High-density Aggregation Research Articles

Impacts of Wildlife Artificial Water Provisioning in an African Savannah Ecosystem: A Spatiotemporal Analysis

The use of artificial water points for wildlife in African savannah ecosystems has been widely criticised for affecting the distribution of wildlife and initiating changes in the heterogeneity of natural landscapes. We examined the spatiotemporal variations in the landscape before and after the installation of an artificial water point by integrating the analysis of vegetation and soil spectral response patterns with a supervised learning random forest model between 2002 and 2022 in Chobe Enclave, Northern Botswana. Our results revealed that the study area is characterised by animal species such as Equus quagga, Aepyceros melampus, and Loxodonta africana. The findings also showed that the main vegetation species in the study area landscape include Combretum elaeagnoides, Vachellia luederitzii, and Combretum hereroense. The artificial water point induced disturbances on a drought-vulnerable landscape which affected vegetation heterogeneity by degrading the historically dominant vegetation cover types such as Colophospermum mopane, Dichrostachys cinerea, and Cynodon dactylon. The immediate years following the artificial water point installation demonstrated the highest spectral response patterns by vegetation and soil features attributed to intense landscape disturbances due to abrupt high-density aggregation of wildlife around the water point. Landscapes were strongly homogenised in later years (2022), as shown by overly overlapping spectral patterns owing to an increase in dead plant-based material and senescent foliage due to vegetation toppling and trampling. The landscape disturbances disproportionately affected mopane-dominated woodlands compared to other vegetation species as indicated by statistically significant land cover change obtained from a random forest classification. The woodlands declined significantly (p < 0.05) within 0–0.5 km, 0.5–1 km, 1–5 km, and 5–10 km distances after the installation of the water point. The results of this study indicate that continuous nonstrategic and uninformed use of artificial water points for wildlife will trigger ecological alterations in savannah ecosystems.

Viscosity reduction mechanism of surface-functionalized Fe3O4 nanoparticles in different types of heavy oil

In-depth investigation of the viscosity reduction mechanism of nanoparticle viscosity reducers in various heavy oil types holds key strategic significance for the rational exploitation of global heavy oil resources. In this work, the dispersion stability mechanism of three surface-functionalized Fe3O4 nanoparticles (NPs) in kerosene was first explored by molecular dynamics (MD) simulation. Then Studies showed that the differences in asphaltene aggregation structures in different types of heavy oils make their initial viscosities significantly different. The addition of NPs could effectively reduce the viscosity of heavy oil and increase the diffusion coefficient of asphaltenes. Importantly, there were differences in the viscosity-reducing ability and viscosity-reducing mode of the NPs in different types of heavy oil. In Oil1, the NPs increased the peak of the radial distribution function curve, the number of hydrogen bonds (2.25–8.63), and the cluster size between asphaltenes (3.72–6.40). However, these property changes of asphaltenes in Oil2 are opposite. The NPs effectively broke the hydrogen bond between asphaltene (number of hydrogen bonds from 22.87–12.50) and reduced its cluster size (8.17–3.25). Among them, Fe3O4-OA and Fe3O4-KH570 showed the most excellent viscosity reduction performance in Oil1 and Oil2, respectively. Finally, by calculating the surface electrostatic potential of each molecule and the weak interaction between molecules, the microcosmic mechanism of the difference in the viscosity-reducing ability and mode of the NPs in different types of heavy oil was revealed. Overall, the NPs effectively depolymerized the high-density aggregation structure of asphaltene, thereby achieving the purpose of reducing the viscosity of heavy oil. However, in Oil1, the viscosity-reducing performance of NPs was mainly related to their ability to adsorb asphaltenes and their dispersion stability. In Oil2, the viscosity-reducing performance of NPs was dominated by their ability to destroy hydrogen bonds between asphaltenes.

A Form of Non-Volatile Solid-like Hexadecane Found in Micron-Scale Silica Microtubule.

