Eucalypts face increasing climate stress

Global climate change is already impacting species and ecosystems across the planet. Trees, although long‐lived, are sensitive to changes in climate, including climate extremes. Shifts in tree species' distributions will influence biodiversity and ecosystem function at scales ranging from local to landscape; dry and hot regions will be especially vulnerable. The Australian continent has been especially susceptible to climate change with extreme heat waves, droughts, and flooding in recent years, and this climate trajectory is expected to continue. We sought to understand how climate change may impact Australian ecosystems by modeling distributional changes in eucalypt species, which dominate or codominate most forested ecosystems across Australia. We modeled a representative sample of Eucalyptus and Corymbia species (n = 108, or 14% of all species) using newly available Representative Concentration Pathway (RCP) scenarios developed for the 5th Assessment Report of the IPCC, and bioclimatic and substrate predictor variables. We compared current, 2025, 2055, and 2085 distributions. Overall, Eucalyptus and Corymbia species in the central desert and open woodland regions will be the most affected, losing 20% of their climate space under the mid‐range climate scenario and twice that under the extreme scenario. The least affected species, in eastern Australia, are likely to lose 10% of their climate space under the mid‐range climate scenario and twice that under the extreme scenario. Range shifts will be lateral as well as polewards, and these east–west transitions will be more significant, reflecting the strong influence of precipitation rather than temperature changes in subtropical and midlatitudes. These net losses, and the direction of shifts and contractions in range, suggest that many species in the eastern and southern seaboards will be pushed toward the continental limit and that large tracts of currently treed landscapes, especially in the continental interior, will change dramatically in terms of species composition and ecosystem structure.     

A decade of seasonal dynamics and co-occurrences within freshwater bacterioplankton communities from eutrophic Lake Mendota,WI, USA

With an unprecedented decade-long time series from a temperate eutrophic lake, we analyzed bacterial and environmental co-occurrence networks to gain insight into seasonal dynamics at the community level. We found that (1) bacterial co-occurrence networks were non-random, (2) season explained the network complexity and (3) co-occurrence network complexity was negatively correlated with the underlying community diversity across different seasons. Network complexity was not related to the variance of associated environmental factors. Temperature and productivity may drive changes in diversity across seasons in temperate aquatic systems, much as they control diversity across latitude. While the implications of bacterioplankton network structure on ecosystem function are still largely unknown, network analysis, in conjunction with traditional multivariate techniques, continues to increase our understanding of bacterioplankton temporal dynamics.     

Spatial and temporal variation in the macroinvertebrate community structure of the lower Elands River,Mpumalanga, South Africa

The Elands River, Mpumalanga, is an ecologically sensitive river that is constantly threatened by a variety of human activities. The influence of a pulp and paper mill on the river's macroinvertebrate assemblages was studied in March and June 2005, representing high- and low-flow seasons, respectively. Macroinvertebrates were collected from various biotopes using a standard sampling net, and were preserved and identified to family level. A range of multivariate and univariate statistical analyses was applied to assess the spatial and temporal variations in the macroinvertebrate communities. Diversity loss and dominance by a single taxon, Melanoides tuberculata, were noted directly below the mill. Other sites did not appear to be affected. Macroinvertebrate communities at all sites showed a strong seasonal variation.     

THE BENTHIC MACROINVERTEBRATE FAUNA OF A SOUTH AFRICAN MOUNTAIN STREAM AND ITS RESPONSE TO FIRE

Summary

The effects of a late-summer prescribed burn on the temperature and benthic macroinvertebrate fauna of a south-western Cape mountain stream were investigated over a period of 12 months. Temperature and discharge regimes appear well-defined and relatively predictable from year to year. As in other mediterranean-type ecosystems, seasonal changes in the structure of the invertebrate community and the relative abundance of different feeding groups appear to be associated primarily with changes in the physical environment. Distinctive summer and winter communities were identified, with chironomids dominating the fauna in summer and simuliids dominant in winter. Although the riparian vegetation was only slightly damaged by the fire, a heavy, aseasonal leaf-fall occurred shortly afterwards. The canopy remained sparse for approximately four months. Stream temperature in the post-burn year was not demonstrably affected by increased exposure to solar radiation, however, probably because the canopy remained open during the winter months. The fire appeared to have little effect on the invertebrate fauna. Apart from five rare elements of the biota, all species recorded in the pre-burn year were present in the post-burn year and in similar densities. It is concluded that the riparian vegetation is of major importance in maintaining the integrity of the stream environment.     

Feeding dynamics of Palaemon peringueyi (Decapoda,Caridea) in the temporarily open/closed Kasouga Estuary,South Africa

The feeding ecology of the caridean shrimp Palaemon peringueyi in the temporarily open/closed Kasouga Estuary, Eastern Cape, was examined during summer and winter employing stomach fullness index (SFI) analysis. Mean SFI values for male and female shrimp during summer ranged from 0.85% to 2.36% and from 0.56% and 2.61% body dry weight, respectively. During winter, SFI values for males and females were lower, and varied between 0.23% and 1.56% and 0.36% and 1.84% body dry weight, respectively. There were no significant differences in the SFI values between males and females during the two seasons. A peak in the feeding activity for both sexes was observed during the daytime during both summer and winter. For both males and females, non-linear regression analysis best explained the change in SFI over time. The gut evacuation rate constants (k) of males and females during summer were estimated at 0.43 h^?1 and 0.30 h^?1, respectively. These values correspond to a daily food intake equivalent to 16.2% body dwt for males and 11.1% body dwt for females. During winter, the gut evacuation rates of the shrimp were estimated at 0.35 h^?1 for males and 0.28 h^?1 for females. The daily ration for adult male and female shrimp during winter was estimated at 6.1% and 6.8% body dwt, respectively. The lower estimates obtained during winter appear largely to reflect the influence of the reduced water temperatures on the metabolic activities of the shrimp.     

