On the regulation of populations of mammals, birds, fish, and insects

A key unresolved question in population ecology concerns the relationship between a population's size and its growth rate. We estimated this relationship for 1780 time series of mammals, birds, fish, and insects. We found that rates of population growth are high at low population densities but, contrary to previous predictions, decline rapidly with increasing population size and then flatten out, for all four taxa. This produces a strongly concave relationship between a population's growth rate and its size. These findings have fundamental implications for our understanding of animals' lives, suggesting in particular that many animals in these taxa will be found living at densities above the carrying capacity of their environments.

The Euro+Med treatment of Hedera (Araliaceae) - recent studies and a new name

For the treatment of the Hedera taxa present in the territories included in the Euro+Med PlantBase project a new name is required and here validated, Hedera rhizomatifera, based on Hedera helix subsp. rhizomatifera.

Sex and outcrossing in a sessile freshwater invertebrate

1. The freshwater bryozoan Cristatella mucedo, in common with other sessile, benthic freshwater taxa, has an unusual life history: sex occurs during a relatively brief period near the start of the growing season, and overwintering occurs in the form of asexually produced dormant propagules (statoblasts). Consistent observed heterozygosity (Ho) deficits in C. mucedo populations have previously suggested that inbreeding is common, although a possible contribution of a Wahlund effect to low Ho could not be discounted. 2. We have used microsatellite data in the first study based on codominant markers to genetically characterise maternal colonies and larval offspring of C. mucedo . The 'population' represented by the larvae was in Hardy-Weinberg equilibrium, which has previously been found in only one of 39 populations of C. mucedo . At least 64% of larvae were the products of outcrossing. We suggest that the unusual early timing of sex may be a strategy to maximise rates of outcrossing within populations of sessile freshwater invertebrates.

Variations in lipophilic and vacuolar flavonoids among European Pulicaria species

Four European Pulicaria species, P. odora, P. paludosa, P. sicula and P. vulgare, were analysed for their surface and vacuolar constituents for comparison with previous data obtained for P. dysenterica. Each species had a distinct flavonoid pattern with notable differences between leaf and inflorescence. 6-Hydroxyflavonols were the major lipophilic components in all of the species and tissues except in the leaves of P. paludosa and P. vulgare, where scutellarein 6-methyl ether was the main constituent. In the leaves of P. sicula a more unusual flavone, 6-hydroxyluteolin 5,6,7,3′,4′-pentamethyl ether, was a major component. Pulicaria odora was distinguished by the presence of a series of methylated 6-hydroxykaempferol derivatives including a 3,5,6,7,4′-pentamethyl ether. Quercetagetin hexamethyl ether occurred in both tissues of P. sicula together with the 3,7,3,4′-tetra methyl ether and other quercetagetin derivatives, which were 5-methylated. Quercetagetin 3,7,3′-methyl ether was present in all species except P. odora. Flavonol glucuronides were characteristic vacuolar constituents of all the taxa studied. Two rare glycosides, patuletin and 6-hydroxykaempferol 6-methyl ether 7-glucuronides were identified in the inflorescence of P. odora. Pulicaria vulgaris, a rare plant of southern England, had the vacuolar flavonoid profile most similar to the other more abundant British plant, P. dysenterica.

Did pterosaurs feed by skimming? Physical modelling and anatomical evaluation of an unusual feeding method

Similarities between the anatomies of living organisms are often used to draw conclusions regarding the ecology and behaviour of extinct animals. Several pterosaur taxa are postulated to have been skim-feeders based largely on supposed convergences of their jaw anatomy with that of the modern skimming bird, Rynchops spp. Using physical and mathematical models of Rynchops bills and pterosaur jaws, we show that skimming is considerably more energetically costly than previously thought for Rynchops and that pterosaurs weighing more than one kilogram would not have been able to skim at all. Furthermore, anatomical comparisons between the highly specialised skull of Rynchops and those of postulated skimming pterosaurs suggest that even smaller forms were poorly adapted for skim-feeding. Our results refute the hypothesis that some pterosaurs commonly used skimming as a foraging method and illustrate the pitfalls involved in extrapolating from limited morphological convergence.

