Response of ants to human‐altered habitats with reference to seed dispersal of the myrmecochore Corydalis giraldii Fedde (Papaveraceae)

Anthropogenic habitat disturbance has potential consequences for ant communities. However, there is limited information on the effects of ant responses on associated ecological processes such as seed dispersal. We investigated the effect of disturbance on the abundance, richness, and composition of ant communities and the resulting seed‐dispersal services for a herbaceous myrmecochore, Corydalis giraldii (Papaveraceae), in an undisturbed habitat (forest understory), moderately disturbed habitat (abandoned arable field), and highly disturbed habitat (road verge) on Qinling Mountains, China. In total, we recorded 13 ant species, and five out of these were observed to transport seeds. The community composition of dispersers was significantly different amongst habitats. The richness of the dispersers did not differ among the habitats, but their total abundance varied significantly across habitats and was 21% lower in the road verge than in the abandoned arable fields. The major seed‐dispersing ant species in both the forest understory and the abandoned arable field were large‐bodied (Myrmica sp. and Formica fusca, respectively), whereas the major seed‐dispersing ants found in the road verge were the small‐bodied Lasius alienus. This difference resulted in lower seed removal rates and dispersal distances in the road verge than in the other two habitats. The different dispersal patterns were attributed primarily to differences in dispersing ant abundance and identity, most likely in response to habitats with different degree of anthropogenic disturbance. The possible influence of disturbance on the ecological specialization of ant‐seed dispersal interaction is also discussed.     

Influence of flood timing on the recovery of macrophytes in a former river channel

Over two vegetation cycles we compared the recovery of macrophytes from flood disturbances that occured at different seasons (July vs December) on patches of a former channel of the Rhône River, France. Some patches were disturbed twice; others were disturbed either in summer or in winter; others were never disturbed and were used as controls.The recovery rate of the vegetation was estimated from the duration of recolonization of the disturbed areas and of growth of the recolonizing species. The influence of the summer disturbance appeared to be strong because the disturbance occurred when the development of the vegetation was maximum. The influence of the winter disturbance was apparently much lower since most species had already declined at this time because of their phenology. The repetition of the two disturbances on the same patch had little influence on the vegetation community.In all cases, the recovery of the vegetation occurred rapidly, both for total vegetation cover and species richness. By the following spring, no significant differences appeared between disturbed and reference patches. The effect of the disturbances varied according to the phenology of the plants, and the macrophyte community studied was more sensitive in summer than in winter.     

Recovery of riverine vegetation after experimental disturbance: a field test of the patch dynamics concept

The Patch Dynamics Concept predicts different recovery patterns of communities after disturbance according to the spatial and temporal heterogeneity of the habitat. The aim of this study was to test the predictions arising from the Patch Dynamics Concept on the recovery of macrophyte communities after an experimental disturbance. The test was based on the comparison of the vegetation recovery in three stations located on former channels of the Rhône River, France, differing by their temporal heterogeneity, which was estimated by the frequency of flood scouring. In each station the experimental disturbance was set up by uprooting the aquatic plants in three experimental sets comprising four 1 m²-plots. The aquatic plants were surveyed in these sets as well as in their reference sets from July to November 1991.As predicted, the most frequently disturbed station recovered its species richness (19 species) and its vegetation cover in less than two months. The biological traits of the species occurring in this station are considered as r-strategies. The species colonizing the experimental sets were not necessarily present on the sets before the disturbance, but occurred regularly on other sites station. The rapidity of the community recovery demonstrates the high resilience of this ecosystem. According to the unpredictable character of its recolonization, the macrophyte community of this station could be said to be founder controlled with competitive lottery for establishment.The station with intermediate temporal heterogeneity was overgrown by some r-selected species but the community recolonization was predictable and this station had intermediate resilience. Its species richness was low (6 species).The less frequently disturbed station presented low resilience with a slow recovery of its community (more than 5 months); the species richness (4 species) and the traits of some species were related to K-strategies while others were related to r-strategies. The macrophyte community of this station could be said to be dominance controlled.Different patterns of recovery of the macrophyte communities of former channels of the Rhône River could be depicted according to their temporal heterogeneity; these patterns were consistent with the hypotheses arising from the Patch Dynamics Concept. However, the competitive lottery appeared to be limited at the scale of our experiment.     

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.     

