Facilitation‐ vs. competition‐driven succession: the key role of resource‐ratio

Symbiotic nitrogen (N)‐fixing plants are abundant during primary succession, as typical bedrocks lack available N. In turn, fixed N accumulates in soils through biomass turnover and recycling, favouring more nitrophilous organisms. Yet, it is unclear how this facilitation mechanism interacts with competition for other limiting nutrients such as phosphorus (P) and how this affects succession. Here, we introduce a resource‐explicit, community assembly model of N‐fixing species and analyze successional trajectories along resource availability gradients using contemporary niche theory. We show that facilitation‐driven succession occurs under low N and high enough P availabilities, and is characterised by autogenic ecosystem development and relatively ordered trajectories. We show that late facilitation‐driven succession is sensitive to catastrophic shifts, highlighting the need to invoke other mechanisms to explain ecosystem stability near the climax. Put together with competition‐driven succession, these results lead to an enriched version of Tilman's resource‐ratio theory of succession.     

Comparing seed removal rates in actively and passively restored tropical moist forests

High rates of seed removal can impede forest recovery, but tropical seed removal studies are few and mainly from the neotropics. Little is known about the comparative influences of active restoration (i.e. planting) and passive restoration (i.e. protection of natural regrowth) on seed removal. We conducted an evaluation of seed removal in grasslands, natural forests (tropical moist semideciduous forest), and actively (21‐, 17‐, 16‐, 11‐, 8‐, and 6‐year‐old) and passively (21‐year‐old) restored forests in Kibale National Park, Uganda. We wanted to compare the effect of vegetation type, time since restoration and restoration actions (i.e. active vs. passive) on removal of seeds of five animal‐dispersed tree species during wet and dry seasons. Seeds were either fully exposed or placed in closed mesh cages or under a mesh roof. We used differential removal rates between these treatments to attribute seed removal to different animal taxa. Seed removal rate (percentage of seed removed over a 4‐day period) was highest in passively restored forests, compared with actively restored forests, grasslands, and natural forests. We detected no significant relationship between time since restoration and seed removal rates within actively restored sites. Seed removal rate from roofed treatments was not significantly different from removal from open treatments but was significantly higher than removal from closed treatments, which we interpret as reflecting the greater effect of small mammals versus insects. Smaller seeds tended to be removed at a greater rate than larger seeds. We discuss the implications of these findings for forest regeneration.     

Biodiversity in different successional stages of Mediterranean enclaves distributed along Sinop Peninsula (Turkey)

The aim of this research was to evaluate plant diversity and the relationships between the distribution of Raunkiaer life forms and community structure, and species richness, at different successional stages in communities of Quercus ilex L., Erica arborea L. and Sarcopoterium spinosum (L.) Spach., distributed as enclaves in Sinop Province. Permanent sample plots were selected to determine plant diversity. The cover percentage of each plant species was recorded monthly during two vegetation periods. Raunkiaer life forms, and the Shannon–Wiener, Evenness, Simpson and Margalef indexes were determined. Twenty-three species in Quercus ilex, 96 species in Erica arborea, and 148 species in Sarcopoterium spinosum were identified. Hemicryptophyte dominancy was observed followed by phanerophytes in the Q. ilex community, and therophyte and hemicryptophyte dominancy in the E. arborea and S. spinosum communities, respectively. It was determined that the S. spinosum community was the most heterogeneous community while the Q. ilex community was more uniform than other communities. The variation in diversity indexes, homogeneity, and composition of life forms among communities adopting a similar climatic environment could result from a differentiation of environmental factors, which impact on community structuring, from biotic to abiotic at different successional stages of Mediterranean communities.     

