‘Race’, community and ongoing conflict

This review explores Rex and Moore's (1967) study of Birmingham as an enduring model of ethnic segregation, stratification, conflict and cooperation. The commentary focuses on the legacy of this research for understanding ethnic segregation, community and the city as a barometer of social change.     

Can metabolic traits explain animal community assembly and functioning?

All animals on Earth compete for free energy, which is acquired, assimilated, and ultimately allocated to growth and reproduction. Competition is strongest within communities of sympatric, ecologically similar animals of roughly equal size (i.e. horizontal communities), which are often the focus of traditional community ecology. The replacement of taxonomic identities with functional traits has improved our ability to decipher the ecological dynamics that govern the assembly and functioning of animal communities. Yet, the use of low-resolution and taxonomically idiosyncratic traits in animals may have hampered progress to date. An animal's metabolic rate (MR) determines the costs of basic organismal processes and activities, thus linking major aspects of the multifaceted constructs of ecological niches (where, when, and how energy is obtained) and ecological fitness (how much energy is accumulated and passed on to future generations). We review evidence from organismal physiology to large-scale analyses across the tree of life to propose that MR gives rise to a group of meaningful functional traits – resting metabolic rate (RMR), maximum metabolic rate (MMR), and aerobic scope (AS) – that may permit an improved quantification of the energetic basis of species coexistence and, ultimately, the assembly and functioning of animal communities. Specifically, metabolic traits integrate across a variety of typical trait proxies for energy acquisition and allocation in animals (e.g. body size, diet, mobility, life history, habitat use), to yield a smaller suite of continuous quantities that: (1) can be precisely measured for individuals in a standardized fashion; and (2) apply to all animals regardless of their body plan, habitat, or taxonomic affiliation. While integrating metabolic traits into animal community ecology is neither a panacea to disentangling the nuanced effects of biological differences on animal community structure and functioning, nor without challenges, a small number of studies across different taxa suggest that MR may serve as a useful proxy for the energetic basis of competition in animals. Thus, the application of MR traits for animal communities can lead to a more general understanding of community assembly and functioning, enhance our ability to trace eco-evolutionary dynamics from genotypes to phenotypes (and vice versa), and help predict the responses of animal communities to environmental change. While trait-based ecology has improved our knowledge of animal communities to date, a more explicit energetic lens via the integration of metabolic traits may further strengthen the existing framework.     

How do earthworms affect microfloral and faunal community diversity?

Much of the work regarding earthworm effects on other organisms has focused on the functional significance of microbial-earthworm interactions, and little is known on the effects of earthworms on microfloral and faunal diversity. Earthworms can affect soil microflora and fauna populations directly and indirectly by three main mechanisms: (1) comminution, burrowing and casting; (2) grazing; (3) dispersal. These activities change the soil's physico-chemical and biological status and may cause drastic shifts in the density, diversity, structure and activity of microbial and faunal communities within the drilosphere. Certain organisms and species may be enhanced, reduced or not be affected at all depending on their ability to adapt to the particular conditions of different earthworm drilospheres. A large host of factors (including CaCO₃, enzymes, mucus and antimicrobial substances) influence the ability of preferentially or randomly ingested organisms to survive (or not) passage through the earthworm gut, and their resultant capacity to recover and proliferate (or not) in earthworm casts. Small organisms, particularly microflora and microfauna, with limited ability to move within the soil, may benefit from the (comparatively) long ranging movements of earthworms. Microflora and smaller fauna appear to be particularly sensitive to earthworm activities, and priming effects enhancing nutrient release, particularly in casts, are common. Larger fauna such as microarthropods, enchytraeids and Isopods may be enhanced under some conditions (e.g., in earthworm middens), but in other cases earthworm activity may lead to a decrease in their populations due to competition for food (microbes and organic materials), and spatial and temporal changes in food abundance. Nevertheless, considering the presently available data, the beneficial interactions of earthworms and microflora and fauna appear to far outweigh the potential negative effects. However, much is still unknown regarding the interactions of earthworms of different ecological categories on the diversity and function of microfloral and faunal communities, and much more interdisciplinary research is needed to assess the potential role of earthworms in regulating the diversity of microflora and fauna in soil systems and the potentially beneficial or harmful effects this regulation may have on ecosystem function and plant growth in different ecosystems.     