Acridids as indicators of disturbance in dry deciduous forest of West Bengal in India

Acridid communities are sensitive to anthropogenic disturbance and the community structure of acridids plays vital role in functioning the forest ecosystem. They are potentially useful bioindicators for conservation planning and habitat disturbances. Acridid assemblages of three different habitat types based on degree of disturbance as follows five natural sites, five moderately disturbed sites and five highly disturbed sites in Chaupahari forest, West Bengal, India were studied. Diversity, abundance, equitability and species richness of acridid were observed in respect to undisturbed and disturbed habitats. The species richness and diversity of the sites tracked the intensity of disturbance, the greatest value being associated with the natural site followed by the moderately disturbed site and highly disturbed site. The highest species richness and diversity index indicate the suitable habitat for acridid population. Statistical analysis infers that different species show different behavior and the sites are also different in relation to different habitat types.     

The Impact of Anthropogenic Disturbance on Assembly Patterns of Termite Communities

Intensification of land‐use threatens biodiversity, especially in tropical ecosystems that harbor the planet's highest species richness. This negative impact of anthropogenic disturbance on species numbers is well established, but the mechanisms underlying the community assembly processes are less well understood. Termites are of fundamental importance in tropical ecosystems where they are critical for nutrient recycling and species diversity. We tested the impact of anthropogenic disturbance on termite species diversity and assembly processes in a West African savanna applying the newest techniques of phylogenetic community analyses. Species richness dropped in areas of intensive land‐use and compositional similarity between intensive land‐use areas was high. This contrasted with a protected National Park where communities were characterized by high species richness and intermediate species turnover between sites. Slightly disturbed areas in the buffer zone surrounding the park were intermediate, they still had high species richness but similarity between sites increased. Strikingly, the assembly pattern also changed with disturbance from more phylogenetic overdispersion to more clustering (coexisting species became phylogenetically more similar), but only when the fungus‐growing termite Macrotermes bellicosus was absent. Our data suggest that the major forces structuring termite communities depend: (1) on the presence of this dominant mound‐building termite; and (2) that they change to more environmental filtering with disturbance. Anthropogenic disturbance seems to function as a filter that allows only a specific subset of species to occur. Such an effect might be widespread in ecology but it is difficult to document quantitatively. Phylogenetic community analyses can help to contribute such evidence.     

Consumer and resource diversity effects on marine macroalgal decomposition

Few manipulative experiments that explicitly test the relationship between biodiversity and ecosystem function have focussed on regenerative processes such as decomposition and nutrient cycling. Of the studies that have taken place, most have concentrated on the effects of leaf litter diversity rather than the effects of consumer diversity on decomposition. In the present study, we established an in‐situ mesocosm experiment on an intertidal mudflat in the Ythan Estuary, Scotland, to investigate the interactive effects of consumer diversity, resource diversity and microbial activity on algal consumption and decomposition. We assembled communities of three commonly occurring macrofaunal species (Hediste diversicolor, Hydrobia ulvae and Littorina littorea) in monoculture and all possible combinations of two and three species mixtures and supplied them with single vs two‐species mixtures of the algae Fucus spiralis and Ulva intestinalis. Further, we also investigated whether algal decomposition changes nutrient remineralisation within the sediment by determining the C:N ratio of the surficial sediment. Data were analysed using extended linear regression with generalized least squares estimation to characterise the variance structure. We found that consumer species diversity effects are best explained by compositional effects and that species richness per se may not be the single most important determinant of resource use and decomposition in this community. Algal identity and invertebrate identity effects underpin the observed response and reflect species‐specific traits associated with algal consumption and processing. The role of the microbial community is comparatively weak, but strongly linked to faunal activities and behaviour. The C:N ratio of the sediment increased with consumer species richness, indicating increased mineralisation in more diverse communities. Overall, our results suggest that although consumer species richness effects per se are weak, decomposition and subsequent incorporation of resources is nevertheless dependent on the composition of the decomposer community, which, in turn, has important implications for biogeochemical nutrient cycling in marine coastal habitats.     

Factors affecting spatial and temporal distribution of Ostracoda assemblages in different macrophyte habitats of a shallow lake (Lake Fehér,Hungary)

Spatial and temporal distribution, abundance and habitat preferences of ostracod assemblages were studied in various habitats of Lake Fehér in Hungary. Of the 20 species Fabaeformiscandona hyalina and Cypridopsis hartwigi are new to Hungary. Significant spatial differences were recorded in the composition and abundance of the Ostracoda assemblages in the different habitats. The most diverse and abundant assemblages were found in the reed-belt, however, the mean abundance of the species differed in the different macrophyte communities of the reed-belt. The species richness and abundance were considerably lower in disturbed sites than in the other habitats. Most of the 20 species showed distinct habitat preferences and ecological tolerances. Especially the presence and coverage of the vegetation and the dissolved oxygen content influenced the distribution and abundance of the species.     

