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Food Supply (food + supply)
Terms modified by Food Supply Selected AbstractsTufa Deposition in Karst Streams Can Enhance the Food Supply of the Grazing Caddisfly Melampophylax mucoreus (Limnephilidae)INTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 3 2006Christian Kock Abstract We studied the effect of carbonate depositions covering stone surfaces on the growth of larvae and the biomass of subsequent adults of the grazing limnephilid caddisfly Melampophylax mucoreus(Hagen, 1861) in a laboratory rearing experiment. M. mucoreus is mainly distributed in karst streams characterized by calcium carbonate precipitations (tufa). We reared larvae of M. mucoreus on stones covered by calcareous tufa crusts as well as on stones from which these crusts were experimentally removed to assess the influence on larval growth and the subsequent adult biomass. The rough surface of the covered stones provided a higher complexity of micro-habitats and supported algal growth compared to the smooth surface of stones without crusts. Larvae of M. mucoreus profited from the enhanced algal biofilm growth on the calcium carbonate precipitation indicated by faster larval growth and higher subsequent adult biomass. Biomass increase of larvae reared on stones covered by tufa crusts exhibited a faster biomass development (0.09 ± 0.015 mg/d) compared to the larvae reared on stones without crusts (0.06 ± 0.002 mg/d). Adult males (5.13 ± 0.25 mg) and females (7.64 ± 0.63 mg) were significantly heavier in the treatment with stones covered by tufa than their conspecifics from the treatment with uncovered stones (males: 4.26 ± 0.25 mg, p = 0.047; females: 4.96 ± 0.47 mg, p = 0.001). Additionally, males from the treatment with crust covered stones emerged significantly earlier (p = 0.003) than the males from the other treatment, whereas no significant difference was found for females. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The Effect of Hurricane Iris on the Food Supply of Black Howlers (Alouatta pigra) in Southern Belize1BIOTROPICA, Issue 1 2005Mary S. M. Pavelka ABSTRACT Hurricanes frequently affect the forests of South and Central America; however, few studies have quantified their effects to forest structure, especially when concentrating on the food supply of an animal population. Hurricane Iris made landfall in Southern Belize on 8 October 2001, severely damaging a 52 hectare site where the behavioral ecology of a population of Central American Black Howlers (Alouatta pigra) had been under study for 2.5 yr. The hurricane resulted in a mortality rate of 35 percent for major food trees, which was primarily attributed to uprooting, snapping, and major delimbing. This damage accounted for 97 percent of the food tree loss between the two sample periods. Tree species differences were found in both the percentage loss and category of damage to food trees. Trees of different heights also experienced different percentage loss and levels of damage; subcanopy and emergent trees experienced higher loss than canopy trees, and subcanopy trees were frequently uprooted. This was partially attributed to a lack of buttressing on these subcanopy trees. Buttressing was found to decrease the frequency of uprooting. Tree size was the only factor that did not influence either damage or death. Trees from which fruit were eaten by black howlers died more than twice as often as did trees eaten for leaves. [source] Linking behavior, life history and food supply with the population dynamics of white-footed mice (Peromyscus leucopus)INTEGRATIVE ZOOLOGY (ELECTRONIC), Issue 3 2007Stephen H. VESSEY Abstract In this paper we review and integrate key aspects of behavioral and life history traits, food supply and population dynamics of the white-footed mouse (Peromyscus leucopus), a species that is abundant and widely distributed across much of eastern North America. Results are based largely on a 33-year mark-and-recapture study in a forest fragment in northwest Ohio, USA. Behavioral plasticity in such reproductive traits as mating system and parental care allows this species to adjust quickly to changing environments. The species has a relatively "fast" life history, with rapid attainment of sexual maturity and high fecundity in the face of high mortality rates. Maximal reproductive effort early in life enables a rapid population response. Food supply, in the form of mast, determines the size of the reproducing population in early spring, which, in turn, influences the size of the late summer peak population. The peak population size is also affected by short-term weather events possibly acting via the food supply. The effects of weather and food on population growth are in part mediated through competition, including defense of space and suppression of reproduction. The inelasticity of female territories appears to set an upper limit to population density. [source] Variable but predictable prey availability affects predator breeding success: natural versus experimental evidenceJOURNAL OF ZOOLOGY, Issue 4 2008A. Millon Abstract Food supply is a major source of variation in breeding success for predators, and to what extent individuals are able to cope with temporal variability in food availability remains an outstanding question in life-history studies. We confronted the natural variation in clutch size and breeding success with results from a food supplementation experiment during egg formation, conducted over several contrasted years of natural food supply in an avian specialist predator, the Montagu's harrier Circus pygargus. This raptor mainly preys on common vole Microtus arvalis a cyclic microtine under temperate latitudes. Vole abundance together with timing of breeding accounted for most of the variance in clutch size and number of fledglings. Results from empirical and experimental data were overall in agreement. Fed pairs consistently increased clutch size compared with controls in all experimental years, whereas no effect of food supplementation on egg volume was detected. Supplemented pairs, however, did not fledge significantly more chicks than controls. The costs entailed by the increase in clutch size appear nevertheless to be limited compared with previous studies. Food supply seemed therefore to display sufficient predictability throughout a breeding season to afford individuals the opportunity to adjust their breeding effort