![]() ![]() ![]() Turner and Miles developed a computerised approach that combined the principles of Warntz and McHarg to produce the first example of what we would now recognise as least-cost modelling. While the work of Warntz and McHarg established the basic principles of calculating a least-cost route and incorporating a diversity of geographic costs respectively, the efficient and repeatable application of these principles was only possible with the adoption of computer technology. At a similar time McHarg presented a map overlay approach that combined geographic information about not only transport costs, but also social and environmental costs, to determine a region within which a highway could be located that balanced positive and negative impacts. Using the analogy of light refraction through different mediums, Warntz provided early examples of how to calculate a route of least-cost between locations separated by regions of differing transport costs, and showed that least-cost routes radiating out from a central location could be mapped as a continuous surface. ![]() Least-cost (or cost-distance) modelling is a quantitative geographic technique to measure nearness that was developed in transport geography where there was a need to be able to identify optimal routes across landscapes with varying costs of travel. However, this does not invalidate Tobler’s first law of geography, but rather means that nearness needs to be measured in geographic space using another approach such as least-cost distance. ![]() So, in some ecological systems, connectivity, and therefore, movement, does not follow nearness relations defined in Euclidean space. However, the importance of landscape structure on connectivity and, therefore, movements across landscapes was soon theorised and demonstrated. Later research applied the same straight-line distance approach to nearness using a patch-matrix landscape model to demonstrate that patches nearer sources were more likely to be occupied by a species. Measuring nearness to quantify connections and infer movement potential in ecology began with the theory of island biogeography, which predicted that islands nearer to population sources in terms of straight-line Euclidean distance had greater immigration rates. This association between nearness and the degree of relation or connection can be used to quantify a variety of geographical patterns and processes including movement between geographic locations, which has ecological implications relating to habitat fragmentation, invasive species, and epidemiology. The question of what is near is a core concept of spatial information, and is emphasised by Tobler’s first law of geography that states “everything is related to everything else, but near things are more related than distant things”. This review aims to describe the concepts of least-cost modelling, demonstrate current applications of least-cost modelling in landscape ecology, and to suggest future opportunities by linking the ecological application of least-cost modelling with recent geographical science developments from which least-cost modelling originally developed. However, perhaps because early applications of least-cost modelling in ecology tended to cite the method with reference to geographic information system software rather than the geographical science literature, ecologists are not currently making full use of available least-cost modelling techniques that have continued to develop. There has been a significant increase in the interest and use of least-cost modelling by ecologists in the last decade. Least-cost modelling is a technique that can incorporate traversal costs across a landscape to measure the least-cost distance between locations as a function of both the distance travelled and the costs traversed. In some ecological systems connectivity does not follow nearness relations defined by Euclidean distances, so distance must be measured another way. The concept of nearness and that nearer things are more connected is useful in quantifying a variety of geographical patterns and processes, including ecological connectivity between geographic locations. ![]()
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