Foraging behavior of ants: Theoretical considerations

This paper describes models of behavior for two ant species recruiting to very different sorts of resource. One species, Solenopsis geminata, recruits to sugar solution. The other, Pogonomyrmex occidentalis, recruits to patches of seeds. The models clarify the assumptions entering into the theoretical analysis of these behaviors and point to measurements that should be made for their experimental analysis.Both models assume that the colony gains energy when a forager gets a load of resource. Energy is lost during the trip to a patch of resource in a manner dependent upon the current physical conditions of the environment. The only factor counterbalancing an ever increasing net energy gain when the recruitment rates are increased is interference among workers at a patch. As the rate of recruitment is elevated this interference decreases the efficiency with which the resource can be used and, thus, sets an optimum at some intermediate rate of recruitment.The limitation of considerations in this paper to energetic efficiency is discussed and justified in terms of components of fitness and ant physiology. It is found that several qualitative predictions can be experimentally tested, but that quantitative predictions require fine measurement of metabolic costs to individual foragers and of complicated gains to the colony as a whole. Both models can be differentiated experimentally from corresponding time minimization models.     

Evolutionary models of metabolism, behaviour and personality

I explore the relationship between metabolism and personality by establishing how selection acts on metabolic rate and risk-taking in the context of a trade-off between energy and predation. Using a simple time budget model, I show that a high resting metabolic rate is not necessarily associated with a high daily energy expenditure. The metabolic rate that minimizes the time spent foraging does not maximize the net gain rate while foraging, and it is not always advantageous for animals to have a higher metabolic rate when food availability is high. A model based on minimizing the ratio of mortality rate to net gain rate is used to determine how a willingness to take risks should be correlated with metabolic rate. My results establish that it is not always advantageous for animals to take greater risks when metabolic rate is high. When foraging intensity and metabolic rate coevolve, I show that in a particular case different combinations of foraging intensity and metabolic rate can have equal fitness.     

Environment-dependent metabolic investments in the mixotrophic chrysophyte Ochromonas

Mixotrophic protists combine photosynthesis and phagotrophy to obtain energy and nutrients. Because mixotrophs can act as either primary producers or consumers, they have a complex role in marine food webs and biogeochemical cycles. Many mixotrophs are also phenotypically plastic and can adjust their metabolic investments in response to resource availability. Thus, a single species's ecological role may vary with environmental conditions. Here, we quantified how light and food availability impacted the growth rates, energy acquisition rates, and metabolic investment strategies of eight strains of the mixotrophic chrysophyte, Ochromonas. All eight Ochromonas strains photoacclimated by decreasing chlorophyll content as light intensity increased. Some strains were obligate phototrophs that required light for growth, while other strains showed stronger metabolic responses to prey availability. When prey availability was high, all eight strains exhibited accelerated growth rates and decreased their investments in both photosynthesis and phagotrophy. Photosynthesis and phagotrophy generally produced additive benefits: In low-prey environments, Ochromonas growth rates increased to maximum, light-saturated rates with increasing light but increased further with the addition of abundant bacterial prey. The additive benefits observed between photosynthesis and phagotrophy in Ochromonas suggest that the two metabolic modes provide nonsubstitutable resources, which may explain why a tradeoff between phagotrophic and phototrophic investments emerged in some but not all strains.     

Rainbow trout in seasonal environments: phenotypic trade‐offs across a gradient in winter duration

Survival through periods of resource scarcity depends on the balance between metabolic demands and energy storage. The opposing effects of predation and starvation mortality are predicted to result in trade‐offs between traits that optimize fitness during periods of resource plenty (e.g., during the growing season) and those that optimize fitness during periods of resource scarcity (e.g., during the winter). We conducted a common environment experiment with two genetically distinct strains of rainbow trout to investigate trade‐offs due to (1) the balance of growth and predation risk related to foraging rate during the growing season and (2) the allocation of energy to body size prior to the winter. Fry (age 0) from both strains were stocked into replicate natural lakes at low and high elevation that differed in winter duration (i.e., ice cover) by 59 days. Overwinter survival was lowest in the high‐elevation lakes for both strains. Activity rate and growth rate were highest at high elevation, but growing season survival did not differ between strains or between environments. Hence, we did not observe a trade‐off between growth and predation risk related to foraging rate. Growth rate also differed significantly between the strains across both environments, which suggests that growth rate is involved in local adaptation. There was not, however, a difference between strains or between environments in energy storage. Hence, we did not observe a trade‐off between growth and storage. Our findings suggest that intrinsic metabolic rate, which affects a trade‐off between growth rate and overwinter survival, may influence local adaptation in organisms that experience particularly harsh winter conditions (e.g., extended periods trapped beneath the ice in high‐elevation lakes) in some parts of their range.     

