Variation In Food Supply Research Articles

Increased diet breadth of little brown bats (Myotis lucifugus) at their northern range limit: a multimethod approach

The distribution of small mammals is constrained by extreme environmental demands and variable food supplies that are commonly incurred at northern latitudes. Little brown bats (Myotis lucifugus (Le Conte, 1831)) are at the northwestern limits of their range in Alaska (USA), where environmental demands are higher and prey availability is more seasonal than elsewhere in their range. We hypothesized that the little brown bat in interior Alaska has adjusted to these constraints by broadening its foraging niche, relative to that of southern conspecifics. We analyzed arthropod fragments (microhistology) in guano to describe prey composition to order. We compared the efficacy of evaluating diet by microhistology with DNA analysis and stable isotope analysis on guano and hair. Bats consumed aerial prey such as Lepidoptera (moths) and Diptera (true flies and mosquitoes), as well as terrestrial arthropods including Araneae (spiders). Shifts in the proportion of aerial prey in the diet were closely linked to ordinal day. Values for δ15N in hair indicated that bats were generalists in interior Alaska, coastal Alaska, and the Yukon (Canada), but significant outliers indicated that some individuals have distinct diets. The little brown bat’s flexibility in feeding strategies likely allows this species to sustain populations in arctic and subarctic regions.

Food supply and size class depending variations in phytodetritus intake in the benthic foraminifer Ammonia tepida.

ABSTRACTAmmonia tepida is a common and abundant benthic foraminifer in intertidal mudflats. Benthic foraminifera are primary consumers and detritivores and act as key players in sediment nutrient fluxes. In this study, laboratory feeding experiments using isotope-labeled phytodetritus were carried out with A. tepida collected at the German Wadden Sea, to investigate the response of A. tepida to varying food supply. Feeding mode (single pulse, constant feeding; different incubation temperatures) caused strong variations in cytoplasmic carbon and nitrogen cycling, suggesting generalistic adaptations to variations in food availability. To study the influence of intraspecific size to foraminiferal carbon and nitrogen cycling, three size fractions (125–250 µm, 250–355 µm, >355 µm) of A. tepida specimens were separated. Small individuals showed higher weight specific intake for phytodetritus, especially for phytodetrital nitrogen, highlighting that size distribution within foraminiferal populations is relevant to interpret foraminiferal carbon and nitrogen cycling. These results were used to extrapolate the data to natural populations of living A. tepida in sediment cores, demonstrating the impact of high abundances of small individuals on phytodetritus processing and nutrient cycling. It is estimated that at high abundances of individuals in the 125–250 µm size fraction, Ammonia populations can account for more than 11% of phytodetritus processing in intertidal benthic communities.

Food supply fluctuations constrain group sizes of kangaroos and in turn shape their vigilance and feeding strategies

Seasonal variation in food resources and predation risk imposes major constraints on herbivores, which must adjust their behaviour to maximize their energy intake and survival. In seasonally driven landscapes, it is not yet clear what the primary drivers are that shape seasonal variation in vigilance and feeding rates. These rates have been shown to vary in relation to various environmental, social and individual factors, but many of these factors also vary through the year, due to variation in food supply. We studied wild female eastern grey kangaroos, Macropus giganteus, under low predation risk over a year to investigate whether vigilance and feeding rates varied seasonally and whether this variation was mainly driven by food quantity or quality, group size or individuals' reproductive states. Both vigilance and feeding rates varied seasonally, as did food quantity and quality and group size. Vigilance, including antipredator (head orientation away from the group) and exclusive (i.e. vigilance without chewing) vigilance, decreased and feeding rate increased with increasing group size. However, because group size increased with food quality and quantity, food resources emerged as the primary driver of variation in behavioural strategies. These results suggest that the observed effects of group size on the trade-off between food acquisition and safety are in fact corollaries of the seasonal variation in food supply in our study system, in which the risk of predation on adults is low, and hence are by-products of the foraging choices made by kangaroos in response to the dynamics of the quantity and quality of food.

