Prevalence and species richness of trematode parasites only partially recovers after the 2011 Tohoku, Japan, earthquake tsunami

Trematode parasites have complex life cycles and use a variety of host species across different trophic levels. Thus, they can be used as indicators of disturbance and recovery of coastal ecosystems. Estuaries on the Pacific coast of northeastern Japan were heavily affected by the 2011 Tohoku earthquake tsunami. To evaluate the effect of the tsunami on the trematode community, we examined trematodes in the mud snail, Batillaria attramentaria, at five study sites (three sites severely exposed to the tsunami and two sites sheltered from the tsunami) in Sendai Bay for 2 years prior to and 8 years after the tsunami. While the trematode prevalence decreased at all study sites, the species richness decreased only at the sites exposed to the tsunami. Although parasitism increased over the study period post-tsunami, the community had not fully recovered 8 years after the event. Trematode community structure has changed every year since the tsunami and has not stabilised. This could be explained by the alteration of first and second intermediate host communities. Our study suggests that it will take more time for the recovery of the trematode community and the associated coastal ecosystem in the Tohoku region.

Threshold-like associations as a function of disturbance

According to the intelligence-creativity threshold hypothesis, there should be a positive association between intelligence and creative potential up to a certain point, the threshold, after which a further increase in intelligence should have no association with creativity. In the present simulation study, the measured intelligence and creativity of virtual subjects were affected by their true abilities as well as a disturbance factor that varied in magnitude between subjects. The results indicate that the hypothesized threshold-like association could be due to some disturbing factor, for example, low motivation, illness, or linguistic confusion, that varies between individuals and that affects both measured intelligence and measured creativity, especially if the actual association between intelligence and creativity is weak. This, together with previous negative findings, calls the validity of the intelligence-creativity threshold hypothesis into question.

A systematic survey of regional multi-taxon biodiversity: evaluating strategies and coverage

Background

In light of the biodiversity crisis and our limited ability to explain variation in biodiversity, tools to quantify spatial and temporal variation in biodiversity and its underlying drivers are critically needed. Inspired by the recently published ecospace framework, we developed and tested a sampling design for environmental and biotic mapping. We selected 130 study sites (40 × 40 m) across Denmark using stratified random sampling along the major environmental gradients underlying biotic variation. Using standardized methods, we collected site species data on vascular plants, bryophytes, macrofungi, lichens, gastropods and arthropods. To evaluate sampling efficiency, we calculated regional coverage (relative to the known species number per taxonomic group), and site scale coverage (i.e., sample completeness per taxonomic group at each site). To extend taxonomic coverage to organisms that are difficult to sample by classical inventories (e.g., nematodes and non-fruiting fungi), we collected soil for metabarcoding. Finally, to assess site conditions, we mapped abiotic conditions, biotic resources and habitat continuity.

Results

Despite the 130 study sites only covering a minute fraction (0.0005%) of the total Danish terrestrial area, we found 1774 species of macrofungi (54% of the Danish fungal species pool), 663 vascular plant species (42%), 254 bryophyte species (41%) and 200 lichen species (19%). For arthropods, we observed 330 spider species (58%), 123 carabid beetle species (37%) and 99 hoverfly species (33%). Overall, sample coverage was remarkably high across taxonomic groups and sufficient to capture substantial spatial variation in biodiversity across Denmark. This inventory is nationally unprecedented in detail and resulted in the discovery of 143 species with no previous record for Denmark. Comparison between plant OTUs detected in soil DNA and observed plant species confirmed the usefulness of carefully curated environmental DNA-data. Correlations among species richness for taxonomic groups were predominantly positive, but did not correlate well among all taxa suggesting differential and complex biotic responses to environmental variation.

Conclusions

We successfully and adequately sampled a wide range of diverse taxa along key environmental gradients across Denmark using an approach that includes multi-taxon biodiversity assessment and ecospace mapping. Our approach is applicable to assessments of biodiversity in other regions and biomes where species are structured along environmental gradient.