Mycorrhizae and forest ecosystems

Summary Mycorrhizae play an important role in regulating patterns of energy and nutrient flux in terrestrial ecosystems. To conceptualize this role I develop the theory behind a simple index of the efficiency of soil resource acquisition by plant root systems (E). The morphological, physiological and demographic characteristics of mycorrhizae that define E appear to vary with environment and with plant community composition. This theory is elaborated with examples drawn from forest ecology literature. Some inconsistencies among observations of fine root dynamics are particularly revealing: (1) belowground carbon allocation vs soil fertility; (2) causes of root mortality; (3) root longevity vs decomposition rates. A comprehensive theory of mycorrhizal and ecosystem dynamics must await resolution of these inconsistencies and better quantitative information on mycorrhizal features affecting E.     

Feeding and metabolic compensations in response to different foraging costs

How energetic cost of locomotion affects foraging decisions, and its metabolic consequences are poorly understood. In several groups of animals, including hermit crabs, exploratory walking enhances the efficiency of foraging by increasing the probability of finding more and better food items; however, the net gain of energy will only be enhanced if the costs of walking are lower than the benefits of enhanced food acquisition. In hermit crabs, the cost of walking increases with the mass of the shell type occupied. Thus, we expected that hermit crabs should adjust their foraging strategy to the cost of movement in different shells. We assessed the foraging, the quantity and quality of food intake, and the energetic cost of maintenance of hermit crabs paying different costs of foraging in the wild. The exploratory walking negatively correlated with shell mass, showing that hermit crabs use different foraging strategies in response to the expenditure required to move. Hermit crabs deal with high energetic costs of foraging in heavy shells by reduces their exploratory walking and overall metabolic rate, as a strategy to maximize the net energy intake. This study integrates behavioral and metabolic compensations as a response to foraging at different costs in natural conditions.     

基于产量效应的间作紫花苜蓿/禾本科牧草光能利用特征

为探究紫花苜蓿/禾本科牧草间作下光能利用特性、光能利用诸因素的产量效应及其调控机理,通过2017—2019年3年田间试验,以紫花苜蓿、饲用小黑麦(C3植物)、饲用玉米(C4植物)3种单作模式为对照,研究了紫花苜蓿/小黑麦和紫花苜蓿/玉米两种间作模式下的产量效应、光能利用各因子对产量形成的影响、光能利用特征差异及机理。结果表明: 两种间作模式的土地当量比均大于1,表明两种间作模式的土地利用率都高于单作,均有高于单作的产量效益,且增产潜力较大的是紫花苜蓿/小黑麦间作模式。光能利用各因子对产量的贡献依次是: 叶面积指数(1.531)＞净光合速率(0.882)＞胞间CO₂浓度(0.282)＞蒸腾速率(-0.229)＞冠层开度(-0.291)＞光合有效辐射截获率(-0.681)＞气孔导度(-0.751)。其中,叶面积指数不仅是表征光合能力的重要指标之一,更是以收获营养体为目标的牧草作物产量的重要构成因子,光合特性诸因素中净光合速率是影响产量的主要因子。与单作相比,间作下紫花苜蓿、小黑麦、玉米的净光合速率均存在差异,且表现为相同的规律。间作下净光合速率提高的主要途径为: 小黑麦和玉米通过增强CO₂的羧化固定能力,提高对强光的利用能力,从而提高净光合速率,促进产量增加;而紫花苜蓿则是通过提高功能叶的叶绿素b含量,改变叶绿素构成,增强对光能的收集和传递,从而提高净光合速率,促进其在弱光下光合能力的提高和正常生长。     

A comparison of muscle energy models for simulating human walking in three dimensions

