Can conditions experienced during migration limit the population levels of birds?

Populations of migratory birds are usually considered to be limited by conditions in breeding or wintering areas, but some might be limited by conditions encountered on migration. This could occur at stopover sites where competition for restricted food supplies can reduce subsequent survival or breeding success, or during the flights themselves, when adverse weather can occasionally kill large numbers of individuals. Competition for food could act in a density-dependent manner and help to regulate populations, whereas weather effects are more likely to act in a density-independent manner. The evidence for these views is explored in this paper. When preparing for migration, birds must normally obtain more food per day than usual, in order to accumulate the body reserves that fuel their flights. Birds often concentrate in large numbers at particular stopover sites, where food can become scarce, thus affecting migratory performance. Rates of weight gain, departure weights, and stopover durations often correlate with food supplies at stopover sites, sometimes influencing the subsequent survival and reproductive success of individuals, which can in turn affect subsequent breeding numbers. Many studies have provided evidence for interference and depletion competition at stopover sites, relatively few for migration conditions influencing the subsequent breeding or survival of individuals, and even fewer for effects on subsequent breeding numbers. Migrants in flight occasionally suffer substantial mortality in storms, especially over water, sometimes involving many thousands of birds at a time. Other mass mortalities have resulted from atypical ‘winter-like’ weather, occurring soon after the arrival of summer migrants in their breeding areas or just before their departure in autumn. Again, many thousands of birds at a time have been killed in such incidents, causing reductions of 30–90% in local breeding densities. In some bird species, migration-related events can at times have substantial effects on the year-to-year changes in breeding population levels. Nonetheless, the difficulties involved in investigating migrating birds at different points on their migration routes have so far limited the number of studies on the influence of events during migration periods on population levels.     

Pollination by passerine birds: why are the nectars so dilute?

Bird-pollinated flowers are known to secrete relatively dilute nectars (with concentrations averaging 20–25% w/w). Many southern African plants that are pollinated by passerine birds produce nectars with little or no sucrose. Moreover, these hexose nectars are extremely dilute (10–15%). This suggests a link between sugar composition and nectar concentration. Nectar originates from sucrose-rich phloem sap, and the proportion of monosaccharides depends on the presence and activity of invertase in the nectary. Hydrolysis of sucrose increases nectar osmolality and the resulting water influx can potentially convert a 30% sucrose nectar into a 20% hexose nectar, with a 1.56 times increase in volume. Hydrolysis may also increase the gradient for sucrose transport and thus the rate of sugar secretion. When sucrose content and refractometer data were compared, some significant correlations were seen, but the occurrence of sucrose-rich or hexose-rich nectars can also be explained on phylogenetic grounds (e.g. Erythrina and Protea). Hexose nectars may be abundant enough to drip from open flowers, but evaporation leads to much variability in nectar concentration and increases the choices available to pollinators.     

Diets of fruit-eating birds: what are the causes of interspecific differences?

Differences in fruit choice among the bird species of a Spanish shrubland were related to the size of fruits and to the lipid content of pulp. Lipid-rich fruits were selected by the bird species with slower food passage rates through the digestive tract. These bird species also fed frequently on insects and seeds. Bird species with faster food passage rates fed less on insects and seeds, and ate mainly fruits with pulp poor in lipids (rich in sugars and water). Studies of digestion in birds indicate that lipids require slower food passage rates for efficient digestion and intestinal transport than simple sugars. The available evidence indicates that the European bird species that show stronger preferences for lipid-rich fruits are no better as seed dispersers, from the point of view of the plants, than species choosing lipidpoor fruits. Thus, the degree of frugivory of birds, their fruit choice patterns and their effects on seed dispersal do not seem to be related to each other in the ways expected by the early models of the evolution of fleshy fruits.     

Channel crossing: how are proteins shipped across the bacterial plasma membrane?

