UV-fluorescence microscopy and the coherence of pollen assemblages in environmental archaeology and Quaternary geology

UV-fluorescence microscopy provides a powerful tool for the assessment of the coherence of pollen and organic-walled microfossil assemblages in situations where recycling or the intrusion of younger pollen is suspected. It also provides sensitive information about the thermal maturity of pollen, important for assessing whether material has been heated. Examples are given from the Palaeolithic sites at Barnham, Suffolk, UK; Stanton Harcourt, Oxfordshire, UK; High Lodge, Suffolk, UK; Niah Cave, Sarawak, Malaysian Borneo; and Holocene sites at Wadi Dana, Jordan; Milldale and Creswell, Derbyshire, UK; and Dooncarton Mountain, County Mayo, Republic of Ireland.

Coastline configuration as a determinant of structure in larval assemblages

The richness and turnover of coastal larval pools set upper limits for biodiversity in coastal systems. For particular local systems, such as embayments, the characteristics of the local larval pool are determined by the relative contributions of locally produced and external larvae. The balance between these sources partially reflects the extent of tidal exchange and is hence related to system size and flushing time. Larvae of benthic marine invertebrates were sampled from 8 bays along the Irish coast to investigate the effect of coastline configuration on the characteristics of the larval pool. Flushing time explained 34.5% of the variability in species richness from a series of daily samples. Many of the potentially relevant environmental variables are correlated, limiting the potential for individual variables to be examined in isolation. We therefore used a principal components analysis to describe the major patterns in environmental variability across bays. The second principal component separated bays along a gradient of increasing depth, salinity, tidal range and flushing time. Scores along this component were generally better predictors of the larval pool than single variables, explaining as much as 61.2% of the variation in species richness, diversity and similarity between dates. Deeper bays, with more saline water and longer flushing times, tended to have richer and more diverse larval pools, with a greater consistency in species composition between sample dates. No relationship was found between environmental variables and larval abundance. Our results suggest that flushing time, particularly when in combination with topographic variables, chlorophyll, tidal range and salinity, may be a useful predictor for the richness and turnover of local larval pools.

Potential roles for differential body size and microhabitat complexity in mediating biotic interactions within invasive freshwater amphipod assemblages

Cannibalism and intraguild predation (IGP) are common amongst freshwater amphipod crustacean aswsemblages, particularly between individuals of different body size, with IGP of smaller by larger species. The decline of Gammarus tigrinus Populations in mainland Europe has been accompanied by the arrival of the Ponto-Caspian invader Dikerogammarus villosus and previous studies have implicated IGP of G. tigrinus by the larger D. villosus as the principal driving force in this replacement. We examined how factors such as microhabitat and body size may mediate both cannibalism within G. tigrinus populations and IGP by D. villosus and thus contribute to field patterns of coexistence and exclusion. A field Survey of an invaded Dutch fake indicated that G. tigrinus and D. villosus differed in distribution. with D. villosus being the numerically dominant amphipod (80-96 %) on the rocky boulder Substrate of the shoreline and G. tigrinus being the dominant amphipod (100 %) in the crushed shell/sand matrix immediately adjacent to this. Laboratory microcosm experiments indicated that G. tigrinus cannibalism, particularly of smaller by larger size classes, may be common. In addition, although D. villosus predation of all G. tigrinus size classes was extreme, the smallest size classes Suffered the highest predation. Indeed, when exposed to D. villosus, predation of larger G. tigrinus was lowest when smaller G. tigrinus were also present. Increasing microhabitat complexity from a simple bare substrate littered with Dreissena polymorpha zebra mussels to a Crushed shell/sand matrix significantly reduced both cannibalism and IGP. Our Study emphasizes the need to consider both life history stages and habitat template, when considering the impacts of biotic interactions and it also emphasizes that complex, interacting factors may be mediating the range expansion of D. villosus.

Like a rolling stone: the mobility of maerl (Corallinaceae) and the neutrality of the associated assemblages

Beds of nonattached coralline algae (maerl or rhodoliths) are widespread and considered relatively species rich. This habitat is generally found in areas where there is chronic physical disturbance such that maerl thalli are frequently moved. Little is known, however, about how natural disturbance regimes affect the species associated with maerl. This study compared the richness, animal abundance, and algal biomass of maerl-associated species over a two-year period in a wave-disturbed bed and a sheltered maerl bed. Changes in associated species over time were assessed for departures from a neutral model in which the dissimilarity between samples reflects random sampling from a common species pool. Algal biomass and species richness at the wave-exposed site and on stabilized maerl at the sheltered site were reduced at times of higher wind speeds. The changes in species richness were not distinguishable from a neutral model, implying that algal species were added at random to the assemblage as the level of disturbance lessened. Results for animal species were more mixed. Although mobile species were less abundant during windy periods at the exposed site, both neutral and non-neutral patterns were evident in the assemblages. Artificial stabilization of maerl had inconsistent effects on the richness of animals but always resulted in more attached algal species. While the results show that the response of a community to disturbance can be neutral, the domain of neutral changes in communities may be relatively small. Alongside non-neutral responses to natural disturbance, artificial stabilization always resulted in an assemblage that was more distinct than would be expected under random sampling from a common pool. Community responses to stabilization treatments did not consistently follow the predictions of the dynamic equilibrium model, the intermediate disturbance model, or a facilitation model. These inconsistencies may reflect site-specific variation in both the disturbance regime and the adjacent habitats that provide source populations for many of the species found associated with maerl.