Variation of nematode indices under contrasting pest management practices in a tomato growing agro-ecosystem

This study examined the variation of generic composition and nematode indices to evaluate the soil health status under differently treated tomato growing experimental plots. The study was conducted from 2016 to 2018 in summer and winter seasons on a traditionally tomato (Lycopersicon esculentum) growing farm in the Northern part of the Kathmandu valley, Nepal. Soil samples were taken from four types of replicating plots (each 5 × 5 m sq.) each using a different pest control method consisting of: cattle manure (MP), chemical pesticides (PP), botanical pesticides (BP), and a control plot (CP). The nematode communities were extracted, colonizer-persister (c-p) values assigned and ecological indices such as maturity index (MI), enrichment indexes (EI), structural index (SI) and channel index (CI) were calculated. The low abundance of all indices in pesticide applied plots during both seasons (winter and summer) was recorded. This result indicated pesticide application can be linked to the sensitivity of nematode genera. Nematode indices such as maturity index (MI), enrichment index (EI) and structural index (SI) were significantly affected with lower mean value especially in chemical pesticides applied plots during both the summer and winter seasons. The decomposition channel index (CI) did not exhibit significant variation in our analysis of treatment plots in either season. There was a positive response towards moisture content, soil temperature and nitrogen-carbon ratios for these indices. Nematode genera and indices showed significant variation for pest management practices in tomato grown plots.

Impact of altitude and anthropogenic disturbance on plant species composition, diversity, and structure at the Wof-Washa highlands of Ethiopia

The study was conducted in Wof-Washa Forest in the central highlands of Ethiopia, aiming at determining the impact of altitude and anthropogenic disturbance on plant species composition, structure, and diversity of the forest. Eighteen transect lines with 632 meters apart from each other were established from top to bottom. A total of 115 main plots for all communities with 20 × 20 m, were established along transect lines from the upper part of the forest to the river's edge. To collect data on seedlings and saplings, 5 m × 5 m and 10 m × 10 m subplots were laid respectively within the main sampling plots. For each plot the plant species were counted, diameter at breast height and height of trees and shrubs were measured. The human disturbance data were visually estimated for each plot in each community. Plant community classification was made following Ethiopia agro-ecological zones. Plant species diversity and richness were found related to human disturbance and altitude. A total of 108 species belonging to 99 genera and 57 families were identified. The results revealed that Asteraceae was the most diverse higher plant family with nine species (8.3%) followed by Fabaceae, Euphorbiaceae, and Rosaceae with six (5.5%) species each. The overall Shannon diversity and evenness index of the forest were 4.02 and 0.86 respectively. Tree/shrub, sapling and seedling densities were 664.4, 757.2 and 805.7 individual's ha⁻¹ respectively. The total basal area of the forest was 55.99 m²ha^-1. About 25.7% of the importance values index was contributed by four species, Juniperus procera, Podocarpus falcatus, Ilex mitis, and Erica arborea. The similarity in species composition within the forest was low, indicating that the different parts of the forest had different floras. The presence of strong human disturbance indicates the need for immediate conservation in order to ensure sustainable utilization and management of the forest.

Enhanced nutrient loading and herbivory do not depress the resilience of subtidal canopy forests in Mediterranean oligotrophic waters

The interaction between top-down and bottom-up forces determines the recovery trajectory of macroalgal forests exposed to multiple stressors. In an oligotrophic system, we experimentally investigated how nutrient inputs affected the recovery of Cystoseira brachycarpa following physical disturbance of varying intensities, both inside forested areas and at the boundary with sea urchin barrens. Unexpectedly, Cystoseira forests were highly resilient to disturbance, as they were able to recover from any partial damage. In general, the addition of nutrients sped up the recovery of Cystoseira. Thus, only the total canopy removal, in combination with either low nutrient availability or intense grazing pressure, promoted the expansion of mat-forming algae or urchin barrens, respectively. Our study suggests that the effects of enhanced nutrient levels may vary according to the trophic characteristics of the waterbody, and hence, are likely to vary among regions of the Mediterranean basin.

Morphological variation of a rapidly spreading native macroalga across a range of spatial scales and its tolerance to sedimentation

Understanding how species' traits can shape winners and losers of environmental change can help resolve drivers of current community composition patterns and predict future drivers. Sedimentation is one of the main environmental stressors shaping coastal marine communities and tolerance of high sedimentation rates (e.g. via morphological variation) may allow for competitive dominance. In New South Wales, Australia, the abundance and range of the native green macroalga Caulerpa filiformis have increased over recent decades, apparently associated with sediment disturbance. We used field measurements to test hypotheses about morphological variability in C. filiformis in relation to local- and large-scale environmental variation in water depth, sediment cover and latitude. Using a lab experiment, we tested hypotheses about survival and morphological change under different sedimentation regimes. In the field, C. filiformis fronds were more elongated and less branched when a sediment veneer is present and when water depth increased (i.e. reduced light). At larger spatial scales, frond length and width decreased with increased latitude, but latitude was less important in explaining the variation C. filiformis' length than were depth or sedimentation. Our lab experiment showed a high tolerance to sedimentation, aided by increased investment in vertical growth. This study shows that rapid morphological plasticity is a likely key attribute of the spreading native macroalga C. filiformis. We argue that having a broad environmental tolerance is key to define a species success under environmental change.

