Many species survive in specialized habitats. When these habitats are destroyed or fragmented the threat of extinction looms. In this paper, we use percolation theory to consider how an environment may fragment. We then develop a stochastic, spatially explicit, individual-based model to consider the e¡ect of habitat fragmentation on a keystone species (the army ant Eciton burchelli ) in a neotropical rainforest. The results suggest that species may become extinct even in huge reserves before their habitat is fully fragmented; this has important implications for conservation. We show that sustainable forest-harvesting strategies may not be as successful as is currently thought. We also suggest that habitat corridors, once thought of as the saviour for fragmented environments, may have a detrimental e¡ect on population persistence.

Quantifying the strengths of feedback loops can bring insight into the way the structure of a system dynamics model helps determine behaviour. This paper proposes the concept of loop impact, using the functional relationship between the second and first derivative from the Pathway Participation Metric method, and describes a numerical method to derive the impacts of feedback loops within a system dynamics model. An algorithm is presented that will identify which loop, or loop combination, explains stock behaviour. The method is applied to the yeast, epidemic and market growth models and compared with previous work. It is shown that the method can deal with loops that change polarity, hidden loops and those that self cancel. A procedure is set out to calculate impacts when loops have junctions and graphical converters. It is anticipated that the method will be adopted by system dynamicists and applied to a broader range of models. Copyright © 2014 System Dynamics Society

As decomposer organisms, pathogens, plant symbionts and nutrient cyclers, fungi are of fundamental importance in the terrestrial environment. Moreover, in addition to their well-known applications in industry, many species also have great potential in environmental biotechnology. The study of this important class of organisms is difficult through experimental means alone due to the heterogeneity of their natural growth habitat and the microscopic scale of growth. In this work we present a mathematical model for colony expansion that is derived through consideration of the growth characteristics on the microscale. The model equations are of mixed hyperbolic-parabolic type and are treated with a numerical scheme that preserves positivity and conserves mass. The numerical solutions are compared against experimental results in a variety of environments. Thus the effect of different translocation mechanisms on fungal growth and function are identified. The derivation and analysis of an approximation to the full model yields further results concerning basic properties of mycelial growth. Finally, the acidification of the growth habitat is considered and the model thus provides important predictions on the functional consequences of the redistribution of internally-located material.

No abstract

Fungi are of fundamental importance in terrestrial ecosystems playing important roles in decomposition, nutrient cycling, plant symbiosis and pathogenesis, and have significant potential in several areas of environmental biotechnology such as biocontrol and bioremediation. In all of these contexts, the fungi are growing in environments exhibiting spatio-temporal nutritional and structural heterogeneities. In this work, a discrete mathematical model is derived that allows detailed understanding of how events at the hyphal level are influenced by the nature of various environmental heterogeneities. Mycelial growth and function is simulated in a range of environments including homogeneous conditions, nutritionally-heterogeneous conditions and structurally-heterogeneous environments, the latter emulating porous media such as soils. Our results provide further understanding of the crucial processes involved in fungal growth, nutrient translocation and concomitant functional consequences, e.g. acidification, and have implications for the biotechnological application of fungi.