Long-term evolution of an ecosystem with spontaneous periodicity of mass extinctions

Twenty years ago, after analysing palaeontological data, Raup and Sepkoski suggested that mass extinctions on Earth appear cyclically in time with a period of approximately 26 million years (My). To explain the 26 My period, a number of proposals were made involving, e.g., astronomical effects, increased volcanic activity, or the Earth's magnetic field reversal, none of which, however, has been confirmed. Here we study a spatially extended discrete model of an ecosystem and show that the periodicity of mass extinctions might be a natural feature of the ecosystem's dynamics and not the result of a periodic external perturbation. In our model, periodic changes of the diversity of an ecosystem and some of its other characteristics are induced by the coevolution of species. In agreement with some palaeontological data, our results show that the longevity of a species depends on the evolutionary stage at which the species is created. Possible further tests of our model are also discussed.     

Long-term behaviour of 15N in an alpine grassland ecosystem

Nitrogen dynamics in semi-natural environments is crucial for the development and ecological stability of these systems. The present paper shows the results of the reinvestigation of a ¹⁵N-tracer experiment, which was established in the Grossglockner massif in Austria at 2300ma.s.l. in 1974/1975. We show that large quantities of nitrogen introduced by a single pulse labelling (amounting to approximately 1.7% of the nitrogen in the system) into an alpine grassland remain in the soil–plant system, with only 55% being lost during 27–28 years. In the first 10cm of the four investigated soil profiles 40% of ¹⁵N was recovered, being mainly bound in organic forms. A simple site specific model was established on the basis of the results considering a biological, residual and labile N-pool, the latter being the source for N-losses. By the model a long mean residence time close to 100 years was derived for the remaining ¹⁵N.     

Bifurcation analysis of piecewise smooth ecological models

The aim of this paper is the study of the long-term behavior of population communities described by piecewise smooth models (known as Filippov systems). Models of this kind are often used to describe populations with selective switching between alternative habitats or diets or to mimic the evolution of an exploited resource where harvesting is forbidden when the resource is below a prescribed threshold. The analysis is carried out by performing the bifurcation analysis of the model with respect to two parameters. A relatively simple method, called the puzzle method, is proposed to construct the complete bifurcation diagram step-by-step. The method is illustrated through four examples concerning the exploitation and protection of interacting populations.     

Effects on ecosystem resilience of biodiversity, extinctions, and the structure of regional species pools

Resilience is a general concept that aims to help understand how ecosystems respond to disturbances such as extinctions and invasions. Here, we propose a measure of one aspect of resilience, R _X , which is one minus the expected change in functional diversity (X) caused by a species extinction or addition. We show how two components of biodiversity, species richness and functional diversity, and the structure of regional species pools affect this measure. Variation in species richness and in functional diversity have opposite effects on R _X . Speciose assemblages generally have higher R _X than depauperate ones, whereas functionally diverse assemblages have low R _X relative to functionally depauperate ones. The effect of an extinction on R _X reflects this tradeoff. In our analyses, extinctions usually cause only a small decrease in both functional diversity and R _X . However, extinctions sometimes cause a large reduction in functional diversity and then tend to increase R _X . Regional assemblages containing all rather unique species tend to result in speciose assemblages with relatively low R _X and in low richness assemblages with relatively high R _X . The opposite is true of regional assemblages containing functionally similar species. Information about the processes that structure regional assemblages will therefore increase understanding of ecosystem resilience. Generally, these results suggest that management for biodiversity may not always result in management for resilience.     

Long-term evolution of multilocus traits

 We analyze monomorphic equilibria of long-term evolution for one or two continuous traits, controlled by an arbitrary number of autosomal loci and subject to constant viability selection. It turns out that fitness maximization always obtains at long term equilibria, but in the case of two traits, linkage determines the precise nature of the fitness measure that is maximized. We then consider local convergence to long term equilibria, for two multilocus traits subject to either constant or frequency dependent selection. From a model of long-term dynamics near an equilibrium we derive a criterion of local long-term stability for 2-dimensional equilibria. It turns out that mutation can be a decisive factor for stability. Received 26 January 1994; received in revised form 26 September 1994     

Asphodelus aestivus,an example of synchronization with the climate periodicity

The phenology ofAsphodelus aestivus Brot. is described by means of a phenological model which has been formulated to fit skewed phenological data. Based on the model parameters the timing of different phenophases of biomass accumulation were determined. The biomass oscillations of leaves, inflorescence stalks and tubers were found to be synchronized with the predictable seasonal climatic changes. In addition, the plant seems to respond to minor random climatic variations. The emergence of leaves and inflorescence stalks depends on stored material in the tubers while leaf and inflorescence stalk elongation as well as flowering depends on current production. The storage part of the tubers seems to be a regulating structure, which is responsible for the synchronization ofA. aestivus productivity with the seasonality of the Mediterranean climate.A. aestivus is considered to be a Competitor Ruderal and Stress tolerant (C-R-S) strategist which may explain the wide distribution of this plant over the Mediterranean Basin.     

