Deterministic extinction effect of parasites on host populations

 Experimental studies have shown that parasites can reduce host density and even drive host population to extinction. Conventional mathematical models for parasite-host interactions, while can address the host density reduction scenario, fail to explain such deterministic extinction phenomena. In order to understand the parasite induced host extinction, Ebert et al. (2000) formulated a plausible but ad hoc epidemiological microparasite model and its stochastic variation. The deterministic model, resembles a simple SI type model, predicts the existence of a globally attractive positive steady state. Their simulation of the stochastic model indicates that extinction of host is a likely outcome in some parameter regions. A careful examination of their ad hoc model suggests an alternative and plausible model assumption. With this modification, we show that the revised parasite-host model can exhibit the observed parasite induced host extinction. This finding strengthens and complements that of Ebert et al. (2000), since all continuous models are likely break down when all population densities are small. This extinction dynamics resembles that of ratio-dependent predator-prey models. We report here a complete global study of the revised parasite-host model. Biological implications and limitations of our findings are also presented. Received: 30 October 2001 / Revised version: 11 February 2002 / Published online: 17 October 2002 Work is partially supported by NSF grant DMS-0077790 Mathematics Subject Classification (2000): 34C25, 34C35, 92D25. Keywords or phrases: Microparasite model – Ratio-dependent predator-prey model – Host extinction – Global stability – Biological control     

Environmental constraints upon locomotion and predator-prey interactions in aquatic organisms: an introduction

Environmental constraints in aquatic habitats have become topics of concern to both the scientific community and the public at large. In particular, coastal and freshwater habitats are subject to dramatic variability in various environmental factors, as a result of both natural and anthropogenic processes. The protection and sustainable management of all aquatic habitats requires greater understanding of how environmental constraints influence aquatic organisms. Locomotion and predator-prey interactions are intimately linked and fundamental to the survival of mobile aquatic organisms. This paper summarizes the main points from the review and research articles which comprise the theme issue 'Environmental constraints upon locomotion and predator-prey interactions in aquatic organisms'. The articles explore how natural and anthropogenic factors can constrain these two fundamental activities in a diverse range of organisms from phytoplankton to marine mammals. Some major environmental constraints derive from the intrinsic properties of the fluid and are mechanical in nature, such as viscosity and flow regime. Other constraints derive from direct effects of factors, such as temperature, oxygen content of the water or turbidity, upon the mechanisms underlying the performance of locomotion and predator-prey interactions. The effect of these factors on performance at the tissue and organ level is reflected in constraints upon performance of the whole organism. All these constraints can influence behaviour. Ultimately, they can have an impact on ecological performance. One issue that requires particular attention is how factors such as temperature and oxygen can exert different constraints on the physiology and behaviour of different taxa and the ecological implications of this. Given the multiplicity of constraints, the complexity of their interactions, and the variety of biological levels at which they can act, there is a clear need for integration between the fields of physiology, biomechanics, behaviour, ecology, biological modelling and evolution in both laboratory and field studies. For studies on animals in their natural environment, further technological advances are required to allow investigation of how the prevailing physico-chemical conditions influence basic physiological processes and behaviour.     

世界维管植物新分类群2021年年度报告

2021年全球共发表维管植物新分类群2,219个, 包括新亚科1个、新族7个、新亚族7个、新属68个、新亚属7个、新组15个、新亚组8个、新系10个、新种1,979个、新亚种46个、新变种59个和新变型12个; 这些新分类群隶属于185科881属, 兰科、菊科和茜草科是本年度最受关注的类群。2,219个维管植物新分类群由来自全球的1,942位学者发表在165个期刊和14部专著中, 其中有42位作者发表了11个以上的新分类群。值得关注的是, Phytotaxa和PhytoKeys是2021年发表维管植物新分类群的主要期刊, 分别发表586个和112个。本年度发表的2,096个新种及种下单元中, 被子植物门1,940个、蕨类植物门147个、裸子植物门9个, 其中兰科植物最多, 共227个。2021年发表的新种及种下单元来自世界115个国家和地区。亚洲和南美洲是新种及种下单元发现的热点地区, 分别发现837个和571个。中国、巴西和马达加斯加是2021年贡献维管植物新种及种下单元最多的前3个国家, 分别发现283、269和169个。考虑到在2021年2月1日之后IPNI对2020年发表的维管植物新种增加了797个, 我们估计在2022年4月16日之后, 各数据库中2021年发表的新种及种下单元会增加700个左右。这将使2021年发表的新种(和种下分类群)数量增加到大约2,800个, 这与2001年以来每年发表的维管植物新种数量相当。     

