On the Evolution of Behavioral Heterogeneity in Individuals and Populations

A wide range of ecological and evolutionary models predict variety in phenotype or behavior when a population is at equilibrium. This heterogeneity can be realized in different ways. For example, it can be realized through a complex population of individuals exhibiting different simple behaviors, or through a simple population of individuals exhibiting complex, varying behaviors. In some theoretical frameworks these different realizations are treated as equivalent, but natural selection distinguishes between these two alternatives in subtle ways. By investigating an increasingly complex series of models, from a simple fluctuating selection model up to a finite population hawk/dove game, we explore the selective pressures which discriminate between pure strategists, mixed at the population level, and individual mixed strategists. Our analysis reveals some important limitations to the ESS framework often employed to investigate the evolution of complex behavior.     

生态学研究中常见的统计学问题分析

在当代生态学研究中统计学方法的应用日益广泛,对于生态科学的发展和研究水平的提高起到了积极的作用。但是不容忽视的是在生态学研究应用统计学方法的过程中存在若干问题,主要表现在:1)回归分析方面的问题。直线回归方程用相关指数R²来描述直线回归的显著性;曲线回归方程往往用相关系数r来表示显著性;多元线性回归方程只对方程进行显著性检验,没有对每一个回归系数进行显著性检验。2)方差分析方面的问题。当处理数超过2时,不恰当地使用t_检验比较平均数的差异显著性。该文分析了产生这些问题的原因,提出了改进的对策。     

Using an individual-based model for assessment of sea turtle population viability

Marine turtle species have a complex life history characterized by interannual variability in reproductive performance and a long life span. These ecological features in combination with the animals highly migratory nature create numerous difficulties when trying to assess population dynamics. This study attempts to couple existing information on species demographics and behavioral strategies with simple energetic rules in a theoretical framework. We study sea turtle population dynamics using an individual-based model that incorporates known behavioral-ecological characteristics of the species. Methodology used to design the model was based on the superindividual approach (Scheffer et al. Ecol Model 80:161–170, 1995). We constructed our simulation experiment on a virtual sea turtle population, which was parameterized by using recent literature reviews with emphasis on reproductive parameters of the Mediterranean loggerhead sea turtle population. Switching rules describing critical processes of reproductive performances were established as theoretical functions of efficiency of energy transfer. In order to explore the significance of variable reproductive patterns upon population dynamics and persistence, a series of simulations was performed. The model was also run under fluctuated demographic variables to perform a sensitivity analysis of critical parameters and life-history stages. Based on the specific model parameterization, simulation results show that population persistence was most sensitive to fecundity and to survival at the pelagic juvenile stage. Additionally a surprising finding is the relatively high importance of egg survival in terms of both hatching and hatchling success. We conclude that enhancing the population with new individuals by increasing survival in the early life stages could compensate for additional losses in other age classes. The need for further research regarding biological and behavioral features as well as basic demographic insights into the endangered loggerhead sea turtle is also highlighted.     

Scope for growth in Gammarus pulex,a freshwater benthic detritivore

Although toxic substances affect the physiological processes of individual organisms, their ecological impacts occur at the population and community levels. However, physiological processes can often be assessed more easily and precisely than population and community ones. Here we argue that scope for growth, the difference between the energy input to an organism from its food and the output from respiratory metabolism, can give a good physiological measure of stress that, at least in principle, is straightforwardly related to population and community processes. We describe, in detail, how scope for growth can be measured in Gammarus pulex (Crustacea, Amphipoda). The results indicate that both zinc and low pH can significantly reduce the scope for growth of individuals and that the most sensitive component of the energy budget is food absorption.     

Namaqualand,South Africa – an overview of a unique winter-rainfall desert ecosystem

Namaqualand is a winter-rainfall desert of some 50000 km₂, located in north-western South Africa. For a desert ecosystem, the region is characterized by a unique selective regime, namely highly predictable annual rainfall and a moderate temperature regime throughout the year. This selective regime is responsible for the unique plant ecological features of Namaqualand. These include: the dominance of communities by dwarf to low, shallow-rooted, short-lived and drought-sensitive leaf succulent shrubs; high abundance and diversity of geophytes; winter growth phenology; regular and spectacular spring flowering displays; rapid population turnover of perennials; weak competitive interactions; and high local and regional plant diversity. This paper provides a physiographical, biogeographical and ecological overview as background to this special issue. First, we outline the physiography and climate of Namaqualand, emphasizing unique components of its selective regime. Next we discuss the region's phytogeographical and floristic characteristics. Then we summarize what is known about plant form and function, focusing on growth form mix, phenology, carbon gain, water relations, and reproduction in vegetation dominated by leaf-succulent shrubs. Finally, we interpret Namaqualand's uniquely rich and dynamic plant communities in terms of plant functional processes. These plant ecological patterns and processes are discussed in terms of the predictions of a simple conceptual model for succulent-rich communities.     