Functional traits associated with plant colonizing and competitive ability influence species abundance during secondary succession: Evidence from subalpine meadows of the Qinghai–Tibetan Plateau

It is widely recognized that colonists and competitors dominate early and late succession, respectively, with selected species having different colonizing and competitive abilities. However, it remains unknown whether colonizing and competitive ability can determine species abundance directly over succession. The data for five key functional traits were collected (photosynthesis rate, leaf turgor loss point, leaf proline content, seed mass, and seed germination rate), which are direct indicators of plant competitive and colonizing abilities including growth, drought and cold stress resistance, dispersal, and seed dormancy. Here, we tested the effects of colonizing and competitive abilities on species abundance, by employing a linear mixed‐effects model to examine the shifts in the relationship between species abundance and these five colonization and competition‐related traits in species‐rich subalpine secondary successional meadows (at 4, 6, 10, 13 years of age, and undisturbed, respectively) of the Qinghai–Tibetan Plateau. The abundant species at the early‐successional meadows tend to have high photosynthetic rate, high leaf proline content, low seed mass, and seed germination rate for having high colonizing ability, but low competitive ability. By contrast, late‐successional communities tend to be dominated by species with high competitive ability, but low colonizing ability, indicated by large seeds, high seed germination rate, low photosynthetic rate, and leaf proline content. The observed directional shifts in the relationships between traits (photosynthetic rate, leaf proline content, seed mass, and seed germination rate) and abundance with successional age, bring two new understandings of community assembly during succession of subalpine meadows in the Qinghai–Tibetan Plateau. First, it discloses that the differences in species abundance over succession can be directly attributed to differences in colonizing and competitive abilities of different species. Second, it expands the effects of multiple life historical differences including growth, resource competitive ability, cold stress resistance, dispersal, and seed germination strategy, represented by functional traits on community assembly along succession, that is, from the species to the community level.     

红松林不同演替阶段夏季鸟类群落研究

红松林不同演替阶段夏季鸟类群落研究常家传鲁长虎刘伯文许青（东北林业大学,哈尔滨１５００４０）ＳｔｕｄｙｏｆｔｈｅＢｉｒｄｓＣｏｍｍｕｎｉｔｙＳｔｒｕｃｔｕｒｅｉｎＤｉｆｅｒｅｎｔＳｕｃｃｅｓｉｏｎＰｅｒｉｏｄｏｆＫｏｒｅａｎＰｉｎｅＦｏｒｅｓｔ．Ｃｈ...     

不同光强下生长的亚热带树苗的光合—光响应特性的比较

鼎湖山亚湖热带森林中的优势树种马尾松、荷木、黛蒴和黄果厚壳桂的幼苗,盆栽于１００％、４０％和１６％的自然光下生长１年。利用氧电极离体测定叶片的光合－光响应曲线,结果表明不同树种及同一种树种不同生长光强处理之间差异明显。比较最大净光合速率、光寂偿点、光饱和点、光抑制点及光能利用效率等的变化可见,黄果厚壳桂为耐阴植物,对高光强的光合适应潜力为有限,１００％,自然光明显抑制最大同化力;其余３种植物均为喜     

Effects of past disturbance and edges on tree community structure and dynamics within a fragment of tropical semideciduous forest in south-eastern Brazil over a five-year period (1987–1992)

Tree community structure and dynamics of a 5.8 ha fragment of montane semideciduous forest in south-eastern Brazil are described based on two successive surveys of trees with dbh 5 cm carried out in 1987 and 1992 in 126 20 × 20 m quadrats. The main purpose was to assess whether the spatial variation of dynamic and structural variables were related to edge-effects and past disturbance regimes. The totals for the two surveys were, respectively, 6528 and 6770 trees, and 94.89 and 108.53 m² of basal area. The forest fragment was at an aggrading sylvigenetic phase, indicated by an overall net increase in density and basal area, and by a declining proportion of trees of smaller size. The overall annual mortality and recruitment rates were 2.6% and 3.0%, respectively. The dynamic process, however, was strongly affected by spatial heterogeneity. The more severely disturbed sectors had lower average canopy heights and basal areas per hectare, and higher tree densities, proportions of smaller trees, and relative area of canopy gaps. They also had higher mortality and recruitment rates, resulting in higher turnover rates compared to the sectors which suffered only moderate disturbance regimes. Edge sectors were also affected by different past disturbance regimes. However, they stood out by having a particularly high frequency of liana tangles and the highest rates of net increase both in density and basal area. A canonical correspondence analysis indicated that the effects of past disturbance regimes and edges were highly related to the species distribution in the area. Pioneer species were concentrated on the edges and more severely disturbed sectors, shade-tolerant species were particularly more abundant on the moderately disturbed sites, while light-demanding ones were more widely distributed. Tree community structure was also undergoing important changes, with less common species enjoying higher recruitment rates and density increase compared to the more common ones. Shade-tolerant species were increasing in relative abundance and had comparatively lower mortality rates and higher recruitment rates. On the other hand, pioneer species were under retreat, with a decreasing relative abundance, higher mortality rates and lower recruitment rates.Nomenclature: Oliveira-Filho et al. 1994a,d.     