A conceptual model of the Amblyomma americanum life cycle in northeast Missouri

The geographic distribution of Amblyomma americanum (the lone star tick) has increased as has its role as a pathogen vector. The objectives of this study were to determine seasonal activity patterns of each life stage of A. americanum in the northwestern part of the species range and the relationship of these activity patterns among life stages and degree days. Tick activity was monitored over four years since 2007 in a forest and old field habitat located in northeast Missouri. Every other week from February to December, ticks were collected using bait and drag methods. Autocorrelations demonstrated yearly seasonal patterns in each life stage and cross‐correlations between life stages depicted a relationship between activity at a life stage and the previous stage's activity. Cross‐correlations indicated that degree days were related to activity. These data indicated that A. americanum generally complete their life cycle in a minimum of two years in northeast Missouri, with overwintering occurring predominantly in the nymphal and adult stages. These data provide a baseline to compare the life cycle of A. americanum in northeast Missouri to populations in different parts of the species range or at different times in the region.     

Persistent versus transient tree encroachment of temperate peat bogs: effects of climate warming and drought events

Peatlands store approximately 30% of global soil carbon, most in moss‐dominated bogs. Future climatic changes, such as changes in precipitation patterns and warming, are expected to affect peat bog vegetation composition and thereby its long‐term carbon sequestration capacity. Theoretical work suggests that an episode of rapid environmental change is more likely to trigger transitions to alternative ecosystem states than a gradual, but equally large, change in conditions. We used a dynamic vegetation model to explore the impacts of drought events and increased temperature on vegetation composition of temperate peat bogs. We analyzed the consequences of six patterns of summer drought events combined with five temperature scenarios to test whether an open peat bog dominated by moss (Sphagnum) could shift to a tree‐dominated state. Unexpectedly, neither a gradual decrease in the amount of summer precipitation nor the occurrence of a number of extremely dry summers in a row could shift the moss‐dominated peat bog permanently into a tree‐dominated peat bog. The increase in tree biomass during drought events was unable to trigger positive feedbacks that keep the ecosystem in a tree‐dominated state after a return to previous ‘normal’ rainfall conditions. In contrast, temperature increases from 1 °C onward already shifted peat bogs into tree‐dominated ecosystems. In our simulations, drought events facilitated tree establishment, but temperature determined how much tree biomass could develop. Our results suggest that under current climatic conditions, peat bog vegetation is rather resilient to drought events, but very sensitive to temperature increases, indicating that future warming is likely to trigger persistent vegetation shifts.     

Genomic Basis of Circannual Rhythm in the European Corn Borer Moth

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川西亚高山不同森林类型土壤呼吸和总硝化速率的季节动态

川西亚高山原始林及其采伐后通过不同恢复措施形成的不同类型森林土壤呼吸和总硝化速率的对比分析及其耦合关系的研究相对匮乏。采用气压过程分离系统(Ba PS)技术研究了川西亚高山岷江冷杉原始林及其砍伐后恢复的粗枝云杉阔叶林、红桦-岷江冷杉天然次生林和粗枝云杉人工林土壤呼吸和总硝化速率的季节动态及其影响因素。结果表明:生长季内平均土壤呼吸速率和总硝化速率分别以粗枝云杉阔叶林和粗枝云杉人工林较高,均以岷江冷杉原始林较低。土壤呼吸和总硝化速率在生长季内具有明显的季节动态,呈以7月份最高的单峰趋势。土壤呼吸和总硝化速率与土壤温度显著相关,而与土壤水分相关性不显著,表明土壤温度是调控呼吸和总硝化作用季节动态的主要因子。土壤呼吸的温度敏感性(Q_(10))介于2.59—4.71,以岷江冷杉原始林最高,表明高海拔的岷江冷杉原始林可能更易受到气候变化的影响。林型间土壤呼吸和总硝化速率主要受凋落物量、p H和有机质的影响。不同林型间土壤呼吸和总硝化速率显著正相关,表明土壤呼吸和总硝化速率存在耦合关系。     

扎龙湿地芦苇种群不同龄级根茎构件的季节动态

克隆植物根茎具有营养繁殖和扩展种群的功能,也是芽和分株生理整合的通道。根茎构件具有出生、死亡及年龄等种群统计特征,不同龄级根茎的季节动态可以反映根茎的存活和衰老过程。采用单位土体挖掘取样,对扎龙湿地4个生境芦苇种群根茎构件进行野外调查,比较不同龄级根茎长度、生物量和干物质贮量的季节动态。结果表明:7—10月份,1a根茎长度、生物量和干物质贮量均呈指数函数增加,在生长季中后期有一个持续时间较长的生长和物质积累时期。6—10月份,2a、3a根茎长度呈线性函数增加,4—6a根茎长度呈线性函数减少;2—4a根茎生物量和2—5a根茎干物质贮量呈二次函数先减少后增加,5a、6a根茎生物量和6a根茎干物质贮量呈幂函数减少。整个生长期内,根茎长度和根茎生物量均以3a最大,根茎长度以最高的6a最小,根茎生物量以最低的1a最小;根茎干物质储量以5a最大,以最低的1a最小。4个生境芦苇种群根茎长度、生物量和干物质贮量在龄级间的差异及差异序位稳定,在新根茎的产生、老根茎的存活以及根茎寿命与养分消耗和储藏上均具有稳定的生物学特性,不同龄级根茎在种群中的地位和作用以及对种群的贡献不同。