Mechanistic Approaches to Community Ecology: A New Reductionism

Mechanistic approaches to community ecology are those whichemploy individual— ecological concepts—those ofbehavioral ecology, physiological ecology, and ecomorphology—as theoretical bases for understanding community patterns. Suchapproaches, which began explicitly about a decade ago, are justnow coming into prominence. They stand in contrast to more traditionalapproaches, such as MacArthur and Levins (1967),which interpretcommunity ecology almost strictly in terms of "megaparameters.". Mechanistic approaches can be divided into those which use populationdynamics as a major component of the theory and those whichdo not; examples of the two are about equally common. The firstapproach sacrifices a highly detailed representation of individual—ecological processes; the second sacrifices an explicit representationof the abundance and persistence of populations. Three subdisciplines of ecology—individual, populationand community ecology—form a "perfect" hierarchy in Beckner's(1974) sense. Two other subdisciplines—ecosystem ecologyand evolutionary ecology—lie somewhat laterally to thishierarchy. The modelling of community phenomena using sets ofpopulation-dynamical equations is argued as an attempt at explanationvia the reduction of community to population ecology. Much ofthe debate involving Florida State ecologists is over whetheror not such a relationship is additive (or conjunctive), a verystrong form of reduction. I argue that reduction of communityto individual ecology is plausible via a reduction of populationecology to individual ecology. Approaches that derive the population-dynamicalequations used in population and community ecology from individual-ecologicalconsiderations, and which provide a decomposition of megaparametersinto behavioral and physiological parameters, are cited as illustratinghow the reduction might be done. I argue that "sufficient parameters"generally will not enhance theoretical understanding in communityecology. A major advantage of the mechanistic approach is that variationin population and community patterns can be understood as variationin individual-ecological conditions. In addition to enrichingthe theory, this allows the best functional form to be chosenfor modeling higher-level phenomena, where "best" is definedas biologically most appropriate rather than mathematicallymost convenient. Disadvantages of the mechanistic approach arethat it may portend an overly complex, massive and special theory,and that it naturally tends to avoid many-species phenomenasuch as indirect effects. The paper ends with a scenario fora mechanistic-ecological utopia.     

Workers, sexuals, or both? Optimal allocation of resources to reproduction and growth in annual insect colonies

Understanding decisions about the allocation of resources into colony growth and reproduction in social insects is one of the challenging issues in sociobiology. In their seminal paper, Macevicz and Oster predicted that, for most annual insect colonies, a bang–bang strategy should be favoured by selection, i.e. a strategy characterised by an “ergonomic phase” with exponential colony growth followed by a “reproductive phase” with all resources invested into the production of sexuals. Yet, there is empirical evidence for the simultaneous investment into the production of workers and sexuals in annual colonies (graded control). We, therefore, re-analyse and extend the original model of Macevicz and Oster. Using basic calculus, we can show that sufficiently strong negative correlation between colony size and worker efficiency or increasing mortality of workers with increasing colony size will favour the evolution of graded allocation strategies. By similar reasoning, graded control is predicted for other factors limiting colony productivity (for example, if queens’ egg laying capacity is limited).     

Power capacity: A key element in sustainability assessment

In the field of complex energetics, human societies to survive follow the same ‘maximum power principle’ as other living systems. In this view, human societies developed because they have been able to increase “their capacity to convert energy at a given time rate” rather than simply increase “their level of energy consumption”. This was translated into an increase of the level of ‘power capacity’ in human societies so far. Yet, one can expect that the level of power capacity will be altered in light of the unavoidable progressive depletion of fossil energy resources. The systemic study of power capacity in sustainability assessment is therefore essential for facing the external constraints ahead.Starting from the characterization commonly used in energy systems engineering, this paper seeks to clarify the concept of power capacity when used in sustainability assessment. It provides explicit methods of assessment for the different types of power capacity used by human societies. Power capacity refers to the converters transforming energy flows at a given time rate. Dealing with societal transitions therefore requires being able to characterize properly those converters in addition to the study of energy flows. However, this requires extending the timescale typically considered in conventional energy analysis which entails several epistemological problems over sustainability assessment.     

