Examinando por Autor "Pescador, David S."

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A dimmer shade of pale: revealing the faint signature of local assembly processes on the structure of strongly filtered plant communities
(Wiley, 2020-10-08) López-Angulo, Jesús; De la Cruz, Marcelino; Pescador, David S.; Sánchez, Ana M.; Escudero, Adrián
Trait-based ecology suggests that abiotic filtering is the main mechanism structuring the regional species pool in different subsets of habitat-specific species. At more local spatial scales, other ecological processes may add on giving rise to complex patterns of functional diversity (FD). Understanding how assembly processes operating on the habitat-specific species pools produce the locally observed plant assemblages is an ongoing challenge. Here, we evaluated the importance of different processes to community assembly in an alpine fellfield, assessing its effects on local plant trait FD. Using classical randomization tests and linear mixed models, we compared the observed FD with expectations from three null models that hierarchically incorporate additional assembly constraints: stochastic null models (random assembly), independence null models (each species responding individual and independently to abiotic environment), and co-occurrence null models (species responding to environmental variation and to the presence of other species). We sampled species composition in 115 quadrats across 24 locations in the central Pyrenees (Spain) that differed in soil conditions, solar radiation and elevation. Overall, the classical randomization tests were unable to find differences between the observed and expected functional patterns, suggesting that the strong abiotic filters that sort out the flora of extreme regional environments blur any signal of other local processes. However, our approach based on linear mixed models revealed the signature of different ecological processes. In the case of seed mass and leaf thickness, observed FD significantly deviated from the expectations of the stochastic model, suggesting that fine-scale abiotic filtering and facilitation can be behind these patterns. Our study highlights how the hierarchical incorporation of ecological additional constraints may shed light on the dim signal left by local assembly processes in alpine environments.
Climate and small scale factors determine functional diversity shifts of biological soil crusts in Iberian drylands
(2014-04-03) Concostrina-Zubiri, Laura; Pescador, David S.; Martínez, Isabel; Escudero, Adrián
Understanding functional diversity is critical to manage and preserve biodiversity and ecosystem functioning in the face of global change. However, the efforts to characterize this functional component have been mostly directed to vascular vegetation. We sampled lichen-dominated biological soil crusts (BSCs) in semiarid grasslands along an environmental gradient in the Iberian Peninsula. We characterized five effect functional traits for 31 lichens species, and evaluated the influence of large scale (i.e. precipitation) and small scale factors (i.e. substrate type, shrub presence, Stipa tenacissima presence) on dominant trait values; i.e. community weighted means, and functional divergence; i.e. Rao quadratic entropy in 580 sampling quadrats. Across the gradient, we found multiple trait shifts and a general increase of functional divergence with increasing precipitation. We also observed that substrate type and small scale biotic factors determined shifts in all traits studied, while these factors affected less to functional divergence. Comparing functional diversity with taxonomic diversity, we found contrasting responses to both large and small scale factors. These findings suggest that BSC community trait composition is influenced by multi-scale abiotic and biotic factors with environmental filtering dominating at large spatial scales and limiting similarity at specific small scales. Also, our results emphasize the potential differences between taxonomic and functional diversity in response to environmental factors. We concluded that functional diversity of BSCs not only provides novel and critical knowledge of BSC community structure, but also it should be considered as a critical tool in biodiversity conservation strategies, ecosystem services assessment and ecological modelling.
Determinants of high mountain plant diversity in the Chilean Andes: From regional to local spatial scales
(2018-07-06) López-Angulo, Jesús; Pescador, David S.; Sánchez, Ana M.; Mihoč, Maritza A.; Cavieres, Lohengrin A.; Escudero, Adrián
Mountains are considered excellent natural laboratories for studying the determinants of plant diversity at contrasting spatial scales. To gain insights into how plant diversity is structured at different spatial scales, we surveyed high mountain plant communities in the Chilean Andes where man-driven perturbations are rare. This was done along elevational gradients located at different latitudes taking into account factors that act at fine scales, including abiotic (potential solar radiation and soil quality) and biotic (species interactions) factors, and considering multiple spatial scales. Species richness, inverse of Simpson’s concentration (Dequiv), beta-diversity and plant cover were estimated using the percentage of cover per species recorded in 34 sites in the different regions with contrasted climates. Overall, plant species richness, Dequiv and plant cover were lower in sites located at higher latitudes. We found a unimodal relationship between species richness and elevation and this pattern was constant independently of the regional climatic conditions. Soil quality decreased the beta-diversity among the plots in each massif and increased the richness, the Dequiv and cover. Segregated patterns of species co-occurrence were related to increases in richness, Dequiv and plant cover at finer scales. Our results showed that elevation patterns of alpine plant diversity remained constant along the regions although the mechanisms underlying these diversity patterns may differ among climatic regions. They also suggested that the patterns of plant diversity in alpine ecosystems respond to a series of factors (abiotic and biotic) that act jointly at different spatial scale determining the assemblages of local communities, but their importance can only be assessed using a multi-scale spatial approach.
