Development and application of a bioenergetics model for juvenile walleye Pollock

A bioenergetics model was parameterized for age-0 walleye pollock, Theragra chalcogramma , based on a synthesis of literature data. The sensitivity of the new parameters was tested by individual parameter perturbation (IPP) analysis. The model was applied to estimate individual and total cohort food consumption of age-0 pollock in two areas of high pollock density in the Gulf of Alaska during the summer of 1990. Total cohort consumption was compared with zooplankton biomass and production estimates for the same areas and times of the year. The model was also used to examine the bioenergetic implications of age-0 pollock diel vertical migration through a thermal gradient. During a 1-month bioenergetics simulation, individual daily consumption decreased from 16·0 to 6·0% of wet body weight. Daily ration estimates corresponded well with independent field estimates of daily ration for the same areas and time of the year. Comparison of total cohort consumption with prey availability (production and biomass) indicated minimal potential for food limitation. Bioenergetic optimization of growth can be a potential benefit of diel vertical migration to age-0 pollock, however more information on prey density and distribution is needed to test this hypothesis thoroughly.     

The influence of hunger and predation risk on group cohesion in a pelagic fish, walleye pollock Theragra chalcogramma

Variation in the intensity of schooling behavior in fishes suggests that the benefits of aggregation are balanced by certain costs. We examined the proximity of group members to each other in juvenile walleye pollock, Theragra chalcogramma, under different environmental conditions. Food availability, simulated by a gradient of six ration treatments, had a major influence on group cohesion, with increasing dispersion as food level decreased. Group cohesion also decreased at night relative to daytime levels. Small juveniles (x=53 mm TL) maintained on high rations were highly responsive to the potential threat of a predator, with groups becoming more cohesive and remaining so for up to an hour after the initial threat. A chronic threat (continual presence of predators) resulted in tighter group cohesion than an acute threat (single simulated attack). Small juveniles maintained on low rations were less responsive to predation threats and recovered quickly, supporting the hypothesis that hunger induces risk-taking behavior. Large juveniles (x=149 mm TL) did not change their degree of aggregation in response to either type of predation threat. An overall plasticity in the degree of cohesiveness among group members indicates that walleye pollock are capable of gradually modifying their schooling behavior according to the environmental context.     

Energy allocation in larval and juvenile Coregonus lavaretus: validation of a bioenergetics model

Food consumption and energy allocation of larval and juvenile whitefish Coregonus lavaretus L. were studied by conducting respirometry experiments at 10, 12 and 15° C. Results from these experiments were compared with those predicted by a bioenergetics model that used observed growth as the major input. The data were used to assess the performance of the model, and evaluate its suitability for estimation of food consumption by whitefish. The mean absolute % error (ɛ) between observed and predicted food consumption was 16·3%, and the modelling efficiency (M_E) was 0·90, indicating that the model was reasonably robust. Linear regression analysis of predicted v. observed food consumption values gave a slope slightly above unity, indicating a tendency for the model to overestimate consumption at higher values. ɛ and M e were also calculated for total metabolic rate (RT), and they equalled 13·0% and 0·85, respectively. Despite some deficiencies, it is concluded that the model can be used for prediction of food consumption by highly active, planktivorous fish such as whitefish.     

Interannual differences in growth and hatch date distributions of age-0 year walleye pollock Theragra chalcogramma (Pallas) sampled from the Shumagin Islands region of the Gulf of Alaska, 1985 – 2001

Daily increments of age-0 year walleye pollock Theragra chalcogramma otoliths from 1985 to 2001 were examined for interannual variability in growth and hatch dates. Fish were collected in summer and autumn surveys near the Shumagin Islands in the western Gulf of Alaska (GOA). Hatch date distributions of these fish were compared with hatch dates of larvae from spawning aggregations located in Shelikof Strait and the Shumagin Islands based on their spawning times. The hatch date distributions of age-0 year fish captured from the Shumagin Islands area were similar to those observed for larvae from the Shelikof Strait spawning group. Age-0 year fish whose hatch dates corresponded to the Shumagin Islands spawning, which occurred earlier in January and February, were not found. Sea surface temperature was associated with variability in hatch date distribution and growth.     

