Polyphagy is a very common trait among insects. In this study, we focus on a generalist bark-beetle predator, Thanasimus formicarius (L.) (Coleoptera, Cleridae), which feeds on many scolytids in spruce, pine and broad-leaf stands. It is known to respond to the pheromones of many scolytids, among which the most harmful spruce bark beetle in Europe, Ips typographus (L.). The adults attack scolytid adults and oviposit on attacked trees where their larvae feed upon immature stages of the prey. However, a bottom-up process limits Thanasimus formicarius’ impact on spruce bark beetles, because in most cases the bark of spruce is too thin for sheltering pupal niches and mature larvae have to leave the trees. On pine however, pupation is quite successful and reproductive success is high. The present work estimates the advantages (complementary prey during gaps among the phenology of pine bark beetles or due to the population fluctuations of most scolytids) and constraints (landing on unsuitable host trees for the predator’s reproduction) for T. formicarius to have a wide range of prey. Passive barrier-trappings showed that the presence and abundance of scolytid species vary strongly from year to year. So, polyphagy in T. formicarius appears as a response to fluctuating prey supplies. This way of foraging may lead T. formicarius towards stands not always favourable for its development (for example, spruces). At the tree level, funnels and pitfall-traps caught high numbers of third-instar T. formicarius larvae walking on the bark surface of standing spruces infested by Ips typographus (respectively 365 and 70 L3s). After feeding into the whole infested part of the trunk, these larvae are obliged to migrate outside of the galleries to favourable pupation site (e.g. the base of the trees where the bark is thicker), or even to leave the trees and search for an acceptable pupation substrate in the litter. At the landscape level, different trapping experiments showed a correlation between catches of T. formicarius and the proportion of pines around each trap. Consequently, in a metapopulation landscape pattern, pines would act as “sources” of predators, whilst spruces are “sinks”. Indeed, Thanasimus formicarius are trapped in higher numbers in mixed stands comprising pines. This observation is also corroborated in a four-year trapping experiment in the North-East of France, following the storms of December 1999. The predator/prey ratios (T. formicarius/I. typographus) were higher in stands comprising pines than in stands without pines. The first step of a method to estimate Ips typographus infestation trends thanks to the predator/prey ratios was also developed.

Microtine rodents are a key component in the boreal ecosystem. Due to unique yearly fluctuation in population numbers, in addition to their central placement within boreal foodwebs, microtine rodent population dynamics control a wide variety of predator populations. Despite their grouping as microtine rodents, many individual species exhibit very different cycles, such as voles and lemmings. As such, the identification of species composition and ratio in each given habitat is of utmost importance. The purpose of this study was to compare the composition of species of small rodents between four different habitats (grassland, wetland, spruce dominated forest and pine dominated forest) and to statistically analyze if the different biotopes hosted significant differences in species composition. The project also aimed to examine differences in weight and numbers between populations of the same species in the different biotopes. To accomplish this, rodents were captured using non-lethal traps, and the resulting data was analyzed using RxC tables and ANOVA. The species captured were A. sylvaticus, C. glareolus and M. agrestis. The result of the analysis showed that the only difference in species composition existed between the grassland habitat and the rest. In addition, there existed no difference between different populations of A. sylvaticus in regards to weight. However, a difference was found between the populations of C.glareolus, with the individuals inhabiting spruce dominated forest being larger than those found in other habitats.

When ovipositing, prey organisms avoid habitat patches containing predator cues because predators consume, and negatively affect the fitness of their prey. Richness of predator species often enhances the strength of consumptive predator effects, but little is known about how multiple predators combined affect prey non-consumptively. We quantified dipteran colonization in aquatic mesocosms in response to varied predator richness. Multiple predator species combined reduced oviposition by Culex mosquitoes, chironomid midges, and the general colonizing dipteran community more than predicted by the effects of the independent predator species. Previous research which quantifies effects of multiple predators on prey as prey abundance, but does not measure consumption by predators, may be underestimating or overestimating the strength of effect by assuming equal colonization. Our findings enhance understanding of the ways predators influence abundances and distributions of their prey, and yields insight into the ways predators may non-consumptively affect prey by changing prey behavior.