Anomalous solid-like liquids at the solid-liquid interface have been recently reported. The mechanistic factors contributing to these anomalous liquids and whether they can stably exist at high vacuum are interesting, yet unexplored, questions. In this paper, thin slices of silica tubes soaked in hexadecane were observed under a transmission electron microscope at room temperature. The H-spectrum of hexadecane in the microtubules was measured by nuclear magnetic resonance. On the interior surface of these silica tubes, 0.2-30 μm in inside diameter (ID), a layer (12-400 nm) of a type of non-volatile hexadecane was found with thickness inversely correlated with the tube ID. A sample of this anomalous hexadecane in microtubules 0.4 μm in ID was found to be formable by an ion beam. Compared with the nuclear magnetic resonance H-spectroscopy of conventional hexadecane, the characteristic peaks of this abnormal hexadecane were shifted to the high field with a broader characteristic peak, nuclear magnetic resonance hydrogen spectroscopy spectral features typical of that of solids. The surface density of these abnormal hexadecanes was found to be positively correlated with the silanol groups found on the interior silica microtubular surface. This positive correlation indicates that the high-density aggregation of silanol is an essential factor for forming the abnormal hexadecane reported in this paper.

Hypothesizing novel mating behaviours in the squaretail grouper based on direct behavioural observations

Historically unfished, high-density spawning aggregations are vanishingly uncommon. Behavioural observations from such aggregations are rare, and may be sometimes novel and unexpected. Given the weight of evidence required to document spawning aggregations, how can we best report rare and unusual behavioural variations in spawning populations? Based on two years of in-water observations of a high-density spawning aggregation of the squaretail grouper in the Lakshadweep Archipelago, we described a previously unreported male alternative reproductive tactic (ART) and an inverse size assortment with large males courting several small females that shoaled mid-water (https://doi.org/10.1186/s12898-017-0120-5). In critiquing our manuscript, it has been suggested that our observations, methodologies and interpretation are inadequate, flawed, and do not fit within currently accepted theory (https://doi.org/10.1186/s12898-018-0206-8). While offering a detailed counter of the main methodological and theoretical criticisms we question how best to document and interpret novel behaviours in poorly known systems. Reporting novelty itself can hardly be the basis of criticism. Our report relied on direct in-water observations, conducted at peak densities over two spawning years. The critique ignores this, choosing instead to focus on a supplementary video which was not the basis of our conclusions. Like other researchers working on this species, we did not directly observe mating, but report courtship as a well-established proxy used across mating systems studies. Apart from these methodological concerns, the authors suggest that there is no theoretical support for our observations. However, sexual selection theory provides well-established frameworks showing that, at very high mating densities, a variety of tactics can emerge, that often vary considerably between populations and locations. In our original paper, we use this broader theory of sexual selection together with detailed behavioural data to propose plausible evolutionary explanations that bear testing in these novel, high-density systems. We agree with the authors that novel observations should be scrutinised carefully as they can challenge our current understanding of the range of behaviours populations display and serve as a springboard for theoretical advancement. Given their rarity, these observations should be evaluated against the rigour of their documentation and the transparency of their reporting. In this context, we hope our carefully documented observations serve as a useful addition to the fascinating and complex natural history of species like the squaretail grouper.

Alternative reproductive tactics and inverse size-assortment in a high-density fish spawning aggregation

BackgroundAt high densities, terrestrial and marine species often employ alternate reproductive tactics (ARTs) to maximize reproductive benefits. We describe ARTs in a high-density and unfished spawning aggregation of the squaretail grouper (Plectropomus areolatus) in Lakshadweep, India.ResultsAs previously reported for this species, territorial males engage in pair-courtship, which is associated with a pair-spawning tactic. Here, we document a previously unreported school-courtship tactic; where territorial males court multiple females in mid-water schools, which appears to culminate in a unique ‘school-spawning’ tactic. Courtship tactics were conditional on body size, local mate density and habitat, likely associated with changing trade-offs between potential mating opportunities and intra-sexual competition. Counter-intuitively, the aggregation showed a habitat-specific inverse size-assortment: large males courted small females on the reef slope while small males courted equal-sized or larger females on the shelf. These patterns remained stable across two years of observation at high, unfished densities.ConclusionsThese unique density-dependent behaviours may disappear from this aggregation as overall densities decline due to increasing commercial fishing pressure, with potentially large consequences for demographics and fitness.

