Time and concentration dependency in the potentially affected fraction of species: The case of hydrogen peroxide treatment of ballast waterby Marie-Adèle Dutertre and Maud Hautier
Published by the December 10, 2018 on 4:32 PM
Globalization and international trade made natural gates easier to cross for species. As a consequence, few species were able to travel long distance and settled in new habitats where they become invasive species.
More than 80% of industrialized goods in the world are transported by the oceans in container ships. In many cases, container ships is discharged in the destination port and go back empty. Whereas, the structure of this kind of ship does not allow them to travel empty and with stability. This is for a problem of stability that ballast exists. Since the 19th century, ballast with rocks was substitute with water. Before ships leave the port , water is loading in tank and at the destination port tanks are discharged.
http://www.seos-project.eu/modules/marinepollution/marinepollution-c04-p05.fr.htmlBallast water transport contribute to invasive species spreading. In order to fight against exotics species, waters ballast are treated with Hydrogen Peroxide (H2O2). But there is a question : how to be sure that ballast water is effective and is not toxic for the marine environment ? In order to evaluate the environmental impact of the treatment, a study has been conducted. Three taxa has been chosen, among them, two crustacean, two algae and one rotifera : C. volutator, A. salina, E. costatum, D. teriolecta, B. plicatilis. The authors of the study consider three dimensions : Hydrogen Peroxyde concentration, the effect of the Peroxide Hydrogen on organism and Hydrogen Peroxide exposure time. In the experiment, they made the tree dimensions varied and they considered as the final aim, the mortality, the immobility and the inactivation of the organism. The results are used in a mechanistic model which is based on the description of Dynamic Energy Budget theory. The DEB theory consists of a simple set of rules that specifies how organisms acquire energy and building blocks from their environment to fuel their life cycle. It is used to rely the observed effects and the hydrogen peroxide concentration in the experiments. The DEB-tox model allows to determine ECx — Effect Concentration — : the concentration which induces a response of x% between the baseline and maximum after a specified exposure time ; and the HCx — Hazardous Concentration — : the concentration which is dangerous for x% of the population. Thanks to this values, it is possible to determine the PAF — Potentially Affected Population— with means the part of an ecosystem potentially affected by a drug concentration. The results show an interspecific response variability with means different interspecific H2O2 sensibility. Sensibility is a combination between time exposure and the concentration. The conclusion of the study is that the hydrogen peroxide is effective for treating ballast water.
Concentrations, effects and time exposure were studied there. The choice of the five species is a wise choice as a result of the representativeness of a wide selection of sensibility which allows to extrapolate this results to other species and then estimate the effect of hydrogen peroxide treatment on other species present in water ballast. Whereas the aim of the study was to assess environmental risks of hydrogen peroxide treatment, and the obtained results here cannot be used to conclude regarding as the environmental risks.
To assess more precisely the risk, it is important to consider the hydrogen peroxide degradation and its potential impact on marine ecosystem. The H2O2 is oxygenated water which would rapidly be decomposed : 2H2O2 => 2H2O + O2. In this case, the hydrogen peroxide would not impact the environment.
Furthermore, sub-lethal effects are sufficient to reduce the viability of the organisms and for that, lower concentration of H2O2 and lower time exposure are sufficient. The purpose is to neutralize exotic species with lower environmental and economic costs. Moreover, in order to reduce again the hydrogen peroxide used quantity, other studies show the efficiency of using UV, Ozone, and ultrasound for neutralizing species. The hydrogen peroxide treatment can also be used with alkaline water which allows to obtain the same result with lower concentration and time exposure.
An other option is to establish regulated areas for discharging and to filter and to purify ballast water before discharging in the environment.