to an optimal number of offspring, in agreement with Lack's anticipation hypothesis. [source] Making Exchange Entitlements Operational: The Food Economy Approach to Famine Prediction and the RiskMap Computer ProgramDISASTERS, Issue 2 2000John Seaman The effect of production failure or some other shock on household income and food supply depends upon: (a) the pattern of household income, and (b) its ability to compensate for any deficit which may have occurred, for example, by the sale of assets or finding additional paid employment. The corollary is that the prediction of the likely effect of some event on the future state of the economy or food supply of a population of households requires an understanding of the economy of the households concerned and the economic context to which these relate. This paper describes an attempt to develop an approach to prediction using a dynamic model of economy based on quantitative descriptions of household economy obtained by systematic rapid field-work and summarises the experience of the use of this approach to date. [source] Supplemental feeding reduces natural selection in juvenile red deerECOGRAPHY, Issue 3 2002Karoline T. Schmidt In red deer, variation in winter and spring weather conditions encountered by the mothers during pregnancy and during the first year of life are a main determinant for individual life-history as well as population dynamics. We tested the hypothesis that supplementary feeding which provides constant food supply throughout winter removes the selective pressure of winter harshness on nutrition-mediated phenotypic traits. We analysed cohort variation in body weight in calves in October, before their first winter, and in yearlings in June, after their first winter, in a food-supplemented population in the Eastern Austrian Alps. Over eleven years, cohort body weight varied between years in calves and yearlings. Contrary to studies on non-supplemented red deer populations we found neither short- nor long-term effects of winter weather on body weight. In calves, autumn body weight was negatively related to April,May and June temperatures, suggesting that cool weather during the main growth period retarded plant senescence and thereby prolonged the period of high protein content of summer forage. In yearlings, variation in June body weight, shortly after the end of the feeding period, was lower after a wet April,May, suggesting a negative effect of a prolonged period of supplemental feeding. For both calves and yearlings intra-cohort variation in body weight was higher, inter-cohort variation was lower as compared to non-supplemented red deer, suggesting that in their first year of life supplemented red deer are under reduced natural selection pressure. [source] Starling foraging success in relation to agricultural land-useECOGRAPHY, Issue 3 2002Ola Olsson Changes in agricultural land-use have been suggested to contribute to the decline of several bird species through negative effects on their food supply during breeding. One important change in land-use has been loss of pastures, especially permanent pastures. In this study we investigated how different forms of agricultural land-use affected foraging success of a declining bird species, the European starling Sturnus vulgaris. We let caged starlings forage in different forms of agricultural fields and determined time spent foraging and foraging success. The starlings' activity level (time spent actively foraging) as well as the number of prey caught per time unit was strongly related to the abundance of prey in soil samples. Also the body mass change during the experiment was positively related to activity level and prey capture rate. We found consistent differences in foraging variables between habitats. In spring sown grain starlings were least active and found fewer prey items at a lower rate than in any other habitat. The other three habitats differed less, but in general mowed hay fields appeared slightly more valuable than the cultivated and natural pastures. We did not find any differences between natural and cultivated pastures in foraging variables. Thus, starling foraging success is higher in grass-covered fields than in cultivated fields, but the management of the grass-covered fields mattered less. The results are consistent with starlings having higher population densities and breeding success in areas with higher availability of pasture. We suggest that the physical structure of the habitat (sward height) and moisture may be additional variables that need to be taken into account to explain starling breeding density and success in the agricultural landscape. [source] Seasonal spatial dynamics and causes of nest movement in colonies of the invasive Argentine ant (Linepithema humile)ECOLOGICAL ENTOMOLOGY, Issue 5 2006NICOLE E. HELLER Abstract 1.,Colony organisation and movement behaviour of the Argentine ant (Linepithema humile) was studied over 3 years in field populations in California and in captive colonies in the laboratory. This invasive species is highly polydomous and unicolonial; colonies consist of expansive and fluid networks of nests and trails. The spatial and temporal organisation of colonies may contribute to ecological dominance. 2.,Argentine ant nests and inter-nest trails shift in size, abundance, and location, so that colony networks are spatially contracted in the winter and expanded spring to autumn. Colonies occupy permanent sites; ants migrated to and from the same winter nest locations year after year, and occupied 30% of the same nests repeatedly during seasonal migrations. 3.,Nests were moved on average 2,3 m. Forty-two per cent were occupied less than 1 month, 4% the entire study, and the other 54% lasted 3.9 ± 2.3 months (mean ± SD). 