Functional responses of intertidal bivalves to repeated sub-lethal, physical disturbances

In coastal habitats, physical disturbances of benthic organisms can be caused by natural events like wave-born objects and human activity like trampling, and these disturbances can be sub-lethal (e.g., resulting in the organism's displacement). We know little of how sessile organisms respond to physical disturbances such as displacements. Using Mytilaster minimus, a mussel that is native to the Mediterranean Sea, we tested how byssus production and oxygen uptake rates changed in response to different frequencies of disturbance events (10-60 events h^-1). Mussels increased oxygen uptake rates but not byssus production with increasing disturbance frequencies (50-60 events h^-1). Our results show that sub-lethal, physical disturbances can cause increased physiological rates in mussels if disturbances repeat rapidly. Therefore, sub-lethal, physical disturbances can have negative consequences for benthic organisms even if they do not cause immediate damage or mortality.

Beta diversity of stream fish communities along anthropogenic environmental gradients at multiple spatial scales

Despite the importance of assessing beta diversity to understand the effects of human modifications on biological communities, there are almost no studies that properly addressed how beta diversity varies along anthropogenic gradients. We developed an algorithm to calculate beta diversity among a set of sites included in a moving window along any given environmental gradient. This allowed us to assess beta diversity among sites with similar conditions in terms of human modifications (e.g., land use or instream degradation). We investigated beta diversity using stream fish community data and indicators of human modification quantified at four spatial scales (whole catchment, riparian, local, and instream). Variation in beta diversity was dependent on the scale of human modifications (catchment, riparian, local, instream, and all four scales combined) and on the type of diversity considered (taxonomic or functional). We also found evidence for non-linear responses of both taxonomic and functional beta diversity to human-induced environmental alterations. Therefore, the response of beta diversity was more complex than expected, as it depended on the scale used to quantify human impact and exhibited opposite responses depending on the location along the environmental impact gradient and on whether the response was taxonomic or functional diversity. Anthropogenic modifications can introduce unexpected variability among stream communities, which means that low beta diversity may not necessarily indicate a degraded environmental condition and high beta diversity may not always indicate a reference environmental condition. This has implications for how we should consider beta diversity in environmental assessments.

Leaf biochemical adjustments in two Mediterranean resprouter species facing enhanced UV levels and reduced water availability before and after aerial biomass removal

Effects of supplemented UV radiation and diminished water supply on the leaf concentrations of phenols and antioxidants of two Mediterranean resprouter species, Arbutus unedo and Quercus suber, were assessed before and after entire aerial biomass removal. Potted seedlings of both species were grown outdoors for 8 months with enhanced UV-A + UV-B, enhanced UV-A or ambient UV, in combination with two watering conditions (field capacity or watering reduction). After this period, all aerial biomass was removed and new shoots (resprouts) developed for a further 8 months under the two treatments. In general, the investment in leaf phenols was substantially greater in A. unedo than in Q. suber, while Q. suber allocated more resources to non-phenolic antioxidants (ascorbate and glutathione). In response to enhanced UV-B radiation, Q. suber leaves rose their UV-screening capacity mainly via accumulation of kaempferols, accompanied by an increased concentration of rutins, being these effects exacerbated under low-watering conditions. Conversely, A. unedo leaves responded to UV-B radiation reinforcing the antioxidant machinery by increasing the overall amount of flavonols (especially quercetins) in seedlings, and of ascorbate and glutathione, along with catalase activity, in resprouts. Nevertheless, UV effects on the amount/activity of non-phenolic antioxidants of A. unedo resprouts were modulated by water supply. Indeed, the highest concentration of glutathione was found under the combination of enhanced UV-B radiation and reduced watering, suggesting an enlargement of the antioxidant response in A. unedo resprouts. Different biochemical responses to enhanced UV and drier conditions in seedlings and resprouts of these two species might modulate their competitive interactions in the near future.