A new assessment model for evacuation vulnerability in urban areas

ABSTRACTIn the high-speed urbanization process of China, the urban population has been increasing significantly, leading to a high-density aggregation of population. However, the sharp increase in population density has not produced commensurate improvements in the road networks. On the contrary, the population increase induced a serious evacuation vulnerability, which cities experience during various hazards and catastrophic events. Therefore, research on evacuation vulnerability is important to urban planning. To assess the evacuation vulnerability, the optimal and worst scenarios should be considered because all possible evacuation plans occur between these extremes. However, most previous evacuation vulnerability studies are based on the worst-case scenario, only providing an upper bound of a potential evacuation assessment. To provide a more comprehensive theoretical basis for decision-makers to understand the consequences caused by all possible evacuations, this paper proposes an optimal evacuation vulnerability assessment model that provides the lower bound on potential evacuation difficulties. The model is solved by a stepwise spreading algorithm based on Graph Theory. Subsequently, to evaluate the effectiveness of the model, the study adopts the model to assess the evacuation capability of different road network topologies. A comparison with previous research was performed. The model was demonstrated in an application to the South Luogu Alley of Beijing, China. The significance of this paper is that the combination of our model with previous research may provide a more complete theoretical basis for an evacuation vulnerability assessment.

秦岭大熊猫种群扩散格局及研究方法

PDF HTML阅读 XML下载 导出引用 引用提醒 秦岭大熊猫种群扩散格局及研究方法 DOI: 10.5846/stxb201504300891 作者: 作者单位: 中国林业科学研究院湿地研究所,国家林业局调查规划设计院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家林业局大熊猫国际合作项目（CM1423） An exploration of giant panda population dispersal patterns and methodology in the Qinling Mountains Author: Affiliation: Institute of Wetland Research, Chinese Academy of Forestry,Academy of Forestry Inventory and Planning, State Forestry Administration Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:种群扩散格局是研究种群扩散规律和机制的关键信息，也是制定物种保护对策的重要基础。大型动物种群扩散格局研究方法为扩散生态学研究的薄弱领域，并制约扩散生态学的发展。以秦岭大熊猫为研究对象，根据2000年以来的种群调查数据，基于大熊猫领域的特性，利用GIS的扩展区分析功能和景观分析方法研究了大熊猫种群分布区及动态；基于聚集的特性，利用GIS的核密度分析功能对大熊猫种群多度和聚集状况及空间变化进行了分析。发现2012年的秦岭大熊猫种群分布区较2000年增加5.5%（即15307.8hm2），高密度种群聚集区从2处变成1处，种群聚集程度进一步增加、聚集格局的完整性大大提升，尤以中密度聚集区增长最显著，种群格局呈明显的分布区扩张、聚集度增加的态势。表明基于物种的生物学特性，立足于种群分布和多度格局变化，通过长期调查和监测可以有效掌握物种的种群扩散格局；大型动物可根据其生物学特性探索可行的方法与量化种群扩散的参数来研究其扩散格局，从而促进大型动物种群扩散研究的开展。 Abstract:Population dispersal is an important life history trait that is influenced by environmental change, and it can alter the distribution, structure, and abundance of a population. In addition, population dispersal allows a species to actively adapt and ensure long-term survival. Patterns of population dispersal can provide key information about the rules and mechanisms of how populations disperse, and they are an important basis for conservation management. Methods for studying population dispersal in large animals are lacking, which therefore restricts the development and application of dispersal ecology. Two crucial issues that need to be taken into account when considering dispersal patterns are population distribution and abundance. Based on the factors of dispersal pattern and the giant panda characteristics of population and home range, this study intends to (1) reveal the dispersal patterns of giant pandas in the Qinling Mountains by comparing the change in their population distribution and aggregation from 2000 to 2012, and (2) explore methods for studying large animal population dispersal. Based on signs of giant pandas obtained from the third and fourth national surveys conducted by the Chinese Forestry Administration (completed in 2000 and 2012, respectively), a circular extension region with a giant panda sign as the center was produced using the buffer function in ArcGIS10.0. The average diameter of the home range of giant pandas was defined as 3 km. Subsequently, using the dissolve function in ArcGIS, we created polygons based on these circles, and established the primary population distribution area around the outer boundary of the polygons. We identified the population dispersal area based on the change in distribution range. Additionally, we mapped population aggregation densities in 2000 and 2012, and divided the population distribution range into areas with different aggregation densities by employing the kernel density analysis function of ArcGIS. We also revealed the population abundance and direction of population dispersal based on the variation in population aggregation. We found that the population distribution area of giant pandas increased by 15307.8 hm2 in the Qinling Mountains since 2000, with an obvious expanding trend in the northwestern and southwestern regions of the study area. However, the population distribution decreased in the eastern and southern regions. Furthermore, the degree of population aggregation increased, especially for areas with medium aggregation density, and two patches of high-density aggregation became one. In addition, the integrity of the population aggregation pattern also greatly improved. In this way, the population pattern showed a detectable trend of expansion and an increase in population aggregation. This study revealed the area and direction of giant pandas dispersal in the Qinling Mountains since 2000, which has important implications for current population safety and conservation. Our study also showed that the population dispersal patterns of giant pandas could be effectively determined with the spatial variation in population distribution and abundance that is based on biological characteristics and long-term monitoring. The methodology developed in this study, combined with ongoing monitoring programs in Chinese nature reserves, can facilitate the study of population dispersal in large animals. 参考文献 相似文献 引证文献