4.,Nests were located within 2,4 m of woody plants, in warm sites in the winter and cool sites in the summer. Both humidity and food availability influenced nest-site choice in laboratory colonies. However, when faced with a trade-off between factors, the ants chose humid nest boxes over nest boxes near food, and ants moved nests only in response to changes in humidity and not distance to food. 5.,The results indicate that L. humile colonies are seasonally polydomous, and that nest movements are driven by changes in microclimate. Colony organisation maintains high local density and increases food supply, which may improve the competitive ability of L. humile colonies and reduce opportunities for species coexistence. [source] Contrasting alternative hypotheses about rodent cycles by translating them into parameterized modelsECOLOGY LETTERS, Issue 3 2001Peter Turchin Ecologists working on population cycles of arvicoline (microtine) rodents consider three ecological mechanisms as the most likely explanations of this long-standing puzzle in population ecology: maternal effects, interaction with specialist predators, and interaction with the food supply. Each of these hypotheses has now been translated into parameterized models, and has been shown to be capable of generating second-order oscillations (that is, population cycles driven by delayed density dependence). This development places us in a unique situation for population ecology. We can now practice "strong inference" by explicitly and quantitatively comparing the predictions of the three rival hypotheses with data. In this review, we contrast the ability of each hypothesis to explain various empirically observed features of rodent cycles, with a particular emphasis on the well-studied case of Microtus agrestis and other small rodents in Fennoscandia (Finland, Sweden and Norway). Our conclusion is that the current evidence best supports the predation hypothesis. [source] Competition for food between Eurasian perch (Perca fluviatilis L.) and ruffe (Gymnocephalus cernuus [L.]) over different substrate typesECOLOGY OF FRESHWATER FISH, Issue 4 2004A. Dieterich Abstract,,, Food consumption by Eurasian perch (Perca fluviatilis L.) and ruffe (Gymnocephalus cernuus [L.]) was studied in single and mixed-species treatments in the laboratory, where alternative food resources, chironomids and zooplankton, were offered simultaneously. The effects of structural complexity, which was represented by substrate grain size, and of feeding level on food consumption were analysed. Across all experiments, the outcome of competition between perch and ruffe depended on food abundance and on the structural complexity of the environment. Perch and ruffe both changed their food consumption in the presence of a heterospecific competitor. With high food supply, perch consumed more benthic food than ruffe. With low food supply, the consumption of perch decreased strongly, while that of ruffe remained high on fine sediment. Under all conditions tested, the mechanism of competition appeared to be of interference rather than of exploitative nature. It is suggested that with decreasing lake productivity caused by re-oligotrophication, habitat shifts of both species will occur, which will alleviate interspecific competition. Ruffe will forage over fine sediment and perch over coarse sediment, whereby both species will achieve the highest foraging efficiency under conditions of low food supply. Resumen 1. Hemos estudiado el consumo alimenticio de Perca fluviatilis L. y Gymnocephalus cernuus (L.) en condiciones de laboratorio. Bajo tratamientos de especies individuales y mezcladas, les ofrecimos, simultáneamente, varios recursos alimenticios alternativos (quironómidos y zooplancton). 2. Analizamos los efectos de la complejidad estructural - representada por el tamaño del sustrato (arena, grava, y guijo) - y del nivel alimenticio, sobre el consumo alimenticio. Pusimos especial atención a la potencial influencia de competidores hetero-específicos sobre los patrones alimenticios de ambas especies, tanto en términos cualitativos como cuantitativos. Además, dado que en un futuro cercano una menor productividad general en lagos debida a re-oligotrofia, probablemente aumente la competición por el alimento en muchos lagos donde ambas especies co-existen, los experimentos se llevaron a cabo bajo niveles de abastecimiento alimenticio alto y bajo. 3. En los experimentos, la aparición de competencia entre P. fluviatilis y G. cernuus dependió de la abundancia del alimento y de la complejidad estructural del ambiente. El consumo de quironómidos por P. fluviatilis dependió del tipo de sustrato a niveles altos de abastecimiento alimenticio pero no a niveles bajos, mientras que en G. cernuus observamos lo contrario. 4. Ambas especies cambiaron el consumo alimenticio en presencia de un competidor hetero-específico. A altos niveles de abastecimiento alimenticio, P. fluviatilis consumió más bentos que G. cernuus. A niveles bajos, el consumo de P. fluviatilis decreció substancialmente mientras que el de G. cernuus permaneció alto en sedimento fino. Bajo todas las condiciones experimentales analizadas, los mecanismos de competición parecieron ser de interferencia más que de naturaleza explotativa. 5. Finalmente, presentamos un escenario sobre como P. fluviatilis y G. cernuus pueden competir por alimento bentónico en lagos con variado sustrato de fondo. Sugerimos que a altos niveles de abastecimiento alimenticio, G. cernuus forrajee más sobre arena y grava mientras que P. fluviatilis puede utilizar todos los sustratos disponibles. Al decrecer el abastecimiento alimenticio por re-oligotrofia, pueden producirse cambios en el hábitat de ambas especies que minimizarán la competencia inter-específica. G. cernuus forrajeará básicamente sobre sedimento fino, allá donde sea claramente superior a P. fluviatilis. Esta última especie forrajeará predominantemente sobre sedimento más grueso donde se enfrentará a competencia intra- e inter-específica. A través de estos cambios de hábitat, ambas especies podrían alcanzar la mayor eficiencia de forrajeo bajo condiciones de bajo abastecimiento alimenticio. [source] Some simple economics of GM foodECONOMIC POLICY, Issue 33 2001Dietmar Harhoff Public opposition to the genetic engineering of food crops (GM food) has not been based solely on concern about biological risks. Economic risks have been widely cited too: the fear that the world's food supply will be concentrated in the hands of a few large firms, the fear that such firms will engage or are already engaging in anti,competitive practices, and the fear of the transfer of ownership rights over genetic resources to the private sector. Are these fears justified? We argue that the GM food industry may be on course for further consolidation, and this could be anti,competitive. In fact, policymakers face a dilemma: a stringent regulatory approval process enhances food safety, but at the cost of increasing market concentration. We argue also that the integration of seed and agri,chemical manufacturers may bias the introduction of GM traits in