Two examples of the interplay between field observations and laboratory experiments from 35 years of research with planktonic organisms

Two studies of complicated ecological phenomena in Lake Maarsseveen (The Netherlands) are presented to illustrate that a combination of field and laboratory analysis might be a successful approach. In the first one, the yearly varying ratio of population abundance of two diatoms, Asterionella formosa and Fragilaria crotonensis during early spring is explained by a combination of abiotic and biotic factors. A fungal parasite blocks population development of the first species at temperatures higher than 3–5 °C . The second species then competes successfully for phosphate and develops a large population. The interaction between Asterionella and the fungus proved to be intricate. Several physiological mechanisms operate together and combined with variable climatic factors makes the prediction of what species will be dominant, impossible. In the second example diel vertical migration of the hybrid Daphnia galeata × hyalina is analysed in the field and the laboratory. Migration is confined to six to seven weeks in June–July when large shoals of juvenile perch are present in the pelagic zone of the lake. These fish exudate a kairomone that enhances the reaction of Daphnia to relative increases in light intensity of dawn. Especially accelerations in rate of relative increases enhance swimming velocity. The extent of enhancement depends, however, on the concentration of the kairomone and on food concentration. A Decision Making Mechanism is introduced and the relation between the response mechanism and the adaptive relevance of diel vertical migration is made.Finally considerations about research strategies and the importance of fundamental research are made. It is concluded that the development of limnology and aquatic ecology might be in danger when the present tendency to give prevalence to applied research continues.     

新疆地卷属地衣植物的研究

新疆地卷属地衣植物计１２种１变种,其中新疆新分布４种,本文报道了它们的正确名称,生境和分布。     

Comparison of aerobic heterotrophic taxa isolated from four root domains of mature sugar beet (Beta vulgaris)

Abstract: The distribution of bacteria in the rhizosphere, rhizoplane, interior root tissues (core) and lower root (all tissues) of mature sugar beet roots ( Beta vulgaris ) was compared. Of 556 isolates, 102 species from 40 genera were identified by fatty acid methyl ester gas-chromatographic (FAME-GC) analysis. The ten most common genera ( Bacillus , 14%; Arthrobacter , 12%; Pseudomonas , 11%; Aureobacterium , 9%; Micrococcus , 6%; Xanthomonas , 5%; Alcaligenes , 4%; Flavobacterium , 3%; Agrobacterium , 3%; Microbacterium , 3%) accounted for 70% of isolates, and were found in each of three root domains (rhizosphere, rhizoplane and interior root tissues) on the two principal sampling occasions. Gram-positive strains were more abundant in the rhizosphere than the rhizoplane. Compared to the rhizoplane, rhizosphere bacterial communities were represented by a less diverse, more hierarchical distribution of species where twice as many isolates formed late developing colonies on isolation plates. Between October and January, the bacteria isolated from root interior tissues acquired a distinct change in taxonomic pattern, with decreased diversity and increased hierarchy. A bacterial continuum of similar taxa was observed which extended from the rhizosphere to interior root tissues.