How does agricultural pollution affect estuarine health in the United Kingdom?by Sven Mellaza and Matia Pavkovic
Published by the October 4, 2021 on 4:39 PM
Estuaries are among the most productive ecosystems on the planet. These habitats deliver many services to humankind. They are characterized by wide ranges of water salinity, currents power and turbidity. To their natural stressors are added human disturbances that affect the natural system.
The rivers, from their sources to the sea, follow a long path through land fields. In a period of important rainfall, a large part of the land pollution defined by Nitrates and Phosphates is collected by the rivers and transported to estuaries. Consequently, the enrichment of the system modifies the relation equilibrium in the food chain; a rich and complex link between the organisms is the base of a healthy resilient ecosystem. The management application is crucial, so estuarine ecosystems can continue to deliver services and host rich life diversity.
Impact analyses of the pollution on the ecosystem
In this study, the scientist aimed to asses estuarine health by considering the relation between all the organisms. They have analyzed two estuaries systems from the United Kingdom. Tamara estuary is a medium-size complex located on the south-west coast of England; it stretches from Gunnislake weir to Plymouth sound. The second estuary, Eden, is smaller compare to the first one. It is positioned between the village of Guardbrige and the town of St Andrews on the East coast of Scotland.
Since the 90’s, the two ecosystems have experienced major nutrient enrichment from the arable and livestock production. This pollution led to the ecosystem “eutrophication”, a biological phenomenon that can cause an increase of algal bloom and a decrease of oxygen concentration in habitats.
For this research, ecologists are using mathematical software called “Ecopath model”. The model is a widely used tool to identify and quantify major energy flow in the ecosystem, to visualize the important interaction between species, evaluate pollution and climate changes in aquatic ecosystems. This approach allows them to examine systems in their entirety to adjust management application.
The aim of this study is to analyze and compare food network structure of these two estuaries at different historical period of nutrient concentration. The results shows that Tamar estuary is 25% more active than Eden estuary in periods of high nutrients concentrations. The activity is defined by the number of matters flowing in the system. The scientists explain here the difference by the greater size and greater freshwater inputs from the rivers in Tamar estuary. The second indicator was the total biomass of the estuary. The productivity of the system decreases with the reduction of nutrients enrichment. Primary producer’s growth is stimulated by the extra nutriments, which improve their development and finally impact the upper trophic levels.
During pollution event, flow of nutrients increases, leading to degradation of the food-chain organization and structure. In addition, wider the estuaries are, slower it recovers from perturbations, especially looking at the trophic structure.
The Ecopath, Ecosim and Ecospace models are tools primely used to evaluate ecosystem impact of fisheries (Pauly et al. 2000). As it gets popular, these models are useful to evaluate trophic systems like estuaries. These well-known models can be useful to predict and analyze the effects of actual global changing. Nevertheless, a bunch of other models exist and are used to analyze trophic system like Bayesian-mixing model. Using different tools to study the same problematic permit comparison and can lead to different approaches.
When a macaque has the choice between two lianasby Marie Delbasty and Julie Viana
Published by the May 10, 2021 on 8:00 AM
Two populations of moor macaques (Macaca maura) were studied in their natural environment in South Sulawesi, Indonesia in order to understand their use of two different habitats in karst forest.
Moor macaque is a species currently classified as "endangered" by the IUCN, mainly due to the disturbance and fragmentation of its habitat. That is why, in order to develop adequate conservation plans and management strategies, it is essential to study the patterns of habitat use in relation to the distribution of essential food resources.
Concerning the two types of habitat, they were characterized according to the vegetation present and its abundance as well as the topography and the presence of any trace of human activity.
The two habitats of this forest are in fact distinguished in two essential aspects:
The forest situated at the highest altitude with a steep slope, has few food resources but is not accessible to humans
vs.
The gently sloping forest, rich in resources but frequented by humans.