Zooplankton research: the contribution of limnology to general ecological paradigms

Biotic interactions and density dependent processes are particularly important in the pelagic zone of a lake. Plankton has numerous properties (e.g., short life cycles, size structure) that makes them suitable objects for testing hypotheses and developing concepts relevant for general ecology. Zooplankton being in the center of aquatic food webs and influenced strongly by both bottom-up and top-down processes have often been used as models for ecological paradigms. The trophic-dynamic concept, the theory of population dynamics, and the analysis of predator-prey relationships are examples of successful contributions of zooplankton research. In recent years, zooplankton research has developed new ideas in community, population and evolutionary ecology. This is illustrated by studies on mechanisms of seasonal succession, competition and phenotypic plasticity. The new concept of physiological ecology is explained with copepod diapause behaviour. The blending of ideas from ecology and evolutionary genetics, which is undergoing a rapid development of new tools, will create new paradigms in the future, and zooplankton research will play an important part in this process.     

Summary and perspective on evolutionary ecology of fishes

This special issue of Evolutionary Ecology provides ten papers that have been presented at a conference on Evolutionary Ecology of Fishes in 2009. In addition to briefly summarizing the main content of the papers which is related to adaptive radiations, processes of ecological divergence, and fisheries-induced evolution, we review and synthesize in short the recent advance in studies on evolutionary ecology of fishes. We conclude that fishes are excellent model systems to study evolutionary ecology of animals, and suggest three promising new research avenues; (1) the contribution of behavioural processes to evolution, in particular the consideration of animal personalities and predator–prey interactions, (2) metabolic physiology and parasite-host interactions as new niche dimensions to be considered for adaptive diversification, and (3) the opportunities for mechanistic understanding of adaptation and speciation emerging from new genetic tools.     

Review Biology and ecology of trombidiid mites (Acari: Trombidioidea)

Most mites of the family Trombidiidae are ectoparasites in the larval stage and free-living predators in the deutonymphal and adult stages on a variety of arthropods, among which are pests of many economic crops. This paper provides an updated review of their systematics, life history, reproduction, behaviour, predator-prey and parasite-host relationships, and population dynamics, with particular reference to their possible role in biological control. © Rapid Science Ltd. 1998     

Linking biodiversity and ecosystems: towards a unifying ecological theory

Community ecology and ecosystem ecology provide two perspectives on complex ecological systems that have largely complementary strengths and weaknesses. Merging the two perspectives is necessary both to ensure continued scientific progress and to provide society with the scientific means to face growing environmental challenges. Recent research on biodiversity and ecosystem functioning has contributed to this goal in several ways. By addressing a new question of high relevance for both science and society, by challenging existing paradigms, by tightly linking theory and experiments, by building scientific consensus beyond differences in opinion, by integrating fragmented disciplines and research fields, by connecting itself to other disciplines and management issues, it has helped transform ecology not only in content, but also in form. Creating a genuine evolutionary ecosystem ecology that links the evolution of species traits at the individual level, the dynamics of species interactions, and the overall functioning of ecosystems would give new impetus to this much-needed process of unification across ecological disciplines. Recent community evolution models are a promising step in that direction.     

