Phenological phases, as adaptive strategies, have been studied in Mediterranean serpentine shrubland vegetation and their endemisms, in the South of the Iberian Peninsula. The aim of this research is to obtain the phenological characterization of the serpentine flora and to make a comparison between endemic serpentine and non?serpentine plants in different years and altitudes. For this purpose, data were taken in the serpentine ecosystem of Sierra Bermeja (Andalusia, Spain) establishing two plots on two altitudinal bioclimatic belts and during two different years. A total of 28 persistent taxa were studied, focusing on serpentinophytes, their allied (magnesicolous) and non?serpentinophytes, trying to detect the possible differences between serpentine endemic taxa and non?endemic plants. Phenological calendars and phenological patterns (phenophasic indexes) were obtained. The species showed phenophasic patterns similar to those of other studied Mediterranean flora: a phenological pause which coincides with summer and most plants behaved as summer semi?deciduous with seasonal dimorphism. There were no statistically significant differences in phenology and in phenological indexes due to the altitude, to the year of sampling and due to the serpentine affinity. The best represented active phenophasic period of the species was 9?11 months of activity although showing the summer phenological pause. Species with low index of reproductive/vegetative activity of the species predominated, employing more time/resources for vegetative functions, and with synchronous phenophases, where flowering and growth coincide (phenophasic pattern type I). The phenophasic period of serpentinophytes and magnesicolous taxa pointed to a certain delay in the period of flowering with respect to the group of non?serpentinophytes, a result which could have reproductive implications.
The leaf economics spectrum (LES) describes covariation of traits relevant to carbon and nutrient economics across plant species, but much less is known about the relationship between the LES and leaf water economy. We propose an approach combining the measurement of two leaf traits related to water use economy, leaf carbon (?13C) and oxygen (?18O) isotopic composition, and the measurement of leaf morphological and nutrient traits to investigate the link between leaf carbon and nutrient economics and water use.
We tested the relationships between leaf traits linked to carbon and nutrient use within the LES and water use traits using leaf ?18O as a proxy of stomatal conductance (gs) and ?13C as a proxy of intrinsic water use efficiency (WUEi) across 15 Mediterranean rangeland species grown in an irrigated common garden and in a natural grassland in Southern France.
The target species spanned a wide range of variation in leaf morphological and nutrient trait values and a wide range of leaf ?18O and ?13C values. PCA analysis revealed multiple associations among leaf morphology, nutrients and isotopic composition, with the first axis alone explaining 56.0% of the total variation across species. Leaf ?18O and ?13C covaried with leaf morphology and leaf nutrient concentrations along a single resource use axis. Species with high leaf ?18O and ?13C (low gs and high WUEi) exhibited a resource-conservative strategy (high LDMC, low leaf N, P and K) whereas species with low leaf ?18O and ?13C (high gs and low WUEi) showed a more resource-acquisitive strategy (high SLA and leaf N, P and K). These leaf trait syndromes and resource use strategies were strongly conserved across sites with contrasting environmental conditions, indicating that foliar ?18O and ?13C can be included as an integral part of the LES for this set of rangeland species.
Overall, the data suggest a tight coupling and coordination between water, carbon and nutrient use strategies across herbaceous plant species. A dual ?18O and ?13C isotope approach combined with LES trait measurements is a promising tool to more comprehensively assess the diversity of resource use strategies among coexisting plant species.
Hotspots of disease transmission can strongly influence pathogen spread. Bee pathogens may be transmitted via shared floral use, but the role of plant species and floral trait variation in shaping transmission dynamics is almost entirely unexplored. Given the importance of pathogens for the decline of several bee species, understanding whether and how plant species and floral traits affect transmission could give us important tools for predicting which plant species may be hotspots for disease spread. We assessed variation in transmission via susceptibility (probability of infection) and mean intensity (cell count of infected bees) of the trypanosomatid gut pathogen Crithidia bombi to uninfected Bombus impatiens workers foraging on 14 plant species, and assessed the role of floral traits, bee size and foraging behavior on transmission. We also conducted a manipulative experiment to determine how the number of open flowers affected transmission on three plant species, Penstemon digitalis, Monarda didyma, and Lythrum salicaria. Plant species differed fourfold in the overall mean abundance of Crithidia in foraging bumble bees (mean including infected and uninfected bees). Across plant species, bee susceptibility and mean intensity increased with the number of reproductive structures per inflorescence (buds, flowers and fruits); smaller bees and those that foraged longer were also more susceptible. Trait-based models were as good or better than species-based models at predicting susceptibility and mean intensity based on AIC values. Surprisingly, floral size and morphology did not significantly predict transmission across species. In the manipulative experiment, more open flowers increased mean pathogen abundance fourfold in Monarda, but had no effect in the other two plant species. Our results suggest that variation among plant species, through their influence on pathogen transmission, may shape bee disease dynamics. Given widespread investment in pollinator-friendly plantings to support pollinators, understanding how plant species affect disease transmission is important for recommending plant species that optimize pollinator health.