In order to carry out this study, each group of macaques was observed after having been accustomed to the presence of the scientists. The largest group consisted of about 30 individuals while the smallest group consisted of 18 macaques. The behaviour of the smallest group was studied from June to November 2016 while the largest group was studied from September 2014 to February 2015. Behavioural activities were defined as feeding, foraging, locomotion, social interactions and resting.
Although both habitats are used on a daily basis by each population, the analysis revealed that for both groups, the only behaviour that differed primarily between the two habitat types was time spent feeding. They spent more time feeding in the more food-rich forest habitat. The larger group spent more time overall in the food-rich forest while the smaller group spent more time in the food-poor forest.
The habitat with fewer resources is more of a refuge area for the macaques as they have no real predators and humans are the main threat. The larger group's use of a more productive but riskier habitat may be due to its history of provisioning, which may have allowed its individuals to have less fear of encountering humans. On the other hand, the individuals of the other group have never experienced provisioning. Another possible explanation is group size. Indeed, individuals in the larger group have less need to be vigilant because of their numbers, compared to the smaller group. In addition, the larger group might dominate the other group from a competitive point of view and thus be given priority for benefiting from resources.
In this context, macaques seem to be ecologically flexible, able to exploit the karst forest as a whole and to cope with human disturbance. It is important to protect the forest to allow the species to persist as habitat fragmentation threatens its survival. Thus, the management of this area would consist of balancing the needs of humans and macaques, and one of the solutions could be to educate local people on the protection of the species.
In a global context of loss of many species, the ideal would be to be able to leave in peace those for whom this is possible. Indeed, it seems preferable not to allow humans to access this area for the good of these macaques especially since this area is probably home to most of the remaining populations. Indeed, forest habitat with more food resources is a crucial part of the landscape for the survival of moor macaques in southern Sulawesi.
Thus, a question then arises:
would it be possible to let these macaques enjoy their habitats in peace while moving from one liana to another like Tarzan and Jane? To be continued…
Read the full study: Albani A., Cutini M., Germani L., Riley E. P., Oka Ngakan P. and Carosi M. (2020) Activity budget, home range, and habitat use of moor macaques (Macaca maura) in the karst forest of South Sulawesi, Indonesia. Primates 61, 673–684 (https://doi.org/10.1007/s10329-020-00811-8).
This post is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.Corals and algae, a relationship in danger: a model to predict their future! by Clara Dignan, Anna Gago and Anabelle Leblond
Published by the March 2, 2020 on 2:14 PM
Bleached branching coral (foreground) and normal branching coral (background). Keppel Islands, Great Barrier ReefCorals that come together to form coral reefs are shelter to 25% of our planet's marine life according to the WWF. This biodiversity is fundamental. It’s both a source of income and food, and it provides irreplaceable services to humanity. But today coral reefs are in danger. They are directly threatened by global warming. In forty years, 40% of the reefs have already disappeared and scientists agree that if nothing is done by 2050, all of them will be gone (Coral guardian).
Coral polyps and algae, an endosymbiotic relationship
Coral bleaching has now become a major global concern for the future of coral reefs. Temperature rise appears to be one of the main causes of bleaching, affecting growth, feeding and other ecological processes on reefs. This bleaching phenomenon is due to the expulsion of zooxanthellae, the symbiotic microalgae living in the tissues of the polyps (the coral is made up of a colony of polyps that participate in the making of its skeleton). These unicellular algae carry out photosynthesis and provide, for the most part, the energy that corals need to develop and grow. Exchanges between the polyp and the zooxanthellae mainly concern nitrogen, phosphorus, carbon and biosynthetic intermediates. The presence of zooxanthellae being responsible for the color of the colonies, bleaching is therefore the symptom of a coral which is no longer in symbiosis, which generally results in the death of the coral.
