Gonzalo García-Baquero

Community Turnover of Wood-Inhabiting Fungi across Hierarchical Spatial Scales

For efficient use of conservation resources it is important to determine how species diversity changes across spatial scales. In many poorly known species groups little is known about at which spatial scales the conservation efforts should be focused. Here we examined how the community turnover of wood-inhabiting fungi is realised at three hierarchical levels, and how much of community variation is explained by variation in resource composition and spatial proximity. The hierarchical study design consisted of management type (fixed factor), forest site (random factor, nested within management type) and study plots (randomly placed plots within each study site). To examine how species richness varied across the three hierarchical scales, randomized species accumulation curves and additive partitioning of species richness were applied. To analyse variation in wood-inhabiting species and dead wood composition at each scale, linear and Permanova modelling approaches were used. Wood-inhabiting fungal communities were dominated by rare and infrequent species. The similarity of fungal communities was higher within sites and within management categories than among sites or between the two management categories, and it decreased with increasing distance among the sampling plots and with decreasing similarity of dead wood resources. However, only a small part of community variation could be explained by these factors. The species present in managed forests were in a large extent a subset of those species present in natural forests. Our results suggest that in particular the protection of rare species requires a large total area. As managed forests have only little additional value complementing the diversity of natural forests, the conservation of natural forests is the key to ecologically effective conservation. As the dissimilarity of fungal communities increases with distance, the conserved natural forest sites should be broadly distributed in space, yet the individual conserved areas should be large enough to ensure local persistence.

Can environmental constraints determine random patterns of plant species co‐occurrence?

Plant community ecologists use the null model approach to infer assembly processes from observed patterns of species co-occurrence. In about a third of published studies, the null hypothesis of random assembly cannot be rejected. When this occurs, plant ecologists interpret that the observed random pattern is not environmentally constrained – but probably generated by stochastic processes. The null model approach (using the C-score and the discrepancy index) was used to test for random assembly under two simulation algorithms. Logistic regression, distance-based redundancy analysis, and constrained ordination were used to test for environmental determinism (species segregation along environmental gradients or turnover and species aggregation). This article introduces an environmentally determined community of alpine hydrophytes that presents itself as randomly assembled. The pathway through which the random pattern arises in this community is suggested to be as follows: Two simultaneous environmental processes, one leading to species aggregation and the other leading to species segregation, concurrently generate the observed pattern, which results to be neither aggregated nor segregated – but random. A simulation study supports this suggestion. Although apparently simple, the null model approach seems to assume that a single ecological factor prevails or that if several factors decisively influence the community, then they all exert their influence in the same direction, generating either aggregation or segregation. As these assumptions are unlikely to hold in most cases and assembly processes cannot be inferred from random patterns, we would like to propose plant ecologists to investigate specifically the ecological processes responsible for observed random patterns, instead of trying to infer processes from patterns.

Grazing exclusion unleashes competitive plant responses in Iberian Atlantic mountain grasslands

Questions Does the absence of equalizing mechanisms after cessation of grazing unleash strong aboveground competitors to create large patches in the community? Do these competitive intraspecific aggregations displace and exclude other species, thereby reducing species diversity? Location Atlantic grasslands in the Aralar Natural Park, Basque Country, Northern Iberian Peninsula. Methods Large herbivores were experimentally excluded from three sites (50 m × 50 m exclusion fences) during nine years in a productive semi-natural grassland system with long history of grazing, using adjacent grazed plots as experimental controls. Sampling was carried out by placing systematically one hundred quadrats (0.5 m × 0.5 m) in each of the six plots. Floristic composition and abundance, as well as eight hydrological and chemical soil properties, were measured in each quadrat. The spatial structures created by competitive species were analysed using Redundancy analysis in conjunction with Morans Eigenvector Maps, and soil variables were simultaneously included in the analyses, thus disentangling the structures likely created by niche effects. Competitive exclusion was further determined using linear regressions between species richness and abundance of competitive species. Results Grazing exclusion unleashed competitive species such as Festuca rubra and Agrostis capillaris, which became dominant in the exclusion plots and created large spatial patches. Furthermore, a negative linear relationship, consistent across exclusion plots, was observed between species richness and abundance of competitive species, indicating that strong aboveground competitors outcompeted other species when herbivores were excluded. However, the outcome of grazing exclusion across sites depended to some extent on local environmental conditions (niche effects). Conclusions This work confirms that the powerful equalizing mechanism of disturbance by herbivores is crucial for species co-existence in productive grasslands. However, important differences observed in environmental effects across sites suggest that, even in highly productive grasslands, plant traits and local environmental characteristics (niche effects) do matter for species co-existence. This article is protected by copyright. All rights reserved.