1.Understanding how different factors mediate the resistance of communities to climatic variability is a question of considerable ecological interest that remains mostly unresolved. This is particularly remarkable to improve predictions about the impact of climate change on vegetation.
2.Here we used a trait-based approach to analyse the sensitivity to climatic variability over nine years of 19 Mediterranean shrubland communities located in southwest Spain. We evaluated the role of functional diversity and soil environment as drivers of community stability (assessed as changes in plant cover, species diversity and composition).
3.The studied shrubland communities were strongly sensitive to inter-annual variability in climate. First, colder and drier conditions caused remarkable decreases in total plant cover but increased functional diversity, likely because the reduction of plant cover after harsh climatic conditions promoted the expansion of functionally dissimilar species in the new open microsites; although communities returned to their initial values of plant cover after nine years, changes in functional diversity and structure persisted over time. Second, drier and colder conditions favoured the predominance of shrubs with a conservative resource-use strategy (i.e. with higher dry matter content in leaves, stems and roots), bigger seeds and a more efficient use of water.
4.The most functionally diverse communities were the most stable over time in terms of species diversity, likely because a higher number of functionally dissimilar species allowed compensatory dynamics among them.
5.Communities inhabiting more acidic and resource-limited environments were less variable over time, probably because they were mainly constituted by slow-growth, stress-tolerant species that are potentially better adapted to harsh climatic conditions.
6.Synthesis: This study highlights the utility of a trait-based approach to evaluate how plant communities respond to climatic variability. We could infer that the increased frequency of extreme climatic events predicted by climatic models will alter the functional structure of shrubland communities, with potential repercussions for ecosystem functioning. Our results also provide new insights into the role of functional diversity and soil environment as buffers of the climate impact on woody communities, as well as potentially useful information to be applied in ecologically-based management and restoration strategies.
1. Many riparian ecosystems in Mediterranean Europe are affected by land use and flow alteration by dams. We focused on understanding how these stressors and their components affect riparian forests in the region. We asked: (i) are there well-defined, responsive riparian guilds?; (ii) do dam-induced stream flows determine abundance and distribution of riparian guilds? and (iii) what are the main drivers governing composition and cover of riparian guilds in regulated rivers? 2. We inventoried the cover of riparian woody species in free-flowing rivers and downstream of dams. We performed a cluster analysis and ordination to derive riparian guilds, using abundance data from 66 riparian woody species and 26 functional plant traits. We used a reduced set of principal components for the environment, land use and hydrology, and general linear modelling to explore the effect of these factors (separately and combined) on riparian guilds. 3. We found that: (i) four dominant guilds are responsive to disturbance in Southwestern European streams, namely the obligate riparian, water-stress tolerant, deciduous competitive, and Mediterranean evergreen guilds ; (ii) a set of land use and hydrological variables differentially affect the diverse co-occurring riparian guilds; (iii) frequency and duration of high flow pulses and the low-flow conditions were major drivers of change in landscapes dominated by intensive agriculture and forestry; (iv) storage reservoirs reduced the cover of obligate riparian and Mediterranean evergreen guilds, and increased the abundance of water-stress tolerant and deciduous competitive guilds, while run-of-river dams, having limited water storage, reduced both obligate and deciduous competitive guilds. 4. Synthesis and applications. Future research, especially in Southwestern Europe, should address the resilience of riparian guilds and the effects of interacting landscape factors and stressors on guild distribution. Stream flow regulations downstream of reservoirs should focus on specific flow components, namely the magnitude of flows, and frequency and duration of extreme flow events. For successful mitigation of the dam-induced effects on riparian vegetation, river management plans must incorporate the environmental and land use site-specific contexts.
Habitat filtering and limiting similarity are well?documented ecological assembly processes that hierarchically filter species across spatial scales, from a regional pool to local assemblages. However, information on the effects of fine?scale spatial partitioning of species, working as an additional mechanism of coexistence, on community patterns is much scarcer.