This post is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.Estimating relative energetic costs of human disturbance to killer whalesby Max Davesne and Quentin Marcon
Published by the November 9, 2018 on 10:22 AM
Some predators are valued by humans, either for their ecological or aesthetic attributes, whereas others are viewed as pests. Increasingly, applied ecologists are asked to consider effects of anthropogenic activities on valued predators (Ormerod 2002). This complexity becomes especially apparent when dealing with conservation and management of cetaceans (whales, dolphins and porpoises), which are long-lived and elusive study animals. Cetaceans are also exposed to a variety of both targeted and incidental human activities in the marine environment. Nowadays, the boat traffic is always increasing as the « whalewatching » and that can cause some trouble as we don’t really knows if that disturb the ecosystem.
Boat approching a killer whale - Mike Baird - CC BY 2.0This study examined the activities of ‘‘northern resident’’ killer whales (Orcinus orca) in Johnstone Strait, British Columbia, Canada, in July and August, from 1995 to 2002. Disturbance from boat traffic has been identified as a conservation concern for this population. This study aims to test whether or not the boat presence altered whale’s activities and want to estimate the energetic cost of this disturbance for the whales.
The time-activity budgets observed with respect to boat presence were converted to rough estimates of the energetic demand of free-ranging killer whales (Kriete 1995). Only Kriete’s data from Hyak (a 4733 kg adult male) and Yaka (a 2800 kg adult female) were used, rather than values for both adult and sub-adult subjects, because data on the sub-adult female were thought to be unreliable (Kriete 1995).
Behaviour change in the presence of boats and avoidance trend and decrease in the likelihood of rubbing in the presence of boats. From Williams et al. 2006.
There is an increase of 3% in global energetic budget and a decrease of rubbing budget from 17% to 3% and for the feeding from 13% to 10%. These lost feeding opportunities lead to a substantial (18%) estimated decrease in energy intakeThis study analyzed the behavioral responses of orcas in the presence of boats. However, the model does not implement the variability between individuals. For example the stress induced by the presence of boats and the physiological differences that this may imply.
Studies demonstrated that many bird species respond to tourism presence by shortening feeding bouts (Burger et al. 1997; Galicia and Baldassarre 1997; Ronconi and St Clair 2002). This has been found also in numerous studies of terrestrial mammals, where feeding activity is easier to observe than in free-ranging cetaceans.
This study only covered one of three killer whale ecotypes. The results of this Northern residents study are difficult to extrapolate to other ecotypes (Southern residents and Migrants).
This post is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.Use of dynamic energy budget and individual based models to simulate the dynamics of cultivated oyster populationsby Maxime Rochet and Jean-Baptiste Valerdi
Published by the October 8, 2018 on 12:45 PM
This paper deals with a test of Dynamic Energy Budget (DEB) apply for predictions of the oyster Crassostrea gigas production in Thau Lagoon. The DEB model is based on physiological and environmental parameters, he predict the growth at indivual level. In the case of oyster production the prediction must be applicate at the cohort levels, its why they choose to integrate the DEB model into a population dynamics concept. Population model choose its the IBM (Indivifual Based Model) method, the equations are used for the predict the harvested production and the stocks in place (total number of individuals). The advantage of this integration its to assess the effect of ecosystem changes on oyster production.
Oyster farming in the Thau Lagoon - Olivier Pessin - CC BY-SA 3.0The models recently used (DEB) have been compared with a more common prediction tool. The partial differential equation (PDE) are empirical equations used for the growth prediction between different class and simulate by individual total mass. This equation are more straightforward than the DEB-IBM models but they use only a single variable to represent individual growth. The DEB model integrate two variable of calibration, the other parameters of the differents equations were estimated from independent datasets using comprehensive studies of oyster growth and ecophysiology under controled conditions. The calibrated parameters are the chlorophyll a concentration proxy of the phytoplacton biomass (principal food of oysters) and the température linked to assimilation and maintenance rates. This technique modelise by this way the indivdual capatcity of food assimilation and the allocation of energy between energical reserve, structural tissues ans reproductive structure and maintenance. To be more likelihood a growth variability showing variability between individuals have been implanted. Some variability have been implanted into the prediction of PDE method and the DEB-IBM model. This variability was integrate by diffusion to reproduce the variability between individual growth in the PDE and by Xk (half saturation coefficient) variability in the DEB-IBM case.
