Modify Community Structure Research Articles

Broad-Spectrum Antibacterial Activity of Antioxidant Octyl Gallate and Its Impact on Gut Microbiome.

In this study, we investigated the antibacterial activity of octyl gallate (OG), an antioxidant food additive, against both Gram-positive and Gram-negative bacterial pathogens. OG demonstrated robust bactericidal activity against Gram-positive bacterial pathogens with minimum inhibitory concentrations (MIC) of 4 to 8 µg/mL and minimum bactericidal concentrations (MBC) of 8 to 16 µg/mL in vitro. However, OG exhibited limited antibacterial activity against Gram-negative bacteria, including E. coli, although it could inhibit bacterial growth in vitro. Importantly, OG administration in mice altered the fecal microbiome, significantly reducing microbial diversity, modifying community structure, and increasing the abundance of beneficial bacteria. Additionally, OG displayed low cytotoxicity and hemolytic activity. These findings suggest that OG could be developed as a novel antibacterial agent, particularly against multi-drug-resistant MRSA. Our results provide new insights into the therapeutic potential of OG in modulating the gut microbiome, especially in conditions associated with microbial imbalance, while ensuring food safety.

Community structure of shallow tropical reefs undergoing invasion by Tubastraea spp. in a Brazilian Marine Protected Area

Invasive sun corals (Tubastraea spp.) are spreading along the Brazilian coast where they compete for space with native species, produce chemical compounds with antifouling and anti-predation properties and modify community structure and function. The tropical rocky shores of the Ilha Grande Bay were the first to be invaded in the southwest Atlantic and the Tamoios Marine Protected Area (MPA) within the bay was directly in the path of the spread of Tubastraea. MPAs aim to conserve biodiversity, preventing habitat loss and fragmentation and maintain healthy ecosystems. As healthy communities might better resist invasion the aim of this study was to investigate to what extent the benthic communities of the MPA are resisting the invasion. Baseline data on the abundance of the invasive corals Tubastraea spp. and community structure (cover) were quantified at eight sites over six years. The benthic communities were dominated by multispecies algal turfs, the mat-forming zooantharian Palythoa caribaeorum and the red alga Asparagopsis taxiformis and fell into five community groups two of which contained Tubastraea spp. The number of invaded sites increased over time as did the abundance of Tubastraea spp. in the communities. Tubastraea spp. sequentially invaded the studied communities within the MPA independently of differing community compositions – i.e. they did not offer better biotic resistance than unprotected areas. This was facilitated by the patchy nature of the communities which allowed Tubastraea spp. to get a foothold by initially avoiding species such as P. caribaeorum which offer greater biological resistance. At one site a significant reduction in Tubastraea spp. was detected after mechanical control. We conclude that the MPA’s status as a conservation unit was important to attract research and thus for establishing a baseline, quantifying change due to the invasion and focusing limited management resources, but not in providing significant biotic resistance to the invasion.

Coexistence, Energy, and Trophic Cascade in a Three-Level Food Chain Integrating Body Sizes

Predation is a biological interaction that influences demographic patterns by modifying community structure. In the current ecological crisis, there is a need to better understand the conditions of coexistence between predators, prey and their resources. The body size is considered a key feature to explain community-scale phenomena, energetic, and evolutionary constraints. This raises the question of how species body size directly or indirectly affects the demographic patterns that enable coexistence. Considering the above, we conducted a theoretical study that implements a Rosenzweig-MacArthur type model, which represents a three-level chain that integrates body sizes and includes a Holling type I functional response. In this model, we characterize coexistence through body size-dependent net reproductive rates. Our results suggest that the body sizes of consumer species strongly affect the size-density relations and energy requirements. We obtain the negative relationship between body size and density of intermediate consumers and discuss the energy equivalence rule. Furthermore, larger predators have a more significant impact on the intensity of the trophic cascade than smaller predators. Finally, we discuss potential extensions and applications of our modeling approach.

