Indicators Of Anthropogenic Disturbance Research Articles

Plant communities as indicators of anthropogenic disturbance on a peri-urban tropical wetland of Lutembe Bay wetland system, Uganda

Plant communities as indicators of anthropogenic disturbance on a peri-urban tropical wetland of Lutembe Bay wetland system, Uganda

Metagenomics-Based Microbial Ecological Community Threshold and Indicators of Anthropogenic Disturbances in Estuarine Sediments.

Assessing the impacts of cumulative anthropogenic disturbances on estuarine ecosystem health is challenging. Using spatially distributed sediments from the Pearl River Estuary (PRE) in southern China, which are significantly influenced by anthropogenic activities, we demonstrated that metagenomics-based surveillance of benthic microbial communities is a robust approach to assess anthropogenic impacts on estuarine benthic ecosystems. Correlational and threshold analyses between microbial compositions and environmental conditions indicated that anthropogenic disturbances in the PRE sediments drove the taxonomic and functional variations in the benthic microbial communities. An ecological community threshold of anthropogenic disturbances was identified, which delineated the PRE sediments into two groups (H and L) with distinct taxa and functional traits. Group H, located nearshore and subjected to a higher level of anthropogenic disturbances, was enriched with pollutant degraders, putative human pathogens, fecal pollution indicators, and functional traits related to stress tolerance. In contrast, Group L, located offshore and subjected to a lower level of anthropogenic disturbances, was enriched with halotolerant and oligotrophic taxa and functional traits related to growth and resource acquisition. The machine learning random forest model identified a number of taxonomic and functional indicators that could differentiate PRE sediments between Groups H and L. The identified ecological community threshold and microbial indicators highlight the utility of metagenomics-based microbial surveillance in assessing the adverse impacts of anthropogenic disturbances in estuarine sediments, which can assist environmental management to better protect ecosystem health.

Oil disturbance reduces infaunal family richness but does not affect phylogenetic diversity

Infaunal organisms are susceptible to disturbances such as hypoxia and sediment contamination; changes in infaunal community structure are therefore often used as indicators of anthropogenic disturbance. Susceptibility to disturbance varies across taxa, either due to physiological factors or to behaviors or functional roles that increase exposure. Both sources of variability are likely to be heritable and shared among related taxa. Thus, we would expect oil disturbance to disproportionately affect related taxa and therefore decrease phylogenetic diversity (PD). We test this hypothesis for a shallow water marine infaunal community using a simulation approach that iteratively removes clades with shared vulnerability to oil exposure. Infauna were sampled at two sites in the Chandeleur Islands, LA, that reflect different exposures to crude oil after the Deepwater Horizon event. Seagrass and adjacent bare sediment habitats were sampled in 2015, 5 years after initial oil exposure, and again in 2016 after an acute re-oiling event. We found that strong correlation between PD and family richness masked any detectable PD patterns with oil exposure. For our full community tree, sensitivity analysis indicated that the removal of larger clades did not disproportionately reduce PD, against our prediction. For this pair of sites, PD did not provide a better metric for assessing the impacts of oil exposure than family richness alone. It is possible, however, that finer-scale taxonomic resolution of infaunal communities may better decouple PD from taxonomic richness. More work is needed to fully evaluate the impacts of disturbance on PD.

Low Densities of the Ghost Crab Ocypode quadrata Related to Large Scale Human Modification of Sandy Shores

Sandy beaches are the most common ecosystems of coastal regions and provide direct and indirect essential services for millions of people, such as coastal protection, fishing, tourism, and recreational activities. However, the natural habitats of sandy shores are being modified at rates never experienced before, making beaches key monitoring sites of marine ecosystems worldwide. The ghost crab species Ocypode quadrata is the most conspicuous crustacean of sandy beaches along the Western Atlantic coast and has been successfully used as an indicator of anthropogenic disturbance and environmental variability. To investigate the potential role of a “triple whammy” [(1) urbanization; (2) use of resources; (3) decreasing resilience] on the most common bioindicator of sandy shores, we compiled a dataset including 214 records of burrows density from 94 microtidal sandy beach sectors covering a range of over 65° of latitude. The response of burrows density to synergetic effects of human modification of natural systems and environmental changes was investigated using linear models. We used the cumulative Human Modification (HMc) index, a standardized geographic projection of changes of natural systems, as a predictor of urbanization, industrialization and use of resources. The predictor wave energy, tidal range and temperature (sea surface and air) were included as potential effects of climate changes. Literature review showed records mainly concentrated at sub-tropical and temperate regions. HMc values were clearly negatively related to burrows density, thereby supporting an effect of modification of natural habitat at large spatial scale. Sea surface temperature and air temperature were positive related with density and the lack of a general pattern of the relationship between burrows density, interactions between wave energy and tide range, supported unclear patterns reported at regional scales. Finally, we argue that ghost crabs are valuable targets for protection actions on sandy beaches that can benefit coexisting species and provide natural habitat conservation.