Estimating belowground plant abundance with DNA metabarcoding
(Wiley, 2019-09) Matesanz, Silvia; Pescador, David S.; Pías, Beatriz; Sánchez, Ana M.; Chacón-Labella, Julia; Illuminati, Angela; De la Cruz, Marcelino; López-Angulo, Jesús; Marí-Mena, Neus; Vizcaíno, Antón; Escudero, Adrián
Most work on plant community ecology has been performed above ground, neglecting the processes that occur in the soil. DNA metabarcoding, in which multiple species are computationally identified in bulk samples, can help to overcome the logistical limitations involved in sampling plant communities belowground. However, a major limitation of this methodology is the quantification of species’ abundances based on the percentage of sequences assigned to each taxon. Using root tissues of five dominant species in a semi-arid Mediterranean shrubland (Bupleurum fruticescens, Helianthemum cinereum, Linum suffruticosum, Stipa pennata and Thymus vulgaris), we built pairwise mixtures of relative abundance (20%, 50% and 80% biomass), and implemented two methods (linear model fits and correction indices) to improve estimates of root biomass. We validated both methods with multispecies mixtures that simulate field-collected samples. For all species, we found a positive and highly significant relationship between the percentage of sequences and biomass in the mixtures (R2 = .44–.66), but the equations for each species (slope and intercept) differed among them, and two species were consistently over- and under-estimated. The correction indices greatly improved the estimates of biomass percentage for all five species in the multispecies mixtures, and reduced the overall error from 17% to 6%. Our results show that, through the use of post-sequencing quantification methods on mock communities, DNA metabarcoding can be effectively used to determine not only species’ presence but also their relative abundance in field samples of root mixtures. Importantly, knowledge of these aspects will allow us to study key, yet poorly understood, belowground processes.
Every little helps: the functional role of individuals in assembling any plant community, from the richest to monospecific ones
(Wiley, 2021-09) Escudero, Adrián; Matesanz, Silvia; Pescador, David S.; De la Cruz, Marcelino; Valladares, Fernando; Cavieres, Lohengrin A.
Plant trait-based ecology is a powerful extension of the attempt of community ecologists to unveil assembly mechanisms. However, the two main expected determinants of community assembly, niche and neutral processes, can be confused under this framework. Here, we propose to move from trait-based to phenotype-based community ecology, accounting for the variation between individuals (phenotypes affected by the abiotic and biotic environment, and vice versa), and explicitly considering their ability to compete with or facilitate its neighbours. This would shift our focus from species’ niche responses to niche specialization of phenotypes, reducing the space for neutrality at the finest scales. The current assembly framework, based mainly on niche complementarity and using species-average functional traits, has been developed exploring mega-diverse communities, but it fails at describing poor plant communities. Under this framework, monospecificity would be interpreted as an arena where functionally similar individuals compete, consequently leading to regular patterns, which are rarely found in nature. Our niche specialization framework could help explaining coexistence in rich plant communities, where the higher fraction of functional variation is found between species, whereas the intraspecific trait variation dominates in poor species and monospecific communities. We propose a guide to conduct massive phenotyping at the community scale based on the use of visible and near-infrared spectroscopy. We also discuss the need to integrate the so-called plant's eye perspective based on the use of spatial pattern statistics in the current community ecology toolbox.