The popular Hill model for muscle activation and contractile dynamics has been extended with several different formulations for predicting the metabolic energy expenditure of human muscle actions. These extended models differ considerably in their approach to computing energy expenditure, particularly in their treatment of active lengthening and eccentric work, but their predictive abilities have never been compared. In this study, we compared the predictions of five different Hill-based muscle energy models in 3D forward dynamics simulations of normal human walking. In a data-tracking simulation that minimized muscle fatigue, the energy models predicted metabolic costs that varied over a three-fold range (2.45–7.15 J/m/kg), with the distinction arising from whether or not eccentric work was subtracted from the net heat rate in the calculation of the muscle metabolic rate. In predictive simulations that optimized neuromuscular control to minimize the metabolic cost, all five models predicted similar speeds, step lengths, and stance phase durations. However, some of the models predicted a hip circumduction strategy to minimize metabolic cost, while others did not, and the accuracy of the predicted knee and ankle angles and ground reaction forces also depended on the energy model used. The results highlights the need to clarify how eccentric work should be treated when calculating muscle energy expenditure, the difficulty in predicting realistic metabolic costs in simulated walking even with a detailed 3D musculoskeletal model, the potential for using such models to predict energetically-optimal gait modifications, and the room for improvement in existing muscle energy models and locomotion simulation frameworks.     

绿洲灌区典型种植模式的水热利用与碳排放和能值分析

合理的种植模式可以提高资源利用效率,降低农业生产的生态环境风险,实现资源节约和增产增效的目的.本文运用能值分析的理论和方法,从资源利用、碳排放、经济效益、能值自给率和净能值产出率等方面对干旱灌区典型种植模式的生产效应进行综合分析与评价,以期为建立减投、减排、高产高效、可持续农田高效生产模式提供理论与实践依据.结果表明:集成免耕秸秆覆盖还田及地膜再利用的高效间作生产模式(NTSI)具有明显的增产效应,与地方传统间作(CTI)和单作玉米(CTM)相比,分别增产13.5%～16.9%和13.8%～17.1%.NTSI较CTI模式水分利用效率和光能利用率分别提高12.4%～17.2%和6.1%～8.1%.高效NTSI模式可降低系统碳排放、提高碳排放效率,与CTI和CTM相比,碳排放总量分别降低618～895和1804～2002 kg·hm^-2,降低幅度分别为12.1%～16.4%和28.6%～31.0%;相反,碳排放效率分别提高29.3%～40.1%和58.9%～71.4%.高效NTSI模式具有明显的资源减投潜力,与CTI和CTM相比,总投入分别降低1424～1431和501～1547 元·hm^-2,减投比例分别为12.6%～13.6%和4.9%～14.6%;总产值分别提高11.2%～11.8%和24.4%～36.3%(增加4309～4603和8439～11057元·hm^-2);纯收益分别增加19.6%～22.4%和40.1%～57.7%(增多5740～6027和9544～11558元·hm^-2).因而,NTSI模式具有较高的产投比和单方水效益,与CTI和CTM相比,产投比分别提高27.9%～29.0%和40.5%～45.6%;单方水效益提高幅度分别达到19.9%～23.2%和27.7%～39.3%.高效NTSI模式能值自给率达到57.2%,较CTI和CTM生产模式分别提高4.0%和12.2%,NTSI模式净能值产出率达到0.173,较CTI高10.0%,但比CTM低11.7%.从资源利用、碳减排、经济效益、可持续发展角度综合考虑,集成免耕秸秆覆盖还田及地膜两年利用的高效小麦间作玉米模式具有较高的经济活力,农业系统整体功能较好,运转效率较高,能值回报率较高,是适用于干旱绿洲灌区的资源减投、减排、高产高效的种植模式.     

马铃薯品种间光合特征的比较研究

马铃薯叶片光合作用是影响其块茎产量和品质的重要因素之一。为了选择适宜湖南栽培的马铃薯品种和提高马铃薯的栽培效益,本文时中薯3号、大西洋、费乌瑞它、东农303、PB04、PB08和滇薯6号7个马铃薯品种(系)在匍匐茎伸长期、块茎形成期、块茎膨大期和块茎完熟期4个时期的光合特征参数(叶片净光合速率、气孔导度、蒸腾速率、胞间CO_2浓度)、SPAD值和相对产量进行了比较研究。结果表明,中薯3号的叶片净光合速率、气孔导度、胞间CO_2浓度、蒸腾速率和平均每株产量都最高,适宜于在湖南栽培。     

Effect of metabolic structures and energy requirements on curdlan production by<Emphasis Type="Italic">Alcaligenes faecalis</Emphasis>

A comprehensive metabolic network was proposed forAlcaligenes faecalis and employed in a stoichiometrically based flux balance model for curdlan production optimization. The maximal yield of curdlan was evaluated for curdlan batch production. Various metabolic structures and metabolic pathway distributions related with the curdlan maximal yield was evaluated. The results showed that the energy efficiency rather than the substrate supply was the major constraint for the enhancement of curdlan production. The increase in specific rate of glucose uptake could enhance curdlan production yield due to the decrease of the ratio of metabolic maintenance to substrate consumption. However, some of the energy loss and nutrient limitation associated with the increase of metabolic maintenance would adversely affect the conversion efficiency of the substrate.     