Movement and home range of pink abalone Haliotis corrugata: implications for restoration and population recovery

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 486:189-201 (2013) - DOI: https://doi.org/10.3354/meps10365 Movement and home range of pink abalone Haliotis corrugata: implications for restoration and population recovery Julia H. Coates1,*, Kevin A. Hovel1, John L. Butler2, A. Peter Klimley3, Steven G. Morgan3 1Department of Biology, San Diego State University, 5500 Campanile Drive, San Diego, California 92182-4614, USA 2National Marine Fisheries Service, Southwest Fisheries Science Center, 3333 North Torrey Pines Court, La Jolla, California 92037-1023, USA 3Graduate Group in Ecology, University of California, Davis, 1005 Wickson Hall, One Shields Avenue, Davis, California 95616, USA *Email: juliahcoates@gmail.com ABSTRACT: Densities of abalone in southern California have been dramatically reduced by overfishing and disease, leading to the collapse of some populations, and low fertilization rates may be hindering population recovery. This is a pattern typical of abalone species globally. However, movement may produce clustered distributions that promote fertilization success in broadcast spawners, such as abalone, even at low regional densities. We translocated wild, adult pink abalone Haliotis corrugata to an existing pink abalone patch to create a high-density aggregation, and then used acoustic telemetry to characterize abalone movement and monitor aggregation maintenance for a period of 14 mo in the Point Loma kelp forest near San Diego, California. Abalone showed a minimal flight response to handling that did not differ between the resident or translocated groups. Most individuals exhibited small home ranges (median area 183 m2) and homing behavior consisting of regular back-and-forth movement to a single point. Nomadic movement was also observed in several individuals. Though site fidelity may help maintain aggregations, abalone density decreased, and nearest neighbor distances increased at our site to near-initial levels after 18 mo via a combination of mortality, large movements of a few individuals, and small, incremental movements of most individuals. No coordinated movements that would suggest spawning behavior were observed. Translocation of wild abalone to produce aggregations may not result in high rates of fertilization success that promote population recovery. However, the homing behavior observed may provide more opportunities for mating than expectations based on static measures of density and aggregation state. KEY WORDS: Movement · Restoration · Homing · Broadcast spawning · Allee effect · Translocation Full text in pdf format Supplementary material PreviousNextCite this article as: Coates JH, Hovel KA, Butler JL, Klimley AP, Morgan SG (2013) Movement and home range of pink abalone Haliotis corrugata: implications for restoration and population recovery. Mar Ecol Prog Ser 486:189-201. https://doi.org/10.3354/meps10365 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 486. Online publication date: July 12, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Input–Output Efficiency of Urban Agglomerations in China: An Application of Data Envelopment Analysis (DEA)

Urban agglomerations (UAs) in China play a vital role in the distribution of productive forces and constitute the most dynamic and potentially rich core areas for future economic development. However, the rapid economic growth and high-intensity interactions seen in relation to these areas, results of the high population densities and aggregation of industries in UAs, also pose significant ecological threats to the environment. This paper attempts to analyse changing trends in the input–output efficiency of UAs in China based on the data envelopment analysis (DEA) approach. The paper investigates the DEA efficiency of UAs with different population sizes and geographical locations, explores the relationship between the elements that make up a decomposed model of efficiency and compares the efficiency performance of China’s UAs with that of 35 central cities. Moreover, the exogenous factors determining the input–output efficiency of UAs, the question of how to improve UAs’ efficiency performance, as well as the focus of future research are also discussed. A number of valuable implications have been drawn from the study, which may be helpful to the task of understanding more deeply the high-density aggregation effects of UAs in China.