undesirable directions. Some business practices (such as tie,in contracts between seeds and complementary products such as herbicides) may have an exclusionary motive that warrants scrutiny on anti,competitive grounds, while some other practices (such as the use of terminator genes) appear more benign. Finally, we argue against granting patents on genes or even on gene ,functions'. Doing so may delay the development of socially beneficial applications. [source] Incubation Feeding and Nest Attentiveness in a Socially Monogamous Songbird: Role of Feather Colouration, Territory Quality and Ambient EnvironmentETHOLOGY, Issue 7 2010Beata Matysioková Parental investment and environmental conditions determine reproductive success in wild-ranging animals. Parental effort during incubation, and consequently factors driving it, has profound consequences for reproductive success in birds. The female nutrition hypothesis states that high male feeding enables the incubating female to spend more time on eggs, which can lead to higher hatching success. Moreover, both male and female parental investment during incubation might be signalled by plumage colouration. To test these hypotheses, we investigated relationships between male and female incubation behaviour and carotenoid and melanin-based plumage colouration, territory quality and ambient temperature in the Great Tit Parus major. We also studied the effect of female incubation behaviour on hatching success. Intensity of male incubation feeding increased with lower temperatures and was higher in territories with more food supply, but only in poor years with low overall food supply. Female nest attentiveness increased with lower temperatures. Plumage colouration did not predict incubation behaviour of either parent. Thus, incubation behaviour of both parents was related mainly to environmental conditions. Moreover, there was no relationship between male incubation feeding, female nest attentiveness and hatching success. Consequently, our data were not consistent with the female nutrition hypothesis. [source] No Plastic Responses to Experimental Manipulation of Sperm Competition per se in a Free-Living FlatwormETHOLOGY, Issue 4 2010Peter Sandner In the absence of sperm competition evolutionary theory predicts low mating rates and low ejaculate expenditure per mating, and sex allocation theory for simultaneous hermaphrodites predicts a strongly female-biased sex allocation. In the presence of sperm competition a shift towards a more male-biased sex allocation and a higher ejaculate expenditure are predicted. The free-living flatworm Macrostomum lignano has been shown to respond plastically in mating rate, testis size, and sperm transfer to manipulation of the social group size, a proxy of the strength of sperm competition. However, manipulation of social group size may manipulate not only sperm competition, but also other factors, such as food supply and metabolite concentration. In this study we therefore manipulated sperm competition per se by repeatedly exposing individuals to partners that have either mated with rivals or not, while keeping the social group size constant. Our results suggest that M. lignano does not have the ability to detect sperm competition per se, as worms experimentally exposed to the presence or absence of sperm competition did not differ in sex allocation, sperm transfer or mating behavior. A response to our manipulation would have required individual recognition, the ability to detect self-referencing tags, or tags or traces left by rivals on or in the mating partners. We first discuss the possibility that highly efficient sperm displacement may have decreased the difference between the treatment groups and then propose three alternative cues that may allow M. lignano to respond plastically to the social group size manipulation used in earlier studies: assessment of the mating rate, chemical cues, or tactile cues. [source] Listeria monocytogenes: epidemiology, human disease, and mechanisms of brain invasionFEMS IMMUNOLOGY & MEDICAL MICROBIOLOGY, Issue 2 2008Douglas A. Drevets Abstract Listeria monocytogenes is a facultative intracellular bacterium that has predilection for causing central nervous systemic infections in humans and domesticated animals. This pathogen can be found worldwide in the food supply and most L. monocytogenes infections are acquired through ingestion of contaminated food. The main clinical syndromes caused by L. monocytogenes include febrile gastroenteritis, perinatal infection, and systemic infections marked by central nervous system infections with or without bacteremia. Experimental infection of mice has been used for over 50 years as a model system to study the pathogenesis of this organism including the mechanisms by which it invades the brain. Data from this model indicate that a specific subset of monocytes, distinguished in part by high expression of the Ly-6C antigen, become parasitized in the bone marrow and have a key role in transporting intracellular bacteria across the blood-brain barriers and into the central nervous system. This Minireview will summarize recent epidemiologic and clinical information regarding L. monocytogenes as a human pathogen and will discuss current in vitro and in vivo data relevant to the role of parasitized monocytes and the pathogenetic mechanisms that underlie its formidable ability to invade the central nervous system. [source] Bacteria in the cold deep-sea benthic boundary layer and sediment,water interface of the NE AtlanticFEMS MICROBIOLOGY ECOLOGY, Issue 2 2000Carol Turley Abstract This is a short review of the current understanding of the role of microorganisms in the biogeochemistry in the deep-sea benthic boundary layer (BBL) and sediment,water interface (SWI) of the NE Atlantic, the gaps in our knowledge and some suggestions of future directions. The BBL is the layer of water, often tens of meters thick, adjacent to the sea bed and with homogenous properties of temperature and salinity, which sometimes contains resuspended detrital particles. The SWI is the bioreactive interface between the water column and the upper 1 cm of sediment and can include a large layer of detrital material composed of aggregates that have sedimented from the upper mixed layer of the ocean. This material is biologically transformed, over a wide range of time scales, eventually forming the sedimentary record. To understand the microbial