A comparison of the diversity and structure of butterfly communities in semi-natural and human-modified grassland habitats at the foot of Mt. Fuji, central Japan

To examine the effects of human land use and disturbance on butterfly communities we compared the diversity and structure of communities in relatively undisturbed, semi-natural grassland habitats and highly disturbed, human-modified ones. Comparisons were based on transect counts conducted at 6 study sites at the foot of Mt. Fuji in the cool temperate zone of central Japan during 1995. Out of the six community parameters used in the analyses, the species richness, species diversities H and 1/, and dominance indices were significantly different between the two habitat types stated above. That is, butterfly communities in semi-natural habitats had higher species richness and diversity, and lower dominance indices than those in human-modified ones. This suggests that heavy land modification and disturbance to semi-natural habitats change greatly its butterfly community structure, which, indeed, leads to decreasing species richness and diversity mainly due to the loss of species that are confined to semi-natural habitats. Through the comparisons of various species' characteristics, it was found that the species confined to semi-natural habitats had lower population abundance, fewer generations per year, more restricted local distributions, and narrower geographic range size in Japan than the other component species. Based on our results, it is critical that the persistence of the species that are limited to semi-natural habitats be ensured in order to maintain high species richness and diversity in grassland butterfly communities. Thus, conservation plans that retain as much semi-natural habitat as possible within the process of human grassland use, development, and modification are needed.     

Competitive abilities and related strategies in four aquatic plant species from an intermediately disturbed habitat

1. High species richness in disturbed habitats is commonly attributed to the coexistence of species with diverse competitive abilities and, more generally, to the coexistence of different plant strategies sensu Grime (1977, 1979). The present study tests this assumption for the case of intermediately disturbed, species-rich macrophyte habitats. 2. Four species, Sparganium emersum, Hippuris vulgaris, Groenlandia densa and Luronium natans that coexist solely in one flood-disturbed, cut-off channel of the Upper Rhone River (France) were selected for this study. Apart from this common, disturbed habitat, they presented different distribution patterns within the floodplain. The present study aimed to establish both a hierarchical ranking of their competitive abilities and their respective strategies according to the C-S-R-model. 3. The study was carried out during one growth season in a de Wit experimental design with supplementary monitoring of growth characteristics. Whereas a clear ranking of species competitiveness could not be established, the experiment revealed differences in their traits and strategies. 4. S. emersum possesses the traits of a competitor, whereas the other species present intermediate secondary strategies, with a C-R-strategy in G. densa, a C-S-strategy in H. vulgaris, and a C-S-R or S-R-strategy in L. natans. These strategies are well matched to the distribution of the species within the floodplain, since the distribution of S. emersum reaches far into weakly disturbed and undisturbed, and supposedly competition intensive sites, whereas Luronium occupies a habitat that is both disturbed and relatively nutrient-poor. Only the presence of Hippuris in disturbed habitats seems not to correspond to the established strategy, but this might be explained by its need for only moderately intensive competition and by particularities of its regeneration strategy. The revealed differences in strategy may also make it possible to interpret the patchy pattern in vegetation cover within disturbed habitats.     

Centennial‐scale changes to the aquatic vegetation structure of a shallow eutrophic lake and implications for restoration

1. We investigate long‐term (>200 years) changes to the composition and spatial structure of macrophyte communities in a shallow, eutrophic lake (Barton Broad, eastern England) and consider the implications for lake restoration. 2. Historical macrophyte data were assembled from a variety of sources: existing plant databases, museum herbaria, journal articles, old photographs and eyewitness accounts. Additionally, two types of sediment core sample were analysed for plant macro‐remains and pollen; bulk basal samples from multiple core sites analysed to provide information on ‘pre‐disturbance’ macrophyte communities and two whole cores analysed to determine historical change. 3. Prior to the late 1800s, macrophyte communities were diverse and included a multilayered mosaic of short‐stature submerged taxa and taller submerged and floating‐leaved species. With the progression of eutrophication after around 1900, the former community was displaced by the latter. Diversity was maintained, however, since an encroaching Schoenoplectus–nymphaeid swamp generated extensive patches of low‐energy habitat affording refugia for several macrophytes otherwise unable to withstand the hydraulic forces associated with open water conditions. When this swamp vegetation disappeared in the 1950s, many of the ‘dependent’ aquatic macrophytes also declined leaving behind a sparse, species‐poor community (as today) resilient to both eutrophication and turbulent open waters. 4. The combination of historical and palaeolimnological data sources offers considerable benefits for reconstructing past changes to the aquatic vegetation of lakes and for setting restoration goals. In this respect, our study suggests that successful restoration might often be better judged by reinstatement of the characteristic structure of plant communities than the fine detail of species lists; when nutrients are low and the structure is right, the right species will follow.     