Fish-trematode systems as indicators of anthropogenic disturbance: Effects of urbanization on a small stream

Parasites have proven to display high responsiveness to anthropogenic stress, having, therefore a considerable value as bioindicators. We analysed the variability in the structure of parasite populations and assemblages of the poeciliid Cnesterodon decemmaculatus caught at partially urbanized stream along a unidirectional gradient with the aim of evaluating their utility as indicators of the effect of urbanization. A total of 209 fish were examined for parasites; some physical parameters of the stream, including the percentage of urbanization (UR) were also recorded. Data were analyzed at the levels of parasite populations and assemblages discriminated by host sex. Fish condition factor was negatively affected by UR, possibly related to flashing hydrology, but it was not related to parasite abundance. Different combinations of variables explained the distribution of parasite populations and assemblages along the creek, with UR being recurrently identified among the best predictors of parasite loads at all levels of analyses. Whereas densities of mollusc first intermediate hosts were considered of little relevance for parasite distribution, distribution of definitive hosts, as well as the presence of pollutants and increased flashiness in urbanized sections of the creek were retained as possible explanations to the observed patterns. As these factors can act simultaneously, the mechanisms driving differences in parasite dynamics of urban streams are difficult to individualize, but the effect of urbanization on both hosts and parasites was clearly identified. Parasites found, with abundances clearly related to UR, can be considered as good ecological indicators, since they are broadly distributed in the region, easy to observe and count, their prevalence and abundance allow reliable quantitative comparisons and are sensitive to variations of environmental stress and/or ecological conditions at small spatial scales. Consequently the susceptibility of fish-trematode systems to variations in both biotic and abiotic stressors makes them a promising tool for detecting urbanization-related disturbances in streams.

Chironomidae traits and life history strategies as indicators of anthropogenic disturbance

In freshwater ecosystems, Chironomidae are currently considered indicators of poor water quality because the family is often abundant in degraded sites. However, it incorporates taxa with a large ecological and physiological diversity and different sensitivity to impairment. Yet, the usual identification of Chironomidae at coarse taxonomic levels (family or subfamily) masks genus and species sensitivities. In this study, we investigate the potential of taxonomic and functional (traits) composition of Chironomidae to detect anthropogenic disturbance. In this context, we tested some a priori hypotheses regarding the ability of Chironomidae taxonomic and trait compositions to discriminate Mediterranean streams affected by multiple stressors from least-disturbed streams. Both taxonomic and Eltonian trait composition discriminated sites according to their disturbance level. Disturbance resulted in the predicted increase of Chironomidae with higher number of stages with hibernation/diapause and of taxa with resistance forms and unpredicted increase of the proportion of taxa with longer life cycles and few generations per year. Life history strategies (LHS), corresponding to multivoltine Chironomidae that do not invest in hemoglobin and lack strong spring synchronization, were well adapted to all our Mediterranean sites with highly changeable environmental conditions. Medium-size animals favored in disturbed sites where the Mediterranean hydrological regime is altered, but the reduced number of larger-size/carnivore Chironomids suggests a limitation to secondary production. Results indicate that Chironomidae genus and respective traits could be a useful tool in the structural and functional assessment of Mediterranean streams. The ubiquitous nature of Chironomidae should be also especially relevant in the assessment of water bodies naturally poor in other groups such as the Ephemeroptera, Plecoptera, and Trichoptera, such as the lowland rivers with sandy substrates, lakes, or reservoirs.

Power analysis as a tool to identify statistically informative indicators for monitoring coral reef disturbances.

