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Journal ArticleDOI

Population growth of the floating weed sal vinia molesta: field observations and a global model based on temperature and nitrogen

01 Dec 1986-Journal of Applied Ecology (Blackwell)-Vol. 23, Iss: 3, pp 1013-1028
TL;DR: A model was built to predict rates of growth for any latitude, altitude, time of year and nitrogen content of the plant, and found that at one site, the intrinsic growth rate was shown to be limited by the seasonal progression of temperature to a smooth annual cycle.
Abstract: SUMMARY (1) Salvinia molesta Mitchell causes serious problems in many tropical countries by forming thick mats on the surface of freshwaters. Some of these problems have been solved by biological control using the beetle Cyrtobagous salviniae Calder & Sands (Coleoptera: Curculionidae). (2) Intrinsic rates of growth by S. molesta were measured every week over periods of from 16 weeks to 2 years at seven sites located near the equator to 330S. The rates varied between zero, at the most southerly site in winter, up to 0. 17 leaves per leaf per day (0. 16 g g-1 d-1). (3) Self-crowding when the water surface was just completely covered, 50% shading, and one adult C. salviniae per five ramets of S. molesta, reduced intrinsic growth rates by 0 04, 0 03 and 0.005 g g-1 d-1 respectively. (4) Among the sites, intrinsic rates of growth and net assimilation rates were generally significantly correlated with air temperature and NPK content of the plant. In contrast, leaf weight ratio, top/root ratio and ramet weight were generally negatively correlated with the same variables. (5) Intrinsic growth rates, when adjusted for temperature effects using a relationship found in earlier controlled-environment studies, had a relationship with the nitrogen content of the plant very similar to that found in controlled-environment studies of the effects of nitrogen. (6) A model, based on the above relationship with N-content and controlled environment studies of the effects of temperature, explained between 40% and 80% of the variance in intrinsic growth rates observed at the different sites. There was little effect on the amount of variance explained if the model was driven by water temperatures calculated from observed air temperatures or by water temperatures calculated from latitude and date, and by mean temperatures or hourly temperatures interpolated from daily maxima and minima. Adding sunshine and P-content of the plant did not increase the fit of predicted to observed rates of growth. (7) At one site, the intrinsic growth rate was shown to be limited by the seasonal progression of temperature to a smooth annual cycle onto which were superimposed shorter frequency peaks and troughs resulting from the sequence: rainfall, runoff, elevated concentration of N in lakewater, elevated concentration of N in tissues of S. molesta, increased rate of growth by the plant. (8) A model was built to predict rates of growth for any latitude, altitude, time of year and nitrogen content of the plant. Predicted mean annual growth rates are presented for latitudes between zero and 50 IC and four different nitrogen contents.
Citations
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Journal ArticleDOI
TL;DR: It is shown that under constant experimental conditions, water hyacinth shows logistic growth, and the resulting model incorporates two of the most important factors (temperature and water nutrient level) that determine whether water Hyacinth is an important environmental problem at a given site.

177 citations

Journal ArticleDOI
TL;DR: The salvinia-herbivore system has been investigated in more detail than most, because of its relative simplicity and ecological principles illustrated bysalvinia and its herbivores.
Abstract: The salvinia-herbivore system has been investigated in more detail than most, because of its relative simplicity due to the absence o f sexual and dormant stages in the plant's life cycle, the apparent genetic uniformity of the plant, the absence of water stress, the uniformity of the water surface habitat and the absence of herbivores outside the plant's native range. This review describes how biological control of salvinia was achieved and discusses ecological principles illustrated by salvinia and its herbivores.

134 citations

01 Jan 2003
TL;DR: A review of the processes of risk analysis used by regulatory bodies around the world to pre-judge biological control releases against weeds is presented in this article, where the authors make recommendations to address this crisis in the making and discuss the outcomes of the review with respect to the inherent social risks of making analysis of biological control release an overly protracted process.
Abstract: Risks of non-target effects resulting from releases of exotic organisms for the biological control of alien pests are a growing major concern because: (a) previous releases (<1%) are having significant negative impacts on rare native species, (b) alien organisms are a recognized global threat to sustainable agriculture and biodiversity, (c) risk analysis, as applied to environmental threats of species invasions and harmful effects of releases of genetically modified organisms, is a burgeoning field, and (d) biological control is increasingly being used in complex natural ecosystems where indirect impacts are harder to predict. As a result, governments are adopting a more risk-averse attitude to biological control as they assess such releases from an environmental and an economic standpoint. This is leading to more expensive and fewer successful release applications. In this paper we review the processes of risk analysis used by regulatory bodies around the world to pre-judge biological control releases against weeds. The aim is to publicize both strengths and weaknesses and to help encourage existing assessments to be fair to all without blunting the value of biological control as an effective tool against invasive alien weeds. The review, based around the five components of formal risk analysis (comparative analysis, risk assessment, risk management, risk evaluation, and risk communication), also focuses on how well the benefits and costs of biological control releases are evaluated in addition to the traditional analysis of the hazards. Currently only the New Zealand approach closely matches a full ecological risk-benefit-cost analysis of biological control releases with a precautionary approach, open consultation, a broad hazard/benefit definition in the release application and a judicial basis to the decision, but it comes at a high cost. Improving the analytical approaches used by countries runs a high risk of grinding biological control releases to a halt in a world where the precautionary approach has been adopted with respect to threats from exotic organisms on biodiversity (in line with the ‘precautionary approach’ set forth in principle 15 of the 1992 Rio Declaration on Environment and Development). The benefits of biological control remain poorly understood by the public, allowing the risks to attain disproportionate attention. We make recommendations to address this crisis in the making and discuss the outcomes of the review with respect to the inherent social risks of making analysis of biological control releases an overly protracted process.

