Complex dynamics near extinction in a predator-prey model with ratio dependence and Holling type III functional response

In this paper, we analyze a recently proposed predator-prey model with ratio dependence and Holling type III functional response, with particular emphasis on the dynamics close to extinction. By using Briot-Bouquet transformation we transform the model into a system, where the extinction steady state is represented by up to three distinct steady states, whose existence is determined by the values of appropriate Lambert W functions. We investigate how stability of extinction and coexistence steady states is affected by the rate of predation, predator fecundity, and the parameter characterizing the strength of functional response. The results suggest that the extinction steady state can be stable for sufficiently high predation rate and for sufficiently small predator fecundity. Moreover, in certain parameter regimes, a stable extinction steady state can coexist with a stable prey-only equilibrium or with a stable coexistence equilibrium, and it is rather the initial conditions that determine whether prey and predator populations will be maintained at some steady level, or both of them will become extinct. Another possibility is for coexistence steady state to be unstable, in which case sustained periodic oscillations around it are observed. Numerical simulations are performed to illustrate the behavior for all dynamical regimes, and in each case a corresponding phase plane of the transformed system is presented to show a correspondence with stable and unstable extinction steady state

The Influence of Mosquito Predators on Population Dynamics of Endemic and Exotic Mosquitoes

The presence of predators can shape the population dynamics of prey. Here, I evaluated the influence of predators on mosquito populations by direct effects through predation, and indirect effects through sub-lethal responses. The predator under investigation was the backswimmer Anisops wakefieldi. I first quantified the relationship between mosquito and predator populations in animal drinking water troughs, and correlated their abundance with water volume and environmental factors. Logistic regression indicated that the presence of mosquitoes was primarily affected by three factors; predator numbers, week of observation, and water volume. A translocation experiment was established to understand the pre- and post-treatment effects on mosquito survival after exposure to the predator Anisops wakefieldi. The presence of these predators in water troughs significantly decreased subsequent survival of mosquito prey within two days posttranslocation. A major hypothesis in invasion ecology suggests that native predators have less impact on exotic species relative to native prey species, enabling exotic species to establish and thrive in novel environments. This is the "escape from natural enemies" hypothesis. Contrary to this hypothesis A. wakefieldi, a native New Zealand predator, showed a greater preference, and consumed more of the exotic mosquito Aedes (Ochleratatus) notoscriptus compared to the native (Culex pervigilans) mosquito larvae. Anisops wakefieldi exhibited a decelerating Type II functional response for both prey species, but consumed more exotic mosquito species at high prey densities and displayed higher attack rates. The effects of the preference of this predator on mosquito behaviour were examined. In the presence of predators the exotic species, Ae. notoscriptus, demonstrated significantly higher levels of "thrashing" behaviours, apparently making itself more obvious to the predators. In contrast Cx. pervigilans fulfilled the "threat sensitivity" hypothesis by altering its behaviour towards "resting", known to be the best strategy for avoiding predators. In addition to lethal effects, predators can substantially alter prey populations by means of sub-lethal influences. To further our understanding of how predators limit mosquito abundance, I developed an experiment based on adult mosquito oviposition. I predicted that the New Zealand native mosquito, Cx. pervigilans would likely avoid containers with A. wakefieldi or their kairomones. Contrary to our predictions, Cx. pervigilans appeared to ignore the presence of predators and their kairomones when choosing oviposition habitats and the number of egg rafts was not significantly affected by the density of predators. Culex pervigilans eggs from the oviposition experiment were reared in two different laboratory conditions: (A) in clean water without any traces of predators, or (B) in water with the same treatments as in field. This experiment was established in order to have better understand on what happens to the next generation after exposure to A. wakefieldi predators or their kairomones. Sub-lethal effects were still apparent in the developing larvae. I observed a significant reduction in the survival rate of Cx. pervigilans in the presence of predators and their kairomones, even when the eggs were only exposed briefly to water containing either predators or kairomones in the field, and were then reared in clean water without any traces of the predator. No effect was observed on the sex ratio of Cx. pervigilans, or the development times of each life stage. Overall, this thesis has highlighted the importance of predators in influencing mosquito populations, not only through direct predation, but also in indirect and sub-lethal ways. This study may have implications for the dynamics of other predator-prey systems. Despite this, we are only beginning to understand the complex interactions between predators and prey

