The Diversity of Amphibians and Reptiles: An Introduction

255 Pages·1999·6.2 MB·English

by  Prof. Dr. John L. Cloudsley-Thompson (auth.)

J.L. Cloudsley-Thompson The Diversity of Amphibians and Reptiles
Springer
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John L. Cloudsley-Thompson
The Diversity
of Amphibians and Reptiles
An Introduction
With 87 Figures
Springer
Prof. Dr. J.L. Cloudsley-Thompson
elo Department of Biology
University College London
Gower Street
London, WCIE 6BT, UK
ISBN-13: 978-3-642-64218-0 e-ISBN-13: 978-3-642-60005-0
DOl: 10.1007/978-3-642-60005-0
l.ibrary of Congress Cataloging in-Publication Data
Cloudsley-Thompson, J.L. The diversity of amphibians and reptiles: an introduction I John L.
Cloudsley-Thompson. p. cm. Includes bibliographical references (p. ) and index.
ISBN-13: 978-3-642-64218-0
l. Reptiles. 2. Amphibians. I. Title.
Ql.6<1l.C57 1999
597.9-ddc21
98-45640
CIP
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C Springer-Verlag Berlin Heidelberg 1999
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Acknowledgements
I would like to extend my warmest thanks to my dearest wife Anne Cloudsley
for her advice on a number of issues, to Mrs. Eileen Bergh for typing the
manuscript, and to Dr. Dieter Czeschlik and Dr. Andrea Schlitzberger, Biology
Editorial Springer-Verlag, for their friendly cooperation.
Contents
1 Introduction 1
2 Evolution 11
3 Convergence and Extinction 29
4 Locomotory Diversity on the Ground 41
5 Arboreal, Aerial and Aquatic Locomotion 61
6 Diversity of Anti-predator Devices 85
7 Nutritional Diversity 109
8 Reproductive Diversity and Life Histories 131
9 Daily and Seasonal Cycles, Hibernation, Aestivation and Migration 157
10 Thermal Diversity and Temperature Regulation 177
11 Water Balance and Excretion 197
12 Relationships with Mankind 213
Bibliography 227
Subject Index 243
1 Introduction
Despite current concern regarding the maintenance of biodiversity in the
world, there is no universally accepted definition of the term 'diversity' and
no single method of measuring it. In the present book, among other things,
the variety of ways in which amphibians and reptiles have become adapted to
live in different environments will be considered - that is, diversity of form
and function - as well as the diversity of species that have evolved and co-exist
within each particular environment or habitat. I have written primarily for
students, amateur herpetologists, and all who are interested in natural history
and wildlife generally. Let me, at the outset, therefore, reassure the reader
both as to what will not be discussed and what will. To begin with the former,
diversity is often regarded as a measure of the richness of species in a com
munity or biome. This concept provides a more useful measurement of the
characteristics of a community when it is combined with an assessment of the
relative abundance of the various species present.
The index of diversity is a mathematical expression of the number of
species, and the number of individuals of each species present. Various for
mulae may be used to quantify diversity. Of these, one of the most commonly
employed is the Shannon-Wiener index. This is used when a community
contains so many individuals that it can only be investigated by means of
sampling. In this case, the index (D) is the ratio of the number of species to
their importance as expressed, say, by their biomes or productivity within
the community. D = - ~ is " log "; where s = total number of species in the
sample, i = total number of individuals in one species, 1t (a decimal fraction)
is the number of one species in relation to the number of individuals in the
population, and the log is to base -2 or base -e. The number of species in the
environment is designated a diversity (intra-habitat), ~ indicates the number
of habitats or communities present (inter-habitat), and y diversity the rate of
turnover.
2 Introduction
Analyses such as this do not, however, take into account the variety
of morphological forms present in a community or biome - terrestrial,
cursorial, fossorial, aquatic, arboreal, aerial and so on. These are the topics
with which this book is concerned. Moreover, related groups or taxa of
smaller animals not only contain more species than do groups of larger
ones living in the same habitat, but also contain more individuals of each
species. This is simply because, on a small scale, there are many more micro
environments in the same region, e.g. areas of shrubs, trees, grasses, rocks,
and so on, than there are in major habitats. The smaller the scale, the greater
is the number of micro-habitats and, consequently, of species and individu
als. Furthermore, it is a matter of opinion whether a diversity should be
reckoned in terms of the number of species present or of the genetic diversity
within each species (see May 1991).
More homogeneous environments must obviously contain fewer species
than do less homogeneous environments, and the most numerous species
occupy the largest habitats. For example, the marine copepod crustacean
Calanus finmarchicus has possibly one of the greatest biomasses of any
animal species because it is adapted to pelagic life throughout the oceans.
Similarly, the yellow-bellied sea snake (Pelamis platurus) is probably the
world's most numerous reptile species, partly on account of its extensive
marine distribution. At the same time, because life began in the sea, there are
many more marine than terrestrial phyla, as the major groupings of animals
are called.
The concept of diversity is so greatly complicated by the numerous criteria
involved in its assessment that I have not attempted to define the term, any
more than I would try to define precisely what is understood by the word
'species'. The reader will have to be content with a general idea as to what,
in this book, is meant by both terms, because it is not possible to be more
precise. Genetic diversity has not been considered in these pages, nor have the
numbers of species in various biomes. I have, however, tried to give some
