Changes In Assemblages Research Articles

Changes in the prokaryotic diversity in response to hydrochemical variations during an acid mine drainage passive treatment

Acid mine drainage (AMD) causes major environmental problems and consequently, several treatments are proposed, favoring the passive systems because of their many advantages. The main goal of these procedures is the neutralization and removal of potentially toxic elements (PTE), yet little is known about the changes in the microbial assemblages in response to the hydrochemical variations during the treatments. Therefore, the main objective of this research was to determine the changes in the diversity and structure of the prokaryotic assemblages in a hybrid abiotic and biological (wetland) passive treatment system. The 16S rRNA gene survey showed that the AMD coming from the mine (pH 2.6) was mainly composed of acidophilic genera such as Acidithiobacillus, Leptospirillum, Ferritrophicum, and Cuniculiplasma (up to 76 % relative abundance). In the abiotic treatment, Acidiphilium was dominant in the sections with limestone filters (pH 2.2–4.8), followed by Limnobacter in the subsequent dolomite/limestone and phosphoric rock filters (pH 5.2–5.8). In these abiotic passive treatment sections, the microbial assemblage showed a limited diversity and richness. However, when the treated AMD reached the two final wetlands (pH ~6.8), the microbial diversity and richness increased, suggesting that further bioattenuation mechanisms might be occurring. Limnobacter and Novosphingobium were the main bacterial genera in the water samples of the wetland sections (Arundo donax). These changes in the composition of the microbial assemblages were highly correlated with the pH and Eh values during the treatment (p-value <0.001); however, the concentration of metal(loid)s such as Al, Cd, Fe, Mn, Ni, and Zn were also significantly related (p-value <0.05). In conclusion, the studied passive AMD treatment system enhanced the chemical quality of the treated AMD, showing high removal efficiencies for Al and Fe (> 99 %), and increasing the microbial diversity and richness in the effluent.

Hellenistic and Roman Gerasa: The Archaeology and History of a Decapolis City. Edited by Achim Lichtenberger and Rubina Raja. Turnhout: Brepols 2020. Pp. xviii + 390. €110. ISBN 978-2-503-58504-8 (paper).

<i>Hellenistic and Roman Gerasa: The Archaeology and History of a Decapolis City</i>. Edited by Achim Lichtenberger and Rubina Raja. Turnhout: Brepols 2020. Pp. xviii + 390. €110. ISBN 978-2-503-58504-8 (paper).

Integration of ABC curve, three dimensions of alpha diversity indices, and spatial patterns of fish assemblages into the health assessment of the Chishui River basin, China.

Index of biotic integrity (IBI) based on fish has been applied globally. However, few have considered that fish assemblages change among different aggregate ecoregions when conducted their health assessment. Indeed, some comprehensive indices, such as functional and phylogenetic diversity indices and ABC curve, can be used to identify aspects that are not captured by traditional metrics. Consequently, we try to integrate comprehensive indices and spatial patterns of fish assemblages to develop IBI systems and then verified their effectiveness and accuracy for assessing the environmental health of the Chishui River basin. The comprehensive disturbance index (CDI), based on 11 water quality parameters and 4 human land use, was set to distinguish reference sites and impaired sites. According to the spatial patterns of fish assemblages, the 40 sites were finally divided into 2 aggregate ecoregions, include wadeable streams and nonwadeable rivers. 97 candidate metrics were selected to develop our IBI systems based on the systematic screening method. The result also showed that our IBI systems performed well in discriminating anthropogenic disturbances at both aggregate ecoregions, which suggests that our systems could provide a reliable evaluation. The mean IBI score of the Chishui River basin was 72.09 ± 16.58, and was classified as good status. However, S1 (Chishuiyuan Town), Baisha River, Tongzi River, and Xishui River were disturbed by various human activities. We conclude that the spatial patterns of fish assemblages should be combined with more comprehensive indices to assess river health. On the other hand, we do believe that the process of developing and verifying our IBI systems could be regarded as a reference for biomonitoring in more mountain river systems.

