Disentangling the divergence and cladogenesis in the freshwater crab species (Potamonautidae: Potamonautes perlatus sensu lato) in the Cape Fold Mountains,South Africa,with the description of two novel cryptic lineages

River networks of major drainages can form barriers that shape the phylogeography of freshwater organisms, particularly those with low dispersal capabilities. Freshwater crab species' distributions can be used to examine hydrological patterns to expose historical drainage interconnectivity. We used molecular sequence data (mitochondrial and nuclear DNA) and divergence time estimations to determine the phylogeography of the freshwater crab, Potamonautes perlatus sensu lato, from six drainage systems along the Cape Fold Mountains, South Africa. Two major clades were detected: clade 1 comprised two geographically discrete haploclades occurring in southern flowing drainages, whereas clade 2 included specimens from western flowing drainages. Divergence time estimations suggested a Pleistocene (c. 2.61 Mya) divergence of P. perlatus s.l. The Pleistocene was associated with arid conditions and drainage contractions. However, it is likely that during the mesic conditions of the Pleistocene, P. perlatus s.l. migrated and diverged into contemporary patterns. We conclude that three lineages are nested within P. perlatus s.l., two representing novel species. Potamonautes perlatus sensu stricto is confined to western flowing drainages. The two novel species both occurring in southern flowing drainages are described here: P otamonautes barbarai sp. nov. occurs in the Gamtoos and Gourits Rivers and P otamonautes barnardi sp. nov. in the Breede River. © 2014 The Linnean Society of London     

降水量与氮添加对荒漠草原生态系统碳交换的影响

为深入了解降水格局改变和氮沉降增加对荒漠草原生态系统碳交换的影响机制，于2017年在宁夏荒漠草原设立了降水量变化（减少50%、减少30%、自然降水量、增加30%以及增加50%）和氮添加（0和5 g m^-2 a^-1）的野外试验，研究了2019年生长季（5-10月份）净生态系统碳交换（Net ecosystem carbon exchange，NEE）、生态系统呼吸（Ecosystem respiration，ER）和总生态系统生产力（Gross ecosystem productivity，GEP）的时间动态，分析了三者与植被组成以及土壤属性的关系。NEE、ER和GEP日动态和月动态均呈先增加后降低，NEE在整个生长季表现为净生态系统碳吸收。0和5 g m^-2 a^-1氮添加下，减少降水量显著降低了NEE、ER和GEP （P<0.05），增加30%降水量显著提高了三者（P<0.05）。相同降水量条件下，氮添加不同程度地提高了NEE、ER和GEP，且其效应在增加50%降水量时较为明显。净生态系统碳吸收（-NEE）、ER和GEP与群落生物量、牛枝子（Lespedeza potaninii）以及草木樨状黄芪（Astragalus melilotoides）生物量正相关。三者亦随Patrick丰富度指数和Shannon-Wiener多样性指数的增加而增加。本文结果意味着，减少降水量降低了土壤水分和养分有效性、抑制了植物生长，从而降低了生态系统碳交换。适量增加降水量则可能通过提高土壤含水量、刺激土壤酶活性、调节土壤C ： N ： P平衡特征等途径，促进了植物生长和物种多样性，从而提高了生态系统碳汇功能；氮添加亦促进了生态系统碳交换，但其与降水的交互作用尚不明显，需通过长期观测进行深入探讨。     

Physiological tolerance of Drosophila simulans to dark environment: A comparison with D. melanogaster

According to ecological and behavioural studies, Drosophila simulans is considered to be less tolerant of darkness than its sibling species D. melanogaster which is well adapted both behaviourally and physiologically to darkness. The relationships between physiological and behavioural adaptations have been analysed by studying the developmental and the reproductive capacities of D. simulans submitted to various light regimes (LL, LD 12:12, DD). This species has a lower reproductive capacity than D. melanogaster but failed to react to light treatment. In particular, D. simulans showed no effect of darkness on either fertilization or ovarian function. The lack of differences between D. melanogaster and D. simulans as regards their physiological capacities in relation to light regime suggests that the selective pressures of light may act at different levels of regulation.     

Chainsawing for conservation: Ecologically informed tree removal for habitat management

Summary In many ecosystems, increases in vegetation density and the resulting closure of forest canopies are threatening the viability of species that depend upon open, sunlight‐exposed habitats. Consequently, we need to develop management strategies that recreate open habitats while minimizing the impacts on non‐target areas. Selective logging creates canopy gaps, but may result in undesirable effects in other respects. Thus, chainsaws have not been a popular tool for conservation. We conducted a landscape‐scale experiment to test whether selective tree removal can restore patch‐level habitat quality for Australia’s most endangered snake (Hoplocephalus bungaroides) and its main prey (the lizard Oedura lesueurii). We selectively removed canopy trees surrounding 25 overgrown rock outcrops and compared the resultant habitat structure and abiotic conditions to 30 overgrown, shady outcrops and 20 open, sunny outcrops. Removing vegetation decreased canopy cover by 19% in experimental plots and increased incident radiation and thermal regimes. These changes increased the availability of suitable shelter sites for our target species by 131%. At the landscape scale, our manipulations had a trivial effect on forest habitat; by increasing the area of sun‐exposed outcrops, we decreased forest cover by <0.1%. Our results show that targeted canopy removal can increase the availability of sun‐exposed habitat patches for endangered species in biologically meaningful ways. Thus, selective tree felling may be an effective conservation tool for open‐habitat specialists threatened by vegetation overgrowth.     