Differential plasticity to water and nutrients between crops and their wild progenitors

Crop domestication has resulted in relevant phenotypic divergences between crop plants and wild progenitors, but domestication effects on phenotypic plasticity are poorly known. We grew plants of domesticated and wild progenitor accessions of seven taxonomically-diverse crops in three experimental glasshouse treatments differing in soil water and nutrient availabilities, and measured growth, morphological and physiological traits that are key in plant responses to water and nutrient limitations. We compared growth performance, trait means, and norms of reaction between domestication statuses and crop species. Phenotypes were significantly affected by the experimental treatments. Under low water and low nutrient availabilities, plants decreased specific leaf area to produce smaller and thicker leaves, and decreased stomatal conductance. Plasticity to changes in water availability was more pronounced than to varying nutrient supply. Domesticated and wild accessions significantly differed in plasticity patterns to limiting water for several key traits (maximum height, total leaf area, plant-level photosynthetic rate and growth performance traits). Our results thus provide initial insight into generalized domestication effects on phenotypic plasticity. Importantly, crop plants outperformed wild plants in favorable conditions, but suffered a higher loss of performance under water stress, which contrasts with studies suggesting that selection for high performance in optimum conditions might also improve it in stressful environments. We propose that the greater phenotypic homeostasis of the wild progenitors may be a target for future breeding focused on selection for adaptive norms of reaction in heterogeneous environments.

Phytoplankton functional diversity increases ecosystem productivity and stability

The effect of biodiversity on ecosystem functioning is one of the major questions of ecology. However, the role of phytoplankton functional diversity in ecosystem productivity and stability under fluctuating (i.e. non-equilibrium) environments remains largely unknown. Here we use a marine ecosystem model to study the effect of phytoplankton functional diversity on both ecosystem productivity and its stability for seasonally variable nutrient supply and temperature. Functional diversity ranges from low to high along these two environmental axes independently. Changes in diversity are obtained by varying the range of uptake strategies and thermal preferences of the species present in the community. Species can range from resource gleaners to opportunists, and from cold to warm thermal preferences. The phytoplankton communities self-assemble as a result of species selection by resource competition (nutrients) and environmental filtering (temperature). Both processes lead to species asynchrony but their effect on productivity and stability differ. We find that the diversity of temperature niches has a strong and direct positive effect on productivity and stability due to species complementarity, while the diversity of uptake strategies has a weak and indirect positive effect due to sampling probability. These results show that more functionally diverse phytoplankton communities lead to higher and more stable ecosystem productivity but the positive effect of biodiversity on ecosystem functioning depends critically on the type of environmental gradient.

Post‐fledging survival of Little Owls Athene noctua in relation to nestling food supply

Among the range of determinants of post‐fledging survival in altricial birds, the energy supply to the growing juveniles is likely to play a central role. However, the exact mechanisms shaping post‐fledging survival are poorly understood. Using a food supplementation experiment, we determined the effect of variation in food supply on the survival of juvenile Little Owls Athene noctua from hatching to 2 months post‐fledging. Experimental broods were food‐supplemented for 36 days during the nestling and the early post‐fledging period. The fate of 307 juveniles (95 of them provided with extra food) was determined by nest monitoring and radiotelemetry. In unsupplemented birds, the rates of survival measured at 5‐day intervals were lowest during the nestling stage, remained low during the early post‐fledging stage and steadily increased after about 2 weeks post‐fledging. Food supplementation substantially increased nestling survival, but we detected no direct treatment effect on post‐fledging survival. Instead, we found a strong indirect effect of food supplementation, in that fledglings of good physical condition had markedly higher chances of surviving the post‐fledging period compared with those in poor condition. Experimental food supplementation increased survival over the first 3 months from 45% to 64.6%. This suggests that energy reserves built up during the nestling stage influence post‐fledging survival and ultimately parental reproductive output. The low nestling and post‐fledging survival shows that the early life‐history stages constitute a crucial bottleneck of reproductive ecology in Little Owls. The strong treatment effects on the number of independent offspring indicate that natural variation in food supply is an important determinant of spatio‐temporal patterns in Little Owl demography.