123 citations


Cites background from "Population growth of the floating w..."

  • ...Most projects now undergo some form of evaluation, although this rarely receives comprehensive ecological (Room & Thomas, 1986; Vogt et al., 1992; Hoffmann & Moran, 1999; Paynter & Hennecke, 2001; Sheppard et al., 2002; Swirepik & Smyth, 2002) or economic (Doeleman, 1989; Le Maitre et al., 2001;…...

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Journal ArticleDOI
03 Feb 2011-Nature
TL;DR: By fitting a process-based nonlinear model to thirteen-year data sets from four billabongs of Kakadu National Park, Australia, it is shown that incomplete control can be explained by alternative stable states—one state in which salvinia is suppressed and the other in which Salvinia escapes weevil control.
Abstract: Suppression of the invasive plant Salvinia molesta by the salvinia weevil is an iconic example of successful biological control. However, in the billabongs (oxbow lakes) of Kakadu National Park, Australia, control is fitful and incomplete. By fitting a process-based nonlinear model to thirteen-year data sets from four billabongs, here we show that incomplete control can be explained by alternative stable states--one state in which salvinia is suppressed and the other in which salvinia escapes weevil control. The shifts between states are associated with annual flooding events. In some years, high water flow reduces weevil populations, allowing the shift from a controlled to an uncontrolled state; in other years, benign conditions for weevils promote the return shift to the controlled state. In most described ecological examples, transitions between alternative stable states are relatively rare, facilitated by slow-moving environmental changes, such as accumulated nutrient loading or climate change. The billabongs of Kakadu give a different manifestation of alternative stable states that generate complex and seemingly unpredictable dynamics. Because shifts between alternative stable states are stochastic, they present a potential management strategy to maximize effective biological control: when the domain of attraction to the state of salvinia control is approached, augmentation of the weevil population or reduction of the salvinia biomass may allow the lower state to trap the system.

88 citations

01 Jun 2004
TL;DR: A review of available information on the growth, distribution, and ecology of Salvinia molesta D. Mitchell is presented in this article, along with a taxonomic status, its field characteristics, phenology, and spread overseas and in the United States.
Abstract: : Over the past 70 years, the free-floating aquatic fern Salvinia molesta D. S. Mitchell (giant salvinia) has spread from its native range in Brazil to many tropical and subtropical regions. Though innocuous within its native range, elsewhere this species is an aggressive menace that has had devastating ecological and socioeconomic impacts on aquatic systems in parts of Africa, Sri Lanka, India, Australia, New Guinea, and the Philippines. In the United States, the plant is established in waterways in at least 10 states (mainly in the south) and is expected to continue to expand in areas generally where Eichhornia crassipes (Mart.) Solms (water hyacinth) persists. Listed as a Federal Noxious Weed since 1984, S. molesta is prohibited from importation to the United States and from transport across state lines. Dense mats of S. molesta can suppress growth of native vegetation and degrade water quality, fish and wildlife habitat, and numerous other ecological values. Notably, massive infestations have occurred in the Swinney Marsh Complex, Texas, in the Lower Colorado River, Arizona/California, and in Lake Wilson and Enchanted Lake, Hawaii. This report presents a review of available information on the growth, distribution, and ecology of S. molesta. Information is provided on the plant's taxonomic status, its field characteristics, phenology, and spread overseas and in the United States. Growth responses of S. molesta in relation to environmental variables (e.g., temperature, nutrients, light, pH, conductivity) are emphasized as are impacts of the species on the environment and other aquatic organisms Different technologies (i.e. physical chemical biological and integrated) applied to control S. molesta infestations are discussed along with information on the effectiveness of these procedures and their need for further study.

68 citations


Cites background from "Population growth of the floating w..."

  • ...In addition to causing the loss of crops and preventing agricultural operations, flooding is a prominent mechanism in breaking up the mats and distributing fragments that can produce new colonies (Sculthorpe 1985)....