Molluscan assemblages on an intertidal sandflat in Princess Royal Harbour, Westren Austrailia

The molluscan fauna of an intertidal sand beach in Princess Royal Harbour, W.A.. is divided into two associations. The upper association, located between +0.10 and +0.59 m relative to tidal datum, is characterized by Hydrococcus graniformis and Batillariella estuarina. The lower assemblage, between +0.09 and -0.29 m is dominated numerically by Zeacumantus diemenensis and Katelysia scalarina. The assemblages are equivalent to the midlittoral- and sublittoral-fringe groupings described on both sandy and rocky shores by other authors. There is no supralittoral-fringe component in the molluscan fauna ofprincess Royal Harbour. The break between the two assemblages occurs at + 0.1 m, just below the minimum tide level in the area. Possible reasons for the zonation patterns are discussed and compared with other studies of intertidal zonation on sandy shores.

Trait assembly in plant assemblages and its modulation by productivity and disturbance

Understanding how communities assemble is a key challenge in ecology. Conflicting hypotheses suggest that plant traits within communities should show divergence to reflect strategies to reduce competition or convergence to reflect strong selection for the environmental conditions operating. Further hypotheses suggest that plant traits related to productivity show convergence within communities, but those related to disturbance show divergence. Data on functional diversity (FD ) of 12 traits from 30 communities ranging from arable fields, mown and grazed grasslands to moorland and woodland were employed to test this using randomisations tests and correlation and regression analysis. No traits showed consistent significant convergence or divergence in functional diversity. When correlated to measures of the environment, the most common pattern was for functional diversity to decline (7 out of 12 traits) and the degree of convergence (7 out of 12 traits) to increase as the levels of productivity (measured as primary productivity, soil nitrogen release and vegetation C:N) and disturbance increased. Convergence or a relationship between functional diversity and the environment was not seen for a number of important traits, such as LDMC and SLA, which are considered as key predictors of ecosystem function. The analysis indicates that taking into account functional diversity within a system may be a necessary part of predicting the relationship between plant traits and ecosystem function, and that this may be of particular importance within less productive and less disturbed systems. © 2011 Springer-Verlag.

Indigenous Arbuscular Mycorrhizal Fungal Assemblages Protect Grassland Host Plants from Pathogens

Plant roots can establish associations with neutral, beneficial and pathogenic groups of soil organisms. Although it has been recognized from the study of individual isolates that these associations are individually important for plant growth, little is known about interactions of whole assemblages of beneficial and pathogenic microorganisms associating with plants. We investigated the influence of an interaction between local arbuscular mycorrhizal (AM) fungal and pathogenic/saprobic microbial assemblages on the growth of two different plant species from semi-arid grasslands in NE Germany (Mallnow near Berlin). In a greenhouse experiment each plant species was grown for six months in either sterile soil or in sterile soil with one of three different treatments: 1) an AM fungal spore fraction isolated from field soil from Mallnow; 2) a soil pathogen/saprobe fraction consisting of a microbial community prepared with field soil from Mallnow and; 3) the combined AM fungal and pathogen/saprobe fractions. While both plant species grew significantly larger in the presence of AM fungi, they responded negatively to the pathogen/saprobe treatment. For both plant species, we found evidence of pathogen protection effects provided by the AM fungal assemblages. These results indicate that interactions between assemblages of beneficial and pathogenic microorganisms can influence the growth of host plants, but that the magnitude of these effects is plant species-specific.

Assessing abundance and diversity patterns of soil microarthropod assemblages in northern Victoria Land (Antarctica)

This study aimed to: (1) assess differences between two quantitative sampling methods of soil microarthropods (visual census vs. stone washing) in ice-free areas located along a latitudinal gradient (from 72 degrees 37'S to 74 degrees 42'S) in northern Victoria Land (Antarctica); (2) furnish preliminary results on the abundance and diversity of mites and springtails in the studied areas. Visual census yielded reliable density estimates for adult collembolans and larger prostigmatic mites but did not detect small species. The study updates the distribution of several mites, including the southernmost record of an Oribatida species at global scale. Species composition was correlated with latitude but the uneven abundance distribution and local high beta-diversity probably reflect habitat fragmentation and population isolation. Under this circumstance nested sampling design should be usefully employed. Priorities and suitable methods for studying terrestrial microarthropod communities in continental Antarctica are discussed.

Wave action modifies the effects of consumer diversity and warming on algal assemblages

To understand the consequences of biodiversity loss, it is necessary to test how biodiversity-ecosystem functioning relationships may vary with predicted environmental change. In particular, our understanding will be advanced by studies addressing the interactive effects of multiple stressors on the role of biodiversity across trophic levels. Predicted increases in wave disturbance and ocean warming, together with climate-driven range shifts of key consumer species, are likely to have profound impacts on the dynamics of coastal marine communities. We tested whether wave action and temperature modified the effects of gastropod grazer diversity (Patella vulgata, Littorina littorea and Gibbula umbilicalis) on algal assemblages in experimental rock pools. The presence or absence of L. littorea appeared to drive changes in microalgal and macroalgal biomass and macroalgal assemblage structure. Macroalgal biomass also decreased with increasing grazer species richness, but only when wave action was enhanced. Further, independently of grazer diversity, wave action and temperature had interactive effects on macroalgal assemblage structure. Warming also led to a reversal of grazer-macroalgal interaction strengths from negative to positive, but only when there was no wave action. Our results show that hydrodynamic disturbance can exacerbate the effects of changing consumer diversity, and may also disrupt the influence of other environmental stressors on key consumer-resource interactions. These findings suggest that the combined effects of anticipated abiotic and biotic change on the functioning of coastal marine ecosystems, although difficult to predict, may be substantial.