The physiological basis for faster growth in the Sydney rock oyster, Saccostrea commercialis

Sydney rock oysters were sampled from a mass selection experiment for growth (the "selected" category) and from a control ("not selected") population and held in the laboratory at three ration levels. We evaluated three models to explain faster rates of growth by selected oysters. Selection resulted in oysters feeding at up to twice the rate and with greater metabolic efficiency than controls. A field experiment confirmed that selection leads to faster rates of feeding across a wide range of food concentrations. Selected oysters also grew more efficiently, at a smaller cost of growth (Cg): mean values for Cg were 0.43 J x J(-1) in selected individuals and 0.81 J x J(-1) in the controls. In contrast, oysters in both categories showed similar metabolic rates at maintenance, i.e., at a ration supporting zero growth. There was no evidence that differential energy allocation affected the balance between total metabolic requirements above and below zero net energy balance. By experimenting with selected and control oysters of different sizes and ages, then standardizing the data for size, we found no effects of age on the differences due to selection. Faster-growing oysters feed more rapidly; invest more energy per joule ingested; show a higher net growth efficiency; and are able to allocate less energy per unit of tissue growth, than slower-growing individuals.     

Positive interactions among competitors can produce species-rich communities

Although positive interactions between species are well documented, most ecological theory for investigating multispecies coexistence remains rooted in antagonistic interactions such as competition and predation. Standard resource-competition models from this theory predict that the number of coexisting species should not exceed the number of factors that limit population growth. Here I show that positive interactions among resource competitors can produce species-rich model communities supported by a single limiting resource. Simulations show that when resource competitors reduce each others' per capita mortality rate (e.g. by ameliorating an abiotic stress), stable multispecies coexistence with a single resource may be common, even while the net interspecific interaction remains negative. These results demonstrate that positive interactions may provide an important mechanism for generating species-rich communities in nature. They also show that focusing on the net interaction between species may conceal important coexistence mechanisms when species simultaneously engage in both antagonistic and positive interactions.     

The effect of temperature on bacterial degradation of EDTA in pH-auxostat

The effect of temperature on the maximum specific growth rate and the cell yield was studied during cultivation of two bacterial strains (LPM-4 and Pseudomonas sp. LPM-410) on EDTA under unlimited cell growth conditions in a pH-auxostat. Both strains displayed linear dependence of reciprocal biomass yield against reciprocal specific growth rate, from which the values of rate of substrate expenditure for cell maintenance and the “maximum” yield (i.e., hypothetical yield without cell maintenance processes) were estimated. Analysis of the maximum yield values based on mass–energy balance theory suggested that oxidation of the carboxylic acid side chains of EDTA by a monooxygenase had zero or low energetic efficiency. An Arrhenius equation with different values of Arrhenius parameters within different temperature ranges gave a good fit with the temperature dependence of both growth rate and biomass yield. Specific growth rates of both strains showed a more pronounced temperature dependence than did the cell yields. A possible kinetic mechanism was suggested which might be responsible for the modes of the temperature dependences of specific growth rate and yield that were found. The mechanism is based on a hypothetical key substance governing the metabolic flows, which is formed in a zero-order reaction and destroyed in a first-order reaction, both rate constants depending on temperature according to the Arrhenius law.     

Adaptive trade-offs in juvenile salmonid metabolism associated with habitat partitioning between coho salmon and steelhead trout in coastal streams