The structure of the first protein-conducting channel was determined more than a decade ago. Today, we are still puzzled by the outstanding problem of protein translocation—the dynamic mechanism underlying the consignment of proteins across and into membranes. This review is an attempt to summarize and understand the energy transducing capabilities of protein-translocating machines, with emphasis on bacterial systems: how polypeptides make headway against the lipid bilayer and how the process is coupled to the free energy associated with ATP hydrolysis and the transmembrane protein motive force. In order to explore how cargo is driven across the membrane, the known structures of the protein-translocation machines are set out against the background of the historic literature, and in the light of experiments conducted in their wake. The paper will focus on the bacterial general secretory (Sec) pathway (SecY-complex), and its eukaryotic counterpart (Sec61-complex), which ferry proteins across the membrane in an unfolded state, as well as the unrelated Tat system that assembles bespoke channels for the export of folded proteins.     

Historical colonization of the Mediterranean Sea by Atlantic fishes: do biological traits matter?

Since its opening 5.33 million years ago, the Gibraltar Strait has always contributed to the Mediterranean fauna and flora. Despite the increasing importance of the phenomenon, ecological determinants underlying colonization success of Atlantic fishes in the Mediterranean Sea have been poorly investigated. Here we reconstruct the recent historical colonization of the whole Mediterranean Sea by Atlantic fishes and we aim to determine where Atlantic fishes preferentially establish and whether some biological traits and ecological factors can be correlated to the colonization success (climate match, position in the water column, maximum body length, propagules, confamilial resistance, depth). A database on Atlantic fish species records from 1810 to 2006 was built and the colonization rate of each introduced species was estimated. Analysis of Variance, Chi squared test and logistic regression were used to investigate the relationships between ecological variables and colonization success. In addition, an index of asymmetry was used to analyse the relative colonization on the two sides of the Mediterranean Sea. Overall 48.33% of Atlantic species introduced in the Mediterranean Sea succeeded in colonizing eastwards. We found that habitat depth of Atlantic species is significantly related to their colonization success due to the obstacle of the shallow depth of the Gibraltar Strait (300 m). It also appears that despite the cyclonic general water circulation on the North Western basin, the northern side is more colonized than the southern one: 70.40% of the studied species colonize the northern side, while only 29.62% colonize the southern one. Two hypotheses may explain this trend: the bottom-up process that enhances the colonization success of Atlantic fishes along the Spanish coast of Alboran Sea owning to its high productivity and the intensiveness of the scientific explorations along the northern Mediterranean side. We conclude that crossing the Gibraltar Strait does not guarantee the colonization success and that species life-history and functional traits are poor predictors. Instead we suggest that environmental factors may determine favourable locations for invasive species installation. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: J. Cambray.     

Can ants equal honeybees as effective pollinators of the energy crop Jatropha curcas L. under Mediterranean conditions?

Jatropha curcas L. is the subject of many research and breeding programs concerned with its potential as an oil crop for biodiesel production. Despite an increasing amount of information regarding this relatively new crop, pollination requirements of this plant are largely neglected. The aim of the study was to evaluate the relative significance of ants and honeybees as potential pollinators of J. curcas grown under Mediterranean conditions. Jatropha curcas plants bloomed throughout the summer and fall, peaking twice, in early summer and late fall. During this period, the plants were visited by 70 species of insects representing 45 families from seven orders, with most species rarely being observed. Ants and Honeybees were the most common species, accounting for >95% of all flower visits. The foraging behavior of the honeybees followed the pattern of bloom phenology, especially during the summer, and mostly promoted cross‐pollination. Ants on the other hand, mostly promoted self pollination showing no such correlative behavior, reacting often too late to nectar availability, and were highly susceptible to climatic changes. Pollinator exclusion treatments revealed that during summer, fruit and seed sets, as well as seed size and oil and protein contents, were relatively similar for ant and bee‐pollinated flowers. During fall, however, reproductive success of bee‐pollinated flowers was relatively high (66%), while fruit set of ant‐pollinated flowers was significantly reduced from 71 to 11%. In conclusion, while both groups are equal in their pollination effectiveness in the summer, during the fall the honeybees are almost the sole pollinators of the plant. Based on bloom phenology and pollination activity data, the honeybees are responsible for the pollination of more than 80% of the annual reproductive potential of J. curcas, under Mediterranean conditions.     

