Seasonal dynamics of macroinvertebrate communities in a semiarid saline spring stream with contrasting environmental conditions

Semiarid saline streams are rare aquatic ecosystem types. Their constituent biota is expected to have adapted evolutionarily to strong hydrological variability and salinity stress; however, their ecology is not well known. In this study, we quantify the seasonal changes in the structure of the macroinvertebrate community in the Reventón Rambla (south-eastern Spain), a permanent saline spring stream which is included in a drainage system consisting of ephemeral dry channels (so-called “ramblas”). Seasonal patterns of community structure were studied in two reaches with contrasting environmental regimes using univariate and multivariate statistics. The upstream site showed more stable environmental conditions than the downstream site, and both sites also differed with regard to species richness, and structural and functional group attributes. On a seasonal basis, community dissimilarity was high during periods when both sites were isolated during summer droughts but dissimilarity decreased when both sites were connected through surface flow. Furthermore, the communities tended to show cyclical trajectories in multivariate ordination space. Rather than being related to salinity stress, these patterns seemed to track the hydrological disturbance regime of this rambla system. Spates tended to disrupt communities, while signs of recovery were evident during low-flow periods. Results suggest that salinity fluctuation does not pose a severe abiotic constraint to these adapted macroinvertebrate communities. Their suits of functional properties provide them with the necessary traits to recover quickly from natural disturbance. While human-caused salinization of streams severely impacts communities eventually reducing their recovery potential, our results suggest that communities in natural saline streams may show similar responses to hydrological disturbance as communities from non-saline streams.     

Impact of logging on the richness and diversity of forest butterflies in a tropical dry forest in Thailand

Studies on the impact of logging on tropical forest butterflies have been almost exclusively conducted in moist forest habitats. This study considers the impacts of small-scale logging on butterfly communities at three sites of varying disturbance intensity in a tropical dry forest in western Thailand. Butterfly species richness was similar at all sites, but the abundance of butterflies and diversity of the butterfly community decreased with increased logging disturbance. The recorded decrease in diversity at the relatively large sampling scale used lends further support to the hypothesis that disturbance effects are scale dependent. Species abundance data for butterflies fitted a log-normal distribution at all sites, but also a log-series distribution at the two disturbed sites. These analyses suggest a more complex butterfly community at the undisturbed site, but also that log-series and log-normal distributions may not to be sufficiently sensitive to be useful indicators of community changes following logging. Community ordination separates both the butterfly species and transect samples into three distinct regions corresponding to the three study locations. Ordination axes are correlated with tree density, understorey cover and understorey plant richness. Species with the smallest geographic ranges tend to be the least abundant and occurred most frequently in the undisturbed site. The observed diverging responses to disturbance among butterfly families diminishes the value of butterfly communities as biodiversity indicators, and forest managers should perhaps focus on restricted range species or of groups of recognized sensitive species for this purpose.     

Non-native grass invasion alters native plant composition in experimental communities

Invasions of non-native species are considered to have significant impacts on native species, but few studies have quantified the direct effects of invasions on native community structure and composition. Many studies on the effects of invasions fail to distinguish between (1) differential responses of native and non-native species to environmental conditions, and (2) direct impacts of invasions on native communities. In particular, invasions may alter community assembly following disturbance and prevent recolonization of native species. To determine if invasions directly impact native communities, we established 32 experimental plots (27.5 m²) and seeded them with 12 native species. Then, we added seed of a non-native invasive grass (Microstegium vimineum) to half of the plots and compared native plant community responses between control and invaded plots. Invasion reduced native biomass by 46, 64, and 58%, respectively, over three growing seasons. After the second year of the experiment, invaded plots had 43% lower species richness and 38% lower diversity as calculated from the Shannon index. Nonmetric multidimensional scaling ordination showed a significant divergence in composition between invaded and control plots. Further, there was a strong negative relationship between invader and native plant biomass, signifying that native plants are more strongly suppressed in densely invaded areas. Our results show that a non-native invasive plant inhibits native species establishment and growth following disturbance and that native species do not gain competitive dominance after multiple growing seasons. Thus, plant invaders can alter the structure of native plant communities and reduce the success of restoration efforts.     

