What Factors Affect Diversity and Species Composition of Endangered Tumbesian Dry Forests in Southern Ecuador?

This paper reports a study on species richness and composition of Tumbesian dry forest communities. We tested two alternative hypotheses about species assemblage processes in tropical dry forests: (1) species assemblage is determined by the filtering effect of environmental conditions and (2) species assemblage is determined by facilitative processes along the gradient of water availability, and thus, species richness and evenness increase as water becomes limited. In addition, we also explored the effect of climate and soil conditions on species composition in tropical dry forests. Species composition was sampled in 109 plots in terms of cover and tree diameter at breast height. Climatic, edaphic, topographic and anthropogenic degradation variables were obtained for each plot. We used generalized linear models and canonical correspondence analyses to evaluate the effect of environmental variables on species composition, richness and evenness. Water availability negatively affected richness and significantly determined the species assemblage. Species richness increased from ridges to valleys and evenness increased at higher altitudes. Soil characteristics showed no effect on richness and evenness but soil moisture, nitrogen concentration and soil temperature explained significant fractions of species composition. Although timber extraction and livestock in our study area were of low intensity, it negatively affected richness but had only a minor effect on species composition. Our results suggest that species composition in these endangered tropical dry forests may be at least partially explained by the stress-gradient hypothesis, with higher species richness at drier conditions probably induced by facilitation processe

Climate and grazing control nurse effects in an Ecuadorian dry shrubby community

Positive plant interactions have strong effects on plant diversity at several spatial scales, expanding species distribution under stressful conditions. We evaluated the joint effect of climate and grazing on the nurse effect of Croton wagneri, by monitoring several community attributes at two spatial scales: microhabitat and plant community. Two very close locations that only differed in grazing intensity were surveyed in an Ecuadorian dry scrub ecosystem. At each location, two 30 × 30-m plots were established at four altitudinal levels (1500, 2630, 1959 and 2100 m asl) and 40 microsites were surveyed in each plot. Croton wagneri acted as community hubs, increasing species richness and plant cover at both scales. Beneath nurses mean richness and cover values were 3.4 and 21.9%, and in open areas 2.3 and 4.5%, respectively. Magnitude of nurse effect was dependent on climate and grazing conditions. In ungrazed locations, cover increased and diversity reduced with altitude, while grazed locations showed the opposite trend. In ungrazed plots the interactions shifted from positive to negative with altitude, in grazed locations interactions remained positive. We conclude that the nurse effect is a key mechanism regulating community properties not only at microsite but also at the entire community scale

GrassPlot - a database of multi-scale plant diversity in Palaearctic grasslands

GrassPlot is a collaborative vegetation-plot database organised by the Eurasian Dry Grassland Group (EDGG) and listed in the Global Index of Vegetation-Plot Databases (GIVD ID EU-00-003). GrassPlot collects plot records (releves) from grasslands and other open habitats of the Palaearctic biogeographic realm. It focuses on precisely delimited plots of eight standard grain sizes (0.0001; 0.001;... 1,000 m(2)) and on nested-plot series with at least four different grain sizes. The usage of GrassPlot is regulated through Bylaws that intend to balance the interests of data contributors and data users. The current version (v. 1.00) contains data for approximately 170,000 plots of different sizes and 2,800 nested-plot series. The key components are richness data and metadata. However, most included datasets also encompass compositional data. About 14,000 plots have near-complete records of terricolous bryophytes and lichens in addition to vascular plants. At present, GrassPlot contains data from 36 countries throughout the Palaearctic, spread across elevational gradients and major grassland types. GrassPlot with its multi-scale and multi-taxon focus complements the larger international vegetationplot databases, such as the European Vegetation Archive (EVA) and the global database " sPlot". Its main aim is to facilitate studies on the scale-and taxon-dependency of biodiversity patterns and drivers along macroecological gradients. GrassPlot is a dynamic database and will expand through new data collection coordinated by the elected Governing Board. We invite researchers with suitable data to join GrassPlot. Researchers with project ideas addressable with GrassPlot data are welcome to submit proposals to the Governing Board

Assemblage of a Semi-Arid Annual Plant Community: Abiotic and Biotic Filters Act Hierarchically

The study of species coexistence and community assembly has been a hot topic in ecology for decades. Disentangling the hierarchical role of abiotic and biotic filters is crucial to understand community assembly processes. The most critical environmental factor in semi-arid environments is known to be water availability, and perennials are usually described as nurses that create milder local conditions and expand the niche range of several species. We aimed to broaden this view by jointly evaluating how biological soil crusts (BSCs), water availability, perennial species (presence/absence of Stipa tenacissima) and plant-plant interactions shape a semi-arid annual plant community. The presence and cover of annual species was monitored during three years of contrasting climate. Water stress acted as the primary filter determining the species pool available for plant community assembly. Stipa and BSCs acted as secondary filters by modulating the effects of water availability. At extremely harsh environmental conditions, Stipa exerted a negative effect on the annual plant community, while at more benign conditions it increased annual community richness. Biological soil crusts exerted a contradictory effect depending on climate and on the presence of Stipa, favoring annuals in the most adverse conditions but showing repulsion at higher water availability conditions. Finally, interactions among co-occurring annuals shaped species richness and diversity of the final annual plant assembly. This study sheds light on the processes determining the assembly of annual communities and highlights the importance of Biological Soil Crusts and of interactions among annua

