The effect of water availability on fuel deposition of two staging Sylvia warblers

In order to succeed in crossing extensive ecological barriers, migratory birds usually deposit fuel en route. High rates of fuel deposition may enable birds to shorten their total migration time and are therefore advantageous for time-minimizing migrants. Several studies have suggested that water provision may increase food utilization in non-migratory birds. The goal of this study was to test the influence of water availability on the fuel deposition of en route migratory passerines. We studied fuel deposition of blackcaps Sylvia atricapilla and lesser whitethroats S. curruca staging in a plantation of Mount Atlas gum-tree Pistacia atlantica in the northern Negev desert, Israel, during the autumns of 2000 and 2002. We manipulated water availability at the site and measured the effect of water supplementation on fuel deposition of birds of both species. We found that when water was available, blackcaps had higher fuel loads and higher fuel deposition rates than during control trials. However, water availability had no effect on fuel deposition of lesser whitethroats. Species-specific differences in adaptations to arid conditions, reflected in the species' winter habitat preferences, may be responsible for the between-species dissimilarity in responding to water provision. We suggest that water availability may have strong ecological and evolutionary consequences for birds migrating through arid environments, by its possible effect on bird behavior and physiology.     

Weak phylogenetic effects on ecological niches of Sylvia warblers

To understand the evolution of ecological niches it is important to know whether niche evolution is constrained by phylogeny. We approached this question for Sylvia warblers by testing if closely related species are more similar in 20 ecologically relevant morphological traits than distantly related species. Phylogenetic relatedness was quantified using a molecular phylogeny based on the mitochondrial cytochrome b gene. By Principal Component Analysis (PCA) two major niche axes were extracted. We tested the individual ecomorphological traits and the positions of the species on the PCA axes for phylogenetic effects using Mantel tests. The results demonstrated small but significant phylogenetic effects only for the length of the middle toe, a trait probably correlated with locomotion. In general, however, phylogenetic effects were very weak. This suggests that ecological niches in passerine birds have the potential to evolve rapidly and are not subject to major phylogenetic constraints.     

Life-history of two African Sylvia warblers: low annual fecundity and long post-fledging care

The investigation of factors that cause differences in life-history traits between temperate and tropical birds is often hampered by a lack of knowledge about tropical species. Even within the well-known warblers of the genus Sylvia , which include resident species from temperate and tropical regions as well as migrants, there are few data from tropical species. We investigated the breeding biology of the tropical species Sylvia lugens and S. boehmi in a 2-year study in Kenya. Both species had a clutch size of 2.0 and laid c.  3.7 clutches per year. Breeding was characterized by long incubation periods ( S. lugens 14.5 days, S. boehmi 15.0 days), long nestling periods (16.0 and 12.9 days, respectively) and high predation rates (Mayfield nest success S. lugens 33.2%, S. boehmi 19.4%). Annual fecundity was 2.3 fledglings in S. lugens and 1.4 fledglings in S. boehmi . After fledging, the young birds were fed for 37.5 days ( S. lugens ) and 58.5 days ( S. boehmi ) (time to independence) and they stayed in their parents' territory for days or weeks, even after feeding had stopped. Fledgling survival until independence was 55.4% in S. lugens and 69.2% in S. boehmi . In general, S. lugens and S. boehmi have smaller but more numerous clutches, longer developmental periods, higher nest predation rates, lower annual fecundity and longer post-fledging care than their temperate congenerics.     

Effects of experience and object complexity on exploration in garden warblers (Sylvia borin)

Animals are increasingly exposed to novel environmental conditions because of human activities. An organism's ability to cope with these challenges is critical to its survival. The decision of whether or not an animal should investigate environmental changes involves a trade-off between the risk and the potential benefit of a novel resource. Novelty often elicits approach (exploratory) as well as avoidance behaviour in animals, and the extent of each of these behaviours may influence learning about the environment. We formulated and tested several hypotheses to determine how external factors (complexity of a novel stimulus) and internal factors (experience with objects) might influence exploration latencies to touch a novel object based on either cost or benefit considerations. Garden warblers were confronted with a simple and a complex novel object in their familiar cages, and latencies until first touch were measured. Additionally, corticosterone levels before and after the experiment were measured to assess whether differences in baseline levels might explain variations in latency to approach and whether presentation of novel objects is stressful. The complex object was touched significantly later than the simple object. Experienced birds investigated both types of objects later than inexperienced birds. Although birds showed marked approach–avoidance behaviour with the complex object, none of the objects elicited a corticosterone stress response. The results indicate that garden warblers consider both costs and benefits when exploring novel objects, and that the relative influence of costs and benefits varies with external and internal factors.     