Evolution and spatial structure interact to influence plant–herbivore population and community dynamics

An individual-based model of plant–herbivore interactions was developed to test the potentially interactive effects of explicit space and coevolution on population and community dynamics. Individual plants and herbivores resided in cells on a lattice and carried linked interaction genes. Interaction strength between individual plants and herbivores depended on concordance between these genes (gene-for-gene coevolution). Mating and dispersal among individuals were controlled spatially within variably sized neighbourhoods. Without evolution we observed high-frequency plant–herbivore oscillations (blue spectra) with small individual neighbourhoods, and stochastic fluctuations (white spectra) with large neighbourhoods. Evolution resulted in decreased interaction strength, decreased herbivore-induced plant mortality, increased population sizes, and longer-term fluctuations (reddened spectra). Small herbivore neighbourhoods led to herbivore extinction only with evolution. To explore the increased population size response to evolution we ran simulations without evolution while tuning plant–herbivore interaction strength from high to none. We found that herbivore populations were maximized at intermediate levels of interaction strength that coincided with the interaction strength achieved when the system tuned itself through evolution. Overall, our model shows that the small-scale details of phenotypically variable individual-level interactions, leading to evolutionary dynamics, affect large-scale population and community dynamics.     

Do temperate tree species diversity and identity influence soil microbial community function and composition?

Studies of biodiversity–ecosystem function in treed ecosystems have generally focused on aboveground functions. This study investigates intertrophic links between tree diversity and soil microbial community function and composition. We examined how microbial communities in surface mineral soil responded to experimental gradients of tree species richness (SR ), functional diversity (FD ), community‐weighted mean trait value (CWM ), and tree identity. The site was a 4‐year‐old common garden experiment near Montreal, Canada, consisting of deciduous and evergreen tree species mixtures. Microbial community composition, community‐level physiological profiles, and respiration were evaluated using phospholipid fatty acid (PLFA ) analysis and the MicroResp^? system, respectively. The relationship between tree species richness and glucose‐induced respiration (GIR ), basal respiration (BR ), metabolic quotient (qCO ₂) followed a positive but saturating shape. Microbial communities associated with species mixtures were more active (basal respiration [BR ]), with higher biomass (glucose‐induced respiration [GIR ]), and used a greater number of carbon sources than monocultures. Communities associated with deciduous tree species used a greater number of carbon sources than those associated with evergreen species, suggesting a greater soil carbon storage capacity. There were no differences in microbial composition (PLFA ) between monocultures and SR mixtures. The FD and the CWM of several functional traits affected both BR and GIR . In general, the CWM of traits had stronger effects than did FD , suggesting that certain traits of dominant species have more effect on ecosystem processes than does FD . Both the functions of GIR and BR were positively related to aboveground tree community productivity. Both tree diversity (SR ) and identity (species and functional identity—leaf habit) affected soil microbial community respiration, biomass, and composition. For the first time, we identified functional traits related to life‐history strategy, as well as root traits that influence another trophic level, soil microbial community function, via effects on BR and GIR .     

How do extreme drought and plant community composition affect host plant metabolites and herbivore performance?

Water availability and plant community composition alter plant nutrient availability and the accumulation of plant defence compounds therefore having an impact on herbivore performance. Combined effects of drought stress and plant community composition on leaf chemicals and herbivore performance are largely unexplored. The objective of our study was, therefore, to find out the impact of extreme drought and of plant community composition on plant–herbivore interactions. Larvae of the generalist butterfly Spodoptera littoralis were reared on leaves of the grass Holcus lanatus which was grown in experimental communities, differing in species- and functional group richness. These communities were either subjected to extreme drought or remained under ambient climatic conditions. Drought decreased relative water content, soluble protein content, nitrogen and total phenol content and increased the content of carbohydrates in the grass. As a consequence, the larvae feeding on drought-exposed plants revealed a longer larval stage, increased pupal weight and higher adult eclosion rates. Plant community composition mainly caused changes to the defensive compounds of the grass, but also marginally affected protein and carbohydrate content. Larvae feeding on species-richest communities without legumes showed the highest mortality. Our findings imply that climate change that is projected to increase the frequency of severe droughts, as well as alter plant community compositions, is likely to affect arthropod–plant interactions through an alteration of leaf chemicals.     