Effect of wave exposure on vegetation abundance, richness and depth distribution of shallow water plants in a New Zealand lake

SUMMARY 1. The effects of physical disturbance in terms of wave exposure, shore slope and substrate mobility on the presence, species richness, cover and depth limits of the low‐growing, shallow water macrophyte community (called the low mixed community) were examined at 41 shore sites in Lake Wanaka, South Island, New Zealand. 2. Wave exposure at a site was described by the previous year's maximum depth of sediment motion and maximum vertical extension of waves, determined from a computer wave model. Shore slope at each site was recorded from ?1 to 0 m depth, and sediment stability was assessed as the cover of small gravel. 3. The low mixed community was only present on sites where the previous year's maximum depth of sediment motion was <8 m, maximum wave run‐up was <0.3 m, shore slope <0.12 m m^?1, and small gravel cover <78%. 4. Species richness, cover and depth limits of the low mixed community decreased with increasing disturbance on the sites. Sixty‐two percentage of the variation in species richness could be explained by physical disturbance variables when all sites were included (N=41). When only sites with a low mixed community were included (N=22), only 18% of the variation was explained. Species richness within sites supporting a low mixed community is thus poorly explained by physical disturbance, whereas presence or absence is better explained. There was no evidence to support the intermediate disturbance hypothesis in this study. 5. Disturbance as a result of waves explained 86% of the variation in cover among sites with a low mixed community and accounted for 68 and 58% of the variation in upper and lower depth limit of the low mixed community, respectively. 6. The models obtained in this study can be used as predictive models for the low mixed community in New Zealand lakes in relation to natural physical disturbance on the shore. By integrating these results with previous studies on the effect of water level fluctuation, we describe a generalised optimum physical habitat for the low mixed community in New Zealand lakes.     

Microbial community diversity and composition varies with habitat characteristics and biofilm function in macrophyte‐rich streams

Biofilms in streams play an integral role in ecosystem processes and function yet few studies have investigated the broad diversity of these complex prokaryotic and eukaryotic microbial communities. Physical habitat characteristics can affect the composition and abundance of microorganisms in these biofilms by creating microhabitats. Here we describe the prokaryotic and eukaryotic microbial diversity of biofilms in sand and macrophyte habitats (i.e. epipsammon and epiphyton, respectively) in five macrophyte‐rich streams in Jutland, Denmark. The macrophyte species varied in growth morphology, C:N stoichiometry, and preferred stream habitat, providing a range in environmental conditions for the epiphyton. Among all habitats and streams, the prokaryotic communities were dominated by common phyla, including Alphaproteobacteria, Bacteriodetes, and Gammaproteobacteria, while the eukaryotic communities were dominated by Stramenopiles (i.e. diatoms). For both the prokaryotes and eukaryotes, the epipsammon were consistently the most diverse communities and the epiphytic communities were generally similar among the four macrophyte species. However, the communities on the least complex macrophyte, Sparganium emersum, had the lowest richness and evenness and fewest unique OTUs, whereas the macrophyte with the most morphological complexity, Callitriche spp., had the highest number of unique OTUs. In general, the microbial taxa were ubiquitously distributed across the relatively homogeneous Danish landscape as determined by measuring the similarity among communities (i.e. Sørensen similarity index). Furthermore, we found significant correlations between microbial diversity (i.e. Chao1 rarefied richness and Pielou's evenness) and biofilm structure and function (i.e. C:N ratio and ammonium uptake efficiency, respectively); communities with higher richness and evenness had higher C:N ratios and lower uptake efficiency. In addition to describing the prokaryotic and eukaryotic community composition in stream biofilms, our study indicates that 1) physical habitat characteristics influence microbial diversity and 2) the variation in microbial diversity may dictate the structural and functional characteristics of stream biofilm communities.     

