Biological control of soilborne plant pathogens using beneficial fungi, such as the mycoparasite Trichoderma harzianum, offers the prospect of environmentally benign pest control. However, biocontrol organisms have th...Biological control of soilborne plant pathogens using beneficial fungi, such as the mycoparasite Trichoderma harzianum, offers the prospect of environmentally benign pest control. However, biocontrol organisms have their own natural enemies;for example the fungivorous nematode Aphelenchoides saprophilus preys on T. harzianum. A trophic cascade occurs when three or more trophic levels are present in a food chain, and consumption of the intermediate species affects biomass or productivity of a lower trophic level;such an interaction in this system might reduce the biocontrol efficacy of T. harzianum. However, the presence of refuges, where intermediate-level species are protected from predation, may reduce the ecological impact of a trophic cascade. Interactions among microscopic organisms in a complex medium such as soil are difficult to observe and quantify. We evaluated the potential of quantitative real-time PCR (qRT-PCR) as a tool to investigate the trophic cascade interaction among T. harzianum, A. saprophilus, and the plant pathogen Sclerotinia sclerotiorum. Results indicate that the mycoparasite colonized and persisted inside structures (sclerotia) of the target plant pathogen, where it was relatively protected from predation compared to the surrounding soil environment. In this way, colonization of sclerotia may provide a refuge that reduces trophic cascade effects in this system. qRT-PCR provided a sensitive method to investigate fungal dynamics over time in this multitrophic system.展开更多
The roles that top predators play in regulating the structure and function of ecosystems have long been controversial. This is particularly the case when predators pose adverse risks for human life and/or economic int...The roles that top predators play in regulating the structure and function of ecosystems have long been controversial. This is particularly the case when predators pose adverse risks for human life and/or economic interests. The critique of literature on dingoes and their ecological roles in Australia provided by Allen et al. （2011） shows that top predators remain a potentially polarising issue. In opposition to Allen et al. we argue that these widespread patterns of species＇ abundances, attributed to the ef- fects of dingoes and evident at scales ranging from the foraging behaviour of individuals through to continental scale patterns of species abundances, constitute strong support for the mesopredator release hypothesis and provide evidence that dingoes benefit biodiversity conservation by inducing community wide trophic cascades. Harnessing the positive ecological effects of dingoes while at the same time minimising their impacts on agriculture is a major socio-political challenge in Australia [Current Zoology 57 （5）： 668-670].展开更多
This paper investigates the stochastic dynamics of trophic cascade chemostat model perturbed by regime switching, Gaussian white noise and impulsive toxicant input. For the system with only white noise interference, s...This paper investigates the stochastic dynamics of trophic cascade chemostat model perturbed by regime switching, Gaussian white noise and impulsive toxicant input. For the system with only white noise interference, sufficient conditions for stochastically ultimate boundedness and stochastically permanence are obtained, and we demonstrate that the stochastic system has at least one nontrivial positive periodic solution. For the system with Markov regime switching, sufficient conditions for extinction of the microorganisms are established. Then we prove the system is ergodic and has a stationary distribution. The results show that both impulsive toxins input and stochastic noise have great effects on the survival and extinction of the microorganisms. Finally, a series of numerical simulations are presented to illustrate the theoretical analysis.展开更多
The knowledge of liminology can be applied in studies of trophic state indexes and morfoedaphic indexes as factors for determining the inference fish production in reservoirs. This work is based on the hypothesis of t...The knowledge of liminology can be applied in studies of trophic state indexes and morfoedaphic indexes as factors for determining the inference fish production in reservoirs. This work is based on the hypothesis of the trophic cascade relations, particularly related to bottom-up and top-down effect in Itaipu Reservoir (Brazil). Using the data available by Itaipu, from 1999 to 2004, analyzes of multiple regressions were accomplished to determine the relationships of the dependent and independent variables. We applied the trophic state indices (TSI) based on readings Secchi disk, total phosphorus and chlorophyll-a density for obtaining TSI medium. Morfoedaphic index was calculated based on the reading of the concentration of dissolved solids and the inference of fishing yield, from this index. The average results of the trophic state indices indicate an oligotrophic status for the entire reservoir as well as for the riverine, transition and lacustrine zones separately. The fish was yieldn Estimated by the relation with cyanobacteria concentration, and this was the best variable que explained this prediction. The use of the morfoedaphic index (MEI), with the recorded catch data, predictive models can generate que estimate the fishing yield in the Itaipu Reservoir. The relations of MEI with chlorophyll-a and water transparency que Indicate this index may be a good predicting factor for future fish captures.展开更多