Linking ecosystem function and hydrologic regime to inform restoration of a forested peatland

Drainage is a globally common disturbance in forested peatlands that impacts peat soils, forest communities, and associated ecosystem functions, calling for informed hydrologic restoration strategies. The Great Dismal Swamp (GDS), located in Virginia and North Carolina, U.S.A., has been altered since colonial times, particularly by extensive ditch networks installed to lower water levels and facilitate timber harvests. Consequently, peat decomposition rates have accelerated, and red maple has become the dominant tree species, reducing the historical mosaic of bald cypress, Atlantic white-cedar, and pocosin stands. Recent repair and installation of water control structures aim to control drainage and, in doing so, enhance forest community composition and preserve peat depths. To help inform these actions, we established five transects of 15 plots each (75 plots total) along a hydrologic gradient where we measured continuous water levels and ecosystem attributes, including peat depths, microtopography, and forest composition and structure. We found significant differences among transects, with wetter sites having thicker peat, lower red maple importance, greater tree density, and higher overall stand richness. Plot-level analyses comported with these trends, clearly grouping plots by transects (via nonmetric multidimensional scaling) and resulting in significant correlations between specific hydrologic metrics and ecosystem attributes. Our findings highlight hydrologic controls on soil carbon storage, forest structure, and maple dominance, with implications for large-scale hydrologic restoration at GDS and in other degraded forested peatlands more broadly.

Topography controls post-fire changes in soil properties in a Chinese boreal forest

Both topography and the occurrence of wildfire can strongly affect soil properties in forest successions. Although numerous studies have examined the effects of fire and topography, few have explored their shifting relative importance with time since fire. We measured physical, chemical, and biological soil properties in two topographic positions (north-facing and south-facing) in a Chinese boreal forest along a gradient of fire history. In the control site, topography strongly influenced soil properties, with north-facing slopes having higher soil moisture (SM), depth of organic matter layer (OML), total carbon and inorganic N concentrations, and lower pH, dissolved organic carbon (DOC) and nitrogen (DON). In the 1-year-post-fire site, wildfire erased topographic effects on soil variables, and greater changes in soil properties occurred on the north-facing slopes. The wildfire significantly increased soil pH, DON, ammonium and nitrate, and decreased SM, OML, DOC and microbial biomass, while no significant differences in soil properties appeared between high- and low-severity plots. In the 11-year-post-fire site, most soil properties were similar to the control except for microbial biomass, OML and DOC; topography again became a significant factor in explaining variations in soil properties. Fire severity was highly correlated only with soil pH in the 1-year-post-fire site, whereas topographic factors were always correlated with some soil properties in the three sites. In the 1-year-post-fire site, wildfire explained almost five times more variance than topography for most soil properties, whereas in the 11-year-post-fire site, the proportion of variance explained by topography increased and even surpassed that by wildfire. These results demonstrate that the resilience of Larix gmelinii forest soils might be controlled by wildfires in the short term but by topography in the long term.

Impact of tourism disturbance on forest vegetation in Wutai Mountain, China

Tourism is one of the primary disturbances to forest vegetation worldwide. To understand the impacts of tourism, it is important to first identify the ecological characteristics of damaged forest vegetation. Here, we investigate different ecological patterns in disturbed and undisturbed regions of Wutai Mountain, China. Comparisons between disturbed and undisturbed forest community were conducted using two-way indicator species analysis (TWINSPAN) and detrended correspondence analysis (DCA). The TWINSPAN analysis identified 13 association types from 76 total samples collected. The DCA correlation analysis showed that forest community was significantly affected by physiographical factors (such as elevation and slope) in the undisturbed region; however, that was correlated with not only physiographical factors but also intensity of tourism, and the effect of tourism disturbance was stronger than that of physiographical factors in the disturbed regions. In addition, some indicator species were discovered. Our findings provide valuable information about conservation and management of sustainable tourism in the region.

