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199 204 Austrheim, G. 2002. Plant diversity patterns in semi-natural grasslands along an elevational gradient in southern Norway. Plant Ecology 161

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Community Ecology
Authors: J. Beck, H. C. Liedtke, S. Widler, F. Altermatt, S. P. Loader, R. Hagmann, S. Lang, and K. Fiedler

Bergmann’s rule predicts increasing body sizes at higher elevations. The elevational Rapoport’s rule predicts an increase of elevational range size with higher elevations. Both rules have often been related to effects of temperature. Larger bodies allow more efficient heat preservation at lower temperature, explaining Bergmann’s rule. Higher temperature variability may select for adaptations that allow increased range sizes, explaining Rapoport’s rule. The generality of both rules has been challenged and evidence towards explanatory mechanisms has been equivocal. We investigated temperature and its variability as explanations for Bergmann’s and Rapoport’s rule in moths along an elevation gradient in Switzerland. In particular, we tested for relationships between elevation, temperature and body size across almost 300 species of Macrolepidoptera along a gradient from 600 to 2400 m a.s.l. The gradient was resampled throughout the vegetation season, which allowed assessing temperature effects independently from elevation. We controlled analyses for covariate traits of moths and their phylogeny. We found a positive relationship between body size and elevation, but no link with temperature. Furthermore, there was no positive link between average elevation and elevational range, but there was between temperature variability and elevational range. We conclude that mechanisms other than temperature can lead to increasing body sizes with elevation (supporting Bergmann’s pattern, but not the mechanism). Contrary to that, data support the mechanism for Rapoport’s rule: high temperature variability is associated with large ranges. However, because temperature variability is not necessarily increasing with elevation, it may not always lead to the geographic pattern predicted.

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Community Ecology
Authors: G. Bacaro, S. Maccherini, A. Chiarucci, A. Jentsch, D. Rocchini, D. Torri, M. Gioria, E. Tordoni, S. Martellos, A. Altobelli, R. Otto, C. G. Escudero, S. Fernández-Lugo, J. M. Fernández-Palacios, and J. R. Arévalo

Invasion by alien plant species may be rapid and aggressive, causing erosion of local biodiversity. This is particularly true for islands, where natural and anthropogenic corridors promote the rapid spread of invasive plants. Although evidence shows that corridors may facilitate plant invasions, the question of how their importance in the spread of alien species varies along environmental gradients deserves more attention. Here, we addressed this issue by examining diversity patterns (species richness of endemic, native and alien species) along and across roads, along an elevation gradient from sea-level up to 2050 m a.s.l. in Tenerife (Canary Islands, Spain), at multiple spatial scales. Species richness was assessed using a multi-scale sampling design consisting of 59 T-transects of 150 m × 2 m, along three major roads each placed over the whole elevation gradient. Each transect was composed of three sections of five plots each: Section 1 was located on the road edges, Section 2 at intermediate distance, and Section 3 far from the road edge, the latter representing the “native community” less affected by road-specific disturbance. The effect of elevation and distance from roadsides was evaluated for the three groups of species (endemic, native and alien species), using parametric and non-parametric regression analyses as well as additive diversity partitioning. Differences among roads explained the majority of the variation in alien species richness and composition. Patterns in alien species richness were also affected by elevation, with a decline in richness with increasing elevation and no alien species recorded at high elevations. Elevation was the most important factor determining patterns in endemic and native species. These findings confirm that climate filtering reflected in varying patterns along elevational gradients is an important determinant of the richness of alien species (which are not adapted to high elevations), while anthropogenic pressures may explain the richness of alien species at low elevation.

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Many taxa show their highest species richness at intermediate elevations, but the underlying reasons for this remain unclear. Here, we suggest that the physiological tolerance hypothesis can explain species richness patterns along elevational gradients, and we used functional diversity to test this hypothesis. We analyzed herb species richness, functional diversity, and environmental conditions along a 1300 m elevational gradient in a temperate forest, Beijing, China. We found that herb richness exhibited a “hump-shaped” relationship with elevation, with peak richness at approximately 1800 m. Functional diversity showed a significant unimodal relationship with elevation. The duration of high temperatures (≥ 300C: DHT) was the best predictor for herb richness and functional diversity along the gradient from 1020 to 1800 m, which suggest richness is limited by high temperature at low elevations. While along the gradient from 1800 to 2300 m, the duration of low temperatures (≤ 0°C: DLT) was the most powerful explanatory variable, which indicated at high elevations, richness reduced due to low temperature. Our analyses showed that the functional diversity of traits related to drought-tolerance (leaf mass per area, leaf area, and leaf hardiness) exhibited negative relationships with DHT, while functional diversity of traits related to freezing-tolerance (leaf thickness and hair density) exhibited negative relationships with DLT. Taken together, our results demonstrated that the richness-elevation relationship is consistent with the physiological tolerance hypothesis: at low elevations, richness is limited by high temperatures, and at high elevations, richness is reduced due to low temperatures. We concluded that our results provide trait-based support for the physiological tolerance hypothesis, suggesting that mid-elevations offer the most suitable environmental conditions, thus higher numbers of species are able to persist.