Indirect interactions in food webs can strongly influence the net effect of global change on ecological communities yet they are rarely quantified and hence remain poorly understood. Using a 22-year time series, we in...Indirect interactions in food webs can strongly influence the net effect of global change on ecological communities yet they are rarely quantified and hence remain poorly understood. Using a 22-year time series, we investigated climate-induced and predator-mediated indirect effects on grazing intensity in the tundra food web of Bylot Island, which experienced a warming trend over the last two decades. We evaluated the relative effects of environmental parameters on the proportion of plant biomass grazed by geese in wetlands and examined the temporal changes in the strength of these cascading effects. Migrating geese are the dominant herbivores on Bylot Island and can consume up to 60% of the annual production of wetland graminoids. Spring North Atlantic Oscillation, mid-summer temperatures and summer abundance of lemmings （prey sharing predators with geese） best-explained annual variation in grazing intensity. Goose grazing impact increased in years with high temperatures and high lemming abundance. However, the strength of these indirect effects on plants changed over time. Grazing intensity was weakly explained by environmental factors in recent years, which were marked by a sharp increase in plant primary production and steady decrease in grazing pressure. Indirect effects do not seem to be reversing the direct positive effect of warming on wetland plants. We suggest that cascading effects on plants may lag considerably behind direct effects in vertebrate dominated arctic communities, especially where key herbivore populations are strongly affected by factors outside of the Arctic [Current Zoology 60 （2）： 189-202, 2014].展开更多
Many experimental studies have contributed to the development of the theory of trophic chains in lacustrine habitats. They have revealed the important role played by fish, a subject that has been mostly ignored by lim...Many experimental studies have contributed to the development of the theory of trophic chains in lacustrine habitats. They have revealed the important role played by fish, a subject that has been mostly ignored by limnological studies for the past few decades. Most of these studies were developed in Europe and in the United States. The general applicability of this theory has not yet been tested in subtropical and tropical habitats. In spite of controversies, the bottom-up: top-down trophic cascade hypotheses are the most adopted conceptual models. In this context, we examined if these hypotheses may be corroborated by data from the subtropical Itaipu Reservoir. A negative effect was verified between water transparency and total suspended solids. The detritivorous fish exerted a controlling effect on chlorophyll-a concentrations. Bottom-up effects were detected in four trophic levels, and top-down was detected in just one trophic level. The limnological variates influenced the chlorophyll-a concentration, which indicated that the lnTKN plus the effect of the quarter and the reservoir zone (and their interaction) were important.展开更多
文摘Biological control of soilborne plant pathogens using beneficial fungi, such as the mycoparasite Trichoderma harzianum, offers the prospect of environmentally benign pest control. However, biocontrol organisms have their own natural enemies;for example the fungivorous nematode Aphelenchoides saprophilus preys on T. harzianum. A trophic cascade occurs when three or more trophic levels are present in a food chain, and consumption of the intermediate species affects biomass or productivity of a lower trophic level;such an interaction in this system might reduce the biocontrol efficacy of T. harzianum. However, the presence of refuges, where intermediate-level species are protected from predation, may reduce the ecological impact of a trophic cascade. Interactions among microscopic organisms in a complex medium such as soil are difficult to observe and quantify. We evaluated the potential of quantitative real-time PCR (qRT-PCR) as a tool to investigate the trophic cascade interaction among T. harzianum, A. saprophilus, and the plant pathogen Sclerotinia sclerotiorum. Results indicate that the mycoparasite colonized and persisted inside structures (sclerotia) of the target plant pathogen, where it was relatively protected from predation compared to the surrounding soil environment. In this way, colonization of sclerotia may provide a refuge that reduces trophic cascade effects in this system. qRT-PCR provided a sensitive method to investigate fungal dynamics over time in this multitrophic system.
文摘The roles that top predators play in regulating the structure and function of ecosystems have long been controversial. This is particularly the case when predators pose adverse risks for human life and/or economic interests. The critique of literature on dingoes and their ecological roles in Australia provided by Allen et al. （2011） shows that top predators remain a potentially polarising issue. In opposition to Allen et al. we argue that these widespread patterns of species＇ abundances, attributed to the ef- fects of dingoes and evident at scales ranging from the foraging behaviour of individuals through to continental scale patterns of species abundances, constitute strong support for the mesopredator release hypothesis and provide evidence that dingoes benefit biodiversity conservation by inducing community wide trophic cascades. Harnessing the positive ecological effects of dingoes while at the same time minimising their impacts on agriculture is a major socio-political challenge in Australia [Current Zoology 57 （5）： 668-670].