The results of the differents simulations have proved a good capacity for the DEB-IBM model to predict the stocks and the harvest productions. The data estimated are close to the observed. He have to advantages to be generic, easy to etablish by the low number of measurables parameters. With the results showed in the study (see figure below) his capacity to take account of the environmment variables have been proved too . The limits are detectable in his sensivity to the variability and the large number of parameters estimated can induce in error.
From Bacher & Gangnery 2006.The comparison of the two models have show the effect of the variability in the predictions values. The values predicted by the DEB-IBM model look closer to the observation than the PDE predictions. For exemple the harvestes productions have been estimated earlier by the PDE method than the DEB-IBM, so the modelisation of DEB parameters can influe strongly the dynamic population and the production previsions.
This post is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.Effects of an exotic prey species on a native specialist: Example of the snail kiteby Mathieu Finkler and Hyppolyte Terrones
Published by the September 11, 2018 on 12:34 PM
Exotic species have largely been studied over the years, their effects on native populations, their consequences... Most of the studies aim to see the competition between a native species and an exotic one. Here the study focus on the effect of an exotic species on a native predator.
Florida snail kite (Rostrhamus sociabilis plumbeus) are endangered, their populations are drastically declining in recent years. It is important to study them and to determine why their numbers are falling to implement an adapted conservation strategy.
The purpose of the study is to assess the effects of the recently introduced island apple snail (Pomacea insularum) on snail kite behavior and energetics comparing with the native prey (Pomacea paludosa).
Juvenile snail kite - Cláudio Dias Timm - CC BY-NC-SA 2.0The authors determined different parameters such as the proportion of snail dropped, the searching and handling time, the consumption rate and proportion of time in flight. Caloric intake of both species has been determined by a model (Sykes 1987) and so is the daily energetic expenditure. Caloric balance seems to be perfectly suitable in this case because the difference in intake calories could affect all the life history traits and be the cause of the fast decline of the kites.
Foraging on exotic snails led to a greater proportion of snails dropped, a lower consumption rate, a longer handling time and a lower energy balance (figure below). These conclusions are particularly true and worrying for juveniles. This results indicates that feeding on exotic snails will decrease their energy and so less energy will be available for others activities (like reproduction, growth, defence against predators...). Finally, lakes where only exotic species are present (Tohopekaliga) could form an ecological trap.
From Cattau et al. 2010Even after this study, it will be hard to conclude on an optimal foraging theory because both snail species were never found together in a lake. Therefore it could be interesting to make the same study in a lake were both species are present. Furthermore, this study has been conducted during the breeding period. During breeding period, species will need more energy to feed their offspring, to protect them, potentially leading to a greater difference in energetic balance.
Further studies may focus on the fact that kites feed on larger exotic preys (compared to native preys). Are the smallest individuals not available for kites or do kites choose to feed on larger exotic preys to compensate for their lower energetic content ?
This method could be used in others studies of trophic relationships and not only on native-exotic conflict. For example if human overfish a species, the predator of this species will have to change preys. So it will be important to calculate the energetic balance with the new prey.
This post is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.Are vulture restaurants needed to sustain the densest breeding population of the African white-backed vulture?by Mikel Cherbero and Tom Laffleur
Published by the August 3, 2018 on 10:00 AM
As obligate scavengers, vultures are entirely dependent on carrion. These last decades, carrion abundance has decreased in many areas. The two main causes of this trend are clearly identified. Natural habitat destruction reduces wild animal carrion abundance, which is the natural resource of scavengers. At the same time, the modification of agricultural practices, essentially the generalization of carcass rendering, has reduced the availability of cattle carrion. These factors have led to a negative trend on scavenger populations. This is especially the case in Africa, where most of avian scavenger species are now endangered. African savanna ecosystems were originally rich in avian scavengers, but most of the species are actually endangered.