Baseline requirements for assessment of mining impact using biological monitoring

Abstract Biological monitoring programmes for environmental protection should provide for both early detection of possible adverse effects, and assessment of the ecological significance of these effects. Monitoring techniques are required that include responses sensitive to the impact, that can be subjected to rigorous statistical analysis and for which statistical power is high. Such issues in baseline research of‘what and how to measure?’and‘for how long?’have been the focus of a programme being developed to monitor and assess effects of mining operations on the essentially pristine, freshwater ecosystems of the Alligator Rivers Region (ARR) in tropical northern Australia. Application of the BACIP (Before, After, Control, Impact, Paired differences) design, utilizing a form of temporal replication, to univariate (single species) and multivariate (community) data is described. The BACIP design incorporates data from single control and impact sites. We argue for modification of the design for particular studies conducted in streams, to incorporate additional independent control sites from adjacent catchments. Inferential power, by way of (i) more confidently attributing cause to an observed change and (ii) providing information about the ecological significance of the change, will be enhanced using a modified BACIP design. In highly valued environments such as the ARR, monitoring programmes require application of statistical tests with high power to guarantee that an impact no greater than a prescribed amount has gone undetected. A minimum number of baseline years using the BACIP approach would therefore be required in order to achieve some desired level of statistical power. We describe the results of power analyses conducted on 2–5 years (depending upon the technique) of baseline data from streams of the ARR and discuss the implications of these results for management.     

河北小五台山国家级自然保护区森林群落与环境的关系

植物与环境之间的关系是一个复杂的演变过程,运用数量生态学方法探讨森林群落的物种组成、种群的生态特征、不同植物群落与环境之间的关系,有助于保护该区森林群落的稳定性和生物多样性。根据148个森林群落样方数据,选用双向指示种分析(TWINSPAN)和典范对应分析(CCA)方法,对河北小五台山国家级自然保护区森林群落进行分类和排序研究。结果表明:(1)TWINSPAN将该区的森林群落分为20个类型;(2)CCA排序结果较好地反映出群落分布格局与环境梯度的关系,各个森林群落类型在前两轴分异明显,在11个环境因子中,海拔、坡位、凋落层厚度、土壤导电率、土壤温度、土壤湿度、土壤厚度和干扰程度这8个环境因子对森林群落的分布起较大的作用,影响森林群落的分布格局,形成不同的植被类型。(3)乔木层优势种的CCA二维排序图所揭示的环境梯度与群落类型的分布有很大的相似性;t值双序图阐明了海拔、凋落层厚度、土壤温度、干扰程度等环境因子对森林群落乔木层优势种有着重要影响。采用TWINSPAN分类与CCA排序的方法,较好地解释了森林群落与环境因子的关系,为小五台山地区森林生态系统的科学管理和保护提供了理论依据,研究结果也为同类地区森林生态系统研究及保护提供参考和借鉴。     

Book reviews

Editing of community data matrices is complementary to analyzing data by multivariate techniques of classification and ordination in the overall task of data analysis. A computer program, DATAEDIT, is described that can perform numerous editing functions, including data transformation, deletion of certain species or samples, deletion of rare species, deletion of outliers, separation of disjunet sample groups, reordering of the species or samples of a data matrix, and the formation of composite samples or of sample subsets. DATAEDIT can use the information in a nonhierarchical or hierarchical classification, and includes its own internal routine for reciprocal averaging ordination.We appreciate valuable suggestions from the late Robert H. Whittaker, and from Philip Dixon, David Hieks, Laura Huenneke, Linda Olsvig-whittaker, and Mark Wilson. Mark O. Hill kindly supplied a fast subroutine for reciprocal averaging.     