Resource subsidies between stream and terrestrial ecosystems under global change

Streams and adjacent terrestrial ecosystems are characterized by permeable boundaries that are crossed by resource subsidies. Although the importance of these subsidies for riverine ecosystems is increasingly recognized, little is known about how they may be influenced by global environmental change. Drawing from available evidence, in this review we propose a conceptual framework to evaluate the effects of global change on the quality and spatiotemporal dynamics of stream–terrestrial subsidies. We illustrate how changes to hydrological and temperature regimes, atmospheric CO₂ concentration, land use and the distribution of nonindigenous species can influence subsidy fluxes by affecting the biology and ecology of donor and recipient systems and the physical characteristics of stream–riparian boundaries. Climate‐driven changes in the physiology and phenology of organisms with complex life cycles will influence their development time, body size and emergence patterns, with consequences for adjacent terrestrial consumers. Also, novel species interactions can modify subsidy dynamics via complex bottom‐up and top‐down effects. Given the seasonality and pulsed nature of subsidies, alterations of the temporal and spatial synchrony of resource availability to consumers across ecosystems are likely to result in ecological mismatches that can scale up from individual responses, to communities, to ecosystems. Similarly, altered hydrology, temperature, CO₂ concentration and land use will modify the recruitment and quality of riparian vegetation, the timing of leaf abscission and the establishment of invasive riparian species. Along with morphological changes to stream–terrestrial boundaries, these will alter the use and fluxes of allochthonous subsidies associated with stream ecosystems. Future research should aim to understand how subsidy dynamics will be affected by key drivers of global change, including agricultural intensification, increasing water use and biotic homogenization. Our conceptual framework based on the match–mismatch between donor and recipient organisms may facilitate understanding of the multiple effects of global change and aid in the development of future research questions.     

Geographical isolation and genetic differentiation: the case of Orestias ascotanensis (Teleostei: Cyprinodontidae), an Andean killifish inhabiting a highland salt pan

Orestias ascotanensis is a killifish endemic to the Ascotán salt pan in the Chilean Altiplano, where it inhabits 12 springs with different degrees of isolation. This species is a suitable model for studying the effect of serial geographical isolations on the differentiation process among populations. The present study examines the genetic variation and structure of the species using mitochondrial DNA control region sequences and eight microsatellite loci, analyzing populations across its distribution range. The evaluation of genetic variation revealed high levels of diversity within the species. The genetic structure analysis showed the existence of four differentiated groups: two groups were formed by the springs located in the northern and southern extremes of the salt pan and two groups were found in the centre of the salt pan. The latter two groups were formed by several springs, most likely as a consequence of the South American summer monsoon that could connect them and allow gene flow. The patterns of genetic differentiation appear to be determined based on the physical isolation of the populations. This isolation may be the result of a combination of factors, including geographical distance, a historical decrease in water levels and altitude differences in the springs of the salt pan. Therefore, this system is a rare example in which hydrological factors can explain genetic differentiation on a very small scale.     

黄河干流与河口湿地生态需水研究进展

通过回顾黄河干流和河口湿地生态需水相关研究的发展历程及主要研究成果，从生态需水研究的研究对象及目标、研究内容、研究方法及应用等方面归纳总结了黄河干流和河口生态需水的研究现状和面临挑战。目前，有关黄河干流和河口湿地的生态需水方面的研究已取得一定的成果，对黄河流域生态需水基础理论基本规律的认识相对清晰，但对黄河干流和河口湿地生态系统认识的不足导致目前生态需水计算方法不统一，计算结果存在一定的误差，从而导致黄河生态需水在流域水资源配置与管理实践中难以达到预期结果。今后仍需在逐步积累的实测资料的基础上进行细化的生态需水研究，重点开展基于河流和湿地生态系统完整性的生态需水研究；基于生态-水文响应关系并综合其他保护目标的生态水文过程研究；还要考虑经济、社会、环境"三赢"的权衡以及未来水沙条件等因素的不确定性，寻求合理的能应用到实际水量配置方案中的生态需水量等。并将生态需水成果与黄河水量生态调度有效结合起来，在水量调度实践中予以论证。