Electrokinetic remediation and microbial community shift of β-cyclodextrin-dissolved petroleum hydrocarbon-contaminated soil

Electrokinetic (EK) migration of β-cyclodextrin (β-CD), which is inclusive of total petroleum hydrocarbon (TPH), is an economically beneficial and environmentally friendly remediation process for oil-contaminated soils. Remediation studies of oil-contaminated soils generally prepared samples using particular TPHs. This study investigates the removal of TPHs from, and electromigration of microbial cells in field samples via EK remediation. Both TPH content and soil respiration declined after the EK remediation process. The strains in the original soil sample included Bacillus sp., Sporosarcina sp., Beta proteobacterium, Streptomyces sp., Pontibacter sp., Azorhizobium sp., Taxeobacter sp., and Williamsia sp. Electromigration of microbial cells reduced the biodiversity of the microbial community in soil following EK remediation. At 200 V m⁻¹ for 10 days, 36% TPH was removed, with a small population of microbial cells flushed out, demonstrating that EK remediation is effective for the present oil-contaminated soils collected in field.     

Unemployment,deindustrialization, and ‘community economy’ in eastern Germany

Drawing from an evening of fieldwork at an eastern German Protestant churchin the rapidly deindustrialized city of Leipzig, this article finalyzes a discussion among church leaders, former ‘dissidents,’ and unemployed workers on the subject of ‘community economy’ (Gemeinschaftsökonomie), a concept people interpret to represent a potential solution to the crisis of mass unemployment. Such local debates on unemployment offer a frame for understanding the re-negotiation of labor and social welfare in eastern Germany following socialism's end. finalyzing this discussion within the context of theoretical debates on ‘civil society,’ I follow Burawoy's and Gramsci's lead in fillustrating that the imagined economic sphere of ‘community economy’ is an ideological battle ground, where hegemonic discourse supporting economic neoliberalism may be either reinforced or subverted.     

Do nutrients and invertebrate herbivory interact in an artificial plant community?

The addition of nutrients has been shown to decrease the species richness of plant communities. Herbivores feed on dominant plant species and should release subdominant species from competitive exclusion at high levels of nutrient availability with a severe competitive regime. Therefore, the effects of nutrients and invertebrate herbivory on the structure and diversity of plant communities should interact. To test this hypothesis, we used artificial plant communities in microcosms with different levels of productivity (applying fertilizer) and herbivory (adding different numbers of the snail, Cepaea hortensis, and the grasshopper, Chorthippus parallelus). For analyses, we assigned species to three functional groups: grasses, legumes and (non-leguminous) herbs. With the addition of nutrients aboveground biomass increased and species richness of plants decreased. Along the nutrient gradient, species composition shifted from a legume-dominated community to a community dominated by fast-growing annuals. But only legumes showed a consistent negative response to nutrients, while species of grasses and herbs showed idiosyncratic patterns. Herbivory had only minor effects, and bottom–up control was more important than top–down control. With increasing herbivory the biomass of the dominant plant species decreased and evenness increased. We found no interaction between nutrient availability and invertebrate herbivory. Again, species within functional groups showed no consistent responses to herbivory. Overall, the use of the functional groups grasses, legumes and non-leguminous herbs was of limited value to interpret the effects of nutrients and herbivory during our experiments.     

Are cladoceran diversity and community structure linked to spatial heterogeneity in urban landscapes and pond environments?