Because differences often exist between species in their tolerances to environmental conditions, locations characterized by extreme parameter values (i.e., high temperature, low DO, high turbidity) may provide refuges from predation or competition by altering the outcome of inter-species interactions. This thesis examined the effects and relative importance of water temperature, dissolved oxygen (DO) and turbidity on habitat use by fish species and resulting changes in community composition. The effects of abiotic factors on predator-prey interactions were tested using field surveys, laboratory experiments, field experiments and computer modeling. Field surveys were conducted in Blind Channel, Delta Marsh, Manitoba, and on Lake Winnipeg, Manitoba, to determine if small bodied forage species preferentially used high temperature, low DO or high turbidity habitats and whether predator species avoided these locations. Prey species were more abundant in these extreme locations at both small (Blind Channel) and large (Lake Winnipeg) spatial scales, but predator avoidance was only documented in Blind Channel. The tolerances of fish species to moderate hypoxia (< 3 mg/L DO) was tested in the laboratory to verify that differences did exist among species and that the observed species distributions were not solely the effect of temperature. To quantify the potential for moderately hypoxic locations to provide a refuge from predation for small fish, a field manipulation was conducted in Blind Channel; hypoxic habitats were created without altering water temperature, decoupling the natural covariation between these two factors that occurs in aquatic systems. The abundance of small forage fish was higher in the hypoxic locations compared to controls and while predators still visited the hypoxic habitats, their mean visit duration was reduced from around 300 min to less than 1 min. An individual based computer model was used to test and illustrate current understanding of the relative importance of temperature, DO and turbidity on predator habitat selection decisions and fish community composition. The model showed that DO had a stronger effect on community composition than temperature, and that reduced foraging success from high turbidity was able to overpower the other two factors. Hypoxia affects habitat selection decisions by fish species and can provide refuges from predation and competition, helping maintain higher species diversity. Water temperature appears to have a weaker effect on fish distributions than DO while turbidity primarily affects visual predators, though the strength of turbidity effects depends on the magnitude and duration of individual events. / February 2008

Even zooplankton can not be utilized directly by human being; it is an important food source for numerous economical fishes. Zooplankton¡¦s predator-prey interactions can affect not only global carbon fixation, but also fisheries yields directly. Copepods and ciliates are the targets of the current study, which act as critical links between classical diatom-copepod-fish webs and microbial food webs. Analyzing their predator-prey interactions can help us understand more about marine food production. The objective of this study is to investigate the differences in swimming behavior of copepods and ciliates under two environments, which are disturbances and no disturbances of predator-prey. We use five locomotive indicators (NGDR, turning rate, diffusion coefficient, kinetic energy and fractal dimension) to quantify swimming patterns. The trajectories of copepods in the undisturbed situation show circuitous, larger turning angle, and more diffusive behavior, which associate with a lower kinetic energy. The patterns of copepod movement with the presence of prey (ciliates) are contrary to the previous situation. The patterns of ciliates in the undisturbed situation are similar to those of copepods in undisturbed situation, except smaller turning angles. The trajectories of ciliates in terms of the turning and diffusive movement when predators (copepods) show up are different from those of copepods when preys (ciliates) are present. In addition to indicators, this study develops a new encoding scheme for accommodating the spatial-temporal information embedded in the original data. By analyzing the encoded data through some data mining techniques, the predator-prey interactive behaviors in the spatial scale can be easily perceived.

Because differences often exist between species in their tolerances to environmental conditions, locations characterized by extreme parameter values (i.e., high temperature, low DO, high turbidity) may provide refuges from predation or competition by altering the outcome of inter-species interactions. This thesis examined the effects and relative importance of water temperature, dissolved oxygen (DO) and turbidity on habitat use by fish species and resulting changes in community composition. The effects of abiotic factors on predator-prey interactions were tested using field surveys, laboratory experiments, field experiments and computer modeling. Field surveys were conducted in Blind Channel, Delta Marsh, Manitoba, and on Lake Winnipeg, Manitoba, to determine if small bodied forage species preferentially used high temperature, low DO or high turbidity habitats and whether predator species avoided these locations. Prey species were more abundant in these extreme locations at both small (Blind Channel) and large (Lake Winnipeg) spatial scales, but predator avoidance was only documented in Blind Channel. The tolerances of fish species to moderate hypoxia (< 3 mg/L DO) was tested in the laboratory to verify that differences did exist among species and that the observed species distributions were not solely the effect of temperature. To quantify the potential for moderately hypoxic locations to provide a refuge from predation for small fish, a field manipulation was conducted in Blind Channel; hypoxic habitats were created without altering water temperature, decoupling the natural covariation between these two factors that occurs in aquatic systems. The abundance of small forage fish was higher in the hypoxic locations compared to controls and while predators still visited the hypoxic habitats, their mean visit duration was reduced from around 300 min to less than 1 min. An individual based computer model was used to test and illustrate current understanding of the relative importance of temperature, DO and turbidity on predator habitat selection decisions and fish community composition. The model showed that DO had a stronger effect on community composition than temperature, and that reduced foraging success from high turbidity was able to overpower the other two factors. Hypoxia affects habitat selection decisions by fish species and can provide refuges from predation and competition, helping maintain higher species diversity. Water temperature appears to have a weaker effect on fish distributions than DO while turbidity primarily affects visual predators, though the strength of turbidity effects depends on the magnitude and duration of individual events.

