ECA: control in ecosystems

Although metabolic control analysis (MCA) cannot be applied directly to microbial ecological systems because of mass conservation and stoichiometric constraints, we demonstrate here that Hierarchical Control Analysis (HCA) can be applied to such systems. We illustrate the approach for a particular ecosystem example of the biological synthesis of acetic acid from glucose, and uncover some surprising aspects to the control of this miniature ecosystem.     

Invasive bivalves in fresh waters: impacts from individuals to ecosystems and possible control strategies

Invasive bivalves may cause great ecological, evolutionary, and economic impacts in freshwater ecosystems. Species such as Corbicula fluminea, Dreissena bugensis, Dreissena polymorpha, Limnoperna fortunei, and Sinanodonta woodiana are widely distributed hyper-successful invaders, but several others not yet invasive (or at least not considered as such) may become so in the near future. These species can affect hydrology, biogeochemical cycling, and biotic interactions through several mechanisms, with impacts ranging from individuals to ecosystems. Freshwater invasive bivalves can create no-analog ecosystems, posing serious difficulties for management, but new techniques are becoming available which may enhance options to detect early introductions and mitigate impacts. Although knowledge about the biology of these bivalves has increased considerably in the last two decades, several fundamental gaps still persist; we suggest new research directions that are worth exploring in the near future.     

Invasion genetics of a human commensal rodent: the black rat Rattus rattus in Madagascar

Studies focusing on geographical genetic patterns of commensal species and on human history complement each other and provide proxies to trace common colonization events. On Madagascar, the unintentional introduction and spread of the commensal species Rattus rattus by people may have left a living clue of human colonization patterns and history. In this study, we addressed this question by characterizing the genetic structure of natural populations of R. rattus using both microsatellites and mitochondrial sequences, on an extensive sampling across the island. Such data sets were analysed by a combination of methods using population genetics, phylogeography and approximate Bayesian computation. Our results indicated two introduction events to Madagascar from the same ancestral source of R. rattus, one in the extreme north of the island and the other further south. The latter was the source of a large spatial expansion, which may have initially started from an original point located on the southern coast. The inferred timing of introduction events—several centuries ago—is temporally congruent with the Arabian trade network in the Indian Ocean, which was flourishing from the middle of the first millennium.     

Cyclic control in ecosystems

The theory of feedback control as a possible stabilizing mechanism has already been introduced into ecosystem analysis. One problem in the theory is the identification of the informational links by which such controls operate. Cyclic controls—for example, zero- mean sine functions added to certain exchange flows in the system—might also contribute to system stability. Their advantage is that they operate without need for information from the rest of the system. The theory of ecosystem cyclic control is presented and applied to data from an oyster reef ecosystem.     

Acceptor control in model ecosystems

The analysis of models of evolutionary games requires explicit consideration of both evolutionary game rules and mutants which infinitesimally break these rules. For example, the Scotch Auction is an evolutionary game which lacks both a rule-obeying evolutionarily stable strategy and an asymptotically stable polymorphism of rule-obeying strategies. However, an infinitesimal rule-breaking, or cheating, mutant can be found which is an evolutionarily stable strategy against rule-obeying strategies. Such cheating strategies can spread through populations initially playing the Scotch Auction, effectively changing the rules of the game. Moreover, the extent of such rule-change will then tend to increase. Thus, the Scotch Auction is a transient evolutionary game, being the initial point of a seemingly orthogenetic game evolutionary process. This sort of transience suggests that the “progressive” nature of evolution may be due in part to those game features of evolutionary processes which make the success of adaptations relative to the level of extant adaptation among competitors, predators, etc.     

Shrubs of Vladivostok: Percentage in green plantings and resistance in urban ecosystems

Many years of study were devoted to fructicose flora of plantings in the city of Vladivostok. Species diversity bearing on the type of planting has been studied. Contribution of each species to the city’s landscaping has been assessed quantitatively. The vitality of shrubs has been diagnosed and their stability in the conditions of urban ecosystems has been estimated.     

