Pattern formation in a model for mountain pine beetle dispersal: linking model predictions to data.

Pattern formation occurs in a wide range of biological systems. This pattern formation can occur in mathematical models because of diffusion-driven instability or due to the interaction between reaction, diffusion, and chemotaxis. In this paper, we investigate the spatial pattern formation of attack clusters in a system for Mountain Pine Beetle. The pattern formation (aggregation) of the Mountain Pine Beetle in order to attack susceptible trees is crucial for their survival and reproduction. We use a reaction-diffusion equation with chemotaxis to model the interaction between Mountain Pine Beetle, Mountain Pine Beetle pheromones, and susceptible trees. Mathematical analysis is utilized to discover the spacing in-between beetle attacks on the susceptible landscape. The model predictions are verified by analysing aerial detection survey data of Mountain Pine Beetle Attack from the Sawtooth National Recreation Area. We find that the distance between Mountain Pine Beetle attack clusters predicted by our model closely corresponds to the observed attack data in the Sawtooth National Recreation Area. These results clarify the spatial mechanisms controlling the transition from incipient to epidemic populations and may lead to control measures which protect forests from Mountain Pine Beetle outbreak.

The effect of habitat fragmentation on cyclic population dynamics: a numerical study.

Through four spatially explicit models, we investigate how habitat fragmentation affects cyclic predator-prey population dynamics. We use a Partial Differential Equation (PDE) framework to describe the dispersal of predators and prey in a heterogeneous landscape made of high quality and low quality habitat patches, subject to increasing fragmentation through habitat separation and/or habitat loss. Our results show that habitat fragmentation decreases the amplitude of the predator-prey population cycles while average population density is not as strongly affected in general. Beyond these simple trends however, the four models show differing responses to fragmentation, indicating that when making predictions about population survival and persistence in the face of habitat fragmentation, the choice of model is important. Our results may inform conservation efforts in fragmented habitats for cyclic species such as the snowshoe hare and Canada lynx.

Phaeohyphomycosis caused by Exophiala jeanselmei treated with itraconazole.

Phaeohyphomycotic cysts developed on the right knee of a 72-year-old woman undergoing immunosuppressive treatment for ulcerative colitis 6 years after accidental inoculation of soil in a bicycle accident. The lesions were red, firm, slightly raised, 0.5-1 cm in size and completely asymptomatic. The diagnosis was made by histopathological examination of three excised cysts and by repeated isolation of Exophiala jeanselmei in pure culture. The excised cyst walls contained large numbers of dematiaceous fungal elements in the form of hyphae, yeast-like cells and some cells dividing internally by a transverse septum. The patient was treated with 200 mg of itraconazole daily, but the treatment had to be stopped because of severe side-effects after 6 weeks. Histologically the cysts were cleared of dematiaceous elements, but E. jeanselmei could still be isolated from one of two skin biopsies 1 month after the end of therapy.