Paleoecology and paleoenvironmental implications of turritelline gastropod-dominated assemblages from the Gatun Formation (Upper Miocene) of Panama

Turritelline-dominated assemblages (TDAs) frequently occur in the middle-late Miocene Gatun Formation, and are not uncommon features in the broader fossil record. By gaining a better understanding of the paleoenvironment and taphonomic processes leading to their formation we can gain insight into the conditions in the Western Atlantic (WA) during the Miocene shoaling of the Central American Seaway, as well as the conditions which may lead to TDA formation generally. TDA and non-TDA beds within the Gatun were examined for shell orientation, sclerobiont coverage, drilling predation frequency and site stereotypy, and sediment composition. The most abundant species, T. altilira, was also examined using oxygen isotopic sclerochronology to compare growth rate and environmental conditions during the formation of TDA and non-TDA beds. Mean annual range of temperature (MART) was found to be 6.2°C, with a moderate associated negative O-C correlation. These data confirm the influence of Tropical Eastern Pacific (TEP) upwelling waters in the WA at this time. Upwelling conditions were found to be associated with all T. altilira, regardless of their source, indicating that Gatun TDAs are not the result of variation in nutrient supply. Orientation data from within a TDA, grain size, and sclerobiont coverage all suggest that TDAs in the Gatun are the result of variation in sediment supply/winnowing. We used the Theoretical Apex System and a calculated minimum number of individuals to determine that the frequency of drilling predation and site stereotypy within and without TDAs was statistically indistinguishable. T. altilira was found to live up to 3years, growing between 50 and 60mm in the first year of life with a subsequent decline in growth rate.

Investigating δ18O of Turbo sarmaticus (L. 1758) as an indicator of sea surface temperatures

The large marine gastropod Turbo sarmaticus was (and still is) an important food item for coastal foragers along the south coast of South Africa. Opercula of this species are well-preserved in both Holocene and Pleistocene archaeological sites, offering the opportunity to reconstruct past sea surface temperatures from δ18O of shell carbonate over much of the last glacial cycle. We have analysed δ18O and δ13C in 16 opercula and one shell of modern animals collected alive from an area with good SST records, in order to explore how reliably this species records water temperature through the year and to investigate possible ‘vital effects’ that may influence the isotope record. We find that T. sarmaticus deposits aragonite in both operculum and shell in oxygen isotopic equilibrium with seawater. Operculum δ18O values of this species reliably reflect water temperatures between c.14 and 24°C, although they do not always capture temperature extremes, especially in winter, likely due to slower growth under stressful growth conditions. These thresholds probably alter according to factors such as variations in nutrient supply. The averaged maximum and minimum values across the set of sixteen serially sampled opercula very closely approximate the temperatures of the warmest and coolest months and therefore provide a good measure of the seasonal temperature range, and of mean annual SST. δ18O of edge increments can, to some extent, be used to indicate season of collection, within the broad categories of warmer/cooler seasons.

Stage-dependent stoichiometric homeostasis and responses of nutrient resorption in Amaranthus mangostanus to nitrogen and phosphorus addition.

Stoichiometric homeostasis is the ability of plants remaining their element composition relatively stable regardless of changes in nutrient availability, via various physiological mechanisms. Nutrient resorption is one of such key mechanisms, but whether and how nitrogen and phosphorus homeostasis and resorption in plants would change with growth-stages under variable nutrient supply was unclear. A nitrogen (N) and phosphorus (P) fertilizer addition experiment was conducted to evaluate the dynamics of N and P homeostasis and resorption efficiency during different growth-stages of Amaranthus mangostanus in a greenhouse. The homeostasis regulation coefficient of green-leaf P varied significantly, while that of green-leaf N maintained relatively stable across growth stages. Moreover, homeostasis regulation coefficient of N was higher at seedling stage but lower at flowering stage than that of P at corresponding stages, suggesting that the growth of A. mangostanus may switch from being more N- to P-limited from vegetative to reproductive stage. N resorption efficiency (NRE) was higher and P resorption efficiency (PRE) was lower at flowering than seed-filling stage. The nutrient dynamics displayed here suggested contrasting nutrient homeostasis and resorption responses of plants to environmental nutrient availability across growth stages. These findings can improve the understanding of nutrition maintenance mechanism of plants during their growth.