Because differences often exist between species in their tolerances to environmental conditions, locations characterized by extreme parameter values (i.e., high temperature, low DO, high turbidity) may provide refuges from predation or competition by altering the outcome of inter-species interactions. This thesis examined the effects and relative importance of water temperature, dissolved oxygen (DO) and turbidity on habitat use by fish species and resulting changes in community composition. The effects of abiotic factors on predator-prey interactions were tested using field surveys, laboratory experiments, field experiments and computer modeling. Field surveys were conducted in Blind Channel, Delta Marsh, Manitoba, and on Lake Winnipeg, Manitoba, to determine if small bodied forage species preferentially used high temperature, low DO or high turbidity habitats and whether predator species avoided these locations. Prey species were more abundant in these extreme locations at both small (Blind Channel) and large (Lake Winnipeg) spatial scales, but predator avoidance was only documented in Blind Channel. The tolerances of fish species to moderate hypoxia (< 3 mg/L DO) was tested in the laboratory to verify that differences did exist among species and that the observed species distributions were not solely the effect of temperature. To quantify the potential for moderately hypoxic locations to provide a refuge from predation for small fish, a field manipulation was conducted in Blind Channel; hypoxic habitats were created without altering water temperature, decoupling the natural covariation between these two factors that occurs in aquatic systems. The abundance of small forage fish was higher in the hypoxic locations compared to controls and while predators still visited the hypoxic habitats, their mean visit duration was reduced from around 300 min to less than 1 min. An individual based computer model was used to test and illustrate current understanding of the relative importance of temperature, DO and turbidity on predator habitat selection decisions and fish community composition. The model showed that DO had a stronger effect on community composition than temperature, and that reduced foraging success from high turbidity was able to overpower the other two factors. Hypoxia affects habitat selection decisions by fish species and can provide refuges from predation and competition, helping maintain higher species diversity. Water temperature appears to have a weaker effect on fish distributions than DO while turbidity primarily affects visual predators, though the strength of turbidity effects depends on the magnitude and duration of individual events.

In Part I of this thesis we extend the Lanchester Ordinary Differential Equations and construct a new physically meaningful set of partial differential equations with the aim of more realistically representing soldier dynamics in order to enable a deeper understanding of the nature of conflict. Spatial force movement and troop interaction components are represented with both local and non-local terms, using techniques developed in biological aggregation modelling. A highly accurate flux limiter numerical method ensuring positivity and mass conservation is used, addressing the difficulties of inadequate methods used in previous research. We are able to reproduce crucial behaviour such as the emergence of cohesive density profiles and troop regrouping after suffering losses in both one and two dimensions which has not been previously achieved in continuous combat modelling. In Part II, we reproduce for the first time apparently complex cellular automaton behaviour with simple partial differential equations, providing an alternate mechanism through which to analyse this behaviour. Our PDE model easily explains behaviour observed in selected scenarios of the cellular automaton wargame ISAAC without resorting to anthropomorphisation of autonomous 'agents'. The insinuation that agents have a reasoning and planning ability is replaced with a deterministic numerical approximation which encapsulates basic motivational factors and demonstrates a variety of spatial behaviours approximating the mean behaviour of the ISAAC scenarios. All scenarios presented here highlight the dangers associated with attributing intelligent reasoning to behaviour shown, when this can be explained quite simply through the effects of the terms in our equations. A continuum of forces is able to behave in a manner similar to a collection of individual autonomous agents, and shows decentralised self-organisation and adaptation of tactics to suit a variety of combat situations. We illustrate the ability of our model to incorporate new tactics through the example of introducing a density tactic, and suggest areas for further research.

In Part I of this thesis we extend the Lanchester Ordinary Differential Equations and construct a new physically meaningful set of partial differential equations with the aim of more realistically representing soldier dynamics in order to enable a deeper understanding of the nature of conflict. Spatial force movement and troop interaction components are represented with both local and non-local terms, using techniques developed in biological aggregation modelling. A highly accurate flux limiter numerical method ensuring positivity and mass conservation is used, addressing the difficulties of inadequate methods used in previous research. We are able to reproduce crucial behaviour such as the emergence of cohesive density profiles and troop regrouping after suffering losses in both one and two dimensions which has not been previously achieved in continuous combat modelling. In Part II, we reproduce for the first time apparently complex cellular automaton behaviour with simple partial differential equations, providing an alternate mechanism through which to analyse this behaviour. Our PDE model easily explains behaviour observed in selected scenarios of the cellular automaton wargame ISAAC without resorting to anthropomorphisation of autonomous 'agents'. The insinuation that agents have a reasoning and planning ability is replaced with a deterministic numerical approximation which encapsulates basic motivational factors and demonstrates a variety of spatial behaviours approximating the mean behaviour of the ISAAC scenarios. All scenarios presented here highlight the dangers associated with attributing intelligent reasoning to behaviour shown, when this can be explained quite simply through the effects of the terms in our equations. A continuum of forces is able to behave in a manner similar to a collection of individual autonomous agents, and shows decentralised self-organisation and adaptation of tactics to suit a variety of combat situations. We illustrate the ability of our model to incorporate new tactics through the example of introducing a density tactic, and suggest areas for further research.

The harbor porpoise is considered a threatened species in Swedish waters. A full understanding of its ecology and relationship to other species is important when designing effective conservation plans. This thesis aims to investigate the relationships between harbor porpoises and their prey by comparing the acoustic activity patterns of harbor porpoises and the movement patterns of some of their prey species available at Kullaberg, Sweden. For this purpose, the scientific literature of porpoise and fish activity patterns has been reviewed. Results show that harbor porpoises may follow vertically migrating herring, but further studies are needed to confirm this. It is also possible that the activity pattern of porpoises does not follow exactly the movements of a certain species of prey, but that they rather feed upon several species, and therefore change their behavior accordingly throughout the diurnal cycle.