Geographical shifts in the successional dynamics of inland dune shrub communities.

Species' environmental requirements and large-scale spatial and evolutionary processes determine the structure and composition of local communities. However, ecological interactions also have major effects on community assembly at landscape and local scales. We evaluate whether two xerophytic shrub communities occurring in SW Portugal follow constrained ecological assembly dynamics throughout large geographical extents, or their composition is rather driven by species' individualistic responses to environmental and macroecological constraints. Inland dune xerophytic shrub communities were characterized in 95 plots. Then, we described the main gradients of vegetation composition and assessed the relevance of biotic interactions. We also characterized the habitat suitability of the dominant species, Stauracanthus genistoides, and Ulex australis, to map the potential distribution of the xerophytic shrub communities. Finally, we examined the relationships between the vegetation gradients and a broad set of explanatory variables to identify the relative importance of each factor driving changes in community composition. We found that xerophytic shrubs follow uniform successional patterns throughout the whole geographical area studied, but each community responds differently to the main environmental gradients in each region. Soil organic matter is the main determinant of community variations in the northern region, Setúbal Peninsula, whereas aridity is so in the South/South-Western region. In contrast, in the central region, Comporta, the variation between S. genistoides and U. australis communities is explained mainly by aridity and temperature seasonality, followed by the individualistic responses of the dominant species and soil organic matter. Overall, these results indicate that, the relative importance of the main factors causing community-level responses varies according to regional processes and the suitability of the environmental conditions for the dominant species in these communities. These responses are also determined by intrinsic community mechanisms that result in a high degree of similarity in the gradient-driven community stages in different regions.

Differential Impact of the Pinewood Nematode on Pinus Species Under Drought Conditions.

The pinewood nematode (PWN), Bursaphelenchus xylophilus, responsible for the pine wilt disease (PWD), is a major threat to pine forests worldwide. Since forest mortality due to PWN might be exacerbated by climate, the concerns regarding PWD in the Mediterranean region are further emphasized by the projected scenarios of more drought events and higher temperatures. In this context, it is essential to better understand the pine species vulnerability to PWN under these conditions. To achieve that, physiological responses and wilting symptoms were monitored in artificially inoculated Pinus pinaster (P. pinaster), Pinus pinea (P. pinea), and Pinus radiata (P. radiata) saplings under controlled temperature (25/30°C) and water availability (watered/water stressed). The results obtained showed that the impact of PWN is species-dependent, being infected P. pinaster and P. radiata more prone to physiological and morphological damage than P. pinea. For the more susceptible species (P. pinaster and P. radiata), the presence of the nematode was the main driver of photosynthetic responses, regardless of their temperature or water regime conditions. Nevertheless, water potential was revealed to be highly affected by the synergy of PWN and the studied abiotic conditions, with higher temperatures (P. pinaster) or water limitation (P. radiata) increasing the impact of nematodes on trees' water status. Furthermore, water limitation had an influence on nematodes density and its allocation on trees' structures, with P. pinaster revealing the highest nematode abundance and inner dispersion. In inoculated P. pinea individuals, nematodes' population decreased significantly, emphasizing this species resistance to PWN. Our findings revealed a synergistic impact of PWN infection and stressful environmental conditions, particularly on the water status of P. pinaster and P. radiata, triggering disease symptoms and mortality of these species. Our results suggest that predicted drought conditions might facilitate proliferation and exacerbate the impact of PWN on these two species, through xylem cavitation, leading to strong changes in pine forests of the Mediterranean regions.

Short- and long-term temporal changes in the assemblage structure of Amazonian dung beetles.