Modeling of the evolution of bacterial densities in an eutrophic ecosystem (sewage lagoons)

The process of wastewater treatment was studied by modeling the relationships between physical, chemical, and biological (bacteria, phytoplankton, zooplankton) components of the sewage treatment lagoons of an urban wastewater center, based upon a two-year sampling program. The models of interactions between variables were tested by path analysis. The path coefficients were computed from the results of ridge regression, instead of linear multiple regression. The results show that fecal coliforms were effectively controlled by the environmental variables included in the model, which have a cyclic seasonal behavior. This control grew stronger with distance from the input (R²=0.71) to the output (R²=0.88) of the treatment plant, resulting in effective elimination of most enteric bacteria. Simultaneously, the ecosystem's community of aerobic heterotrophic bacteria became more independent from the model's predictive variables, with increased distance from the sewage input, thus demonstrating its maturation as an autonomous community in the lagoon ecosystem. Consequences of modeling are discussed, with respect to the understanding of biological wastewater treatment mechanisms and ecosystem dynamics and to plant management.     

Keystone effects of an alien top-predator stem extinctions of native mammals

Alien predators can have catastrophic effects on ecosystems and are thought to be much more harmful to biodiversity than their native counterparts. However, trophic cascade theory and the mesopredator release hypothesis predict that the removal of top predators will result in the reorganization of trophic webs and loss of biodiversity. Using field data collected throughout arid Australia, we provide evidence that removal of an alien top-predator, the dingo, has cascading effects through lower trophic levels. Dingo removal was linked to increased activity of herbivores and an invasive mesopredator, the red fox (Vulpes vulpes), and to the loss of grass cover and native species of small mammals. Using species distribution data, we predict that reintroducing or maintaining dingo populations would produce a net benefit for the conservation of threatened native mammals across greater than 2.42 × 10⁶ km² of Australia. Our study provides evidence that an alien top predator can assume a keystone role and be beneficial for biodiversity conservation, and also that mammalian carnivores more generally can generate strong trophic cascades in terrestrial ecosystems.     

一个具有性别结构的食铒-捕食者系统周期解的存在性

利用重合度理论的延拓定理,导出了一个具有性别结构的食饵-捕食者系统正周期解的存在性准则.     

一类稀疏效应下的捕食系统存在唯一极限环的充要条件

给出了如下一类稀疏效应下的捕食系统：x=bx^2k-x)-bxy,y=-cy (βx-γy)y存在唯一极限环的充要条件。     

Experiments with an ecosystem adaptation model of biological treatment

In the wake of an earlier advanced multicomponent-multispecies biological treatment model, the authors suggest algorithms to substantially decrease the number of free coefficients. Operation of a number of experiments with the multicomponent-multispecies model has helped to further our understanding of the mechanism of biological treatment.     

Long-term follow-up of spontaneous development in a boy with familial male precocious puberty

BACKGROUND/AIMS: Limited data are available about spontaneous growth, pubertal growth spurt and the long-term outcome of patients suffering from familial male precocious puberty (FMPP). We report on a boy with FMPP whose growth pattern and pubertal development was studied longitudinally without treatment. METHODS: Long-term prospective follow-up without treatment of a 6.2-year-old boy with FMPP having inherited a mutation of the LH receptor gene (A568V) from his father. RESULTS: The pubertal growth spurt was of unusual maximal amplitude (growth rate 12.4 cm/year at the age of 5-6 years) and of extraordinary duration lasting for 5.2 years from age 3.8 to 9.0 years. No deterioration of height potential was observed. Height (174 cm) was within target height range (171.5-188.5 cm) at age 13 years. No central precocious puberty occurred. CONCLUSION: FMPP is an experiment of nature demonstrating that the amplitude and duration of the pubertal growth spurt are much more variable than previously described. Furthermore, this case emphasizes that the indication for treatment is highly dependent on intrafamilial and individual factors.     

