we study the seasonality (spring vs. summer) in a community of cavity-nesting solitary bees and wasps ('hosts') and their nest associates ('parasitoids'). We analyze seasonal changes in taxonomic compostion and structure, as well as in functional traits, of the host and parasitoid communities. We also analyze whether these changes result in changes in percent parasitism and interaction network structure. Our host and parasitoid communities are strongly seasonal. Host species richness increases from spring to summer. This results in important seasonal changes in functional composition of the host community. The spring community (almost exclusively composed of bees) is characterized by large, univoltine, adult-wintering host species. The summer community (composed of both bees and wasps) is dominated by smaller, bivoltine, prepupa-wintering species. Host functional diversity is higher in summer than in spring. Importantly, these functional changes are not only explained by the addition of wasp species in summer. Functional changes in the parasitoid community are much less pronounced, probably due to the lower parasitoid species turnover. Despite these important taxonomic and functional changes, levels of parasitism did not change across seasons. Two network metrics (generality and interaction evenness) increased from spring to summer. These changes can be explained by the seasonal increase in species richness (and therefore network size). The seasonal shift from a bee-dominated community in spring to a wasp-dominated community in summer suggests a change in ecosystem function, with emphasis on pollination in spring to emphasis on predation in summer. © 2018 Osorio-Canadas et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Shik J.Z., Rytter W., Arnan X., Michelsen A. (2018) Disentangling nutritional pathways linking leafcutter ants and their co-evolved fungal symbionts using stable isotopes. Ecology. 99: 1999-2009.LinkDoi: 10.1002/ecy.2431
Leafcutter ants are the ultimate insect superorganisms, with up to millions of physiologically specialized workers cooperating to cut and transport vegetation and then convert it into compost used to cultivate co-evolved fungi, domesticated over millions of years. We tested hypotheses about the nutrient-processing dynamics governing this functional integration, tracing 15N- and 13C-enriched substrates through colonies of the leafcutter ant Atta colombica. Our results highlight striking performance efficiencies, including rapid conversion (within 2 d) of harvested nutrients into edible fungal tissue (swollen hyphal tips called gongylidia) in the center of fungus gardens, while also highlighting that much of each colony's foraging effort resulted in substrate placed directly in the trash. We also find nutrient-specific processing dynamics both within and across layers of the fungus garden, and in ant consumers. Larvae exhibited higher overall levels of 15N and 13C enrichment than adult workers, supporting that the majority of fungal productivity is allocated to colony growth. Foragers assimilated 13C-labeled glucose during its ingestion, but required several days to metabolically process ingested 15N-labeled ammonium nitrate. This processing timeline helps resolve a 40-yr old hypothesis, that foragers (but apparently not gardeners or larvae) bypass their fungal crops to directly assimilate some of the nutrients they ingest outside the nest. Tracing these nutritional pathways with stable isotopes helps visualize how physiological integration within symbiotic networks gives rise to the ecologically dominant herbivory of leafcutter ants in habitats ranging from Argentina to the southern United States. © 2018 The Authors Ecology published by Wiley Periodicals, Inc. on behalf of Ecological Society of America.
Doblas-Miranda, E., Alonso, R., Arnan, X., Bermejo, V., Brotons, L., de las Heras, J., Estiarte, M., Hódar, J.A., Llorens, P., Lloret, F., López-Serrano, F.R., Martínez-Vilalta, J., Moya, D., Peñuelas, J., Pino, J., Rodrigo, A., Roura-Pascual, N., Valladares, F., Vilà, M., Zamora, R., Retana, J. (2017) A review of the combination among global change factors in forests, shrublands and pastures of the Mediterranean Region: Beyond drought effects. Global and Planetary Change. 148: 42-54.LinkDoi: 10.1016/j.gloplacha.2016.11.012
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