Changes in benthic macro-invertebrate assemblages in an estuary in southern Thailand after invasion by non-native bivalves &lt;i&gt;Mytilopsis sallei&lt;/i&gt; and &lt;i&gt;Mytella strigata&lt;/i&gt;

Mytilopsis sallei (Récluz, 1849), an invasive bivalve, has been established for more than two decades in Pawong Canal, which is a part of the largest lagoon system in Thailand. A recent survey in 2019 revealed the presence in the canal of another invasive species, the mytilid mussel Mytella strigata (Hanley, 1843). Both species are byssally attached bivalves that can change soft bottoms into hard substrata composed of bivalve shells, with consequent effects on benthic communities. Data of benthic macro-invertebrate species collected 25 years ago, before the arrival of both invasive species, were compared with data from a recent survey. Although 28 different species were observed in each study, only five were present in both. However, there is no significant change in the diversity and evenness of this benthic community. A few species of hard-bottom dwellers appeared in the canal after invasion while some soft-sediment inhabitants were absent. Given that the full dataset from the previous study was not available and a long-term series of observations was not made, it is difficult to distinguish the effects of bivalve invasion from the effects of physical change in the environment. However, we documented the current condition of this complex estuarine ecosystem and discussed some possible effects of non-native bivalve invasion on the local benthic macroinvertebrate assemblages.

Long-term changes in the macrobenthic assemblages at a harbour sediment disposal site in the southern North Sea

This study focussed on the long-term, sediment-driven changes of macrobenthic assemblages in dredged harbour sediment from Rotterdam harbour disposed of in excavated sand extraction pits off the Dutch coast. Macrobenthic species and sediment grain size composition were studied in samples from two disposal sites and the surrounding environment over ten years after the cessation of disposal activities.There was a strong association between the sediment granulometry and the benthic assemblage composition. Shortly after the last discharge, the top layer of the sediments in the pits contained 20%–60% mud (particles <63 μm) and was colonised by benthic species typical for these sediments. The pit sediments and benthic assemblages contrasted strongly with the surrounding medium-coarse sediment, extremely low in mud (<0.01%). Over eight to ten years, the top layers of the disposal sites became significantly less muddy (ca. 5%–15% mud), and the benthic assemblages changed over this period from mud-favouring species dominated by annelids to species preferring fine sand with relatively low mud percentages dominated by molluscs. The two different disposal sites converged in sediment composition and benthic assemblages over the ten years of monitoring. The contrast with the medium-coarse sediments with very low mud percentages remained even after this period. The use of sand extraction pits as disposal sites for dredged harbour sediments may be seen as an economically sound beneficial use option in dredged material management, albeit with long-term ecological effects.

Ductile Shearing and Focussed Rejuvenation: Records of High-P (eo-)Alpine Metamorphism in the Variscan Lower Crust (Serre Massif, Calabria—Southern Italy)

In the present study, we unveil the real significance of mylonitic reworking of the polymetamorphic crystalline basement in the Serre Massif of Calabria (Southern Italy). We use a multidisciplinary approach to comprehend the structural, microstructural and petrologic changes that occurred along a, so far, not much considered shear zone affecting the Variscan lower crustal rocks. It was never before studied in detail, although some late Cretaceous ages were reported for these mylonites, suggesting that this shear zone is of prime importance. Our observations reveal now that the formation of the new structural fabric within the shear zone was accompanied by changes in mineral assemblages, in a dominant compressive tectonic regime. During this tectono-metamorphic event, high-P mylonitic mineral assemblages were stabilized, consisting of chloritoid, kyanite, staurolite, garnet and paragonite, whereas plagioclase became unstable. Average peak P–T conditions of 1.26–1.1 GPa and 572–626 °C were obtained using THERMOCALC software. These data question (i) that the Serre Massif represents an undisturbed continuous section of the Variscan crust, as generally suggested in the literature, and (ii) highlight the role of (eo-)Alpine high-P tectonics in the Serre Massif, recorded within mylonite zones, where the Variscan basement was completely rejuvenated.