Long-term changes in Krill biomass and distribution in the Barents Sea: are the changes mainly related to capelin stock size and temperature conditions?

Krill plays a significant role in the Barents Sea ecosystem, providing energy transport between different trophic levels. The current paper presents the results of a long-term study (1980–2009) based on pelagic trawl catches from August to September. Our investigations show that the krill species were distributed widely in the Barents Sea and that the largest krill concentrations were restricted to the west-central and eastern parts of the Barents Sea. The current paper presents the relative biomass indices, and the estimates must be interpreted as minimum biomass. The mean annual krill biomass was estimated to be 22 million tonnes in wet weight, with the highest values being as much as 48 million tonnes. Capelin is the largest pelagic stock, and in some years, their biomass can amount to 4–7 million tonnes, which can impose high predation pressure on krill. When their biomass is high, capelin may consume close to 26 million tonnes annually. The predation from pelagic (herring and blue whiting) and bottom (cod and haddock) fish species was much lower, being 9 and 1 million tonnes, respectively. A negative relationship between krill biomass and capelin stock size above 74°N was observed during the study period. However, during the last decade, the krill biomass has increased despite heavy predation from capelin in some years. A positive significant linear relationship between the mean annual Kola temperature and the krill biomass seems to indicate that the recent warming conditions have favourable impacts on the krill populations in the Barents Sea.     

Red to Mediterranean Sea bioinvasion: natural drift through the Suez Canal,or anthropogenic transport?

The biota of the eastern basin of the Mediterranean Sea has experienced dramatic changes in the last decades, in part as a result of the massive invasion of Red Sea species. The mechanism generally hypothesized for the 'Red-to-Med' invasion is that of natural dispersal through the Suez Canal. To date, however, this hypothesis has not been tested. This study examines the mode of invasion, using as a model the mussel Brachidontes pharaonis, an acclaimed 'Lessepsian migrant' that thrives along the eastern Mediterranean coast. Our findings reveal two distinct lineages of haplotypes, and five possible explanations are discussed for this observation. We show that the genetic exchange among the Mediterranean, Gulf of Suez and the northern Red Sea is sufficiently large to counteract the build up of sequential genetic structure. Nevertheless, these basins are rich in unique haplotypes of unknown origin. We propose that it is historic secondary contact, an ongoing anthropogenic transport or both processes, that participate in driving the population dynamics of B. pharaonis in the Mediterranean and northern Red Sea.     

Developmental rules in the hematopoietic and immune systems of birds: how general are they?

Fundamental rules about the development of the hematopoietic and immune systems have been established in birds, some of which are reviewed here. The organ rudiments belonging to this system provide the stroma, that has to be seeded by extrinsic stem cells. This particular developmental pattern makes it possible to create chimeric organs with stromal cells and stem cells from different origins. Grafting the thymic epithelium alone in a young embryo is sufficient to induce tolerance to tissues of the same origin as that of epithelium, even in a xenogeneic combination. Stem cells that seed the rudiments during development are born in the embryo rather than in the yolk sac and are responsible for definitive hematopoiesis. Data in frog and mouse indicate that these conclusions may be valid in other classes of vertebrates.     

Why is the mediterranean more readily colonized than the Red Sea,by organisms using the Suez Canal as a passageway?