典型资源型城市生态承载力评价——以唐山市为例

资源型城市生态承载力评价研究的开展对促进资源型城市自然-经济-社会复合生态系统健康可持续发展具有指导意义。以唐山市作为案例城市,基于资源型城市独特的生态系统特点,从生态弹性力、承载媒体的支撑力、承载对象的压力三方面提出对生态承载力进行量化的研究方法,构建了较完整的生态承载力综合评价指标体系,利用主客观相结合的赋权方法,对唐山市生态承载力状况进行评价,探讨了2001—2010年10年间唐山市生态承载力变化趋势。结果表明:唐山市在研究时段内,生态弹性力指数波动强烈,表明生态系统的稳定性较差;承载媒体的支撑力指数逐渐增大,指数由0.111上升至0.898,显示系统的承载指数越来越高;承载对象的压力变化较为复杂,呈现先降后升,近几年又略有下降的趋势;系统的生态承载力整体上呈现波动性上升趋势,综合指数由0.345上升至0.720,说明唐山市生态系统的承载能力不断提高,但资源依赖型发展模式带来的资源短缺、环境污染和生态破坏等问题仍是制约生态承载力进一步提高的主要因素。研究成果客观地反映了唐山市生态承载力状况,对于唐山市未来的发展提出了合理的对策和建议,可为其他地区生态承载力研究提供一定借鉴。     

Growth and Dry-weight Distribution in Callistephus chinensis as Influenced by Lighting Treatment

Plants of two cultivars of Callistephus chinensis (Queen ofthe Market and Johannistag) were grown in 8 h of daylight perday with one of the following treatments given during the 16h dark period: (a) darkness—‘uninterrupted night’,(b) I h of light in the middle of the dark period—a ‘nightbreak’, (c) I min of light in every hour of the dark period—‘cycliclighting’, (d) light throughout—‘continuouslight’. The plants receiving uninterrupted dark periods remained compactand rosetted in habit with small leaves, while leaf expansion,stem extension, and flower initiation were promoted in all threeillumination treatments (b, c, d). Although these three treatmentsproduced similar increases in leaf area, continuous light wasthe most effective for the promotion of both stem growth andflower initiation while cyclic lighting was generally more effectivethan a I-h night break. Continuous light also caused more dry matter to be divertedto stems at any given vegetative dry weight and it was shownthat the stem weight ratio of both varieties was correlatedwith stem length.     

Saltatory Processes and Altricial to Precocial Forms in the Ontogeny of Fishes

SYNOPSIS. Development is not a gradual but a saltatory process.A combination of qualitative changes in form and function—thresholds—createsboundaries between a succession of quantitative intervals—steps.Thresholds can be modified by an altered time of appearanceof structures and functions (heterochrony), especially duringearly ontogeny, to form an operational basis for the prolongationof juvenile characters and adaptability into later ontogeny.Whereas such prolongation enables juvenilization in phylogeny,analogous principles may operate on a much shorter time scaleto produce the r-selection-like altricial and the K-selection-likeprecocial trends in ontogeny. The inherited capacity to adjustconstantly to the environment (heterochrony) selects for structural,biochemical and behavioral improvements. The tendency is towardthe precocial but the way back to altricial forms is left open.The heterochronous adaptations in early ontogeny can "reverse"the vulnerable specialization, should the environment becomeless stable and/or the community less competitive. Juvenilization,capable of turning gerontomorphosis into paedomorphosis in evolution,and heterochronous shifts of character anlagen, capable of turninga precocial trend into an altricial trend in ontogeny are bothpart of the same biological process which operates during earlyontogeny.     