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Abiotic and biotic factors have the potential to alter herb communities, however, few studies consider feedback between them. This study explores how variation of species interaction and climatic conditions associated with changes in altitude affect herb community composition. We sampled accumulated temperatures of growth duration (June-November) (ATGD), maximum summer temperatures (MST) and herb community composition (herb height, abundance, richness) on non-gaps and forest-gaps site across an elevational gradient. A significant negative relationship was detected between MST and herb richness. The temperature of non-gaps was cooler than that of forest gaps, and overstory cover positively correlated with herb abundance. However, the ATGD exhibited a negative relationship with overstory cover, in that overstory cover decreased with ATGD. We suggested that temperature has a profound effect on height and richness of herb communities, while the overstory cover is moderating the effect of temperature on herb community structure and influence the abundance of herb community. Conversely, decreases in ATGD weakened the relative importance of overstory cover. We concluded that the interaction of temperature and overstory cover shapes the morphology, abundance and richness of herb communities.

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We studied the floristic composition in the pastures of the Southern Alps (Trento Province, Italy). One hundred and five plots in seven different pasture plant communities were sampled: (1) nitrophilous, (2) montane mesic, (3) subalpine mesic, (4) calcareous montane, (5) calcareous subalpine, (6) acid montane, and (7) acid subalpine pastures. Forward selection and variation partitioning were applied to identify the most important factors controlling the species composition and plant traits in the pastures. Aggregated weighted averages were calculated for each plot using the published values of average height, specific leaf area, and seed mass for each species. Explanatory variables were recorded for each site to reflect climate, soil properties, and grazing pressure. We hypothesised that species composition and functional variation in pastures of the Southern Alps are controlled by three main environmental filters: climate, resource availability, and grazing pressure. We found that variables of climate and soil properties had a major role in explaining the species composition and variations in plant traits, while grazing pressure showed a lower independent effect. Species composition and plant traits depended mainly on temperature, soil fertility, and variables of bedrock type — soil pH. Our results confirm the importance of taking the effects of climate and resource availability into account when describing plant and community functions of grasslands.

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. Monocotyledons: Alismataceae-Orchidaceae 2005 Burke, A. 2003. How special are Etendeka mesas? Flora and elevation gradients in an

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47 52 Franceschi, E.A. and D.E. Prado. 1989: Distribution of herbaceous communities of the river Paraná valley along an elevation gradient after a catastrophic flood. Coenoses

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474 Zhang, J-T. and T.G. Chen. 2004. Variation of plant communities along an elevation gradient in the Guandi Mountains, North China. Community Ecology 5: 227

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How are bryophyte alpha and beta diversities distributed across spatial scales along an elevational gradient in an oceanic island? Which mechanisms and drivers operate to shape them? Starting from a multiscale hierarchical sampling approach along an 1000 m elevational transect, we used additive diversity partitioning and null modeling to evaluate the contributions of the alpha and beta diversity components to overall bryophyte diversity in Terceira Island, Azores. Substrate-level diversity patterns were explored by means of the Sørensen Similarity Index and the Lloyd Index of Patchiness. Elevation-level beta diversity was decomposed into its replacement and richness differences components, with several environmental variables being evaluated as diversity predictors. Bryophyte diversity proved to be primarily due to beta diversity between elevation sites, followed by diversity among substrates. Compositional differences between neighboring sites decreased with elevation, being mainly caused by species replacement and correlating with differences in relative humidity and disturbance. At the substrate level, we found a great homogeneity in terms of species composition, coupled with a low substrate specialization rate. We conclude that, in Terceira’s native vegetation patches, regional processes, such as environmental gradients associated with elevation, play a greater role in shaping bryophyte diversity than local processes. Moister and less disturbed areas at mid-high elevation harbor a richer bryoflora, consistently more similar and stable between neighbouring sites. Simultaneously, the different substrates available are somewhat ecologically redundant, supporting few specialized species, pointing to these areas providing optimal habitat conditions for bryophytes. Our findings provide a better understanding of how bryophyte diversity is generated in Terceira Island, indicating that management and conservation measures should focus on island-level approaches, aiming to protect and rehabilitate additional natural vegetation patches at different elevations, especially in the severely disturbed lowlands.

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