In this study, we quantified the importance of fine?scale spatial partitioning, relative to habitat filtering and limiting similarity in structuring grassland communities in the western Swiss Alps. To do so, 298 vegetation plots (2 m × 2 m) each with five nested subplots (20 cm × 20 cm) were used for trait?based assembly tests (i.e., comparisons with several alternative null expectations), examining the observed plot and subplot level ??diversity (indicating habitat filtering and limiting similarity) and the among?subplot ??diversity of traits (indicating fine?scale spatial partitioning). We further assessed variations in the detected signatures of these assembly processes along a set of environmental gradients.
We found habitat filtering was the dominating assembly process at the plot level with diminished effect at the subplot level, whereas limiting similarity prevailed at the subplot level with weaker average effect at the plot level. Plot?level limiting similarity was positively correlated with fine?scale partitioning, suggesting that the trait divergence resulted from a combination of competitive exclusion between functionally similar species and environmental micro?heterogeneities. Overall, signatures of assembly processes only marginally changed along environmental gradients, but the observed trends were more prominent at the plot than at the subplot scale.
Synthesis. Our study emphasises the importance of considering multiple assembly processes and traits simultaneously across spatial scales and environmental gradients to understand the complex drivers of plant community composition.
PLEASE NOTE, THESE DATA ARE ALSO REFERRED TO IN TWO OTHER PUBLICATIONS. PLEASE SEE http://dx.doi.org/10.1111/j.1365-2486.2008.01766.x AND http://dx.doi.org/10.1111/2041-210X.12222 FOR MORE INFORMATION. Aim: This study compares the direct, macroecological approach (MEM) for modelling species richness (SR) with the more recent approach of stacking predictions from individual species distributions (S-SDM). We implemented both approaches on the same dataset and discuss their respective theoretical assumptions, strengths and drawbacks. We also tested how both approaches performed in reproducing observed patterns of SR along an elevational gradient.
Location: Two study areas in the Alps of Switzerland. Methods: We implemented MEM by relating the species counts to environmental predictors with statistical models, assuming a Poisson distribution. S-SDM was implemented by modelling each species distribution individually and then stacking the obtained prediction maps in three different ways – summing binary predictions, summing random draws of binomial trials and summing predicted probabilities – to obtain a final species count. Results: The direct MEM approach yields nearly unbiased predictions centred around the observed mean values, but with a lower correlation between predictions and observations, than that achieved by the S-SDM approaches. This method also cannot provide any information on species identity and, thus, community composition. It does, however, accurately reproduce the hump-shaped pattern of SR observed along the elevational gradient. The S-SDM approach summing binary maps can predict individual species and thus communities, but tends to overpredict SR. The two other S-SDM approaches – the summed binomial trials based on predicted probabilities and summed predicted probabilities – do not overpredict richness, but they predict many competing end points of assembly or they lose the individual species predictions, respectively. Furthermore, all S-SDM approaches fail to appropriately reproduce the observed hump-shaped patterns of SR along the elevational gradient. Main conclusions: Macroecological approach and S-SDM have complementary strengths. We suggest that both could be used in combination to obtain better SR predictions by following the suggestion of constraining S-SDM by MEM predictions.
Anthropogenic impact represents a major pressure on ecosystems, yet little is known about how it affects symbiotic relationships, such as mycorrhizal symbiosis, which plays a crucial role in ecosystem functioning. We analyzed the effects of three human impact types – increasing urbanity, introduction of alien plant species (alienness) and modifications in plant species distribution ranges (as a proxy for naturalness) – on plant community mycorrhization and arbuscular mycorrhization (indicating the degree of forming mycorrhizal symbiosis at plant community level using the relative abundance of mycorrhizal and arbuscular mycorrhizal plants, respectively). The study was carried out in three habitat types, each dominated by a distinct mycorrhizal type – ectomycorrhizal woodlands, ericoid mycorrhizal heathlands and arbuscular mycorrhizal grasslands - at the regional scale in the Netherlands. The response of community mycorrhization and arbuscular mycorrhization to anthropogenic influence showed contrasting patterns, depending on the specific aspect of human impact. Community mycorrhization responded negatively to urbanity and positively to increasing alienness, while arbuscular mycorrhization showed the reverse trend. More natural heathlands were found to be more mycorrhizal and less arbuscular mycorrhizal. The strongest responses were detected in woodlands and heathlands, while mycorrhization in grasslands was relatively insensitive to human impact. Our study highlights the importance of considering mycorrhizal symbiosis in understanding and quantifying the effects of anthropogenic influence on plant communities, especially in woodlands and heathlands.