Use of terrestrial invertebrates for biodiversity monitoring in Australian rangelands,with particular reference to ants

Abstract Taken literally, the aim of biodiversity monitoring is to track changes in the biological integrity of ecosystems. Given the overwhelmingly dominant contribution of invertebrates to biodiversity, no biodiversity monitoring programme can be considered credible if invertebrates are not addressed effectively. Here we review the use of terrestrial invertebrates, with a particular focus on ants, as bioindicators in Australia in the context of monitoring biodiversity in Australia's rangelands. Ant monitoring systems in Australia were initially developed for assessing restoration success following mining, and have since been applied to a wide range of other land‐use situations, including grazing impacts in rangelands. The use of ants as bioindicators in Australia is supported by an extensive portfolio of studies of the responses of ant communities to disturbance, as well as by a global model of ant community dynamics based on functional groups in relation to environmental stress and disturbance. Available data from mining studies suggest that ants reflect changes in other invertebrate groups, but this remains largely undocumented in rangelands. The feasibility of using ants as indicators in land management remains a key issue, given the large numbers of taxonomically challenging specimens in samples, and a lack of invertebrate expertise within most land‐management agencies. However, recent work has shown that major efficiencies can be achieved by simplifying the ant sorting process, and such efficiencies can actually enhance rather than compromise indicator performance.     

Detecting anthropogenic disturbance in an environment with multiple gradients of physical disturbance,Manukau Harbour,New Zealand

Demonstrating spatial or temporal gradients of effects on macrobenthic communities can be a useful way of providing strong empirical evidence of natural or anthropogenic disturbance. Gradient designs for environmental assessment are sensitive to change for point source data, enabling the scale of the effects of a disturbance to be readily identified. If the spatial scale that is sampled from the point source is adequate, problems of selecting control sites can be avoided. However, sources of spatial variation in macrobenthic communities, which are not related to the impact, can confound the use of gradient designs. This can occur if the natural spatial structure overlaps that of the gradient and cannot be identified either as a location or environmental covariable. The ability to detect point source impacts using a gradient design against natural spatial variability was tested using benthic macrofaunal data collected from Manukau Harbour, New Zealand. Treated sewage wastewater is discharged into the north-west area of the Manukau Harbour. Sandflats in the vicinity of the outfall are also subject to physical disturbance from wind-waves and strong tides. Ordination techniques and the testing of a priori predictions were used to try and separate the relative effects of organic and physical disturbance on the benthic communities. While the occurrence of other environmental disturbances along a gradient of anthropogenic disturbance makes interpretation of community pattern more difficult, the use of a gradient sampling layout, ordination analysis and the testing of a priori predictions enabled impacts of the anthropogenic and natural environmental disturbances to be interpreted. Gradient designs, therefore, provide a method of assessing complex impacts that operate over broad spatial and temporal scales.     

Multivariate analysis of plant communities in the Narok district, Kenya: The influence of environmental factors and human disturbance

Species type in 42 samples was examined using ordination analysis to establish whether the vegetation pattern displays gradation due to environmental factors, and whether the pattern was being altered by human disturbance. The analysis displayed two patterns. First, the ordination on axis 1 demonstrated vegetation gradation from xeric communities on the plains to humid forests on the highland. This pattern is explained on the basis of moisture and nutrient variations. Vegetation vectors based on species presence-absence were correlated with average rainfall, carbon, nitrogen and zinc.The second was separation of disturbed and undisturbed forest and bushland site categories on axis 2 of the ordination space. This pattern suggests that disturbance response is interactive with moisture so that only in moist communities does a significant vegetation response to disturbance occur.     

