Photosynthetically elevated pH in acid waters with high nutrient content and its significance for the zooplankton community

The pH of undisturbed surface waters in the New Jersey Pine Barrens is very acidic (pH 3.5–4.5). Surface waters disturbed by residential and agricultural development typically exhibit significantly elevated pH. Detailed analyses of a disturbed and undisturbed pond showed that the elevated pH of the disturbed pond was primarily the result of enhanced primary productivity. At night and during the winter, when productivity was reduced, the pH dropped to levels more characteristic of the undisturbed pond. The phenomenon of fluctuating pH had significant implications for the zooplankton in the disturbed pond. Though nutrients were significantly greater in the disturbed pond, zooplankton species composition and general abundance patterns were nearly identical in the two ponds. Thus, in these and other poorly buffered waters, it is hypothesized that the lowest pH values were the ones effectively regulating the zooplankton community.     

Interaction between disturbance and primary productivity in determining stream invertebrate diversity

Invertebrate diversity patterns were examined in 10 streams that differed in substrate disturbance rates, in Taranaki, New Zealand, between April 1999 and January 2000. Two sites on each stream were sampled, one under native forest canopy where light was postulated to limit periphyton growth and a similar site 225–3800 m downstream in open grassland. Periphyton biomass was considerably higher at open stable sites than at closed or unstable sites. Associated with the higher algal biomass, species number and total abundance of animals were higher at open canopy sites. Species number exhibited a negative linear relationship with disturbance but only at open sites. In contrast, rarefied species richness exhibited a negative linear relationship with disturbance at both open and closed sites. This was a result of communities at the more disturbed sites being numerically dominated by only a few taxa compared to the more evenly distributed communities at stable sites. The observed patterns provide little support for contemporary diversity disturbance models but suggest diversity of invertebrates in streams is a function of time since the last disturbance, mediated through recovery of the food base in autotrophic streams.     

Effects of disturbance frequency,intensity, and area on assemblages of stream macroinvertebrates

Disturbance frequency, intensity, and areal extent may influence the effects of disturbance on biological communities. Furthermore, these three factors may have interacting effects on biological diversity. We manipulated the frequency, intensity, and area of disturbance in a full-factorial design on artificial substrates and measured responses of benthic macroinvertebrates in a northern Vermont stream. Macroinvertebrate abundance was lower in all disturbance treatments than in the undisturbed control. As in most other studies in streams, species density (number of species/sample) was lower in disturbed treatments than in undisturbed controls. However, species density is very sensitive to total abundance of a sample, which is usually reduced by disturbance. We used a rarefaction method to compare species richness based on an equivalent number of individuals. In rarefied samples, species richness was higher in all eight disturbed treatments than in the undisturbed control, with significant increases in species richness for larger areas and greater intensities of disturbance. Increases in species richness in response to disturbance were consistent within patches, among patches with similar disturbance histories, and among patches with differing disturbance histories. These results provide some support for Huston’s dynamic-equilibrium model but do not support the intermediate-disturbance hypothesis. Our analyses demonstrate that species richness and species density can generate opposite patterns of community response to disturbance. The interplay of abundance, species richness, and species density has been neglected in previous tests of disturbance models. Received: 20 July 1999 / Accepted: 26 January 2000     

Disturbance frequency and functional identity mediate ecosystem processes in prairie streams

A major consequence of climate change will be the alteration of precipitation patterns and concomitant changes in the flood frequencies in streams. Species losses or introductions will accompany these changes, which necessitates understanding the interactions between altered disturbance regimes and consumer functional identity to predict dynamics of streams. We used experimental mesocosms and field enclosures to test the interactive effects of flood frequency and two fishes from distinct consumer groups (benthic grazers and water-column minnows) on recovery of stream ecosystem properties (algal form and biomass, invertebrate densities, metabolism and nutrient uptake rates). Our results generally suggest that periphyton communities under nutrient limitation are likely to recover more quickly when grazing and water-column minnows are present and these effects can diminish or reverse with time since the disturbance. We hypothesized that increased periphyton production and biomass was the result of increased nutrient turnover, but decreased light limitation and indirect effects on other trophic levels are alternative explanations. Recovery of stream ecosystem properties after a natural flood differed from mesocosms (e.g. lower algal biomass and no long algal filaments present) and species manipulations did not explain recovery of ecosystem properties; rather, ecosystem processes varied along a downstream gradient of increasing temperature and nutrient concentrations. Different results between field enclosures and experimental mesocosms are attributable to a number of factors including differences in algal and invertebrate communities in the natural stream and relatively short enclosure lengths (mean area=35.8 m²) compared with recirculating water in the experimental mesocosms. These differences may provide insight into conditions necessary to elicit a strong interaction between consumers and ecosystem properties.     