The effect of metabolic fuel availability on thermoregulation and torpor in a marsupial hibernator

The physiological signal for torpor initiation appears to be related to fuel availability. Studies on metabolic fuel inhibition in placental heterotherms show that glucose deprivation via the inhibitor 2-deoxy-D-glucose (2DG) initiates a torpor-like state, whereas fatty acid deprivation via mercaptoacetate (MA) does not. As previous studies using inhibitors were limited to quantifying body temperature in placentals, we investigated whether inhibition of glucose or fatty acids for cellular oxidation induces torpor in the marsupial hibernator Cercartetus nanus, and how the response of metabolic rate is related to body temperature. Glucoprivation initiated a torpor-like state in C. nanus, but animals had much higher minimum body temperatures and metabolic rates than those of torpid food-deprived animals and arousal rates were slower. Moreover, 2DG-treated animals were thermoregulating at ambient temperatures of 20 and 12 °C, whereas food-deprived torpid animals were thermo-conforming. We suggest that glucoprivation reduces the hypothalamic body temperature set point, but only by about 8 °C rather than the approximately 28 °C during natural torpor. Reduced fatty acid availability via MA also induced a torpor-like state in some C. nanus, with physiological variables that did not differ from those of torpid food-deprived animals. We conclude that reduced glucose availability forms only part of the physiological trigger for torpor initiation in C. nanus. Reduced fatty acid availability, unlike for placental heterotherms, may be an important cue for torpor initiation in C. nanus, perhaps because marsupials lack functional brown adipose tissue.Abbreviations BAT brown adipose tissue - BMR basal metabolic rate - 2DG 2-deoxy-D-glucose - FD food deprived - GLM general linear models - MA mercaptoacetate - MR metabolic rate - RQ respiratory quotient - T_a ambient temperature - T_b body temperature - T_set body temperature set pointCommunicated by I.D. Hume     

When and where to fuel before crossing the Sahara desert – extended stopover and migratory fuelling in first-year garden warblers Sylvia borin

Large numbers of passerine migrants cross the Sahara desert every year on their way to-and-from wintering areas in tropical Africa. In the desert, hardly any fuelling opportunities exist and most migrants have to prepare in advance. A central question is how inexperienced birds know where to fuel. Inexperienced garden warblers Sylvia borin were studied in Greece just before the desert crossing in autumn. Body mass data collected at two sites indicate that most birds do not fuel for the desert crossing further north. For the first time, detailed information about stopover duration close to the Sahara desert was studied by using light weight radio-transmitters. Results from Crete show that most first-year garden warblers arrive with relatively small fuel loads in relation to lean body mass (<30%), stay for 13–20 d and depart with an average fuel load of about 100%. Radio-tagged birds performed small scale movements initially and took advantage of fig fruits. Birds trapped at fig trees were heavier than birds trapped with tape lures, showing that tape lures can bias the sample of migrants trapped. The precise fuelling pattern found indicates that first-year migrants must also include external spatial cues to make the preparation for crossing the desert in the right area.     

Recognizability of different food types in faeces and in alimentary flushes of Sylvia warblers

The efficiency of the analysis of faeces and flushes of the digestive tract was examined by feeding captive Garden Warblers Sylvia borin and Blackcaps S. atricapilla with different food types (arthropods, fruits). Faecal analysis underestimated aphids; the analysis of flushes overestimated beetles and underestimated aphids and fruits. Correction factors to remove these biases are given. Flushing free-living birds showed no noticeable effect on recapture rates and body mass. Methods of calculating the number of prey items from different fragments are evaluated.     