GrowScreen-PaGe, a non-invasive, high-throughput phenotyping system based on germination paper to quantify crop phenotypic diversity and plasticity of root traits under varying nutrient supply.

New techniques and approaches have been developed for root phenotyping recently; however, rapid and repeatable non-invasive root phenotyping remains challenging. Here, we present GrowScreen-PaGe, a non-invasive, high-throughput phenotyping system (4 plants min-1) based on flat germination paper. GrowScreen-PaGe allows the acquisition of time series of the developing root systems of 500 plants, thereby enabling to quantify short-term variations in root system. The choice of germination paper was found to be crucial and paper☓root interaction should be considered when comparing data from different studies on germination paper. The system is suitable for phenotyping dicot and monocot plant species. The potential of the system for high-throughput phenotyping was shown by investigating phenotypic diversity of root traits in a collection of 180 rapeseed accessions and of 52 barley genotypes grown under control and nutrient-starved conditions. Most traits showed a large variation linked to both genotype and treatment. In general, root length traits contributed more than shape and branching related traits in separating the genotypes. Overall, results showed that GrowScreen-PaGe will be a powerful resource to investigate root systems and root plasticity of large sets of plants and to explore the molecular and genetic root traits of various species including for crop improvement programs.

Marked variation between winter and spring gut microbiota in free-ranging Tibetan Macaques (Macaca thibetana).

Variation in the availability and distribution of food resources is a strong selective pressure on wild primates. We explored variation in Tibetan macaque gut microbiota composition during winter and spring seasons. Our results showed that gut microbial composition and diversity varied by season. In winter, the genus Succinivibrio, which promotes the digestion of cellulose and hemicellulose, was significantly increased. In spring, the abundance of the genus Prevotella, which is associated with digestion of carbohydrates and simple sugars, was significantly increased. PICRUSt analysis revealed that the predicted metagenomes related to the glycan biosynthesis and metabolic pathway was significantly increased in winter samples, which would aid in the digestion of glycan extracted from cellulose and hemicellulose. The predicted metagenomes related to carbohydrate and energy metabolic pathways were significantly increased in spring samples, which could facilitate a monkey’s recovery from acute energy loss experienced during winter. We propose that shifts in the composition and function of the gut microbiota provide a buffer against seasonal fluctuations in energy and nutrient intake, thus enabling these primates to adapt to variations in food supply and quality.

βIII-Tubulin alters glucose metabolism and stress response signaling to promote cell survival and proliferation in glucose-starved non-small cell lung cancer cells.

Non-small cell lung cancer (NSCLC) survival rates are dismal and high βIII-tubulin expression is associated with chemotherapy drug resistance and tumor aggressiveness in this disease. Mounting evidence supports a role for βIII-tubulin in promoting cell survival in the harsh tumor microenvironment, which is characterized by poor nutrient supply. This study aimed to investigate the role of βIII-tubulin in glucose stress response signaling and the survival and proliferation of NSCLC cells. This study revealed that βIII-tubulin regulates cellular metabolism and glucose stress response signaling in NSCLC cells to promote cell survival and proliferation in glucose starvation. βIII-Tubulin decreases the reliance of cells on glycolytic metabolism, priming them to cope with variable nutrient supply present within the tumor microenvironment. βIII-Tubulin protects cells from endoplasmic reticulum (ER) stress and reduces both basal and glucose starvation-induced autophagy to maintain cell survival and proliferation. βIII-Tubulin enables rapid Akt activation in response to glucose starvation and co-immunoprecipitates with the master regulator of the ER stress response GRP78. Furthermore, suppression of βIII-tubulin delays the association of GRP78 with Akt in response to glucose starvation with the potential to influence Akt activation and ER homeostasis under these conditions. Together these results identify that βIII-tubulin regulates glucose metabolism and alters glucose starvation stress signaling to promote cell proliferation and survival in NSCLC cells. This elucidates a hitherto unknown role for this microtubule protein and provides insight into correlations between high βIII-tubulin expression and poor patient outcome in this disease.

