Genetical and ecological differentiation across a hybrid zone

ABSTRACT.

• 1 There is a narrow hybrid zone between two chromosomal races of the grasshopper Podisma pedestris (L.) in the French Alps.
• 2 There are no gross differences in habitat across the zone, and a multivariate analysis of the vegetation composition detected no significant transition either.
• 3 The hatch and development rates of Podisma in hybrid populations were lower than those found in matched habitat types outside the zone.
• 4 The simplest explanation for the persistence of the parapatric distribution of the two races is that hybrid disadvantage is maintaining a tension zone between them.

     

生态交错带（Ecotone）理论研究进展

生态交错带（Ｅｃｏｔｏｎｅ）理论研究进展高洪文（东北师范大学草地研究所,长春１３００２４）ＡｄｖａｎｃｅｍｅｎｔｏｆＴｂｅｏｒｅｔｉｃａｌＲｅｓｅａｒｃｈｉｎＥｃｏｔｏｎｅ．￥ＧａｏＨｏｎｇｗｅｎ（ＩｎｓｔｉｔｕｔｅｏｆＧｒａｓｓｌａｎｄＲｅ－ｓｅａ...     

Management of land/inland water ecotones: needs for regional approaches to achieve sustainable ecological systems

Evidence suggests that the boundaries between rivers, floodplain wetlands, and adjacent upland communities are among the most important components of landscapes. In a landscape context, floodplain wetlands and their ecotones are important transition zones between uplands and aquatic ecosystems. Management of wetland patches and ecotones to achieve sustainable ecosystems requires action on a broad scale, giving consideration to all factors affecting wetlands and the drainage basins of which they are a part. In northeastern United States, a struggle to identify new sources of water has focussed attention on the sustainability of aquatic ecosystems.     

As above,not so below: Long-term dynamics of net primary production across a dryland transition zone

Drylands are key contributors to interannual variation in the terrestrial carbon sink, which has been attributed primarily to broad-scale climatic anomalies that disproportionately affect net primary production (NPP) in these ecosystems. Current knowledge around the patterns and controls of NPP is based largely on measurements of aboveground net primary production (ANPP), particularly in the context of altered precipitation regimes. Limited evidence suggests belowground net primary production (BNPP), a major input to the terrestrial carbon pool, may respond differently than ANPP to precipitation, as well as other drivers of environmental change, such as nitrogen deposition and fire. Yet long-term measurements of BNPP are rare, contributing to uncertainty in carbon cycle assessments. Here, we used 16 years of annual NPP measurements to investigate responses of ANPP and BNPP to several environmental change drivers across a grassland–shrubland transition zone in the northern Chihuahuan Desert. ANPP was positively correlated with annual precipitation across this landscape; however, this relationship was weaker within sites. BNPP, on the other hand, was weakly correlated with precipitation only in Chihuahuan Desert shrubland. Although NPP generally exhibited similar trends among sites, temporal correlations between ANPP and BNPP within sites were weak. We found chronic nitrogen enrichment stimulated ANPP, whereas a one-time prescribed burn reduced ANPP for nearly a decade. Surprisingly, BNPP was largely unaffected by these factors. Together, our results suggest that BNPP is driven by a different set of controls than ANPP. Furthermore, our findings imply belowground production cannot be inferred from aboveground measurements in dryland ecosystems. Improving understanding around the patterns and controls of dryland NPP at interannual to decadal scales is fundamentally important because of their measurable impact on the global carbon cycle. This study underscores the need for more long-term measurements of BNPP to improve assessments of the terrestrial carbon sink, particularly in the context of ongoing environmental change.     

The effects of recreated instream and ecotone structures on the fish fauna of an epipotamal river

Investigations of fifteen sections of seven Austrian epipotamal (barbel region) streams between 1981 and 1984 demonstrate the impact of instream river bed structures on fish communities. Reduced spatial heterogeneity due to river straightening resulted in decreasing species number, diversity, stock density and biomass. Reincreased variability of the river bed in the frame of a subsequent restructuring project improved all community-specific values significantly within a 3-year investigation period (1988–1990). Besides the regained habitat variability in form of riffle pool sequences and other instream structures, the newly created riparian zones obviously provided important niches, e.g. as refuge areas during flooding and as nursery grounds for fish fry. The positive effects of the recreated land/water ecotone are discussed with respect to river restoration projects.     