Density dependence,population persistence,and largely futile arguments

Wolda and Dennis (1993) suggest that no valid conclusions about population regulation can be drawn on the basis of statistical tests of density dependence in time series data of population abundance. They give some examples in which a population persists even if it is not regulated by a density-dependent process: a sequence of independent, identically distributed random variables, the numbers of the migrant moth Autographa gamma in Britain, annual rainfall data. We suggest that such time series data may show persistence because of a static constraint, which compels the numbers to remain within finite, positive limits, or to fit some prescribed distribution. But this mechanism can explain persistence in a biological population only when the population represents a sample from a regulated population (the case of A. gamma). We also comment on some suggestions made by Wolda and Dennis (1993) concerning the general value of statistical tests of density dependence, frequency of delayed versus non-delayed density dependence in natural populations, relative performance of different kinds of insect traps in sampling local populations, and the wider issue of how ecologists are likely to make progress in the study of population dynamics.     

Modelling food web complexity: The consequences of individual-based, spatially explicit behavioural ecology on trophic interactions

We present a prototype simulator that enables one to explore the influence of individual behaviour on the dynamics and structural complexity of food webs. In the simulations, individuals act according to simple, biologically plausible rules in a spatially explicit setting. We present the results of a series of simulation experiments on artificial, tri-trophic level food chains used to calibrate the simulator against real-world systems and to demonstrate the simulators promise for ecological modelling. Our primary objective was to discover the biological features leading to stability of artificial food chains over ecological time and under different conditions of trophic efficiency. This involved a qualitative analysis of food chains comprised of a plant, a herbivore and a carnivore species. We explored the consequences of allowing individual heterotrophs to make active choices about resource selection (perception and intentional behaviour) under high and low degrees of trophic efficiency. We found that individuals had to adopt realistic behavioural ecological strategies, such as active resource selection, for systems to persist, especially under conditions in which trophic efficiencies were of the magnitude observed in real systems (e.g. 10%). Our results reaffirm previous convictions that a better understanding of food web interactions in real-world systems will require approaches that blend animal behavioural ecology with population and community ecology. However, the evidence comes from a new mathematical perspective.     

Ecological outbreak dynamics and the cusp catastrophe

Many ecological processes exhibit trajectories which can be suitably represented by stable equilibria or smooth limit cycles. However, a third kind of ecological process involves intermittent, abrupt, and drastic changes in densities, here termed outbreak dynamics, which require different modelling frameworks. One such framework, the cusp catastrophe, is used here in a modelling study of a particular outbreak insect, the forest tent caterpillar. This model is then generalized to cover a set of related ecological systems. The particular form of the model for each system depends on whether the major controlling ecological variables are externally imposed, or are incorporated in the model equations. It is concluded that the simple cusp catastrophe is an appropriate metaphor for understanding outbreak dynamics.     

Light-and electron-microscopic studies of the somatostatin-immunoreactive plexus in the cat retina

Summary Two monoclonal antibodies directed against somatostatin 14 were used to study immunoreactive neurons, their processes and their synapses in the cat retina. In retinal whole-mounts, a sparse population of wide-field displaced amacrine cells was observed predominantly in the ventral retina and near the retinal margin. Processes of these cells ramified mainly in two distinct strata within the inner plexiform layer: one near the inner nuclear layer (INL), and the other near the ganglion cell layer (GCL). The length of immunoreactive fibres within each plexus was measured: 232±32 mm/mm² near the INL and 230±74 mm/mm² near the GCL in all retinal regions. The immunoreactive processes were studied using electron-microscopic techniques; conventional and some ribbon-containing synapses (dyads) were found. Immunolabelled processes received input synapses from other amacrine cell processes. These investigations provide further evidence that this cell population has a diffuse, regulatory or modulatory role for visual-information processing in the inner plexiform layer.     