Permafrost thaw and intense thermokarst activity decreases abundance of stream benthic macroinvertebrates

Intensification of permafrost thaw has increased the frequency and magnitude of large permafrost slope disturbances (mega slumps) in glaciated terrain of northwestern Canada. Individual thermokarst disturbances up to 40 ha in area have made large volumes of previously frozen sediments available for leaching and transport to adjacent streams, significantly increasing sediment and solute loads in these systems. To test the effects of this climate‐sensitive disturbance regime on the ecology of Arctic streams, we explored the relationship between physical and chemical variables and benthic macroinvertebrate communities in disturbed and undisturbed stream reaches in the Peel Plateau, Northwest Territories, Canada. Highly disturbed and undisturbed stream reaches differed with respect to taxonomic composition and invertebrate abundance. Minimally disturbed reaches were not differentiated by these variables but rather were distributed along a disturbance gradient between highly disturbed and undisturbed sites. In particular, there was evidence of a strong negative relationship between macroinvertebrate abundance and total suspended solids, and a positive relationship between abundance and the distance from the disturbance. Increases in both sediments and nutrients appear to be the proximate cause of community differences in highly disturbed streams. Declines in macroinvertebrate abundance in response to slump activity have implications for the food webs of these systems, potentially leading to negative impacts on higher trophic levels, such as fish. Furthermore, the disturbance impacts on stream health can be expected to intensify as climate change increases the frequency and magnitude of thermokarst.     

茂县土地岭植被恢复过程中物种多样性动态特征

植被恢复是退化生态系统重建的重要途径,植被恢复过程物种多样性的变化反映了植被的恢复程度.通过群落调查和多样性分析,研究了岷江上游土地岭植被恢复过程中群落物种多样性特征.结果表明： 恢复过程中6类不同类型群落分别表现其对于不同环境特征、干扰及更新方式等的响应;森林是较灌丛更适合当地环境状况的植被类型;人工恢复无干扰和轻度干扰群落的多样性相对较高,是较好的恢复模式.重度干扰使得1年生植物与地下芽植物比例增加,其它口食性较好的多年生草本减少.较强的干扰是群落无法更新、长期处于灌丛阶段且多样性较低的重要原因.本地区人工恢复群落在更新进程和多样性维持上优于自然更新群落,种植华山松加速了本地区植被演替进程.建议以适合恢复区域的多种恢复配置方式进行造林,并避免较强干扰,可以加速群落演替进程并保持恢复群落较高的物种丰富度与多样性.     

The stream as a habitat templet for bryophytes: species' distributions along gradients in disturbance and substratum heterogeneity

1. The structure of bryophyte communities in streams in relation to habitat characteristics, especially disturbance, is described. Disturbance in rivers is quantified as movement of the stream bed, whereas in small streams water level fluctuation is used as an indicator of disturbance frequency. 2. Canonical correspondence analysis differentiated frequently disturbed sites from more stable ones. The existence of a disturbance gradient was confirmed in a subset of the study sites using long-term records of discharge variation. A parallel change was detected in the species composition of bryophyte communities with low-statured, potentially fast colonizers dominating the disturbed end and large perennial species the stable end of the gradient. 3. A consistent pattern of zonation of bryophyte species was found along the gradient from continually submersed to persistently dry conditions in small streams and lake outlets. An abrupt increase in species richness occurred at or just above the water line, where facultatively aquatic species tolerant of both conditions formed the bulk of the community. 4. The relationship between species richness and standing crop in stream bryophyte communities was consistent with the hump-backed model of Grime (1979), especially at the within-habitat scale. Quadrats of low and very high standing crop were characterized by low species richness, while peak richness was observed at intermediate standing crops. 5. A few perennial species (e.g. Fontinalis spp. and Rhynchostegium riparioides) capable of monopolizing space dominated the most stable habitats. Species composition in low biomass sites was more variable, yet only one basic growth-form (small-statured species with high allocation to spore production) seemed possible in these highly disturbed streams. In habitats of intermediate biomass, small-scale disturbances apparently allow the formation of a more varied bryophyte community. 6. A habitat templet for stream bryophyte life strategies and community structure is presented. Disturbance is proposed to be the factor filtering out traits unsuitable for a given environment. The potential of stream bryophytes for testing and developing general ecological theory is emphasized.     