The coral-symbiont relationship and its interaction with the overlying water column.Prediction models
Since few year, scientists analyze corals and try to predict their bleaching evolution. In this aim, a collaboration between several organizations such as CSIRO have set up a first hydrodynamic, sedimentary and biogeochemical model called: « eReef ». This model simulates the environmental conditions as the temperature, the background light and the organic nutrient concentration of the Great Barrier Reef at several scales. It allows accurate prediction of factors influencing coral processes from satellite remote sensing images.
However, for more representative modelling, it is necessary to apply models that take into account the coral-symbiont relationship and the stress related to environmental variations. In this framework, Baird et al. have developed a model which, in parallel to the environmental conditions obtained from the « eReef » model, also takes into account essential parameters in the symbiotic process such as biomass and growth rate of zooxanthellae, pigment concentration, nutritional status as well as tolerance characteristics such as sensitivity to reactive oxygen concentration (oxidative stress).
The eReefs coupled hydrodynamic, sediment, optical, biogeochemical model. Orange labels represent components that either scatter or absorb light levels. (For a better understanding of the colour used and the abbreviations, the reader is referred to the web version of the article)Take home message
This coral bleaching model applied under realistic environmental conditions has the potential to generate more detailed predictions than satellite coral bleaching measurements. In addition to predicting coral bleaching, this model will now make it possible to evaluate management strategies, such as the introduction of temperature-tolerant individuals or species or localized shading.
Nevertheless, this model is still too simplistic to make real predictions. It is based only on the process of a single type of coral and macro-algae and does not take into account all phenomena related to bleaching. It is therefore seen as a step forward for science that could allow for future reevaluations of the effects of bleaching.
Bibliography
Why should we think about cougars when planning our cities?by Amaïa Lamarins and Gautier Magné
Published by the February 3, 2020 on 2:02 PM
A puma family above the nighttime lights of San Jose - National Geographic - (photo courtesy of Chris Fust)Humans have modified 75% of earth land surface which has important consequences on wildlife. In fact, human presence and activities are perceived as a threat by animals which adapt their behaviors to avoid it. Gaynor and his collaborators’ meta-analysis showed that many species are modifying their daily activities and identified 117 diurnal mammals becoming more and more active at night. Consequently, these animals face constrained access to resources and are susceptible to shifting their diet to nocturnal prey. Thus, anthropic activities influence growth, breeding, survival and community interactions of wild animals.
Shift in rhythmic activity of diurnal species due to human disturbance - Ana Benítez-López.In southern California, the habitat of cougars, an apex nocturnal predator, is reduced by the expansion of cities. No, we’re not talking about the rampant nightclub predators (whose habitats remain undisturbed), we’re talking about mountain lions! You’ve probably already heard about pumas roaming across big cities like Santa Cruz, California. They likely are not curious tourists hoping to take in the sites, but are rather disturbed by human activities, which cause their nighttime activity to be higher in developed areas than in natural ones. This shift increases their daily energy expenditure: because of humans, pumas need to eat around 160-190 kg of additional meat per year (for females and males, respectively)! Are there sufficient deer populations to meet these needs? Unfortunately, it seems not, since a significant number of puma attacks on cattle have been recorded.
These results, showing human-induced behavioral change for pumas, come from a recent study published by members of the Santa Cruz puma project. By wide-scale monitoring of 22 wild pumas, they were able to link their behavior with their subsequent energetic expenditures: pumas’ behavior and movement were measured through spatial GPS location data, recorded every 15min, and energetic cost of movement was estimated considering their weight and travel velocity. An interesting methodological point to note: in order to avoid underestimating the energy expenditures via GPS tracking, scientists calibrated their estimations using accelerometers. Thanks to these methods they figured out the effect of housing densities on pumas’ activity and energetic costs, taking into consideration the time of day and sex of the animal.