Larger aboveground neighbourhood scales maximise similarity but do not eliminate discrepancies with belowground plant diversity in a Mediterranean shrubland
(Springer, 2021-01-15) Illuminati, Angela; López-Angulo, Jesús; De la Cruz, Marcelino; Chacón-Labella, Julia; Pescador, David S.; Pías, Beatriz; Sánchez, Ana M.; Escudero, Adrián; Matesanz, Silvia
Aims An unresolved question in plant ecology is whether diversity of the aboveground and belowground compartments of a plant community is similar at different neighbourhood scales. We investigated how the similarity between both compartments varies with the aboveground sampling grain and if significant discrepancies exist between aboveground and belowground plant diversity at the maximum similarity scale. Methods We fully mapped the aboveground perennial plant community of a 64 m2 plot in a Mediterranean shrubland and analysed this compartment by assessing diversity in 5 to 50 cm radii circles centred in soil cores. We sampled 2.5 cm radius root cores at two different depths and identified plant species by using DNA metabarcoding to characterise the belowground compartment. We quantified differences in species richness, composition and species’ spatial distribution above- and belowground. Results The differences between aboveground and belowground communities were affected by the size of the aboveground sampling grain and were minimised when considering a circle of 20 cm radius in the aboveground. We found a significant dissimilarity in richness and composition between the two compartments, with larger differences when considering the deeper soil layer only. Conclusions Our results showed that the spatial grain selected to sample a plant community aboveground and belowground is critical to characterise them in a comparable manner. Although their composition is related, species distribution patterns strongly differ, suggesting the simultaneous action of different assembly mechanisms. Our results call for caution when studying community assembly considering only the standing vegetation, since total plant diversity can be underappreciated.
Maintaining distances with the engineer: Patterns of coexistence in plant communities beyond the patch-bare dichotomy
(2014-06-20) Pescador, David S.; Chacón-Labella, Julia; de la Cruz, Marcelino; Escudero, Adrián
Two-phase plant communities with an engineer conforming conspicuous patches and affecting the performance and patterns of coexisting species are the norm under stressful conditions. To unveil the mechanisms governing coexistence in these communities at multiple spatial scales, we have developed a new point-raster approach of spatial pattern analysis, which was applied to a Mediterranean high mountain grassland to show how Festuca curvifolia patches affect the local distribution of coexisting species. We recorded 22 111 individuals of 17 plant perennial species. Most coexisting species were negatively associated with F. curvifolia clumps. Nevertheless, bivariate nearest-neighbor analyses revealed that the majority of coexisting species were confined at relatively short distances from F. curvifolia borders (between 0–2 cm and up to 8 cm in some cases). Our study suggests the existence of a fine-scale effect of F. curvifolia for most species promoting coexistence through a mechanism we call ‘facilitation in the halo’. Most coexisting species are displaced to an interphase area between patches, where two opposite forces reach equilibrium: attenuated severe conditions by proximity to the F. curvifolia canopy (nutrient-rich islands) and competitive exclusion mitigated by avoiding direct contact with F. curvifolia.
Rainy years counteract negative effects of drought on taxonomic, functional and phylogenetic diversity: Resilience in annual plant communities
(Wiley, 2022) López-Rubio, Roberto; Pescador, David S.; Escudero, Adrián; Sánchez, Ana M.
Climate models forecast changes in the amount and distribution of rain, which may affect ecosystems worldwide, especially in drylands where water is already the limiting factor for plant life. Annual plant communities are common in drylands where they can complete their entire life cycle during the rainy period while avoiding the dry season. Moreover, seed dormancy allows them to disperse over time by remaining in the seed bank for long periods. However, the extent to which these communities will be able to tolerate increasing drought is uncertain.We performed a 5-year rainfall reduction treatment under field conditions and determined its effects on annual plant communities in a Mediterranean gypsum ecosystem. We assessed the taxonomic, functional and phylogenetic diversity of these communities each year for 5 years.The taxonomic and functional diversity decreased under the rainfall reduction treatment, whereas the phylogenetic diversity increased. Moreover, the relative importance of species with drought-resistant functional designs increased in the community assemblages. However, after a rainy season with above average rainfall, all of the diversity values recovered completely even under the rainfall reduction treatment.Our results provide important insights into the responses of these plant communities under a climate change scenario, where they indicate high losses of diversity during drought events but rapid recovery in milder years.Synthesis. Our findings highlight the great resilience of annual plant communities in drylands, which may allow them to tolerate increased drought under the present climate change scenario.
