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Contents:

1 - Introduction; 2 - Range edges; 3 - Range size; 4 - Abundance structure; 5 - Implications.

Review:

One of the first ideas in ecology is that species have defined areas in which they can exist. There are a few general ideas as to why this is but generally it would appear to be accepted rather than questioned in detail. Once we actually get beyond the simplest notion we start to find that the issue is far from clear (or, for that matter, simple). Why do some species have a set spatial distribution? More importantly, why do others not have! This book is an attempt to investigate these issues.

We start with the green-backed heron! In the introduction we see the distribution of this largely tropical bird is global but this hides a number of issues. It might be found in many tropical nations but only in parts of these so instantly we have a general pattern in which there are gaps. To this must be added the fact that a record could be one bird or thousands (the map gives no indication of density at a given area - which is not helped by the reclusive nature of the bird!). This particular species is not recorded as being endangered but if it were then what would be the significance of one area with an abundance of the species? To get anywhere near these questions we need to set up comprehensive research programmes. These are rare so the author then gives examples of studies which have addressed some aspect of the range of a species. Here we see an obvious problem - the research is not even - to gather information one needs to cast a wide net. Finally, the author states his aims: to draw together disparate information and subject it to critical analysis so as to improve knowledge about this area.

The remainder of the book looks at some of the key issues arising from this. Any range has three qualities - a defined boundary, a size and a population within it. Thus chapter two examines the ways in which the edge can be defined. Rather than the simple line we see a complex ecotone-like arrangement whereby species may exist beyond a given 'edge' but be sterile. Alternatively, there may be gaps inside the traditional range caused by one or more environmental factors. Having put forward the idea of edge, the author then describes the factors which control the limits of distribution. Physical barriers such as oceans and mountains are discussed from whence the study moves to climatic factors. Competition (both intra- and inter-specific) can alter edges as can population structure. Chapter three looks at range size. This can vary from a few mountain tops for the rarest of species to an almost unlimited global distribution for others. If we add to this the idea that the range used may not be the same as that which is potentially available we find that the difficulties expand. Since we are not restricted by time then it is possible that long-term changes such as speciation may play a part in range size. There's no guarantee that a species keeps its characteristics throughout its lifespan so we might be seeing geographic ranges affected not by climate but by evolution. We also see that species size is not necessarily a prefect indicator of range size. Chapter four looks at the way in which the target species is distributed within the range and the factors which control such a distribution. Demographic studies such as those mentioned in this chapter have much to tell us about population numbers. A final chapter considers the implications of this work. For example, speciation and extinction affect range especially where niches are similar. Pollution and global warming already affect distribution and may continue to do so. Finally, global transport also means global shipping for alien species which often thrive away from home to the detriment of the native flora and fauna. Out task must be to see how this can be dealt with.

Overall, this is a very stimulating book. The range of cases and sources is impressive: it gives the study weight and provides us with one of the few detailed treatments of this subject. It should appeal to a wide audience. Educators will find ideas about range in one text (and have enough material to demonstrate the key ideas irrespective of location). For those studying the distribution of species this book is an excellent introduction. Hopefully, it will stimulate further discussion in this neglected area.