Plant invasion alters community structure and decreases diversity of arbuscular mycorrhizal fungal communities

Invasive plants often pose serious threats to the natural biodiversity of invaded ecosystems and in this way are likely to alter ecosystem services. This applies to arbuscular mycorrhizal (AM) fungi, in which the invaders have been reported to modify community structure, which facilitates their further intrusion. Information as to the impact of such invasion on AM fungal communities is insufficient and therefore needed. In particular, little is known about how AM fungal communities shift in response to individual invasive species. To ascertain whether invasion changes the structure of indigenous AM fungal communities, we examined changes in AM fungal community composition and diversity in soil and in roots of native neighboring plants in response to incursion of five invasive plant species from the family Asteraceae: Conyza canadensis, Erigeron annuus, Echinops sphaerocephalus, Solidago canadensis, and Symphyotrichum novi-belgii. We found that invasions of tested invasive plant species altered composition of the AM fungal community and reduced the diversity of AM fungi in soil and in the roots of some native plants. Statistical significance of the invasions' effects depended on composition of AM fungal communities in roots of the native plant species and/or site and was not connected with changes in soil parameters. Our results confirm the notable influence of plant invasion on indigenous AM fungal biodiversity and the need for further study in various environmental conditions.

Factors shaping community patterns of protists and bacteria on a European scale.

Factors shaping community patterns of microorganisms are controversially discussed. Physical and chemical factors certainly limit the survival of individual taxa and maintenance of diversity. In recent years, a contribution of geographic distance and dispersal barriers to distribution patterns of protists and bacteria has been demonstrated. Organismic interactions such as competition, predation and mutualism further modify community structure and maintenance of distinct taxa. Here, we address the relative importance of these different factors in shaping protists and bacterial communities on a European scale using high-throughput sequencing data obtained from lentic freshwater ecosystems. We show that community patterns of protists are similar to those of bacteria. Our results indicate that cross-domain organismic factors are important variables with a higher influence on protists as compared with bacteria. Abiotic physical and chemical factors also contributed significantly to community patterns. The contribution of these latter factors was higher for bacteria, which may reflect a stronger biogeochemical coupling. The contribution of geographical distance was similar for both microbial groups.

Mistletoe generates non‐trophic and trait‐mediated indirect interactions through a shared host of herbivore consumers

AbstractIndirect interactions emerge among a wide range of herbivores sharing the same plant resource. Consumers usually belong to different trophic guilds, from folivores and sapsuckers to parasitic plants. We propose that mistletoes parasitizing pines could play a key role acting as herbivores on host pines and coming indirectly into competition with other herbivores feeding on the same host. Changes caused by mistletoes on its host have been well studied, but its effects running across trophic webs remain unrevealed. In this study, we investigate the effect of European mistletoe (Viscum album subsp. austriacum) on the host‐feeding herbivores via trait‐mediated indirect interactions (TMIIs) across their shared pine host (Pinus nigra subsp. salzmannii). We performed field and laboratory experiments, and analyzed the net effect of different mistletoe parasite loads on three host‐phytophagous species: the sapsucker Cinara pini (Aphididae), the winter folivore Thaumetopoea pityocampa (Thaumetopoeidae), and the summer folivore Brachyderes sp. (Curculionidae), all being members of different functional feeding groups (FFGs). We summarize the mistletoe–host–herbivore interactions by means of a TMII, where mistletoe parasitism causes non‐trophic links and detrimental indirect interactions on pine‐feeding herbivores across its shared host, suggesting a worsening of host quality as food. These indirect interactions vary according to three parameters. First, the intensity has a non‐proportional relation with parasite load, showing an impact threshold on highly parasitized pines. Second, the movement capacity of insect herbivores determines their response, by decreasing the abundance of herbivores with low movement ability (aphids and pine processionary caterpillars) while altering the behavior (plant selection) of more mobile herbivores (pine weevils). Finally, FFG determines the intensity of mistletoe parasitism effects, folivores being more responsive than sapsuckers. Overall, mistletoe generates non‐trophic interaction linkages in the forest able to modify community structure by becoming a nexus of the entire herbivore community of the pine canopy.