ecology of deep-sea bacteria, we need to appreciate the food supply in the upper ocean, its packaging, passage and transformation during the delivery to the sea bed, the seasonality of variability of the supply and the environmental conditions under which the deep-sea bacteria grow. We also need to put into a microbial context recent geochemical findings of vast reservoirs of intrinsically labile organic material sorped onto sediments. These may well become desorped, and once again available to microorganisms, during resuspension events caused by deep ocean currents. As biotechnologists apply their tools in the deep oceans in search of unique bacteria, an increasing knowledge and understanding of the natural processes undertaken and environmental conditions experienced by deep-sea bacteria will facilitate this exploitation. [source] Seasonal and long-term changes in fishing depth of Lake Constance whitefishFISHERIES MANAGEMENT & ECOLOGY, Issue 5 2010G. THOMAS Abstract, The ecosystem of Lake Constance in central Europe has undergone profound modifications over the last six decades. Seasonal and inter-annual changes in the vertical distribution patterns of whitefish were examined and related to changes in biotic and abiotic gradients. Between 1958 and 2007, the average fishing depth in late summer and autumn was related to two factors influencing food supply of whitefish , lake productivity and standing stock biomass. In years with low food supply, whitefish were harvested from greater depths, where temperatures were up to 4 °C lower. The whitefish's distribution towards colder water might be a bioenergetic optimisation behaviour whereby fish reduce metabolic losses at lower temperatures, or it may result from a reassessment of habitat preference under conditions of limited food supply, according to the ideal free distribution theory. [source] Variability in the spawning habitat of Pacific sardine (Sardinops sagax) off southern and central CaliforniaFISHERIES OCEANOGRAPHY, Issue 6 2003Ronald J. Lynn Abstract The spatial pattern of sardine spawning as revealed by the presence of sardine eggs is examined in relation to sea surface temperature (SST) and mean volume backscatter strength (MVBS) measured by a 150 kHz acoustic Doppler current profiler (ADCP) during four spring surveys off central and southern California in 1996,99. Studies in other regions have shown that MVBS provides an excellent measure of zooplankton distribution and density. Zooplankton biomass as measured by survey net tows correlates well with concurrently measured MVBS. The high along-track resolution of egg counts provided by the Continuous Underway Fish Egg Sampler (CUFES) is a good match to the ADCP-based data. Large interannual differences in the pattern and density of sardine eggs are clearly related to the concurrently observed patterns of surface temperature and MVBS. The strong spatial relationship between sardine eggs and MVBS is particularly evident because of the large contrast in zooplankton biomass between the 1998 El Niño and 1999 La Niña. The inshore distribution of sardine spawning appears to be limited by the low temperatures of freshly upwelled waters, although the value of the limiting temperature varies between years. Often there is an abrupt offshore decrease in MVBS that is coincident with the offshore boundary of sardine eggs. Possible reasons for this association of sardine eggs and high zooplankton biomass include an evolved strategy that promotes improved opportunity of an adequate food supply for subsequent larval development, and/or adult nutrient requirements for serial spawning. Hence, the distribution of these parameters can be used as an aid for delineating the boundaries of sardine spawning habitat. [source] Decadal-scale variability in the Kuroshio marine ecosystem in winterFISHERIES OCEANOGRAPHY, Issue 4-5 2003Kaoru Nakata Abstract Interannual variation of winter copepod biomass during the last three decades of the twentieth century was examined in the Kuroshio, off central Japan in relation to climate regime shifts. The biomass levels of large copepods in the period before 1977 and in 1999 and 2000 were higher than those in the period between 1977 and 1998. The biomass of large copepods was positively related with the Southern Oscillation Index (SOI), in winter in the Northern Hemisphere, which also showed steplike shifts in 1976/77 and 1998/99. The biomass of large copepods was largely influenced by abundance of Calanus sinicus that has high rates of production compared with small copepods under food satiated conditions. Accordingly, the climatic regime shift accompanied by the climatic change in the tropical region seems to regulate interannual variation of winter biomass of large copepods in the Kuroshio through effects on food supply. There is less decadal variablity in the small copepod (SC) biomass than large copepod (LC) biomass, but more variablity in SC than in LC at periods 2,4 years. In contrast to the large copepods, the biomass of small copepods was not related to global climate indices but with the local climate factors such as SST in the Kuroshio and variability in the Kuroshio flow path. Causes for the differences in the biomass trends between large and small copepods are discussed. [source] How well are velocity effects on ,13C signatures transmitted up the food web from algae to fish?FRESHWATER BIOLOGY, Issue 6 2010JOSEPH B. RASMUSSEN Summary 1. Benthic algae fractionate carbon isotopes less at low water velocities because of reduced boundary layer exchange, and this effect on ,13C is passed on to consumers via trophic transfer. This study examines the relationships between ,13C signatures of consumers (invertebrates and salmonid fishes) and water velocity in the Sainte Marguerite River, QC, Canada, and compares them to patterns for periphyton, both along the river main-stem and in a small tributary. 2. Relationships of ,13C signatures of herbivore/grazers and collector/gatherers with water velocity were strong and similar to those of periphyton, but relationships for filter-feeders were weak, probably reflecting the effect of spatial averaging of their food supply as a result of downstream transport. 3. Velocity effects on salmonid signatures were much weaker than those of lower trophic levels, being barely significant except in the small tributary where the fish were resident and isolated from the main river. In the river main-stem, even when reach standardised (reach mean subtracted from each data point), fish signatures were only weakly related to water velocity. 