Spontaneous trail formation in populations of auto-chemotactic walkers

We study the formation of trails in populations of self-propelled agents that make oriented deposits of pheromones and also sense such deposits to which they then respond with gradual changes of their direction of motion. Based on extensive off-lattice computer simulations aiming at the scale of insects, e.g., ants, we identify a number of emerging stationary patterns and obtain qualitatively the non-equilibrium state diagram of the model, spanned by the strength of the agent–pheromone interaction and the number density of the population. In particular, we demonstrate the spontaneous formation of persistent, macroscopic trails, and highlight some behaviour that is consistent with a dynamic phase transition. This includes a characterisation of the mass of system-spanning trails as a potential order parameter. We also propose a dynamic model for a few macroscopic observables, including the sub-population size of trail-following agents, which captures the early phase of trail formation.

Active Inferants: An Active Inference Framework for Ant Colony Behavior

In this paper, we introduce an active inference model of ant colony foraging behavior, and implement the model in a series of in silico experiments. Active inference is a multiscale approach to behavioral modeling that is being applied across settings in theoretical biology and ethology. The ant colony is a classic case system in the function of distributed systems in terms of stigmergic decision-making and information sharing. Here we specify and simulate a Markov decision process (MDP) model for ant colony foraging. We investigate a well-known paradigm from laboratory ant colony behavioral experiments, the alternating T-maze paradigm, to illustrate the ability of the model to recover basic colony phenomena such as trail formation after food location discovery. We conclude by outlining how the active inference ant colony foraging behavioral model can be extended and situated within a nested multiscale framework and systems approaches to biology more generally.

Winged fruits of rutaceous affinity from the Eocene of western North America

A new kind of fin-winged fruit is recognized from lacustrine shales of the early Eocene Tepee Trail Formation of northwestern Wyoming and from the middle Eocene Clarno Formation of central Oregon, USA. The fruits are obovate with five thick lateral wings, borne on a thick pedicel and bearing scars of hypogynous perianth and disk. The fruit surface is covered with small circular dots interpreted as glands. This combination of characters leads us to infer affinities with the Rutaceae, although no identical modern genus is known. We establish the new genus and species, Quinquala obovata.

The effects of post-fire forest management on soil erosion rates 3 and 4 years after a wildfire, demonstrated on the 2010 Mount Carmel fire

During 2–5 December 2010, an area of 2500ha in the Carmel forests was consumed by a severe wildfire, causing soil erosion from the exposed slopes. Whereas most studies show that post-fire erosion rates tend to decline after the second year, in this case, we aim to address the ongoing consequences that different management practices had on soil erosion 3 and 4 years after a fire. Three management operations were applied: (a) preservation management (PM) – mulching wood chips on the burned area; (b) tree-clearing management (TCM) – burned trees were cut and removed; and (c) skid-trail formation (ST) – provisional pathways were formed while trees were dragged outside. Consequently, the objectives of the study were: (1) to monitor the effects of these post-fire practices 3 and 4 years after fire; and (2) to characterise the physical features of the eroded soil. The sediments were collected after every effective rain event over two rainy seasons (2013–14, 2014–15). TCM and ST practices resulted in significantly elevated soil-erosion yields compared to PM. The sediments following PM had a high percentage of fine material. Furthermore, PM had an evident positive effect on the soil, whereas all other practices inhibited vegetation renewal and system rehabilitation.