The evolution of imperfect mimicry

Examples of imperfect resemblance between Batesian mimics andtheir models appear widespread in the natural world, but sofar few quantitative models have been proposed to explain thephenomenon. I used a simple signal detection model to showthat the relationship between model—mimic similarity and mimic effectiveness is typically nonlinear. In particular, Ifound that there will be little or no further selection toimprove model—mimic resemblance beyond a certain levelif the model species is costly to attack, if the mimic speciesis not particularly profitable (e.g., hard to catch), or ifthe mimic is relatively rare. When there are two different sympatricmodel species, then mimics should usually evolve a phenotypicsimilarity to one or the other model species, but not to both.In contrast, when several model species occur in differentareas (or emerge at different times) and individual mimicsuse each of these areas, then the optimal phenotype should bea "jack-of-all-trades" intermediate phenotype that does notclosely resemble any particular model species. Somewhat surprisingly,the theory predicts that if mimics spend an equal amount oftime with each model species, then the optimal intermediatephenotype should more closely resemble the least numerous andleast noxious model. This phenomenon arises because a vague similarity to an extremely noxious species is usually sufficientto guarantee significant protection, whereas a much closerresemblance to a mildly noxious model species is necessaryto afford a similar level of benefit.     

Sustainable Water Management in the Southwestern United States: Reality or Rhetoric?

Background

While freshwater sustainability is generally defined as the provisioning of water for both people and the environment, in practice it is largely focused only on supplying water to furnish human population growth. Symptomatic of this is the state of Arizona, where rapid growth outside of the metropolitan Phoenix-Tucson corridor relies on the same groundwater that supplies year-round flow in rivers. Using Arizona as a case study, we present the first study in the southwestern United States that evaluates the potential impact of future population growth and water demand on streamflow depletion across multiple watersheds.

Methodology/Principal Findings

We modeled population growth and water demand through 2050 and used four scenarios to explore the potential effects of alternative growth and water management strategies on river flows. Under the base population projection, we found that rivers in seven of the 18 study watersheds could be dewatered due to municipal demand. Implementing alternative growth and water management strategies, however, could prevent four of these rivers from being dewatered.

Conclusions/Significance

The window of opportunity to implement water management strategies is narrowing. Because impacts from groundwater extraction are cumulative and cannot be immediately reversed, proactive water management strategies should be implemented where groundwater will be used to support new municipal demand. Our approach provides a low-cost method to identify where alternative water and growth management strategies may have the most impact, and demonstrates that such strategies can maintain a continued water supply for both people and the environment.     

Modelling the depletion and conservation of forestry resources: effects of population and pollution

 In this paper, a mathematical model is proposed to study the depletion of resources in a forest habitat due to the increase of both population and pollution. It is shown that if the rate of pollutant emission into the environment is either population dependent, constant, or periodic, the equilibrium biomass density of the resource settles down to a lower equilibrium than its original carrying capacity, the magnitude of which decreases as the equilibrium levels of the density of population and the concentration of pollutant increase. However, in the case of an instantaneous spill of pollutant into the environment, the equilibrium biomass density decreases with the increase of the equilibrium density of population only. It is found that if the population density and the emission rate of pollutant increase without control, the forestry resource may become extinct. A conservation model is also proposed, the analysis of which shows that the resource biomass can be maintained at a desired level by conserving the forestry resource and by controlling the growth of population and the emission rate of pollutant in the habitat. Received 1 June 1993; received in revised form 1 January 1997     

Expanding networks: Signaling components in and a hypothesis for the evolution of metamorphosis

