Basic Biogeography

N.V. Pears, N V Pears

• Publisher: Routledge
• Year: 2014
• Print ISBN: 9780367239855
• eBook ISBN: 9781317885252
• Edition: 2
• Topic: Physical Sciences
• Subtopic: Geography
• Index: Geography

First published in 1985. This is the is the second edition of a study looking at ecology and biogeography with updated chapters including current research. It starts with the with the study of plants to gain an understanding of the complexities of ecological relationships.

Part 1

BASIC CONSIDERATIONS

1

INTRODUCTION

DEFINITIONS

Geography students quickly become aware of the problems of defining their subject. Whereas the subject matter of some branches of the discipline can be easily stated this is not so with biogeography. Geography itself has been variously defined as the study of: areal distributions, spatial patterns, locational analysis, man-land relationships, the environmental relationships of man. Biogeography implies a linkage between Biology and Geography. It studies the distribution of biological materials over the earth’s surface and the factors responsible for the observed spatial variations. This provides a spatial pattern for study as fundamental as the variations in rock type (geology), land forms (geomorphology) or atmospheric processes (climatology). We seek not simply to describe these patterns but also to explain them: the question ‘Where?’ must be followed by the question ‘Why?’.

Biologists also ask these same questions. If past or present global distribution patterns of species (e.g. the great spread of coniferous trees in the high latitudes of the Northern Hemisphere; the floral elements comprising the vegetation of Australia; the world distribution of a particular species) are examined, then this study is what biologists call biogeography but what the geographer refers to as Plant or Animal Geography. But if the study is at the more local level (large scale) and centres on the interaction of species with their effective immediate environment, then the study becomes Plant or Animal Ecology. This can be sub-divided into autecology which deals with individual organisms or factors, and synecology which studies groups of organisms or complexes of factors.

Now the biogeographer may study the same phenomena as the ecologist but he usually places as much emphasis on the distributional aspects as on the environmental relationships in the study. Further, he will tend to stress the role of man in these patterns and processes or the importance for man of the findings in terms of past, present or future man-land relationships. Over the years it is this study which increasingly has become what the geographer regards as biogeography. Quite obviously the distinctions are not clear cut and, like ecology, biogeography draws heavily on information obtained from many sources (e.g. botany, zoology, meteorology, geomorphology, geology, archaeology, sociology). Both aim at an explanation through a synthesis of these data. Hill has examined the position of biogeography as a sub-field of geography, noting the various definitions and possible research themes. Naveh has recently reviewed changing attitudes to the role of man in ecological studies. For many years man was seen solely as an external, destructive agent. Naveh now argues strongly for a ‘Landscape Ecology’, which moves man to a central position in such studies, thus blurring the distinctions even more.

Whilst the contribution of the biologist to the subject is apparent, the geographical or spatial element should not be underrated. In another context, Darwin was aware of this when he declared in a letter to Joseph Dalton Hooker in 1845: ‘… that grand subject, that almost keystone of the laws of creation, Geographical Distribution.’

In the seventeenth century Francis Bacon unwittingly stated a fundamental principle for biogeography, namely, ‘we cannot command Nature unless we obey her’. Only recently has the vital importance of this dictum been appreciated. With the industrial and scientific revolutions of the eighteenth, nineteenth and twentieth centuries there grew up a feeling that man was becoming somehow independent of Nature and would eventually be able to control many aspects of his environment. Now we are painfully aware that our relationship with the other parts of Nature is becoming not less but more important. Resources are not unlimited, and if we continue to destroy, pollute or over-exploit our physical environment then we severely threaten our own existence. We are now the dominant species over most of the globe, either by virtue of our actual presence or as a consequence of our activities. The emphasis of biogeography on the role of man in ecological studies makes it a subject of increasing relevance for the future well-being of our population.

THE IMPORTANCE OF THE PLANT COVER

The central themes in elementary biogeography are usually illustrated by examples drawn from the plant world. There are good reasons for this emphasis on vegetation. Not all aspects can be covered in the time available at the introductory level and so concentration on selected areas and topics is necessary. Because animals are generally more mobile and elusive than plants and require more time-consuming and sophisticated techniques to study their ecology, they are less suitable for an introductory study. Moreover, vegetation makes up the most conspicuous element in the non-urban landscape. It profoundly influences processes operating at the interface between the atmosphere and the lithosphere (e.g. microclimates, soil properties). Plants are good site indicators and modify many habitat factors, creating a background or environment for the associated animal communities. But the influences are not all one way: plants and animals interact and influence each other in a most complex manner. The environment is holocoenotic, a term expressing the idea that the factors of the environment act collectively and simultaneously and the action of any one factor may be qualified by the other factors. The holocoenotic nature of the environment lies at the very core of all biogeographical thinking.