Extensive biological field surveys are costly and time consuming. To optimize sampling and ensure regular monitoring on the long term, identifying informative indicators of anthropogenic disturbances is a priority. In this study, we used 1800 candidate indicators by combining metrics measured from coral, fish, and macro-invertebrate assemblages surveyed from 2006 to 2012 in the vicinity of an ongoing mining project in the Voh-Koné-Pouembout lagoon, New Caledonia. We performed a power analysis to identify a subset of indicators which would best discriminate temporal changes due to a simulated chronic anthropogenic impact. Only 4% of tested indicators were likely to detect a 10% annual decrease of values with sufficient power (>0.80). Corals generally exerted higher statistical power than macro-invertebrates and fishes because of lower natural variability and higher occurrence. For the same reasons, higher taxonomic ranks provided higher power than lower taxonomic ranks. Nevertheless, a number of families of common sedentary or sessile macro-invertebrates and fishes also performed well in detecting changes: Echinometridae, Isognomidae, Muricidae, Tridacninae, Arcidae, and Turbinidae for macro-invertebrates and Pomacentridae, Labridae, and Chaetodontidae for fishes. Interestingly, these families did not provide high power in all geomorphological strata, suggesting that the ability of indicators in detecting anthropogenic impacts was closely linked to reef geomorphology. This study provides a first operational step toward identifying statistically relevant indicators of anthropogenic disturbances in New Caledonia's coral reefs, which can be useful in similar tropical reef ecosystems where little information is available regarding the responses of ecological indicators to anthropogenic disturbances.

Can biotic indicators distinguish between natural and anthropogenic environmental stress in estuaries?

Because estuaries are naturally stressed, due to variations in salinity, organic loadings, sediment stability and oxygen concentrations over both spatial and temporal scales, it is difficult both to set baseline reference conditions and to distinguish between natural and anthropogenic environmental stresses. This contrasts with the situation in marine coastal and offshore locations. A very large benthic macroinvertebrate dataset and matching concentrations for seven toxic heavy metals (i.e. Cr, Ni, Cu, Zn, Cd, Hg and Pb), compiled over three years as part of the UK's National Marine Monitoring Programme (NMMP) for 27 subtidal sites in 16 estuaries and 34 coastal marine sites in the United Kingdom, have been analysed. The results demonstrate that species composition and most benthic biotic indicators (number of taxa, overall density, Shannon–Wiener diversity, Simpson's index and AZTI's Marine Biotic Index [AMBI]) for sites in estuarine and coastal areas were significantly different, reflecting natural differences between these two environments. Shannon–Wiener diversity and AMBI were not significantly correlated either with overall heavy metal contaminant loadings or with individual heavy metal concentrations (‘normalized’ as heavy metal/aluminium ratios) in estuaries. In contrast, average taxonomic distinctness (Δ+) and variation in taxonomic distinctness (Λ+) did not differ significantly between estuarine and coastal environments, i.e. they were unaffected by natural differences between these two environments, but both were significantly correlated with overall heavy metal concentrations. Furthermore, Δ+ was correlated significantly with the Cu, Zn, Cd, Hg and Pb concentrations and Λ+ was correlated significantly with the Cr, Ni, Cu, Cd and Hg concentrations. Thus, one or both of these two taxonomic distinctness indices are significantly correlated with the concentrations for each of these seven heavy metals. These taxonomic distinctness indices are therefore considered appropriate indicators of anthropogenic disturbance in estuaries, as they allow a regional reference condition to be set from which significant departures can then be determined.

Can roads, railways and related structures have positive effects on birds? – A review

The urbanization process affects faunal distributions and movement patterns, contributing directly to biotic homogenization and representing an important threat to biodiversity. In particular, birds, which have been well studied as indicators of anthropogenic disturbance, are especially valuable in evaluating these impacts.While the negative impact of these processes and structures, most notably road and railway networks, are now well appreciated (e.g. habitat loss, disturbance, noise, mortality by collisions, barrier effects), the potentially positive effects on wildlife are less appreciated (the number of documented negative effects of roads on animal abundance outnumbered the number of positive effects by a factor of 5). Here, were reviewed a total of 92 peer-reviewed publications for the period of 36years between 1978 and 2014, which reported positive effects of roads and associated anthropogenic structures on birds. Our results show that roads, railways and several associated constructions, commonly implicated in the decline of biodiversity, may also have positive effects on certain bird species or communities. The main types of positive effects on birds identified were classified as: (1) roads: providing foraging habitat; reducing the predation pressures; and providing a warm surface assists in conserving metabolic energy; (2) lights of streets: prolonging diurnal activity; (3) powerlines, fences, etc. along roads: providing perches for hunting activities; and (4) bridges, pylons, tree lines along roadsides, bases of powerline pylons: providing nesting sites and cover from predators. From this review, we provide a useful tool for ecologists, road planners and other stakeholders engaged on conservation or landscape planning.

