Effects of changing spatial scale on the analysis of landscape pattern

Abstract

The purpose of this study was to observe the effects of changing the grain (the first level of spatial resolution possible with a given data set) and extent (the total area of the study) of landscape data on observed spatial patterns and to identify some general rules for comparing measures obtained at different scales. Simple random maps, maps with contagion (i.e., clusters of the same land cover type), and actual landscape data from USGS land use (LUDA) data maps were used in the analyses. Landscape patterns were compared using indices measuring diversity (H), dominance (D) and contagion (C). Rare land cover types were lost as grain became coarser. This loss could be predicted analytically for random maps with two land cover types, and it was observed in actual landscapes as grain was increased experimentally. However, the rate of loss was influenced by the spatial pattern. Land cover types that were clumped disappeared slowly or were retained with increasing grain, whereas cover types that were dispersed were lost rapidly. The diversity index decreased linearly with increasing grain size, but dominance and contagion did not show a linear relationship. The indices D and C increased with increasing extent, but H exhibited a variable response. The indices were sensitive to the number (m) of cover types observed in the data set and the fraction of the landscape occupied by each cover type (Pk); both m and Pk varied with grain and extent. Qualitative and quantitative changes in measurements across spatial scales will differ depending on how scale is defined. Characterizing the relationships between ecological measurements and the grain or extent of the data may make it possible to predict or correct for the loss of information with changes in spatial scale.

Finescale topographical correlates of behavioural investment in offspring by female grey seals, Halichoerus grypus

“…Through our use of accurate DTMs we have achieved a measurement resolution sufficiently fine to distinguish broadly similar sub-sites as topographically and functionally different. This spatial grain was also appropriate for assessing topography at a resolution that individual seals use when making decisions (Forman & Gordon 1986, Kolasa & Rollo 1991, Turner et al 1989, Wiens 1989. Our topographic analyses suggested that the Tarbet site was a relatively higher "cost" site than that of WRB.…”

“…Whilst it may be obvious that topography is likely to impact significantly on an individual animal's behaviour (Stamps 1995) topography is quantified at a spatial grain relevant to the behaviours being studied, that is, at a resolution whereby topographic features will actually impact upon individuals' decision making processes (Forman & Gordon 1986;Turner et al 1989;Wiens 1989). Very few studies have achieved both these aims (e.g.…”

“…These topographically induced behavioural differences are likely to affect the quantity and quality of pup provisioning by mothers and influence individual pupping site selection. Less costly sites are likely to be colonised preferentially and by larger, older and more dominant females, potentially generating fine scale spatial heterogeneity in female quality within the breeding colony.Whilst it may be obvious that topography is likely to impact significantly on an individual animal's behaviour (Stamps 1995) topography is quantified at a spatial grain relevant to the behaviours being studied, that is, at a resolution whereby topographic features will actually impact upon individuals' decision making processes (Forman & Gordon 1986;Turner et al 1989;Wiens 1989). Very few studies have achieved both these aims (e.g.…”

“…Anderson & Harwood 1985;Campagna & Le Boeuf 1988;Reid & Weatherhead 1988). In addition, when examining individual behaviour in relation to their physical surroundings it is important that topography is quantified at a spatial grain relevant to the behaviours being studied, that is, at a resolution whereby topographic features will actually impact upon individuals' decision making processes (Forman & Gordon 1986;Turner et al 1989;Wiens 1989). Very few studies have achieved both these aims (e.g.…”

Use and misuse of landscape indices

“…Difficulties in collecting data at multiple scales of observation have forced most studies of scale effects to concentrate on the scales of analysis. A common approach is to obtain data at one scale of observation, artificially change the grain or extent of the map data through rescaling, and perform analysis and modeling with the newly generated multi-scale data ͑Gard-ner et Turner et al 1989;Wu 2000;Wu 2003;Saura and Martinez-Millan 2001;. Changing scale by manipulating data can be a surrogate for observing the landscape directly with two or more sensors ͑or sampling schemes͒ of different resolutions.…”