The chemical origins of life and its early evolution: an introduction

Can we look at contemporary biology and couple this with chemical insight to propose some plausible mechanisms for the origin of life on the planet? In what follows, we examine some promising chemical reactions by which the building blocks for nucleic acids might have been created about a billion years after the Earth formed. This could have led to self-assembling systems that were based on an all-RNA metabolism, where RNA is both catalytic and informational. We consider the breadth of RNA enzymes presently existing in biology, and to what extent these might have covered a wider range of chemistry in the RNA world. Ultimately, the RNA world would probably have given way to protein-based life quite quickly, and the origins of peptidyl transferase activity are discussed below.     

Long-term kinetic study of beta-carotene, using accelerator mass spectrometry in an adult volunteer

We present a sensitive tracer method, suitable for in vivo human research, that uses beta-[(14)C]carotene coupled with accelerator mass spectrometry (AMS) detection. Using this approach, the concentration-time course of a physiological (306 microgram 200 nCi) oral dose of beta-[(14)C]carotene was determined for 209 days in plasma. Analytes included beta-[(14)C]carotene, [(14)C]retinyl esters, [(14)C]retinol, and several [(14)C]retinoic acids. There was a 5.5-h lag between dosing and the appearance of (14)C in plasma. Labeled beta-carotene and [(14)C]retinyl esters rose and displayed several maxima with virtually identical kinetic profiles over the first 24-h period; elevated [(14)C]retinyl ester concentrations were sustained in the plasma compartment for >21 h postdosing. The appearance of [(14)C]retinol in plasma was also delayed 5.5 h postdosing and its concentration rose linearly for 28 h before declining. Cumulative urine and stool were collected for 17 and 10 days, respectively, and 57.4% of the dose was recovered in the stool within 48 h postdosing. The stool was the major excretion route for the absorbed dose. The turnover times (1/k(el)) for beta-carotene and retinol were 58 and 302 days, respectively. Area under the curve analysis of the plasma response curves suggested a molar vitamin A value of 0.53 for beta-carotene, with a minimum of 62% of the absorbed beta-carotene being cleaved to vitamin A.In summary, AMS is an excellent tool for defining the in vivo metabolic behavior of beta-carotene and related compounds at physiological concentrations. Further, our data suggest that retinyl esters derived from beta-carotene may undergo hepatic resecretion with VLDL in a process similar to that observed for beta-carotene.     

A minimum model of prey-predator system with dormancy of predators and the paradox of enrichment

In this paper, a mathematical model of a prey-predator system is proposed to resolve the paradox of enrichment in ecosystems. The model is based on the natural strategy that a predator takes, i.e, it produces resting eggs in harsh environment. Our result gives a criterion for a functional response, which ensures that entering dormancy stabilizes the population dynamics. It is also shown that the hatching of resting eggs can stabilize the population dynamics when the switching between non-resting and resting eggs is sharp. Furthermore, the bifurcation structure of our model suggests the simultaneous existence of a stable equilibrium and a large amplitude cycle in natural enriched environments.      

一类稀疏效应下食饵—捕食系统极限环的存在唯一性

本文研究如下一类具有稀疏效应的食饵－捕食模型dx/dt=bx^2(k-x)-bxy,dy/dt=-cy (βx-γy）y。应用常微分方程定性理论,对该系统的平衡点进行分析,得到了该系统极限环存在唯一的充分条件,并给出了生态解释。     

Excitability of an age-structured plankton ecosystem

 We adapt a simple two-component model of a plankton ecosystem to account for the life spans of individual predatory organisms. We investigate the system’s short-term dynamics, in particular its excitability, and its long-term dynamics, and show how both can be highly sensitive to initial conditions. We discover that this effect is enhanced by imposing age structure on the system. Received: 21 June 1996 / Revised version: 19 October 1998     

以x(m/n)为功能性反应函数的食饵-捕食系统的定性分析

研究了功能性反应函数ψ(x)为x(m/n)(0＜m/n＜1)的食饵-捕食系统dx/dt=ax-bψ(x)y-cx2,dy/dt=-dy+eψ(x)y-fy2.证明了此系统当1/2≤m/n＜1时至多存在唯一正平衡点;当0＜m/n＜1/2时必有出现三个正平衡点的可能.并讨论了此系统的拓扑结构,给出了数值例子.