Taxonomic, functional, and phylogenetic diversity of lizard assemblages across habitats and seasons in a Brazilian Cerrado area

AbstractOne of the core issues in community ecology is the understanding of mechanisms that determine community structure. In this study, we examine how two structurally distinct habitats (campo sujo – a grassy savanna habitat with low shrubby cover – and seasonal semi‐deciduous forest) and distinct hydrological seasons (dry and rainy) influence the taxonomic, functional and phylogenetic diversity of lizard assemblages in a savanna area in the Brazilian Cerrado. We used pitfall traps to sample lizards from May 2000 to February 2002. To quantify spatio‐temporal changes in the lizard assemblages, we used parameters of taxonomic (species richness – SR), functional (functional diversity – SES.FD, functional redundancy – FR and functional dispersion – FDis), and phylogenetic diversity (phylogenetic species richness – PSR and phylogenetic species variability – PSV). We also estimate functional and phylogenetic structure of the assemblages in each habitat during dry and rainy seasons. We recorded 182 lizards distributed among 14 species. Species composition differed among habitat types, but did not differ seasonally within habitats. SES.FD, FDis, and FR also differed among habitat types but not among seasons, with SES.FD and FDis being greater in seasonal semi‐deciduous forest, while FR was greater in campo sujo. SR, PSR, and PSV were not influenced by the factors analysed. The lizard assemblage of campo sujo was functionally clustered in the dry season and phylogenetically clustered in the rainy season. These results demonstrate that differences among habitat types and seasons are important in shaping the taxonomic, functional, phylogenetic diversity and structure of lizard assemblages in the savanna area studied. Our study also demonstrates the importance of using different measures of diversity to obtain a better understanding on the mechanisms that influence the lizard assemblages in a highly seasonal environment.

Hydropower development impacts on the benthic macroinvertebrates in the Indian Himalayan region

ABSTRACT Two operational hydroelectric projects have modified the Alaknanda river ecosystem. The paper reports the impact of these projects on the benthic macroinvertebrate assemblages and their functional feeding groups. The characteristics considered were richness, density, assemblages and functional feeding groups (FFG). The taxon richness decreased from S1 to S2 but increased from S3 to S5 and then decreased again at S6. No fauna was recorded at S7 and S8. Density decreased from S1 to S2 but increased substantially at S3. The trend decreased from S4 to S6. Longitudinal trends revealed changes in macroinvertebrate assemblages. In terms of dominants, Heptageniidae dominated the assemblages at all stations except S4 and S6. Collector-gatherers prevailed among the functional feeding groups indicating a heterotrophic state all along the river.

Pervasive changes in algal indicators since pre-industrial times: A paleolimnological study of changes in primary production and diatom assemblages from ~200 Canadian lakes

Anthropogenic stressors affect lakes around the world, ranging in scale from catchment-specific pollutants to the global impacts of climate change. Canada has a large number and diversity of lakes, yet it is not well understood how, where, and when human impacts have affected these lakes at a national scale. The NSERC Canadian Lake Pulse Network sought to create the first nationwide database of Canadian lake health, undertaking a multi-year survey of 664 lakes spanning 12 ecozones across Canada. A key objective of the network is to determine where, by how much, and why have Canadian lakes changed during the Anthropocene. To address this objective, we compared sedimentary chlorophyll a and diatoms from modern and pre-industrial sediment intervals of ~200 lakes. The lakes spanned a range of sizes, ecozones, and degrees of within-catchment land use change. We inferred the quantity of chlorophyll a, its isomers and main diagenetic products using visible reflectance spectroscopy. We found widespread increases in primary production since pre-industrial times. Primary production increased, on average, across all ecozones, human impact classes, and stratification classes. Likewise, an increase in planktonic diatom taxa over time was detected in the majority of sampled lakes, likely due to recent climate warming. However, regional factors (ecozones) explained the most variation in modern diatom species assemblages as well as their temporal turnover. Furthermore, lakes with high human impact (i.e., higher weighted proportions of human land use in the catchment) exhibited greater taxonomic turnover than lakes with a low human impact class. The greatest diatom turnover was found in the agriculture-rich Prairies and the lowest in the sparsely populated Boreal Shield and Taiga Cordillera ecozones. Overall, our study highlights that drivers operating at different geographic scales (i.e., climatic and land-use changes) have led to significant alterations in algal indicators since pre-industrial times across the country.