4. The fidelity with which velocity effects are transmitted to consumers from benthic algae is highly variable, and depends on a combination of consumer and resource movements, in addition to the trophic position of the consumer. [source] Stream temperature and the potential growth and survival of juvenile Oncorhynchus mykiss in a southern California creekFRESHWATER BIOLOGY, Issue 7 2007DAVID A. BOUGHTON Summary 1.,We asked whether an increase in food supply in the field would increase the ability of fish populations to withstand climate warming, as predicted by certain bioenergetic models and aquarium experiments. 2.,We subsidised the in situ food supply of wild juvenile steelhead (Oncorhynchus mykiss) in a small stream near the species' southern limit. High-quality food (10% of fish biomass per day) was added to the drift in eight in-stream enclosures along a naturally-occurring thermal gradient. 3.,The temperatures during the experiment were well below the upper thermal limit for the species (means of enclosures ranged from 15.1 to 16.5 °C). Food supplements had no discernible effect on survival, but raised mean (± SD) specific growth rate substantially, from 0.038 ± 0.135 in controls to 2.28 ± 0.51 in feeding treatments. Food supplements doubled the variation in growth among fish. 4.,The mean and variance of water temperature were correlated across the enclosures, and were therefore transformed into principal component scores T1 (which expressed the stream-wide correlation pattern) and T2 (which expressed local departures from the pattern). Even though T1 accounted for 96% of the variation in temperature mean and variance, it was not a significant predictor of fish growth. T2 was a significant predictor of growth. The predicted time to double body mass in an enclosure with a large T2 score (cool-variable) was half that in an enclosure with a low T2 score (warm-stable). 5.,Contrary to expectation, temperature effects were neutral, at least with respect to the main axis of variation among enclosures (cool-stable versus warm-variable). Along the orthogonal axis (cool-variable versus warm-stable), the effect was opposite from expectations, probably because of temperature variation. Subtle patterns of temperature heterogeneity in streams can be important to potential growth of O. mykiss. [source] Survival and development of five species of cyclopoid copepods in relation to food supply: experiments with algal food in a flow-through systemFRESHWATER BIOLOGY, Issue 9 2005ULRICH HOPP Summary 1. Cyclops spp. generally develop and grow during favourable food conditions in spring and undergo a diapause in summer, while Acanthocyclops robustus, Mesocyclops leuckarti and Thermocyclops crassus develop and grow in summer when they face poorer food conditions and more competition from Cladocera. Since nauplii are the bottleneck in copepod development, we tested the hypothesis that Cyclops abyssorum and C. vicinus nauplii have higher food requirements for survival and development than the nauplii of A. robustus, M. leuckarti and T. crassus. We also tested survivorship and development from hatching to adulthood. 2. Survivorship and development of the copepods was studied in a flow-through system using five concentrations of the phytoflagellate Chlamydomonas reinhardtii in the range from 1 × 104 to 4.5 × 105 cells mL,1 (approximately 0.5,22.5 mg C L,1). 3. Nauplii of both species of Cyclops died at intermediate to low (C. abyssorum) and low (C. vicinus) food concentrations, while nauplii of A. robustus, M. leuckarti and T. crassus survived at all concentrations. 4. The negative effects of low food concentration were also reflected in development. In C. abyssorum and C. vicinus, development duration increased at low food concentration while development was much less affected in A. robustus and T. crassus. Mesocyclops leuckarti was intermediate between Cyclops spp. and A. robustus/T. crassus, with an increase in development duration at the lowest food concentration. 5. Our results support the hypothesis that summer diapause in Cyclops spp. has developed as a strategy to avoid a food bottleneck for nauplii. [source] Timing of predation by rainbow trout controls Daphnia demography and the trophic status of a Minnesota lakeFRESHWATER BIOLOGY, Issue 6 2005LEIF K. HEMBRE Summary 1. Stocking of lakes with rainbow trout is a common practice that presents a potential conflict for lake managers who must balance the interests of anglers with those concerned that zooplanktivory by trout may trigger a trophic cascade and result in decreased water clarity. 2. This study examined how the timing of trout stocking (autumn versus spring) in a Minnesota (U.S.A.) lake affected (i) the population dynamics of their zooplankton food supply (Daphnia pulicaria), (ii) phytoplankton biomass and water clarity and (iii) trout survival. Sizes of both Daphnia and trout populations were estimated acoustically with high-frequency (192 kHz) sonar. 3. Daphnia were nearly eliminated from the lake during winters after trout were stocked in autumn. In both of these years (1996 and 1997), the Daphnia population was small in the spring, and grew during the summer and into the autumn as the trout population diminished. 4. The lake was then stocked in spring for 2 years (1998 and 1999). This fisheries manipulation alleviated predation over the winter, but increased predation on D. pulicaria during the spring, summer and autumn. However, the high mortality caused by the spring-stocked trout was offset by even higher rates of reproduction by the relatively large populations of fecund Daphnia that survived the winter in 1998 and 1999. 5. Grazing by these dense populations of Daphnia produced clear-water phases during May and June that were inhibited in autumn stocking years. In addition, the large Daphnia populations present during the spring and early summer of 1998 and 1999 provided abundant forage for trout. 