Seasonal and interannual effects of hypoxia on fish habitat quality in central Lake Erie

1. Hypoxia occurs seasonally in many stratified coastal marine and freshwater ecosystems when bottom dissolved oxygen (DO) concentrations are depleted below 2–3 mg O₂ L^?1. 2. We evaluated the effects of hypoxia on fish habitat quality in the central basin of Lake Erie from 1987 to 2005, using bioenergetic growth rate potential (GRP) as a proxy for habitat quality. We compared the effect of hypoxia on habitat quality of (i) rainbow smelt, Osmerus mordax mordax Mitchill (young‐of‐year, YOY, and adult), a cold‐water planktivore, (ii) emerald shiner, Notropis atherinoides Rafinesque (adult), a warm‐water planktivore, (iii) yellow perch, Perca flavescens Mitchill (YOY and adult), a cool‐water benthopelagic omnivore and (iv) round goby Neogobius melanostomus Pallas (adult) a eurythermal benthivore. Annual thermal and DO profiles were generated from 1D thermal and DO hydrodynamics models developed for Lake Erie’s central basin. 3. Hypoxia occurred annually, typically from mid‐July to mid‐October, which spatially and temporally overlaps with otherwise high benthic habitat quality. Hypoxia reduced the habitat quality across fish species and life stages, but the magnitude of the reduction varied both among and within species because of the differences in tolerance to low DO levels and warm‐water temperatures. 4. Across years, trends in habitat quality mirrored trends in phosphorus concentration and water column oxygen demand in central Lake Erie. The per cent reduction in habitat quality owing to hypoxia was greatest for adult rainbow smelt and round goby (mean: ?35%), followed by adult emerald shiner (mean: ?12%), YOY rainbow smelt (mean: ?10%) and YOY and adult yellow perch (mean: ?8.5%). 5. Our results highlight the importance of differential spatiotemporally interactive effects of DO and temperature on relative fish habitat quality and quantity. These effects have the potential to influence the performance of individual fish species as well as population dynamics, trophic interactions and fish community structure.     

Application of a bioenergetics model for analysis of growth and food consumption of subarctic whitefish Coregonus lavaretus (L.) in Lake Kilpisjärvi, Finnish Lapland

A bioenergetics model was used to estimate daily food consumption and growth of benthic whitefish Coregonus lavaretus (L.) of age groups 1+ to 10+, in oligotrophic Lake Kilpisjärvi, northern Finnish Lapland. Fish and zooplankton samples and water temperature data were collected twice per month from February to December 1993. Simulation results indicated wide seasonal variations in consumption and growth rates. Growth was in general slow; especially in age-group 6 the net increase in weight was slight. The fit of the model to the weight data was good, and the model was able to follow even rapid seasonal variations in the weight. There were clear changes in the diet during the year. In March, when the food intake was reduced, copepods, mainly adult calanoids, formed the bulk of the food consumed. The most intensive consumption period lasted from June to late September. Chironomid pupae and planktonic cladocerans were the major summer food items. The largest individuals fed mainly on molluscs during summer. Zooplankton survey and consumption estimates did not show directly that the population density of copepodids and adults of Eudiaptomus graciloides were affected by whitefish predation although their population density decreased in spring. Nauplii, showing the maximum population density in April, were not consumed. The role of copepod consumption in the timing of Diphyllobothrium ditremum plerocercoid transmission to whitefish was also discussed. The increased copepod consumption rate during winter results in high energy intake but also an increased risk of food transmitted parasite infection.     