Nutrient consumption and chain tuning in diatoms exposed to storm-like turbulence

Current information on the response of phytoplankton to turbulence is linked to cell size and nutrient availability. Diatoms are considered to be favored by mixing as dissolved nutrients are more easily accessible for non-motile cells. We investigated how diatoms exploit microscale turbulence under nutrient repletion and depletion conditions. Here, we show that the chain-forming diatom Chaetoceros decipiens, continues to take up phosphorus and carbon even when silicon is depleted during turbulence. Our findings indicate that upon silica depletion, during turbulence, chain spectra of C. decipiens remained unchanged. We show here that longer chains are maintained during turbulence upon silica depletion whereas under still conditions, shorter chains are enriched. We interpret this as a sign of good physiological state leading to a delay of culture senescence. Our results show that C. decipiens senses and responds to turbulence both in nutrient repletion and depletion. This response is noteworthy due to the small size of the species. The coupling between turbulence and biological response that we depict here may have significant ecological implications. Considering the predicted increase of storms in Northern latitudes this response might modify community structure and succession. Our results partly corroborate Margalef’s mandala and provide additional explanations for that conceptualization.

Single gene locus changes perturb complex microbial communities as much as apex predator loss.

Many bacterial species are highly social, adaptively shaping their local environment through the production of secreted molecules. This can, in turn, alter interaction strengths among species and modify community composition. However, the relative importance of such behaviours in determining the structure of complex communities is unknown. Here we show that single-locus changes affecting biofilm formation phenotypes in Bacillus subtilis modify community structure to the same extent as loss of an apex predator and even to a greater extent than loss of B. subtilis itself. These results, from experimentally manipulated multitrophic microcosm assemblages, demonstrate that bacterial social traits are key modulators of the structure of their communities. Moreover, they show that intraspecific genetic variability can be as important as strong trophic interactions in determining community dynamics. Microevolution may therefore be as important as species extinctions in shaping the response of microbial communities to environmental change.

Factors shaping bacterial phylogenetic and functional diversity in coastal waters of the NW Mediterranean Sea

To evaluate the main factors shaping bacterioplankton phylogenetic and functional diversity in marine coastal waters, we carried out a two-year study based on a monthly sampling in Blanes Bay (NW Mediterranean). We expected the key factors driving bacterial diversity to be (1) temperature and nutrient concentration, together with chlorophyll a concentration as an indicator of phytoplankton biomass and, hence, a carbon source for bacteria (here called bottom-up factors), and (2) top-down pressure (virus- and protist-mediated mortality of bacteria). Phylogenetic diversity was analyzed by denaturing gradient gel electrophoresis (DGGE) of 16S rRNA. Functional diversity was assessed by using monomeric carbon sources in Biolog EcoPlates and by determining the activity of six extracellular enzymes. Our results indicate that the bacterial phylogenetic and functional diversity in this coastal system is shaped mainly by bottom-up factors. A dendrogram analysis of the DGGE banding patterns revealed three main sample clusters. Two clusters differed significantly in temperature, nitrate and chlorophyll a concentration, and the third was characterized by the highest losses of bacterial production due to viral lysis detected over the whole study period. Protistan grazing had no effect on bacterial functional diversity, since there were no correlations between protist-mediated mortality (PMM) and extracellular enzyme activities, and utilization of only two out of the 31 carbon sources (N-acetyl-d-glucosamine and α-cyclodextrin) was correlated with PMM. In contrast, virus-mediated mortality correlated with changes in the percentage of use of four carbon sources, and also with specific leu-aminopeptidase and β-glucosidase activity. This suggests that viral lysate provides a pool of labile carbon sources, presumably including amino acids and glucose, which may inhibit proteolytic and glucosidic activity. Our results indicate that bottom-up factors play a more important role than top-down factors (i.e. viral lysis and protistan grazing) in shaping bacterial community structure and activity. Furthermore, they suggest that viruses play a more important role than protists in modifying community structure and functional diversity of bacteria in oligotrophic marine coastal waters.