Variability of riparian soil diatom communities and their potential as indicators of anthropogenic disturbances

Riparian soils are affected by both natural and anthropogenic disturbances occurring in the water bodies and on the catchment area. These riparian areas are also rich in microhabitats and therefore host various soil biota, including diatoms. Diatoms are known for their bioindication abilities in water and could potentially be used in that context in the riparian zone. Therefore the possibility of riparian soil diatoms acting as indicators of both terrestrial and aquatic disturbances is worth discussion. We analysed diatom community structure and their variability between different study areas and sites. We also quantified diatom species diversity and richness and evenness of the riparian topsoils. Possible effects of various anthropogenic disturbances on diatom communities, alkaline air pollution, and the effects of mining waters pumped into the area were studied in north- eastern Estonia. These results were compared with results from an area with low human influence in south-eastern Estonia. Additionally, we evaluated the potential of diatoms as indicators of various anthropogenic disturbance levels and a water contamination gradient based on sulphate concentrations. Community parameters, including species richness, diversity, and evenness, indicated some differences between the studied communities both when the separate study sites and distinguishable anthropogenic disturbance levels were compared. Diatom assemblages also showed moderate variability between the study sites, which could be influenced by variable moisture conditions, variable organic matter content, and the trophic level of the water body. Despite the variable levels of human influence the two compared areas shared about 51.4% of the species. Our findings show that the diatom community composition of riparian soils could potentially indicate anthropogenic disturbance levels, especially through the abundance, absence, or presence of specific species (e.g. Hantzschia amphioxys, Fragilaria zeilleri var. elliptica, Pinnularia lata).

Evaluating performance of macroinvertebrate-based adjusted and unadjusted multi-metric indices (MMI) using multi-season and multi-year samples

Multimetric indices (MMI) are extremely useful indicators of anthropogenic disturbance, but that usefulness is a function of how well they have been calibrated for natural spatial and temporal variability. Nonetheless, there have been very few studies regarding the effects of such natural variability on MMI scores and metric selection, and even fewer studies on the effects of minimizing the mean of metric correlations. To do so, we calibrated and validated several adjusted and unadjusted MMI for natural gradients with different metric compositions via datasets from 161 samples collected at 83 stream sites from 2008 to 2012 across the Li River Basin, China. We used random forests to model the variation of individual metrics with natural gradients, then used their residual distributions as the adjusted response range of each metric, independent of natural environmental influence. To select core metrics for MMI, the candidate adjusted and unadjusted metrics were all screened through reproducibility, sensitivity, and redundancy tests. The adjusted MMI were more precise, less biased, and more sensitive than the unadjusted MMI. Although the unadjusted MMI were as responsive as the adjusted MMI, the unadjusted MMI increased risks of inferring type I and type II errors. Minimizing the mean of metric correlations as well as avoiding biological information redundancy improved the performance of unadjusted and adjusted MMI, but only improved precision for the adjusted MMI. Using multi-season and multi-year samples proved to be an effective and efficient assessment method to diminish natural seasonal variation in adjusted MMI, but not unadjusted MMI. We found that the adjusted MMI with the lowest mean of metric correlations using multi-season and multi-year samples performed best and reduced seasonal variability.