Quantitative food webs and invertebrate assemblages of a large River: a spatiotemporal approach in floodplain shallow lakes

To test the hypothesis that the hydrological regime of large Rivers affects the structure of invertebrate communities and food webs in floodplain lakes, we studied invertebrate assemblages and stomach contents of fish and decapods in two shallow lakes in the Paraná River floodplain, Argentina, with different connectivity (indirect and permanent, IPC; direct and temporal, DTC) to the fluvial system over three hydroperiods (flooding, transition, drought). Invertebrate assemblages exhibited temporal variation, with higher dissimilarity during the drought phase. However, zooplanktonic and pleustonic attributes varied spatiotemporally, and were better explained by other environmental variables. The food webs in the two lakes differed, with higher connectance and fewer predators in the DTC Lake. In general, the use of trophic resources by fish and decapods reflected the local and abundant resources in the system. The persistence of communities in floodplain lakes with temporary connectivity to the river may relate to the foraging decisions of consumers to buffer environmental fluctuations. The consumption of abundant resources highlighted the importance of autochthonous inputs into floodplain lakes. However, the variation in food supply as a key factor governing food-web structure and stability should be further investigated.

Environmental connotations of benthic foraminiferal assemblages from coastal West Antarctica

Abstract This paper examines the variability in foraminiferal assemblages in surface samples from coastal settings along the northwestern Antarctic Peninsula, as well as in the Pine Island Bay area. Material comes from water-depths ranging between 20 and 1257 m, latitudes between 62° and 73°S, and bottom water temperatures from − 1.5 to 1.2 °C. The microfossil analysis within this broad geographical and environmental context provides a basis for paleo-environmental studies. Environmental affinities of the assemblages were interpreted based on a wide array of ecological conditions, including CTD data, as well as on faunal indices and ecological affinities of the key taxa. Six foraminiferal assemblages are dominated by calcareous taxa. Among other factors, they correspond to variable food supply, terrigenous sedimentation, and water mass properties. Another two assemblages are dominated by arenaceous foraminifera and reflect conditions corrosive to carbonate. Our findings indicate that preserved fossil assemblages in cores from these locations may not be accurate representations of living assemblages.

Population dynamics and factors controlling somatic degrowth of the common jellyfish, Aurelia aurita, in a temperate semi-enclosed cove (Kertinge Nor, Denmark)

Life expectancy of the scyphomedusa Aurelia aurita seems closely linked to seasonal shrinkage, or somatic degrowth, which occurs synchronously with sexual reproduction in temperate regions. In the present study, the mechanisms controlling body mass losses and subsequent disappearance of medusae were examined by following seasonal dynamics in population density, individual size, and sexual reproduction of A. aurita during 2013 and 2014 in the shallow, semi-enclosed Kertinge Nor, and the adjacent Great Belt, Denmark. After sexual maturation in early summer, medusae were characterized by a distinct phase of somatic degrowth, expressed by weight-specific individual growth rates of −0.5 to −1.4 % day−1, which was followed by the absence of A. aurita populations in both ecosystems during winter. The number of planula larvae per female (N L , ind.) was positively correlated with medusa diameter (d, mm), following the exponential relationship N L = 160.8 × e 0.029d . The percentage of body mass made up by planulae ranged from 6 to 11 % in Kertinge Nor and 10 to 33 % in Great Belt. ≤15 % of total size-specific body mass losses were due to the release of planulae in Kertinge Nor, suggesting shortage of zooplankton prey during autumn as main factor causing degrowth in A. aurita. Starving medusae produced significantly fewer oocytes and revealed increased mortality compared to well-fed individuals in supplementary laboratory experiments, indicating that degrowth controls the energetic investment into sexual reproduction. Seasonal variability in food supply, rather than energy allocation to reproduction, appears to shorten life spans of A. aurita medusae in temperate Danish waters.

