Find research datasets worth reusing

Data from: Inferring skeletal production from time-averaged assemblages: skeletal loss pulls the timing of production pulses towards the modern period

Age-frequency distributions of dead skeletal material on the landscape or seabed—information on the time that has elapsed since the death of individuals—provide decadal- to millennial-scale perspectives both on the history of production and on the processes that lead to skeletal disintegration and burial. So far, however, models quantifying the dynamics of skeletal loss have assumed that skeletal production is constant during time-averaged accumulation. Here, to improve inferences in conservation paleobiology and historical ecology, we evaluate the joint effects of temporally variable production and skeletal loss on postmortem age-frequency distributions (AFDs) to determine how to detect fluctuations in production over the recent past from AFDs. We show that, relative to the true timing of past production pulses, the modes of AFDs will be shifted to younger age cohorts, causing the true age of past pulses to be underestimated. This shift in the apparent timing of a past pulse in production will be stronger where loss rates are high and/or the rate of decline in production is slow; also, a single pulse coupled with a declining loss rate can, under some circumstances, generate a bimodal distribution. We apply these models to death assemblages of the bivalve Nuculana taphria from the Southern California continental shelf, finding that: (1) an onshore-offshore gradient in time averaging is dominated by a gradient in the timing of production, reflecting the tracking of shallow-water habitats under a sea-level rise, rather than by a gradient in disintegration and sequestration rates, which remain constant with water depth; and (2) loss-corrected model-based estimates of the timing of past production are in good agreement with likely past changes in local production based on an independent sea-level curve.

opencc-zeroJul 2019View details →

Data from: Long-term responses of desert ant assemblages to climate

1. Productivity is a key driver of ecosystem structure and function, so long-term studies are critical to understanding ecosystems with high temporal variation in productivity. In some deserts, productivity, driven by moisture availability, varies immensely over time (rainfall) and space (landscape factors). At high productivity, species richness is expected to be driven in opposing directions by abundance (More Individuals Hypothesis – MIH), and competition. While studies investigating the impacts of spatial variation in productivity on community structure are common, the impacts of temporal variability on productivity are poorly understood. 2. We tested how well rainfall predicted the activity, species numbers and assemblage composition of ants and if responses were moderated by landscape position. We also asked whether the number of species (richness per sampling unit and estimated species richness) responded directly to rainfall or was moderated by ant activity or competition from dominant ants. 3. Over a 22-year period, when annual rainfall fluctuated between 79 mm and 570 mm, we sampled ants using pitfall traps in paired dune and swale habitats in the Simpson Desert, Australia. We used climate records over this period to model changes in ant assemblages. 4. Activity of dominant ants responded primarily to long-term rainfall, increasing exponentially, while subordinate ants responded to short-term weather and time. Consistent with the MIH, the number of ant species was best predicted by activity, particularly that of subordinate ants. Activity of dominant ants had a declining positive effect on numbers of species. Landscape position strongly predicted species composition, while long-term rainfall determined composition at genus- but not species-level. Over time, species composition fluctuated, but several genera consistently increased in activity.

opencc-zeroDec 2013View details →

Data from: Rat eradication and the resistance and resilience of passerine bird assemblages in the Falkland Islands

Norway rats (Rattus norvegicus) were introduced to the Falkland Islands and are detrimental to native passerines. Rat eradication programs are being used to help protect the avifauna. The present study assesses the effectiveness of eradication programs while using this conservation practice as a natural experiment to explore the ecological resistance, resilience, and homeostasis of bird communities. We conducted bird surveys on 230 islands: 85 in the presence of rats, 108 that were historically free of rats, and 37 from which rats had been eradicated. Bird detection data were used to build occupancy models for each species and estimate species-area relationships. Count data were used to estimate relative abundance and community structure. Islands with invasive rats had reduced species richness of passerines and a different community structure than islands on which rats were historically absent. Although the species richness of native passerines was remarkably similar on eradicated and historically rat-free islands, community structure on eradicated islands was more similar to that of rat-infested islands than to historically rat-free islands. The results suggest that in the Falkland Islands, species richness of passerines is not resistant to invasive rats, but seems to be resilient following their removal. In contrast, community structure seems to be neither resistant nor resilient. From a conservation perspective, rat eradication programs in the Falkland Islands appear to be effective at restoring native species richness, but they are not necessarily beneficial for species of conservation concern. For species that do not recolonize, translocations following eradications may be necessary.