6. This fisheries manipulation achieved seemingly mutually exclusive management objectives: a robust planktivorous sport fishery, and clear water for other forms of recreation. [source] Contrasting population changes in sympatric penguin species in association with climate warmingGLOBAL CHANGE BIOLOGY, Issue 3 2006JAUME FORCADA Abstract Climate warming and associated sea ice reductions in Antarctica have modified habitat conditions for some species. These include the congeneric Adélie, chinstrap and gentoo penguins, which now demonstrate remarkable population responses to regional warming. However, inconsistencies in the direction of population changes between species at different study sites complicate the understanding of causal processes. Here, we show that at the South Orkney Islands where the three species breed sympatrically, the less ice-adapted gentoo penguins increased significantly in numbers over the last 26 years, whereas chinstrap and Adélie penguins both declined. These trends occurred in parallel with regional long-term warming and significant reduction in sea ice extent. Periodical warm events, with teleconnections to the tropical Pacific, caused cycles in sea ice leading to reduced prey biomass, and simultaneous interannual population decreases in the three penguin species. With the loss of sea ice, Adélie penguins were less buffered against the environment, their numbers fluctuated greatly and their population response was strong and linear. Chinstrap penguins, considered to be better adapted to ice-free conditions, were affected by discrete events of locally increased ice cover, but showed less variable, nonlinear responses to sea ice loss. Gentoo penguins were temporarily affected by negative anomalies in regional sea ice, but persistent sea ice reductions were likely to increase their available niche, which is likely to be substantially segregated from that of their more abundant congeners. Thus, the regional consequences of global climate perturbations on the sea ice phenology affect the marine ecosystem, with repercussions for penguin food supply and competition for resources. Ultimately, variability in penguin populations with warming reflects the local balance between penguin adaptation to ice conditions and trophic-mediated changes cascading from global climate forcing. [source] The effect of habitat complexity on the functional response of a seed-eating passerineIBIS, Issue 3 2009DAVID J. BAKER Recent population declines of seed-eating farmland birds have been associated with reduced overwinter survival due to reductions in food supply. An important component of predicting how food shortages will affect animal populations is to measure the functional response, i.e. the relationship between food density and feeding rate, over the range of environmental conditions experienced by foraging animals. Crop stubble fields are an important foraging habitat for many species of seed-eating farmland bird. However, some important questions remain regarding farmland bird foraging behaviour in this habitat, and in particular the effect of stubble on farmland bird functional responses is unknown. We measured the functional responses of a seed-eating passerine, the Chaffinch Fringilla coelebs, consuming seeds placed on the substrate surface in three different treatments: bare soil, low density stubble and high density stubble. Stubble presence significantly reduced feeding rates, but there was no significant difference between the two stubble treatments. Stubble reduced feeding rates by reducing the maximum attack distance, i.e. the distance over which an individual food item is targeted and consumed. The searching speed, handling time per seed, proportion of time spent vigilant, duration of vigilance bouts and duration of head-down search periods were unaffected by the presence of stubble. The frequency of vigilance bouts was higher in the bare soil treatment, but this is likely to be a consequence of the increased feeding rate. We show the influence of a key habitat type on the functional response of a seed-eating passerine, and discuss the consequences of this for farmland bird conservation. [source] Tawny Owls Strix aluco with reliable food supply produce male-biased broodsIBIS, Issue 1 2007KASI B. DESFOR Tawny Owls Strix aluco have been reported to skew the sex ratio of their offspring towards males when facing food shortage during the nestling period (and vice versa), because female fitness is more compromised by food shortage during development than male fitness. To test the generality of these results we used a DNA marker technique to determine the sex ratio in broods of Tawny Owls in Danish deciduous woodland during two years of ample food supply (rodent population outbreak) and two years of poor food supply. Of 268 nestlings, 59% were males (95% CI: 53,65%). This proportion was higher than previously reported for the species (49% in Northumberland, UK, and 52% in Hungary), but consistent with Fisherian sex allocation, which predicts a male bias of c. 57% based on inferred differences in energy requirements of male and female chicks. Contrary to previous results, brood sex ratios were not correlated with the resource abundance during the breeding seasons, despite considerable variation in breeding frequency, brood size or hatching date across years. Brood sex ratios were unaffected by brood reduction prior to DNA sampling, and nestling mortality rates after DNA sampling were not related to gender. The inconsistency between the sex ratio allocation patterns in our study and previous investigations suggests that adaptive sex allocation strategies differ across populations. These differences may relate to reproductive constraints in our population, where reproductive decisions seem primarily to concern whether to lay eggs at all, rather than adjust the sex ratio to differences in starvation risk of nestlings. [source] The role of food supply in the dispersal behaviour of juvenile Tawny Owls Strix alucoIBIS, Issue 2 2003C. F. Coles We investigated the effects of food supply on decisions made by dispersing juvenile Tawny Owls Strix aluco in Kielder Forest, Northumberland, in 1996 and 1997. Field Voles Microtus agrestis were the main food of the owls and clear-cuts the main habitat for voles. A vole sign index was used to estimate vole abundance. In areas near to roosting owls, mean vole densities were 83 and 115 ha,1 in 1996 and 1997, respectively. The prediction that birds would perform area-restricted searches when prey was more abundant was not confirmed. Moreover, we found no evidence that juveniles avoided conspecifics. Owls appeared to have an imperfect knowledge of the environment as they responded to variability in Field Vole densities by altering the time spent in different areas rather than