Species diversity varies in space and time. Temporal changes in the structure and dynamics of communities can occur at different scales. We investigated the temporal changes of dung beetle assemblages in the Amazonian region along seasons, years, and successional stages. We evaluated if assemblage structure changes between temporal scales and whether such changes affect the functional structure of communities. To achieve these goals, we sampled dung beetles using linear transects of baited pitfall traps during the dry and rainy seasons at two natural reserves in the Amazon region, each representing different time scales: one covering successional variations (80, 30, 5, and 1 years of recovery from logging) and the other one encompassing three consecutive years at two successional stages (20 and 10 years from logging). We used Generalized Linear Models to analyze interannual and successional changes in diversity, described assemblage structure with a NMDS, and examined compositional variation by partitioning beta diversity into its nestedness and turnover components. Abundance and richness decrease from the rainy to the dry season and towards earlier successional stages but do not differ between years. Assemblage diversity changes differently in interannual and successional scales. During succession, dung beetle assemblages change drastically, following a nested structure due to the appearance of species and functional groups in later successional stages. In contrast, functional group composition does not show consistent changes between years, displaying a turnover structure. This pattern supports non-deterministic changes in dung beetle assemblage structure along forest succession.

Groundwater drawdown drives ecophysiological adjustments of woody vegetation in a semi-arid coastal ecosystem.

Predicted droughts and anthropogenic water use will increase groundwater lowering rates and intensify groundwater limitation, particularly for Mediterranean semi-arid ecosystems. These hydrological changes may be expected to elicit differential functional responses of vegetation either belowground or aboveground. Yet, our ability to predict the impacts of groundwater changes on these ecosystems is still poor. Thus, we sought to better understand the impact of falling water table on the physiology of woody vegetation. We specifically ask (a) how is woody vegetation ecophysiological performance affected by water table depth during the dry season? and (b) does the vegetation response to increasing depth to groundwater differ among water-use functional types? We examined a suite of physiological parameters and water-uptake depths of the dominant, functionally distinct woody vegetation along a water-table depth gradient in a Mediterranean semi-arid coastal ecosystem that is currently experiencing anthropogenic groundwater extraction pressure. We found that groundwater drawdown did negatively affect the ecophysiological performance of the woody vegetation. Across all studied environmental factors, depth to groundwater was the most important driver of ecophysiological adjustments. Plant functional types, independent of groundwater dependence, showed consistent declines in water content and generally reduced C and N acquisition with increasing depths to groundwater. Functional types showed distinct operating physiological ranges, but common physiological sensitivity to greater water table depth. Thus, although differences in water-source use exist, a physiological convergence appeared to happen among different functional types. These results strongly suggest that hydrological drought has an important impact on fundamental physiological processes, constraining the performance of woody vegetation under semi-arid conditions. By disentangling the functional responses and vulnerability of woody vegetation to groundwater limitation, our study establishes the basis for predicting the physiological responses of woody vegetation in semi-arid coastal ecosystems to groundwater drawdown.

Environmental niche divergence among three dune shrub sister species with parapatric distributions.

Background and Aims: The geographical distributions of species are constrained by their ecological requirements. The aim of this work was to analyse the effects of environmental conditions, historical events and biogeographical constraints on the diversification of the three species of the western Mediterranean shrub genus Stauracanthus , which have a parapatric distribution in the Iberian Peninsula. Methods: Ecological niche factor analysis and generalized linear models were used to measure the response of all Stauracanthus species to the environmental gradients and map their potential distributions in the Iberian Peninsula. The bioclimatic niche overlap between the three species was determined by using Schoener's index. The genetic differentiation of the Iberian and northern African populations of Stauracanthus species was characterized with GenalEx. The effects on genetic distances of the most important environmental drivers were assessed through Mantel tests and non-metric multidimensional scaling. Key Results: The three Stauracanthus species show remarkably similar responses to climatic conditions. This supports the idea that all members of this recently diversified clade retain common adaptations to climate and consequently high levels of climatic niche overlap. This contrasts with the diverse edaphic requirements of Stauracanthus species. The populations of the S. genistoides-spectabilis clade grow on Miocene and Pliocene fine-textured sedimentary soils, whereas S. boivinii , the more genetically distant species, occurs on older and more coarse-textured sedimentary substrates. These patterns of diversification are largely consistent with a stochastic process of geographical range expansion and fragmentation coupled with niche evolution in the context of spatially complex environmental fluctuations. Conclusions: : The combined analysis of the distribution, realized environmental niche and phylogeographical relationships of parapatric species proposed in this work allows integration of the biogeographical, ecological and evolutionary processes driving the evolution of species adaptations and how they determine their current geographical ranges.