Shift in functional traits along soil fertility gradient reflects non-random community assembly in a tropical African rainforest
(SOC ROYAL BOTAN BELGIQUE, 2017-11-22) Libalah, Moses B.; Droissart, Vincent; Sonké, Bonaventure; Hardy, Olivier J.; Drouet, Thomas; Pescador, David S.; Kenfack, David; Thomas, Duncan W.; Chuyong, George B.; Couteron, Pierre
Background and aims – There is increasing recognition that plant traits mediate environmental influence on species distribution, justifying non-random community assembly. We studied the influence of local scale edaphic factors on the distribution of functional traits in a tropical rainforest of Cameroon with the aim to find correlations between the main edaphic gradient and community functional trait metrics (weighted mean trait, functional divergence and intraspecific variation). Methods – Within the Korup Forest Dynamics Plot (50 ha), we randomly selected 44 quadrats of 0.04 ha each, collected soils and analysed 11 topography and soil variables. Leaves were harvested from all 98 tree species found in the quadrats to calculate community trait metrics [quadrat-level weighted mean ( q k ) and functional divergence ( FDiv k )] for leaf area (LA), specific leaf area (SLA), leaf phosphorus (LPC), leaf nitrogen concentration (LNC) and nitrogen to phosphorus ratio (N:P ratio). We examined relationships between the main edaphic gradient with q k , with FDiv k and with intraspecific variation and interpreted correlations as the effects of abiotic filtering and competitive interaction. Key results – Soil fertility was the main edaphic gradient and was significantly correlated with q k for LPC, LNC and LA and with FDiv k for LPC, N:P ratio, LA and SLA, confirming the influence of abiotic filtering and competitive interaction by the soil fertility gradient, respectively. For a given trait, quadrats were either over-dispersed or under-dispersed, accounting for 7–33 % of non-random trait distribution along the soil fertility gradient. Trends in intraspecific traits variation were consistently lower than quadrat-level mean traits along the soil fertility gradient. Conclusions – This study demonstrates the influence of soil fertility gradient on local scale community trait distribution and its contribution to non-random community assembly.
Soil under nurse plants is always better than outside: a survey on soil amelioration by a complete guild of nurse plants across a long environmental gradient
(2016-05-01) Mihoc, Maritza A. K.; Giménez-Benavides, Luís; Pescador, David S.; Sánchez, Ana María; Cavieres, Lohen; Escudero, Adrián
Aims Soil under nurse plants is more fertile than in the harsh surroundings. This is a primary mechanism involved in plant to plant facilitation and it is critical in structuring plant communities under stressful conditions. However we do not know how this soil enrichment process varies along complex environmental gradients and among coexisting nurse plants. Methods Soil properties related to structure, resource stocks and microbial activity, were compared among up to ten nurse plant species and adjacent barren soil areas, along a 1600 m elevation gradient above the treeline in central Chilean Andes. Shifts in Relative Interaction Index (RII) sensu Armas (Ecology 85: 2682–2686, 2004) and in coefficient of variation on soil properties were also modelled. Results Soil under nurse plants was always richer than on barren areas irrespective of altitude, except in the case of texture with more small particles in the intermediate altitude. β-glucosidase activity was higher under cushion plants than under nurse plants with other growth habit. Besides β-glucosidase and phosphatase activities were more variable at higher altitudes. Nitrogen was more variable under nurse plants than in barren areas and its RII values were lower at intermediate altitudes. Conclusions Soil amelioration by nurse plants occurred all along the studied environmental gradient promoting islands of fertility and a general increase on soil niches heterogeneity.