Biodiversity patterns in cladoceran communities were investigated in urban waterbodies in relation with residential land use, pond management, and waterbody environments. We evaluated species richness in the pelagic and littoral zones of eighteen waterbodies of a large Canadian city. Gamma diversity (26 species) observed at a small scale in the urban survey was important comparatively to large-scale surveys of lakes. Beta diversity ranged from 1 to 8 species among waterbodies. We tested if littoral species greatly contributed to regional diversity in urban waterbodies. Littoral species (Chydoridae, Ilyocryptidae, Macrothricidae, Polyphemidae) accounted for 58% of the total species pool. We distinguished five cladoceran assemblages associated to different waterbodies (temporary ponds, permanent lakes, and wetlands). Cladoceran communities were more diverse and variable in permanent lakes than in temporary ponds. Changes in cladoceran species assemblages among waterbodies were driven by variations in waterbody size and phosphorus enrichment, macrophyte and algal biomass, urban density, pond management practices, and the presence of potential predators as fish and macroinvertebrates. Our study indicates that both artificial ponds and lakes and natural wetlands are valuable habitats for the conservation of cladoceran biodiversity and rare endemic species in urban regions. Further research on pond management strategies promoting urban aquatic biodiversity should be undertaken.     

Host–parasitoid development and survival strategies in a non-pollinating fig wasp community

In a tritrophic system, parasitoid development and galler host survival strategies have rarely been investigated simultaneously, an approach crucial for a complete understanding of the complexity of host–parasitoid interactions. Strategies in parasitoids to maximize host exploitation and in gallers to reduce predation risk can greatly affect the structure of tritrophic communities. In this study, the developmental strategies of galler hosts and their associated parasitoids in the tritrophic fig–fig wasp system are experimentally investigated for the first time. In this highly co-evolved system, wasp development is intrinsically tied with the phenology of the wasp brood sites that are restricted to the enclosed urn-shaped fig inflorescence called the syconium which can be regarded as a microcosm. Wasp exclusion experiments to determine host specificity, gall dissections and developmental assays were conducted with non-pollinating fig wasps in Ficus racemosa. Our results provide evidence for exceptions to the widely accepted koinobiont–idiobiont parasitoid dichotomy. This is also the first time fig wasps were raised ex situ from non-feeding stages onwards, a technique that enabled us to monitor their development from their pre-pupal to adult stages and record their development time more accurately. Based on variation in development time and host specificity, the possibility of a cryptic parasitoid species is raised. The frequency of different wasp species eclosing from the microcosms of individual syconia is explained using host–parasitoid associations and interactions under the modulating effect of host plant phenology.     

Fire temperatures and postfire plant community dynamics in Ecuadorian grass páramo

Three aspects of the páramo vegetation's response to fires were investigated: the measurement of fire temperatures, general observations of changes in plant communities following fires, and monitoring the fate of individual plants after burning.Fire temperatures were strongly influenced by the physiognomy of the vegetation, dominated by tussocks of Calamagrostis spp. Temperatures were highest amongst the upper leaves of the tussock (sometimes >500°C). The middle levels of the tussock experienced temperatures in excess of 400°C, but in the dense leaf bases temperatures were often below 65°C. On the ground between tussocks, temperatures were variable, whereas 2 cm below ground temperatures failed to reach 65°C.Plant survival depended on the intensity of the fire and the plant's position within the tussock structure. Survival was often the result of high temperature avoidance (with buds shielded by other plant parts or buried beneath the soil surface).Post-fire Calamagrostis tiller mortality rates were high and tussock regrowth was slow. Some other species appear to maintain their populations by exploiting this recovery phase for seedling establishment on tussocks.Between tussocks, changes of occupancy at the level of the individual plants were greater after fire than in control vegetation. Most transitions were random. Those which departed from random often involved gaps and were related to post-fire mortality, regrowth from below-ground parts, colonisation or, in the case of a clonal mat-forming species, to spatial rearrangement of rosettes. Recovery was slower at higher altitude. Recovery was much slower in burned plots when the upper 2 cm of soil was removed (along with buried plant parts) compared with burned plots.Qualitative observations suggest that recovery may consist of a cyclical process, mediated by the serial dominance of several species that are physiognomically important.The frequency of fires determines the amount of fuel accumulated within grass tussocks and some plants may be unable to survive repeated burning. Chance survival of species in unburned patches of vegetation and random colonisation of gaps may be important determinants of subsequent community structure.     