Variability of water temperature may influence food-chain length in temperate streams

Food-chain length (FCL) is commonly used in ecological investigations to gain insight into how ecosystems function. Several studies have investigated the mechanisms underlying FCL patterns, but none has specifically examined the effect of temperature variability. In river ecosystems, water temperature variability can modify community structure, individuals’ activity, and individuals’ physiological rates, among other things. As such, we expected that it would negatively influence FCL. To test this prediction, we took advantage of a dataset comprising five streams, which mainly differ according to their temperature variability. At each stream, we (i) studied the species composition of macroinvertebrates and fish, and using nitrogen and carbon stable isotopes, (ii) estimated realized FCL, and (iii) examined food web structure. For macroinvertebrates, but not for fish, species composition differed among sites displaying low and high temperature variability. FCL was negatively influenced by temperature variability. Confirming this trend, we found a highly significant linear relationship between FCL and temperature variability using data from the literature. As for food web structure, the trophic position of filter-feeders/shredders may explain the FCL differences among sites. Our study gives additional support to the “dynamic stability” hypothesis and advances a step further by suggesting that temperature variability alone may reduce FCL.

Differential effects of grazer species on periphyton of a temperate rocky shore

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 484:63-78 (2013) - DOI: https://doi.org/10.3354/meps10297 Differential effects of grazer species on periphyton of a temperate rocky shore Moisés A. Aguilera1,*, Sergio A. Navarrete2, Bernardo R. Broitman1 1Centro de Estudios Avanzados en Zonas Áridas (CEAZA), Facultad de Ciencias del Mar, Universidad Católica del Norte, Larrondo 1281, Coquimbo, Chile 2Estación Costera de Investigaciones Marinas, Las Cruces, and Center for Marine Conservation, Pontificia Universidad Católica de Chile, Casilla 114-D, Santiago, Chile *Email: moises.aguilera@ceaza.cl ABSTRACT: Species-specific traits are relevant to understand variation in the effect of grazers on primary producers and are critical in determining their functional roles as controllers of productivity in marine ecosystems. In intertidal habitats, periphyton, composed of bacteria, cyanophytes, microalgae and early stages of macroalgae, constitutes the main food for many benthic grazers. Using field experiments, we examined the overall effect of grazers and the importance of direct and indirect effects of different grazer species on periphyton composition, richness, diversity and productivity. We manipulated the main grazer species present along Chilean rocky shores, enclosing adult individuals of the keyhole limpet Fissurella crassa, the chiton Chiton granosus, the scurrinid limpet Scurria araucana and the pulmonate limpet Siphonaria lessoni. These organisms overlap broadly in diet but exhibit differences in foraging behavior. Differences in the individual effects of grazer species on periphyton productivity, as well as on richness and diversity characterized the assemblage. C. granosus grazing led to lower periphyton productivity, richness and diversity compared with all other grazers, who had positive effects for all variables. Richness and diversity of the major periphyton groups were maximal at intermediate levels of total grazing pressure, highlighting the importance of ecological interactions within the periphyton assemblage. Our results demonstrate the complexity of functional roles and relationships of grazers involved in the control of composition and production of the periphyton assemblage. Given the importance of direct and indirect effects of grazers, understanding species interactions within the microbenthic community can shed light on the mechanisms through which herbivores modify community structure and productivity. KEY WORDS: Grazer assemblage · Periphyton · Productivity · Diversity · Foraging behavior Full text in pdf format Supplementary material PreviousNextCite this article as: Aguilera MA, Navarrete SA, Broitman BR (2013) Differential effects of grazer species on periphyton of a temperate rocky shore. Mar Ecol Prog Ser 484:63-78. https://doi.org/10.3354/meps10297 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 484. Online publication date: June 12, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Integration of non-indigenous species within the interspecific abundance–occupancy relationship