城市生态网络分析研究进展

自生态网络分析方法提出40多年来,其理论发展和应用实践不断拓展,但直至21世纪才不断引入到城市生态系统研究中,用以分析城市内部多个主体和多种生态流构成的关联网络。目前,城市生态网络分析集中于生态网络分析方法与指标的拓展及多尺度的应用研究,而生态网络分析方法又形成了上升性分析和环境元分析两大分支,多尺度应用涵盖了城市镶嵌的区域背景尺度和城市内部产业部门之间的细节尺度。然而,当前研究仍存在着多尺度融合、多种生态网络分析方法集成不足等问题,这限制了城市生态网络分析方法在城市规划设计中的应用。未来城市生态网络分析研究集中于如下3点:(1)开展多尺度城市生态网络分析,包括城市群-城市-园区/社区等,构建多级嵌套生态网络模型;(2)集成上升性与环境元分析方法,提出由外在表征到内在过程的城市生态系统评价模式及模拟方法;(3)强调自然节点在城市生态网络中的重要作用,形成社会经济节点与自然节点并重的生态网络模型,并强调构建多精度的生态网络模型服务于不同的研究目的。     

Fine-root morphological trait variation in tropical forest ecosystems: an evidence synthesis

Plant Ecology - Key functions of fine roots are often related to their morphological traits, yet little is known about the patterns and controls on fine-root morphological traits in the tropical...     

Redox control of N:P ratios in aquatic ecosystems

The ratio of dissolved fixed inorganic nitrogen to soluble inorganic phosphate (N:P) in the ocean interior is relatively constant, averaging ~16 : 1 by atoms. In contrast, the ratio of these two elements spans more than six orders of magnitude in lakes and other aquatic environments. To understand the factors influencing N:P ratios in aquatic environments, we analyzed 111 observational datasets derived from 35 water bodies, ranging from small lakes to ocean basins. Our results reveal that N:P ratios are highly correlated with the concentration of dissolved O₂ below ~100 µmol L⁻¹. At higher concentrations of O₂, N:P ratios are highly variable and not correlated with O₂; however, the coefficient of variation in N:P ratios is strongly related to the size of the water body. Hence, classical Redfield ratios observed in the ocean are anomalous; this specific elemental stoichiometry emerges not only as a consequence of the elemental ratio of the sinking flux of organic matter, but also as a result of the size of the basins and their ventilation. We propose that the link between N:P ratios, basin size and oxygen levels, along with the previously determined relationship between sedimentary δ¹⁵N and oxygen, can be used to infer historical N:P ratios for any water body.     

A mathematical model for assessing control strategies against West Nile virus

Since its incursion into North America in 1999, West Nile virus (WNV) has spread rapidly across the continent resulting in numerous human infections and deaths. Owing to the absence of an effective diagnostic test and therapeutic treatment against WNV, public health officials have focussed on the use of preventive measures in an attempt to halt the spread of WNV in humans. The aim of this paper is to use mathematical modelling and analysis to assess two main anti-WNV preventive strategies, namely: mosquito reduction strategies and personal protection. We propose a single-season ordinary differential equation model for the transmission dynamics of WNV in a mosquito-bird-human community, with birds as reservoir hosts and culicine mosquitoes as vectors. The model exhibits two equilibria; namely the disease-free equilibrium and a unique endemic equilibrium. Stability analysis of the model shows that the disease-free equilibrium is globally asymptotically stable if a certain threshold quantity , which depends solely on parameters associated with the mosquito-bird cycle, is less than unity. The public health implication of this is that WNV can be eradicated from the mosquito-bird cycle (and, consequently, from the human population) if the adopted mosquito reduction strategy (or strategies) can make . On the other hand, it is shown, using a novel and robust technique that is based on the theory of monotone dynamical systems coupled with a regular perturbation argument and a Liapunov function, that if , then the unique endemic equilibrium is globally stable for small WNV-induced avian mortality. Thus, in this case, WNV persists in the mosquito-bird population.     

Genetic connectivity in the Florida reef system: comparative phylogeography of commensal invertebrates with contrasting reproductive strategies