Statistical methods for temporal and space–time analysis of community composition data

This review focuses on the analysis of temporal beta diversity, which is the variation in community composition along time in a study area. Temporal beta diversity is measured by the variance of the multivariate community composition time series and that variance can be partitioned using appropriate statistical methods. Some of these methods are classical, such as simple or canonical ordination, whereas others are recent, including the methods of temporal eigenfunction analysis developed for multiscale exploration (i.e. addressing several scales of variation) of univariate or multivariate response data, reviewed, to our knowledge for the first time in this review. These methods are illustrated with ecological data from 13 years of benthic surveys in Chesapeake Bay, USA. The following methods are applied to the Chesapeake data: distance-based Moran''s eigenvector maps, asymmetric eigenvector maps, scalogram, variation partitioning, multivariate correlogram, multivariate regression tree, and two-way MANOVA to study temporal and space–time variability. Local (temporal) contributions to beta diversity (LCBD indices) are computed and analysed graphically and by regression against environmental variables, and the role of species in determining the LCBD values is analysed by correlation analysis. A tutorial detailing the analyses in the R language is provided in an appendix.     

Structure and floristic composition of the Heard Island “pool complex” community

Summary The stratigraphy, hydrology and vegetation of the Heard Island (sub-Antarctic; 53°05S, 73°30E) pool complex bogs are described. Spatial variation in processes that might have contributed to their formation are discussed. This community occurs where drainage is impeded. with Callitriche antarctica being the indicator species. Particular attention is paid to the interaction of the vegetation, pools and animals. Surface stratigraphy, peat depth, water depth and vegetation composition were measured along transect lines. Species cover abundance data of 300 quadrats were classified using a two-way indicator species analysis program and ordinated using detrended correspondence analysis. The major factors determining vegetation composition were found to be peat depth, surface topography, and the degree and type of animal disturbance. Similarities between the pool complexes on Heard Island and corresponding bogs in Tasmania, and the northern hemisphere temperate and boreal zones appear to diminish as the density of the animals occupying this habitat increases.     

Plant–animal interactions in seagrass beds: ongoing and future challenges for understanding population and community dynamics

Seagrass beds are some of the most productive parts of coastal ecosystems, hosting a wide variety of associated fauna. This paper reviews recent studies of animal–plant interactions in seagrass beds, focusing particularly on studies conducted in Japan and Thailand. Although the positive effect of seagrass habitat structure on animals has been widely acknowledged, the magnitude of this effect varies greatly among studies. A comparative study on epifaunal communities and a manipulative experiment using an infaunal bivalve revealed that behavioral and life-history traits of component species and their interactions influence the observed variation. Some recent studies have challenged the previously accepted view that direct herbivory on seagrasses is rare, and has a minor effect on the seagrass community. A series of studies of dugong herbivory revealed that the marine mammal has great impacts not only on seagrass productivity but also on the infaunal community. Furthermore, it has been found that seed predators have a negative influence on seed production and the subsequent recruitment of seagrass. Recent studies have also demonstrated significant effects of fine-scale landscape patterns in seagrass vegetation on productivity, species interactions and community structure in seagrass beds. Future research integrating new concepts and theories in ecology, such as metapopulation and hierarchy theories, with new research tools, such as molecular-genetic analyses and remote-sensing techniques, may aid in developing a more comprehensive understanding of population and community dynamics in seagrass beds.This article is an invited review contributed by the winner of the 2003 Population Ecology Young Scientist Award.     