北方农牧交错带温性盐碱化草地土壤呼吸对不同形态氮添加和刈割的响应

农牧交错带草地生态系统兼受农业和牧业的影响, 属于脆弱生态系统, 尤其是养分贫瘠的盐碱化草地, 其生态系统结构和功能对外界干扰的响应更加强烈。位于晋西北地区的农牧交错带盐碱化草地, 地理位置独特, 区别于天然牧区草地生态系统。由于毗邻农田, 农业氮肥的过量使用促进了活性氮气体排放, 同时使得农牧交错带草地土壤碳氮循环发生改变。刈割是北方农牧交错草地生态系统的主要管理方式, 为了深入探究氮添加和刈割管理方式对农牧交错带草地碳循环的影响, 进一步厘清该区域草地生态系统的碳动态问题, 该研究设置了一个不同形态氮添加和刈割的裂区实验, 测定土壤呼吸对不同形态氮肥添加和刈割的响应, 为进一步科学管理该区域草地提供可靠的依据。实验样地位于山西省右玉县境内的“山西农业大学农牧交错带草地生态系统野外观测研究站”, 于2017年设置不同形态氮添加和刈割处理, 实验处理包括对照(不刈割和刈割)、尿素添加、缓释尿素添加、刈割+尿素添加、刈割+缓释尿素添加, 每种处理6个重复, 共36个小区。在不同处理条件下测定土壤呼吸速率、土壤温度、土壤水分、土壤微生物生物量、土壤无机氮含量、植物地上和地下生物量, 并计算土壤累积碳排放量及CO₂通量。研究结果表明: (1)短期(2017-2018年)尿素和缓释尿素的添加显著提高了该地区土壤呼吸速率和土壤累积碳排放量。与添加缓释尿素相比, 添加尿素处理下的土壤呼吸速率和累积碳排放量更高; (2)刈割显著降低土壤呼吸速率和累积碳排放量; (3)短期氮添加和刈割的交互作用对土壤呼吸速率没有显著影响。因此, 短期氮添加促进了北方农牧交错带盐碱化草地土壤碳释放, 刈割抑制土壤呼吸, 降低了累积碳排放量, 这可能是由于刈割移除地上植物, 减少了凋落物的输入, 底物减少导致土壤微生物活性降低。但是随着处理时间的延长, 氮添加和刈割对该农牧交错带盐碱化草地土壤碳动态的影响还有待进一步探究和发现。     

Intraspecific trait variability shapes leaf trait response to altered fire regimes

Background and AimsUnderstanding impacts of altered disturbance regimes on community structure and function is a key goal for community ecology. Functional traits link species composition to ecosystem functioning. Changes in the distribution of functional traits at community scales in response to disturbance can be driven not only by shifts in species composition, but also by shifts in intraspecific trait values. Understanding the relative importance of these two processes has important implications for predicting community responses to altered disturbance regimes.MethodsWe experimentally manipulated fire return intervals in replicated blocks of a fire-adapted, longleaf pine (Pinus palustris) ecosystem in North Carolina, USA and measured specific leaf area (SLA), leaf dry matter content (LDMC) and compositional responses along a lowland to upland gradient over a 4 year period. Plots were burned between zero and four times. Using a trait-based approach, we simulate hypothetical scenarios which allow species presence, abundance or trait values to vary over time and compare these with observed traits to understand the relative contributions of each of these three processes to observed trait patterns at the study site. We addressed the following questions. (1) How do changes in the fire regime affect community composition, structure and community-level trait responses? (2) Are these effects consistent across a gradient of fire intensity? (3) What are the relative contributions of species turnover, changes in abundance and changes in intraspecific trait values to observed changes in community-weighted mean (CWM) traits in response to altered fire regime?Key ResultsWe found strong evidence that altered fire return interval impacted understorey plant communities. The number of fires a plot experienced significantly affected the magnitude of its compositional change and shifted the ecotone boundary separating shrub-dominated lowland areas from grass-dominated upland areas, with suppression sites (0 burns) experiencing an upland shift and annual burn sites a lowland shift. We found significant effects of burn regimes on the CWM of SLA, and that observed shifts in both SLA and LDMC were driven primarily by intraspecific changes in trait values.ConclusionsIn a fire-adapted ecosystem, increased fire frequency altered community composition and structure of the ecosystem through changes in the position of the shrub line. We also found that plant traits responded directionally to increased fire frequency, with SLA decreasing in response to fire frequency across the environmental gradient. For both SLA and LDMC, nearly all of the observed changes in CWM traits were driven by intraspecific variation.     

Evolutionary heritage shapes tree distributions along an Amazon‐to‐Andes elevation gradient

Understanding how evolutionary constraints shape the elevational distributions of tree lineages provides valuable insight into the future of tropical montane forests under global change. With narrow elevational ranges, high taxonomic turnover, frequent habitat specialization, and exceptional levels of endemism, tropical montane forests and trees are predicted to be highly sensitive to environmental change. Using plot census data from a gradient traversing > 3,000 m in elevation on the Amazonian flank of the Peruvian Andes, we employ phylogenetic approaches to assess the influence of evolutionary heritage on distribution trends of trees at the genus‐level. We find that closely related lineages tend to occur at similar mean elevations, with sister genera pairs occurring a mean 254 m in elevation closer to each other than the mean elevational difference between non‐sister genera pairs. We also demonstrate phylogenetic clustering both above and below 1,750 m a.s.l, corresponding roughly to the cloud‐base ecotone. Belying these general trends, some lineages occur across many different elevations. However, these highly plastic lineages are not phylogenetically clustered. Overall, our findings suggest that tropical montane forests are home to unique tree lineage diversity, constrained by their evolutionary heritage and vulnerable to substantial losses under environmental changes, such as rising temperatures or an upward shift of the cloud‐base.     

Further records for Skye

As one of the most conspicuous boundaries between different types of ecosystem, the alpine timberline has attracted the interest of researchers in Innsbruck for more than 85 years. It is evident that the tree life form here reaches its absolute limit and is constrained by the harsh environment. However, the nature of constraints is less obvious and requires detailed ecophysiological analyses as exemplified in this review, which concentrates on the Central Tyrolean Alps. After focusing on the timberline environment, effects of elevation on the water relations and the CO₂ gas exchange of timberline-associated conifer species will be outlined towards conclusions on tree growth and treeline fluctuations. Presently, temperature is suggested to be the key environmental factor in determining the transition from forests to alpine shrub and grassland. As many physiological aspects are influenced directly or indirectly by the temperature regime at the alpine timberline, tree life at the timberline exists close to a number of physiological limits which interact to determine the position of the alpine timberline and modulate the upper boundary of tree life. Nevertheless, understanding of the altitude of the treeline must also consider seedling establishment, especially when evaluating treeline advances and global change effects in a changing environment.