Climate impacts alter fisheries productivity and turnover on coral reefs

Alteration of benthic reef habitat after coral bleaching and mortality induces changes in fish assemblages, with implications for fisheries. Our understanding of climate impacts to coral reef fisheries is largely based on fish abundance and biomass. The rates at which biomass is produced and replenished (productivity and turnover) are also important to sustaining fisheries, yet the responses of these metrics following bleaching are largely unknown. Here, we examine changes in fish productivity and turnover after mass coral bleaching events in Seychelles, on reefs that were recovering to coral-dominated habitats and those that shifted to macroalgae-dominated regimes. Productivity of fish assemblages increased on all recovering reefs, particularly on fished reefs resulting in levels similar to protected reefs 19 years after bleaching. Herbivore-detritivores, such as scraping and excavating parrotfish, appeared to drive biomass production through increased abundance on recovering reefs. Productivity on regime-shifted reefs remained stable at 1994 levels in fished areas, with increases observed on protected reefs. Large increases in browser productivity (particularly on protected reefs), combined with increases for invertivores, maintained post-bleaching productivity on macroalgal reefs. For all diet groups, net turnover was generally higher on fished regime-shifted reefs than on recovering reefs, suggesting fish biomass is more readily replenished on macroalgal reefs. Reef structural complexity was a positive predictor of productivity for all diet groups. These findings indicate that post-bleaching reef fish productivity is strongly influenced by benthic recovery trajectories, and demonstrates the importance of herbivore and invertivore species in sustaining small-scale inshore fisheries following climatic disturbances.

Phylogeographic Patterns of Haemoproteid Assemblages of Selected Avian Hosts: Ecological and Evolutionary Implications.

Background: While the dynamics of disease emergence is driven by host–parasite interactions, the structure and dynamics of these interactions are still poorly understood. Here we study the phylogenetic and morphological clustering of haemosporidian parasite lineages in a local avian host community. Subsequently, we examine geographical patterns of parasite assemblages in selected avian hosts breeding in Europe. Methods: We conduct phylogenetic and haplotype network analyses of Haemoproteus (Parahaemoproteus) lineages based on a short and an extended cytochrome b barcode region. Ordination analyses are used to examine changes in parasite assemblages with respect to climate type and geography. Results: We reveal relatively low phylogenetic clustering of haemoproteid lineages in a local avian host community and identify a potentially new Haemoproteus morphospecies. Further, we find that climate is effectively capturing geographical changes in parasite assemblages in selected widespread avian hosts. Moreover, parasite assemblages are found to vary distinctly across the host’s breeding range, even within a single avian host. Conclusions: This study suggests that a few keystone hosts can be important for the local phylogenetic and morphological clustering of haemoproteid parasites. Host spatio-temporal dynamics, both for partially and long-distance migratory birds, appear to explain geographical variation in haemoproteid parasite assemblages. This study also gives support to the idea that climate variation in terms of rainfall seasonality can be linked to the propensity for host switching in haemosporidians.

Reef larval recruitment in response to seascape dynamics in the SW Atlantic

Advances in satellite observation have improved our capacity to track changes in the ocean with numerous ecological and conservation applications, which are yet under-explored for coastal ecology. In this study, we assessed the spatio-temporal dynamics in invertebrate larval recruitment and the Seascape Pelagic Habitat Classification, a satellite remote-sensing product developed by the Marine Biodiversity Observation Network (MBON) and delivered by the US National Oceanic and Atmospheric Administration to monitor biodiversity globally. Our ultimate goal was to identify and predict changes in coastal benthic assemblages at tropical reefs in the SW Atlantic based on integrated pelagic conditions, testing the use of MBON Seascape categorization. Our results revealed that the pelagic Seascapes correlated with monthly and seasonal variations in recruitment rates and assemblage composition. Recruitment was strongly influenced by subtropical Seascapes and was reduced by the presence of warm waters with high-nutrient contents and phytoplankton blooms, which are likely to affect reef communities in the long term. Recruitment modeling indicates that Seascapes may be more efficient than sea surface temperature in predicting benthic larval dynamics. Based on historical Seascape patterns, we identified seven events that may have impacted benthic recruitment in this region during the last decades. These findings provide new insights into the application of novel satellite remote-sensing Seascape categorizations in benthic ecology and evidence how reef larval supply in the SW Atlantic could be impacted by recent and future ocean changes.