opencc-zeroDec 2011View details →

Data from: Spatial scaling of functional structure in bird and mammal assemblages

Differences in trait composition, or functional structure, of assemblages across spatial scales may stem from the ability to tolerate local conditions (environmental filters) and from assembly rules (biological filters). However, disentangling their respective roles has proven difficult, and limited generalities have emerged from research on the spatial scaling of functional structure. Here we quantify differences in trait composition among 679 spatially nested (i.e., paired regional pool and local community) bird and mammal assemblages worldwide. Among the regional pool, we identify species with trait combinations within the range observed locally as the ecological species pool. The ecological species pool has a trait structure that is generally different from that of the regional pool, consistent with the operation of environmental filters. In contrast, local species trait structure generally shows little difference from that of the ecological pool. We find notable deviations from expectations based on equiprobable draws from the ecological pool. However, these deviations vary little across scales and broad environmental gradients. For mammals, but not birds, this is consistent with assembly rules. Thus, by conceptualizing ecological pools, we demonstrate that functional structure is jointly determined by processes causing both low and high functional differences between scales and are able to quantify their relative importance.

opencc-zeroDec 2016View details →

Data from: Evidence for stratigraphy in molluscan death assemblages preserved in seagrass beds: St. Croix, U.S. Virgin Islands

Death assemblages that occupy the upper tens of centimeters of sediment in shallow-marine settings are often subject to extensive mixing, thereby limiting their usefulness in assessing environmentally mediated compositional changes through time in the local biota. Here, we provide evidence that dense, Thalassia-rich seagrass beds preserve a stratigraphic record of biotic variation because their dense root–rhizome mats inhibit mixing. We sampled benthic mollusk assemblages at seven localities in Thalassia-rich beds around St. Croix, USVI, collecting three separate sediment intervals of ~13 cm each to a total depth of ~40 cm below the sediment–water interface, and found evidence that sedimentary intervals preserved compositional stratigraphy. Further, some localities displayed systematic, directional changes down-core. An examination of interval-to-interval changes in composition revealed that compositional variation was unique from locality to locality rather than reflecting coordinated, island-wide transitions. In general, however, relative abundances of epifaunal gastropods and small lucinid bivalves tended to decrease with depth below the sediment–water interface. Quantitative comparisons of life-to-death assemblages from each successive sedimentary interval demonstrated that the shallowest death assemblages were typically more similar to the life assemblages than were deeper assemblages, suggesting that deeper intervals provide records of earlier community states.

Data from: Geographic mosaic of plant evolution: extrafloral nectary variation mediated by ant and herbivore assemblages

Herbivory is an ecological process that is known to generate different patterns of selection on defensive plant traits across populations. Studies on this topic could greatly benefit from the general framework of the Geographic Mosaic Theory of Coevolution (GMT). Here, we hypothesize that herbivory represents a strong pressure for extrafloral nectary (EFN) bearing plants, with differences in herbivore and ant visitor assemblages leading to different evolutionary pressures among localities and ultimately to differences in EFN abundance and function. In this study, we investigate this hypothesis by analyzing 10 populations of Anemopaegma album (30 individuals per population) distributed through ca. 600 km of Neotropical savanna and covering most of the geographic range of this plant species. A common garden experiment revealed a phenotypic differentiation in EFN abundance, in which field and experimental plants showed a similar pattern of EFN variation among populations. We also did not find significant correlations between EFN traits and ant abundance, herbivory and plant performance across localities. Instead, a more complex pattern of ant–EFN variation, a geographic mosaic, emerged throughout the geographical range of A. album. We modeled the functional relationship between EFNs and ant traits across ant species and extended this phenotypic interface to characterize local situations of phenotypic matching and mismatching at the population level. Two distinct types of phenotypic matching emerged throughout populations: (1) a population with smaller ants (Crematogaster crinosa) matched with low abundance of EFNs; and (2) seven populations with bigger ants (Camponotus species) matched with higher EFN abundances. Three matched populations showed the highest plant performance and narrower variance of EFN abundance, representing potential plant evolutionary hotspots. Cases of mismatched and matched populations with the lowest performance were associated with abundant and highly detrimental herbivores. Our findings provide insights on the ecology and evolution of plant–ant guarding systems, and suggest new directions to research on facultative mutualistic interactions at wide geographic scales.