Plasticity to salinity and transgenerational effects in the nonnative shrub Baccharis halimifolia: Insights into an estuarine invasion

PREMISE OF THE STUDY Abiotic constraints act as selection filters for plant invasion in stressful habitats. Adaptive phenotypic plasticity and transgenerational effects play a major role in colonization of heterogeneous habitats when the scale of environmental variation is smaller than that of gene flow. We investigated how plasticity and parental salinity conditions influence the performance of the invasive dioecious shrub Baccharis halimifolia, which replaces heterogeneous estuarine communities in Europe with monospecific and continuous stands. METHODS In two greenhouse experiments, we grew plants derived from seeds and cuttings collected through interspersed patches differing in edaphic salinity from an invasive population. We estimated parental environmental salinity from leaf Na(+) content in parental plants, and we measured fitness and ion homeostasis of the offspring grown in contrasting salinity conditions. KEY RESULTS Baccharis halimifolia tolerates high salinity but experiences drastic biomass reduction at moderate salinity. At moderate salinity, responses to salinity are affected by the parental salinity: flowering initiation in seedlings and male cuttings is positively correlated with parental leaf Na(+) content, and biomass is positively correlated with maternal leaf Na(+) in female cuttings and seedlings. Plant height, leaf production, specific leaf area, and ionic homeostasis at the low part of the gradient are also affected by parental salinity, suggesting enhanced shoot growth as parental salinity increases. CONCLUSIONS Our results support plasticity to salinity and transgenerational effects as factors with great potential to contribute to the invasive ability of B. halimifolia through estuarine communities of high conservation value.

Does functional soil microbial diversity contribute to explain within-site plant β-diversity in an alpine grassland and a dehesa meadow in Spain?

SummaryQuestions Once that the effects of hydrological and chemical soil properties have been accounted for, does soil microbial diversity contribute to explain change in plant community structure (i.e. within-site beta-diversity)? If so, at which spatial scale does microbial diversity operate? Location: La Mina in Moscosa Farm, Salamanca, western Spain (dehesa community) and Laguna Larga in the Urbion Peaks, Soria, central-northern Spain (alpine grassland). Methods The abundance of vascular plant species, soil gram-negative microbial functional types and soil chemical properties (pH, available phosphorus, and extractable cations) were sampled at both sites, for which hydrological models were available. Redundancy analysis (RDA) was used to partition variation in plant community structure into hydrological, chemical and microbial components. Spatial filters, arranged in scalograms, were used to test for the spatial scales at which plant community structure change. Results In the case of the dehesa the diversity of soil gram-negative microbes, weakly driven by soil pH, contributed to a small extent (adj-R2 = 2%) and at a relative medium spatial scale to explain change in plant community structure. The abundance of a few dehesa species, both annual (Trifolium dubium, Vulpia bromoides) and perennial (Poa bulbosa, Festuca ampla), was associated with either increasing or decreasing soil microbial diversity. In the alpine meadow the contribution was negligible. Conclusions Microbial diversity can drive community structure, though in the hierarchy of environmental factors structuring communities it appears to rank lower than other soil factors. Still, microbial diversity appears to promote or restrain individual plant species. This paper aims to encourage future studies to use more comprehensive and insightful techniques to assess microbial diversity and to combine this with statistical approaches such as the one used here. This article is protected by copyright. All rights reserved.

Climate and Human Pressure Constraints Co-Explain Regional Plant Invasion at Different Spatial Scales.

Alien species invasion represents a global threat to biodiversity and ecosystems. Explaining invasion patterns in terms of environmental constraints will help us to assess invasion risks and plan control strategies. We aim to identify plant invasion patterns in the Basque Country (Spain), and to determine the effects of climate and human pressure on that pattern. We modeled the regional distribution of 89 invasive plant species using two approaches. First, distance-based Moran’s eigenvector maps were used to partition variation in the invasive species richness, S, into spatial components at broad and fine scales; redundancy analysis was then used to explain those components on the basis of climate and human pressure descriptors. Second, we used generalized additive mixed modeling to fit species-specific responses to the same descriptors. Climate and human pressure descriptors have different effects on S at different spatial scales. Broad-scale spatially structured temperature and precipitation, and fine-scale spatially structured human population density and percentage of natural and semi-natural areas, explained altogether 38.7% of the total variance. The distribution of 84% of the individually tested species was related to either temperature, precipitation or both, and 68% was related to either population density or natural and semi-natural areas, displaying similar responses. The spatial pattern of the invasive species richness is strongly environmentally forced, mainly by climate factors. Since individual species responses were proved to be both similarly constrained in shape and explained variance by the same environmental factors, we conclude that the pattern of invasive species richness results from individual species’ environmental preferences.

Testing wastewater treatment plant effluent effects on microbial and detritivore performance: A combined field and laboratory experiment

