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121.
中国梧桐属(Firmiana)在世界梧桐属中占比较大,且除梧桐外其余种均为中国特有且分布范围狭窄的植物种,灭绝风险大,研究气候变化对中国梧桐属树种的影响对于维护生物多样性具有重要的意义。结合多时期第六次国际气候耦合模式比较计划(CMIP6)气候变量数据和中国八种梧桐属树种的分布数据,基于R语言kuenm程序包优化的最大熵(Maxent)模型模拟分析中国八种梧桐属树种在多尺度下的潜在适生区,得出梧桐属最适宜的模拟尺度、潜在适生区的面积变化和迁移方向、梧桐属多样性保护关键区域及保护空缺。结果表明:(1)梧桐属最适宜的模拟尺度为亚洲;(2) Maxent模型的接收者操作特征曲线下面积(AUC)值均大于0.9,表明模型对梧桐属潜在适生区预测结果具有较高准确度;(3)气候变化影响下除云南梧桐(Firmiana major)外其它树种的潜在适生区都将在未来有所扩大;(4)中国八种梧桐属树种潜在适生区迁移方向主要为东西向,南北向大跨度迁移较少,纬度变化不大;(5)丹霞梧桐(Firmiana danxiaensis)的稳定潜在适生区最小;(6)中国梧桐属多样性保护关键区域主要分布于广西壮族自治区及云南、广东、海南等省区;(7)中国梧桐属多样性保护空缺区域主要分布于广西壮族自治区中部及海南省北部;(8)梧桐属多样性保护关键区域正在为人造地表所侵蚀。研究分析气候变化对中国八种梧桐属树种的影响及其潜在适生区变化、中国梧桐属多样性保护状态,可为中国梧桐属建立多样性保护廊道提供相关建议,为制定多样性保护规划及相应措施提供参考。 相似文献
122.
123.
《African Journal of Aquatic Science》2013,38(3):289-297
The effect of variations in the density of a submerged macrophyte, Lagarosiphon ilicifolius, on epiphytic macroinvertebrate community structure in the shallow waters of a sheltered bay of Lake Kariba were investigated. The body size class distributions of a mayfly, Cloeon (Ephemeroptera: Baetidae), and the damselfly family, Coenagrionidae, were also assessed with respect to variation in vegetation density. Macroinvertebrates were sampled from low-, moderate- and high-density beds of L. ilicifolius. There were no significant differences in individual taxon and total macroinvertebrate abundances, macroinvertebrate richness and diversity with respect to vegetation density. In all three density categories the functional feeding group (FFG) composition was dominated by collector-gatherers and collector-filterers. The abundance of the two FFGs did not change significantly within each, as well as among, the three vegetation-density categories (ANOVA, p > 0.05). The largest size class of Cloeon occurred only in high-density beds, whereas the largest coenagrionid individuals were obtained from low- and moderate-density beds and were absent from high-density beds. The results suggest that variation in the density of Lagarosiphon does not affect epiphytic macroinvertebrate community structure, but does affect body-size distributions of macroinvertebrate taxa, probably by affecting predator-prey interactions. 相似文献
124.
Type 1 insulin-like growth factor receptor (IGF1R) is a membrane-spanning glycoprotein of the insulin receptor family that has been implicated in a variety of cancers. The key questions related to molecular mechanisms governing ligand recognition by IGF1R remain unanswered, partly due to the lack of testable structural models of apo or ligand-bound receptor complexes. Using a homology model of the IGF1R ectodomain IGF1RΔβ, we present the first experimentally consistent all-atom structural models of IGF1/IGF1RΔβ and IGF2/IGF1RΔβ complexes. Our explicit-solvent molecular dynamics (MD) simulation of apo-IGF1RΔβ shows that it displays asymmetric flexibility mechanisms that result in one of two binding pockets accessible to growth factors IGF1 and IGF2, as demonstrated via an MD-assisted Monte Carlo docking procedure. Our MD-generated ensemble of structures of apo and IGF1-bound IGF1RΔβ agrees reasonably well with published small-angle X-ray scattering data. We observe simultaneous contacts of each growth factor with sites 1 and 2 of IGF1R, suggesting cross-linking of receptor subunits. Our models provide direct evidence in favor of suggested electrostatic complementarity between the C-domain (IGF1) and the cysteine-rich domain (IGF1R). Our IGF1/IGF1RΔβ model provides structural bases for the observation that a single IGF1 molecule binds to IGF1RΔβ at low concentrations in small-angle X-ray scattering studies. We also suggest new possible structural bases for differences in the affinities of insulin, IGF1, and IGF2 for their noncognate receptors. 相似文献
125.
