Quantification of the effects of spatial heterogeneity on animals at different spatial scales

Landscape ecology is an ecological discipline that considers four main principles: “the development and dynamics of spatial heterogeneity, interactions and exchanges across heterogeneous landscapes, the influences of spatial heterogeneity on biotic and abiotic processes, and the management of spatial heterogeneity”. Spatial heterogeneity refers to the characteristics of a landscape. A landscape can be seen as an environmental mosaic, with a pattern that can be classified at several scales, with an influence at abiotic and biotic processes, for instance at animals. Not all processes and parameters have the same effect at various scales, therefore it is important to determine the effect of spatial heterogeneity on organisms at various scales. This overview demonstrates which methods are used to determine this effect. Differences between studies are the kind of environment, size of study area and samples, classification and number of spatial scales, kind of species and the aim of the research. The methods for dividing the area in studies used for this overview can be classified into nested or hierarchical design, a design with several circles with a range of radii, a block design or a design that depends on animals or vegetation. The spatial heterogeneity has been determined with already existing surveys, but topographic maps, aerial photographs, satellite images, and computer software are also used. Combinations of the methods are used as well. The variables measured to determine the spatial heterogeneity of the area are divers. The study area can be divided in patches with vegetation variables, with traces of animals or with other variables. Examples of influences of spatial heterogeneity on animals are the species richness, the diversity and the species composition or community structure, the abundance, distribution and movement patterns of animals, the species survival, the locations of nests sites, size of a home range, selection of feeding sites or the size and biomass of organisms. The majority of the studies observes or counts individual animals, but there are also methods that make use of traces of the animals, such as occupied tree cavities, sounds or density of preferred food to determine the influence. It is clear that there are many ways to measure the influence of spatial heterogeneity on animals at several spatial scales. A method to dividing a landscape into an appropriate amount of scales, with clear definitions of those scales is not established, but most of the studies emphasize the importance of research done at various spatial scales. None of the methods for dividing the area in studies used for this overview was considered useless or more useful than others and a clear definition of spatial heterogeneity, patchiness and patch makes it difficult define the heterogeneity of the area. A study should quantify the patchiness of the area first with a combination of all methods and the measure of a lot of environmental variables and then use a circle design or a block design and use one of the appropriate methods for the species where is focused on. But each study has specific circumstances and other methods may be better to use. So, choosing a method to determine the influence of the heterogeneity is difficult and complex and further research is needed to define which amount of scales should be used and to clarify the definition of the different scales and the definition of spatial heterogeneity.