Chapter 1: What Is Ecology?
There are many different definitions of what ecology is. They all share the notion that ecology is the study
of the factors that explain distribution and abundance of organisms.
Distribution and abundance are straightforward ideas. How many of a species are there, and where are they?
The causes for those distributions and abundances are more complex. They involve the physical and
biological environment including other species present and their abundance, history of both the physical and
biological conditions over space and time, and relationships among these factors.
The basic ideas in this definition are not new. The word, based upon the Greek word oikos, meaning home,
was first applied to the scientific study of organisms and environment by Ernst Haeckel in 1870.
"By ecology, we mean the body of knowledge concerning the economy
of nature - the investigation of the total relations of the animal
to both its organic and to its inorganic environment. … In a word,
ecology is the study of all the complex interrelationships
referred to by Darwin as the conditions for the struggle for
existence."
Short Biography of Ernst Haeckel:
Ernst Haeckel was born in 1834 and died in 1919. Haeckel was
an early and ardent supporter of Darwin's theory of evolution.
However, some of his ideas might today be regarded as racist.
He thought that humans comprised 12 different species. He
expected the "superior" Germanic group would eventually drive
other "inferior" groups to extinction. In 1866, Haeckel published
General Morphology, a genealogical tree of vertebrates, that
represented the first ordering of life according to the principles
of Darwinism. The definition of ecology we use is drawn from
that book. In 1868, in History of Creation, he argued for an
evolutionary scheme in 22 steps, of which the 21 st step was the
'missing link' between apes and humans. In 1899 he published The Riddle of the Universe,
which attacked the religious view of life, and attempted to place mankind in a dynamic
universe. Haeckel had chosen a career in science, rather than art. Late in life he combined his
two passions, using his own illustrations in Art Forms in Nature.
As these factors are complex individually, and even more complex collectively, ecology is a rapidly growing
and evolving discipline. To achieve its goals of understanding relationships and causes, it draws on many
other disciplines. Geology is useful because, for example, soil chemistry is important in determining plant
distributions, and therefore species dependent on the plants for food and/or homes. Geology also teaches us
about continental drift, which is important in understanding the distributions of many species. Physiology is
important to understand the mechanisms involved in energy assimilation and use. Behavior is important in
understanding population structure and mating strategies. Genetics, because genes determine what the
organisms are like, how they function physiologically, thus where they can potentially live, and, at least in
part, how they will behave is critical to modern ecology. An argument could easily be made that ecology
draws on every major area of biology to achieve its goals.
The History of Ecology
The history of ecology can, in one sense, be suggested to begin with observations of the ancient philosophers
of Egypt and Greece. However, their observations fall into what we would now class as "natural history".
The data gathered was about what species were found and where they were found. Associations with
physical conditions of the environments of the species were noted, but quantitative information was not a
part of these data. Evolution generally was not a part of the story. Plato's writings were metaphysical: there
was a clear distinction between the "real" world of ideal species and the imperfect observations we make
with our senses. Aristotle believed in a "scala naturae", which was a scale of increasing complexity along
which species could be ordered. Species remain unchanging on their rungs of this ladder, and evolution does
not occur. The philosophical notions were abstract, and clearly did not consider the abundance of species
and the reasons underlying either distribution or abundance.
Quantification in "ecology" can probably be traced to observations collected during the middle ages,
at the time of the Black Plague. The disease aroused such fear that it became important to document its
occurrence in neighborhoods. In England, matrons in each parish acted as amateur coroners, trying to
determine the causes of death. The parish records, many still preserved in the Guildhall Museum Library in
London, record the numbers of births and christenings and the probable causes of death for each corpse on a
regular and an annual basis. They, of course, indicated any sign of deaths due to the plague so that whatever
protective action was possible could be taken. The records are still a sort of quantitative natural history.
The Origins of Population Biology
The Bills of Mortality and Christening provided the data for the first calculations of population growth rate.
In 1662, John Graunt published "Natural and Political Observations", in which he estimated the doubling
time for the population of London from rates of birth and death in the bills. His estimate was that the
population of London should have been doubling every 56 years. As a religious man, this produced a
conundrum. Working through the generations reported in the bible, chroniclers figured that creation
occurred in 3948 BC.