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  • ...As the plants die, organic debris accumulates at the bottom of the water column and can threaten fisheries by creating a shallow-water environment less suited to fish breeding (Sculthorpe 1985)....

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  • ...Even when the mats are not fully impenetrable, the clusters of rhizomes and submerged leaves quickly become entangled around boat propellers, so that the watercraft may sooner or later be immobilized (Sculthorpe 1985)....

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  • ...…(L.) All., S. nymphellula Desv., S. oblongifolia Mart., S. minima Baker, S. sprucei Kuhn], seven of which (S. oblongifolia, S. sprucei, S. minima, S. auriculata, S. herzogii, S. biloba, and S. molesta) originated in the neotropics (Mitchell and Thomas 1972; Sculthorpe 1985; Jacono and Pitman 2001)....

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  • ...Occasionally, plants of various species will colonize thick S. molesta mats, forming “floating islands” of vegetation or mixed sudd communities (Sculthorpe 1985; Holm et al. 1977)....

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References
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Book
01 Jan 1982
TL;DR: In this article, the Physiological determinants of crop growth were investigated and shown to be important determinants for crop growth in terms of yield and quality of the crop, and their influence on crop growth.
Abstract: Physiological determinants of crop growth , Physiological determinants of crop growth , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

233 citations

Journal ArticleDOI
28 Jul 1981-Nature
TL;DR: Successful control of the largest salvinia infestation in Australia using the beetle Cyrtobagous singularis Hustache (Curculionidae) is reported and it is suggested why this beetle has potential for controlling salvinian infestations elsewhere.
Abstract: The floating fern Salvinia molesta D. S. Mitchell (Salviniaceae) originated in southeastern Brazil1, but since about 1930, it has been introduced into various tropical and subtropical regions where it has become as great a menace as the water hyacinth2–4. Biological control of salvinia has clear economic and environmental advantages over other methods of control, but earlier attempts either failed or achieved inconclusive results5–7. We report here successful control of the largest salvinia infestation in Australia using the beetle Cyrtobagous singularis Hustache (Curculionidae) and suggest why this beetle has potential for controlling salvinia infestations elsewhere.

217 citations

Journal ArticleDOI
TL;DR: Fitness appeared to be maximized in infertile water by the retention of senescing ramets so that the nutrients they contained could be reallocated within colonies, and in fertile water by rapid proliferation of small colonies which could act as dispersal units.
Abstract: (1) Colonies of Salvinia molesta ramets were sampled from populations at several different densities growing on waters high and low in nutrient concentration. A colony consisted of a group of ramets connected together by a single, intact, usually branched, piece of rhizome. (2) All rhizomes were planar and rhizome segments zigzagged between ramets enabling parent branches to be distinguished from side branches which were produced on alternate sides of successive ramets. (3) Ramets bore up to three ranks of side branches and the degree of branching was positively correlated with concentration of nutrients in the ambient water. Branching was not correlated with the degree of crowding. (4) Rhizomes from infertile water were tough and most contained no second or third rank side branches. Their oldest ramets were senescent and had a mean age of 12 ramet generations. These rhizomes appeared to fragment when their oldest segments degenerated. (5) Rhizomes from fertile water were brittle and most contained three ranks of side branches. Their oldest ramets were not senescent and had a mean age of 7 ramet generations. These rhizomes appeared to fragment when repeated branching forced segments to bend beyond the limits of their elasticity. (6) Fitness appeared to be maximized in infertile water by the retention of senescing ramets so that the nutrients they contained could be reallocated within colonies, and in fertile water by rapid proliferation of small colonies which could act as dispersal units. (7) Rhizome architecture could not be explained as an optimal solution to the problem of tesselating a plane to maximize light utilization. (8) A model of branching growth was found to give a good description of increase in the population of ramets under conditions optimal for branching. The population (yx) in generation (x) was given by

99 citations

Journal ArticleDOI
TL;DR: Field observations and laboratory studies showed that C. singularis severely damaged S. molesta and that the weevil is suitable as a control agent for this weed in tropical and subtropical areas in Australia.
Abstract: Cyrtobagous singularis Hust. was recorded from Brazil, Paraguay, Uruguay and Argentina in association with six species of Salvinia (aquatic ferns). Field observations and laboratory studies in Brazil and Australia showed that C. singularis severely damaged S. molesta and that the weevil is suitable as a control agent for this weed in tropical and subtropical areas in Australia. In host-specificity studies using 46 plant species that occur in Australia, development of the immature stages took place only on S. molesta. Minor leaf scarring occurred on sweet potato when in contact with water, but starvation tests excluded this plant as a possible terrestrial host. Adults fed, but were unable to reproduce, on water lettuce (Pistia stratiotes). The high degree of host specificity indicated that establishment of this weevil in Australia is without risk to non-target plants. C. singularis was first released and became established in Australia in 1980.

79 citations