Comparisons of host mitochondrial, nuclear and endosymbiont bacterial genes reveal cryptic fig wasp species and the effects of Wolbachia on host mtDNA evolution and diversity

Background Figs and fig-pollinating wasp species usually display a highly specific one-to-one association. However, more and more studies have revealed that the "one-to-one" rule has been broken. Co-pollinators have been reported, but we do not yet know how they evolve. They may evolve from insect speciation induced or facilitated by Wolbachia which can manipulate host reproduction and induce reproductive isolation. In addition, Wolbachia can affect host mitochondrial DNA evolution, because of the linkage between Wolbachia and associated mitochondrial haplotypes, and thus confound host phylogeny based on mtDNA. Previous research has shown that fig wasps have the highest incidence of Wolbachia infection in all insect taxa, and Wolbachia may have great influence on fig wasp biology. Therefore, we look forward to understanding the influence of Wolbachia on mitochondrial DNA evolution and speciation in fig wasps. Results We surveyed 76 pollinator wasp specimens from nine Ficus microcarpa trees each growing at a different location in Hainan and Fujian Provinces, China. We found that all wasps were morphologically identified as Eupristina verticillata, but diverged into three clades with 4.22-5.28% mtDNA divergence and 2.29-20.72% nuclear gene divergence. We also found very strong concordance between E. verticillata clades and Wolbachia infection status, and the predicted effects of Wolbachia on both mtDNA diversity and evolution by decreasing mitochondrial haplotypes. Conclusions Our study reveals that the pollinating wasp E. verticillata on F. microcarpa has diverged into three cryptic species, and Wolbachia may have a role in this divergence. The results also indicate that Wolbachia strains infecting E. verticillata have likely resulted in selective sweeps on host mitochondrial DNA.

Phylogenetic systematics of Sternbergia (Amaryllidaceae) based on plastid and ITS sequence data

The phylogenetics of Sternbergia (Amaryllidaceae) were studied using DNA sequences of the plastid ndhF and matK genes and nuclear internal transcribed spacer (ITS) ribosomal region for 38, 37 and 32 ingroup and outgroup accessions, respectively. All members of Sternbergia were represented by at least one accession, except S. minoica and S. schubertii, with additional taxa from Narcissus and Pancratium serving as principal outgroups. Sternbergia was resolved and supported as sister to Narcissus and composed of two primary subclades: S. colchiciflora sister to S. vernalis, S. candida and S. clusiana, with this clade in turn sister to S. lutea and its allies in both Bayesian and bootstrap analyses. A clear relationship between the two vernal flowering members of the genus was recovered, supporting the hypothesis of a single origin of vernal flowering in Sternbergia. However, in the S. lutea complex, the DNA markers examined did not offer sufficient resolving power to separate taxa, providing some support for the idea that S. sicula and S. greuteriana are conspecific with S. lutea

Stops making sense: translational trade-offs and stop codon reassignment

Background Efficient gene expression involves a trade-off between (i) premature termination of protein synthesis; and (ii) readthrough, where the ribosome fails to dissociate at the terminal stop. Sense codons that are similar in sequence to stop codons are more susceptible to nonsense mutation, and are also likely to be more susceptible to transcriptional or translational errors causing premature termination. We therefore expect this trade-off to be influenced by the number of stop codons in the genetic code. Although genetic codes are highly constrained, stop codon number appears to be their most volatile feature. Results In the human genome, codons readily mutable to stops are underrepresented in coding sequences. We construct a simple mathematical model based on the relative likelihoods of premature termination and readthrough. When readthrough occurs, the resultant protein has a tail of amino acid residues incorrectly added to the C-terminus. Our results depend strongly on the number of stop codons in the genetic code. When the code has more stop codons, premature termination is relatively more likely, particularly for longer genes. When the code has fewer stop codons, the length of the tail added by readthrough will, on average, be longer, and thus more deleterious. Comparative analysis of taxa with a range of stop codon numbers suggests that genomes whose code includes more stop codons have shorter coding sequences. Conclusions We suggest that the differing trade-offs presented by alternative genetic codes may result in differences in genome structure. More speculatively, multiple stop codons may mitigate readthrough, counteracting the disadvantage of a higher rate of nonsense mutation. This could help explain the puzzling overrepresentation of stop codons in the canonical genetic code and most variants.

Community patterns of soil bacteria and nematodes in relation to geographic distance

Ecosystems consist of aboveground and belowground subsystems and the structure of their communities is known to change with distance. However, most of this knowledge originates from visible, aboveground components, whereas relatively little is known about how soil community structure varies with distance and if this variability depends on the group of organisms considered. In the present study, we analyzed 30 grasslands from three neighboring chalk hill ridges in southern UK to determine the effect of geographic distance (1e198 km) on the similarity of bacterial communities and of nematode communities in the soil. We found that for both groups, community similarity decayed with distance and that this spatial pattern was not related to changes either in plant community composition or soil chemistry. Site history may have contributed to the observed pattern in the case of nematodes, since the distance effect depended on the presence of different nematode taxa at one of the hill ridges. On the other hand, site-related differences in bacterial community composition alone could not explain the spatial turnover, suggesting that other factors, such as biotic gradients and local dispersal processes that we did not include in our analysis, may be involved in the observed pattern. We conclude that, independently of the variety of causal factors that may be involved, the decay in similarity with geographic distance is a characteristic feature of both communities of soil bacteria and nematodes.