Previously we described the mosquito larvicidal properties of decomposed leaf-litter from deciduous trees, especially the alder Alnus glutinosa (L) Gaertn., due to toxic polyphenols and other secondary compounds. To further examine the biocontrol potential of toxic leaf-litter for mosquito control, feeding rates of third-instar mosquito larvae were assessed for examples of three genera: Anopheles stephensi Liston, Aedes aegypti (L) and Culex pipiens L. (Diptera: Culicidae). When immersed in a suspension of non-toxic leaf-litter particles (approximately 0.4 mm), pre-starved larvae of all three species ingested sufficient material in 30 min to fill the anterior gut lumen (thorax plus two to three abdominal segments). Gut filling peaked after 1-2 h ingestion time, filling the intestine up to six to seven abdominal segments for Ae. aegypti, but maxima of five abdominal segments for Cx. pipiens and An. stephensi. Using three methods to quantify consumption of three materials by third-instar larvae of Ae. aegypti, the average amount of leaf-litter (non-toxic 0.4 mm particles) ingested during 3 h was determined as approximately 20 microg/larva (by dry weight and by lignin spectrophotometric assay). Consumption of humine (approximately 100 microm particles extracted from leaf-litter) during 3 h was approximately 80 microg/larva for Ae. aegypti, but only approximately 30 microg/larva for Cx. pipiens and 15 microg/larva for An. stephensi, with good concordance of determinations by dry weight and by radiometric assay. Cellulose consumption by Ae. aegypti was intermediate: approximately 40 microg/larva determined by radiometric assay. Apparent differences between the amounts of these materials ingested by Ae. aegypti larvae (humine four-fold, cellulose two-fold more than leaf-litter) may be attributed to contrasts in palatability (perhaps related to particle size or form), rather than technical discrepancies, because there was good concordance between results of both methods used to determine the amounts of humine and leaf-litter ingested. Bioassays of toxic leaf-litter (decomposed 10 months) with 4-h exposure period (ingestion time) ranked the order of sensitivity: Ae. aegypti (LC50 < 0.03 g/L) > An. stephensi (LC50 = 0.35 g/L) > Cx. pipiens (LC20 > 0.4 g/L). When immersed in the high concentration of 0.5 g/L toxic leaf-litter (0.4 mm particles), as little as 15-30 min ingestion time (exposure period) was sufficient to kill the majority of larvae of all three species, as soon as the gut lumen was filled for only the first few abdominal segments. Possibilities for mosquito larval control with toxic leaf-litter products and the need for standardized ingestion bioassays of larvicidal particles are discussed. 相似文献
126.
ABSTRACT Woody plant succession is hypothesized to threaten many reptile populations by reducing the amount of solar energy available for thermoregulation. Mitigation via vegetation management is often recommended; however, the need for such management practices rarely has been evaluated. We examined the need for basking-site enhancement for the eastern massasauga rattlesnake (Sistrurus c. catenatus; hereafter EMR) in New York, USA, where only 2 populations remain: one at an open-canopy site and another at a closed-canopy site. Microhabitat temperatures were substantially lower at the closed-canopy site, where EMRs selected the warmest available basking sites. Eastern massasauga rattlesnakes in the open-canopy population selected basking sites that afforded greater cryptic cover. We recommend experimental reduction of shrub cover to improve EMR basking habitat at the closed-canopy site. More generally, we caution that management efforts to reduce shrub cover for basking EMRs should maintain adequate cryptic cover. 相似文献
127.
Trait variations of ground flora species disentangle the effects of global change and altered land‐use in Swedish forests during 20 years 下载免费PDF全文
Northern forest ecosystems are exposed to a range of anthropogenic processes including global warming, atmospheric deposition, and changing land‐use. The vegetation of northern forests is composed of species with several functional traits related to these processes, whose effects may be difficult to disentangle. Here, we combined analyses of spatio‐temporal dynamics and functional traits of ground flora species, including morphological characteristics, responses to macro‐ and microclimate, soil conditions, and disturbance. Based on data from the Swedish National Forest Inventory, we compared changes in occurrence of a large number of ground flora species during a 20‐year period (1994–2013) in boreal and temperate Sweden respectively. Our results show that a majority of the common ground flora species have changed their overall frequency. Comparisons of functional traits between increasing and declining species, and of trends in mean trait values of sample plots, indicate that current floristic changes are caused by combined effects of climate warming, nitrogen deposition and changing land‐use. Changes and their relations with plant traits were generally larger in temperate southern Sweden. Nutrient‐demanding species with mesotrophic morphology were favored by ongoing eutrophication due to nitrogen deposition in the temperate zone, while dwarf shrubs with low demands on nitrogen decreased in frequency. An increase of species with less northern and less eastern distribution limits was also restricted to temperate Sweden, and indicates effects of a moister and milder macroclimate. A trend toward dense plantation forests is mirrored by a decrease of light‐demanding species in both vegetation zones, and a decrease of grassland species in the temperate zone. Although denser tree canopies may buffer effects of a warmer climate and of nitrogen deposition to some extent, traits related to these processes were weakly correlated in the group of species with changing frequency. Hence, our results indicate specific effects of these often confounded anthropogenic processes. 相似文献
128.