Summary Since the opening of the Suez Canal, more than 120 Red Sea species colonized the eastern Mediterranean, whereas less than 10 Mediterranean species colonized the Red Sea. For most of the species involved in this colonization, the mode of dispersal from the source to the colonized area is through free-drifting propagules. In order to examine whether the current regime of the Suez Canal may be involved in this assymetry in colonization, a mathematical hydraulic model that forecasts the direction and velocity of water currents through the year, along the length of the Canal, was utilized. The movements of free-floating propagules that occur at either entrance of the Canal, was simulated on a computer, and it was found that the completion of a Mediterranean-bound passage of Red Sea propagules is far faster and much more likely than a completion of a Red Sea-bound passage of Mediterranean propagules.Paper No. 7 in the series Colonization of the Eastern Mediterranean by Red Sea species immigrating through the Suez Canal     

But next time?: Unsuccessful Establishment of the Mediterranean Strain of the Green Seaweed Caulerpa taxifolia in the Sea of Japan

We conducted a survey of 63 public aquariums in Japan by means of a questionnaire asking if a green seaweed, Caulerpa taxifolia, was cultured or exhibited in aquariums under the network of the public aquarium association of Japan in 1997. Of 51 aquariums, 16 cultured or exhibited C. taxifolia. Most of the public aquariums possessing C. taxifolia purchased them from aquarium shops or received them from another public aquarium as a donation. Notojima aquarium reported temporal establishment of C. taxifolia in the Sea of Japan between the summer and autumn of 1992 and 1993. C. taxifolia was released into the sea from a 1 m³ cage that was submerged in an open pool. Two colonies with diameters less than 2 m were found near the mouth of a water outflow pipe in both years. Molecular analysis of the ITS rDNA gene of the aquarium strain of Notojima clarified that the seaweed is the same as the aquarium-Mediterranean and Californian invasive strain. Unsuccessful establishment of the invasive strain of C. taxifolia in the Sea of Japan is probably due to water temperatures in winter that are lethal for C. taxifolia. C. taxifolia remains present in many public and private aquariums. If C. taxifoliawere to be released in more temperate waters of Japan, there would be a high risk of establishment and, thus, impact on the marine ecosystem. This suggests that the trade, culture and exhibition of C. taxifolia should be strongly avoided to reduce the chances of accidental release of this harmful species.     

Do systematic daily counts reflect the total number of birds using stopover sites during migration? A test with Eurasian Spoonbill

Many migratory waterbird populations are declining and wetland connectivity is a major conservation challenge. The importance of stopover sites has been typically assessed by peak counts of birds, which underestimate the total number of individuals using the site over a migratory season, especially in small wetlands. We analysed the accuracy of different daily count schemes to estimate the total number of Eurasian Spoonbill that stop over at two tidal wetlands during their autumn migration and compared them with the birds observed leaving the area each day. Total number of birds was obtained by combining numbers of each flock of birds leaving during the season. We obtained different accurate predictors for birds departing daily from each stopover area. Daily low-tide counts were the best predictor of the daily number of birds that stopover in a tidal wetland mainly used to refuel (staging site), whereas daily high-tide counts were best at a wetland mainly used to rest (stopover site). Each measure also accurately predicted annual trends for each area, respectively. Daily low-tide counts could be used as an easy census method to estimate the daily number of individuals using a staging site consistently during the entire migratory season, as well as indicating trends, without the necessity of estimating turnover rates. By contrast, daily high-tide counts would be especially suitable for determining the minimum relevance and the population trends of other tidal wetlands (especially the smaller ones), which regularly support moderate numbers of spoonbills during migration where birds use to stop over for less than one day. This method developed for the spoonbill, a flagship and umbrella species, could represent a first step in improving the conservation of other endangered migratory waterbird populations.     

Quantifying threats in a Mediterranean wetland: are there any changes in their evaluation during a training course?