Application of proteomics to ecology and population biology

Proteomics is a relatively new scientific discipline that merges protein biochemistry, genome biology and bioinformatics to determine the spatial and temporal expression of proteins in cells, tissues and whole organisms. There has been very little application of proteomics to the fields of behavioral genetics, evolution, ecology and population dynamics, and has only recently been effectively applied to the closely allied fields of molecular evolution and genetics. However, there exists considerable potential for proteomics to impact in areas related to functional ecology; this review will introduce the general concepts and methodologies that define the field of proteomics and compare and contrast the advantages and disadvantages with other methods. Examples of how proteomics can aid, complement and indeed extend the study of functional ecology will be discussed including the main tool of ecological studies, population genetics with an emphasis on metapopulation structure analysis. Because proteomic analyses provide a direct measure of gene expression, it obviates some of the limitations associated with other genomic approaches, such as microarray and EST analyses. Likewise, in conjunction with associated bioinformatics and molecular evolutionary tools, proteomics can provide the foundation of a systems-level integration approach that can enhance ecological studies. It can be envisioned that proteomics will provide important new information on issues specific to metapopulation biology and adaptive processes in nature. A specific example of the application of proteomics to sperm ageing is provided to illustrate the potential utility of the approach.     

Dynamics of stage-structure predator-prey systems under density-dependent effect and mortality

We develop a four dimensional predator-prey system in continuous time with stage-structure for both the communities. The reproduction rate of the prey and the transition rate for the predator, in our model, are assumed to be density-dependent. The stability results for the coexisting equilibrium are obtained by making use of Routh–Hurwitz criteria. Because of the density-dependent effects, numerical simulations are applied in complex situations. We observe that increasing values of the coefficients linked with density-dependent term promote the stability of the coexisting steady state. Our main focus is to understand the variation of stocks when mortality rates on different stage classes are increased. We verified that stable stock on mature predator increases with its increasing mortality rate in three different modeling frameworks. However, no such positive effect on the biomass of the immature predator occurs when immature predators are removed, culled or harvested. Therefore, we could conclude that the appearance of hydra effect on many unstructured predator-prey models is due to the mortality of the mature predator only. No hydra effect is also detected when mature prey is removed in several situations we discussed. Overall, the obtained results are new and could be interesting contribution in theoretical ecology.     

Harvesting as a disease control measure in an eco-epidemiological system - A theoretical study

Epidemiology and ecology are traditionally treated as independent research areas, but there are many commonalities between these two fields. It is frequently observed in nature that the former has an encroachment into the later and changes the system dynamics significantly. In population ecology, in particular, the predator-prey interaction in presence of parasites can produce more complex dynamics including switching of stability, extinction and oscillations. On the other hand, harvesting practices may play a crucial role in a host-parasite system. Reasonable harvesting can remove a parasite, in principle, from their host. In this paper, we study theoretically the role of harvesting in a predator-prey-parasite system. Our study shows that, using impulsive harvesting effort as control parameter, it is not only possible to control the cyclic behavior of the system populations leading to the persistence of all species, but other desired stable equilibrium including disease-free can also be obtained.     

Population equilibria and stability in plant-animal pollination systems

Differential equation models of the change in population size with change in time have provided valuable insight into nature and have served as tools for management of both predator-prey and competition systems. Presented here is an extension of the differential equation models for application to pollination ecology plant-animal interactions. Analyses define conditions for equilibria and for equilibrium stability for a one-plant one-animal pollinator system. Predictions about plant speciation and pollinator foraging behavior are discussed.     

Pools versus Queues: The Variable Dynamics of Stochastic “Steady States”

Mathematical models in ecology and epidemiology often consider populations “at equilibrium”, where in-flows, such as births, equal out-flows, such as death. For stochastic models, what is meant by equilibrium is less clear – should the population size be fixed or growing and shrinking with equal probability? Two different mechanisms to implement a stochastic steady state are considered. Under these mechanisms, both a predator-prey model and an epidemic model have vastly different outcomes, including the median population values for both predators and prey and the median levels of infection within a hospital (P < 0.001 for all comparisons). These results suggest that the question of how a stochastic steady state is modeled, and what it implies for the dynamics of the system, should be carefully considered.     