The amount of pollutants and nutrients entering rivers via point sources is increasing along with human population and activity. Although wastewater treatment plants (WWTPs) greatly reduce pollutant loads into the environment, excess nutrient loading is a problem in many streams. Using a Community and Ecosystem Function (CEF) approach, we quantified the effects of WWTP effluent on the performance of microbes and detritivores associated to organic matter decomposition, a key ecosystem process. We measured organic matter breakdown rates, respiration rates and exo-enzymatic activities of aquatic microbes. We also measured food consumption and growth rates and RNA to body-mass ratios (RNA:BM) of a dominant amphipod Echinogammarus berilloni. We predicted responses to follow a subsidy-stress pattern and differences between treatments to increase over time. To examine temporal effects of effluent, we performed a laboratory microcosm experiment under a range of effluent concentrations (0, 20, 40, 60, 80 and 100%), taking samples over time (days 8, 15 and 30; 4 and 10 replicates to assess microbe and detritivore performance respectively, per treatment and day). This experiment was combined with a field in situ Before-After Control-Impact Paired (BACIP) experiment whereby we added WWTP effluent poured (10 L s-1 during 20-40 min every 2 h) into a stream and collected microbial and detritivore samples at days 8 and 15 (5 and 15 replicates to assess the microbe and detritivore performance respectively, per period, reach and sampling day). Responses were clearer in the laboratory experiment, where the effluent caused a general subsidy response. Field measures did not show any significant response, probably because of the high dilution of the effluent in stream water (average of 1.6%). None of the measured variables in any of the experiments followed the predicted subsidy-stress response. Microbial breakdown, respiration rates, exo-enzymatic activities and invertebrate RNA:BM increased with effluent concentrations. Differences in microbial respiration and exo-enzymatic activities among effluent treatments increased with incubation time, whereas microbial breakdown rates and RNA:BM were consistent over time. At the end of the laboratory experiment, microbial respiration rates increased 156% and RN:BM 115% at 100% effluent concentration. Detritivore consumption and growth rates increased asymptotically, and both responses increased with by incubation time. Our results indicate that WWTP effluent stimulates microbial activities and alters detritivore performance, and stream water dilution may mitigate these effects.

The High Mountain Flora and Vegetation

The orophile flora of the Iberian Peninsula is analysed in order to extract the basic biogeographical patterns of the plant diversity contained in this group. A total of 999 taxa at the level of species and subspecies have been identified as the Iberian cold-adapted plants living in the mountains, representing 15% of the total Iberian flora. Their distribution patterns across the six main mountain ranges, including all the ranges with significant areas above 1600 m, have been analysed. Species richness is correlated with the area above that altitude. Four main floristic elements have been distinguished within the orophile flora: the Arctic-Boreal, the European Orophile, the Endemic and the Iberian-North African. The first two elements are mainly spread across the northern mountain ranges in a pattern symmetrical to the distribution of the Iberian-North African element. The Endemic element is the largest one and is better represented in the ranges with the highest summits. After an analysis of the taxonomic diversity (TD) of all ranges, it is evident that, if phylogenetic diversity is taken into account, the southern ranges are less diverse than expected, in contrast to the northern ones, in spite of the fact that they host a larger number of endemics. This means that, even when an element contains many species, biodiversity values may be diminished in case those species are phylogenetically related. This particularly concerns the Endemic element, composed mainly of narrowly related geo-vicariants. Concerning the vegetation, the communities inhabiting rupicolous habitats such as crevices and screes, as well as the psychro-xerophilous grasslands, are the main contributors to this flora. The biogeographical distribution of the vegetation units follows a north-south pattern, with a preference for the siliceous mountains in the Boreal and Temperate units and for the calcareous mountains in the case of the Mediterranean units. A number of Iberian units has their optimum in the central siliceous ranges, such as the Nardus grasslands.

Anomalous diameter growth and population age structure in mature Canary Islands pine stands

Canary Islands pine (Pinus canariensis Chr. Sm. ex DC) is often described as serotinous, even though most serotinous attributes are absent or weakly developed and the trees do not seem to experience a natural fi re regime that would favor and sustain serotiny. We studied the age structure of 22 old-growth stands on the slopes of Mt. Teide on Tenerife, Canary Islands. Statistically robust relationships between trunk diameter at breast height and tree age allowed us to use diameter-age regressions to summarize population age structures and to reconstruct disturbance history. The age structure of only one stand statistically fi t the null hypothesiss expectation of a smoothly declining L-shaped negative exponential, non-disturbance population model. Departures from the model commonly featured high densities of seedlings and saplings in the absence of recent fi res (indicating that regeneration is independent of fi re) and age structures that exhibited one or more peaks of establishment, the average number of years between peaks being 78 yr. Onset of sexual reproduction averaged 46 yr, and the age of mature overstory individuals often exceeded 200 yr. Anomalously, variation in most vegetation attributes, including stem diameter growth, failed to signifi cantly correlate with major abiotic gradients-elevation, temperature, precipitation, exposure to trade wind clouds, slope aspect and steepness, and geological substrate in habitats where P. canariensis dominated.

Caracterización fitosociológica del hábitat de la especie amenazada Androsace rioxana A. Segura

Androsase rioxana es un endemismo demandes amenazado del que solo se conocen dos localidades en el mundo, ambas ubicadas en el lugar de interes comunitario (L.IC.) Sierras de La Demanda, Urbion, Cebollera y Cameras. Usando los metodos de la Fitosociologia sigmatista y analisis multivariante (Analisis de Componentes Principates y ClusterAnalysis), caracterizamos su habitat. Se trata de pastizales psicroxerofilos relacionados con la asociacion Antennario dioiecae-Festucetum curvinfoliae , un habitat usado en la delimitacion de la Red Natura-2000.