There is a broad consensus that habitat disturbance and introduction of non-indigenous species may dramatically modify community structure, particularly in insular ecosystems. However, it is less clear whether emergent macroecological patterns are similarly affected. The positive interspecific abundance–occupancy relationship (IAOR) is one of the most pervasive macroecological patterns, yet has rarely been analyzed for oceanic island assemblages. We use an extensive dataset for arthropods from six islands within the Azorean archipelago to test: (1) whether indigenous and non-indigenous species are distributed differently within the IAOR; and (2) to the extent that they are, can differences can be attributed to two indices of disturbance. We implemented modeling averaged methods using five of the most common IAOR models to derive an averaged IAOR fit for each island. After testing if species colonization status (indigenous versus non-indigenous) may explain the residuals of the IAOR, we identified true negative and positive outliers and tested the effect of colonization status on the likelihood of a species being a positive or negative outlier. We found that the indigenous and non-indigenous species are randomly distributed on both sides of the overall IAOR. Only for Flores Island, were non-indigenous species more aggregated than indigenous species. We were unable to detect a meaningful relationship between deviation from the IAOR and disturbance, despite the undoubted impact of both severe habitat loss and non-indigenous species on these oceanic islands. Our results show that the non-indigenous species have been integrated alongside indigenous species in the contemporary Azorean arthropod communities such that they are mostly undetectable by the study of the IAOR.

Response to variable light intensity in photoacclimated algae and cyanobacteria exposed to atrazine

Atrazine is frequently detected in freshwater ecosystems exposed to agricultural waste waters and runoffs worldwide and it can affect non-target organisms (mainly photoautotrophic) and modify community structure. Meanwhile, light environment is known to vary between aquatic ecosystems, but also before and during the exposure to atrazine and these variations may modify the sensitivity to atrazine of photoautotroph organisms. In this study, 10 species of phytoplankton (chlorophytes, baccilariophytes and cyanophytes) acclimated to low or high light intensities were exposed to atrazine and light of different intensities to compare their combined effect. Our data showed that chlorophytes and baccilariophytes were more resistant to atrazine compared to cyanophytes for all light conditions. Atrazine was found to inhibit Φ′M, Ψ0, PM and non-photochemical quenching for all species indicating an effect on electron transport, primary production and photoregulation processes. These data also indicate a higher sensitivity of Ψ0 (average Ψ0-EC50 of 91±11nM or 19.6±0.9μgL−1) compared to Φ′M (average Φ′M-EC50 of 217±19nM or 46.8±4.1μgL−1) and suggest that photoregulation processes activated in presence of light decrease the effect of atrazine. We also showed that increasing light intensity decreased Φ′M-EC50 in both low (except baccilariophytes) and high light acclimated conditions. Despite this similarity, most species acclimated to high light were found to have higher or similar Φ′M-EC50 compared to low light acclimated cells and thus, were less sensitive to atrazine in low light and high light environments. We concluded that an increase in the plastoquinone pool induced by acclimation to high light decreased the sensitivity to atrazine in phytoplankton and we hypothesized that the effect observed was the result of a dilution of atrazine toxicity through increased binding site availability (quinones) combined with increased photoregulation processes capacity.

Comparative Composition, Diversity and Trophic Ecology of Sediment Macrofauna at Vents, Seeps and Organic Falls

Sediments associated with hydrothermal venting, methane seepage and large organic falls such as whale, wood and plant detritus create deep-sea networks of soft-sediment habitats fueled, at least in part, by the oxidation of reduced chemicals. Biological studies at deep-sea vents, seeps and organic falls have looked at macrofaunal taxa, but there has yet to be a systematic comparison of the community-level attributes of sediment macrobenthos in various reducing ecosystems. Here we review key similarities and differences in the sediment-dwelling assemblages of each system with the goals of (1) generating a predictive framework for the exploration and study of newly identified reducing habitats, and (2) identifying taxa and communities that overlap across ecosystems. We show that deep-sea seep, vent and organic-fall sediments are highly heterogeneous. They sustain different geochemical and microbial processes that are reflected in a complex mosaic of habitats inhabited by a mixture of specialist (heterotrophic and symbiont-associated) and background fauna. Community-level comparisons reveal that vent, seep and organic-fall macrofauna are very distinct in terms of composition at the family level, although they share many dominant taxa among these highly sulphidic habitats. Stress gradients are good predictors of macrofaunal diversity at some sites, but habitat heterogeneity and facilitation often modify community structure. The biogeochemical differences across ecosystems and within habitats result in wide differences in organic utilization (i.e., food sources) and in the prevalence of chemosynthesis-derived nutrition. In the Pacific, vents, seeps and organic-falls exhibit distinct macrofaunal assemblages at broad-scales contributing to ß diversity. This has important implications for the conservation of reducing ecosystems, which face growing threats from human activities.