by moving to areas with successively greater vole densities. Vole abundance explained 25.7% of the variation in the time spent in different areas. Movements did not decrease with time after dispersal, although the detection of such movements was prone to error. This study supports recent work suggesting that although dispersal may be initiated by a variety of proximate and ultimate factors, individual decisions made during dispersal may depend partly on environmental conditions encountered during the process itself. [source] Survival analysis of Little Penguin Eudyptula minor chicks on Motuara Island, New ZealandIBIS, Issue 4 2001MARTIN RENNER Chick survival of Little Penguins Eudyptula minor was studied on predator-free Motuara Island, Cook Strait, New Zealand (41d,05'S, 174d,15'E), in 1995 and 1996. We used the Kaplan-Meier estimator and robust Cox regression to estimate chick survival rate (pL se) at 0.325 pL 0.044, leading to an estimated survival from laying to fledging of 0.13 or a reproductive output of 0.26 chicks per pair and breeding attempt. Starvation posed the greatest mortality risk, followed by unknown factors and rain. Risk of death due to rain was restricted to the guard stage, whereas starvation occurred throughout the nesting period, though with a peak in the early guard stage. Significant seasonal differences in survival rate were detected in both years, but with reversed trends, survival decreasing with the season in 1995 and increasing in 1996. Failure of adults to relieve their partner on the nest after chicks hatched accounted for 16% mortality or 34% of all chick deaths. Differences in chick survival rate between nest types were significant in 1995, a year with high rainfall, but not in 1996. Nests in the base of hollow trees had the highest chick survival rate. Of chicks in open nests - a nest type that is unusual for this species - 5.4% fledged. Our results suggest that on Motuara Island good breeding sites are scarce and that the food supply has been poor during the years of this study. [source] Molecular strategies of plant defense and insect counter-defenseINSECT SCIENCE, Issue 1 2005KEYAN ZHU-SALZMAN Abstract The prediction of human population growth worldwide indicates there will be a need to substantially increase food production in order to meet the demand on food supply. This can be achieved in part by the effective management of insect pests. Since plants have co-evolved with herbivorous insects for millions of years, they have developed an array of defense genes to protect themselves against a wide variety of chewing and sucking insects. Using these naturally-occurring genes via genetic engineering represents an environmentally friendly insect pest-control measure. Insects, however, have been actively evolving adaptive mechanisms to evade natural plant defenses. Such evolved adaptability undoubtedly has helped insects during the last century to rapidly overcome a great many human-imposed management practices and agents, including chemical insecticides and genetically engineered plants. Thus, better understanding of the molecular and genetic basis of plant defense and insect counter-defense mechanisms is imperative, not only from a basic science perspective, but also for biotechnology-based pest control practice. In this review, we emphasize the recent advance and understanding of molecular strategies of attack-counterattack and defense-counter-defense between plants and their herbivores. [source] Linking behavior, life history and food supply with the population dynamics of white-footed mice (Peromyscus leucopus)INTEGRATIVE ZOOLOGY (ELECTRONIC), Issue 3 2007Stephen H. VESSEY Abstract In this paper we review and integrate key aspects of behavioral and life history traits, food supply and population dynamics of the white-footed mouse (Peromyscus leucopus), a species that is abundant and widely distributed across much of eastern North America. Results are based largely on a 33-year mark-and-recapture study in a forest fragment in northwest Ohio, USA. Behavioral plasticity in such reproductive traits as mating system and parental care allows this species to adjust quickly to changing environments. The species has a relatively "fast" life history, with rapid attainment of sexual maturity and high fecundity in the face of high mortality rates. Maximal reproductive effort early in life enables a rapid population response. Food supply, in the form of mast, determines the size of the reproducing population in early spring, which, in turn, influences the size of the late summer peak population. The peak population size is also affected by short-term weather events possibly acting via the food supply. The effects of weather and food on population growth are in part mediated through competition, including defense of space and suppression of reproduction. The inelasticity of female territories appears to set an upper limit to population density. [source] Trends in the start of the wet season over AfricaINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 9 2009D. R. Kniveton Abstract A quarter of a century of daily rainfall data from the Global Telecommunications System are used to define the temporal and spatial variability of the start of the wet season over Africa and surrounding extreme south of Europe and parts of the Middle East. From 1978 to 2002, the start of the wet season arrived later in the year for the majority of the region, as time progressed. In some parts of the continent, there was an annual increase in the start date of up to 4 days per year. On average, the start of the wet season arrived 9,21 days later from 1978 to 2002, depending on the threshold used to define the start of the rains (varying from 10,30 mm over 2 days, with no dry period in the following 10 days). It is noted that the inter-annual variability of the start of the wet season is high with the range of start dates varying on average from 116 to 142 days dependent on the threshold used to determine the start date. These results may have important implications for agriculturists on all levels (from the individual farmer to those responsible for regional food supply), as knowledge of potential future climate changes starts to play an increasingly important role in the agricultural decision-making process, such as sowing and harvesting times. Copyright © 2008 Royal Meteorological Society [source] | ||||||||||||||||||||||||||||||||||||||||||||||