Metamorphosis is a substantial morphological transition between2 multicellular phases in an organism's life cycle, often markingthe passage from a prereproductive to a reproductive life stage.It generally involves major physiological changes and a shiftin habitat and feeding mode, and can be subdivided into an extendedphase of substantial morphological change and/or remodeling,and a shorter-term phase (for example, marine invertebrate "settlement,"insect "adult eclosion," mushroom fruiting body emergence) wherethe actual habitat shift occurs. Disparate metamorphic taxadiffer substantially with respect to when the habitat shiftoccurs relative to the timing of the major events of morphogeneticchange. I will present comparative evidence across a broad taxonomicscope suggesting that longer-term processes (morphogenetic changes)are generally hormonally regulated, whereas nitric oxide (NO)repressive signaling often controls the habitat shift itself.Furthermore, new evidence from echinoids (sea urchins, sanddollars) indicates a direct connection between hormonal andNO signaling during metamorphosis. I incorporate 2 hypothesesfor the evolution of metamorphosis—one involving heterochrony,the other involving phenotypic integration and evolutionarilystable configurations (ESCs)—into a network model formetamorphosis in echinoderms (sea urchins, starfish, and theirkin). Early indications are that this core regulatory networkcan be acted upon by natural selection to suit the diverse ecologicalneeds of disparate metamorphic organisms, resulting in evolutionaryexpansions and contractions in the core network. I briefly speculateon the ways that exposure to xenobiotic pollutants and othercompounds might influence successful settlement of juvenilesin the wild. Indeed, environmentally regulated life historytransitions—such as settlement, metamorphosis, and reproductivematuration—may be developmental periods that are especiallysensitive to such pollutants.     

Management of a German cockroach population with a juvenoid bait formulation: computer simulation

A computer model was applied to simulate responses of German cockroach populations to feeding on juvenoid baits during an equilibrium, exponential, and the earliest phase of population growth. The simulations show that the renewal potential of the cockroach populations will be exhausted when about 80% or more adults become sterile. The attainment of this activity threshold will be preceded by a lag time with no apparent control effect. The time delay appears substantially shorter for both growing populations (30–60 days) than for the equilibrious one (90–120 days), but, the former ones will continue growing throughout this lag. The simulations predict that even a worse baits' performance can give sufficient control effect in the field if the baits are laid in an early phase of population growth. Thus, optimum tactics should integrate administration of juvenoid baits with an introductory reduction of cockroach population.     

A lotka-volterra model of coexistence between a sexual population and multiple asexual clones

At carrying capacity, small advantages in competitive ability can compensate a sexual population for its two-fold disadvantage in growth capacity when facing invasion by asexual mutants. In this paper, we develop a generic analytical model to consider the ecology of a sexual population comprising equal numbers of males and females, competing for shared prey resources with multiple female-only clones. We assume that the clones arise from the sexual population and are distinguished from it only by having narrower resource niches and twice the growth capacity. For sexual populations, at density-dependent carrying capacity, intra-specific competition between clonal individuals prevents them from realizing their two-fold advantage in intrinsic growth. This prediction leads to three novel outcomes: (i) a sexual population can coexist with any number of clones, provided their combined competitive impact remains less than the impact of the clones on each other; (ii) a sexual species can immediately exclude asexual invaders if it is a fast growing and strong competitor of shared resources and also has refuge in an abundant alternative resource; (iii) the rate of accumulation of clones in a sexual population will be slowed by intra and inter-specific competition amongst the clones themselves, in addition to the competitive impact from the original sexual population.     

Seed weevils living on the edge: pressures and conflicts over body size in the endoparasitic Curculio larvae

Abstract 1. Body size in parasitic insects can be subjected to contrasting selective pressures, especially if they complete their development within a single host. On the one hand, a larger body size is associated with a higher fitness. On the other hand, the host offers a discrete amount of resources, thus constraining the evolution of a disproportionate body size. 2. The present study used the weevil Curculio elephas as a study model. Larvae develop within a single acorn, feeding on its cotyledons, and larval body size is strongly related to individual fitness. 3. The relationship between larval and acorn size was negatively exponential. Larval growth was constrained in small acorns, which did not provide enough food for the weevils to attain their potential size. Larval size increased and levelled off in acorns over a certain size (inflexion point), in which cotyledons were rarely depleted. When there were more than one larva per acorn, a larger acorn was necessary to avoid food depletion. 4. The results show that C. elephas larvae are sometimes endoparasitic, living on the edge of host holding capacity. If they were smaller they could avoid food depletion more easily, but the fitness benefits linked to a larger size have probably promoted body size increase. The strong negative effects of conspecific competition may have possibly influenced female strategy of laying a single egg per seed. 5. Being larger and fitter, but always within the limits of the available host sizes, may be one main evolutionary dilemma in endoparasites.     