impression of the general diversity of amphibians and reptiles with reference
to the ways in which they have become adapted to life on earth. This approach
may not, by some, be considered sufficiently rigorous. Nevertheless, other
readers may find it more interesting than to consider genetic diversity among
individuals within a population - as is currently fashionable in biological
circles.
To some people, specialization is particularly rewarding; for others there is
more interest in taking a generalized approach to biology. In most research it
Introduction 3
may be convenient to specialize - to investigate a rather narrow range of
topics - but important discoveries are often made when generalized knowl
edge is focused onto a narrow subject, or when different specialists com
bine to attack a large problem, such as the chemistry of snake venoms. Both
amphibians and reptiles are interesting not only in their own right and in the
study of evolution - especially perhaps the fossil Mesozoic dinosaurs, ptero
dactyls, ichthyosaurs and plesiosaurs - but also as material for physiological
and embryological research. Until comparatively recently, every student of
biology was at some time in his or her career asked to compare the early
stages of development of the fish, frog and fowl.
My own liking for amphibians and reptiles seems almost to be innate. I
can just remember, at the age of five, collecting some animals from a pond
and taking them to my father in part of a broken glass milk bottle. An older
boy had told me they were 'tadpoles', but my father soon disillusioned me.
He explained that they were mosquito pupae, and took me to another pond
to catch real tadpoles. During my early childhood, and later at boarding
school, I delighted in pond life. In those far-off days, ponds and streams
were scattered throughout the English countryside. On holiday picnics with
the family, and on free afternoons whilst at boarding school, I was able to
indulge my hobby of collecting aquatic plants and animals for my aquarium
and the garden pond. Amphibia were easy to come by - crested, smooth and
palmate newts, frogs and toads - but reptiles were naturally less common,
although, according to my diary, we found four adders, two of them black,
within 100 yards of each other at Effingham, Surrey, on 6 May 1935. Grass
snakes were more common. (I also had a pet Greek tortoise and a couple
of European pond tortoises.) I mention this to indicate the extent to which
amphibians and reptiles have decreased in Britain during the last 60 years or
so. At the same time, there has been an alarming decline in amphibians,
especially frogs, worldwide. This will be discussed in Chapter 12. On the
other hand, it is very much easier to travel these days, and to visit tropical
and subtropical countries where amphibians and reptiles are easily seen.
Moreover, whereas before World War II comparatively few people in Europe
or America were interested in amphibians and reptiles, today there are
many herpetologists in both continents and elsewhere who possess exten
sive vivaria and maintain their captives in conditions suitable for breeding.
This requires both skill and knowledge. These herpetologists are also fre
quently involved in conservation which is most beneficial to the environment
generally.
4 Introduction
At this point it may be advisable to clarify a few matters of nomenclature.
First, the family Salamandridae (order Urodela* or Caudata) contains a large
number of species, some of which are usually referred to as newts, others as
salamanders. There are 12 species of newts in Europe and at least lO other
species that are known as salamanders. European newts are members of the
genus Triturus: they tend to be less terrestrial than salamanders, but there are
many exceptions to this generalization (see discussion in Griffiths 1996). Most
North American Salamandridae are known as salamanders, but members of
the genera Taricha and Notophthalmus are also sometimes called newts.
Clearly, too much importance should not be placed on these common names.
Other English names that require explanation are turtle, tortoise and terra
pin. In the United States all Chelonia are known as turtles, but in Britain this
term is restricted to marine turtles. Terrestrial Testudinidae are called tor
toises while the Emydidae, a large and varied assemblage of freshwater and
semi-terrestrial turtles, are usually referred to as terrapins - although Emys
orbicularis is sometimes known as the European pond tortoise! In general,
throughout this book I have tended to use the term that is applied in the
country in which the animal in question resides or by which it is known in the
publications cited.
Some people are intimidated by the use of Latin names. This is unfortunate
and unnecessary. It does not bother them to consult a telephone directory
which is full of names, some of which will be unfamiliar but may be necessary
for identification of the number one wants to phone. Generic names, the
first of a pair of names in italics, are the equivalent of a surname. They
are accorded a capital for the first letter, e.g. Alligator. The specific
name follows the generic name and is spelled with a lower case first letter,
e.g. mississippiensis. When the name is being used frequently the generic
name may be abbreviated to its initial, e.g. A. mississippiensis, but this is only
possible where no confusion is incurred. Family names, e.g. Alligatoridae,
and subfamily names, e.g. Alligatorinae, should not be placed in italics. It is
quite surprising how seldom these simple conventions are understood by the
popular press! In this book I have usually given the Latin name (as well as the
common name, where there is one) of each species in the hope that repetition
will enable the reader to become familiar with the concept as painlessly as
possible.
Herpetology, like arachnology, is a subject in which professionals and
amateurs can meet on equal terms, at least as far as most field work is
,. Caudata has priority, but Urodela is frequently used especially in older literature.