Graded Autocatalysis Replication Domain (GARD): Kinetic Analysis of Self-Replication in Mutually Catalytic Sets

A Graded Autocatalysis Replication Domain (GARD) model is proposed, which provides a rigorous kinetic analysis of simple chemical sets that manifest mutual catalysis. It is shown that catalytic closure can sustain self-replication up to a critical dilution rate, _c, related to the graded extent of mutual catalysis. We explore the behavior of vesicles containing GARD species whose mutual catalysis is governed by a previously published statistical distribution. In the population thus generated, some GARD vesicles display a significantly higher replication efficiency than most others. GARD thus represents a simple model for primordial chemical selection of mutually catalytic sets.     

A brief history of the many faces of detection in ecology and wildlife management

In the early years of the development of ecological methods, detection was considered a relatively simple parameter to estimate. The early closed population estimation techniques of Lincoln and Petersen and the more sophisticated open population models of Leslie, Chitty, Chitty and Jolly, and Seber assumed a relative ease of estimating the detection probability. Wildlife ecologists who knew their animals were always concerned about unequal catchability, and fisheries biologists like Ricker provided models to compensate for unequal catchability in fishery estimation, but it was not until the Colorado mafia published their monograph in 1978 on a series of models that allowed for certain classes of unequal detection that the problem was formalized for closed populations in Program CAPTURE. From the mid-1970s there was a groundswell of publications and a generation of cooperation between mathematicians and ecologists to attack the problem of detection, not only for population estimation but more importantly for disease analysis and pest management. This new synthesis of mathematical and statistical power with ecological insights of the clever ways that animals and plants avoid detection has produced a series of methods that recognised as a critical part of wildlife management in this century.     

The Study of the Hydraulic Conductivity of the Plasmodesmal Transport Channels by the Pulse NMR Method

Radial self-diffusion of water in the absorbing zone of the roots of winter wheat (Triticum aestivumL.) seedlings was studied by the pulse-gradient-spin-echo NMR method. At the fixed time of diffusion observation, the diffusion decay of proton spin-echo was nonexponential; however, it could be reliably separated into three exponential components differing in the self-diffusion coefficients (SDC) of water molecules. Our experimental data corroborate the modern concept of two transport channels in plant plasmodesmata, which connect cytoplasmic and vacuolar (endoplasmic) compartments of adjacent cells into the unified supracellular continuums. Two SDC obtained by the kinetic analysis of diffusion decay were shown to depend on the expected changes in the hydraulic conductivity of the two above-mentioned plasmodesmal channels. To elucidate the role of ATP-dependent actomyosin proteins in the regulation of the hydraulic conductivity of plasmodesmata, we followed the changes in the water SDC induced by treating the roots with cytochalasin B (5 M, 30 min), the inhibitor of actin polymerization; 2,3-butanedione monoxime (10 mM, 1 h), the inhibitor of myosin ATPase activity; and antimycin A (5 M, 1 h) and sodium azide (10 mM, 30 min), the inhibitors of energy generation. The data thus obtained provided the basis for elaborating a new methodological approach to simultaneously monitoring the functional state of both plasmodesmal channels without any wound effect impairing their functions.     

Toward a more expansive conception of ecological science

There are two competing conceptions of the nature and domain of ecological science in the popular and academic literature, an orthodox conception and a more expansive conception. The orthodox conception conceives ecology as a natural biological science distinct from the human social sciences. The more expansive conception views ecology as a science whose domain properly spans both the natural and social sciences. On the more expansive conception, non-traditional ecological disciplines such as ecological psychology, ecological anthropology and ecological economics may legitimately be regarded as sub-disciplines of ecology, and the practitioners of such disciplines as ecologists. The orthodox-expansionist issue is significant both for the practice of ecology and for the self-identity of the philosophy of ecology. I argue in favour of the expansionist conception of ecology on general conceptual grounds, and by developing the case for one particular non-traditional ecological discipline, ecological psychology.     