Changes in benthic microfossil assemblages before, during and after the early Toarcian biotic crisis in the Portland-Wight Basin (Kerr McGee 97/12-1 well, offshore southern England)

The uppermost Pliensbachian (Margaritatus Zone) - upper Toarcian (Pseudoradiosa Zone) sediments (silty and variably calcareous claystones, marlstones, silty sandstones, and sandy limestones) recovered from the Kerr McGee 97/12–1 well were deposited in the Portland-Wight Basin. The foraminiferal assemblages of these sedimentary succession are dominated by calcareous forms of the suborder Lagenina and locally Robertinina. Three main ecostratigraphic intervals have been identified, based on changes in the foraminiferal and ostracod assemblages that occurred before, during and after the sedimentation of the earliest Toarcian black, organic-rich, non-calcareous claystones. The ecostratigraphic interval I (upper Pliensbachian) is characterized by a diverse assemblage with specialist, opportunist and intermediate forms, but dominated by Lenticulina muensteri. The ostracods in this interval are dominated by Metacopina. This assemblage is interpreted to represent a phase that pre-dates the biotic crisis. The ecostratigraphic interval II, related to the deposition of the lower Toarcian black claystones, shows an abrupt increase in the opportunist form Reinholdella (91%) with very low diversity and a high abundance of specimens, mainly Reinholdella macfadyeni and R. dreheri. In this interval the ostracods Metacopina dissapear. The top of the black claystones is almost barren of foraminifera and ostracods (only two specimens recorded of Trochammina eoparva). This second interval represents the biotic crisis phase related to the Jenkyns Event. The ecostratigraphic interval III (upper part of the lower Toarcian through to the upper Toarcian) is characterized by an increase in the diversity and abundance of foraminifera, as well as the dominance of Lenticulina. The ostracod assemblage shows a turnover with respect to the upper Pliensbachian assemblage with dominance of Cytherocopina, Platycopina and Bairdiocopina. This assemblage is interpreted to reflect the increased availability of oxygen from deep-infaunal to epifaunal microhabitats and the return to normal conditions at the sea floor. The incidence of the global warming related to the Jenkyns Event in the biotic crisis is also considered. Ecostratigraphic fluctuations in microfossil assemblages from the Kerr McGee 97/12–1 well across the T-OAE event are comparable with those described from the Mochras Borehole (west Wales), the Lusitanian Basin (Portugal), and the Atlassic Basin (North Africa).

Testate Amoeba and Chironomid assemblages from Balma Lake (Piedmont, Italy): a multi-proxy record to identifying recent climate and environmental changes in alpine areas

Alpine lakes are well known as “environmental sentinels”, which are sensitive to anthropogenic impacts, and paleoecological studies provide useful information regarding the effects of local and global changes. In the present study we investigate, for the first time, the temporal variations in testate amoeba assemblages in relation to environmental factors and anthropogenic impacts in a high-altitude lake located in the Italian Alps (Balma Lake, Piedmont, Italy). The testate amoebae are well-suited as bioindicators and have been employed to reconstruct past climate and environmental changes from lake sediments. However, these organisms have not been thoroughly studied in alpine lakes, especially in Europe. We detected significant changes in testate amoeba assemblages along an alpine lake sedimentary profile over the last 2000 years. These changes were mainly associated with variations of trace elements, nutrients, and grain size. Moreover, five different time periods were identified and related to pluvial/drought events of the last 2000 years and to the “Late Antique Little Ice Age” (LALIA). Alpine lakes are originally fishless and fish introductions for recreational purposes could cause important changes in these ecosystems. However, the introduction of brook trout in Balma Lake during the 1970s seems to have had little influence on testate amoeba assemblages. The present work provides new insights for the evaluation of temporal changes in testate amoebae through paleoecological investigations. Similarly, the comparison of testate amoeba and chironomid proxies offered an important tool for analyzing recent climatic and environmental changes in alpine lakes (in lacustrine environments), especially for the European Alps.

Timing of Sedimentary Evolution and Transgressions in the Bohai Sea During the Last ∼200 ka: Constraints from Luminescence Dating of a Core from the Yellow River Delta