Plant life on gypsum: a review of its multiple facets

The adaptation of plants to particular soil types has long intrigued biologists. Gypsum soils occupy large areas in many regions of the world and host a striking biological diversity, but their vegetation has been much less studied than that developing over serpentine or saline soils. Herein, we review all aspects of plant life on gypsum ecosystems, discuss the main processes driving their structure and functioning, and highlight the main conservation threats that they face. Plant communities in gypsum habitats typically show distinctive bands at very small spatial scales, which are mainly determined by topography. Plants living on gypsum soils can be classified into three categories: (i) wide gypsophiles are specialists that can penetrate the physical soil crust during early life stages and have physiological adjustments to cope with the chemical limitations imposed by gypsum soils; (ii) narrow gypsophiles are refugee plants which successfully deal with the physical soil crust and can tolerate these chemical limitations but do not show specific adaptations for this type of soils; and (iii) gypsovags are non-specialist gypsum plants that can only thrive in gypsum soils when the physical crust is absent or reduced. Their ability to survive in gypsum soils may also be mediated by below-ground interactions with soil microorganisms. Gypsophiles and gypsovags show efficient germination at low temperatures, seed and fruit heteromorphism within and among populations, and variation in seed dormancy among plants and populations. In gypsum ecosystems, spatio-temporal changes in the composition and structure of above-ground vegetation are closely related to those of the soil seed bank. Biological soil crusts (BSCs) dominated by cyanobacteria, lichens and mosses are conspicuous in gypsum environments worldwide, and are important drivers of ecosystem processes such as carbon and nitrogen cycling, water infiltration and run-off and soil stability. These organisms are also important determinants of the structure of annual plant communities living on gypsum soils. The short-distance seed dispersal of gypsophiles is responsible for the high number of very narrow endemisms typically found in gypsum outcrops, and suggests that these species are evolutionarily old taxa due to the time they need to colonize isolated gypsum outcrops by chance. Climate change and habitat fragmentation negatively affect both plants and BSCs in gypsum habitats, and are among the major threats to these ecosystems. Gypsum habitats and specialists offer the chance to advance our knowledge on restrictive soils, and are ideal models not only to test important evolutionary questions such as tolerance to low Ca/Mg proportions in soils, but also to improve the theoretical framework of community ecology and ecosystem functioning.A.E. was funded by projects CGL-2012-38427 (MOUNTAINS) of the Spanish Economy and Competitiveness Ministry, REMEDINAL2 (P2009/AMB-1783) and ECONECT funded by OHL S.A. F.T.M. was supported by the European Research Council under the European Community's Seventh Framework Programme (FP7/2007-2013)/ERC Grant agreement n° 242658. S.P. was funded by a Juan de la Cierva contract (MEC, Spain). We acknowledge two anonymous referees for their valuable comments. We thank Lori De Hond for revising the text.Peer reviewe

Plant affinity to extreme soils and foliar sulphur mediate species-specific responses to sheep grazing in gypsum systems

[Background] Plants growing on extreme soils have mainly been described in relation to their adaptations to edaphic conditions, although herbivores may also be an important factor in these ecosystems. Gypsum soils occur in drylands often where livestock practices occur. However, it is unknown whether plant traits related to gypsum soil constraints are associated with resistance to herbivory.[Aims] In order to assess whether gypsum specialist species might be favoured at higher grazing levels and to detect the traits involved, we evaluated the responses of gypsum specialists vs. generalists to three intensities of livestock pressure.[Methods] We analysed the relative cover shifts of species along a livestock gradient, and variation in canopy height, canopy area, leaf carbon (C), nitrogen (N), and sulphur (S), specific leaf area (SLA) and leaf dry matter content (LDMC).[Results] We found that gypsum-specialists responded by increasing or maintaining their cover at medium and high grazing pressure, whereas most generalists responded by decreasing it. Gypsum-specialists showed higher leaf S than generalists, regardless of grazing intensity. All species showed similar patterns for traits linked to loss of above-ground biomass when grazing increased.[Conclusions] Plant affinity to gypsum soils mediates vulnerability to grazing with foliar S possibly being a defence trait.This work was supported by Gobierno de España [MICINN, CGL2015-71360-P, CGL2016-80783-R and PID2019-111159GB-C31]; by European Union’s Horizon 2020 [H2020-MSCA-RISE-777803]; and by Consejo Superior de Investigaciones Científicas [COOPB20231]. AC and SP were funded by a FPI fellowship [MICINN, BES-2016-076455] and a Ramón y Cajal Fellowship [MICINN, RYC-2013-14164], respectively.Peer reviewe

Theoretical framework of our study.

<p>It shows the environmental variables acting as abiotic and biotic filters in the studied annual community, and the hypotheses evaluated in this study. The main theoretical framework of our study considers three ecological filters that act in a hierarchical fashion during the species assembly process, the first filter consists on dispersal restrictions that downsizes the species pool from the regional to the local scale <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0041270#pone.0041270-Zobel1" target="_blank">[75]</a>, subsequently, the available species pool is filtered by the abiotic environment, especially in stressful environmental conditions <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0041270#pone.0041270-Chase1" target="_blank">[60]</a>, and finally, the biotic filter that encompasses the intra- and inter-specific interactions mostly act at the plant-to plant spatial scales <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0041270#pone.0041270-Bycroft1" target="_blank">[76]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0041270#pone.0041270-Stoll1" target="_blank">[77]</a> and define the final species assembly.</p