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cambridge university press 978 0 521 78727 7 environmental biology michael reiss and jenny chapman excerpt more information chapter 1 introduction to environmental biology by the end of this chapter ...

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    Cambridge University Press
    978-0-521-78727-7 - Environmental Biology
    Michael Reiss and Jenny Chapman
    Excerpt
    More information
           CHAPTER  1
                                Introduction to 
                                environmental biology
                                 By the end of this chapter you should be able to:
                                 1 explain the meanings of the terms habitat, microhabitat, niche and population;
                                 2 distinguish between a community and an ecosystem;
                                 3 describe similarities and differences between the growth in numbers of the human
                                    population and other animal populations;
                                 4 outline the effects of human activity on the natural environment;
                                 5 explain the value of monitoring the environment.
                  What is ecology?                                             amount that falls in a year, how it is distributed
                                                                               throughout the seasons, and significant informa-
                  This book is about ecology and conservation.                 tion about the temperature, sunlight and soil
                  Ecology is the study of organisms in their natural           type. The jigsaw pieces interlock with one another
                  surroundings. The word ecology comes from two                in numerous, subtle ways.
                  Greek words – oikos meaning home and logos                      In many ways ecology is a relatively new 
                  meaning understanding. So ecology is all about               science. Indeed, the word was only coined by the
                  understanding the homes of animals, plants and               German biologist Ernst Haeckel in 1869, fully ten
                  other organisms. The surroundings of an organism             years after Charles Darwin published his theory of
                  are known as its environment. Environments con-
                  sist of many components including both physical
                  features, such as climate and soil type, and 
                  biological features, such as predators and prey. The
                  term environmental biology has wider connota-
                  tions than ecology because it includes the study of
                  humans in the environment, so you will find such
                  subjects as agriculture, pollution and the unnatu-
                  ral surroundings we create in this book too.
                    Understanding the ecology of an area is like try-
                  ing to put together a gigantic, multidimensional
                  jigsaw. Some pieces are the individual species in
                  the area. In an oak wood, for example (figure 1.1),
                  the species might include bluebells, oak trees,
                  earthworms, snails, hedgehogs, wood ants and
                  tawny owls. Other pieces in the jigsaw are the               ● Figure 1.1 Stoneywell Wood, Leicestershire, in
                  important aspects of the physical environment,                 spring. The leaves on the oak trees are just
                  for example the pH of the rainwater, the total                 emerging above the carpet of bluebells.
    © Cambridge University Press                                                                                                 www.cambridge.org
     Cambridge University Press
     978-0-521-78727-7 - Environmental Biology
     Michael Reiss and Jenny Chapman
     Excerpt
     More information
                  2 Introduction to environmental biology
                  natural selection. Yet, in little over a century 
                  ecology has grown to become one of the most
                  important disciplines within biology. Like all
                  branches of science, it has its own language. This
                  includes the terms habitat, population, commu-                   10
                  nity and ecosystem, which you will have already                                97
                                                                                    8
                  met in Biology 1.
                     A habitat is the place where an organism lives.                          96     98
                                                                                    6
                  The word is Latin and literally means ‘it dwells’.
                  Actually, organisms from a single species can live                4        95
                  in a number of habitats. For example, the common                                           99
                  rat (Rattus norvegicus) is typically found associated
                                                                                  Height above ground (m)2        99.5
                  with farms, refuse tips, sewers and warehouses.
                  However, it also occurs in hedgerows close to                     0
                  cereal crops or sugar beet, and in salt marshes. On                     2      4      6      8      10     12     14
                  islands (e.g. the Isle of Man, Rhum and Lundy) rats                                Prey length (mm)
                  also occupy grassland and the sea shore.                       ● Figure 1.2 The feeding niche of the blue-grey
                     With small organisms, especially those living in              gnatcatcher (Polioptila caerulea). The contours show
                  a restricted area such as in the soil or on a single             the feeding frequencies for adult birds during the
                  plant or animal, it is worth being more precise                  nesting period in July and August in oak
                  about exactly where they live. The term                          woodlands in California. 95% of their diet is taken
                  microhabitat – ‘a small habitat’ – is used to                    within the contour marked 95, 96% within the
                                                                                   contour marked 96, and so on.
                  describe this. A single habitat may have many
                  microhabitats. For example, if you are an insect               Polioptila caerulea, a North American bird. This is
                  living on an oak tree, life is very different depend-          an insectivore and the horizontal axis shows the
                  ing on whether you live on the upper surface of                length of the insects on which it feeds. The verti-
                  the leaves, the lower surface of the leaves or inside          cal axis shows the height above ground at which
                  them. It is even more different if you live under              it forages. The contour lines with numbers 
                  the bark, next to the roots or inside an acorn. Each           indicate the frequency with which the birds feed
                  of these different places is a microhabitat.                   at a particular height and on a particular length
                     A niche is a complete description of how the                of prey. You can see that the birds concentrate on
                  organism relates to its physical and biological                prey 4mm in length, which they catch about
                  environment. Just as in a jigsaw puzzle each piece             3–6m off the ground.