Basal and stress-induced corticosterone levels of garden warblers,Sylvia borin,during migration

Summary Plasma levels of the metabolically and behaviorally active corticosteroid hormone, corticosterone, were studied in garden warblers in the laboratory and in the field during the autumnal migratory phase. Garden warblers showing nocturnal migratory activity in the laboratory had elevated levels of corticosterone at the end of the dark phase and low levels during daytime. When nocturnal migratory activity was experimentally disrupted by food deprivation and subsequent refeeding or after spontaneous termination of migratory activity this rhythm was absent. Garden warblers stopping over in the Sahara desert during autumnal migration had low levels of corticosterone. Levels were negatively correlated with fat stores and body mass in birds sampled throughout the day. These levels were generally lower than those associated with stress in response to repeated handling and blood sampling. The results suggest (1) the existence of diel changes in adrenocortical hormonal activity that could be involved in regulation of migration, and (2) that garden warblers carrying large fat depots are not stressed by prolonged flight or lack of appropiate feeding areas during migration over the desert.Abbreviations ACTH adrenocorticotrope hormone - cpm counts per minute - EtOH ethanol - RIA radioimmunoassay     

Molecular phylogeny and the historical biogeography of the warblers of the genus Sylvia (Aves)

A molecular phylogeny based on DNA/DNA hybridization revealed that the Sylvia-Parisoma complex is monophyletic and includes three main groups of species, the “mid-European” warblers, the genus Parisoma, and the “eu-Mediterranean” Sylvia species sensu stricto. The latter can be assigned to three main clusters, a “West-Mediterranean” group, a “Central-Mediterranean group”, and an “East-Mediterranean” group. The radiation of the whole complex is much more ancient than formerly believed. It started ca 12–13 Ma ago and the ancestors of the main extant groups differentiated during the Pliocene. Only speciation events within the “eu-Mediterranean” lineages occurred during the Pleistocene. The paleoclimatical and paleoecological history of the Mediterranean region is too complicated to provide any evidence for direct relationships between past events and evolutionary steps of these taxa which did not leave any reliable fossil record. However, some major speciation events may be related to well documented climatical crises as well as paleobotanical data. The largely man-induced extension of matorrals over several millenia presumably extended the range of several species that were formerly much more restricted, which complicates reconstruction of the spatio-temporal course of speciation.     

Migratory stopover conditions affect the developmental state of male gonads in garden warblers (Sylvia borin)

Long-distance migrants face the challenge of a short window for reproduction that requires optimal timing and full functional gonads. Male garden warblers (Sylvia borin) meet these demands by initiating testicular recrudescence during spring migration, enabling them to reproduce immediately after arrival at the breeding grounds. In a combined field and laboratory study, we investigated testicular size, plasma levels of luteinizing hormone (LH), androstenedione (AE), 5α-dihydrotestosterone (DHT), testosterone and nocturnal migratory restlessness (Zugunruhe) under different stopover conditions. We manipulated food availability, the duration of stopover and simulated migration by food deprivation. Garden warblers showed significantly retarded testicular development after nine days of stopover under limited food conditions compared to birds that had ad libitum access to food. However, there was no significant difference in Zugunruhe between the two groups. Thus, the degree of Zugunruhe was unaffected by the quality of the stopover site and migration continued independent of the developmental state of the testis. We suggest that male garden warblers face the necessity to either compensate for slowed testicular recrudescence during the subsequent leg of migration and delay arrival at the breeding grounds, or arrive with less developed testes. Either of these may reduce annual reproductive success.     