David Gonzlez del Portillo Beatriz Arroyo Guillermo García Simn Manuel B. Morales 《Ecology and evolution》2021,11(7):3219
Agriculture intensification threatens farmland bird populations because, among other reasons, it reduces the availability of food resources required to rear their offspring. In our study, we sampled and analyzed total arthropod abundance, biomass and richness, and orthopteran and coleopteran abundance and biomass in different agricultural habitats (alfalfa fields, stubble fields, grazed fields, and field margins) across 4 study localities with different levels of agriculture abandonment–intensification, comparing between areas used and not used by one of the most threatened farmland birds in Europe, the little bustard (Tetrax tetrax), during the chick‐rearing season. Field margins were the taxonomically richest habitat, while alfalfa fields presented significantly higher total arthropod abundance and biomass than other habitats. All arthropod variables were the highest in the localities with clear conservation‐focused agrarian management, and the lowest in the most intensive one. Areas used by little bustards had higher orthopteran and coleopteran abundance and biomass than nonused areas, except for coleopteran biomass in grazed fields. These results highlight the relevance of these arthropods for the species, the importance of dry alfalfa fields as food reservoirs in this critical time of year, the food scarcity in sites where agrarian management disregards farmland bird conservation, and the role of stubbles as providers of food resources during the chick‐rearing season in areas used by the species. The adequate management of alfalfa fields and stubbles to provide those key resources seems crucial to improve little bustard breeding success. 相似文献
129.
1. Ship‐induced waves can affect the physical characteristics of lake and river shorelines, and laboratory studies have shown effects on littoral invertebrates. Here, we explored whether these effects could be observed under field conditions along a natural lake shore affected by wave sequences (trains) produced by boats. 2. Individuals of five invertebrate species (Bithynia tentaculata, Calopteryx splendens, Dikerogammarus villosus, Gammarus roeselii, Laccophilus hyalinus) were exposed to waves with increasing shear stress in five habitats differing in structural complexity. 3. Detachment of invertebrates increased with increasing shear stress and was best modelled using sigmoid response curves. Habitat structural complexity mitigated the effects of shear stress, and detachment rate was influenced more by habitat type than by species. A threshold (90% of the individual invertebrates unaffected) stress level of 0.64 N m?2 was found for a structurally complex reed habitat, compared to 0.37 N m?2 for a simple sand habitat. 4. Shear stress associated with wave trains created by recreational boating at a distance of 35 m from the shore and at a speed of 11 km h?1 resulted in 45% detachment of littoral invertebrates. Decreasing the boat‐to‐shore distance to 20 m increased wave shear stress by 30% and invertebrate detachments up to 75%. 5. Disturbance of littoral habitats and invertebrate assemblages are widespread in inland waters used for recreational and/or commercial navigation. Our findings show that the integrity of littoral zones of navigable surface waters could be much improved by implementing management measures such as physically protecting complex habitats with dense reed belts and tree roots, and reducing boat speeds and increasing their minimum shoreline distance. 相似文献
130.
Mauricio Cantor Leonardo L. Wedekin Fábio G. Daura‐Jorge Marcos R. Rossi‐Santos Paulo C. Simões‐Lopes 《Marine Mammal Science》2012,28(1):63-83
This study represents the first attempt to study the population dynamics of Guiana dolphins (Sotalia guianensis), by evaluating a set of demographic parameters. The population of the Caravelas River estuary, eastern Brazil, was systematically monitored through a long‐term mark‐recapture experiment (2002–2009). Abundance estimates revealed a small population (57–124 dolphins), comprised of resident dolphins and individuals that temporarily leave or pass through the study area. Temporary emigration from the estuary to adjacencies (γ″= 0.33 ± 0.07 SE) and return rate (1 ?γ′= 0 .67) were moderate and constant, indicating that some dolphins use larger areas. Survival rate (?= 0.88 ± 0.07 SE) and abundance were constant throughout the study period. Power analysis showed that the current monitoring effort has high probability of detecting abrupt population declines (1 ?β= 0.9). Although the monitoring is not yet sensitive to subtle population trends, sufficient time to identify them is feasible (additional 3 yr). Despite such apparent stability, this population, as many others, inhabits waters exposed to multiple human‐related threats. Open and closed population modeling applied to photo‐identification data provide a robust baseline for estimating several demographic parameters and can be applied to other populations to allow further comparisons. Such synergistic efforts will allow a reliable definition of conservation status of this species. 相似文献