Timing is everything: priority effects alter community invasibility after disturbance

Theory suggests that communities should be more open to the establishment of regional species following disturbance because disturbance may make more resources available to dispersers. However, after an initial period of high invasibility, growth of the resident community may lead to the monopolization of local resources and decreased probability of successful colonist establishment. During press disturbances (i.e., directional environmental change), it remains unclear what effect regional dispersal will have on local community structure if the establishment of later arriving species is affected by early arriving species (i.e., if priority effects are important). To determine the relationship between time‐since‐disturbance and invasibility, we conducted a fully factorial field mesocosm experiment that exposed tundra zooplankton communities to two emerging stressors – nutrient and salt addition, and manipulated the arrival timing of regional dispersers. Our results demonstrate that invasibility decreases with increasing time‐since‐disturbance as abundance (nutrient treatments) or species richness (salt treatments) increases in the resident community. Results suggest that the relative timing of dispersal and environmental change will modify the importance of priority effects in determining species composition after a press disturbance.     

Exploring the symbiont diversity of ancient western redcedars: arbuscular mycorrhizal fungi of long‐lived hosts

Arbuscular mycorrhizal fungi (AMF) are globally distributed, monophyletic root symbionts with ancient origins. Their contribution to carbon cycling and nutrient dynamics is ecologically important, given their obligate association with over 70% of vascular plant species. Current understanding of AMF species richness and community structure is based primarily on studies of grasses, herbs and agricultural crops, typically in disturbed environments. Few studies have considered AMF interactions with long‐lived woody perennial species in undisturbed ecosystems. Here we examined AMF communities associated with roots and soils of young, mature and old western redcedar (Thuja plicata) at two sites in the old‐growth temperate rainforests of British Columbia. Due to the unique biology of AMF, community richness and structure were assessed using a conservative, clade‐based approach. We found 91 AMF OTUs across all samples, with significantly greater AMF richness in the southern site, but no differences in richness along the host chronosequence at either site. All host age classes harboured AMF communities that were overdispersed (more different to each other than expected by chance), with young tree communities most resembling old tree communities. A comparison with similar clade richness data obtained from the literature indicates that western redcedar AMF communities are as rich as those of grasses, tropical trees and palms. Our examination of undisturbed temperate old‐growth rainforests suggests that priority effects, rather than succession, are an important aspect of AMF community assembly in this ecosystem.     

From species to communities: the signature of recreational use on a tropical river ecosystem

Disturbance can impact natural communities in multiple ways. However, there has been a tendency to focus on single indicators of change when examining the effects of disturbance. This is problematic as classical diversity measures, such as Shannon and Simpson indices, do not always detect the effects of disturbance. Here, we instead take a multilevel, hierarchical approach, looking for signatures of disturbance in the capacity and diversity of the community, and also in allocation and demography at the population level. Using recreational use as an example of disturbance, and the freshwater streams of Trinidad as a model ecosystem, we repeatedly sampled the fish communities and physical parameters of eight pairs of recreational and nonrecreational sites every 3 months over a 28‐month period. We also chose the Trinidadian guppy (Poecilia reticulata) as the subject of our population‐level analyses. Regression tree analysis, together with analysis of deviance, revealed that community capacity and community species richness were greater at sites with higher levels of recreational use. Interestingly, measures of community diversity that took into account the proportional abundance of each species were not significantly associated with recreational use. Neither did we find any direct association between recreational use and proportion of guppy biomass in the community. However, population‐level differences were detected in the guppy: Sex ratio was significantly more female‐biased at more disturbed sites. Our findings emphasize the importance of considering multiple levels when asking how disturbance impacts a community. We advocate the use of a multilevel approach when monitoring the effects of disturbance, and highlight gaps in our knowledge when it comes to interpreting these effects.     

Factors determining the centrifugal organization of remnant Festuca grassland communities in Alberta

Abstract. This paper describes the species composition of remnant grasslands in the aspen parkland region of Alberta and its relation to soil characteristics and small‐scale disturbance. Our findings are consistent with the centrifugal model of communities with Festuca hallii dominating undisturbed ‘core’ habitat and the composition of more ‘peripheral’ habitats varying in soil properties and in the magnitude of disturbance. Invasive non‐native species are not present in the core habitat and are present only in the disturbed sites, most abundantly in those with the highest soil nitrogen. The centrifugal model, as it applies to these remnant grasslands, differs from its previous application to wetlands and forests in that the core communities are not on the most fertile sites, but on the least disturbed. These findings have implications for the management of prairie remnants to exclude invasive exotic species.     