Nitrogen availability and uptake by grassland in mesocosms at two water levels and two water qualities

We studied the effect of water table (-5 or -30 cm) and water type (rain- or groundwater) on the above- and below-ground phytomass production, species composition and nitrogen uptake of grassland.Nitrogen mineralization, nitrification, methane production, redox potential and pH at different depths in the profile were measured and used to monitor gradual changes in variables influencing phytomass production.The rise in the water level lowered the nitrogen uptake in the above-ground phytomass from 14.1 to 11.4 g N per m², but the DM production did not decrease and varied from 566 to 690 g per m². The total root mass increased from 82 to 363 g DM per m², with the proportion in the 5 to 10 cm layer increasing the most from 13 to 24%.The high water level lowered the potential N mineralization in the upper 5 cm of the soil from 16.1 to 4.3 g N per m² and in the deeper 5 to 30 cm layer from 12.6 to 9.4 g N per m² respectively, so the importance of the deeper layer as a source of N increased. The total amount of mineral N that accumulated in the 40 cm deep soil cores decreased from 31.3 to 15.5 g N per m². The above-ground vegetation took up 71 to 76% of this amount in the high water level treatment and only 37 to 57% under drier conditions.Redox potential and methane production indicated anaerobic conditions below 5 cm in both level treatments and in the top 5 cm of the high water level treatment. But some nitrification was measured there also, thus aerobic and anaerobic conditions occurred together. The low N mineralization was attributed to low soil respiration.Raising the water level brought about an increase in the above ground biomass of Glyceria fluitans and an increase in root mass, especially deeper in the soil. Both are responsible for the relatively greater fraction of nitrogen that was taken up from the soil, although less N was available. The nitrification indicates that oxygen is transported by the root system to soil microsites and partly compensates for the anaerobic conditions caused by water saturation.The calcareous groundwater raised the pH in the upper soil layer from 5.3 to 5.8 but no effect on N mineralization was measured.     

Competitive strategies for water availability in two Mediterranean Quercus species

Competition for water availability was studied in a mixed natural stand of Quercus suber L. and Quercus cerris L. growing in Sicily by measuring diurnal changes of leaf conductance to water vapour ( g _L), water potential ( Ψ _L) and relative water content ( RWC ) in April, July and October 1997 as well as the seasonal changes in root hydraulic conductance per unit leaf surface area ( K _RL). Quercus cerris behaved as a drought-tolerant species, with strong reductions of K _RL, Ψ _L, and RWC in the summer. By contrast, Q. suber appeared to withstand summer drought by an avoidance strategy based on reducing g _L, maintaining Ψ _L and RWC high and K _RL at the same level as that measured in the spring. A 'conductance ratio' ( CR ) was calculated in terms of the ratio of g _L to K _RL. Seasonal changes of this ratio contrasted in the two species, thus suggesting that Q. suber and Q. cerris did not really compete for available water. In the summer, when Q. suber was extracting water from the soil to maintain high leaf hydration, Q. cerris had restricted water absorption, thus suffering drought but tolerating its effects. The possibility that cohabitation of drought-tolerant with drought-avoiding species can be generalized is also discussed.     

Oxygen availability effect on the performance of air‐breathing cathode microbial fuel cell

The effect of the oxygen availability over the performance of an air‐breathing microbial fuel cell (MFC) was studied by limiting the oxygen supply to the cathode. It was found that anodic reaction was the limiting stage in the performance of the MFC while oxygen was fully available at cathode. As the cathode was depleted of oxygen, the current density becomes limited by oxygen transport to the electrode surface. The exerted current density was maintained when oxygen mole fraction was higher than 10% due to the very good performance of the cathodic catalysts. However, the current density drastically falls when working at lower concentrations because of mass transfer limitations. In this sense it must be highlighted that the maximum exerted power, when oxygen mole fraction was higher than 10%, was almost three times higher than that obtained when oxygen mole fraction was 5%. Regarding to the wastewater treatment, a significant decrease in the COD removal was obtained when the MFC performance was reduced due to the limited availability of oxygen, which indicates the significant role of the electrogenic microorganisms in the COD removal in MFC. In addition, the low availability of oxygen at the cathode leads to a lower presence of oxygen at the anode, resulting in an increase in the coulombic efficiency. © 2015 American Institute of Chemical Engineers Biotechnol. Prog., 31:900–907, 2015     

Morphological and physiological responses of two coffee progenies to soil water availability