Spatially explicit models for interacting populations in a changing landscape: A case study on Namibian dragonflies (Odonata)

In arid regions like the ephemeral river catchments of western Namibia the population dynamics of dragonflies is strongly influenced by the dynamic of drying and re-flooding of the habitats. Global climate change and shortage of water as a resource will deteriorate the life conditions for dragonflies. To draw conclusions about the influences of the landscape on the biodiversity of dragonflies, the present thesis shows the development and application of a spatially explicit population dynamic model for Odonata in changing landscapes. The model consists of four parts. In the first submodel habitat suitability models are introduced, which describe the presence of the species in dependency of habitat parameters. The second model is a population dynamic model at the base of Leslie matrices. The matrix parameters are mainly determined by food supply in the habitat. This enables the model to depict inter- and intraspecific competition effects. With this model the importance of colonisation sequences at the habitat is being analysed. The third submodel describes the implementation of theoretical and real landscapes by means of a grid based approach (= cellular automaton). Effects of landscape dynamics on the development of the species’ populations are shown by the use of landscape metrics. The fourth submodel deals with the rules for the dispersal of different ecological types of Namibian dragonflies. All four submodels are integrated into the spatially explicit dispersal model. The effects of the scenarios on the modelled species communities are discussed. The model has shown amongst others that permanent habitats with a well-developed vegetation structure are of great importance for the less mobile resident species as a kind of refuge. The results of the model showed a good accordance with actual monitoring data for the modelled speciesIn ariden Gebieten wie beispielsweise in den ephemeren Flusseinzugsgebieten West-Namibias wird die Populationsdynamik von Libellen stark von der Dynamik des Austrocknens und Wiederbefeuchtens der Habitate geprägt. Globaler Klimawandel und Verknappung der Ressource Wasser werden die Lebensbedingungen für Libellen weiterhin verschlechtern. Um Aussagen über die Einflüsse der landschaftsökologischen Rahmenbedingungen auf die Biodiversität der Libellen zu treffen, wird in der vorliegenden Arbeit ein räumlich explizites Modell zur Populationsdynamik von Libellen in sich verändernden Landschaften entwickelt und angewendet. Das Modell besteht aus vier Teilmodellen. Im ersten Teil werden Habitateignungsmodelle, die das Vorkommen der Arten in Abhängigkeit von Habitatparametern beschreiben, vorgestellt. Das zweite Teilmodell ist ein populationsdynamisches Modell auf Basis von Leslie-Matrizen. Die Matrixparameter werden im Wesentlichen durch Nahrungsverfügbarkeit im Habitat bestimmt, wodurch inter- und intraspezifische Konkurrenzeffekte abgebildet werden. Mit diesem Modell wird die Bedeutung der Besiedlungsreihenfolge der Gewässer analysiert. Das dritte Teilmodell beschreibt die Implementierung von theoretischen und realen Landschaften in einem rasterbasierten Ansatz (=zellulärer Automat). Auswirkungen der Landschaftsdynamik auf die Populationsentwicklung der Arten werden mit „landscape metrics“ aufgezeigt. Das vierte Teilmodell beschreibt Ausbreitungsregeln verschiedener ökologischer Typen von Libellen in Namibia. Alle vier Teilmodelle werden in das Gesamtmodell integriert. Die Auswirkungen der Szenarien auf die modellierten Artengemeinschaften werden diskutiert. Es konnte unter anderem gezeigt werden, dass Gewässer mit einer gut entwickelten Vegetationsstruktur für die weniger mobilen residenten Arten als wichtige Rückzugshabitate von großer Bedeutung sind. Der Vergleich der Modellergebnisse mit Monitoring-Daten zeigte gute Übereinstimmungen für die modellierten Arten

Behavioural ecology of the Redbilled Woodhoopoe Phoeniculus purpureus in South Africa