                  has its own unique shape and pattern, and only                    However, there are many other aspects to an
                  fits in one place, so each species has a unique                 organism’s niche in addition to its feeding niche.
                  niche – the way it fits into its environment.                   In theory, other axes could be added at right-
                     Consider a particular species, the grey heron               angles to those in figure 1.2. Temperature could be
                  (Ardea cinerea). Its habitats are water meadows,               shown on a third axis, risk of predation at differ-
                  rivers, lakes and the sea shore. A complete                    ent times of the year on a fourth, height above
                  account of its niche would include a description               ground of the bird’s nest on a fifth, and so on. In
                  both of its physical environment (such as the type             practice, though, no more than two or three axes
                  of water it needs, the temperature range in which              can be shown on a graph. Computers, however,
                  it can survive and reproduce) and of its biological            can store and compute data for many more.
                  environment (such as the prey it eats, its competi-               The ecological principle that each species has
                  tors and the vegetation it needs for its nest).                its own unique niche and that no two species can
                     It is difficult to provide a quantitative descrip-           coexist if they occupy the same niche is known as
                  tion of an organism’s niche. Figure 1.2 shows the              Gause’s competitive exclusion principle. The 
                  feeding niche of the blue-grey gnatcatcher,                    biologist G. F. Gause gets the credit because of his
     © Cambridge University Press                                                                                                    www.cambridge.org
    Cambridge University Press
    978-0-521-78727-7 - Environmental Biology
    Michael Reiss and Jenny Chapman
    Excerpt
    More information
                                                                                            Introduction to environmental biology 3
                 research on single-celled ciliates in the genus              The term ‘community’ is a valuable one in ecol-
                 Paramecium.                                               ogy. However, in 1935 Sir Arthur Tansley invented
                   A population is a group of individuals within a         the term ecosystem because he realised that the
                 species that have the opportunity to breed with           organisms that make up a community cannot
                 one another because they live in the same area at         realistically be considered independently of their
                 the same time. It follows from this definition that        physical environment. The term ecosystem, there-
                 individuals from two different species cannot             fore, applies to a community of organisms and its
                 belong to the same population. This is because,           associated physical environment.
                 with occasional exceptions, species are reproduc-            There is one other feature of ecosystems and
                 tively isolated from one another. Tawny owls do           their associated communities worth stressing.
                 not breed with short-eared owls, for example.             This is that ecosystems are dynamic. Indeed, some
                   Most species are divided into many populations          ecosystems change as new species invade and 
                 that are geographically separated. Bluebells in one       others die out. A grassland invaded by shrubs and
                 wood, for example, will belong to a different             trees will change gradually as scrubland and then
                 population from the bluebells in another wood             woodland develops. In a mature ecosystem, such
                 several kilometres away. Indeed, in a large wood          as oak woodland, the population sizes and activi-
                 there may be several populations of bluebells,            ties of the different species will alter from season
                 though the boundaries between populations may             to season and year to year. The bluebells in figure
                 be somewhat arbitrary.                                    1.1 flower so beautifully in spring, but by late 
                   A communityis an association of species that            summer they have set seed, the leaves have died
                 live together in some common environment or               back and the bluebell bulbs are ready to lie 
                 habitat. Most communities are composed of a mix-          dormant until the next spring.
                 ture of prokaryotes, protoctists, fungi, plants and
                 animals. The organisms in a community interact            SAQ 1.1 
                 with one another in all sorts of ways. For a start,       Arrange the following terms in a hierarchy of
                 there will be feeding relationships. In most com-         descending size and complexity: community, habitat,
                 munities, autotrophs (also known as producers             ecosystem, microhabitat.
                 and comprising green plants, photosynthetic
                 algae, photosynthetic bacteria and chemosynthetic
                 bacteria) provide food for herbivores (also known         SAQ 1.2
                 as primary consumers). In turn, herbivores are            What parts of an ecosystem are also found in its
                 eaten by first-level carnivores (also known as             community?
                 secondary consumers), and these may be eaten by
                 second-level carnivores (or tertiary consumers).