Summer Freezing Resistance: A Critical Filter for Plant Community Assemblies in Mediterranean High Mountains
(Frontiers, 2016-02-22) Pescador, David S.; Sierra-Almeida, Ángela; Torres, Pablo J.; Escudero, Adrián
Assessing freezing community response and whether freezing resistance is related to other functional traits is essential for understanding alpine community assemblages, particularly in Mediterranean environments where plants are exposed to freezing temperatures and summer droughts. Thus, we characterized the leaf freezing resistance of 42 plant species in 38 plots at Sierra de Guadarrama (Spain) by measuring their ice nucleation temperature, freezing point (FP), and low-temperature damage (LT50), as well as determining their freezing resistance mechanisms (i.e., tolerance or avoidance). The community response to freezing was estimated for each plot as community weighted means (CWMs) and functional diversity (FD), and we assessed their relative importance with altitude. We established the relationships between freezing resistance, growth forms, and four key plant functional traits (i.e., plant height, specific leaf area, leaf dry matter content (LDMC), and seed mass). There was a wide range of freezing resistance responses and more than in other alpine habitats. At the community level, the CWMs of FP and LT50 responded negatively to altitude, whereas the FD of both traits increased with altitude. The proportion of freezing-tolerant species also increased with altitude. The ranges of FP and LT50 varied among growth forms, and only leaf dry matter content was negatively correlated with freezing-resistance traits. Summer freezing events represent important abiotic filters for assemblies of Mediterranean high mountain communities, as suggested by the CWMs. However, a concomitant summer drought constraint may also explain the high freezing resistance of species that thrive in these areas and the lower FD of freezing resistance traits at lower altitudes. Leaves with high dry matter contents may maintain turgor at lower water potential and enhance drought tolerance in parallel to freezing resistance. This adaptation to drought seems to be a general prerequisite for plants found in xeric mountains.
Tales from the underground: Soil heterogeneity and not only above-ground plant interactions explain fine-scale species patterns in a Mediterranean dwarf-shrubland
(Wiley, 2020-05) Pescador, David S.; De la Cruz, Marcelino; Chacón-Labella, Julia; Pavón-García, Javier; Escudero, Adrián
Questions The current paradigm of plant community assembly relies on a set of processes operating at particular spatial scales. It is assumed that as the spatial scale becomes finer, environmental filtering loses its importance in favor of biotic interactions and neutral processes. Thus, at the very fine spatial scale represented by a rectangular plot of 72.25 m2 in a Mediterranean semiarid dwarf-shrubland, we ask: (a) are the spatial distributions of individuals of the different species explained by neutral models; (b) are these distributions dependent on above-ground plant interactions with the dominant species in the community; and/or (c) are they responding to the spatial variation of different soil variables, in a kind of fine-scale environmental filtering? Location Central Spain. Methods To assess the correlates of fine-scale (i.e., from 0.05–2.00 m) spatial patterns of the species in the community, we fully mapped all perennial individuals inside the rectangular plot. For each species, we fitted one complete spatial randomness (CSR) model that does not assume spatial heterogeneity and three weighted-average inhomogeneous Poisson process (IPP) models using six soil covariates, distribution patterns of the four above-ground dominant plants in the community or both types of covariates. All models were evaluated and compared to select the best-fitting weighted-average model. Results We recorded 7,988 individuals of 22 species. Patterns of all species were appropriately explained by IPP models. For most species the best-fitting weighted-average model included both soil and dominant plants (i.e., 15) or only soil covariates (i.e., 6). The improvement provided by the best-fitting weighted-averaging model in comparison with the CSR model was consistently high (81%). Conclusions Our approach suggests that species in this dwarf-shrubland are mainly structured by soil heterogeneity and modulated in some cases by the interactions established with the dominant species.
The role of root community attributes in predicting soil fungal and bacterial community patterns
(Wiley, 2020-11) López-Angulo, Jesús; De la Cruz, Marcelino; Chacón-Labella, Julia; Illuminati, Angela; Matesanz, Silvia; Pescador, David S.; Pías, Beatriz; Sánchez, Ana M.; Escudero, Adrián
Roots are assumed to play a major role in structuring soil microbial communities, but most studies exploring the relationships between microbes and plants at the community level have only used aboveground plant distribution as a proxy. However, a decoupling between belowground and aboveground plant components may occur due to differential spreading of plant canopies and root systems. Thus, soil microbe–plant links are not completely understood. Using a combination of DNA metabarcoding and spatially explicit sampling at the plant neighbourhood scale, we assessed the influence of the plant root community on soil bacterial and fungal diversity (species richness, composition and β-diversity) in a dry Mediterranean scrubland. We found that root composition and biomass, but not richness, predict unique fractions of variation in microbial richness and composition. Moreover, bacterial β-diversity was related to root β-diversity, while fungal β-diversity was related to aboveground plant β-diversity, suggesting that plants differently influence both microbial groups. Our study highlights the role of plant distribution both belowground and aboveground, soil properties and other spatially structured factors in explaining the heterogeneity in soil microbial diversity. These results also show that incorporating data on both plant community compartments will further our understanding of the relationships between soil microbial and plant communities.