opencc-zeroSep 2019View details →

Data from: Bird assemblages on Amazonian river islands: patterns of species diversity and composition

The principles of island biogeography are rarely used to investigate the animal assemblages of Amazonian river islands. Here, we apply this approach to compare bird assemblages of Amazonian river islands with a variety of mainland habitats. We also examine how bird species diversity and composition are related to island physical attributes. Birds were sampled with mist nets and qualitative censuses on 11 river islands and at 24 mainland sites on the lower reaches of the Rio Negro in the Brazilian Amazon. Island bird assemblages are characterized by lower species richness and a higher abundance of a few dominant species. Additionally, species composition of the islands was significantly distinct from the mainland, including the nearby floodplain habitats. Number of bird species increased with island size and habitat diversity, and decreased with degree of isolation. In addition, small islands tended to harbour an impoverished subset of the species present on larger ones. Bird species diversity and composition on Amazonian river islands are likely influenced by the ecological succession and historical events affecting island formation. Considering their small total area across the Amazon basin, these insular fluvial environments could be disproportionally threatened by river channel disturbances such as climate change events, and hydroelectric building.

Data from: Explaining high-diversity death assemblages: undersampling of the living community, out-of-habitat transport, time-averaging of rare taxa, and local extinction

Molluscan benthic assemblages provide unique opportunities for understanding both spatial and temporal patterns of biodiversity. Species richness in the shell remains found at a site (i.e. the death assemblage) is typically several times higher than in the counterpart living assemblage, reflecting a complex history of settlement, dissemination and decomposition post-mortem. We used high-density temporal and spatial sampling (>37'000 individuals representing 196 taxa) of a shallow (5-8 m) nearshore sandy habitat off the coast of south-east Sardinia (Italy, Mediterranean Sea) to study the factors responsible for differences in the relative diversity of living and death assemblages. We found that death assemblages at all sites were considerably more diverse than living communities (1.5-3.5x more dead than living taxa after sample-size standardization), with 78% of all taxa solely recovered as empty shells, resulting in low live-dead agreement. By carefully filtering the raw data and combining them with habitat information extracted from the literature, we disentangled the major causes of this discordance and quantified their individual effects. Increased dead diversities could not be attributed to undersampling of the living community, but instead resulted from three phenomena of decreasing importance: the post-mortem, out-of-habitat transport of non-indigenous taxa (57% of dead-only taxa were allochthonous), the time-averaged presence of rare indigenous taxa (40% of dead-only taxa), and the likely local extirpation of a small number of species (3% of dead-only taxa). Our approach demonstrates how ecological inferences based on death assemblages can be improved by restricting analyses to demonstrably indigenous taxa, and highlights how mollusc shell remains can be used to provide information over both ecological and evolutionary timescales.

opencc-zeroDec 2018View details →

Data from: Testing species assemblage predictions from stacked and joint species distribution models