Decadal post-fire succession of soil invertebrate communities is dependent on the soil surface properties in a northern temperate forest

Although fires are common disturbances in North American forests, the extent to which soil invertebrate assemblages recover from burning remains unclear. Here, we examine long-term (14- to 101-yr) recoveries of soil invertebrate communities from common cut and burn treatments conducted at 6 to 26-yr intervals since 1911 in a deciduous forest in the upper Great Lakes region (USA). We characterize soil surface macro-invertebrate communities during both fall and spring across a long-term, experimental fire chronosequence to characterize invertebrate community recovery at decadal time-scales and community changes between seasons. We posited that changes in invertebrate community structure might, in turn, impact decomposition process. We sampled active organisms at the soil surface using pitfall traps. We described understory vegetation, measured soil properties, and conducted a 4-year litter bag study with big-toothed aspen leaves (Populus grandidentata). Invertebrate community responses followed a habitat accommodation model of succession showing that invertebrate succession is dependent on the soil surface properties. The fall and spring measures revealed that the densities of active invertebrates were highest 101 years after fire. For a given pair of stands, a pattern of sharing higher percentage of taxa was denoted when stands were of similar age. Some species such as the beetle Stelidota octomaculata appeared to be indicator of the chronosequence succession stage because it tracks the successional increase of Quercus and acorn production at the study site. We also found a significant positive correlation between leaf decomposition of soil macrofaunal accessible leaves and millipedes density across the chronosequence. We show that vegetation cover changes and related shifts in habitat structure occurring during post-fire succession are important in shaping communities assemblages. This finding highlights the importance of simultaneously considering abiotic-biotic factors together with above- and belowground measurements to better characterize controls on successional community dynamics after disturbance.

The accuracy of rapid treadmill-belt movements as a means to deliver standing postural perturbations

Treadmill-induced postural perturbations are a promising tool in assessing and reducing the risk of falls. We evaluated the accuracy with which two treadmills (Simbex ActiveStep^® and an AMTI instrumented treadmill) achieved commanded displacements, peak velocities, and average initial accelerations. To do so, we included a range of perturbation magnitudes (20, 30, and 40 cm displacements) applied in unweighted and weighted (body mass = 46-84 kg) conditions. Across treadmills and perturbation magnitudes, absolute errors in displacement (< 0.5 cm) and peak velocity (< 4 cm/s) were small (relative error < 5%). Between-treadmill differences in displacement and peak velocity were marginal (< 3%), regardless of the perturbation magnitude and participant body mass. Observed accelerations were more than 5% smaller than commanded values. The front, but not back, AMTI belt demonstrated less acceleration accuracy than the ActiveStep^® (≈ 5% difference). In summary, both treadmills demonstrated a reasonable, consistent level of accuracy in delivering postural perturbations.

Environmental correlates of food-chain length, mean trophic level and trophic level variance in invaded riverine fish assemblages

Examining how the trophic structure of biotic assemblages is affected by human impacts, such as habitat degradation and the introduction of alien species, is important for understanding the consequences of such impacts on ecosystem functioning. We used general linear mixed models and hierarchical partitioning analyses of variance to examine for the first time the applicability of three hypotheses (ecosystem-size, productivity and disturbance) for explaining food-chain length (FCL) in invaded fish assemblages. We used Fishbase trophic level (TL) estimates for 16 native and 18 alien fish species in an extensive riverine system in north-eastern Spain (99,700 km², 15 catchments, 530 sites). The FCL of assemblages ranged from 2.7 to 4.42. Ecosystem size-related variables (Strahler stream order, physical habitat diversity) and human-disturbance (conductivity) made the largest contribution to the explained variance in the FCL model after accounting for spatial confounding factors and collinearity among predictors. Within-assemblage TL also was positively associated with Strahler stream order, suggesting that large rivers have the highest trophic diversity. High conductivity was negatively associated with FCL, as did with the mean TL of fish assemblages. However, an inverse association was found between mean TL and Strahler stream order, possibly because the presence of fish species of high TL may be offset by larger numbers of alien species of lower TL in large rivers. Given that there may be trophic replacements among native and alien species, this inference needs to be addressed with detailed trophic studies. However, reducing water conductivity by improved wastewater treatment and better agricultural practices probably would help to conserve the fish species on the apices of aquatic food-webs.