The shape is more important than we ever thought: Plant to plant interactions in a high mountain community
(2019-07-01) Pescador, David S.; de la Cruz, Marcelino; Chacón‐Labella, Julia; Escudero, Adrián
Plant to plant interactions are probably the most important driver of species coexistence at fine spatial scales, but their detection represents a challenge in Ecology. Spatial point pattern analysis (SPPA) is likely the approach most used to identify them, however, it suffers from some limitations related to the over-simplification of individuals to points. Here, we propose a new approach called Overlapping Area Analysis (OAA) to test whether the consideration of the shape and orientation of the individuals reveal signs of interactions between species that would remain undetected with SPPA. We used this approach to analyse a fully mapped cryophilic grassland in the Sierra de Guadarrama National Park (Spain), where the crown of each individual plant (i.e. the species canopy) was approximated by a polygon. We then computed and compared the total overlapping area between the canopy of a focal species and that of any other species in the community with the expectations of a null model of random rotation of each plant around its centroid. We complemented the results of our new approach by comparing with that of SPPA of plants’ centroids. Results of OAA showed that up to 41% of species pairs had less canopy overlap than expected, suggesting that many interspecific canopy associations in this plant community were significantly negative at the finest spatial scale. Contrarily, SPPA estimated that 12% of species pairs were positively associated at spatial scales up to 20 cm, confirming the facilitative effect displayed by the main engineer in the community (Festuca curvifolia Lag.) and by some other dominant species. Our new approach quantifying canopy associations provides new insights into the processes guiding community assembly. While the results of SPPA suggested the prevalence of traditional ‘stress gradient hypothesis’ (i.e. prevalence of positive interactions under stressful abiotic conditions), OAA revealed that many interspecific canopy associations were significantly negative. Overall, most facilitated species optimized this positive effect by placing their centroids as close to the benefactor species as their foraging behaviour allowed while avoiding crown overlap. The method proposed is available in a dedicated r-package that will facilitate its application by other ecologists.
Winter is coming: plant freezing resistance as a key functional trait for the assembly of annual Mediterranean communities
(2018-01-23) Pescador, David S.; Sánchez, Ana M.; Luzuriaga, Arantzazu L.; Sierra-Almeida, Ángela; Escudero, Adrián
Background and Aims In Mediterranean annual plants, germination mainly occurs during the autumn and only those seedlings that survive winter freezing can flower and produce seedlings in spring. Surprisingly, the effect of freezing events as an abiotic determinant of these communities remains unexplored. The present study aimed to investigate how freezing events affect annual Mediterranean communities and whether their functional structure as related to freezing resistance is linked to the main biotic and abiotic determinants of these communities. Methods In 120 plots located on a semi-arid Mediterranean steppe (Spain), the community functional structure related to the lethal temperature causing 50 % frost damage (LT50 trait) in seedlings was estimated and summarized as the community-weighted mean (CWM-LT50) and its functional diversity (FD-LT50). Plots were stratified according to distance to rabbit shelters and latrines as a proxy for rabbit density, proximity to Stipa tenacissima and spring water availability, where annual species abundance was recorded in all plots over three consecutive years. Key Results Annual species were able to resist a threshold temperature of –4 °C and most had LT50 values around the absolute minimum temperature (–9.5 °C) in the three years. Higher rabbit densities led to lower CWM-LT50 and higher FD-LT50 values. Plots close to Stipa tussocks had higher CWM-LT50 values whereas water availability had no effects. Conclusions High freezing resistance was extended among winter annual species, suggesting the presence of an association between historical environmental filtering and low winter temperatures. However, the community functional structure related to freezing resistance remained variable among scenarios with differences in herbivory pressure and distance to perennial vegetation. The trends observed indicate that traits that allow plants to deal with herbivory may also promote freezing resistance, and that tussocks can act as nurses via microclimatic amelioration of harsher winter conditions.