Biography of John Graunt:
John Graunt was born in 1620 and died in 1674. Graunt,
like many of the figures important in the early history of
Ecology and Population Biology, was not primarily a scientist.
He had no university education. He had been apprenticed to
a haberdasher, and he earned his living in that trade. He was,
however, influential in London, holding various political offices,
and was made a member of the Royal Society. It is clear from
this that his scientific endeavors were respected by his peers.
He wrote only one major work, Observations on the Bills of
Mortality (1662). In it he established that more female babies
were born than males, as well as, on average, longer lifespans
for females. (There are no known portraits of John Graunt. The
closest we can come is this photograph of an actor portraying
him.)
Assuming that biological rates had not changed, that meant there had been 87 doublings from the time of
Adam and Eve. If that were true, the population would have reached 1026 individuals, or about 100 million
per square centimeter of habitable ground. Even Graunt knew this could not be; he recognized that a pattern
of regular doubling could not continue indefinitely. This was the first formal recognition of limits to growth.
Regular doubling has a name as a pattern of growth. It is called exponential or geometric increase. This term
is not one that originated in 20th century quantitative ecology. Instead, the term was coined by Sir Matthew
Hale in 1677.
Biography of Sir Matthew Hale:
Sir Matthew Hale lived from 1609 to 1676. After studying law
at Oxford, he was admitted to Lincoln's Inn, where he studied
mathematics, physics, anatomy and architecture. His law career
advanced rapidly, from being a judge in the court of common
pleas beginning in 1653 to Lord Chief Justice in 1664. He held
that position until retiring due to ill health in 1676. Hale presided
over a famous and controversial trial of witches in Suffolk, and
wrote what remains a basic treatise on the common law
associated with criminal offences, History of the Pleas of the
Crown. He apparently was able to serve free of political, religious,
or social biases, and thus remained an important jurist through
Oliver Cromwell's parliament and the rule of Charles II. His
mathematical training led to his contribution of the terminology
for geometric increase in population size.
His career is indicative of the breadth of interests and education at the time. Population biology was at most
a hobby for him. His 'real' job was as Chief Justice of the King's Bench, the equivalent in North American
courts of being chief justice of the Supreme Court.
Another of Graunt's friends recognized the implications of Graunt's calculations. William Petty, in
"Another Essay in Political Arithmetic" (1683) established the notion of a maximum sustainable
population size. We call that population size the carrying capacity, K.
His estimate of sustainable population density was supported three centuries later by the best and brightest
thinkers assembled by the Rockefeller Foundation, whose work was published as "The Limits to Growth"
in 1960. He estimated the K as a density of 2 people for every 5 acres of habitable land. However, he did not
know the total amount of habitable land on earth, and mistakenly estimated that area as 50 billion acres. He
over-estimated by approximately a factor of two, and, in parallel, his estimate of a K of 20 billion was
similarly too large by the same factor. The Rockefeller Foundation estimate of K is 10 billion. It is
interesting to think about what the similarity of modern and historical estimates of K for the human
population means. Is it that our resource needs and our resource base per person and per unit area are still
the same? Is the reason our much improved standard of living (and associated energy costs) have had no
impact is because we are living on a historical energy surplus (fossil fuels) that cannot be indefinitely
maintained?
Biography of William Petty
William Petty was born in 1623 and died in London in 1687.
His family apparently was poor, and he was sent to sea as
a cabin boy at age 15. After he returned, he studied at a
number of universities, eventually earning an M.D. at Oxford
in 1650, though he apparently never earned a Bachelor's
degree. While he is considered the father of quantitative
demography, based on Natural and Political Observations
(1662), he may not have been the author. Most of his works
were in the field of economics, in which he was apparently
the first to use statistics to arrive at his conclusions. Among
his works in economics are Treatise of Taxes and
Contributions (1662), Political Anatomy of Ireland (c.1672),
and Political Arithmetick (1690). Some believe he was the
author of the book we have listed as John Graunt's, but that is not widely accepted. He, too,
was a member of the Royal Society. While a student, he earned his living as a jeweller.