Indeed, they were right in taking into account these factors because, according to their findings, response to human activities differs between day and night and between males and females. During the day pumas are more likely to stay inactive, especially near urban areas. At night, being close to houses increases time spent active by 8.8% and 5.8%, respectively, for males and females. Consequently, estimated daily caloric expenditure increases by 11.6% for males and 10.1% for females in high housing density areas. Below you will find an outline summarizing these results:
Urban development negatively affects pumas by increasing nighttime activity and energy expenditure.Such studies underline the role of bioenergetics to estimate the costs of human-induced behavioral changes but do not provide insight on global energetic allocation. Further work is needed to understand the consequences of energetic balance disturbances and identify which individual functions are affected (growth, maintenance, maturation or reproduction). Besides, human impact could be underestimated because such tracking doesn’t allow us to know if pumas get all available energy from their prey near humans; some observations reported they often have to leave their prey because they fear humans. This partial feeding would constrain pumas to hunt more prey!
Unfortunately, this is not the only human-induced threat affecting pumas. In the region of Santa Cruz and southern California, they are targeted by ranchers, resulting in political tension about their conservation. In fact, cougars have been protected since 1990. However, 98 pumas are killed each year due to depredation hunting permits. It appears necessary to ensure coexistence between urban development, human activities, puma populations and their prey. In a recent study, development strategies are suggested, such as rural residence development, to ensure landscape connectivity and conservation of parcels where pumas have been geo-located. Nowadays, no cities are expanding regarding puma, deer or other wild animals’ living areas (to our modest knowledge!). The only measures taken when pumas are too close to urban zones consist in doing nothing or frightening or relocating it, and in the worst case killing it. And if designing our lives and activities regarding nature and wildlife was the challenge of tomorrow, would you be ready?
Ideal residential development maintaining pumas landscape connectivity. Graphical abstract of the paper of Smith and al 2019
This post is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.What does the future has in store for red salmon in a context of global climate change?by Camille Sestac and Amandine Tauzin
Published by the November 1, 2019 on 1:18 PM
Pacific salmon have extremely complex life histories and may be threatened by global climate change, as Peter S. Rand and colleagues investigate in their recent study.
Life cycle of Sockeye SalmonAmong all species, fishes must adapt to face disruptions caused by global climate change. Sockeye salmon (Oncorhyncus nerka), an anadromous species of salmon found in the Northern Pacific Ocean and rivers discharging into it, has a complex life cycle. As a migratory species, their energetic demands are high during spawning migration. Climate change might have important impacts on populations and their migration via variation of river discharge, increase of water temperature and decline of growth conditions. Aiming to better understand the impacts of these disruptions on the migratory performance of this species of salmon, Peter S. Rand from Wild Salmon Center teamed up with researchers from British Columbia. Their goal is to evaluate the effects of past and future trends in river discharge and temperature on the migratory performance of Sockeye Salmon in the Fraser River.
In a context of global climate change, it is crucial to understand the effects of disruptions on ecosystems and the populations living in them. Indeed, it is important to know the impacts of these disruptions on every stage of their life cycle (the juvenile freshwater period, the estuarine period, and the subadult marine period) so that we can maintain the populations stock. It’s especially important for fishery management because the fishing quota has greatly increased over the last decades and has threatened populations of Pacific salmon, particularly during their spawning migration. That’s why with three main objectives, these scientists used analysis to improve the understanding of how changes in river conditions can affect the energy use and the mortality rate in Sockeye salmon population. To do so, they used several models: one to search a link between energetic conditions of individuals and en route mortality, one to simulate the energy use during spawning migration and one to hindcast and forecast energy use by simulating fish’s behaviour and migration conditions (for more information, a tip, read the article!).
Long-range forecasts of lower Fraser river temperature during the summer of 2018Using these friendly models, Rand and his colleagues proved that energy reserves and energy depletion of early Stuart Sockeye salmon are major factors that can affect their ability to reach their spawning grounds. They also stated that energy depletion is a function of both river temperature and discharge. Therefore, this population is structured by condition-dependant mortality. Nevertheless, this group of researchers brought to light a mechanism that allows fishes to cope with some environmental variability, providing a certain degree of resilience over time. Therefore, even if energetic demands and migration mortality increase as a result of exposure to warmer temperatures, it will be compensated by reduced time travel to the spawning ground as the river flow will be lower.