Epiphyte grazing enhances productivity of remnant seagrass patches

Anthropogenic nutrient enrichment is increasingly modifying community structure and ecosystem functioning in terrestrial and aquatic ecosystems. In marine ecosystems, the paradigm is that nutrient enrichment leads to a decline of seagrasses by stimulating epiphytic algal growth, which shades and overgrows seagrasses. This ignores the potential for herbivores, which graze upon epiphytic algae, to partially or wholly counter such nutrient effects. We conducted a field experiment to assess the role that the trochid gastropod Calthalotia fragum plays in reducing nutrient impacts on the seagrass, Posidonia australis, in an urbanized Australian estuary, Botany Bay, Sydney. In a field experiment, where nutrient loading and grazer density were orthogonally manipulated, nutrient enrichment failed to promote epiphyte biomass or diminish growth and primary productivity of P. australis. To the contrary, nutrient enrichment enhanced photosynthesis of the seagrass in plots where the grazer was present at higher density. Epiphytic growth was negatively affected by increased C. fragum density, while P. australis shoot growth was positively influenced. Thus, in this study system, grazing appears to play a much greater role in determining seagrass primary productivity and above-ground growth than moderate nutrient loading, suggesting that the interaction between grazers and nutrients depends on the relative levels of each. Our study contributes to a growing body of literature suggesting that effects of nutrient loading on benthic assemblages are not universally negative, but are dependent on the biotic and abiotic setting.

Above- and belowground responses to nitrogen addition in a Chihuahuan Desert grassland

Increased available soil nitrogen can increase biomass, lower species richness, alter soil chemistry and modify community structure in herbaceous ecosystems worldwide. Although increased nitrogen availability typically increases aboveground production and decreases species richness in mesic systems, the impacts of nitrogen additions on semiarid ecosystems remain unclear. To determine how a semiarid grassland responds to increased nitrogen availability, we examined plant community structure and above- and belowground net primary production in response to long-term nitrogen addition in a desert grassland in central New Mexico, USA. Plots were fertilized annually (10 g N m(-2)) since 1995 and NPP measured from 2004 to 2009. Differences in aboveground NPP between fertilized and control treatments occurred in 2004 following a prescribed fire and in 2006 when precipitation was double the long-term average during the summer monsoon. Presumably, nitrogen only became limiting once drought stress was alleviated. Belowground NPP was also related to precipitation, and greatest root growth occurred the year following the wettest summer, decreasing gradually thereafter. Belowground production was unrelated to aboveground production within years and unrelated to nitrogen enrichment. Species richness changed between years in response to seasonal precipitation variability, but was not altered by nitrogen addition. Community structure did respond to nitrogen fertilization primarily through increased abundance of two dominant perennial grasses. These results were contrary to most nitrogen addition studies that find increased biomass and decreased species richness with nitrogen fertilization. Therefore, factors other than nitrogen deposition, such as fire or drought, may play a stronger role in shaping semiarid grassland communities than soil fertility.

Fine-scale community and genetic structure are tightly linked in species-rich grasslands

Recent evidence indicates that grassland community structure and species diversity are influenced by genetic variation within species. We review what is known regarding the impact of intraspecific diversity on grassland community structure, using an ancient limestone pasture as a focal example. Two genotype-dependent effects appear to modify community structure in this system. First, the abundance of individual constituent species can depend upon the combined influence of direct genetic effects stemming from individuals within the population. Second, the outcome of localized interspecific interactions occurring within the community can depend on the genotypes of participating individuals (indicating indirect genetic effects). Only genotypic interactions are thought to be capable of allowing the long-term coexistence of both genotypes and species. We discuss the implications of these effects for the maintenance of diversity in grasslands. Next, we present new observations indicating that losses of genotypic diversity from each of two species can be predicted by the abundance of other coexisting species within experimental grassland communities. These results suggest genotype-specific responses to abundance in other coexisting species. We conclude that both direct and indirect genetic effects are likely to shape community structure and species coexistence in grasslands, implying tight linkage between fine-scale genetic and community structure.