The parasites of Anolis lizards the northern Lesser Antilles

Summary The communities of parasitic helminths from ten species of lizards on seven islands in the Caribbean were examined to ascertain the relative importance of predictable deterministic factors and unpredicatable colonization or extinction events in determining the structure of the parasite community. A simple graphical model of community structure is used as a null model to describe the features of a community that are dependent only upon the size of the host population and features of the life histories of the constituent parasite species. This model predicts that parasite species will exhibit a nested pattern of local and global relative abundance. The observed data correspond fairly well to this pattern. The absences of individual parasite species from communities where they might be expected to be present emphasizes the role of stochastic colonization and extinction events in delineating the constituent members of the community on any island.Statistical analysis of the distribution of parasite species per host illustrates that this pattern is random in habitats where parasite species diversity is low, but decreasingly variable in habitats where more diverse parasite communities occur. Increased parasite diversity also leads to an increase in the proportion of hosts that contain mixed species infections. Comparisons of worm burdens from single and mixed species infections within individual hosts suggest that interactions between parasite species only rarely leads to reduced worm burdens.     

Testing for spatial autocorrelation in ecological studies

We describe a statistical method appropriate for the analysis of spatial autocorrelation in data varying in time as well as space. In particular, the technique was developed lo address the issue of geographic synchrony in ecological variables that may change markedly from year to year such as population density of animals or seed production of trees. The method yields 'modified correlograms" that test for significant autocorrelation between sites located within any given range of distances apart. This technique facilitates detecting and understanding spatial processes m a variety of ecological phenomena, including testing the plausibility of causational hypotheses using cross-correlational analyses. Several examples are discussed, including population densities of squirrels in Finland, winter densities of two hawk species in California, and acorn production and radial growth by individual blue oak Quercus douglasii trees in central coastal California.     

On synchronization in semelparous populations

Synchronization, i.e., convergence towards a dynamical state where the whole population is in one age class, is a characteristic feature of some population models with semelparity. We prove some rigorous results on this, for a simple class of nonlinear one- population models with age structure and semelparity: (i) the survival probabilities are assumed constant, and (ii) only the last age class is reproducing (semelparity), with fecundity decreasing with total population. For this model we prove: (a) The synchronized, or Single Year Class (SYC), dynamical state is always attracting. (b) The coexistence equilibrium is often unstable; we state and prove simple results on this. (c) We describe dynamical states with some, but not all, age classes populated, which we call Multiple Year Class (MYC) patterns, and we prove results extending (a) and (b) into these patterns.Acknowledgement Boris Kruglikov contributed the nonlinear part of the formulation as well as the proof of Theorem 1. The authors are grateful for critical and constructive comments by N. Davydova and O. Diekmann. E.M. is also grateful for discussions with Marius Overholt concerning problems of proving Theorem 2.     

On the evolutionary ecology of marking pheromones

Summary Many parasitic insects mark hosts with a pheromone after oviposition. The evolutionary ecology of such marking pheromones was studied to determine (i) under what ecological and behavioral conditions such pheromones could evolve and (ii) why so many of these marking pheromones are water-soluble and thus short-lived. We used a number of different techniques. First, the fitness values of individual normal (nonmarking) and mutant (marking) insects foraging for hosts were computed using dynamic state-variable models. Second, population level models were used to study when a population of non-marking individuals can be invaded by marking individuals. Third, behavior-rich simulations (developed originally for apple maggot,Rhagoletis pomonella) were used to test experimentally some of the hypotheses generated using the individual and population-level models. Finally, we developed a model for the benefit over time to an individual by marking. This model shows that when benefit is measured in terms of larval survival, nearly all of the benefit to a mother is obtained from short-lived marks. Genetical theories of pheromone evolution and the connection between our results and existing theories of altruistic behavior are discussed.     

Statistical methods in spatial genetics

The joint analysis of spatial and genetic data is rapidly becoming the norm in population genetics. More and more studies explicitly describe and quantify the spatial organization of genetic variation and try to relate it to underlying ecological processes. As it has become increasingly difficult to keep abreast with the latest methodological developments, we review the statistical toolbox available to analyse population genetic data in a spatially explicit framework. We mostly focus on statistical concepts but also discuss practical aspects of the analytical methods, highlighting not only the potential of various approaches but also methodological pitfalls.     

On non-linear species response models in ordination

Ordination techniques are plagued by the non-linearity of vegetation data. The purpose of ordination is discussed and considered to be the process of arranging samples (or species) in relation to one or more environmental gradients or abstract axes that may represent such gradients, the arrangement to be ecologically significant. The appropriateness of various models of vegetation to current ordination techniques is considered, particularly the gaussian species response curve. Two alternatives are suggested based on -functions and an ecological response curve model incorporating competition between species.