However, increase of temperature means increase of diseases appearing and developing and that stress added may be a direct cause of increased mortality during migration. Finally, as if it wasn’t already bad enough for our salmons, ocean productivity can be affected by climate change and thus affect their river migration success. In fact, this can lead to a decrease of body size and body energy content. It implies that individuals will start their migration with lower energy densities and will be more likely to exhaust their energy stock before even reaching the spawning grounds.
Salmon jumping over a weirAccording to the US-Canada Commission, a 21° C temperature spike was measured on the Fraser River in 2009. However, sockeye salmon show signs of physiological stress and migratory difficulties above 19°C and from 20°C, the first signs of illness and death appear. But migration of Sockeye salmon is not only threatened by climate change. In fact, migration of salmon specially is impacted by humans or natural obstacles. Dams and weirs form large obstacles for this migratory species and can be very difficult to cross. Many studies have already proved that this kind of obstacles, even when equipped with crossing devices, delay their migration and thus jeopardize their reproduction. This can lead to a decline of the population and in some cases to its extinction, as it happened in Belgium.So, whilst some questions have been answered, it seems that more studies need to be carried out to improve our knowledge about the impact of global change which seems to be another sword of Damocles hanging over the head of Sockeye salmon.
Cited paper: Rand, P.S. et al. (2011) Effects of River Discharge, Temperature, and Future Climates on Energetics and Mortality of Adult Migrating Fraser River Sockeye Salmon. Trans. Am. Fish. Soc. 135(3), 655-667. https://doi.org/10.1577/T05-023.1
Featured images: Life cycle of Sockeye salmon by Camille Sestac, graph from https://www.pac.dfo-mpo.gc.ca/science/habitat/frw-rfo/index-eng.html , Sockeye Salmon from www.ryanvolberg.com
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Organisms and their environment: Dangerous liaisonsby Marius Dhamelincourt and Charlie Sarran
Published by the October 14, 2019 on 9:15 AM
Preface
Whatever the incredulous think, organisms are necessarily linked to their environment to survive, science says. However, this relation, unstable, can be problematic for those concerned when variations overtake their acceptable thresholds. Although often natural, these variations can be exacerbated by anthropogenic actions, like putting fish on a grill.
Global changes are often reduced to temperature increases, illustrated in the media with alarming news about ice melting and forest fires. While many people thus omit the complex mechanisms behind this black box, the necessity of a more “polar bear’s” respectful way of life is commonly accepted. In order to better understand how to respect such adorable creatures, scientists need to investigate their relationships with the environment.
Chapter 1: Shells under investigation
In order to scrutinize these relationships, selected species must be accessible, easy to catch/manipulate and in sufficient number. For instance, the study of the great white shark aggressivity over humans would require too many intern’s sacrifices. In response to this challenge, a valiant research team from Germany looked for the importance of these relations by studying in the Rhine a remarkable (body and soul), accessible, cheap and lovely species: Corbicula fluminea, a shell. This study is related to the mass mortalities events of this species, which occurred in the summer, especially in that of 2003. Their investigations aim to understand how these organisms are linked with their environment, and their reactions to changes.
Chapter 2: Shells cooking in science
Corbicula fluminea shellsMany tools exist to perform this type of search. Field searches can involve the scientist’s life (be bitten by a pigeon is a terrible experience…) and obstruct a long-term individual experiment. Now that researchers have selected the perfect organism, they must choose an appropriate way to analyse their problem. For this shell, scientists chose to use a modelling approach, a method dark and full of terrors. More precisely, they modelled several aspects of the metabolism of this organism at different scales: individual and population levels, using respectively DEBM (Dynamic Energy Budget Model) and PSPM (Physiologically Structured Population Model). This method, widespread in ecology, consists to “simulate the annual growth in length and mass and the reproductive success under different environmental scenarios”. This approach is suitable because an organism can respond differently relatively to their peers. Such fact can be proved by looking at many places and species, humans included… Ultimately, scientists aim to better understand the complex relation between the energy available in the environment and its utilization by shells.