“Threats analysis” is a conservation discipline directed to identify, quantify, rank, map the human-induced threats occurring in a specific study area, assessing their spatial-temporal regime (e.g., the extension and intensity on specific targets of conservation concern). This approach may be particularly useful in order to define the priorities in the management strategies to be adopted by nature reserves, especially those that are situated in human-altered multi-disturbed contexts. In a remnant Mediterranean wetland of central Italy, where 15 human-induced threats were identified, we compared the assessment given for two regime parameters (scope and severity) of each threat by a panels of not-expert students (n = 13) during different phases of a training academic course, thus evaluating perception modifications during three steps. We applied an experience-based method, then comparing the assessments obtained during the training course with the values obtained previously from a panel of experts (n = 10). Two direct threats (pollution and alien species) significantly changed their mean values in scope during the three steps, and three threats (habitat conversion, garbage, and aircraft) significantly changed as for severity. Students tended to significantly correct their responses in such a way to progressively match with the experts’ responses for a set of threats either for scope (habitat conversion, linear infrastructures, grazing, garbage, fires on reed-beds) or severity (pollution, garbage, fires on reed-beds). Despite the responses were not clear for some threats (aircraft), we suppose that students could assign a initial emphasis towards more charismatic threats as pollution, garbage, fires that instead locally did not appear of priority concern, while threats being uneasily detected (as alien species) were underestimated. Our study showed that a training course with field surveys allows to better define and contextualize the threats affecting a given area, reducing the perception effect that each student had prior to the beginning of the course, when their education information was mainly mass-media based.     

Investigation of 0.2 µm filterable bacteria from the Western Mediterranean Sea using a molecular approach: dominance of potential starvation forms

Although the existence of 0.2 μm filterable bacteria has been known since the early 80's, they are not taken into consideration when modeling microbial food webs, due to an overall lack of information concerning this specific size class. According to physiological studies on starvation forms and investigations on small bacterial cells in marine ecosystems, a 0.2 μm filtrate may consist of different phenotypes: starvation forms of typical marine bacteria, ultramicrobacteria or bacterial cells, even larger than 0.2 μm, but flexible enough to pass the nominal filter pore-size. In this pilot study we examined three filtered seawater fractions from the Western Mediterranean Sea (Bay of Calvi, Corsica/France) - the total bacterial population, the bacterial fraction above 0.2 μm and the 0.2 μm filtrate - to investigate the bacterial community structure of each of those fractions by the molecular approach of denaturing gradient gel electrophoresis (DGGE) of 16S rDNA fragments. The analysis of the resulting DGGE profiles revealed different patterns of dominant bands for the 0.2 μm filterable and the total bacterial populations within the samples. Additionally the 0.2 μm filterable bacterial compartment exhibited obvious differences in band patterns for winter and summer samples, which were not observed for the total bacterial fraction. According to the current knowledge concerning the status of 0.2 μm filterable bacteria, DGGE patterns indicate that most of the fragments representing 0.2 μm filterable bacteria were rather starvation forms of marine bacteria than ultramicrobacteria. The sequencing of excised and cloned DNA bands of the DGGE profiles characterized the phylogenetic affiliation of the corresponding 0.2 μm filterable bacteria, clustering mainly with known, typical marine isolates of both alpha-subclass and gamma-subclass of the Proteobacteria and the Cytophaga-Flavobacterium-Bacteroides branch.     

Connectivity in the network macrostructure of Tursiops truncatus in the Pelagos Sanctuary (NW Mediterranean Sea): does landscape matter?

The bottlenose dolphin (Tursiops truncatus Montagu, 1821) is a regularly observed species in the Mediterranean Sea, but its network organization has never been investigated on a large scale. We described the network macrostructure of the bottlenose dolphin (meta)population inhabiting the Pelagos Sanctuary (a wide protected area located in the north-western portion of the Mediterranean basin) and we analysed its connectivity in relation to the landscape traits. We pooled effort and sighting data collected by 13 different research institutions operating within the Pelagos Sanctuary from 1994 to 2011 to examine the distribution of bottlenose dolphins in the Pelagos study area and then we applied a social network analysis, investigating the association patterns of the photo-identified dolphins (806 individuals in 605 sightings). The bottlenose dolphin (meta)population inhabiting the Pelagos Sanctuary is clustered in discrete units whose borders coincide with habitat breakages. This complex structure seems to be shaped by the geo-morphological and ecological features of the landscape, through a mechanism of local specialization of the resident dolphins. Five distinct clusters were identified in the (meta)population and two of them were solid enough to be further investigated and compared. Significant differences were found in the network parameters, suggesting a different social organization of the clusters, possibly as a consequence of the different local specialization.