Environmental drivers of α-diversity patterns in monsoonal tropical stream fish assemblages: a case study from tributaries of Narmada basin,India

Environmental factors, such as local physico-chemical water parameters, habitat-structural conditions, geography and human disturbances can have a profound impact on the structure and composition of biotic communities. This study investigates the relationship of these factors with fish diversity in medium to small streams in Central India and identifies the key determinants of species richness and diversity in habitats increasingly facing impacts of urban development. Data on fish diversity on eighteen sites, representative of undisturbed and disturbed aquatic habitats, located in the Narmada river basin were collected across different seasons over two years. Seasonal patterns of alpha diversity for this region were analysed and the effect of environmental drivers on seasonal patterns of alpha diversity were assessed. Analyses of species data revealed significant differences in diversity patterns across seasons for both species richness and Shannon diversity. Results of generalized linear mixed models showed that along with disturbance, altitude and substrate heterogeneity, dissolved oxygen, pH and stream width proved to be important environmental variables that predict species richness. Further, variations in pH, dissolved oxygen, temperature, stream width, stream depth and stream width heterogeneity were found to also predict Shannon diversity index. Our study revealed that seasonal changes across the year play a crucial role in shaping diversity patterns. This study is relevant as an important step in identifying roles of various ecological factors driving fish diversity in the region and towards developing long term management plans for critical catchment areas of major rivers in tropical systems.     

Feral pigs in a temperate rainforest ecosystem: disturbance and ecological impacts

Feral pigs (Sus scrofa) are a widespread invasive species, and cause biotic disturbance. This study evaluated the impacts associated with ground disturbance by feral pigs in the North Island of New Zealand. Exclosure cages were erected over feral pig-disturbed ground and visually undisturbed ground (the latter as controls). Buried resin bags and litter bags were located in these plots to examine differences in soil nutrients and decomposition rates and seedling/sapling recruitment (abundance, species composition and richness) was monitored over 21 months. No difference was found in the litter decomposition between the disturbed and visually undisturbed plots. Significantly more nitrate (NO₃-N/NO₂-N) was found in the disturbed exclosures. Seedling density was not significantly affected by feral pig disturbance. However, seedling/sapling species richness was lower in disturbed areas. Species composition changes occurred at disturbed sites with species increasing and decreasing in density after feral pig disturbance. However, no pattern was observed between species that were negatively affected by feral pig disturbance. This study shows that feral pig disturbance affects vegetation through direct removal, but also indirectly through increased nitrate, potentially leading to seedling and sapling species composition changes. Feral pigs are known to return to previously disturbed areas to re-disturb. These areas may remain in a re-disturbed state if not protected, and through continued disturbance and increased nitrate, ecosystem changes may occur, especially in characteristically nutrient poor environments.     

Deterministic control on community assembly peaks at intermediate levels of disturbance

Despite long-standing research, the processes that drive community assembly remain poorly understood. We censused macroinvertebrate communities and measured flood disturbance in 17 Scandinavian mountain streams to assess the hypothesis that communities are shaped by stochastic processes under stable conditions, and increasingly by deterministic processes as disturbance becomes more severe. Each study stream was categorized as being stable (n=5), intermediate (n=7), or disturbed (n=5) depending on the severity of scouring floods. Following spring floods, the number of potential colonisers decreased with increasing disturbance, suggesting that disturbance filtered out species unable to cope with the stress involved. Communities at stable sites had the highest beta diversity, indicating that stochastic processes of community assembly were most important under the least disturbed conditions. In partial contrast with our predictions, the lowest beta diversity occurred between intermediate (not disturbed) sites, suggesting that increasing disturbance first enhances determinism but then rekindles stochasticity at severity levels beyond intermediate. Macroinvertebrate communities were shaped by deterministic processes, which recruit potential regional colonists depending on niche differences and disturbance conditions and by stochastic processes, which distribute the selected species randomly among individual localities. Although often considered opposing, stochastic and deterministic processes interact hierarchically, with relative strength modified by disturbance.     