空间直观景观模型LANDIS在大兴安岭呼中林区的应用

应用空间直观景观模型(LANDIS),研究有采伐和无采伐预案下大兴安岭呼中林区的森林景观的长期变化。用APACK计算每一个物种及各年龄级的分布面积。为了研究物种分布格局的变化,计算了物种分布的聚集度指数。研究结果如下：(1)在无采伐预案下。火干扰模式为低频率大面积高强度火烧;在有采伐预下,火干扰模式为高频率小面积低强度火烧;(2)在无采伐预案下,火会造成各种群分布面积的强烈波动,但是对种群的年龄结构没有很大影响;在有采伐预案下,火对种群分布面积和年龄结构都没有很大的影响;(3)采伐能完全改变各种群的年龄结构。降低种群分布的聚集度,但是对各种群的分布面积并没有很大影响;(4)在有采伐预案下,各种群为增长型种群,增长量通过采伐取走,群落处于演替的干扰顶极状态;在无采伐预案下,各种群为稳定型种群(樟子松和偃松除外),大面积高强度火烧使群落产生较大的波动。结果表明,在呼中林业局,在没有人为干扰情况下,火干扰是森林景观变化的主导因素。自从有了人为干扰,采伐开始逐渐取代火干扰成为影响森林景观变化的主导因素。空间直观景观模型的一个挑战是模型的验证。由于缺乏详细的空间数据及模型模拟中的随机性,很难通过模型模拟结果与实地调查或遥感数据的比较进行验证。通过对火模拟、物种分布和物种组成的生态或生物学实现对模型进行验证。     

Effects of temperature on prey consumption and growth in mass of juvenile trahira Hoplias aff. malabaricus (Bloch, 1794)

The influence of temperature on prey consumption and growth in mass of juvenile trahira Hoplias aff. malabaricus were investigated. Consumption of small-sized lambari Astyanax altiparanae (mean standard length, L _S, 5·43 cm) varied from zero to 65 over a period of 30 days. Temperatures ranged from 14 to 34° C and the size of trahiras ranged from 17·5 to 24·7 cm L _S. Prey consumption differed significantly among temperatures. Trahiras at 18° C consumed significantly less than those at 30° C. A linear multiple regression model including temperature, prey consumption and L _S explained 89·4% of the variability in growth in mass. Some caution is suggested when inferring the impact of H. aff. malabaricus piscivory on assemblage structures in systems that, despite their location in tropical regions, are subjected to seasonal thermal variations.     

Temperature effects on bioenergetics of growth, assimilaton efficiency and thyroid activity in juvenile varand lizards

When varanid lizards, Varanus niloticus, were allowed to select their preferred body temperature (c. 34°C) they exhibited swifter growth, larger food intake and superior efficiency of conversion when compared with animals restricted to a maximum body temperature of 24°C. At the higher temperature the animals also exhibited a higher metabolic rate and increased thyroid activity, while those at the lower temperature lostproportionately more energy via respiration. A complete energy budget over a period of 6 weeks is presented.     

基于个体的空间显性模型和遥感技术模拟入侵植物扩张机制

基于个体的空间显性模型和遥感技术,以互花米草为例,模拟了自1997到2010年的种群扩张动态,揭示了土地利用变化与潮间带高程的影响;并通过全局敏感性分析揭示了种子扩散、成体存活率、有性和无性繁殖等种群统计学特征对互花米草种群扩张的相对重要性。研究结果发现:1)有性繁殖与无性繁殖共同决定互花米草种群快速扩张;2)潮间带高程和土地利用变化显著影响模型预测的精度,对互花米草种群扩张有非常重要的影响;3)成体存活率与种子长距离扩散是影响互花米草种群扩张速度最重要的因素;无性繁殖比有性繁殖对种群扩张的影响更大;种子长距离扩散比本地扩散更为重要,同时,小概率的种子长距离扩散事件对种群扩张有非常重要的影响。为了经济有效地控制外来入侵植物的扩张,应该抑制种子的长距离扩散和移除种子长距离扩散形成的位于入侵前沿的小斑块。     