Aim: Predicting the spatial distribution of species assemblages remains an important challenge in biogeography. Recently, it has been proposed to extend correlative species distribution models (SDMs) by taking into account (a) covariance between species occurrences in so-called joint species distribution models (JSDMs) and (b) ecological assembly rules within the SESAM (spatially explicit species assemblage modelling) framework. Yet, little guidance exists on how these approaches could be combined. We, thus, aim to compare the accuracy of assemblage predictions derived from stacked and from joint SDMs. Location: Switzerland Taxon Birds, tree species Methods: Based on two monitoring schemes (national forest inventory and Swiss breeding bird atlas), we built SDMs and JSDMs for tree species (at 100m resolution) and forest birds (at 1km resolution). We tested accuracy of species assemblage and richness predictions on holdout data using different stacking procedures and ecological assembly rules. Results Despite minor differences, results were consistent between birds and tree species. Cross-validated species-level model performance was generally higher in SDMs than JSDMs. Differences in species richness and assemblage predictions were larger between stacking procedures and ecological assembly rules than between stacked SDMs and JSDMs. On average, predictions were slightly better for stacked SDMs compared to JSDMs, probabilistic stacks outperformed binary stacks, and ecological assembly rules yielded best predictions. Main conclusions: When predicting the composition of species assemblages, the choice of stacking procedure and ecological assembly rule seems more decisive than differences in underlying model type (SDM vs. JSDM). JSDMs do not seem to improve community predictions compared to SDMs or improve predictions for rare species. Still, JSDMs may provide additional insights into community assembly and may help deriving hypotheses about prevailing biotic interactions in the system. We provide simple rules of thumb for choosing appropriate modelling pathways. Future studies should test these preliminary guidelines for other taxa and biogeographic realms as well as for other JSDM algorithms.

opencc-zeroSep 2019View details →

Data from: A Changhsingian (late Permian) nautiloid assemblage from Gujiao, South China.

A c. 0.30 m thick cherty limestone bed in the Dalong Formation at Gujiao (Guizhou) yielded a highly diverse Changhsingian nautiloid assemblage. Its age is late Changhsingian, indicated by the co-occurring ammonoid Pseudotirolites sp. This assemblage is composed of nine species and five taxa in open nomenclature in nine genera, including one new genus and three new species: Neotainoceras zhaoi sp. nov., Nodopleuroceras gujiaoense sp. nov. and Gujiaonautilus longliensis gen. nov., sp. nov. Sholakoceras is for the first time recorded in South China. Compared with literature data from 52 sites in various regions worldwide, the material described here presents the most diverse Changhsingian nautiloid assemblage. Among the genera of the Gujiao assemblage, Pleuronautilus, Tainoceras and Liroceras are cosmopolitan, while the others are more endemic or genera known so far only from South China .

opencc-zeroDec 2010View details →

Data from: Molecular profiling of diatom assemblages in tropical lake sediments using taxon-specific PCR and Denaturing High-Performance Liquid Chromatography (PCR-DHPLC)

Here we present a protocol to genetically detect diatoms in sediments of the Kenyan tropical Lake Naivasha, based on taxon-specific PCR amplification of short fragments (approx. 100 bp) of the small subunit ribosomal (SSU) gene and subsequent separation of species-specific PCR products by PCR-based DHPLC. An evaluation of amplicons differing in primer specificity to diatoms and length of the fragments amplified demonstrated that the number of different diatom sequence types detected after cloning of the PCR products critically depended on the specificity of the primers to diatoms and the length of the amplified fragments whereby shorter fragments yielded more species of diatoms. The DHPLC was able to discriminate between very short amplicons based on the sequence difference, even if the fragments were of identical length. and if the amplicons differed only in a small number of nucleotides. Generally the method identified the dominant sequence types from mixed amplifications. A comparison with microscopic analysis of the sediment samples revealed that the sequence types identified in the molecular assessment corresponded well with the most dominant species. In summary, the PCR-based DHPLC protocol offers a fast, reliable, and cost-efficient possibility to study DNA from sediments and other environmental samples with unknown organismic content, even for very short DNA fragments.

