Introduction

Mosaics have common properties that allow us to apply well-tested indexes to measure their spatial properties.

Size, shape, and context are the more important attributes of each mosaic. The meaning of such measures that are often used without a clear statement is fundamental. Some measures are redundant or statistically correlated.

Nevertheless, today many indexes are available to evaluate a mosaic: Turnover, contagion, lacunarity, diversity, dominance, fractal characters are some of the more used metrics.

Most of these indexes are derived from landscape ecology, others from community or population ecology, but all are extremely important for evaluating the complexity of the mosaics.

The indexes can be divided into two broad categories: structural indexes and context indexes.

The structural indexes measure the inherent characteristics of a patch:

• Size (dimension of largest, smallest, etc.)

• Shape (relationship area/perimeter)

• Patch-matrix contrast

• Turnover (temporal replacement of patch types)

• Contagion (level of aggregation)

• Lacunarity (level of dispersion)

• Diversity (richness)

• Evenness (equal distribution)

• Dominance (level of concentration)

To evaluate species in a mosaic we can use spatial statistics like spatial autocorrelation defined by Sokal and Thomson (1987) as "the dependence of the value of a variable on values of the same variable at geographically adjoining locations." See also Hu and Moskat (1994).

A. Farina, Ecology, Cognition and Landscape, Landscape Series 11, 95

DOI 10.1007/978-90-481-3138-9_7, © Springer Science+Business Media B.V. 2010

Generally the structural indexes deal with size and shape of the composing patches of a mosaic.

The context indexes measure the spatial attributes of the different categories of patches and the overall characteristics of the mosaic per se.

All the indexes can be applied efficiently only if a comparative action follows the measures.

The structural indexes are based on the assumption that every component of a mosaic is the product of interfering processes and that every typology of patches has per se a different behavior and role in the environment. Every patch may have specific characters, but it is not always true that these characters are perceived by a species that utilizes the patch. It seems important to calibrate the analysis to the organisms which we are interested in investigating. Often we use maps created by our interpretation of the mosaic and this is the great limit of spatial analysis.

A mosaic fragmented for a species can only be heterogeneous for another species (Fig. 7.1). The term fragmented means insulation of suitable patches, dispersed into a hostile matrix. Heterogeneous means that the resources are not found everywhere inside the suitable matrix.

(B) Patchiness

(B) Patchiness

y noise

Fig. 7.1 The different perception of the environmental discontinuity according to the specific caliber. A species can intercept an environmental discontinuity as a noise (heterogeneity) (A) or the patchiness as a barrier (hostility) (B)

y noise

Fig. 7.1 The different perception of the environmental discontinuity according to the specific caliber. A species can intercept an environmental discontinuity as a noise (heterogeneity) (A) or the patchiness as a barrier (hostility) (B)

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