Drought is a major environmental constraint affecting growth and production of coffee. The effects of water supply on growth, biomass allocation, water relations, and gas exchange in two coffee progenies representing drought-tolerant (Siriema) and drought-sensitive (Catucaí) genotypes were compared. They were grown in 12-L pots until 4-months old, when they were submitted to two watering treatments for 60 d: plants receiving either 100% transpired water (control plants) or a fraction (about 40%) of the amount of water transpired by control plants (drought-stressed plants). Under control conditions, Siriema grew faster than Catucaí. Regardless of the watering regimes and progenies, relative growth rate (RGR) was positively correlated both with net assimilation rate (NAR) and long-term water-use efficiency (WUE), but not with differences in biomass allocation. Both progenies responded to drought stress through (i) similar decreases in both RGR and NAR with marginal, if any, changes in allocation; (ii) decreases in leaf water potential, which occurred to a greater extent in Catucaí than in Siriema, even though they have showed similar abilities to adjust osmotically and elastically; (iii) similar reductions in net photosynthesis due mainly to nonstomatal factors; and (iv) decreases in transpiration rate coupled with increased long-term WUE. However, the lower transpiration rate and the higher long-term WUE as found in Siriema relative to Catucaí under control conditions persisted under drought conditions. Overall, the major differences between these progenies were largely associated with differences in plant water use, which was likely related to the improved water status of Siriema. The possible implications of selecting coffee genotypes for high WUE are discussed.     

Biometry and phenology of two sibling Phylloscopus warblers on their circum-Mediterranean migrations

The Mediterranean Sea is known as an ecological barrier for numerous migratory birds flying from European breeding grounds to African wintering sites. Birds generally avoid migration over open sea and fly over land. In the Mediterranean Basin, few land bridges or bottlenecks for migratory birds exist. The narrowest are at the western and eastern extremes: the Strait of Gibraltar and Israel. Comparative studies between these locations are extremely rare to date. Therefore, in order to elucidate the differences between the two flyways, we compared data collected simultaneously for two sister leaf warbler species, the Bonelli’s Warbler complex, Phylloscopus bonelli and Phylloscopus orientalis, at ringing stations in the western Mediterranean Basin Gibraltar, and the eastern Eilat, Israel. Data on biometrics and passage dates of individuals trapped at Gibraltar and Eilat were used, and it was found that mean arrival date of Western Bonelli’s Warblers at Gibraltar was 15 days later than Eastern Bonelli’s Warblers at Eilat. Furthermore, Western Bonelli’s Warblers had shorter wings than Eastern Bonelli’s Warblers. On the other hand, birds in Eilat were in poorer body condition than individuals in Gibraltar. The comparison between geographically distant stop-over sites contributes to furthering our understanding of the development of migration strategies across ecological barriers in sibling species. Our study showed that populations that breed in southwestern Europe migrate through Gibraltar and winter in West Africa are able to accomplish migration in comparatively good body condition. This is in contrast to those that winter in East Africa, migrate through Israel and have to endure the combined challenge of crossing the Sahel, Sahara and Sinai deserts before reaching their breeding grounds across southeast Europe and southwest Asia. Hence, the discrepancies described between the western and the eastern flyway suggest that individuals in the west, in general, migrate shorter distances, have a physiologically less demanding crossing of the North African deserts and appear to stage before their crossing the Strait of Gibraltar, a privilege unavailable to the migrants of the eastern flyway.     

液态地膜覆盖对土壤水分有效性的影响

采用田间微区试验方式,观测和分析了液膜地表覆盖下土壤含水量、花生植株伸长速率、叶面积指数、叶片光合速率、水分利用效率及产量等指标,并利用隶属函数法进行数值转换后,对液膜覆盖的土壤水分有效性进行了分析.结果表明,液膜覆盖提高土壤含水量103％ ～ 167％,且随液膜浓度的增大有效性提高;不同土层间,花生耗水量差异显著,其中以土层深度为20 ～ 40 cm差异最大;液膜覆盖也明显提高了光合速率,增幅为1.9％～15.6％;叶面积指数提高0.3％ ～26.4％,改善了植株光合形态.综合全部指标表明,液膜类型为3号,液膜浓度为高水平时,覆盖效应最为明显.     

