The Effect of Map Boundary on Estimates of Landscape Resistance to Animal Movement

Abstract

BackgroundArtificial boundaries on a map occur when the map extent does not cover the entire area of study; edges on the map do not exist on the ground. These artificial boundaries might bias the results of animal dispersal models by creating artificial barriers to movement for model organisms where there are no barriers for real organisms. Here, we characterize the effects of artificial boundaries on calculations of landscape resistance to movement using circuit theory. We then propose and test a solution to artificially inflated resistance values whereby we place a buffer around the artificial boundary as a substitute for the true, but unknown, habitat.Methodology/Principal FindingsWe randomly assigned landscape resistance values to map cells in the buffer in proportion to their occurrence in the known map area. We used circuit theory to estimate landscape resistance to organism movement and gene flow, and compared the output across several scenarios: a habitat-quality map with artificial boundaries and no buffer, a map with a buffer composed of randomized habitat quality data, and a map with a buffer composed of the true habitat quality data. We tested the sensitivity of the randomized buffer to the possibility that the composition of the real but unknown buffer is biased toward high or low quality. We found that artificial boundaries result in an overestimate of landscape resistance.Conclusions/SignificanceArtificial map boundaries overestimate resistance values. We recommend the use of a buffer composed of randomized habitat data as a solution to this problem. We found that resistance estimated using the randomized buffer did not differ from estimates using the real data, even when the composition of the real data was varied. Our results may be relevant to those interested in employing Circuitscape software in landscape connectivity and landscape genetics studies.

Distribución potencial y conectividad del paisaje: criterios para reevaluar el grado de amenaza de Campylorhynchus yucatanicus (Aves: Troglodytidae)

“…Después de depurar los datos de campo quedaron 28 nodos focales, que se corresponden a un conjunto de ocurrencias cercanas entre sí (< 500 m). El área analizada es un recorte del mapa de la Península de Yucatán que contenía la distribución potencial obtenida, lo cual permitió adquirir modelos de resistencia más certeros (Koen et al, 2010). En primera instancia, se confeccionó un mapa de idoneidad de 200 m de resolución, teniendo en cuenta los tipos de vegetación y usos de suelo (INEGI, 2013), la distancia a los asentamientos humanos y la distancia a las carreteras asfaltadas.…”

“…Entre las aproximaciones más ampliamente difundidas para analizar la conectividad del paisaje, están aquellas basadas en modelos de circuitos (McRae et al, 2008), donde se puede caracterizar el paisaje espacialmente de una manera explícita. Esto permite evaluar la importancia de los elementos individuales para el mantenimiento o fomento de la conectividad del paisaje en su conjunto, constituyendo una herramienta muy útil para orientar decisiones dirigidas al manejo de vida silvestre (Koen, Garroway, Wilson, & Bowman, 2010;Shimazaki et al, 2016).…”

Rural avenues as dispersal corridors for the vulnerable saproxylic beetle Elater ferrugineus in a fragmented agricultural landscape

“…The area used for the analyses was the minimum convex polygon enclosing all of the sample points, with a 2 km buffer surrounding this polygon added to minimize the increase of resistance values due to the grid boundary (Koen et al 2010). We assigned a 'no data' value to cells outside of this area and excluded them from all calculations.…”

Modelling seasonal habitat suitability and connectivity for feral pigs in northern Australia: towards risk-based management of infectious animal diseases with wildlife hosts

“…We detected increased current density at some tile corners. This artefact of tile buffering (Koen et al 2010;Pelletier et al 2014) occurred mostly in low quality habitat, when resistance in the tile greatly exceeded resistance in its randomly filled buffer. While this had minimal impact on our analyses of patch connectivity (affected tiles contained no or few patches), it may disturb other applications.…”

“…While this had minimal impact on our analyses of patch connectivity (affected tiles contained no or few patches), it may disturb other applications. In heterogeneous study areas, we suggest filling buffers with resistance values drawn randomly from each tile rather than the entire study area (Koen et al 2010) to ensure matching value ranges and eliminate border effects.…”