Includes bibliographies.A study was made of two Redbilled (Green) Woodhoopoe Phoeniculus purpureus populations spanning an eight year period (1981-1988) and 258 'flock-years', in the eastern Cape Province of South Mrica. The main objectives of the study were to investigate (1) why woodhoopoes live in groups; (2) why nonbreeders do not breed; and, (3) why nonbreeders provision young that are not their own? Ecological and demographic data were gathered in addition to detailed behavioural observations of 54 woodhoopoe flocks. The following experimental manipulations were performed: (1) breeders were removed from flocks to (a) monitor dispersal patterns and restructuring of flocks; and, (b) observe behavioural reactions by remaining birds; (2) cavity availability was (a) decreased, to enable quantification of availability; and, (b) increased, by addition of nest/roost boxes to an area which supported no permanent woodhoopoe territories; and, (3) stimuli, associated with the food provisioning response of adult birds, were manipulated to investigate the evolutionary basis of allofeeding behaviour Variability in social and reproductive behaviour reflects environmental selection pressures, in the form of roost-cavity availability, with a reduction in cavity availability leading to increased group size. The group-territorial social system and high level of inbreeding of Redbilled Woodhoopoes have evolved primarily in response to environmental constraints on dispersal, rather than by particular benefits that arise from group living. Therefore, the habitat-saturation hypothesis best explains group living of woodhoopoes. Behavioural dominance hierarchies ensure that dominance relationships are well-defined among potential competitors (for breeding status), and thereby minimize disruption to flock cohesion upon the death (or removal) of a breeder. If competition for a breeding vacancy arose at the time of the breeder's death, the resultant delay in occupancy of the breeding vacancy would increase the likelihood of competition from unrelated birds. The establishment of such hierarchies is therefore adaptive in the context of the direct component of kin selection. The presence of nonbreeding helpers do not increase fledgling success, breeding frequency, survivorship (of any age, sex or social class), or number of breeder-offspring produced. Because no unambiguous indirect fitness benefits could be shown to result from helping behaviour (specifically allofeeding), I propose that the unselected (misdirected parental care) hypothesis is a viable alternative to the 'functional hypotheses.' This hypothesis is supported by observations/manipulations of misdirected food provisioning by both breeders and helpers

Behavioural consistency and foraging specialisations in the Australasian gannet (Morus serrator)

This study reports behavioural consistency in Australian gannets, and give insights about its potential drivers. It contributes with the understanding of resource partitioning among individuals, crucial information for the conservation of this species. Also, it reveals ecological opportunity as a major component for foraging specialisations development in wildlife populations

Dynamical Systems

Complex systems are pervasive in many areas of science integrated in our daily lives. Examples include financial markets, highway transportation networks, telecommunication networks, world and country economies, social networks, immunological systems, living organisms, computational systems and electrical and mechanical structures. Complex systems are often composed of a large number of interconnected and interacting entities, exhibiting much richer global scale dynamics than the properties and behavior of individual entities. Complex systems are studied in many areas of natural sciences, social sciences, engineering and mathematical sciences. This special issue therefore intends to contribute towards the dissemination of the multifaceted concepts in accepted use by the scientific community. We hope readers enjoy this pertinent selection of papers which represents relevant examples of the state of the art in present day research. [...

The effect of pond dyes on mosquitoes and other freshwater invertebrates

Freshwater habitats are important because they represent two percent of Earth’s water resources, are highly diverse in aquatic organisms and are the most productive and threatened ecosystem worldwide. Pollution, urbanization and climatic changes are responsible for drastic changes in these ecosystems. The creation of new ponds offers an opportunity to increase biodiversity, landscape connectivity and provide new habitat for organisms. However, new ponds might be a good habitat for mosquitoes to lay eggs. Mosquitoes have worldwide distribution and are responsible for most of the vector-borne diseases, affecting thousands of people and causing millions of deaths. British mosquitoes currently do not carry human diseases, but they are a biting nuisance. Their distribution, abundance, species composition and potential for mosquito disease transmission are intimately linked to the physical environment. Culex pipiens is commonly found in UK gardens and is a potential vector of viruses including the West Nile Virus. However, any environmental factors that significantly change the distribution and population of Cx. pipiens could impact future risks of disease transmission. Pond dyes are a cosmetic product for garden ponds and lakes; they inhibit algal growth and improve the overall appearance of the water body reflecting surrounding planting. The dyes block red light from entering the water, interrupting the process of photosynthesis and therefore inhibiting the growth of certain aquatic plants such as algae. Although these dyes are non-toxic to fish and invertebrates, their use in urban gardens raises questions linked to mosquito oviposition, since coloured water can be an attractant