_on_zebra_carcass_..._(33282103735)_201x301.jpg "White-backed vultures feeding on zebra carrion - Bernard Dupont - CC BY-SA 2.0")
White-backed vultures feeding on zebra carrion - Bernard Dupont - CC BY-SA 2.0In this study, authors model the carrion ecology of an ecosystem in Swaziland which is home to the densest breeding population of the African white-backed vulture (Gyps africanus), a critically endangered species. They also study other threatened scavenger species of Swaziland: white-headed vulture (Trigonoceps occipitalis), Nubian vulture (Torgos tracheliotos), marabou stork (Leptoptilos crumenifer), tawny eagle (Aquila rapax) and bateleur (Terathopius ecaudatus). The purpose of this work is to better understand the feeding activity of the white backed vulture and to modelize population trends for these six species (using life-history traits and modelization of carrion availability), and based on these results authors discuss if the establishment of vulture restaurants would be beneficious.
They first calculated the foraging radius (r) of the white-backed vulture, based on the Foraging radius concept theory. The foraging radius represents the radial distance from the nest in which the energy inputs are greater than the costs of feeding and needs of the vulture and its litter. This theory is adapted to this species, because vulture always comes back to the nest after feeding. They compiled available bibliography and collected data on metabolism and life-history parameters of the species. Using this data, they applied a model created with the same purpose by Ruxton & Houston in 2002 for the Ruppell’s vulture (Gyps rueppellii), which is phylogenetically and ecologically close to the white backed vulture.
The results shows that the foraging radius is 260 km in the main part of the year. This radius is large, vultures can feed in neighboring countries (South Africa, Mozambique), it implies an international cooperation in the management of these endangered populations. A positive aspect is that individuals can spread over large area, so the studied population can form or sustain other populations. On the other hand this radius is much greater than the natural reserve surface, thus vultures can be exposed to several risks, like poisoning, when they are feeding. When vulture have to feed a chick, energy needs are logically greater so the foraging radius is reduced to 40 km. Carrion availability is more problematic during this period, which should therefore be targeted if vulture restaurants are setted up.
Using novel Population Dynamics P-Systems, they show that carrion provided by wild ungulates biomass is currently enough to sustain this vulture species. According to the model, white-backed vulture population will continue increasing in Swaziland, and will pass from approximately 300 pairs to more than 500 in twenty years. The other studied avian scavenger populations will follow the same trend, but are far less abundant than white-backed vulture. The model shows also that three main species are composing vultures’ food: the Impala (Aepyceros melampus), the blue wildebeest (Connochaetes taurinus) and the plains zebra (Equus burchelli) represent 55 % of total carrion.
However, in light of the forecasted population increases, food will become a limiting factor. This is particularly true for the period from November to April, for which the model show a carrion deficit. During this period African vultures are not breeding so they can go far away to feed themselves. But the model also shows a carrion deficit during the breeding season after five to thirteen years of simulation. This lack of food resources can be considered as a natural limiting factor. According to the model, the area has probably reach its maximum carrying capacity after twenty years.
To conclude, authors suggest that setting up supplementary feeding stations in Swaziland should be seriously considered, especially during the breeding season. Good managed restaurants would have several advantages : secure the viability of the population and thus increase its capacity to act as a source population, avoid poisoning risks and create the opportunity to capture and tag vultures. This last point would allow to improve knowledge about the avian scavenger species, necessary for a more effective conservatory management.