Chapter 3: Corbicula’s deadly summers
Heat waves are often responsible for changes that every scientist can observe on living organisms. For instance, it is known that coral reefs are affected by increased temperatures, as shown in an article published in “Free Radical Biology and Medicine”. Many other examples such as lobster’s behavioural response to boiling water could be developed. Regarding our shellfish, scientists found an interesting pattern comforting our previous remark: temperature causes shell’s mortalities… Oh wait, no, it’s more complicated.
In fact, mass mortalities events were probably related to a melting pot of many events like temperature increases and/or starvation. Moreover, these situations are also in relation with individual conditions. Indeed, researchers hypothesized that a combination of factors (biotic and/or abiotic), usually non-lethal under regular summers, can be problematic at high temperatures. Unfortunately, models developed were not able to explain completely the observed mass lethal events.
Chapter 4: Life is not so simple
Researchers finally enhance the comprehension of population dynamics, enlightening its complex mechanisms. However, in such cases, wishing to be exhaustive is useless and unproductive, like politics. That is why scientists look for compromise between easy-to-use and complicated (highly realistic) tools. For example, the authors of the Corbicula’s study proposed that it could be interesting to test other parameters, such as parasitism.
To put it in a nutshell (you got it, right?), things are not always what they seem to be, even in environmental studies. Main hypotheses are not always validated, and measures considered can be only a part of a more complex system, or sometimes even unappropriated. On the flip side, model’s development can help to understand the life cycle of organisms like Corbicula, thus helping to manage populations concerned.
This post is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.A damned energy loss for migratory fishes: dams!by Manon Salerno
Published by the June 10, 2019 on 9:42 AM
Many species of fish grow in the sea and breed in rivers. These migratory fish are called anadromous. When a migratory fish is ready to breed, it leaves the sea and up a river to lay watershed upstream. It will find the optimum conditions to reproduce and allow the development of its offspring. But to do so, they spend a lot of energy on the upstream and sometimes, obstacles like dams in their path does not make it easy for them. This is the case of American Shad in the Connecticut River in the United States. Since the 1970s, 4 hydroelectric dams have been built in the river. Even if they are equipped with fish ladders, these obstacles require the Shad more energy to cross them than if they were not present. We know energy availability can be a limiting factor in migration. Thus, in 1999, scientists wanted to understand energy management in these fish, especially when it is modified by the presence of such.
Any organism needs energy to perform the movements / migrations necessary for its life cycle. When they are heading into a period that will not allow them to feed (overwintering, migration), some species store energy, such as the bear before hibernating. For American Shad, this stock has to be created before migration because it will not feed during this move. First, scientists have found these are subcutaneous lipid reserves and skin constitute a special tissue for energy storage, which is rather unusual. Salmon, for example, usually mobilizes lipids from muscles and viscera. In contrast, for migration, somatic tissues (red and white muscles and skin) provide about 90% of the energy required in shad.
Although fish ladders are quite efficient at the upstream for the American Shad, it is sometimes not suitable for other species. In addition, the outmigration can also present risks of mortality (water retention, drop height etc ...). It is therefore essential to remove the dams for which their function is not provided anymore. But in the United States, the erasure of small dams often meets opposition from local communities. Even though many dams have been removed, they represent a strong historical or landscape value for the inhabitants, creating tensions between the supporters of the restoration and the local communities. This situation reminds the context existing in France, where the aesthetic and historical arguments are very powerful. Many dams are attached to mills and water plants of olden times are therefore seen as a "living historical landscape" very characteristic of their landscape. Because of the local character of each operation, an opposition not necessarily collective but influential and well directed, is enough to block some sites.
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.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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