Persisting responses of salt marsh fungal communities to the Deepwater Horizon oil spill

The plant microbiome, composed of diverse interacting microorganisms, is thought to undergird host integrity and well-being. Though it is well understood that environmental perturbations like oil pollution can alter the diversity and composition of microbiomes, remarkably little is known about how disturbance alters plant-fungal associations. Using Next-Generation sequencing of the 18S rDNA internal transcribed spacer (ITS1) region, we examined outcomes of enduring oil exposure on aboveground leaf and belowground endophytic root and rhizosphere fungal communities of Spartina alterniflora, a highly valued ecosystem engineer in southeastern Louisiana marshes affected by the 2010 Deepwater Horizon accident. We found that aboveground foliar fungal communities exhibited site-dependent compositional turnover with consequent loss in diversity according to oiling history. Rhizosphere soil communities also exhibited shifts in community composition associated with oiling history, whereas root endophytic communities did not. Oiling did not increase or decrease similarities among aboveground and belowground communities within an individual host, indicating that host plant characteristics exert stronger control than external factors on fungal community composition. These results show that fungal community responses to oiling vary within tissues of the same host plant, and that differences in the local environment, or alternatively, site-specific differences in residual oil constrain the magnitude of exposure responses. Our study offers novel perspectives on how environmental contaminants and perturbations can influence plant microbiomes, highlighting the importance of assessing long-term ecological outcomes of oil pollution to better understand how shifts in microbial communities influence plant performance and ecosystem function. Our findings are relevant to coastal management programs tasked with responding to oil spills and increasing pressures arising from intensifying development and climate change. Understanding how modification of plant-microbiome associations influences plant performance, particularly of ecosystem engineers like S. alterniflora, can help guide efforts to protect and restore at-risk coastal ecosystems.

Linking conservation implications of modified disturbance regimes, plant communities, plant associations, and arthropod communities

Modifications to disturbance regimes have landscape-level effects on plant communities and have the potential to influence organisms at multiple trophic levels. We examined differences in the arthropod community across a gradient of oak/hickory dominance, a plant community maintained by disturbance such as periodic fires and extensive land clearing. In southern Illinois, we used patches of forest that varied in tree dominance ranging from 94 to 0% oak/hickory composition dependent on prior land usage that occurred > 50 years ago at minimum, to test two predictions: (1) oak (Quercus) and hickory (Carya) species contain more arthropod biomass and diversity than mesic tree species [e.g., American beech (Fagus grandifolia) and maples (Acer spp.)] and (2) due to plant associations, arthropod communities are more diverse and abundant on host trees within oak/hickory stands than non-oak/hickory stands. Our results were consistent with the prediction that arthropod biomass, guild Shannon diversity, and guild richness are higher on oaks, hickories and tulip tree (Liriodendron tulipifera) than beech and maples. We also found support for the prediction that due to plant associations, % non-oak/hickory stand composition negatively influenced arthropod guild Shannon diversity and guild richness on host trees, including maples and beech. These results are the first to demonstrate that modified disturbance regimes can influence multiple trophic levels both directly due to species-specific variation in susceptibility of plants to herbivory and indirectly through effects of plant associations. This result is concerning as modified disturbance regimes are influencing large-scale plant community composition among biomes worldwide.

Temperature and hydrologic alteration predict the spread of invasive Largemouth Bass (Micropterus salmoides)

The successful establishment of an aquatic invasive alien species can be mediated by a suite of environmental factors, including climate and anthropogenic disturbance. Dams and reservoirs are thought to promote freshwater fish invasion success through hydrological alterations but the evidence for their role in the global invasion of Largemouth Bass (Micropterus salmoides) on a landscape scale is limited. Here, we examine the distribution of Largemouth Bass, one of the most widely introduced fish in the world, from the Iberian Peninsula using species distribution models (SDMs), including an ensemble forecast. We used these models to test the role of twelve environmental predictors expected to influence the distribution of Largemouth Bass, including the reservoir storage capacity at local and upstream reaches. We found that the predictive accuracy, based on AUC criteria, of the ensemble model was higher than any of the six individual SDMs for Largemouth Bass. The most influential predictor of bass distribution included in our model of the Iberian Peninsula was temperature, where warmer temperatures were generally associated with bass presence, and cooler temperatures with absence. In addition to warmer temperatures, increasing storage of local and upstream reservoirs increased predicted presence, suggesting an important role of reservoirs in mediating the invasive success of this fish. Our results indicate that although natural climatic factors may be crucial in the successful invasion of Largemouth Bass, hydrological alteration (e.g., regulated flow regimes and lentic habitats associated with dams and reservoirs) may be important. Understanding the drivers promoting the establishment of this global invader will be important in identifying areas at risk and in developing future efforts to control its spread, especially when those drivers are ongoing anthropogenic disturbances such as the construction and operation of dams and reservoirs.