Assessing continental-scale risks for generalist and specialist pollinating bee species under climate change

Increased risks of extinction to populations of animals and plants under changing climate have now been demonstrated for many taxa. This study assesses the extinction risks to species within an important genus of pollinating bees (Colletes: Apidae) by estimating the expected changes in the area and isolation of suitable habitat under predicted climatic condition for 2050. Suitable habitat was defined on the basis of the presence of known forage plants as well as climatic suitability. To investigate whether ecological specialisation was linked to extinction risk we compared three species which were generalist pollen foragers on several plant families with three species which specialised on pollen from a single plant species. Both specialist and generalist species showed an increased risk of extinction with shifting climate, and this was particularly high for the most specialised species (Colletes anchusae and C. wolfi). The forage generalist C. impunctatus, which is associated with Boreo-Alpine environments, is potentially threatened through significant reduction in available climatic niche space. Including the distribution of the principal or sole pollen forage plant, when modelling the distribution of monolectic or narrowly oligolectic species, did not improve the predictive accuracy of our models as the plant species were considerably more widespread than the specialised bees associated with them.

Characterisation of Bolivian savanna ecosystems by their modern pollen rain and implications for fossil pollen records

The majority of vegetation reconstructions from the Neotropics are derived from fossil pollen records extracted from lake sediments. However, the interpretation of these records is restricted by limited knowledge of the contemporary relationships between the vegetation and pollen rain of Neotropical ecosystems, especially for more open vegetation such as savannas. This research aims to improve the interpretation of these records by investigating the vegetation and modern pollen rain of different savanna ecosystems in Bolivia using vegetation inventories, artificial pollen traps and surface lake sediments. Two types of savanna were studied, upland savannas (cerrado), occurring on well drained soils, and seasonally-inundated savannas occurring on seasonally water-logged soils. Quantitative vegetation data are used to identify taxa that are floristically important in the different savanna types and to allow modern pollen/vegetation ratios to be calculated. Artificial pollen traps from the upland savanna site are dominated by Moraceae (35%), Poaceae (30%), Alchornea (6%) and Cecropia (4%). The two seasonally-inundated savanna sites are dominated by Moraceae (37%), Poaceae (20%), Alchornea (8%) and Cecropia (7%), and Moraceae (25%), Cyperaceae (22%), Poaceae (19%) and Cecropia (9%), respectively. The modern pollen rain of seasonally-inundated savannas from surface lake sediments is dominated by Cyperaceae (35%), Poaceae (33%), Moraceae (9%) and Asteraceae (5%). Upland and seasonally-flooded savannas were found to be only subtly distinct from each other palynologically. All sites have a high proportion of Moraceae pollen due to effective wind dispersal of this pollen type from areas of evergreen forest close to the study sites. Modern pollen/vegetation ratios show that many key woody plant taxa are absent/under-represented in the modern pollen rain (e.g., Caryocar and Tabebuia). The lower-than-expected percentages of Poaceae pollen, and the scarcity of savanna indicators, in the modern pollen rain of these ecosystems mean that savannas could potentially be overlooked in fossil pollen records without consideration of the full pollen spectrum available.

Sensitivity of Bolivian seasonally-dry tropical forest to precipitation and temperature changes over glacial-interglacial timescales

We used fossil pollen to investigate the response of the eastern Chiquitano seasonally-dry tropical forest (SDTF), lowland Bolivia, to high-amplitude climate change associated with glacial–interglacial cycles. Changes in the structure, composition and diversity of the past vegetation are compared with palaeoclimate data previously reconstructed from the same record, and these results shed light on the biogeographic history of today’s highly disjunct blocks of SDTF across South America. We demonstrate that lower glacial temperatures limited tropical forest in the Chiquitanía region, and suggest that SDTF was absent or restricted at latitudes below 17°S, the proposed location of the majority of the hypothesized ‘Pleistocene dry forest arc’ (PDFA). At 19500 yrs b.p., warming supported the establishment of a floristically-distinct SDTF, which showed little change throughout the glacial–Holocene transition, despite a shift to significantly wetter conditions beginning ca. 12500–12200 yrs b.p. Anadenanthera colubrina, a key SDTF taxon, arrived at 10000 yrs b.p., which coincides with the onset of drought associated with an extended dry season. Lasting until 3000 yrs b.p., Holocene drought caused a floristic shift to more drought-tolerant taxa and a reduction in α-diversity (shown by declining palynological richness), but closed-canopy forest was maintained throughout. In contrast to the PDFA, the modern distribution of SDTF most likely represents the greatest spatial coverage of these forests in southern South America since glacial times. We find that temperature is a key climatic control upon the distribution of lowland South American SDTF over glacial-interglacial timescales, and seasonality of rainfall exerts a strong control on their floristic composition.