Regional Patterns of Major Nonnative Invasive Plants and Associated Factors in Upper Midwest Forests

Nonnative invasive plants (IPs) are rapidly spreading into natural ecosystems (e.g., forests and grasslands). Potential threats of IP invasion into natural ecosystems include biodiversity loss, structural and environmental change, habitat degradation, and economic losses. The Upper Midwest of the United States encompasses the states of Illinois, Indiana, Iowa, Michigan, Minnesota, Missouri, and Wisconsin, a region populated with 46 million people. Concerns of IP threats to the productive timberlands in the region have emerged with rapid expansion of urban areas and associated land cover changes caused by increasing human disturbances. Using the strategic inventory data from the 2005-2006 US Department of Agriculture Forest Service Forest Inventory and Analysis program and other data such as forestland cover and transportation coverage/layers, we modeled the regional patterns of IPs by using a combination of nonparametric techniques, including classification and regression tree analysis, kernel density smoothing, and bootstrapping. For the Midwest region, a probability map and historical records of human-related introduction of IPs of interest suggests that invasive shrubs, herbs, and grasses were initially introduced into the central (sparsely forested) areas and then spread north and south (densely forested areas), whereas invasive vines spread primarily from the south into other parts of the region. The probability of IPs in densely forested areas (0.1) was one-fifth of that in sparsely forested areas. Shrubs are the predominant IP threat and are distributed across the vast region with the exception of the northern part. Invasive grasses and herbs are most abundant in the central part of the region, and invasive vines are most common in the southern part. Percent forest cover and road proximity (distance to roads) as indicators of anthropogenic disturbances, were the most significant drivers of IP occurrence/abundance. Site factors, including forest productivity and stand biodiversity, were significantly correlated with the occurrence of vines.

Young-of-the-year fish assemblages as indicators of anthropogenic disturbances in large tributaries of the Seine River Basin (France)

A variety of indices targeting a number of different biological assemblages have been developed to assess aquatic ecosystem condition, identify the drivers of alteration and provide information on possible restoration measures. Fish-based indices, commonly focused on adult assemblages, are capable of indicating declines in condition, but often provide limited information on the ultimate causes for the observed changes. Using young-of-the-year (YOY) fish assemblages has been suggested as a means of improving the sensitivity of fish-based indicators. To verify this assumption, we first model, using boosted regression trees, the occurrence of 16 YOY fish species as a function of twenty two environmental factors in 227 reference (i.e., least disturbed) habitats located in the river Seine (France) and its two main tributaries (i.e., Oise and Marne rivers). We then validate the species models using an independent dataset of 74 reference habitats. Finally, using three independent data sets reflecting different categories of disturbances (i.e., physico-chemical disturbances, physical disturbances induced by navigation and a mix of both disturbances), we measure the deviation between expected and observed species occurrences to evaluate our species models ability in detecting these disturbances. The models are ecologically meaningful and overall perform well in discriminating between reference and disturbed habitats, showing a stable response for all unimpaired habitats and highlighting the main habitat disturbances tested.

Determining Sources of Water to Great Lakes Coastal Wetlands: A Classification Approach

Water and associated nutrients can enter freshwater and marine coastal wetlands from both watershed and offshore sources. Identifying the relative contribution of these potential sources, and the spatial scale at which sources are influenced by anthropogenic activities, are critical steps in wetland protection and restoration. We developed a hydrology-based classification scheme for Great Lakes coastal wetlands for the purpose of identifying dominant hydrologic influences and water sources. Classes were determined through analysis of data quantifying hydrologic linkages to lake (seiche) and watershed (watershed area, tributary discharge) in 57 wetlands distributed along the U.S. shoreline of the Laurentian Great Lakes. Wetlands were partitioned into four classes of hydrology that were predicted to differ in sources of water. Source water predictions were tested by comparing Chloride (Cl-) concentrations in wetland, lake, and tributary waters of the wetlands in each class. Results confirmed that classification based on quantitative hydrology data was successful in identifying groups of wetlands with similar water sources. Correlations between wetland Cl-, an indicator of anthropogenic disturbance, and agricultural and urban land uses suggest that differences among classes in water sources resulted in differences in the scale at which wetlands were connected to and influenced by landscapes.