1. Adaptive trade-offs are fundamental to the evolution of diversity and the coexistence of similar taxa and occur when complimentary combinations of traits maximize efficiency of resource exploitation or survival at different points on environmental gradients. 2. Standard metabolic rate (SMR) is a key physiological trait that reflects adaptations to baseline metabolic performance, whereas active metabolism reflects adaptations to variable metabolic output associated with performance related to foraging, predator avoidance, aggressive interactions or migratory movements. Benefits of high SMR and active metabolism may change along a resource (productivity) gradient, indicating that a trade-off exists among active metabolism, resting metabolism and energy intake. 3. We measured and compared SMR, maximal metabolic rate (MMR), aerobic scope (AS), swim performance (UCrit) and growth of juvenile hatchery and wild steelhead and coho salmon held on high- and low-food rations in order to better understand the potential significance of variation in SMR to growth, differentiation between species, and patterns of habitat use along a productivity gradient. 4. We found that differences in SMR, MMR, AS, swim performance and growth rate between steelhead trout and coho salmon were reduced in hatchery-reared fish compared with wild fish. Wild steelhead had a higher MMR, AS, swim performance and growth rate than wild coho, but adaptations between species do not appear to involve differences in SMR or to trade-off increased growth rate against lower swim performance, as commonly observed for high-growth strains. Instead, we hypothesize that wild steelhead may be trading off higher growth rate for lower food consumption efficiency, similar to strategies adopted by anadromous vs. resident brook trout and Atlantic salmon vs. brook trout. This highlights potential differences in food consumption and digestion strategies as cryptic adaptations ecologically differentiating salmonid species. 5. We hypothesize that divergent digestive strategies, which are common and well documented among terrestrial vertebrates, may be an important but overlooked aspect of adaptive strategies of juvenile salmonids, and fish in general.     

METABOLIC AND DIGESTIVE RESPONSES TO ARTIFICIAL SELECTION IN CHICKENS

Compared to ancestral wild jungle fowl, domestic broiler chickens have been consciously selected for large body size, relatively large pectoral muscles, rapid growth, and high feed efficiency. Hence intraspecific comparisons of these two strains could help identify consequences of unconscious artificial selection, trade-offs in energy allocation, and factors limiting energy budgets. We therefore compared our measurements of many corresponding parameters in both strains: growth rate, energy intake, digestive efficiency, metabolic rate and its components, organ masses, and intestinal brush-border nutrient transporter and hydrolase activities and capacities, as functions of age and body mass in zero- to nine-week-old chicks. Both strains prove to have the same digestive efficiency. Compared to equal-sized jungle fowl, broilers have higher daily energy intake and activity costs. Broilers have relatively longer and wider, hence heavier, small intestines, and their other gut compartments are also relatively larger. Offsetting these increases, broilers have relatively smaller brains and leg bones, these being much less important to a captive bird than to a wild bird exposed to predators. Broilers have generally lower intestinal transporter activities, but relatively higher transporter capacities because of their larger guts. Among domestic chicken strains, comparison of broilers with layers, the former having been consciously selected for much higher growth rates, yields generally similar conclusions. Thus, as recognized in broad outline by Darwin, domestication provides clear examples of conscious selection, of unconscious selection for traits prerequisite to the consciously selected traits, and of unconscious selection against traits rendered less important or competing for space or energy.     

The flight speed of parent birds feeding young

I review previous models of the speed at which parent birds should fly when delivering food to their young. Norberg gives a graphical method of finding a parent's best flight speed. This speed maximizes the overall rate at which energy is delivered to the young. An alternative assumption is that a parent maximizes the net rate of delivery of energy. I suggest that in general we cannot distinguish between net rate and overall rate on the basis of whether the parent feeds itself. The best way to distinguish between these currencies may be to use qualitative predictions. I present new results on the effect of a constraint on energy expenditure on the parent's optimal speed. I show that the optimal speed when foraging should be less than the optimal speed when traveling. I also analyse the advantage to a parent of flying faster than the maximum range speed and evaluate previous empirical studies of the speed at which parent birds fly. Only one study claims that parent birds fly at the speed identified by Norberg, but I raise doubts about this claim.     

Isolation of tomato strains varying in potassium acquisition using a sand-zeolite culture system

One hundred tomato strains, representing widely diverse geographic areas, were evaluated in a sand-zeolite culture medium for their response to both low (0.25 mM) and adequate (1.0 mM) K levels. Three types of strains differing in K acquisition were classified: (1) efficient strains characterized by their ability to acquire K under low-K stress and with dry matter accumulation comparable to the strains grown under adequate-K supply, (2) inefficient strains that grew well under adequate-K supply but with a low capacity to acquire K at low-K stress and correspondingly lesser dry weight production, and (3) slowly growing strains featured by low K content in tissue and low dry matter accumulation irrespective of external K levels. The efficient and slowly growing strains came mostly from South and Central America, where tomato originated and was domesticated. Strains from other regions, however, mostly showed inefficiency in K acquisition. Two distinct features associated with the efficiency of K acquisition were identified. One was the proliferation of root length and another was high net K-influx rates per unit root length under low-K stress. Our results suggested that mechanisms for efficient acquisition of nutrients were lost during the cultivation of plants, and centers of plant origin and domestication contain valuable genetic resources for improving plant efficiency in nutrient acquisition.