A Perspective on the Consequences for Insect Herbivores and Their Natural Enemies When They Share Plant Resources

Thousands of insect species consume both animal and plant-derived food resources. However, little recognition is given to the fact that omnivory is a general feeding strategy common to all higher trophic levels. Species in multitrophic interactions can all directly rely on the same plant resources. Nonetheless, little is known about the effect of a change in the relative abundance of a shared plant resource on trophic dynamics. Here we describe how a relative change of resource availability can affect multitrophic interactions and we emphasise its importance. Changes in multitrophic interactions can be induced by unequal alterations of individual fitness across trophic levels, possibly leading to changes in population structure of interacting species. At least ten ecological mechanisms can be involved and these are explored here. It is concluded that shared plant resources that are differentially used over several trophic levels have the potential to modify community structure and energy flow within food webs and ecosystems in more complex ways than previously recognised. The synthesis presented here provides an understanding of this complexity and can lead to improved deployment of biodiversity when manipulating food webs to protect ecological communities or to enhance ecosystem services such as biological control of agricultural pests.

Do habitat size and shape modify abiotic factors and communities in artificial treeholes?

Community composition may be determined by a variety of factors, including habitat dimension, abiotic conditions, and biotic interactions. Habitat dimensions may influence abiotic conditions, thus modifying community structure or biotic interactions. We used six different mesocosm sizes, two depths crossed with three surface areas, to test hypotheses regarding the direct and indirect effects of habitat dimensions (depth and surface area) on dissolved oxygen concentration and insect communities in artificial water-filled treeholes. Containers were monitored for dissolved oxygen concentrations and insect community composition from June 2002 to November 2003. We predicted that deep mesocosms would have lower species richness and insect larval densities than shallow due to less dissolved oxygen at deeper depths, and that large surface area mesocosms would have greater species richness and abundance of insects than small. Larger surface area habitats may attract more insects because they are easier to find and perceived by ovipositing females to be more stable. Dissolved oxygen concentrations ([DO]) at depth were consistently lower in deep than shallow habitats, and mosquito densities and species richness were lower in those deep mesocosms compared to shallow mesocosms. We found higher insect richness at certain times of the year in large and medium than in small surface area mesocosms. By modifying abiotic factors such as [DO], dimensional aspects of the habitat, in this case depth, may affect community structure in ways not predicted simply by habitat size.

Onshore-Offshore Biofacies Patterns, Greenhorn Eustatic Cycle, Western Interior Cretaceous Epicontinental Seaway, North America: ABSTRACT

The Cretaceous Western Interior foreland basin provides an ideal testing ground for models of evolution and dispersion among benthic communities. Biological patterns of adaptation, diversity, life habit, population structure, trophic strategies, community composition/structure, and biogeography define biofacies in this epeiric sea. Biofacies distributions are documented for the 6-m.y. Greenhorn eustatic cyclothem (latest Albian-middle Turonian). Two high-resolution cross sections provide a stratigraphic framework: (1) Utah/Arizona to Minnesota, transecting diverse tectonic/sedimentologic provinces within the same warm temperate climatic zone and (2) Alberta to Oklahoma/New Mexico, crossing three biogeographic subprovinces within basinal facies. Plotting biofacies distributions on the cross sections allows the spatial and temporal evolution of Western Interior benthic communities to be studied. Resulting patterns suggest four points. (1) Onshore-offshore and latitudinal trends in shell size, thickness, and ornamentation, community diversity/structure, and the development and dispersion of adaptive characters reflect changes in temperature, benthic oxygen levels, and substrate characteristics. (2) These trends indicate that diverse short-term and long-term oxygen depletion events occurred during Greenhorn deposition, modifying community structure and reflecting dynamic paleooceanographic changes in the seaway. (3) Biofacies/lithofacies data in conjunction with paleogeographic reconstructions allow modeling of community dispersion in response to trends in chemical and physical sedimentologic events. (4) Integration ofmore » community data and paleooceanographic models with latest Albian through middle Turonian eustatic history furthers their understanding of the relationship between sea level changes and community evolution in epeiric seas.« less