The southwestern coast of the Bohai Sea is a favorable area to study land-sea interactions and palaeoenvironmental changes. The Bohai Sea hosts vast volumes of sediment discharged from rivers of mainland China and has undergone large-scale sea-level fluctuations during the Quaternary. Three transgressions have been previously determined for the Bohai Sea since the late Pleistocene. However, the timings of the two earlier transgressions are still unclear. Here we present chronological, micropalaeontological, and sedimentological data for an 80-m-long sediment core recovered from the modern Yellow River delta. The changes in grain size and foraminiferal assemblages suggest the occurrence of three marine sedimentary units, M-3, M-2, and M-1, that represent transgressions of the Bohai Sea. We applied optically stimulated luminescence dating using both quartz and feldspar minerals on 15 samples obtained from core YRD-1401 and eight radiocarbon ages using fragments of microfossils shells and organic carbon. Our quartz optically stimulated luminescence ages for M-2 (ca. 60 ka), are consistent with K-feldspar post-infrared stimulated luminescence ages, suggesting that M-2 on the southwestern coast of the Bohai Sea was deposited during early MIS 3. The sea level of the Bohai Sea during early MIS 3 is estimated to have ranged from 26.8 to 19.9 m below the present sea level. Luminescence ages and foraminiferal assemblages indicate that M-3 was likely formed during MIS 5 and a tidal-river environment prevailed on the southwestern coast of the Bohai Sea during MIS 6 or earlier.

High-frequency modification of the central Mediterranean seafloor environment over the last 74 ka

Here we present a high-resolution record of benthic foraminiferal assemblages for the last 74 kyr from the Sicily Channel Ocean Drilling Program Leg 160 Site 963. Benthic foraminiferal results are compared with geochemical (benthic and planktic δ 18 O and δ 13 C) and calcareous plankton data, previously acquired on the same marine core sediments. Within the succession, three benthic foraminifera compositional zones were defined. Temporal changes in the assemblages are interpreted in the context of the modification of subtropical and temperate climate systems that affected the Mediterranean thermohaline circulation. A close connection between bottom conditions in the Sicily Channel and eastern Mediterranean Sea is evident in two intervals, characterized in the ODP Site 963 by reduced oxygen conditions. The first one, around 53–51 ka, is tentatively attributed to the ‘missing’ sapropel S2 while the second, between 35 and 29 ka, is marked by short and recurrent episodes of bottom-water oxygen decrease. Both are related to a weakening of the intermediate circulation in the Sicily Channel connected with relatively high northern hemisphere summer insolation and increase in Nile River discharge, which inhibited vertical mixing and intermediate water ventilation in Eastern Mediterranean Sea. Over the last deglaciation, the African humid period (AHP) and the sea level rise, also influenced the water mass structure in the Sicily Channel and a reduction of the bottom ventilation is suggested by a strong reduction of deep-water Miliolids. Decreased bottom oxygen levels, which testifies for a weakening of intermediate circulation in Sicily Strait, also characterized the interval corresponding to S1 deposition. Yet, the strong decrease of benthic foraminiferal abundance related to a low surface water trophic level, appears to be conditioned by the reduction of trophic levels in the western Mediterranean. The very high relative abundance of U. mediterranea recorded during this interval is explained by the availability of organic matter during a limited short year period and/or the availability of more degraded organic matter from river runoff. In general, compositional data analysis highlighted a quite complex response of benthic foraminifera to paleoclimatic changes. However, changes in the benthic foraminiferal assemblages recorded during the last glacial are coherent with surface paleoproductivity dynamics connected with D-O oscillation, and support oligotrophic, meso-eutrophic and oligo-mesotrophic conditions during the early interstadials, late interstadials and stadials, respectively. • High-resolution ODP963 (Sicily Channel) Last Glacial to Holocene benthic record. • Dansgaard-Oeschger imprints in bottom environments. • Connection between western and eastern Mediterranean dynamics. • Relationships between Levantine Intermediate Water flow and bottom ventilation.

Palynomorph assemblages evidence for river reorganization 8.5 million years ago in Southeast Asia

River reorganization occurs frequently in Southeast Asia, due to the rugged topography and heavy precipitation. However, accurately constraining the age of past reorganization events is difficult. Here we apply a novel palynological approach to evaluate how rivers evolved during the late Cenozoic (~12–0 Ma), based on three deep-sea drilling cores from the South China Sea (SCS): International Ocean Discovery Program (IODP) Sites U1499 in the north and U1433 in the central SCS, and Ocean Drilling Program (ODP) Site 1143 in the south. A rapid, dramatic runoff reorganization event at 8.5 Ma is identified in the cores by a sharp decrease in terrestrial pollen and freshwater algae input in the northern SCS, coeval with a contrasting increase in the South SCS, which is supported by contemporaneous changes in neodymium isotopes composition (εNd), and sediment rates and budgets across the SCS. We postulate that the reorganization of rivers was the main dynamic driver of rapid changes in palynomorph assemblages, which took place against a background of tectonic and climatic changes.