Temporal variation in water intrusion of a tidal frontal system and distribution of chlorophyll in the Seto Inland Sea, Japan

Monthly field surveys conducted from April to November 2009 in a tidal front in the Seto Inland Sea, Japan provided a spatial and temporal dataset for investigating seasonal variations in nutrient supply and the formation of a chlorophyll a (Chl-a) maximum. The upward diffusive flux of nutrients is estimated from observational data but it accounted for less than 5% of the nutrients needed to support the primary production of phytoplankton in the front area of the stratification region when the density difference between the surface layer and bottom layer is greater than 0.5kgm−3. Instead of vertical diffusion, the lateral intrusion of water with high nutrient concentration from the mixed area represented the major nutrient supply in the front area. The depth of the lateral intrusion changed with the month: the surface layer in July became the middle layer in August. According to the calculation of numerical model, an anti-clockwise circulation is intensified by removing river runoff (i.e., low precipitation) in this study area, and the change of lateral intrusion is likely caused by the change of anti-clockwise circulation along with the temporal variation in river runoff. Consequently, the Chl-a peak appeared in the vicinity of the surface front (up to 3µgL−1) in July, but was in the subsurface (up to 9µgL−1) in August. Diatom species were a relatively minor taxa of the phytoplankton community up to July, although a relatively high Si(OH)4-Si concentration (up to 20µmolL−1) was confirmed. In contrast, the subsurface Chl-a maximum (SCM) in August was mainly comprised of diatoms as evidenced by the reduction of both Si(OH)4-Si and Si/N from the surface to subsurface layer (0–20m depth). Therefore, the supply of both nutrients and the seed population necessary for the formation of the SCM results from the tidal frontal system and phytoplankton assemblages within the tidal front system should be varied on a monthly basis.

Conservation tillage and sustainable intensification of agriculture: regional vs. global benefit analysis

Climate change is expected to affect both the amount of global crop production, and annual variability in food supply. Agriculture is a major source of greenhouse gas emissions, but also considered to mitigate climate change. Conservation tillage, as a climate-smart agricultural practice, is repeatedly reported to mitigate net greenhouse gas emissions by increasing soil organic carbon (SOC). However, with reduced tillage, less litter is moved from the surface deeper into the soil profile, so SOC increase is very likely constrained to topsoil layers. Further adaptation benefits, such as increasing crop yield and resilience to famine, have recently been questioned after averaging yields from field studies. However, such global averaging masks the geographic extent individual studies apply to. This paper attempts a holistic regional analysis on the benefits of conservation tillage, in particular its fundamental principle no-tillage (NT), on the Chinese Loess Plateau. Based on a review of almost 20 years of conservation tillage plot experiments, the potential of NT to increase SOC stocks and to adapt to lower but more variable rainfall in the future has been assessed. The results show that the difference of total SOC stocks between NT and CT decreased with soil depth, confirming that the SOC benefits of NT are concentrated to the immediate topsoil still subject to direct seeding. The topsoil achieved maximum SOC stocks after about 10 years of NT. Crop yields from NT increased by up to 20% for years with average and below average precipitation, demonstrating the advantages of NT in stabilizing crop yields in dry years. However, the results in previous reports are not weighted by the actual spatial extent of drylands and humid regions after counting individual plot studies. As a consequence of such global and unweighted averaging, the benefits from NT to increase SOC stocks are likely to misrepresent the actual impact. Therefore, given the size of the Loess Plateau and its relevance for food security in China, our analysis illustrates the need to assess the benefits of a tillage and residue management system for each combination of eco-region and farming practice, weighted by their area and the affected population, rather than just using a global average for policy development on sustainable productivity.

Phenolic content and growth of wetland macrophytes: Is the allocation to secondary compounds driven by nutrient availability?