The effect of hummingbird flower mites on nectar availability of two sympatric Heliconia species in a Brazilian Atlantic forest

BACKGROUND AND AIMS: Hummingbird flower mites feed and reproduce in flowers of host plants pollinated by hummingbirds, and use the nostrils and bill of the hummingbird to move from plant to plant. These mites compete with the pollinator for the nectar produced by flowers. An investigation was made of the relationship between the pattern of nectar production and the effects of hummingbird flower mites in the flowers of two sympatric species of Heliconia (Heliconiaceae). METHODS: Nectar production was sampled by carrying out two experiments: 2-hour intervals and accumulated nectar. Flowers with and without mites were used in both experiments. KEY RESULTS: Exclusion of mites increased nectar production, especially in accumulated daily production (a maximum of 49 % more nectar). Both Heliconia species had the same pattern of nectar production: a high concentration in the morning, which was progressively reduced as the day passed. This pattern of nectar production coincides with the behaviour of the pollinator, which makes more frequent visits in the morning, as observed in a previous study. CONCLUSIONS: The results suggest that the impact of mites on nectar availability of Heliconia is more important with regard to total volume of nectar produced irrespective of flower longevity. A high variation among individuals in nectar produced in the populations was also observed. Hummingbird flower mites strongly affect availability of nectar for hummingbirds.     

Impacts of long-term enhanced UV-B radiation on bryophytes in two sub-Arctic heathland sites of contrasting water availability

Background and Aims

Anthropogenic depletion of stratospheric ozone in Arctic latitudes has resulted in an increase of ultraviolet-B radiation (UV-B) reaching the biosphere. UV-B exposure is known to reduce above-ground biomass and plant height, to increase DNA damage and cause accumulation of UV-absorbing compounds in polar plants. However, many studies on Arctic mosses tended to be inconclusive. The importance of different water availability in influencing UV-B impacts on lower plants in the Arctic has been poorly explored and might partially explain the observed wide variation of responses, given the importance of water in controlling bryophyte physiology. This study aimed to assess the long-term responses of three common sub-Arctic bryophytes to enhanced UV-B radiation (+UV-B) and to elucidate the influence of water supply on those responses.

Methods

Responses of three sub-Arctic bryophytes (the mosses Hylocomium splendens and Polytrichum commune and the liverwort Barbilophozia lycopodioides) to +UV-B for 15 and 13 years were studied in two field experiments using lamps for UV-B enhancement with identical design and located in neighbouring areas with contrasting water availability (naturally mesic and drier sites). Responses evaluated included bryophyte abundance, growth, sporophyte production and sclerophylly; cellular protection by accumulation of UV-absorbing compounds, β-carotene, xanthophylls and development of non-photochemical quenching (NPQ); and impacts on photosynthesis performance by maximum quantum yield (F_v /F_m) and electron transport rate (ETR) through photosystem II (PSII) and chlorophyll concentrations.

Results

Responses were species specific: H. splendens responded most to +UV-B, with reduction in both annual growth (–22 %) and sporophyte production (–44 %), together with increased β-carotene, violaxanthin, total chlorophyll and NPQ, and decreased zeaxanthin and de-epoxidation of the xanthophyll cycle pool (DES). Barbilophozia lycopodioides responded less to +UV-B, showing increased β-carotene and sclerophylly and decreased UV-absorbing compounds. Polytrichum commune only showed small morphogenetic changes. No effect of UV-B on bryophyte cover was observed. Water availability had profound effects on bryophyte ecophysiology, and plants showed, in general, lower growth and ETR, together with a higher photoprotection in the drier site. Water availability also influenced bryophyte responses to +UV-B and, in particular, responses were less detectable in the drier site.

Conclusions

Impacts of UV-B exposure on Arctic bryophytes were significant, in contrast to modest or absent UV-B effects measured in previous studies. The impacts were more easily detectable in species with high plasticity such as H. splendens and less obvious, or more subtle, under drier conditions. Species biology and water supply greatly influences the impact of UV-B on at least some Arctic bryophytes and could contribute to the wide variation of responses observed previously.