Contributions of pre- versus post-settlement processes to fluctuating abundance of crown-of-thorns starfishes (Acanthaster spp.)

Numerous hypotheses have been put forward to account for population outbreaks of crown-of-thorns starfishes (CoTS, Acanthaster spp.), which place specific importance on either pre- or post-settlement mechanisms. The purpose of this review is to specifically assess the contributions of pre- versus post-settlement processes in the population dynamics of CoTS. Given the immense reproductive potential of CoTS (>100 million eggs per female), persistent high densities would appear inevitable unless there were significant constraints on larval development, settlement success, and/or early post-settlement growth and survival. In terms of population constraints, pre- and post-settlement processes are both important and have additive effects to suppress densities of juvenile and adult CoTS within reef ecosystems. It is difficult, however, to assess the relative contributions of pre- versus post-settlement processes to population outbreaks, especially given limited data on settlement rates, as well as early post-settlement growth and mortality. Prioritising this research is important to resolve potential effects of anthropogenic activities (e.g., fishing) and habitat degradation on changing population dynamics of CoTS, and will also improve management effectiveness.

The palaeoenvironment of the Upper Cretaceous (Cenomanian-Turonian) portion of the Winton Formation, Queensland, Australia

The Winton Formation is increasingly recognised as an important source of information about the Cretaceous of Australia, and, more broadly, the palaeobiogeographic history of eastern Gondwana. With more precise dating and stratigraphic controls starting to provide temporal context to the geological and palaeontological understanding of this formation, it is timely to reassess the palaeoenvironment in which it was deposited. This new understanding helps to further differentiate the upper, most-studied portion of the formation (Cenomanian-Turonian) from the lower portions (Albian-Cenomanian), allowing a coherent picture of the ecosystem to emerge. Temperatures during the deposition of the Upper Cretaceous portion of the Winton Formation were warm, with high, seasonal rainfall, but not as extreme as the modern monsoon. The landscape was heterogeneous, a freshwater alluvial plain bestrode by low energy, meandering rivers, minor lakes and mires. Infrequent, scouring flood events were part of a multi-year cycle of drier and wetter years. The heavily vegetated flood plains supported abundant large herbivores. This was the final infilling of the great Eromanga Basin.

Synergy between roads and disturbance favour Bromus tectorum L. invasion

Background

Global change produces pervasive negative impacts on biodiversity worldwide. Land use change and biological invasions are two of the major drivers of global change that often coexist; however, the effects of their interaction on natural habitats have been little investigated. In particular, we aimed to analyse whether the invasion of an introduced grass (Bromus tectorum; cheatgrass) along roads verges and the disturbance level in the natural surrounding habitat interact to influence the degree of B. tectorum invasion in the latter habitats in north-western Patagonia.

Methods

Along six different roads, totalling approximately 370 km, we set two 50 m × 2 m sampling plots every 5 km (73 plots in total). One plot was placed parallel to the road (on the roadside) and the other one perpendicular to it, towards the interior of the natural surrounding habitat. In each plot, we estimated the B. tectorum plant density in 1 m² subplots placed every 5 m. In the natural habitat, we registered the vegetation type (grassy steppe, shrub-steppe, shrubland, and wet-meadow) and the disturbance level (low, intermediate, and high). Disturbance level was visually categorized according to different signs of habitat degradation by anthropogenic use.

Results

B. tectorum density showed an exponential decay from roadsides towards the interior of natural habitats. The degree of B. tectorum invasion inside natural habitats was positively related to B. tectorum density on roadsides only when the disturbance level was low. Shrub-steppes, grassy steppes and shrublands showed similar mean density of B. tectorum. Wet-meadows had the lowest densities of B. tectorum. Intermediate and highly disturbed environments presented higher B. tectorum density than those areas with low disturbance.

Discussion

Our study highlights the importance of the interaction between road verges and disturbance levels on B. tectorum invasion in natural habitats surrounding roads of north-western Patagonia, particularly evidencing its significance in the invasion onset. The importance of invasion in road verges depends on disturbance level, with better conserved environments being more resistant to invasion at low levels of B. tectorum density along road verges, but more susceptible to road verges invasion at higher levels of disturbance. All the habitats except wet-meadows were invaded at a similar degree by B. tectorum, which reflects its adaptability to multiple habitat conditions. Overall, our work showed that synergies among global change drivers impact native environments favouring the invasion of B. tectorum.

