Applied Geography: Principles and Practice: an Introduction to Useful Research in Physical, Environmental and Human Geography

By Michael Pacione | Go to book overview

15

Maintaining biodiversity

Nick Brown


INTRODUCTION

Conservation is a management discipline that has traditionally looked to the biological sciences for its paradigms. However, many of the problems that have been encountered during the last decade have revealed that a strictly biological approach to conservation has proved inadequate. Conservation biology has, until quite recently, failed to take a geographical perspective and has no theoretical framework within which the role of human societies can be incorporated. Conservation needs to take account of both the geographical and social context within which management operations are occurring. This chapter will attempt to illustrate how conservation of biological diversity is a problem that geography is uniquely positioned to address.


TYPES AND SCALES OF BIODIVERSITY

Although it is common to think of biodiversity as synonymous with species richness, this is only one level at which variety is measured in organisms. There is a hierarchy of organismic variation from the genetic through the species and population levels to diversity in ecosystems. Functional, structural and age diversity may also be of great importance to the way that ecosystems operate. For example, structural diversity in British woodlands is one of the most important determinants of animal species richness.

Biological diversity is so widely accepted as being valuable that the reasons why it is valued are rarely carefully analysed. Table 15.1 lists a crude classification of the reasons for valuing biological diversity and examines the scales at which these might best operate. Not all levels of variation are equally valuable for all reasons. For example, the diversity of species in an ecosystem may fluctuate, while the diversity of functional or morphological types may remain relatively constant. Hawthorne (1993) has shown that logging of a Ugandan rain forest may actually increase species diversity. High levels of disturbance allow widespread pioneer species, including common agricultural weeds, to colonise along logging tracks and in clearings. These new arrivals more than compensate for the immediate loss of some forest species. Although the total species diversity increased, there was considerable turnover in composition, and functional and morphological diversity may well have decreased.

Mares (1992) has pointed out that hotspots of species diversity may not necessarily coincide with areas of the highest genetic diversity. Tropical rain forests contain large numbers of very closely related species. For instance, on the island of Borneo there are approximately 267 species in the family Dipterocarpaceae. All are trees with very similar ecology. Closely related species may differ in less than 5 per cent of their nuclear DNA sequences. Conservation of all species of dipterocarp may preserve less genetic information than the conservation of many fewer but more distantly related species. In contrast, it is well established that many marine ecosystems have extraordinarily high levels of phylum diversity. As a consequence, although they may

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