Data from: A hierarchical model of whole assemblage island biogeography

Island systems have long played a central role in the development of ecology and evolutionary biology. However, while many empirical studies suggest species differ in vital biogeographic rates, such as dispersal abilities, quantitative methods have had difficulty incorporating such differences into analyses of whole-assemblages. In particular, differences in dispersal abilities among species can cause variation in the spatial clustering and localization of species distributions. Here, we develop a single, hierarchical Bayes, assemblage-wide model of 252 bird species distributions on the islands of Northern Melanesia and use it to investigate a) whether dispersal limitation structures bird assemblages across the archipelago, b) whether species differ in dispersal ability, and c) test the hypothesis that wing aspect ratio, a trait linked to flight efficiency, predicts differences inferred by the model. Consistent with island biogeographic theory, we found that individual species were more likely to occur on islands with greater area, and on islands near to other islands where the species also occurred. However, species showed wide variation in the importance and spatial scale of these clustering effects. The importance of clustering in distributions was greater for species with low wing aspect ratios, and the spatial scale of clustering was also smaller for low aspect ratio species. These findings suggest that the spatial configuration of islands interacts with species dispersal ability to affect contemporary distributions, and that these species differences are detectable in occurrence patterns. More generally, our study demonstrates a quantitative, hierarchical approach that can be used to model the influence of dispersal heterogeneity in diverse assemblages and test hypotheses for how traits drive dispersal differences, providing a framework for deconstructing ecological assemblages and their drivers.

Data from: Beyond size – morphological predictors of bite force in a diverse insectivorous bat assemblage from Malaysia

1. Bite force is used to investigate feeding performance in a variety of vertebrates. In all taxa studied, bite force is strongly correlated with body and head size. Studies of bite force in bats have largely centred on neotropical species with a particular focus on species that maximize dietary differences. Little is known about the bite force of bats from the Old World tropics, nor of variation in bite force within diverse assemblages of obligate insectivores. Moreover, factors other than size are poorly known but may be important in driving interspecific differences in bite force, and thereby diet. 2. Here, we examine the correlation between morphological variation and bite force of 35 species of insectivorous bats from a single palaeotropical assemblage. We confirmed the overall relationship between size and bite force across species, but found that bite force is predicted more strongly by head length than body mass or forearm length. 3. From the combined action of jaw muscles and muscle-bone mechanisms, bats generate a mechanical advantage that creates pressure during biting. We calculated the size-independent mechanical advantage for each of five mandible lever systems (three delineated by the temporalis muscle and two delineated by the masseter muscle) operating through three function points (molar, canine, and incisor). Size-independent mechanical advantage of the suprazygomatic portion of the temporalis muscle at the molar function point was the only significant predictor of size-independent maximum bite force across all species. 4. Within families, the size-independent mechanical advantage of the superficial portion of the masseter muscle plays a significant role in predicting size-independent maximum bite force in both the Rhinolophidae and Vespertilionidae. For the family Hipposideridae, however, size-independent mechanical advantage showed no role in predicting size-independent maximum bite force, suggesting that size really matters in predicting the maximum bite force capacity for this family.

Data from: A bust but no boom: responses of floodplain bird assemblages during and after prolonged drought

1. Climate change alters the frequency and severity of extreme events, such as drought. Such events will be increasingly important in shaping communities as climate change intensifies. The ability of species to withstand extreme events (resistance) and to recover once adverse conditions abate (resilience) will determine their persistence. 2. We estimated the resistance and resilience of bird species during and after a 13-year drought (the 'Big Dry') in floodplain forests in south-eastern Australia. 3. We conducted bird surveys at the beginning and end of the Big Dry, and after the abrupt end to the drought (the 'Big Wet'), to evaluate species-specific changes in reporting rates among the three periods. We assessed changes in bird-breeding activity before and after the Big Wet to estimate demographic resilience based on breeding. 4. Between the start and the end of the Big Dry (1998 vs. 2009), 37 of 67 species declined substantially. Of those, only two had increased reporting rates after the Big Wet (2009 vs. 2013) that were equal to or larger than their declines, while three partially recovered. All other declining species showed low resilience: 25 showed no change in reporting rates and seven declined further. The number of breeding species and total breeding activity of all species declined after the Big Wet, and there was no change in the number of young produced. 5. The Big Dry caused widespread declines in the floodplain avifauna. Despite the drought being broken by 2 years of well-above-average rainfall and subsequent near-average rainfall, most species showed low resilience and there was little indication that overall breeding had increased. The effects of drought appeared to be pervasive for much of the floodplain avifauna, regardless of species traits (species body mass, fecundity, mobility or diet). Ecosystems such as these are likely to require active management and restoration, including reinstatement of natural flooding regimes, to improve ecological condition, to enhance resistance and resilience to extreme climate events.