Secure centralized spectrum sensing for cognitive radio networks

Spectrum utilization becomes more and more important while new communication techniques keep increasing and the spectrum bands remain finite. Cognitive radio is a revolutionary technology to make use of the spectrum more effectively. In order to avoid the interference to the primary user, spectrum sensing must be sensitive and reliable. Cooperative spectrum sensing (CSS) is one of the ways to increase the reliability of spectrum sensing. The information fusion technique is a key component of CSS. In this paper, we proposed a novel fusion scheme based on spatial correlation technique. We utilize geographical information with reputational weights to propose a two-level fusion scheme called secure centralized spectrum sensing (SCSS). The simulation results show that as the attackers present high density aggregation at some areas, the correct sensing ratio of SCSS is increasing as well even when the number of attackers is very large.

Ecological correlates of population density and behavior in the circumtropical black triggerfish Melichthys niger (Balistidae)

The remarkable swarming of black triggerfish Melichthys niger (Balistidae) on oceanic islands led us to undertake a comparative ecological study of high-density and low-density populations of this unusual circumtropical species. Abundance, distribution, and aggressive encounters were recorded in the field from the high-density Johnston Atoll (JA) population, the low-density Belize (BE) population, and a local high-density aggregation from Puerto Rico (PR). JA and PR populations of M. niger occurred at significantly higher densities and were more aggregated than in BE. Intraspecific aggression (chases/min/fish) was an order of magnitude higher in BE than in JA, while interspecific aggression was similar among sites. Size frequency, growth rate, diet composition, body condition (liver-somatic index LSI) were assessed from collected specimens. JA grew more slowly than BE as determined by back-calculations from dorsal spine rings, suggesting density-dependent growth limitation. Size frequency analysis reflected this difference with significantly more large fish in the BE sample. Maximum age of triggerfish in both populations was estimated at 11 years, and 35–40% of growth occurred in the first year. Diet composition was similar in all three locations and indicated broad omnivory. Percent organic composition of gut contents (food quality measure) and LSI (body condition assay) were both significantly higher in the PR population, but no difference was detected between JA and BE. An increase in consumption of algae on the degraded PR reef may explain this pattern.

High-density aggregation in queen conch Strombus gigas: formation, patterns, and ecological significance

Queen conch Strombus gigas L. , an important fisheries species, is often found in large aggregations of very high density (20 to 300 conch m-2), which move over the bottom in seagrass meadows of the Bahamas. Over the 6 yr period from 1987 to 1992, 25 high-density aggregations were observed in the southern Exuma Cays, Bahamas, 12 of them in a single, well-studied nursery ground. Except for 1 aggregation, all were oriented across tidal currents, but movements in both ebb and flood directions were observed. Aggregations occurred in all months, but predominantly between October and April. This 'mass migration' was hypothesized to serve the purpose of carrying conch from juvenrle to adult habitats. Given the lack of progression toward deep-water adult habitats, and the fact that aggregations consisted of different age groups from the l + year class to early adults, it is unlikely that this phenomenon represents ontogenetic movement. Aggregations sometimes formed in the center of homogeneous seagrass beds and are probably not feeding fronts. Most commonly, high-density aggregations formed when juvenile populations were large and when density was increased experimentally. suggesting that formation IS density-dependent. A tethenng experiment showed that conch in an aggregation experience lower predatory mortality than those in the surrounding nursery area. The most important ecological significance of high-density aggregation appears to be probability refuge from predation, or dilutlon effect.

Density-dependent mate searching strategies of male woodfrogs

Individually marked male woodfrogs, Rana sylvatica, were monitored throughout the night in an unmanipulated aggregation and in an aggregation with artificially reduced density. Males were less active in the low density aggregation. Movement was modelled using a computer simulation that assumed that male movement patterns resulted from chance encounters between searching males. The model success-fully predicted the results observed at the low density, but was unable to predict those observed at the high density. This suggest that males may assess density and actively respond to it. A second result was that males in the low density aggregation were more likely to search for mates at the oviposition site, but males in the high density aggregation were more likely to search at the aggregation periphery. This change in behaviour is predicted by a simple evolutionarily stable strategy model.