                 Eventually organisms die and their remains are            Humans in the environment
                 broken down by decomposers. These feeding 
                 relationships can be represented by food chains or        We have given ourselves a Latin binomial, Homo
                 by food webs that show the interrelationships             sapiens, just like all the other species we have 
                 between the various food chains in a community.           classified. However, it is obvious that the impact
                   The species in a community also interact with           humans have on the environment is unlike that
                 one another in other ways. They may rely on one           of any other species. Ancient humans evolved in
                 another for reproduction, as is the case in insect-       Africa and migrated out into Asia and Europe a
                 pollinated plants. Or one species may act as a            million or more years ago. A second wave of
                 home for another, as a humpback whale carries             migration of modern humans spread out of Africa
                 barnacles. Or the interaction may be more subtle          about 130000 years ago resulting in the colonisa-
                 – all the species in a woodland, for example, rely        tion of every continent. 
                 on the activities of the various soil organisms              Before humans evolved, of course, all the com-
                 which recycle nutrients.                                  munities in the world were natural. In Britain,
    © Cambridge University Press                                                                                           www.cambridge.org
     Cambridge University Press
     978-0-521-78727-7 - Environmental Biology
     Michael Reiss and Jenny Chapman
     Excerpt
     More information
                  4 Introduction to environmental biology
                     a                                                                      b
                                                  overshoot
                          carrying                                                               carrying
                          capacity                                                               capacity
                       Number in populationexponential growth                                         exponential growth
                                                                                              Log of number in population
                       0                     Time                                             0                     Time
                  ● Figure 1.3 Population growth.       a Normal plot of population increasing exponentially
                     until the carrying capacity is reached, when the population stabilises.       b A log-normal
                     plot of the same data as a. With population plotted on a log scale an exponential curve is
                     represented by a straight line.
                  natural vegetation during the Ice Ages was tree-                species, the population initially grows at a rate of
                  less Arctic grassland called tundra; during                     increase related to the reproductive rate of the
                  warmer interglacials, after the ice sheets melted,              species. Plotting the log of the numbers of 
                  trees invaded. In the south, forests of oaks, ash,              individuals in the population against a linear plot
                  lime and hornbeam grew; in the Scottish high-                   of time gives a straight line (figure 1.3b). Eventually
                  lands, the main vegetation was Scots pine conifer               there will be competition for resources that are in
                  forest. These mature forests are called the climax              limited supply. This competition is intraspecific
                  vegetation, but such vegetation is now rare due to              because it occurs between individuals belonging
                  human activities.                                               to the one species. The result of this increasing
                     Humans learned to make and use fire early in                  competition is that the population growth slows
                  their history, about half a million years ago – very            down. Eventually the population should reach the
                  useful during Ice Ages! Before this, only lightning             maximum size that the environment can sustain,
                  started wildfires that had the potential to damage               a figure known as the environment’s carrying
                  vegetation. About 10000 years ago humans also                   capacity. The population may overshoot the 
                  began to change the natural vegetation by cultivat-             numbers the environment can support, but will
                  ing crops. Animals were domesticated at about the               then fall to stabilise at the carrying capacity.
                  same time. Captive animals graze areas of vegeta-                  However, human population biology is more
                  tion in much greater densities than natural animal              complex, and seems to have gone through differ-
                  populations do. The practice of burning and                     ent phases of growth. As you can see from figure
                  grazing led to the vegetation in many areas of the              1.4, anthropologists and archaeologists think that
                  world developing into grasslands (see page 10). As              the world’s human population was stable, or only
                  human populations grew, their dwellings – in                    rising very slowly, up to about 10000 years ago
                  villages, towns and then cities – also restructured             and that it was rather small – somewhere between
                  or even destroyed the vegetation.                               5 and 10 million. Archaeological evidence 
                     As humans are animals, human population                      indicates that about 10000 years ago the popula-
                  biology might be expected to follow the same                    tion started to rise more rapidly; there was a
                  rules as those of other animal populations (figure               change in the rate of increase of population and
                  1.3a and Biology 2, chapter 3). In other animal                 in the carrying capacity. This reflects the change
     © Cambridge University Press                                                                                                      www.cambridge.org
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...Cambridge university press environmental biology michael reiss and jenny chapman excerpt more information chapter introduction to by the end of this you should be able explain meanings terms habitat microhabitat niche population distinguish between a community an ecosystem describe similarities differences growth in numbers human other animal populations outline effects activity on natural environment value monitoring what is ecology amount that falls year how it distributed throughout seasons signicant informa book about conservation tion temperature sunlight soil study organisms their type jigsaw pieces interlock with one another surroundings word comes from two numerous subtle ways greek words oikos meaning home logos many relatively new understanding so all science indeed was only coined homes animals plants german biologist ernst haeckel fully ten organism years after charles darwin published his theory are known as its environments con sist components including both physical feat...

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