Covariance between disturbance and soil resources dictates the invasibility of northern fescue prairies

Increasing environmental impacts of exotic organisms have refocused attention on the ability of diverse communities to resist biological invaders. Although resource availability, often related to natural and anthropogenic disturbances, appears central to the invasibility of biological communities, understanding the links between resources, diversity and invasibility is often confounded by the covariance among key variables. To test the hypothesis that community invasibility remains contingent on the type and intensity of disturbance and their impacts on plant community diversity and resource availability, we designed an experiment testing the invasibility of northern fescue prairies by smooth brome (Bromus inermis Leyss.), a Eurasian perennial grass, threatening the structure and function of prairie remnants throughout the Great Plains. Using soil disturbances and herbicide, we imposed treatments manipulating the diversity and resource availability of native prairies. Our observations demonstrate that the vulnerability of native prairies to exotic plant invasions remains contingent on resources. While the establishment of smooth brome seedlings increased with increasing disturbance, its impact depended on the availability of soil nitrogen. As a result, soil burial treatments, simulating disturbance by northern pocket gophers, provided poor recruitment areas for smooth brome, and their low levels of soil moisture and nitrogen, combined with the rapid recovery of the prairie community, compromised seedling establishment. Emphasizing the covariance of diversity and key environmental variables following disturbance, our findings illustrate the importance of disturbance type and intensity on community invasibility. Such a consideration is critical in the conservation and restoration of native prairie remnants throughout the Great Plains.     

Predicting the impacts of biological and physical disturbances: Does theoretical ecology hold any answers?

Biological and physical disturbance has had a severe impact on New Zealand's endemic flora and fauna. Along with the lessons of the past, predicting the sensitivity of communities to disturbance in the future may help direct more attention to those communities with a greater need for preservation (i.e., a lower ability to recover from any such disturbances). In theory it is possible to measure the resilience (or local stability) of a community by constructing a matrix to describe that community and then examining its eigenvalues. Local stability characteristics of invertebrate communities in 11 aquatic habitats were examined with respect to differing levels of habitat disturbance. It was predicted that communities in more unstable habitats would be more resilient in order to persist despite more frequent disturbances. All communities had eigenvalues outside the stability criteria, although those in the unstable habitats did have eigenvalues closer to these criteria. The open and/or patchy nature of stream communities may explain why local stability is not a prerequisite for these communities, however examining the local stability of community matrices still remains a potentially useful tool for predicting the effects of physical and biological disturbances.     

Fuzzy set ordination and classification of Serengeti short grasslands,Tanzania

Abstract. Species abundance data from 32 representative stands are used to evaluate the vegetation in the heavily grazed Serengeti short grasslands. The abundant species are: Kyllinga nervosa, Sporobolus ioclados, S. kentro-phyllus and Eustachys paspaloides, all occurring in elevated areas, and Hypoestes forskalei, which is found in the drainage areas. Numerical classification and fuzzy set ordination revealed four main grassland communities associated with a topographic gradient. The communities are considered distinct since their niches, as computed in the community and environmental fuzzy system space are not overlapping. Leaching, erosion and animal disturbance effects correlated with the topographic gradient are found to determine species composition and overall community structure in the grasslands.     

Effects of disturbance intensity and frequency on bacterial community composition and function

Disturbances influence community structure and ecosystem functioning. Bacteria are key players in ecosystems and it is therefore crucial to understand the effect of disturbances on bacterial communities and how they respond to them, both compositionally and functionally. The main aim of this study was to test the effect of differences in disturbance strength on bacterial communities. For this, we implemented two independent short-term experiments with dialysis bags containing natural bacterial communities, which were transplanted between ambient and 'disturbed' incubation tanks, manipulating either the intensity or the frequency of a salinity disturbance. We followed changes in community composition by terminal restriction fragment analysis (T-RFLP) and measured various community functions (bacterial production, carbon substrate utilization profiles and rates) directly after and after a short period of recovery under ambient conditions. Increases in disturbance strength resulted in gradually stronger changes in bacterial community composition and functions. In the disturbance intensity experiment, the sensitivity to the disturbance and the ability of recovery differed between different functions. In the disturbance frequency experiment, effects on the different functions were more consistent and recovery was not observed. Moreover, in case of the intensity experiment, there was also a time lag in the responses of community composition and functions, with functional responses being faster than compositional ones. To summarize, our study shows that disturbance strength has the potential to change the functional performance and composition of bacterial communities. It further highlights that the overall effects, rates of recovery and the degree of congruence in the response patterns of community composition and functioning along disturbance gradients depend on the type of function and the character of the disturbance.     