Glycosylation sites identified by solid-phase Edman degradation: O-linked glycosylation motifs on human glycophorin A

The human red blood cell sialoglycoprotein, glycophorin A (GpA),contains a ‘mucin-like’ extensively O-glycosylatedextracellular domain which carries the MN blood group antigens.We have revised the sites of O-glyccsylation in the extracellulardomain of GpA by automated solid-phase Edman degradation, whichallowed positive identification and quantitation of O-glycosylatedSer and Thr residues, as well as the single N-glycosylationsite. One N-linked and 16 O-linked sites were identified. Carbohydratewas absent on Ser 1, Ser14, Ser15, Ser23, Thr28 and Thr58 inGpA. We propose that the glycosyltransferases present in erythrocytesrecognize specific flanking sequences around potential O-glycosylationsites. All 16 O-glycosylation sites are explained on the basisof four motifs. Three motifs are associated with Thr-glycosylation:Xaa—Pro—Xaa—Xaa where at least one Xaa = Thr;Thr—Xaa—Xaa—Xaa where at least one Xaa = Thr;Xaa—Xaa—Thr—Xaa where at least one X = Argor Lys. The fourth motif is associated with Ser-glycosylation:Ser—Xaa—Xaa—Xaa where at least one Xaa = Ser.These simple rules explain the glycosylation (or lack of it)on 21 of 22 Ser/Thr in the extracellular domain of GpA. glycophorin A O-glycosylation motif solid-phase Edman degradation     

Studies on the vegetative life cycle of Chlamydomonas reinhardi Dangeard in synchronous culture II. Effects of chloramphenicol and cycloheximide on the length of cell cycle

Cells of Chlamydomonas reinhardi Dangeard were synchronouslygrown under a 12 hr light— 12 hr dark regime. When thesecells were brought into contact with chloramphenicol for a shortperiod at early stages in the cell cycle, zoospore liberationwas delayed for a period which was nearly the same as that ofthe duration of contact with the antibiotic. When given at laterstages, the antibiotic caused no such effect. Cycloheximide,on the other hand, caused—when provided at some intermediatestage of the cell cycle— two different prolonging effectson the length of the cell cycle: one doubled the normal length(observed when the drug was administered at certain stages)and the other caused a delay similar to that caused by chloramphenicol.Interestingly, no prolonging effect was observed when cycloheximidewas given either at early stages or at later stages, such asduring the last 1/4 period of the cell cycle preceding zoosporeliberation. Based on these results, three phases were distinguishedin the algal cell cycle: "chloramphenicolsensitive", "cycloheximide-sensitive"and "insensitive" phases. Considering the known facts aboutthe modes of action of the two antibiotics inhibiting proteinsynthesis, discussions were made on the significance of proteinsynthesis in chloroplasts and in cytoplasm in determining thelength of the cell cycle. (Received October 12, 1970; )     

The anthropogenic stock extended abiotic depletion potential (AADP) as a new parameterisation to model the depletion of abiotic resources

Purpose  

Raw material availability is a cause of concern for many industrial sectors. When addressing resource consumption in life cycle assessment (LCA), current characterisation models for depletion of abiotic resources provide characterisation factors based on (surplus) energy, exergy, or extraction–reserve ratios. However, all indicators presently available share a shortcoming as they neglect the fact that large amounts of raw materials can be stored in material cycles within the technosphere. These “anthropogenic stocks” represent a significant source and can change the material availability significantly. With new characterisation factors, resource consumption in LCA will be assessed by taking into account anthropogenic material stocks in addition to the lithospheric stocks. With these characterisation factors, the scarcity of resources should be reflected more realistically.     