Health food versus fast food: the effects of prey quality and mobility on prey selection by a generalist predator and indirect interactions among prey species

1. In order to understand the relative importance of prey quality and mobility in indirect interactions among alternative prey that are mediated by a shared natural enemy, the nutritional quality of two common prey for a generalist insect predator along with the predator's relative preference for these prey was determined. 2. Eggs of the corn earworm Helicoverpa zea (Lepidoptera: Noctuidae) were nutritionally superior to pea aphids Acyrthosiphum pisum (Homoptera: Aphididae) as prey for big‐eyed bugs Geocoris punctipes (Heteroptera: Geocoridae). Big‐eyed bugs survived four times as long when fed corn earworm eggs than when fed pea aphids. Furthermore, only big‐eyed bugs fed corn earworm eggs completed development and reached adulthood. 3. In two separate choice experiments, however, big‐eyed bugs consistently attacked the nutritionally inferior prey, pea aphids, more frequently than the nutritionally superior prey, corn earworm eggs. 4. Prey mobility, not prey nutritional quality, seems to be the most important criterion used by big‐eyed bugs to select prey. Big‐eyed bugs attacked mobile aphids preferentially when given a choice between mobile and immobilised aphids. 5. Prey behaviour also mediated indirect interactions between these two prey species. The presence of mobile pea aphids as alternative prey benefited corn earworms indirectly by reducing the consumption of corn earworm eggs by big‐eyed bugs. The presence of immobilised pea aphids, however, did not benefit corn earworms indirectly because the consumption of corn earworm eggs by big‐eyed bugs was not reduced when they were present. 6. These results suggest that the prey preferences of generalist insect predators mediate indirect interactions among prey species and ultimately affect the population dynamics of the predator and prey species. Understanding the prey preferences of generalist insect predators is essential to predict accurately the efficacy of these insects as biological control agents.     

Early development of milkfish: effects of salinity on embryonic and larval metabolism, yolk absorption and growth

During embryogenesis of Chanos chanos , more than half of the yolk was consumed and the majority of it was converted into larval tissue. Salinity affected both yolk absorption and embryonic and larval growth. Larvae hatched in 20% had larger yolk reserves but were smaller and grew more slowly than larvae in 35 and 50%. Larvae hatched in 35 and 50% had equal amounts of yolk but those from 35% were larger. Oxygen consumption rates increased during development (from 0.06 ± 0.01 μl O₂ egg^–1 h^–1 by blastulae to 0.37 ± 0-01 μl O₂ egg^–1 h^–1 by prehatch embryos and 0–43 ± 0–03 μl O₂ larva ^–1 h ^–1 by newly-hatched larvae) and were significantly affected by salinity. Eggs and yolk-sac larvae incubated in 35% consumed more oxygen than those in the low and high salinities. Salinity affected both the rate and pattern of yolk utilization but salinity-related differences in metabolism, yolk absorption, and growth were not related directly to the osmotic gradient. Low salinity retarded yolk absorption while high salinity reduced yolk utilization efficiencies. Differences in oxygen consumption rates were probably related to variations in the relative amounts of metabolically active embryonic and larval tissue and/or higher activity levels rather than differential osmoregulatory costs. 35% is probably the most suitable salinity for incubation and larval rearing of milkfish.     