Linking Industrial Ecology and Ecological Economics: A Theoretical and Empirical Foundation for the Circular Economy

The circular economy (CE) is a new model for the production and consumption of goods, which has attracted wide political attention as a strategy toward sustainability. However, the theoretical foundation of CE remains poorly structured and insufficiently explored. Recent studies have shown that the CE model draws on different schools of thought and that its origins are mainly rooted in fields such as industrial ecology (IE) and ecological economics (EE). In this article, we investigate the links between CE, IE, and EE and provide an overview of the similarities and differences between these fields. At the same time, we analyze to what extent the linkages between IE and EE can create a coherent body of knowledge for CE, and be used to identify further research opportunities. This paper shows that, until now, research on CE seems to be mainly rooted in the field of IE and based on concepts and tools that already exist in other fields, rather than inventing new ones. The reconciliation of IE and EE could provide a mechanism to extend beyond such a narrow focus, and increase knowledge of the theoretical and practical framework of CE to benefit sustainability.     

Effects of crop species richness on pest-natural enemy systems based on an experimental model system using a microlandscape

The relationship between crop richness and predator-prey interactions as they relate to pest-natural enemy systems is a very important topic in ecology and greatly affects biological control services. The effects of crop arrangement on predator-prey interactions have received much attention as the basis for pest population management. To explore the internal mechanisms and factors driving the relationship between crop richness and pest population management, we designed an experimental model system of a microlandscape that included 50 plots and five treatments. Each treatment had 10 repetitions in each year from 2007 to 2010. The results showed that the biomass of pests and their natural enemies increased with increasing crop biomass and decreased with decreasing crop biomass; however, the effects of plant biomass on the pest and natural enemy biomass were not significant. The relationship between adjacent trophic levels was significant (such as pests and their natural enemies or crops and pests), whereas non-adjacent trophic levels (crops and natural enemies) did not significantly interact with each other. The ratio of natural enemy/pest biomass was the highest in the areas of four crop species that had the best biological control service. Having either low or high crop species richness did not enhance the pest population management service and lead to loss of biological control. Although the resource concentration hypothesis was not well supported by our results, high crop species richness could suppress the pest population, indicating that crop species richness could enhance biological control services. These results could be applied in habitat management aimed at biological control, provide the theoretical basis for agricultural landscape design, and also suggest new methods for integrated pest management.     

The subcritical collapse of predator populations in discrete-time predator-prey models.

Many discrete-time predator-prey models possess three equilibria, corresponding to (1) extinction of both species, (2) extinction of the predator and survival of the prey at its carrying capacity, or (3) coexistence of both species. For a variety of such models, the equilibrium corresponding to coexistence may lose stability via a Hopf bifurcation, in which case trajectories approach an invariant circle. Alternatively, the equilibrium may undergo a subcritical flip bifurcation with a concomitant crash in the predator's population. We review a technique for distinguishing between subcritical and supercritical flip bifurcations and provide examples of predator-prey systems with a subcritical flip bifurcation.     

Are classical predator-prey models relevant to the real world?

Mathematical models of predator-prey population dynamics are widely used for predicting the effect of predators as biocontrol agents, but the assumptions of the models are more relevant to parasite-host systems. Predator-prey systems, at least in insects, substantially differ from what is assumed by these models. The main differences are: (i) Juveniles and adults have to be considered as two different entities, as the former stay within a patch and do not reproduce, while the latter move between patches of prey and reproduce there. (ii) Because of their high mobility, food availability is likely to be less restrictive for adults than juveniles, which are confined to one patch. Therefore, a functional response to prey abundance may not be important for adults. (iii) Egg and larval cannibalism are common in insect predators. Therefore, the quality of patches of prey for their larvae determines the reproductive strategy of adult predators more than the availability of food for the adults. Here we develop a new model, based on the above considerations, which is suitable for modelling these interactions. We show that selection should favour mechanisms that enable predators to avoid reproducing in patches with insufficient prey and those already occupied by predators.     

