Vilis O. Nams* Abstract Emergent Properties of Patch Shapes Affect Edge Permeability to Animals Department of Environmental Sciences, Nova Scotia Agricultural College, Truro, Canada, and School of Marine and Tropical Biology, James Cook University, Townsville, Australia Animal travel between habitat patches affects populations, communities and ecosystems. There are three levels of organization of edge properties, and each of these can affect animals. At the lowest level are the different habitats on each side of an edge, then there is the edge itself, and finally, at the highest level of organization, is the geometry or structure of the edge. This study used computer simulations to (1) find out whether effects of edge shapes on animal behavior can arise as emergent properties solely due to reactions to edges in general, without the animals reacting to the shapes of the edges, and to (2) generate predictions to allow field and experimental studies to test mechanisms of edge shape response. Individual animals were modeled traveling inside a habitat patch that had different kinds of edge shapes (convex, concave and straight). When animals responded edges of patches, this created an emergent property of responding to the shape of the edge. The response was mostly to absolute width of the shapes, and not the narrowness of them. When animals were attracted to edges, then they tended to collect in convexities and disperse from concavities, and the opposite happened when animals avoided edges. Most of the responses occurred within a distance of 40% of the perceptual range from the tip of the shapes. Predictions were produced for directionality at various locations and combinations of treatments, to be used for testing edge behavior mechanisms. These results suggest that edge shapes tend to either concentrate or disperse animals, simply because the animals are either attracted to or avoid edges, with an effect as great as 3 times the normal density. Thus edge shape could affect processes like pollination, seed predation and dispersal and predator abundance. Citation: Nams VO (2011) Emergent Properties of Patch Shapes Affect Edge Permeability to Animals. PLoS ONE 6(7): e21886. doi:10.1371/journal.pone.0021886 Editor: Robert Planque, Vrije Universiteit, Netherlands Received August 25, 2010; Accepted June 14, 2011; Published July 1, 2011 Copyright: 2011 Vilis O. Nams. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This study was funded by the Natural Science and Engineering Research Council of Canada (http://www.nserc-crsng.gc.ca/Index_eng.asp). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The author has declared that no competing interests exist. * E-mail: vnams@nsac.ca Introduction Animal travel between habitat patches affects populations, communities and ecosystems. On a large scale this affects metapopulation dynamics, where extinction rates of subpopula- tions are crucially dependent on dispersal rates [1]. On a small scale this affects population dynamics, where foraging success [2] and predation [3] are affected by travel across patchy landscapes. Thus it is important to understand the process of traveling from one habitat patch to another. One can separate this process into two separate behavioral components: the action of crossing the edge and entering the matrix, and then traveling through the matrix. This paper will focus on the component of edge-crossing. There are three levels of organization of edge properties, and each of these can affect animals. At the lowest level are the different habitats on each side of an edge, then at a higher level there is the edge itself, and finally, at the highest level of organization, is the geometry or structure of the edge - for example, perimeter:area ratio, corridors and edge shapes (con- vexities vs. concavities). This paper will focus on the highest level of edge organization, edge geometry. One fundamental and widespread type of edge geometry is edge shape. The idea that animals might be affected by edge shape was first suggested by Hardt and Forman [4], who found that woody colonization of revegetated mines was affected by the shape of the edge between grassland mine spoils and the surrounding forested habitat. Specifically, woody colonizers preferentially settled in grassland areas adjacent to edges that were concave into the forest. Hardt and Forman [4] hypothesized that this was a result of how animals responded to edge shape - that in grassland, for protection, browsing herbivores would concentrate where the edge intrudes into the forest. These herbivores would then disperse seeds of woody colonizers in their faeces. However, even though this hypothesis was proposed more than 20 years ago, and even though all edges have either convexities or concavities, there have been no studies on how animals react to the shape of habitat edges. We need theoretical studies to generate testable hypotheses for different mechanisms of response, we need field observational studies to find out what kinds of responses animals show to different edge shapes, and we need experimental studies to test the different mechanisms of edge shape effects. Edge properties are important in two ways: ecologically, what is important is whether the edge property affects the animal’s movement, but mechanistically, what is important is whether the animal responds behaviorally to that edge property. And these might not be the same, because an animal’s behavior to an edge property at a lower organizational level might cause an emergence effect at a higher level. For example, at a lower level, most animals respond differently to different habitats. If an animal avoids a habitat, then the edge will affect that animal’s movement, without the animal recognizing the edge itself. Similarly, at a higher level, sleepy orange (Eurema nicippe) butterflies selectively travel through PLoS ONE | www.plosone.org 1 July 2011 | Volume 6 | Issue 7 | e21886