The effect of powdery mildew on the number of prey consumed by Typhlodromus pyri (Acari: Phytoseiidae)

Abstract:  Prey consumption by Typhlodromus pyri Scheuten was studied in the presence and absence of apple powdery mildew, Podosphaera leucotricha (Ell. and Everh.) under constant laboratory conditions. Eggs of Tetranychus urticae Koch were offered to predatory mites as a prey. Seven densities ranging from five to 100 T. urticae eggs per arena were used. Mildew conidia (approximately 0.5 mg) were added to half of the arenas by brushing them from infected apple leaves. A single adult female of T. pyri was introduced onto each arena and number of prey eggs consumed was counted 12 h later when the predator was offered new T. urticae eggs again and the procedure was repeated once. Data showed that predators consumed in both experimental periods nearly all prey in experiments with densities up to 40 eggs per arena and no mildew. However, the number of eggs consumed decreased more than twofold when mildew conidia were supplied, even at high prey densities. Differences in predation rate between treatments with and without mildew were highly significant. The results thus indicate that availability of mildew as an alternative food can reduce prey suppression by T. pyri . Possible implications of these findings in biological control of spider mites by generalist predatory mites are discussed.     

Long‐term patterns in growth of Oneida Lake walleye: a multivariate and stage‐explicit approach for applying the von Bertalanffy growth function

Total length ( L _T) and its inter annual variation of walleye Sander vitreus from Oneida Lake, New York, based on 51 years (1950–2000) of data for ages 1 to 7 years were analysed. Growth increased over time at young ages, did not change at intermediate ages and decreased at old ages. Total length at age increased over time to age 4 or 5 years, but was stable at older ages. Principle component analysis was used to study the pattern of variations in annual L _T increments among years. More than 92 and 91% of inter annual variability in growth was described by the first three principal components for males and females, respectively. The first principal component was a general indicator of annual growth at all ages, but was dominated by annual growth at intermediate ages. The second and third principal components represented contrasts among yearling L _T, yearling growth and growth at older ages. Therefore, changes in the three stage‐specific parameters, yearling L _T, yearling growth and asymptotic L _T, explained most of the variance in observed growth. Using these three stage‐specific parameters for the von Bertalanffy growth function facilitated interpretations of growth comparisons.     

Effect of starvation time on the prey capture behaviour, functional response and population growth of Asplanchna sieboldi (Rotifera)

1. We examined the effect of different periods of prior starvation(from 30 min to 16 h) on the prey capture behaviour, and functional and numerical responses of the predatory rotifer Asplanchna sieboldi using the rotifer Brachionus calyciflorus as prey.
2. Feeding activity (i.e. encounter, attack, capture and ingestion) by Asplanchna increased significantly with increasing prey densities from 2 to 16 mL⁻⁻¹ and with increasing prior starvation periods from 0.5 to 8 h.
3.  Asplanchna sieboldi showed a type II functional response at all the prior starvation periods tested. The asymptotic prey density was highest after 8 h of starvation.
4. The instantaneous population growth rate of A. sieboldi ranged from 0.089 ± 0.044 (when starved for 8 h in every 24 h and at a prey density of 2 individuals mL⁻⁻¹ for the other 16 h) to 1.015 ± 0.142 in the control (no starvation and at a prey density of 16 individuals mL⁻⁻¹). The effect of starvation time on the numerical response was evident only at the higher prey density.     

Production,consumption and prey availability of northern pike (Esox lucius), pikeperch (Stizostedion lucioperca) and European catfish (Silurus glanis): a bioenergetics approach

Bioenergetics models were applied for the assessment of food consumption of northern pike, pikeperch and European catfish in drainable ponds of 0.4 ha. The ponds were stocked with known numbers of the 0⁺ predators. The prey fish consisted of naturally recruited 0⁺ cyprinids (rudd, roach and bream). The study shows that the impact of the three 0⁺ piscivores on the aquatic system differs, which is related to the feeding behaviour and habitat use of the fish. All piscivores realised part of their production on a non-fish diet.     