This study compares soluble phenolics and lignin content in two wetland macrophytes with contrasting life strategies grown under a varying nutrient supply in the field and in a greenhouse experiment. The differences are explained in terms of the protein competition model (PCM) hypothesis relating changes in secondary metabolites to changing nutrient limitation. The two study species, Eleocharis cellulosa (EC) and Typha domingensis (TD), are both widespread in tropical and subtropical freshwater and brackish marshes of the New World, and are often found in P-limited rather than N-limited conditions. TD is a fast-growing competitor with large nutrient requirements. EC is a stress tolerator, quite well adapted to growth in nutrient-limiting environments. In both species, the concentration of phenolics was negatively correlated with increasing growth (due to increasing nutrient levels). This is in agreement with the PCM hypothesis, which predicts an increase in phenolic synthesis when protein synthesis (and consequently growth) is low due to limited resource availability. An interesting difference was found in the correlation between tissue nutrients and phenolics. TD from both the field and the greenhouse showed a negative correlation between tissue P and phenolics, while EC displayed a significant negative correlation between tissue N and phenolics. EC is adapted to low P, and increased tissue P content represents luxury consumption (uptake of P for storage) which is not reflected in increased growth and thus is not correlated with phenolics. These are the first steps in elucidating the relationship among nutrient availability, growth and phenolic content in two important primary producers of tropical and subtropical marshes.

Sex-Specific Habitat Utilization and Differential Breeding Investments in Christmas Island Frigatebirds throughout the Breeding Cycle.

In seabirds, equal bi-parental care is the rule, as it is considered crucial for raising chicks successfully because seabirds forage in an environment with unpredictable and highly variable food supply. Frigatebirds forage in poor tropical waters, yet males reduce and even stop parental care soon after chick brooding, leaving the female to provision the chick alone for an extended fledging period. Using bird-borne tracking devices, male and female Christmas Island Frigatebirds (Fregata andrewsi) were investigated during the brooding, late chick rearing and post-fledging period to examine whether sexes exhibit foraging strategies that may be linked to differential breeding investments. During brooding, males and females showed similar foraging behaviour under average marine productivity of oceanic waters close to the colony, but males shifted to more distant and more productive habitats when conditions deteriorated to continue with reduced chick provisioning. During the late chick rearing period, females progressively increased their foraging range to the more distant but productive marine areas that only males had visited during brooding. Birds spent the non-breeding period roosting in highly productive waters of the Sunda Shelf. The sex-specific utilisation of three different foraging habitats with different primary productivity (oceanic, coastal, and shelf areas) allowed for temporal and spatial segregation in the exploitation of favourable habitats which seems to enable each sex to optimise its foraging profitability. In addition, post-fledging foraging movements of females suggest a biennial breeding cycle, while limited information on males suggests the possibility of an annual breeding cycle.

Feeding history can influence physiological responses of copepods: an experimental study comparing different cohorts of Temora longicornis from the Southern North Sea

Calanoid copepods in boreal and polar habitats are confronted with a strong variability in food supply. The abundant species in the Southern North Sea, Temora longicornis, cannot accumulate extensive energy stores to buffer longer periods of food paucity. These copepods react immediately to dietary changes, and therefore, recent trophic conditions must strongly influence their metabolic and functional responses. To elucidate the implications of feeding history, we collected two cohorts of T. longicornis females, which were characterized by different feeding histories and consequently different physiological backgrounds. In the North Sea in April 2005, females fed at a higher trophic level than in May, were poor in lipids, showed low proteinase activity and produced 41 eggs female−1 d−1. In May, females were significantly smaller than in April, contained more lipids, had a higher proteinase activity, and produced 26 eggs female−1 d−1. In the laboratory, females from each group were fed with either autotrophic diatoms or heterotrophic dinoflagellates for 3days. Irrespective of different initial conditions, all T. longicornis females incorporated diet-specific fatty acids within 24h. Also in both experiments and each dietary treatment, egg production increased after 24h, indicating that females were food-limited in situ in April and in May. Responses differed, however, with regard to lipid accumulation and enzyme activities. Total lipid contents increased significantly in females during Experiment I (April), but not during Experiment II (May), despite higher algal lipid levels during Experiment II. Proteolytic activity increased during Experiment I, but decreased during Experiment II. These deviating responses of T. longicornis females to food conditions suggest that detailed knowledge about the initial physiological state of specimens is required, when investigating adaptive mechanisms and metabolic performances of copepods by means of experiments.