Ecology of European Barbel Barbus Barbus: Implications for River, Fishery, and Conservation Management

The rheophilic European barbel Barbus barbus is an aggregative fish typically encountered in the middle reaches of European rivers that range from southeastern England and France in the west to the Black Sea basin in the east. An important angler-target species and indicator of anthropogenic disturbance, they are vagile, moving considerable distances for activities such as spawning when movements of over 20 km may be undertaken. Their habitat requirements vary with development; areas in the littoral zone with minimal flow are important for larvae, riffle areas for juveniles, and mid-channel habitats for adults. Within populations, individuals may be present to at least 18 years old, with the older, larger fish likely to be female. A range of threats to their populations exist, with the primary ones relating to aspects of river engineering that reduce habitat diversity (e.g., channelization) and river connectivity (e.g., flow gauging weirs) as this may impact nursery habitats and access to spawning gravels. Successful conservation and fishery management of barbel is thus reliant on sympathetic river management that maintains or restores habitat heterogeneity and connectivity.

The effects of four types of anthropogenic disturbances on composition and abundance of terrestrial isopods (Isopoda: Oniscidea)

The Brazilian Atlantic Forest is currently reduced to about 12% of its original range. Among the components that make up its great diversity, there are species with the potential to be bioindicators, which can be very important for conservation-oriented studies. This study compares the species composition, abundance and sex ratio of terrestrial isopods in sites that show different anthropogenic disturbance histories and are located within four reserves in the Atlantic Forest of southwestern Brazil. Our study explores these crustaceans as indicators of anthropogenic disturbance. The influence of one of the following factors was explored in each protected area: 1) history of vegetation harvesting, 2) trail management, 3) Eucalyptus planting, and 4) edge effect. A total of 2,217 individuals of six species (Atlantoscia sp., Benthana werneri Lemos de Castro, 1958, Pseudodiploexochus tabularis (Barnard, 1932), Pudeoniscus obscures Lemos de Castro, 1973, Styloniscus spinosus (Patience, 1907), and Trichorhina sp.) were captured in pitfall traps. The composition of isopod species was different between most of the contrasting sites within reserves, and was similar among the less disturbed sites of different reserves. The total number of isopod individuals and the sex ratio were not different between the contrasting sites within most of the reserves and only the sex ratio of Atlantoscia sp. differed between contrasting sites of one protected area. Upon an individual analysis of each species, S. spinosus (an exotic species) was most abundant in more disturbed sites. The distributions of B. werneri and Atlantoscia sp. over time were relatively synchronous, except where S. spinosus was abundant. Our results also indicate that the exotic species S. spinosus may benefit from the vegetation mosaic produced by disturbance, so differences in abundance of this species may be useful for bioindication. A change in the spatial and temporal structure of Oniscidea communities caused by anthropogenic disturbance may have a cascade effect on ecological cycles because terrestrial isopods play a fundamental role in nutrient cycling.

Nonconstituent species in soil seed banks as indicators of anthropogenic disturbance in forest fragments

Forest fragmentation is prevalent in regions with high human population density, but also with high biological diversity, such as southwestern China. Predicting potential changes in species composition in native forest ecosystems resulting from forest fragmentation is an important approach in assessing forest ecosystems and sustainable management of forests. The term nonconstituent species is proposed for plant species that occur in a natural landscape but are not native to it. We hypothesized that fragmentation of continuous forests significantly increases both the richness and the size of soil seed banks of nonconstituent species. To test our hypothesis we compared soil seed banks in three small fragments and one large tract of subtropical evergreen broad-leaved forest in Yunnan Province, southwestern China. In total, 249 species were identified in all soil samples from the four sites. Nonconstituent species represented 36.4%–61.5% of the total taxa and 33.8%–59.6% of total germinants from soil samples in the three forest fragments, but only 3.7%–7.9% of total taxa and 7.5%–9.4% of total germinants from soil samples in the continuous forest tract. Both richness and size of soil seed banks of nonconstituent species were greater under forest fragments than under continuous forest. A majority of nonconstituent species were native weeds and annual herbs with wind-dispersed seeds; most were present in soil seed banks but not in aboveground vegetation. We suggest that nonconstituent species in soil seed banks could be used as an indicator species group for assessing human disturbance. If so, the richness and size of soil seed banks of nonconstituent species could play an important role in quantifying disturbance in forests.

Are alien fish a reliable indicator of river health?