Cuckoos, cowbirds and hosts: adaptations, trade-offs and constraints

The interactions between brood parasitic birds and their host species provide one of the best model systems for coevolution. Despite being intensively studied, the parasite-host system provides ample opportunities to test new predictions from both coevolutionary theory as well as life-history theory in general. I identify four main areas that might be especially fruitful: cuckoo female gentes as alternative reproductive strategies, non-random and nonlinear risks of brood parasitism for host individuals, host parental quality and targeted brood parasitism, and differences and similarities between predation risk and parasitism risk. Rather than being a rare and intriguing system to study coevolutionary processes, I believe that avian brood parasites and their hosts are much more important as extreme cases in the evolution of life-history strategies. They provide unique examples of trade-offs and situations where constraints are either completely removed or particularly severe.     

Connectance and parasite diet breadth in flea-mammal webs

The number of links in webs of species interactions, which lies at the heart of the biodiversity-stability debate, has given rise to controversy during the last 20 yr. Studies exploring these web properties have mainly focused on symmetric webs where each species can potentially feed on any other species; asymmetric webs such as host-parasite webs, where one set of species feed on another set of species, have been overlooked. However, food webs are incomplete without parasites and the study of parasite-host sub-web properties deserves attention. Here, using a large database involving 33 regional interaction webs between mammals and their flea parasites, we found a negative relationship between species richness and host-parasite connectance. We suggest that some phylogenetic constraints on flea diet may explain our observed patterns because we found that parasite diet breadth, measured as host taxonomic diversity, was invariant along our host richness gradient. We found that the slope of the logarithmic relationship between the number of realized links and species richness is lower than slope values reported for food webs. We suggest that connectance may not respond to increasing species richness as rapidly in host-parasite webs as in predator-prey food webs due to stronger coevolutionary requirements.     

Seasonal dynamics of microcrustacean and rotifer communities in Malaysian rice fields used for rice-fish farming

The abundance, seasonal dynamics and species composition of microcrustacean and rotifer communities in rice fields used for rice-cum-fish culture were examined. The shallow littoral-like nature of rice fields resulted in the presence of cladoceran and rotifer species, but copepods were numerically more abundant. Abundance and seasonal dynamics were affected by factors such as pesticides and herbicide use, predator-prey relationships, presence of hydrophytes and interactions among microcrustaceans and rotifers. The implications of microcrustacean and rotifers abundance and seasonal dynamics on rice-fish farming are discussed.     

Generation of periodic waves by landscape features in cyclic predator-prey systems

The vast majority of models for spatial dynamics of natural populations assume a homogeneous physical environment. However, in practice, dispersing organisms may encounter landscape features that significantly inhibit their movement. We use mathematical modelling to investigate the effect of such landscape features on cyclic predator-prey populations. We show that when appropriate boundary conditions are applied at the edge of the obstacle, a pattern of periodic travelling waves develops, moving out and away from the obstacle. Depending on the assumptions of the model, these waves can take the form of roughly circular 'target patterns' or spirals. This is, to our knowledge, a new mechanism for periodic-wave generation in ecological systems and our results suggest that it may apply quite generally not only to cyclic predator-prey interactions, but also to populations that oscillate for other reasons. In particular, we suggest that it may provide an explanation for the observed pattern of travelling waves in the densities of field voles (Microtus agrestis) in Kielder Forest (Scotland-England border) and of red grouse (Lagopus lagopus scoticus) on Kerloch Moor (northeast Scotland), which in both cases move orthogonally to any large-scale obstacles to movement. Moreover, given that such obstacles to movement are the rule rather than the exception in real-world environments, our results suggest that complex spatio-temporal patterns such as periodic travelling waves are likely to be much more common in the natural world than has previously been assumed.