Differentiated free-living and sediment-attached bacterial community structure inside and outside denitrification hotspots in the river–groundwater interface

This study assessed the functional significance of attached and free-living bacterial communities involved in the process of denitrification in a shallow aquifer of a riparian zone (Garonne River, SW France). Denitrification enzyme activity (DEA), bacterial density (BD) and bacterial community composition (BCC) were measured in two aquifer compartments: the groundwater and the sandy fraction of the sediment deposit. Samples were collected in wells located inside (IHD) and outside (OHD) identified hotspots of denitrification. Despite high BD values (up to 1.14 × 10¹² cells m⁻³), DEA was not detected in the water compartment (< 0.32 mg N–N₂O m⁻³ d⁻¹). The sandy fraction showed detectable DEA (up to 1,389 mg N–N₂O m⁻³ d⁻¹) and, consistent with BD pattern, higher DEA values were measured in IHD zones than in OHD zones. The BCC assessed by 16S rDNA polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) partly supported this result: attached and free-living communities were significantly different (< 30% similarity) but patterns of BCC did not cluster according to IHD and OHD zones. Targeting the denitrifying communities by means of a culture enrichment step prior to 16S rDNA PCR-DGGE showed that the free-living and sediment attached communities differed. Most sequences obtained from DGGE profiles of denitrifying communities were affiliated to Proteobacteria and showed low genetic distance with taxa that have already been detected in aquifers (e.g., Azoarcus sp., Acidovorax sp. and Pseudomonas spp.). This study confirms that in the aquifer the sediment-attached fraction exhibits different functions (DEA) from free-living communities and suggests that this functional difference is related to the communities’ structure.     

What determines emergence and net recruitment in an early succession plant community? Disentangling biotic and abiotic effects

Question: How do different regeneration scenarios shape species composition at two stages of plant community establishment (emergence and net recruitment) in an early succession? Location: Northern Spain. Methods: In a recently ploughed field, we created eight regeneration scenarios with light, water and nitrogen availability (five replicates each). Seedlings of all species were monitored from emergence to death during one year. Abiotic and biotic variables were measured per quadrat, i.e. soil texture, nutrient contents, seed bank densities and composition, neighbour plant species densitiy and cover. We used partial ordination methods in order to separate the effect of each environmental variable on species composition during emergence and adult net recruitment. Results: Light treatment determined annual plant density at time of emergence and recruitment, while water addition controlled the recruitment of perennials. Resource levels explained the emerged species composition; this effect was not translated into the recruited species composition. N‐addition and N + water addition were strongly associated to species abundances at the time of emergence. Seedling composition in summer was correlated with seed abundance of Cerastium spp. Neighbour species density and cover (mainly Arrhenatherum bulbosum, Agropyron repens and Picris echioides) explained significant fractions of species composition in the emergence and recruitment of the different cohorts. Interactions between species seem to vary in intensity among cohorts and in the key plant species that determined species abundance along succession. Conclusions: Our scenarios exerted contrasting and multilevel effects on the development of our early succession community. Resource availability differently affected plant density and species composition at different life stages. It is relevant to consider different life stages in plant community studies. However, regeneration conditions and other abiotic factors are not enough to explain how community composition varies.     

How do pollinator visitation rate and seed set relate to species’ floral traits and community context?

Differences among plant species in visitation rate and seed set within a community may be explained both by the species’ floral traits and the community context. Additionally, the importance of species’ floral traits vs. community context on visitation rate and seed set may vary among communities. In communities where the pollinator-to-flower ratio is low, floral traits may be more important than community context, as pollinators may have the opportunity to be choosier when visiting plant species. In this study we investigated whether species’ floral traits (flower shape, size and number, and flowering duration) and community context (conspecific and heterospecific flower density, and pollinator abundance) could explain among-species variation in visitation rate and seed set. For this, we used data on 47 plant species from two Norwegian plant communities differing in pollinator-to-flower ratio. Differences among species in visitation rate and seed set within a community could be explained by similar variables as those explaining visitation rate and seed set within species. As expected, we found floral traits to be more important than community context in the community with a lower pollinator-to-flower ratio; whereas in the community with a higher pollinator-to-flower ratio, community context played a bigger role. Our study gives significant insights into the relative importance of floral traits on species’ visitation rate and seed set, and contributes to our understanding of the role of the community context on the fitness of plant species.