Effective spatial management of coral reefs including design of marine protected areas requires an understanding of interpopulation genetic connectivity. We assessed gene flow along 355 km of the Florida reef system and between Florida and Belize in three commensal invertebrates occupying the same host sponge (Callyspongia vaginalis) but displaying contrasting reproductive dispersal strategies: the broadcast-spawning brittle star Ophiothrix lineata and two brooding amphipods Leucothoe kensleyi and Leucothoe ashleyae. Multiple analytical approaches to sequence variation in the mitochondrial COI gene demonstrated a high degree of overall connectivity for all three species along the Florida reef system. Ophiothrix lineata showed significant genetic structuring between Florida and Belize, and a pattern of isolation by distance but no significant genetic structuring along the Florida coastline. Bayesian estimates of migration detected a strong southerly dispersal bias for O. lineata along the Florida reef system, contrary to the general assumption of northerly gene flow in this region based on the direction of the Florida Current. Both amphipods, despite direct development, also showed high gene flow along the Florida reef system. Multiple inferences of long-distance dispersal from a nested clade analysis support the hypothesis that amphipod transport, possibly in detached sponge fragments, could generate the high levels of overall gene flow observed. However, this transport mechanism appears much less effective across deep water as connectivity between Florida and Belize (1072 km) is highly restricted.     

Pressure and life: some biological strategies

All biological processes of life on Earth experience varying degrees of pressure. Aquatic organisms living in the deep-sea, as well as chondrocytic cells of articular cartilage are exposed to hydrostatic pressures that rise up to several hundred times that of atmospheric pressure. In the case of marine larvae that disperse through the oceanic water column, pressure changes might be responsible for stress conditions during development, limiting colonisation capabilities. In a number of biological systems, life strategies may be significantly influenced by pressure. In this review, we will focus on the consequences of pressure changes on various biological processes, and more specifically on animals living in the deep-sea. Revisiting general principles of pressure effects on biological systems, we present recent data illustrating the diversity of effects pressure may have at different levels in biological systems, with particular attention to effects on gene expression. After a review of the main pressure equipments available today for studying species living naturally at high pressure, we summarise what is known concerning pressure impact during animal development.     

Dispersal strategies and spatial organization of vegetation in arid ecosystems

Seed dispersal and establishment are critical stages for plants in arid environments, where vegetation is spatially organized in patches with suitable and unsuitable sites for establishment. Theoretical studies suggest that the ability of vegetation to self‐organize in patchy spatial patterns is a critical property for plant survival in arid environments, and is a consequence of a scale‐dependent feedback between plants and resource availability. Field observations show that plants of arid environments evolved towards short dispersal distance (proxichory) and that the investment in reproduction increases along an aridity gradient. Here, we investigated how plant dispersal strategies affect spatial organization and associated scale‐dependent feedback in arid ecosystems. We addressed this research question using a model where the spatio‐temporal vegetation patterns were driven by scale‐dependent feedbacks between plants and soil water availability. In the model, water availability limited vegetation growth, seed production and establishment ability. Seed dispersal was modelled with an integrodifferential equation that mimicked important plant dispersal characteristics (i.e. fecundity, mean dispersal distance and establishment ability). Results showed that, when the investment in fecundity was relatively high, short seed dispersal helped maintaining higher mean biomass in the system, improving the vegetation efficiency in water use. However, higher fecundity induced a large cost, and high mean biomass could be sustained only with high establishment ability. Considering low establishment ability, intermediate fecundity was more efficient than low fecundity in maintaining high plant biomass under the most arid conditions. Consistently, plant dispersal strategies that maintained more biomass were related to a vegetation spatial organization that allowed the most efficient soil water redistribution, through the strengthening of the scale‐dependent feedback. The efficient dispersal strategies and spatial patterns in the model are commonly observed in plants of arid environments. Thus, dispersal strategies in arid environments might contribute to a favourable spatial organization and associated scale‐dependent feedback.     

Digestive strategies in the South American subterranean rodent Ctenomys talarum

Ctenomys talarum is a subterranean herbivorous rodent which due to its particular life style is frequently exposed to variations in surface environmental conditions (i.e. food quality and availability, temperature). Thus, unlike other subterranean rodents, C. talarum has to buffer both the surface and burrow challenging environmental conditions. We studied the occurrence of digestive strategies at different levels of C. talarum living in their natural habitat. We determined the dimensions of different parts of the gastrointestinal tract and organs along as the activity of key digestive enzymes (disaccharidase, N-aminopeptidase) in different parts of the gut in individuals seasonally caught. The results show that C. talarum exhibits characteristics in the gut at the biochemical level (high disaccharidase activities in small intestine, high N-aminopeptidase activity in the caecum and large intestine, and a seasonal differential modulation of N-aminopeptidase activity in small and large intestines), which could represent adaptive strategies to face seasonal variations in key environmental factors.