The effects of archipelago spatial structure on island diversity and endemism: predictions from a spatially‐structured neutral model

Islands are particularly suited to testing hypotheses about the ecological and evolutionary mechanisms underpinning community assembly. Yet the complex spatial arrangements of real island systems have received little attention from both empirical studies and theoretical models. Here, we investigate the extent to which the spatial structure of archipelagos affects species diversity and endemism. We start by proposing a new spatially structured neutral model that explicitly considers archipelago structure, and then investigate its predictions under a diversity of scenarios. Our results suggest that considering the spatial structure of archipelagos is crucial to understanding their diversity and endemism, with structured island systems acting both as “museums” and “cradles” of biodiversity. These dynamics of diversification may change the traditionally expected pattern of decrease in species richness with distance from the mainland, even potentially leading to increasing patterns for taxa with high speciation rates in archipelagos off species‐poor continental areas. Our results also predict that, within spatially structured archipelagos, metapopulation dynamics and evolutionary processes can generate higher diversity on islands more centrally placed than at the periphery. We derive from our results a set of theoretical predictions, potentially testable with empirical data.     

Patch selection by juvenile black surfperch (Embiotocidae) under variable risk: Interactive influence of food quality and structural complexity

The influence of risk on the selection of foraging patches by young-of-year black surfperch, Embiotoca jacksoni Agassiz, was investigated by laboratory and field experiments. These foragers harvest crustacean prey from a variety of benthic algal substrata. In field environments, patch types vary in two ways. First, substrata differ in structural complexity and probably afford different degrees of protection from predators. Second, substratum types vary in prey richness. There was no correlation between structural complexity and prey richness, and either or both factors could be a component of foraging patch value. Each patch is small and individual foragers are simultaneously confronted with arrays of patches encompassing the full range of variation in structure and prey richness. Furthermore, a major predator of young-of-year black surfperch, the kelp bass, Paralabrax clathratus (Girard), is patchily distributed in space and time. Thus similar arrays of patch types can be characterized by different levels of overall risk. Risk to foragers is dependent on light level as well as the presence and density of predators.The interplay between food quality and shelter potential in influencing patch choice was examined under different regimes of risk. Both laboratory and field experiments indicated patch preference was based primarily on food quality. However, the physical structure of a patch did become a component of patch choice as risk increased. The relative value of physical structure under high risk was dependent on the prey richness of a patch; food-poor substrata with high shelter potential remained unfavored even in situations of high risk.     

Temperature and salinity effects on post-marsupial growth of Neomysis integer (Crustacea: Mysidacea)

There has been an increasing interest in using the brackish water mysid Neomysis integer as a toxicological test species for Western European estuarine systems. In this respect, more data on growth, moulting and development in this species is needed. The influence of prevailing environmental variables (e.g. temperature, salinity) and age on these processes as well as their optimal range have to be known in order to develop optimal laboratory cultures and to differentiate between chemically induced variability and natural variability in toxicity testing. Individual post-marsupial growth (size, intermoult period, growth factor) was studied from first day neonates until adulthood at eight environmentally relevant temperature-salinity conditions. Three salinities (5, 15 and 30 psu) were tested at 15 and 20 °C, and two more extreme temperatures (8 and 25 °C) were tested at a salinity of 5 psu.Survival and growth of N. integer were detected within the whole range tested, but sexual maturation was only possible in the narrower range of 15-25 °C and 5-15 psu. The size at maturity of N. integer increased with decreasing temperature and increasing salinity. Salinity seems to have a stronger effect than temperature on the duration of maturation. The sigmoid von Bertalanffy growth model was fitted to the individual and pooled data, except for the 8 °C experiment where growth was linear. Estimates from pooled data were comparable with individually based estimates, but generally underestimated the asymptotic length. Temperature was negatively correlated with the asymptotic length and positively correlated with the growth constant K. Higher temperatures caused smaller intermoult periods but had no effect on the growth increment, while salinity effects were less straightforward and dependent on the water temperature. A tool is provided to estimate the age, moult number, intermoult period, growth factor and growth rate from the body standard length of N. integer. Experimentally derived von Bertalanffy parameter estimates resulted in a higher growth performance index compared with field-based estimates for the Schelde estuary and Galgenweel populations of N. integer.