Summary1. The ability of many introduced fish species to thrive in degraded aquatic habitats and their potential to impact on aquatic ecosystem structure and function suggest that introduced fish may represent both a symptom and a cause of decline in river health and the integrity of native aquatic communities.2. The varying sensitivities of many commonly introduced fish species to degraded stream conditions, the mechanism and reason for their introduction and the differential susceptibility of local stream habitats to invasion because of the environmental and biological characteristics of the receiving water body, are all confounding factors that may obscure the interpretation of patterns of introduced fish species distribution and abundance and therefore their reliability as indicators of river health.3. In the present study, we address the question of whether alien fish (i.e. those species introduced from other countries) are a reliable indicator of the health of streams and rivers in south‐eastern Queensland, Australia. We examine the relationships of alien fish species distributions and indices of abundance and biomass with the natural environmental features, the biotic characteristics of the local native fish assemblages and indicators of anthropogenic disturbance at a large number of sites subject to varying sources and intensities of human impact.4. Alien fish species were found to be widespread and often abundant in south‐eastern Queensland rivers and streams, and the five species collected were considered to be relatively tolerant to river degradation, making them good candidate indicators of river health. Variation in alien species indices was unrelated to the size of the study sites, the sampling effort expended or natural environmental gradients. The biological resistance of the native fish fauna was not concluded to be an important factor mediating invasion success by alien species. Variation in alien fish indices was, however, strongly related to indicators of disturbance intensity describing local in‐stream habitat and riparian degradation, water quality and surrounding land use, particularly the amount of urban development in the catchment.5. Potential confounding factors that may influence the likelihood of introduction and successful establishment of an alien species and the implications of these factors for river bioassessment are discussed. We conclude that the potentially strong impact that many alien fish species can have on the biological integrity of natural aquatic ecosystems, together with their potential to be used as an initial basis to find out other forms of human disturbance impacts, suggest that some alien species (particularly species from the family Poeciliidae) can represent a reliable ‘first cut’ indicator of river health.

Tree species richness complementarity, disturbance and fragmentation in a Mexican tropical montane cloud forest

Tropical montane cloud forest exhibits great heterogeneity in speciescomposition and structure over short geographic distances. In central Veracruz,Mexico, the conservation priority of seven cloud forest fragments was assessedby considering differences in woody plant species richness and complementarityof species among sites, forest structure, tree mortality, and timber andfirewood extraction as indicators of anthropogenic disturbance. Densities oftrees ≥5 cm dbh (360–1700 trees/ha) weredifferent among the sites, but basal area (35.3–89.3m2/ha) did not differ among fragments. The number of dead trees rangedfrom 10–30 to 170–200 trees/ha. The fragments'species composition was different but complementary. The Morisita–Hornindex indicated low similarity between fragments. A non-parametric estimator ofspecies richness indicated that more sampling effort would be necessary tocomplete the inventory (15 additional trees and two understory shrub species).Unfortunately, most of the fragments are threatened with deforestation. The numberof cut trees was similar among sites (0–15 cut trees/0.1 ha).Sites with immediate need for conservation were close to settlements, with highnumbers of cut trees and no legal protection. The selected sites represent thevariety of situations that exist in the region. Given the high complementarityobserved between fragments, a regional conservation approach will be required topreserve the last repositories of part of the tremendous biodiversity of theonce continuous forest in this region.

Outline of A New Approach to Evaluate Ecological Integrity of Salt Marshes

The integrity of coastal salt marshes can be determined from the extent to which they provide key ecosystem services: food and habitat for fish and wildlife, good water quality, erosion and flood control, and recreation and cultural use. An outline of a new approach for linking ecosystem services with metrics of structure and function to evaluate the ecological integrity of salt marshes is described. One main objective of the approach is to determine whether differences in structure and function can be detected among salt marshes with similar geomorphology and hydrology but different degrees of anthropogenic stress. The approach is currently being applied to salt marshes of Narragansett Bay, RI, USA. Stable nitrogen isotopic ratios of the marsh biota reflected the nitrogen sources from the adjacent watersheds and were significantly correlated with percent residential land use. Results show that plant zonation significantly ( r = —0.82; p < 0.05) relates with percent residential land use and is potentially a sensitive indicator of anthropogenic disturbance of New England salt marshes. We are currently examining species diversity, denitrification rates, and susceptibility to erosion among the sites for additional indicators of salt marsh condition. Our results to date suggest that this approach will provide the methods needed for managers to systematically monitor and evaluate the integrity of salt marshes