Seed Bank Effects on Recovery after Disturbance in Reconstructed Tallgrass Prairies

Litter‐removing disturbances such as fire in grasslands temporarily increase available resources for plants, opening a window of opportunity for new establishment as communities recover. At this time, new individuals or species could be added to the community as a result of germination from the local seed bank. In reconstructed grasslands this may be problematic, as the seed bank may contain a suite of undesired species reflective of prior and surrounding land uses. In two, 25‐year‐old, low‐diversity reconstructed grasslands, we tested the effect of local seed bank establishment following litter‐removing disturbance using seedling removal plots (1 m²) and plots where natural seedling establishment was allowed. Following disturbance, the vegetation was either left intact or hayed to enhance seedling establishment (a common practice following inter‐seeding efforts). Although the seed bank and seedling community were dominated by resident grasses (Andropogon gerardii and Poa pratensis), recruitment from the seed bank increased species richness and reduced evenness through the addition of forb species (including Cirsium arvense) in one of the study sites. Haying temporarily altered the abundances of the dominant grasses, but did not consistently affect seedling recruitment. Disturbances that facilitate seed bank recruitment may promote establishment of undesired species within reconstructed grassland communities, and we need to take steps to better manage the contributions into and recruitment from the seed bank to reconstruct sustainable grasslands.     

Effects of Nutrient Manipulations and Grass Removal on Cover,Species Composition,and Invasibility of a Novel Grassland in Colorado

Cover and richness of a 5‐year revegetation effort were studied with ,respect to small‐scale disturbance and nutrient manipulations. The site, originally a relict tallgrass prairie mined for gravel, was replanted to native grasses using a seed mixture of tall‐, mixed‐, and short‐grass species. Following one wet and three relatively dry years, a community emerged, dominated by species common in saline soils not found along the Colorado Front Range. A single species, Alkali sacaton (Sporobolus airoides), composed nearly 50% of relative vegetation cover in control plots exhibiting a negative relationship between cover and richness. Seeded species composed approximately 92% of vegetation cover. The remaining 8% was composed of weeds from nearby areas, seed bank survivors, or mix contaminants. Three years of soil nutrient amendments, which lowered plant‐available nitrogen and phosphorus, significantly increased relative cover of seeded species to 97.5%. Fertilizer additions of phosphate enhanced abundance of introduced annual grasses (Bromus spp.) but did not significantly alter cover in control plots. Unmanipulated 4‐m² plots contained an average of 4.7 planted species and 3.9 nonplanted species during the 5‐year period, whereas plots that received grass herbicide averaged 5.4 nonplanted species. Species richness ranged from an average 6.9 species in low‐nutrient, undisturbed plots to 10.9 species in the relatively high‐nutrient, disturbed plots. The use of stockpiled soils, applied sparingly, in conjunction with a native seed mix containing species uncommon to the preexisting community generated a species‐depauperate, novel plant community that appears resistant to invasion by ruderal species.     

Ants as Indicators of Restoration Success: Relationship with Soil Microbial Biomass in the Australian Seasonal Tropics

Ants are widely used as bioindicators in Australian land assessment and monitoring programs, particularly in relation to ecosystem restoration following mining. Little is known, however, about the relationship between ant community development and key ecological processes such as nutrient cycling. We have examined the relationship between ant species richness and soil microbial biomass at 17 sites subject to disturbance by mining in the Kakadu region of Australia's Northern Territory. The number of ant species recorded ranged from 7 at an unvegetated site undergoing restoration to 43 at a site that was undisturbed except for edge effects. Soil microbial biomass ranged from 19.3 to 134.3 μgC/g. Ant species richness was positively correlated with soil microbial biomass (r= 0.638), more so than was plant species richness (r= 0.342 for total plant species, r= 0.499 for woody species only). Our findings demonstrate a correlation between aboveground ant activity and belowground decomposition processes at disturbed sites, thereby providing support for the use of ants as indicators of restoration success following disturbance. Interestingly, when a range of undisturbed sites in the region was considered, a negative rather than positive relationship between ant richness and soil microbial biomass was found. This illustrates the importance of distinguishing between variation within a habitat due to disturbance and variation across different habitats when searching for indicators of ecological change.