Road effects on vegetation composition in a saline environment

Aims Road effects from maintenance and traffic have the potential to alter plant communities, but the exact relationships between these effects and changes in plant community composition have not often been studied in diverse environments. To determine the direction and level of community composition changes in saline environment due to road effects, we conducted a study along roads of different ages and in nearby non-road (i.e. natural) areas in the Yellow River Delta, China. Additionally, to potentially elucidate the mechanisms underlying the changes in the richness and composition of plant communities along roads, we evaluated physiochemical changes in soil of roadside and non-road areas.Methods Floristic and environmental data were collected along roadside of different ages and nearby non-road areas. To evaluate plant communities at each site, six 2 m × 2 m quadrats were placed at 3-m intervals along roads and six quadrats were arranged randomly in non-road areas. To determine the difference in plant community composition between roadside and non-road areas, we measured species richness and the abundance of each species, examined species turnover and floristic dissimilarity between the two areas and positioned plant species and sites in an abstract multivariate space. Plant community (species richness, percentage of halophytes) and soil physicochemical properties (pH, salinity, moisture content, bulk density, nitrate and ammonium nitrogen concentration) were compared between roadside and non-road areas (young roadside vs. corresponding non-road areas, old roadside vs. corresponding non-road areas) by using t -tests. Classification and ordination techniques were used to examine the relationship between vegetation and related environmental variables in both roadside and non-road areas.Important findings For both the young and old roadside areas, species richness in roadside areas was significantly higher than in non-road areas and high floristic dissimilarity values indicated that roadside and non-road areas differed greatly in community composition. In both the young and old roadside areas, the plant communities in roadside areas had lower percentages of halophytes than non-road communities. Correspondence analysis and two-way indicator species analysis showed that halophytes dominated in the non-road areas, while a number of typical non-salt-tolerant species dominated in the roadside areas. Compared to non-road areas, activities associated with roads significantly decreased soil moisture, bulk density and salinity and increased soil pH and nitrate content. Forward selection for the environmental variables in canonical correspondence analysis showed that soil salinity was the most important factor related to the variation of species composition between roadside and non-road areas. Our study demonstrates that road effects have a significant impact on the associated vegetation and soil, and these changes are consistent across roads of different ages in our system.     

The impact on the Senjogahara ecosystem of extreme run-off events from the river Sakasagawa,Nikko National Park

Vegetational data from Senjogahara moor, Nikko National Park, Japan have been analysed using two contrasting but parallel multivariate approaches as a basis for future studies. The plant communities objectively defined using a divisive polythetic classificatory approach (TWINSPAN) have been successfully overlayed on an ordination of the same data using detrended correspondence analysis (DCA). The results reveal a vegetational mosaic reflecting differential levels of flood damage to the vegetation and its subsequent rates of recovery, in a space-time continuum. The results from the TWINSPAN classification show that 13 plant communities are present in the sample area and these correlate closely with complete absence, slight, or extremely heavy disturbance. The form of the disturbance as either channel erosion or alluvial depositional features is shown to also correspond quite closely with the vegetational types and is reflected in the ordination axes derived from DCA.     