Effects of multiple disturbance on macroinvertebrate communities in the Acheron River,Victoria

In the Acheron River, southern Victoria, patches of riffle substratum (ca 1 m²) were disturbed every 10 days by kicking and raking. After 20 days, i.e. three disturbances, a further set of patches was disturbed once. For the next 70 days macroinvertebrate dynamics were monitored in the two sets of disturbed patches and also in contiguous control patches. There were no differences in the temporal changes in total species richness, number of species per sample, densities of individuals, or species diversity (H’) between the two disturbance regimes. The composition of the fauna colonizing each disturbance regime was similar, and after 33 days the number of species per sample was similar in disturbed and control patches. The fauna appears to be well adapted to physical disturbance and current ideas linking species richness and disturbance cannot be readily applied to stream communities at the temporal and spatial scales of this experiment.     

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.     

Life History and Secondary Production of Mayflies (Ephemeroptera) Indicate Disturbance in Two Small Carpathian Streams

The life histories and the secondary production of 9 mayflies (Ephemeroptera) species were studied at two sites in a submountain stream (West Carpathians, Slovakia). The disturbed site has a deforested and converted to meadows and pastures catchment and the undisturbed one is a well‐preserved submountain stream with 60% of the catchment covered by spruce forests. Differences in the forest cover and in the thermal regime of both streams were reflected in the structural as well as the functional measures. At the undisturbed site, the total secondary production of mayfly community was more than two times higher (3568 mg DW m^–2 y^–1) than at the disturbed site (1446 mg DW m^–2 y^–1). Species could be divided according to their affinity to particular disturbance level. Ecdyonurus picteti, Rhithrogena carpatoalpina, Habrophlebia lauta and Habroleptoides confusa appeared to prefer undisturbed conditions. On the contrary, Ecdyonurus aurantiacus and Habrophlebia fusca occurred only at the disturbed site. The dominant species Baetis rhodani and Electrogena samalorum did not show any clear preference regarding the catchment disturbance. However, nymphs of Electrogena samalorum seem to be more successful at the disturbed site, where they reached bigger body sizes (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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.     

Interactive community responses to disturbance in streams: disturbance history moderates the influence of disturbance types

Both disturbance history and disturbance type act to structure communities through selecting for particular species traits but they may also interact. For example, flooding selects for species with flood‐resistant traits in streams, but those traits could make communities susceptible to other disturbances and so could cause shifts in community composition due to anthropogenic climate change. To better understand the interactive influences of disturbance history and type on community composition, we investigated the response of macroinvertebrate communities to disturbance using in‐stream channels. Using a split‐plot design, individual channels in five ‘stable’ streams and five ‘frequently disturbed’ streams (disturbance history) were subject to different disturbance type treatments (flooding, drying and a control). Disturbance type independently drove effects on species diversity, but all other effects of disturbance type depended on disturbance history. In particular, the interaction of disturbance type and history determined overall community response. Both disturbance types tested produced similar community responses in frequently disturbed streams, including changes in community composition and alterations to the abundance of less mobile taxa, but low‐flow had a significantly greater effect in stable streams. Macroinvertebrate drift was greatest in the rock‐rolling treatments and significantly less in the low‐flow treatment for both disturbance histories. Therefore, disturbance history moderated the effects of disturbance type and determined the mechanism of community response by determining how well species were adapted to disturbance. This outcome suggests that previous disturbances strongly influence how vulnerable communities are to changes in disturbance, and so should be considered when predicting how changes in disturbance regimes will affect future community composition.     

Temporal effects of disturbance on community composition in simulated stage‐structured plant communities

In an era of global environmental change, understanding how disturbance affects the dynamics of ecological communities is crucial. However, few studies have theoretically explored the potential influence of disturbance including both intensity and frequency on compositional change over time in communities with stage structure. A spatially explicit, individual‐based model was constructed incorporating the various demographic responses to disturbance of plants at two different growth stages: seedlings and adults. In the model, we assumed that individuals within each stage were demographically equivalent (neutral) but differed between stages. We simulated a common phenomenon that seedlings suffered more from disturbance such as grazing and fire than adults. We showed how stage‐structured communities of seedlings and adults responded to disturbance with various levels of disturbance frequency and intensity. In “undisturbed” simulations, the relationship between average species abundance (defined here as the total number of individuals divided by species richness) and community composition turnover (measured by the Bray–Curtis similarity index) was asymptotic. However, in strongly “disturbed” simulations with the between‐disturbance intervals greater than one, this relationship became unimodal. Stage‐dependent response to disturbance underlay the above discrepancy between undisturbed and disturbed communities.     

