Modelling the future of the Hawaiian honeycreeper : an ecological and epidemiological problem

The Hawaiian honeycreeper (Drepanididae) faces the threat of extinction; this is believed to be due primarily to predation from alien animals, endemic avian malaria (Plasmodium relictum) and climate change. A deterministic SI modelling approach is developed, incorporating these three factors and a metapopulation approach in conjunction with a quasi-equilibrium assumption to simplify the vector populations. This enables the qualitative study of the behaviour of the system. Numerical results suggest that although (partial) resistance to avian malaria may be advantageous for individual birds, allowing them to survive infection, this allows them to become carriers of infection and hence greatly increases the spread of this disease. Predation obviously reduces the life-expectancy of honeycreepers, but in turn this reduces the spread of infection from resistant carriers; therefore the population-level impact of predation is reduced. Various control strategies proposed in the literature are also considered and it is shown that predation control could either help or hinter, depending upon resistance of the honeycreeper species. Captive propagation or habitat restoration may be the best feasible solution to the loss of both heterogeneity within the population and the loss of the species as a whole

Wolves contribute to disease control in a multi-host system

We combine model results with field data for a system of wolves (Canis lupus) that prey on wild boar (Sus scrofa), a wildlife reservoir of tuberculosis, to examine how predation may contribute to disease control in multi-host systems. Results show that predation can lead to a marked reduction in the prevalence of infection without leading to a reduction in host population density since mortality due to predation can be compensated by a reduction in disease induced mortality. A key finding therefore is that a population that harbours a virulent infection can be regulated at a similar density by disease at high prevalence or by predation at low prevalence. Predators may therefore provide a key ecosystem service which should be recognised when considering human-carnivore conflicts and the conservation and re-establishment of carnivore populations

Dual fear phenomenon in an eco-epidemiological model with prey aggregation

This study presents a thorough analysis of an eco-epidemiological model that integrates infectious diseases in prey, prey aggregation, and the dual fear effect induced by predators. We establish criteria for determining the existence of equilibrium points, which carry substantial biological significance. We establish the conditions for the occurrence of Hopf, saddle-node, and transcritical bifurcations by employing fear parameters as key bifurcation parameters. Furthermore, through numerical simulations, we demonstrate the occurrence of multiple zero-Hopf (ZH) and saddle-node transcritical (SNTC) bifurcations around the endemic steady states by varying specific key parameters across the two-parametric plane. We demonstrate that the introduction of predator-induced fear, which hinders the growth rate of susceptible prey, can lead to the finite time extinction of an initially stable susceptible prey population. Finally, we discuss management strategies aimed at regulating disease transmission, focusing on fear-based interventions and selective predation via predator attack rate on infectious prey

EcoDemics, Modelling Epidemic Spread in a Simulated Predator-Prey Evolutionary Ecosystem

Modeling the progress of an epidemic in a population has received significant attention among various fields of science. Many epidemiological models assume random mixing of the population, homogeneous hosts, and a static environment. We are interested in modeling epidemic spread in a dynamic evolving ecosystem with behavioral models associated to its individuals. To this end, we present EcoDemics; which integrates the classical SIR (Susceptible-Infected-Removed) disease model to an individual-based evolutionary predator-prey ecosystem simulation, EcoSim. The behavioral model of each agent in EcoDemics is based on a fuzzy cognitive map (FCM) that determines the heterogeneous interactions between individuals. We present the disease model used and we demonstrate how the epidemic spread in a random mixing ecosystem differs from a heterogeneous ecosystem with its behavioral model. We observed that dynamics of the ecosystem, along with the spatial distribution of agents, play a significant role in disease progression. Due to the high mitigation capacity and significance of the immunization intervention, we explore vaccination techniques with various time delays and population proportions in EcoDemics. Based on the herd immunity theory, the whole population can be protected against a contagious disease by vaccination of a fraction of individuals. We investigate this principle in EcoDemics and compare our results with real epidemics data. A number of mathematical simulations have been used to analyze host-pathogen dynamics in the presence of predators; however, to the best of our knowledge, this is the first individual-based modeling study exploring the effect of predators on prey infection dynamics in a predator-prey ecosystem simulation. We used the EcoDemics framework to investigate the effect of predation on infection dynamics in EcoDemics. Our results are in agreement with both numerical and field studies

Wildlife Population Monitoring

Wildlife management is about finding the balance between conservation of endangered species and mitigating the impacts of overabundant wildlife on humans and the environment. This book deals with the monitoring of fauna, related diseases, and interactions with humans. It is intended to assist and support the professional worker in wildlife management

Predator Defense and Host Selection Behavior of Billbugs (Coleoptera: Dryophthoridae)

Billbugs are a complex of weevils that feed on the roots of turfgrass, causing severe damage to the plants. These pests are traditionally managed with applications of insecticides. However, there is a need for non-chemical management tools. Here I investigate billbug behavior in relation to two potential avenues for more sustainable management: using resident predators to suppress billbugs (Chapter II) and selecting specific turfgrasses that resist billbug damage (Chapter III). In Chapter II, I investigate the effects of predator presence and cues associated with their presence on billbug behavior. Though resident predators contribute very little to billbug suppression through directly killing and consuming billbugs, I found that the presence of predators caused billbugs to spend less time feeding and mating, and more time on predator avoidance behaviors. Moreover, predator odor alone induced similar changes, suggesting that adult billbug detect predators using their odor. Although predators do not often directly consume billbugs, their presence may still contribute to billbug suppression. My findings also provide the framework for further investigation of predator chemicals as a potential billbug management tool. In chapter III, I examine adult billbug preferences for water stressed turfgrasses, and turfgrass cultivars with different drought resistance traits. I found that billbugs were more abundant in drier areas, and that billbug damage was higher in turfgrass with low drought resistance. While billbugs did prefer some turfgrasses over others, they did not prefer drought stressed or drought susceptible plants. Drought resistant turfgrasses are available to alleviate drought stress and may generally suffer less billbug damage, however, this does not appear to be a function of repelling adult billbugs. Continued evaluation of the factors that drive billbug preferences among turfgrasses, and turfgrass of traits associated with lower billbug damage could guide cultivar development against two key stressors, drought and billbugs, in the Intermountain West. Overall, my research shows that short term changes in turfgrass management practices, such as conserving the natural predator community and selecting specific types of turfgrass, could assist in billbug management. In the long term, investigation of billbug management using predator chemicals and development of turfgrasses that resist billbug damage could form the basis of sustainable billbug management programs

MS ENVIRONMENTAL BIOLOGY CAPSTONE PROJECT

MS ENVIRONMENTAL BIOLOGY CAPSTONE PROJECT 202

Pathogen exclusion from eco-epidemiological systems

Increasing concerns about the changing environment and the emergence of pathogens that cross species boundaries have added to the urgency of understanding the dynamics of complex ecological systems infected by pathogens. Of particular interest is the often counterintuitive way in which infection and predation interact and the consequent difficulties in designing control strategies to manage the system. To understand the mechanisms involved, we focus on the pathogen exclusion problem, using control maps (on which the network of exclusion thresholds are plotted) in order to readily identify which exclusion strategies will work and why others will not. We apply this approach to the analysis of parasite exclusion in two game bird ecologies. For higher dimensions, we propose a computational scheme that will generate the optimal exclusion strategy, taking into account all operational constraints on the pathogen invasion matrix, populations, and controls. The situation is further complicated when external forcing distorts pathogen thresholds. This distortion is highly sensitive to the lags between forcing components, a sensitivity that can be exploited by management using correctly lagged cyclically varying controls to reduce the effort involved in pathogen exclusion