安太堡矿区人工植被在恢复过程中的生态关系

采用TWINSPAN、DCA和DCCA,从植物种、植物群落与环境因子关系方面对平朔安太堡矿区的人工植被在恢复过程中的生态关系进行了研究.结果表明,将63个样方划分为12个群落类型,反映了植物群落与环境梯度之间的关系,并列举了各群落的特征.DCA排序图明显反映出排序轴的生态意义,随着复垦时间的增加,土壤含水量也不断升高.DCCA排序进一步表明了土壤有机质含量是所有因子中对植物群落发展起决定性作用的主要环境因素.     

Forb diversity and community similarity of kopjes in the Serengeti National Park, Tanzania

The forb communities of kopjes (rock outcrops) in the Simba, Maasai and Loliondo areas of the Serengeti National Park were examined to determine differences in species composition from surrounding grassland communities, and among sites within kopje and grassland communities. Species diversity measures and multivariate ordination techniques were used to examine the community similarity and species turnover between sites. All measures of forb species diversity were higher on the kopje sites with the exception of one grassland site, and the community composition significantly differed between these two habitat types, with more species and families exclusive to the kopje habitat. Species turnover was very high in grassland habitats, with two of the three areas (Simba and Loliondo) exhibiting a complete change in species composition. Kopjes, on the other hand, had remarkably similar forb communities, suggesting that the populations of the species present on these rock outcrops form patch structures. The distinct flora and higher diversity of kopje forbs raise interesting questions regarding distribution, dispersal and patch dynamics.     

Community divergence in a tropical forest following a severe cyclone

Cyclones are relatively infrequent, may cause massive and widespread disturbance to tropical regions, and are recognized as important determinants of the structure of tropical rainforest communities. Climate change scientists predict that the intensity of cyclones will increase in the future; understanding the long‐term implications of these major disturbances for tropical forest composition and structure will be vital in anticipating and adapting to future changes and impacts. We established a long‐term monitoring site in a rainforest area impacted by severe tropical Cyclone Larry which crossed the North Queensland coast of Australia in March 2006. We monitored recruitment, growth and mortality of nearly 17 000 seedlings in 90 quadrats across the study area for almost 5 years following the cyclone and measured the impact of variation in cyclone disturbance and debris load on community diversity, composition and dispersion as the forest recovered. We show that the level of structural disturbance sustained by the forest has a strong and immediate influence on community dynamics. Quadrats in severely disturbed areas, which were characterized by multiple treefalls and extensive canopy loss, had higher levels of diversity and variation in community assemblage than quadrats in areas characterized primarily by branch loss and defoliation. A rapid divergence in community composition between quadrats in the most‐ and least‐severely disturbed areas resulted in the development of statistically distinct community states across relatively small scales. This provides further evidence that severe cyclones are important in maintaining species diversity in tropical forests.     

Evaluating soil seed banks of phosphate mining restoration in the hyper-arid Negev desert

Ecological systems are severely damaged by the anthropogenic disturbance of mining. Phosphate open-pit mining fields cover over 200 km² of the Negev desert, Israel. However, the effects of the ongoing mine site restoration efforts on the plant community have not been studied. Plants and their seed banks have a major role in ecosystem processes and restoration. In this study, we focused on three mining sites, restored in different years, along Zin River valley. We compared the plant community of restored mining plots within these areas to adjacent natural plots. We asked whether plant community germination potential from the soil seed bank differs between the restored plots and the adjacent natural plots within a mining site. We hypothesized that: (1) there is a lack of seed bank in the restored plots; (2) the altered soil composition at the restored plots inhibits germination. We used soil samples collected from the different mining sites and set up greenhouse experiments. One experiment compared natural and restored areas with different soil treatments. In another experiment, we added native seeds to test their germination potential on restored soil. Our results indicate that lack of seed bank is the major limiting factor hindering germination and not the composition of the soil after restoration. Our findings shed light on the constraints of seed bank establishment in post-mining areas of hyper-arid regions. We suggest considering active restoration practices to facilitate natural dispersal and improve seed bank establishment.