The waiting game: a "battle of waits" between predator and prey

Many prey respond to the presence of a predator by retreatinginto a shell or burrow, or by taking refuge in some other waythat guarantees their safety but restricts further informationfrom being obtained about the predator's continued presence.When this occurs, the individual predator and prey involvedbecome opponents in a "waiting game." The prey must decide howlong to wait for the predator to depart before re-emerging andpotentially exposing itself to attack. The predator must decidehow long to wait for the prey to re-emerge before departingin search of other foraging opportunities. I use a numericalapproach to determine the evolutionarily stable waiting strategyof both players and examine the effects of various parameterson the ESS. The model predicts that each player's waiting distribution—thedistribution of waiting times one would expect to observe forindividuals in that role—will have a characteristic shape:the predator's distribution should resemble a negative exponentialfunction, whereas the waiting time of the prey is predictedto be more variable and follow a positively skewed distribution.The model also predicts that very little overlap will occurbetween the players' waiting distributions, and that the predatorwill rarely outwait the prey. Empirical studies relating tothe model and comparisons between the waiting game and the asymmetricwar of attrition are discussed.     

From signal to form: aspects of the cytoskeleton-plasma membrane--cell wall continuuum in root hair tips

Root hairs are excellent cells for the study of the exocytoticprocess that leads to growth in higher plants, because the exocytoticevent takes place locally and because the cells are directlyaccessible for signals, drugs, fixatives, microinjection, andmicroscopic observation. Well—characterized lipochito—oligosaccharides,signal molecules excreted by Rhizobium bacteria, induce roothair growth which can be recorded microscopically in a roothair deformation assay developed for Vicia sativa L. Root hairdeformation is a morphogenetic process involving swelling ofthe hair tip and subsequent new hair outgrowth from that swelling.This response to the signal occurs at a specific developmentalstage, namely when hairs are terminating growth. Thus, sincepolar growth can be triggered intentionally, the system allowsthe study of growth phenomena in higher plants at the cellularlevel. Furthermore, important advances are being made with moleculargenetics that will allow the unravelling of the signal transductionpathways in root hair morphogenesis leading to growth. Thispaper first discusses cytological phenomena involved in theprocess of polar growth, such as cytoplasmic polarity, cyto—plasmicstreaming and the organization of actin filaments, the locationof a spectrin—like antigen, the distribution of intracellularcalcium, cortical microtubules and cell wall texture, endocytosisby means of coated pits, and physical aspects of the incorporationof exocytotic vesicles into the plasma membrane. In the secondpart, changes are discussed that occur in some of these phenomenawhen growth is influenced by growth regulators and mutations. Key words: Cytoskeleton, exocytosis, plant growth regulators, Nodulation factors, root hair, tip growth     

基于综合承载力的吉林省适度人口分析

运用状态空间法构建区域适度人口模型,利用主成分分析求取权重,对2005—2014年吉林省适度人口进行测算,并探讨其形成原因,提出解决对策.结果表明: 2005—2014年,吉林省适度人口一直处于赤字状态,说明吉林省人口、资源与环境处于一种不协调状态;吉林省资源承载人口显著高于经济承载人口和生态承载人口,说明吉林省经济发展是以牺牲环境为代价;吉林省土地资源承载人口远高于水资源承载人口和能源承载人口,处于赤字状态,说明吉林省经济发展是以耗竭自身能源和水资源为基础.今后应因地制宜,提高水资源承载力;开发新能源,提高能源利用效率;由粗放型、消耗型资源利用方式向集约型、低碳型转变;改变人类的生产方式和消费模式,注重保护生态环境.