基金the National Natural Science Foundation of China (No.12271308)the Research Fund for the Taishan Scholar Project of Shandong Province of ChinaShandong Provincial Natural Science Foundation of China (ZR2019MA003)。
文摘This paper investigates the stochastic dynamics of trophic cascade chemostat model perturbed by regime switching, Gaussian white noise and impulsive toxicant input. For the system with only white noise interference, sufficient conditions for stochastically ultimate boundedness and stochastically permanence are obtained, and we demonstrate that the stochastic system has at least one nontrivial positive periodic solution. For the system with Markov regime switching, sufficient conditions for extinction of the microorganisms are established. Then we prove the system is ergodic and has a stationary distribution. The results show that both impulsive toxins input and stochastic noise have great effects on the survival and extinction of the microorganisms. Finally, a series of numerical simulations are presented to illustrate the theoretical analysis.
文摘The knowledge of liminology can be applied in studies of trophic state indexes and morfoedaphic indexes as factors for determining the inference fish production in reservoirs. This work is based on the hypothesis of the trophic cascade relations, particularly related to bottom-up and top-down effect in Itaipu Reservoir (Brazil). Using the data available by Itaipu, from 1999 to 2004, analyzes of multiple regressions were accomplished to determine the relationships of the dependent and independent variables. We applied the trophic state indices (TSI) based on readings Secchi disk, total phosphorus and chlorophyll-a density for obtaining TSI medium. Morfoedaphic index was calculated based on the reading of the concentration of dissolved solids and the inference of fishing yield, from this index. The average results of the trophic state indices indicate an oligotrophic status for the entire reservoir as well as for the riverine, transition and lacustrine zones separately. The fish was yieldn Estimated by the relation with cyanobacteria concentration, and this was the best variable que explained this prediction. The use of the morfoedaphic index (MEI), with the recorded catch data, predictive models can generate que estimate the fishing yield in the Itaipu Reservoir. The relations of MEI with chlorophyll-a and water transparency que Indicate this index may be a good predicting factor for future fish captures.
文摘Indirect interactions in food webs can strongly influence the net effect of global change on ecological communities yet they are rarely quantified and hence remain poorly understood. Using a 22-year time series, we investigated climate-induced and predator-mediated indirect effects on grazing intensity in the tundra food web of Bylot Island, which experienced a warming trend over the last two decades. We evaluated the relative effects of environmental parameters on the proportion of plant biomass grazed by geese in wetlands and examined the temporal changes in the strength of these cascading effects. Migrating geese are the dominant herbivores on Bylot Island and can consume up to 60% of the annual production of wetland graminoids. Spring North Atlantic Oscillation, mid-summer temperatures and summer abundance of lemmings （prey sharing predators with geese） best-explained annual variation in grazing intensity. Goose grazing impact increased in years with high temperatures and high lemming abundance. However, the strength of these indirect effects on plants changed over time. Grazing intensity was weakly explained by environmental factors in recent years, which were marked by a sharp increase in plant primary production and steady decrease in grazing pressure. Indirect effects do not seem to be reversing the direct positive effect of warming on wetland plants. We suggest that cascading effects on plants may lag considerably behind direct effects in vertebrate dominated arctic communities, especially where key herbivore populations are strongly affected by factors outside of the Arctic [Current Zoology 60 （2）： 189-202, 2014].
基金part of a postdoctoral report submitted by the senior author to the Programa de Pos Graduacao em Ciencias Biologicas-Zoologia(IB-UNESP,Rio Claro),under MPJr supervisionFAPESP(Processo no.07/50986-9)CNPq,UNESP,UEM/Nupelia and ITAIPUBINACIONAL for their financial support
文摘Many experimental studies have contributed to the development of the theory of trophic chains in lacustrine habitats. They have revealed the important role played by fish, a subject that has been mostly ignored by limnological studies for the past few decades. Most of these studies were developed in Europe and in the United States. The general applicability of this theory has not yet been tested in subtropical and tropical habitats. In spite of controversies, the bottom-up: top-down trophic cascade hypotheses are the most adopted conceptual models. In this context, we examined if these hypotheses may be corroborated by data from the subtropical Itaipu Reservoir. A negative effect was verified between water transparency and total suspended solids. The detritivorous fish exerted a controlling effect on chlorophyll-a concentrations. Bottom-up effects were detected in four trophic levels, and top-down was detected in just one trophic level. The limnological variates influenced the chlorophyll-a concentration, which indicated that the lnTKN plus the effect of the quarter and the reservoir zone (and their interaction) were important.