The study of plants provides a logical starting point for an understanding of the complexities in ecological relationships. The green plant stands as an intermediary between the inorganic and organic worlds. The basic source of energy for the biosphere is solar radiation but only plants can utilize this solar energy directly. All animals, including man, must obtain their chemical energy indirectly from solar energy through plant life. This dependency can be traced by constructing food chains for each animal species, e.g.

Food chains are seldom as simple as indicated but usually have numerous loops and interconnections. Animal life is thus, in this sense, parasitic on plant life. Man not only obtains his chemical energy (food) either directly from plants or indirectly as meat and other products from grazing animals but also many other necessities from the plant cover, such as wood products, fibres and drugs. It is therefore essential to know how the various types of plant cover originate, what relationships exist within the vegetation, what changes are taking place and what processes are involved.

Man’s basic crops (wheat, barley, maize, etc.) have been in existence for several thousand years. Only recently have we begun a systematic study of man’s relationship with these crop plants. Now, for the first time, we may soon be able, at a cost, to control environments completely to suit our crops or produce by genetical engineering tailor-made species to suit our environments. This is one of the main reasons for the conservation of all species so as to maintain the genetic variability of the biosphere. By wisely exploiting this ‘gene pool’ found in the wild, plant and animal breeders will be able to increase yields, improve quality, enhance environmental adaptability and improve disease and pest resistance in our crops.

Vegetation is one of man’s most important resources and it is a renewable resource in a world of resource depletion. The plant cover also plays a vital role in the atmospheric balance of oxygen and carbon dioxide and it is a considerable element in the water budget of any area. But another important function of vegetation is its scenic role. Much that we value visually in the landscape is the result of a subtle blend of vegetation and topography, whether occurring naturally or as a man-made entity. Our aesthetic appreciation of these landscape elements and our ranking of them indicates a role for perception studies in biogeography as in other branches of geography.

These then are some of the main reasons why biogeography must have as a strong foundation the systematic study of the earth’s plant cover.

PLANT CLASSIFICATION

Students reading biological literature frequently encounter difficulties with the wide use of Latin or Greek derivatives. At one level this centres on their use for the main sub-divisions of the Plant or Animal Kingdoms (classification) and at another it concerns the naming of individual species mentioned in particular studies (nomenclature).

The main sub-division in the Plant Kingdom is between the Cryptogams and Phanerogams, The classification is based on the morphological variations shown by plants, especially the expression of the reproductive process in morphological terms. Cryptogams are non-flowering plants and reproduction is by means of spores rather than seeds; the whole reproductive apparatus is rather inconspicuous or hidden, making up a small, less obvious part of the plant body. In contrast, Phanerogams display their reproductive mechanisms prominently, as cones or flower heads, and are seed-bearing.

Cryptogams, having less complex internal structures, are the so-called ‘lower plants’. They can be further sub-divided into the following main groups:

(a) Bacteria – single-celled plants sometimes referred to as the Schizophyta because they reproduce by simply dividing the cell into two parts.

(b) Algae – seaweed is a common example but not typical of the group. Most are much smaller, often existing as microscopic forms in soil or still water.

(c) Fungi – mushrooms and toadstools are obvious examples but, once again, most species are much smaller and many occur microscopically in the soil.

(d) Bryophytes – all the mosses and liverworts belong to this group. The small capsule on a thin stalk growing up from the moss cushion and usually visible to the naked eye in many species is, in fact, the spore-containing organ of the plant.

(e) Lichens – they exist in several growth forms but in all cases lichens are composite plants, consisting of algae and fungi living together in a mutually beneficial (symbiotic) relationship.

The above sub-divisions are grouped together as the non-vascular Cryptogams: plants that have not developed a system of specialized tissue, a vascular system, for the movement of fluids (e.g. nutritional solutions) around the plant body. Instead, transport is achieved by general diffusion. The rest of the Plant Kingdom has such a system which, of course, is also a feature of higher animals and represented in man by the heart, veins and arteries.

(f) Pteridophytes – this group of Cryptogams are vascular and most examples are conspicuous, upstanding plants (e.g. ferns, horsetails). Many have an ancestry traceable to the Devonian Period, some 250 million years ago.

Phanerogams (or Spermatophyta) are of more recent origin and the evolution of structural complexity is reflected in a corresponding morphological diversity. Two main sub-divisions are recognized:

(a) Gymnosperms – these are seed producers in which the seed is said to be naked or not enclosed in attractive or protective tissues (cf. the cherry seed encased in a hard shell which in turn is surrounded by soft, fleshy tissue). Most are cone-bearing and the seeds are released after the cone ripens. Conifer trees are typical examples but the Maidenhair tree is a more primitive type in this group.

(b) Angiosperms – here the seeds are enclosed in tissues and the group is usually known as the true ...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Preface to the Second Edition
• Acknowledgements
• PART 1 BASIC CONSIDERATIONS
• PART 2 SELECTED EXAMPLES FROM THE BRITISH ISLES
• General Index
• Species Index