Forest Modification Affects Diversity (But Not Dynamics) of Speciose Tropical Pyraloid Moth Communities

We studied temporal and spatial dynamics of extremely diverse moth ensembles (Lepidoptera: Pyraloidea) along a gradient of forest disturbance ranging from undisturbed primary tropical rain forest to different kinds of modified forest and open cultivated land at the margin of Mount Kinabalu National Park (Sabah, East Malaysia). We sampled moths by light trapping during two periods (March‐May and August‐September 1997). We collected a total of 7724 individuals representing 680 species during 78 light‐trapping nights at six study sites. Species diversity (Fisher's α) of ensembles in undisturbed primary forest was distinctly higher than in disturbed or secondary forest. More pyraloid moths were attracted in undisturbed primary forest. Samples from disturbed primary or old‐growth secondary forest were statistically indistinguishable from the undisturbed primary forest ensemble in regard to species composition. Thus, pyraloid ensembles from disturbed forest with tall trees remaining appeared to represent impoverished subsets of the undisturbed primary forest community. The more heavily disturbed sites had a distinct fauna and showed a stronger faunal differentiation among each other. Four species of the genus Eoophyla, in which aquatic larvae feed on algae in fast‐running streams benefited prominently from forest disturbance. Temporal variation of ensembles was remarkably concordant across the disturbance gradient. Relative abundance variation of the commonest species was identical at all sites. Overall, pyraloid moths responded more sensitively to anthropogenic habitat alteration than most other moth taxa studied thus far in tropical regions and allowed for an analysis of diversity patterns at a high temporal resolution.     

Effect of periphyton biomass on hydraulic characteristics and nutrient cycling in streams

The effect of periphyton biomass on hydraulic characteristics and nutrient cycling was studied in laboratory streams with and without snail herbivores. Hydraulic characteristics, such as average water velocity, dispersion coefficients, and relative volume of transient storage zones (zones of stationary water), were quantified by performing short-term injections of a conservative tracer and fitting an advection-dispersion model to the conservative tracer concentration profile downstream from the injection site. Nutrient cycling was quantified by measuring two indices: (1) uptake rate of phosphorus from stream water normalized to gross primary production (GPP), a surrogate measure of total P demand, and (2) turnover rate of phosphorus in the periphyton matrix. These measures indicate the importance of internal cycling (within the periphyton matrix) in meeting the P demands of periphyton. Dense growths of filamentous diatoms and blue-green algae accumulated in the streams with no snails (high-biomass streams), whereas the periphyton communities in streams with snails consisted almost entirely of a thin layer of basal cells of Stigeoclonium sp. (low-biomass streams). Dispersion coefficients were significantly greater and transient storage zones were significantly larger in the high-biomass streams compared to the low-biomass streams. Rates of GPP-normalized P uptake from water and rates of P turnover in periphyton were significantly lower in high biomass than in low biomass periphyton communities, suggesting that a greater fraction of the P demand was met by recycling in the high biomass communities. Increases in streamwater P concentration significantly increased GPP-normalized P uptake in high biomass communities, suggesting diffusion limitation of nutrient transfer from stream water to algal cells in these communities. Our results demonstrate that accumulations of periphyton biomass can alter the hydraulic characteristics of streams, particularly by increasing transient storage zones, and can increase internal nutrient cycling. They suggest a close coupling of hydraulic characteristics and nutrient cycling processes in stream ecosystems.     

Effects of stream size on taxa richness and other commonly used benthic bioassessment metrics

Benthic macroinvertebrate samples were collected from natural substrates in disturbed and undisturbed South Carolina upper coastal plain streams to determine if taxa richness and other bioassessment metrics were significantly related to stream size as predicted by the River Continuum Concept (RCC). Linear, quadratic, and lognormal regression models indicated that stream width was positively related to total number of taxa; number of Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa; and total number of organisms. Linear regression showed that the expected number of taxa at undisturbed sites ranged from 35 in 2.0 m wide streams to 64 in 16.0 m streams. Comparable values were 8–20 for EPT and 109–261 for number of organisms. Stream width was inversely related to biotic index values indicating a decrease in average organism tolerance with increasing stream size. ANCOVA showed that the effects of stream size were similar for disturbed and undisturbed sites. Rank correlations and multidimensional scaling (MDS) showed that Lepidoptera and Trichoptera were more abundant in larger streams and Annelida in smaller streams. Stream size related changes in benthic macroinvertebrate community composition are often ignored in bioassessment protocols; however, failure to adjust metrics for stream size can lead to erroneous conclusions. Adjustments are possible by analyzing regression residuals stripped of stream size related variance, dividing the area beneath the maximum taxa richness line into equal size units for metric scoring, or scaling metrics based on predicted reference values. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.