opencc-zeroDec 2016View details →

Data from: The effect of bioturbation by polychaetes (Opheliidae) on benthic foraminiferal assemblages and test preservation

Biological activity such as burrowing can alter benthic foraminiferal shell preservation and may also modify benthic foraminiferal assemblages by vertical mixing, inducing sediment homogenization. Here, we analyse benthic foraminiferal assemblages and taphonomy of upper Miocene marine deposits from Conil de la Frontera (Cádiz, south-western Spain). The deposits consist of marls displaying a pervasive alternation of intensively bioturbated beds dominated by Macaronichnus segregatis traces (ichnofabric index 4–5) and non-bioturbated beds. Benthic foraminiferal assemblages are dominated by Cibicidoides mundulus and Cibicides refulgens, indicating that the marls were deposited on an oligotrophic, well-oxygenated upper slope. The impact of burrowing on the preservation of benthic foraminiferal tests was tested using Q-mode cluster analysis, which found two well-differentiated groups of samples, one including the non-bioturbated beds and the other encompassing the bioturbated ones. Fragmentation and recrystallization account for the differentiation of these groups, both being higher in the bioturbated sediments. Aggressive chemical digestion by the Macaronichnus trace-makers, assumed to be a polychaete worm of the family Opheliidae, etched the microfossil shells, making them more vulnerable to fragmentation. Intense bioturbation favoured the circulation of pore fluids, encouraging recrystallization. Pervasive burrowing resulted in significant vertical reworking of microfossils. As a consequence, benthic foraminiferal assemblages in the bioturbated beds were homogenized in the mixed layer; that is, the uppermost layer of the substrate totally burrowed. The alternation of bioturbated and non-bioturbated beds reflects episodic transfer of food particles down slope from shallower parts of the shelf as well as from the continent due to storms under otherwise homogeneous oligotrophic marine conditions.

Data from: Repeated invasions into the twilight zone: evolutionary origins of a novel assemblage of fishes from deep Caribbean reefs

Mesophotic and deeper reefs of the tropics are poorly known and underexplored ecosystems worldwide. Collectively referred to as the 'twilight zone', depths below ~30–50 m are home to many species of reef fishes that are absent from shallower depths, including many undescribed and endemic species. We currently lack even a basic understanding of the diversity and evolutionary origins of fishes on tropical mesophotic reefs. Recent submersible collections in the Caribbean have provided new specimens that are enabling phylogenetic reconstructions that incorporate deep-reef representatives of tropical fish genera. Here, we investigate evolutionary depth transitions in the family Gobiidae (gobies), the most diverse group of tropical marine fishes. Using divergence-time estimation coupled with stochastic character mapping to infer the timing of shallow-to-deep habitat transitions in gobies, we demonstrate at least four transitions from shallow to mesophotic depths. Habitat transitions occurred in two broad time periods (Miocene, Pliocene–Pleistocene), and may have been linked to the availability of underutilized niches, as well as the evolution of morphological/behavioural adaptations for life on deep reefs. Further, our analysis shows that at least three evolutionary lineages that invaded deep habitats subsequently underwent speciation, reflecting another unique mode of radiation within the Gobiidae. Lastly, we synthesize depth distributions for 95 species of Caribbean gobies, which reveal major bathymetric faunal breaks at the boundary between euphotic and mesophotic reefs. Ultimately, our study is the first rigorous investigation into the origin of Caribbean deep-reef fishes and provides a framework for future studies that utilize rare, deep-reef specimens.

opencc-zeroDec 2011View details →

Data from: Biomass responses to elevated CO2, soil heterogeneity and diversity: an experimental assessment with grassland assemblages