Differentiation between Neotropical rainforest, dry forest and savannah ecosystems by their modern pollen spectra and implications for the fossil pollen record

Accurate differentiation between tropical forest and savannah ecosystems in the fossil pollen record is hampered by the combination of: i) poor taxonomic resolution in pollen identification, and ii) the high species diversity of many lowland tropical families, i.e. with many different growth forms living in numerous environmental settings. These barriers to interpreting the fossil record hinder our understanding of the past distributions of different Neotropical ecosystems and consequently cloud our knowledge of past climatic, biodiversity and carbon storage patterns. Modern pollen studies facilitate an improved understanding of how ecosystems are represented by the pollen their plants produce and therefore aid interpretation of fossil pollen records. To understand how to differentiate ecosystems palynologically, it is essential that a consistent sampling method is used across ecosystems. However, to date, modern pollen studies from tropical South America have employed a variety of methodologies (e.g. pollen traps, moss polsters, soil samples). In this paper, we present the first modern pollen study from the Neotropics to examine the modern pollen rain from moist evergreen tropical forest (METF), semi-deciduous dry tropical forest (SDTF) and wooded savannah (cerradão) using a consistent sampling methodology (pollen traps). Pollen rain was sampled annually in September for the years 1999–2001 from within permanent vegetation study plots in, or near, the Noel Kempff Mercado National Park (NKMNP), Bolivia. Comparison of the modern pollen rain within these plots with detailed floristic inventories allowed estimates of the relative pollen productivity and dispersal for individual taxa to be made (% pollen/% vegetation or ‘p/v’). The applicability of these data to interpreting fossil records from lake sediments was then explored by comparison with pollen assemblages obtained from five lake surface samples.

Palynological differentiation between genera of the Moraceae family and implications for Amazonian palaeoecology

The Moraceae family is one of the most abundant and ecologically important families in Neotropical rainforests and is very well-represented in Amazonian fossil pollen records. However, difficulty in differentiating palynologically between the genera within this family, or between the Moraceae and Urticaceae families, has limited the amount of palaeoecological information that can be extracted from these records. The aim of this paper is to analyse the morphological properties of pollen from Amazonian species of Moraceae in order to determine whether the pollen taxonomy of this family can be improved. Descriptive and morphometric methods are used to identify and differentiate key pollen types of the Moraceae (mulberry) and Urticaceae (nettle) families which are represented in Amazonian rainforest communities of Noel Kempff Mercado National Park (NKMNP), Northeast Bolivia. We demonstrate that Helicostylis, Brosimum, Pseudolmedia, Sorocea and Pourouma pollen can be identified in tropical pollen assemblages and present digital images of, and a taxonomic key to, the Moraceae pollen types of NKMNP. Indicator species, Maquira coriacea (riparian evergreen forest) and Brosimum gaudichaudii (open woodland and upland savanna communities), also exhibit unique pollen morphologies. The ability to recognise these ecologically important taxa in pollen records provides the potential for much more detailed and reliable Neotropical palaeovegetation reconstructions than have hitherto been possible. In particular, this improved taxonomic resolution holds promise for resolving long-standing controversies over the interpretation of key Amazonian Quaternary pollen records.

Species richness declines and biotic homogenization have slowed down for NW-European pollinators and plants

Concern about biodiversity loss has led to increased public investment in conservation. Whereas there is a widespread perception that such initiatives have been unsuccessful, there are few quantitative tests of this perception. Here, we evaluate whether rates of biodiversity change have altered in recent decades in three European countries (Great Britain, Netherlands and Belgium) for plants and flower visiting insects. We compared four 20-year periods, comparing periods of rapid land-use intensification and natural habitat loss (1930–1990) with a period of increased conservation investment (post-1990). We found that extensive species richness loss and biotic homogenisation occurred before 1990, whereas these negative trends became substantially less accentuated during recent decades, being partially reversed for certain taxa (e.g. bees in Great Britain and Netherlands). These results highlight the potential to maintain or even restore current species assemblages (which despite past extinctions are still of great conservation value), at least in regions where large-scale land-use intensification and natural habitat loss has ceased.