Local and landscape correlates of coccinellid species richness, abundance, and assemblage change along a rural–urban gradient in Quintana Roo, Mexico

AbstractCoccinellids are important predators and provide important ecosystem services. The coccinellid fauna, drivers of assemblage composition, and species richness in the tropics are poorly known. We studied changes in species composition of coccinellids in domestic gardens along a rural‐urban gradient in southeastern Mexico and identified the local and landscape variables that determine abundance and species richness. We surveyed coccinellids through monthly visual surveys, yellow sticky and pan traps in nine domestic gardens, and measured local variables (flower and prey abundance, plant diversity, garden size, temperature, and relative humidity), and gathered information on landscape heterogeneity in buffers around gardens (0.05 km, 1 km, and 3 km radius). We collected 40 coccinellid morphospecies, including two exotic species: Chilocorus nigrita and Delphastus catalinae. Coccinellid species composition differed along the gradient. Assemblages did not exhibit a nested pattern; species turnover was the main contributor of observed beta diversity. Overall coccinellid abundance was highest in the suburban zone, while overall species richness was highest in the rural zone. Mean abundance and mean species richness did not vary significantly along the gradient. The gradient negatively affected coccinellid diversity; diversity was highest in the rural zone which harbored several exclusive species. At the local scale, coccinellid abundance and species richness correlated positively with prey abundance and temperature, and negatively with plant diversity. Urbanization filtered more than half the species in the community, yet urban gardens in southeastern Quintana Roo, especially those providing abundant prey, might assist coccinellid conservation.Abstract in Spanish is available with online material

Brachyuran crab diversity and the population biology of Panopeus americanus on a tropical Sabellariidae (Polychaeta: Annelida) reef

This paper describes the species composition, abundance, and diversity of brachyuran crabs and the population structure of Panopeus americanus on a Sabellaria wilsoni reef on Caixa D’Água beach, a macrotidal sandy beach on the Amazon coast. Samples were collected monthly throughout a single natural growth–destruction cycle of the reef. Ten crab species were recorded, of which the most abundant were Panopeus americanus (83% of the individuals collected), Panopeus occidentalis (6.8%), and Menippe nodifrons (5.3%). The highest crab species richness was recorded during the eroded reef phase, reflecting the increase in habitat complexity, whereas the highest crab density was recorded during the reef recuperation period, reflecting an intense recruitment process. Juveniles and adults (including ovigerous females) of P. americanus and P. occidentalis were found at certain times on the reef, while for M. nodifrons, the largest species, most of the captured individuals were juveniles, and no ovigerous females were captured. These findings reflect the importance of the biogenic substrate provided by the S. wilsoni reef to the population biology of the crabs on the Amazon coast, with some species using the reef more permanently, including as breeding and nursery grounds. The results also showed that the structural cycle of bioconstructions determines changes in the crab assemblages.

Competitive effects of plant invaders on and their responses to native species assemblages change over time

Alien plant invaders are often considered to be more competitive than natives, and species-rich plant communities are often considered to be more resistant to invaders than species-poor communities. However, the competitive interactions between invaders and assemblages of different species richness are unlikely to be static over time (e.g. during a growth season). To test this, we grew five alien and five native species as invaders in a total of 21 artificial assemblages of one, two or four native competitor species. To test for temporal changes in the reciprocal effects of invaders and the competitor assemblages on each other, and how these depend on the species richness of the assemblages, we harvested plants at three growth stages (weeks 4, 8 and 12). We found that the invaders and competitor assemblages had negative effects on each other. Aboveground biomass of invaders was reduced by the presence of a competitor assemblage, irrespective of its species richness, and this difference gradually increased over time. Alien invaders accumulated more aboveground biomass than the native invaders, but only after 12 weeks of growth. Meanwhile, the invaders also negatively affected the biomass of the competitor assemblages. For multi-species assemblages, the increase in the negative effect of the presence of the invader occurred mainly between weeks 4 and 8, whereas it happened mainly between weeks 8 and 12 for the one-species assemblages. Our results suggest that although alien invaders are more competitive than native invaders, the competitive effects of the invaders on and their responses to native competitor assemblages changed over time, irrespective of the origin of the invaders.