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Temperature-dependent body size effects determine population responses to climate warmingby Alison Arraud and Laura Duran
Published by the July 5, 2018 on 1:55 PM
Up to now, neither the size nor the stage of the individual were considered to studying the population responses to climate warming. On 2014, a scientific group proposed another way to understand the temperature effects on fish populations. They improved the interaction effects of temperature-dependence with the size and the stage of fish on their energetic thresholds responses. Energetic thresholds themselves act on the dynamic of stade-structured population (e.g. parr, smolt, adult).
Flathead mullet (Mugil cephalus) - Roberto Pillon - CC BY 3.0 UnportedFinally, this study found that increasing temperature could redistribute biomass across life stages and modify the regulation of the population by reworking the intra-specific competition. Other studies have shown that high temperature during ontogenesis can accelerate the development and growth of individuals or, give individuals of smaller sizes early maturation.
This study points out the importance of taking into account the interactions between temperature and size-specific (maturing, reproduction, etc.) that will lead to a set of behavioral responses that have consequences on the structuring of a population. This is all the more important in the context of global warming.
This post is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.Can bioenergetic models help the re-introduction of the native Rio Grande cutthroat trout in a Southwestern headwater stream?by Emmanuel Bourgoin and Aurélien Callens.
Published by the May 16, 2018 on 1:47 PM
Re-introduction of native species is far from being simple: many parameters must be accounted for! To illustrate that, we are going to take a closer look at a study made by Kalb and Huntsman (2017) on a stream in southcentral New Mexico which was deemed suitable for re-introduction of the native Rio Grande cutthroat trout (Oncorhynchus clarkii virginalis). Before re-introducing this species, researchers wanted to know if the habitat was able to sustain it. Thus, they evaluated habitat using resource selection functions with a mechanistic drift-foraging model to explain rainbow trout distributions. They studied rainbow trouts because they are present on the stream and are close relative to the Rio grande cutthroat trout, consequently all the results of this study can be extended to this native species.
Rainbow trout - Timothy Knepp/U.S. Fish and Wildlife Service - Public domainEach month, the available habitat and foraging locations were evaluated along the stream. Foraging locations were defined as the location where they could observe a foraging fish. For each foraging site, the length of the fish was estimated and physical characteristics such as discharge, focal velocity (current velocity at the head of the fish), depth, cover distance and temperature were measured on the exact fish location. These parameters were also measured on the available sites. Macroinvertebrate drift was estimated on all the locations (available and foraging). All these parameters were used in bioenergetic models which allow the researchers to estimate all the intakes of the fish (net energy intake, energy assimilated…) and all the costs associated with foraging (capturing a prey, swimming…).
First, they observed that macroinvertebrate drift was strongly season- and temperature-dependant with high values in summer and fall and low values in winter and spring. Moreover, as we must expect it, water temperature, depth and discharge were found to be seasonal parameters too. Secondly, models identified the depth as the most limiting factor for habitat selection: trout of all ages preferred habitat location with a greater depth. The most interesting thing about the models is that they can show the characteristics of the chosen habitat according to the age of the trout and the season. In fact, they showed that during the winter the smaller size-classes were more likely to choose a position closer to cover. Additionally, they highlighted that spring was the season with the greater energy intake for all the size-classes expect the 4+. Finally, drift-foraging models identified that 81% of observed trout selected positions could meet maintenance levels throughout the year and 40% of selected habitats could sustain maximum growth. Despite these last observations, the larger size-classes were energetically more limited throughout the year.
This study showed that trout population prefers deep pool habitats with slow moving water and that this stream was able to sustain a great population of rainbow trout and could consequently sustain a great native population of Rio grande cutthroat trout. However, authors warn us about the risk of hybridization and interspecific competition and suggest removing the non-native fishes first.
To answer the question in the title: yes, bioenergetic models can help to re-introduce a native species in a given environment. Nonetheless, this example is really specific: author had the chance to find and study a close relative to the native trout in the stream! The main thing to remember is that bioenergetic models give a lot of useful information on how a species uses an habitat and must be taken into account (if applicable) in the management of species.
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