While it is well-established that the spatial distribution of soil nutrients (soil heterogeneity) influences the competitive ability and survival of individual plants, as well as the productivity of plant communities, there is a paucity of data on how soil heterogeneity and global change drivers interact to affect plant performance and ecosystem functioning. To evaluate the effects of elevated CO2, soil heterogeneity and diversity (species richness and composition) on productivity, patterns of biomass allocation and root foraging precision, we conducted an experiment with grassland assemblages formed by monocultures, two- and three-species mixtures of Lolium perenne, Plantago lanceolata and Holcus lanatus. The experiment lasted for 90 days, and was conducted on microcosms built out of PVC pipe (length 38 cm, internal diameter 10 cm). When nutrients were heterogeneously supplied (in discrete patches), assemblages exhibited precise root foraging patterns, and had higher total, above- and belowground biomass. Greater aboveground biomass was observed under elevated CO2. Species composition affected the below:aboveground biomass ratio and interacted with nutrient heterogeneity to determine belowground and total biomass. Species richness had no significant effects, and did not interact with either CO2 or nutrient heterogeneity. Under elevated CO2 conditions, the two- and three-species mixtures showed a clear trend towards underyielding. Our results show that differences among composition levels were dependent on soil heterogeneity, highlighting its potential role in modulating diversity–productivity relationships.

Data from: Neogene sloth assemblages (Mammalia, Pilosa) of the Cocinetas Basin (La Guajira, Colombia): implications for the Great American Biotic Interchange

We describe sloth assemblages from the Cocinetas Basin (La Guajira peninsula, Colombia), found in the Neogene Castilletes and Ware formations, located in northernmost South America, documenting otherwise poorly known biotas. The tentative referral of a specimen to a small megatherioid sloth, Hyperleptus?, from the early–middle Miocene Castilletes Formation, suggests affinities of this fauna with the distant Santa Cruz Formation and documents a large latitudinal distribution for this taxon. The late Pliocene Ware Formation is much more diverse, with five distinct taxa representing every family of 'ground sloths'. This diversity is also remarkable at the ecological level, with sloths spanning over two orders of magnitude of body mass and probably having different feeding strategies. Being only a few hundred kilometres away from the Isthmus of Panama, and a few hundred thousand years older than the classically recognized first main pulse of the Great American Biotic interchange (GABI 1), the Ware Formation furthermore documents an important fauna for the understanding of this major event in Neogene palaeobiogeography. The sloths for which unambiguous affinities were recovered are not closely related to the early immigrants found in North America before GABI 1.

opencc-zeroDec 2010View details →

Data from: Macrobenthic assemblage structure in a cool-temperate intertidal dwarf-eelgrass bed in comparison to those in lower latitudes.

The evolution and ecology of latitudinal patterns in marine macrofaunal biodiversity and assemblage structure are contentious. With the aim of investigating the occurrence of such patterns in intertidal dwarf-eelgrass beds (Nanozostera spp.), those at cool-temperate Scolt Head Island, UK (latitude 52°N), were examined and compared to equivalent systems in warm-temperate Knysna, South Africa (34°S), and subtropical Moreton Bay, Australia (27°S); systems that had earlier been examined using identical methodology. The Scolt Head bed supported the highest faunal density (mean 6,568 0.1m-2), lowest observed and estimated species richness (32 and 33 spp respectively), lowest species diversity (Simpson's Index 0.34), highest mean Constancy Index (23.0), lowest proportion of total numbers contributed by singletons or doubletons (0.06%), largest Berger-Parker Dominance (0.81), and least degree of variability between component samples. The beds at Knysna were intermediate between those at Scolt Head and Moreton Bay in all those respects, as well as in nature and composition of the fauna. Similar dwarf-eelgrass beds at Arcachon, France, likewise appear intermediate between those of Scolt Head and Knysna. Community variance in all three regions was greatest at the smallest spatial scale of ≤1 m, at which scale two of the three also displayed randomly organized faunal assemblages, although this changed to non-random at larger spatial scales. Assemblages were deterministically structured at all spatial scales at Knysna. A consistent series of changes in structural characteristics of macrofaunal dwarf-eelgrass assemblages therefore occurred along the latitudinal sequence of Scolt Head (530): Arcachon (450): Knysna (340): Moreton Bay (270). Community assembly patterns did not change with latitude, however, but did so with spatial scale in two of the three regions.