Intermediate Levels of Antibiotics May Increase Diversity of Colony Size Phenotype in Bacteria

Antibiotics select for resistant bacteria whose existence and emergence is more likely in populations with high phenotypic and genetic diversity. Identifying the mechanisms that generate this diversity can thus have clinical consequences for drug-resistant pathogens. We show here that intermediate levels of antibiotics are associated with higher levels of phenotypic diversity in size of colony forming units (cfus), within a single bacterial population. We examine experimentally thousands of populations of bacteria subjected to different disturbance levels that are created by varying antibiotic concentrations. Based on colony sizes, we find that intermediate levels of antibiotics always result in the highest phenotypic variation of this trait. This result is supported across bacterial densities and in the presence of three different antibiotics with two different mechanisms of action. Our results suggest intermediate levels of a stressor (as opposed to very low or very high levels) could affect the phenotypic diversity of a population, at least with regards to the single trait measured here. While this study is limited to a single phenotypic trait within a single species, the results suggest examining phenotypic and genetic variation created by disturbances and stressors could be a promising way to understand and limit variation in pathogens.

Context-dependent effects of fire and browsing on woody alien invasion in mountain ecosystems

Anthropogenic activities have increased disturbances and alien woody invasion in mountain ecosystems worldwide. Whether disturbances promote or counteract upward movement of woody aliens is poorly understood. We assessed if the most successful woody invader of low mountains of central Argentina (Gleditsia triacanthos) might expand its elevational distribution in response to the principal disturbances of these ecosystems (fire and livestock browsing) across increasing climatic severity. We assessed seedling emergence, growth and mycorrhizal colonization on sown plots distributed in burned and unburned sites, with and without browsing at the lower and upper elevation belts (i.e. 1000 and 2400 m a.s.l.). Additionally, several abiotic variables were measured to relate their influence on the seedling establishment. Disturbances reduced seedling emergence at both elevations. Burned conditions increased seedling growth and arbuscular colonization only in the lower belt. Seedling success (total seedling biomass per plot) was not modified by disturbances at the upper elevation, but was reduced by browsing and enhanced by fire in the lower elevation. The overall reduction in seedling emergence and growth in the upper elevation despite the higher soil nutrient content places climate as the strongest regulator of G. triacanthos seedling establishment. Accordingly, climate rather than disturbances would be the main limiting factor of upward expansion of this woody alien. Our findings differ from general patterns described for mountain invasion by herbaceous species, highlighting that mountain invasibility is highly growth-form dependent, and that upper range expansion by woody aliens interacting with multiple disturbances should be assessed worldwide.

Distribution and ecological segregation on regional and microgeographic scales of the diploid Centaurea aspera L., the tetraploid C. seridis L., and their triploid hybrids (Compositae)

Although polyploidy is considered a ubiquitous process in plants, the establishment of new polyploid species may be hindered by ecological competition with parental diploid taxa. In such cases, the adaptive processes that result in the ecological divergence of diploids and polyploids can lead to their co-existence. In contrast, non-adaptive processes can lead to the co-existence of diploids and polyploids or to differentiated distributions, particularly when the minority cytotype disadvantage effect comes into play. Although large-scale studies of cytotype distributions have been widely conducted, the segregation of sympatric cytotypes on fine scales has been poorly studied. We analysed the spatial distribution and ecological requirements of the tetraploid Centaurea seridis and the diploid Centaurea aspera in east Spain on a large scale, and also microspatially in contact zones where both species hybridise and give rise to sterile triploid hybrids. On the fine scale, the position of each Centaurea individual was recorded along with soil parameters, accompanying species cover and plant richness. On the east Spanish coast, a slight latitudinal gradient was found. Tetraploid C. seridis individuals were located northerly and diploid C. aspera individuals southerly. Tetraploids were found only in the habitats with strong anthropogenic disturbance. In disturbed locations with well-developed semi-fixed or fixed dunes, diploids and tetraploids could co-exist and hybridise. However, on a fine scale, although taxa were spatially segregated in contact zones, they were not ecologically differentiated. This finding suggests the existence of non-adaptive processes that have led to their co-existence. Triploid hybrids were closer to diploid allogamous mothers (C. aspera) than to tetraploid autogamous fathers (C. seridis). This may result in a better ability to compete for space in the tetraploid minor cytotype, which might facilitate its long-term persistence.