Perspectives in Plant Ecology Evolution and Systematics最新文献

Ecological theory shows that, as resource availability increases, the number of related species (S) rises from zero at first, reaches a peak (optimum), and then falls to zero again to form a unimodal (hump-shaped) curve. Although rarely demonstrated, I show support for the unimodal, S-environment model exists among studies of soil nutrients and pH, substrate water, air temperature, evapotranspiration, sunlight, fire frequency (as a surrogate for resource turnover), herbivory, and plant density and productivity (as surrogates for resource availability). The rising left-hand side of the curve is due to a positive response to the controlling variable (e.g., soil nutrients) and the falling right-hand side to metabolic suppression by supraoptimal levels (e.g., protein denaturation by heat) or the retarding effect of secondary variables (e.g., increasing self shading). Statistically significant shape outcomes depend on range of the variable tested, scale of the study, taxonomy and life form of the targeted species assemblage, extent that species are distributed along the gradient, type of curve hypothesized, and extent to which the study continues to zero S. Interpretations should consider whether the left tail of the curve will terminate at the origin (0,0). Mechanistic explanations for the unimodal pattern may involve species interactions, such as individual fitness at the microscale optimizing at moderate abundance in the species mix, the inevitable increasing presence of inhibitory secondary effects, and existence of more resource-use generalists than specialists. Six reasons for lack of support for the unimodal hypothesis are noted. Support for the unimodal model is more likely the greater the range of the variable tested and the greater its causative link to S. The concept of ‘prediction’ in ecology needs to go beyond the tradition of (curvi)linear relationships and accept that most relationships in nature are (must be) unimodal.

The biosynthesis of secondary metabolites in plants, especially that of phenolic compounds, is stimulated to protect against several environmental stress factors such as cold temperatures, drought, and UV-irradiance. As a result, when a species occurs under different climatic conditions, differences in phenolic accumulation are expected across species distribution in response to the environmental cues. However, our understanding of phenolic compounds' natural variation is limited, as most of our knowledge on secondary metabolite biosynthesis stems from experimental studies conducted under controlled conditions. In this study we analyze phenolic content and its relation to climatic and geographic variation in three closely related Hedera species (H. helix, H. hibernica and H. iberica) across their southwestern range limits in the Iberian Peninsula (82 populations, 401 individuals). The Iberian Peninsula concentrates the highest global species richness of Hedera, with the three species sharing range boundaries along the latitudinal and longitudinal climatic gradient of the region. We found that the three species exhibited different climatic and geographic patterns of phenolic content variation in the study area. The phenolic production in H. helix increased with elevation in relation to the decrease of temperature and the increase of temperature contrast, whereas in H. hibernica varies with latitude in relation to summer temperature and precipitation regimes, increasing in areas with no summer drought. In contrast, we did not find any environmental variables associated with phenolic content in H. iberica, likely due to its narrow geographic and climatic range and a higher influence of microclimatic conditions. Although the three Hedera species are closely related, our results suggest that leaf phenolic production may be triggered by different environmental conditions in each species. Our study underscores the species-specific nature of phenolic compounds' role in plant stress response.

Understanding the abiotic factors influencing biodiversity patterns on Earth is a crucial task for conservation scientists. At the regional level, meso-climate factors, primarily associated with elevational gradients, are of great importance. However, disentangling these factors can be challenging due to the influence of other variables, such as geological substrata. To address this issue and better understand elevational gradients, it is essential to study geologically homogeneous terrains, particularly in Mediterranean islands where such research is lacking. In this study, we investigated the distribution of plant species richness along the elevational gradient of the Limbara massif, which consists predominantly of granite rocks and ranks as the third-highest peak in Sardinia at 1359 m a.s.l. We employed generalized linear models to analyze richness patterns, considering various factors, including all plant species, functional species groups categorized by Raunkiær life forms, chorological groups of species, alien species and phylogenetic diversity. Our findings revealed a hump-shaped model of species richness along the elevational gradient, with lower elevations exhibiting the highest species richness. Additionally, endemic species richness increased with higher elevations, while alien species were predominantly found at lower elevations. These results indicate that the Limbara massif possesses a significant elevational gradient in species composition, likely reflecting a unique plant evolutionary history. Furthermore, we emphasize the importance of published floras as valuable sources of biodiversity data for such studies.