Later he prepared anatomical specimens and was a professor of Anatomy at Oxford. He
left Oxford and became a professor of Music at Gresham College. He surveyed and drew
Narration continues:
maps of Ireland that are considered the foundation of Irish geography. Late in life he
became wealthy, but, possibly because of his heritage, never became powerful, even
though he contributed so much to economics, demography and cartography.
Petty also did some corrective surgery on Graunt's doubling time. He recognized that a portion of the
increase in London's population was not due to the balance between birth and death. Instead, an important
part was due to the immigration into London associated with the onset of the industrial revolution. His
revised estimate of the inherent doubling time was 360 years.
That is far slower than Graunt had figured. Petty went further, and suggested that the rate of population
growth had slowed since biblical times. That slowing is a preliminary hint on the path to describing logistic
population growth, which has a maximum population size, the carrying capacity K.
The Origins of the Theory of Evolution
Historically, the next important development was Thomas Malthus' recognition that population growth may
potentially be exponential, but the growth of needed resources is generally linear.
He suggested, in "An Essay on the Principle of Population" that population growth would eventually
overwhelm the amount of resource available. When that happened, there would be "misery and vice". The
misery part seems apparent: starvation and disease in a population weakened by lack of food. By vice he
meant artificial means of reducing the number of children born, as parents could not adequately feed them.
In later editions, under pressure from his peers, he added a third means of restricting population growth,
moral restraint. The importance of Malthus's ideas was not recognized widely until they underpinned a
major part of Darwin's theory of evolution.
Short biography of Thomas Malthus:
Thomas Malthus was born in 1766 just south of London.
Like many people known today for their contributions to
science, he was educated to be a cleric. In 1805 he took
a position as professor of Political Economy at the college
of Haileybury. The college educated those who worked in
the East India Company. He completed his working life at
the college. His key work was An Essay on the Principle of
Population…, initially published in 1798, but revised and
expanded a number of times during the first years of the
19th century. Two key principles were presented:
1) Populations in crease geometrically, while the resources
needed to support them increase arithmetically (by which
he meant linearly) and 2) mankind has two basic drives,
for food and for sex. A key quotation from the book indicates where Darwin drew one of his
major ideas:
"Through the animal and vegetable kingdoms, nature has scattered the seeds of life
abroad with the most profuse and liberal hand. She has been comparatively sparing in the
room, and the nourishment necessary to rear them… The race of plants and the race of
animals shrink under this great restrictive law. And the race of man cannot, by any efforts of
reason, escape from it."
Short biography of Georges Cuvier:
Georges Cuvier lived from 1769 to 1832. He contributed to
geology, but also added to paleontology and comparative
anatomy. He could well be regarded as the father of this
last subject. He was one of the first to recognize that
species had gone extinct during the history of the earth,
and also to suggest the great age of the planet. In finding
fossils in sediments, he indicated that those sediments were
"thousands of centuries old". He believed (correctly) that life
in the sea had preceded life on land, and (correctly) that
reptiles had preceded mammals. However, he also believed
that species do not change during their spans of existence,
that the earth had undergone a series of geological
catastrophes.
Short biography of Charles Lyell:
Lyell lived from 1797-1875. His most important contribution
to science was a painstakingly established principle of
uniformitarianism. The principle, published in The Principles
of Geology: Being an Attempt to Explain the Former
Changes of the Earth's Surface, by Reference to Causes
now in Operation (1830), was that what is happening
geologically in the present can explain the history of the earth.
Geological processes are ongoing. Darwin took a copy of this
book along on the expedition of the Beagle, and it helped him
understand how he could find marine fossils on the slopes of
the Andes. Lyell was influential in persuading Darwin to publish
his theory of evolution in the same issue that also contained
Alfred Russell Wallace's essentially identical theory.
Short biography of James Hutton:
James Hutton (1726-1797) was the first to recognize the
dynamic geological history of the earth. He found layers of
sedimentary rock set one on top of another, and saw this as
evidence of sequential deposition and a vast age for the earth.
In Scotland, he found intrusions of granite into sedimentary
layering, and took this as evidence of enormous heat in the
core of the earth. In both these observations and interpretations
he was correct, but, without modern knowledge, took the age of
the earth to be limitless. His ideas of geological dynamism were
a critical influence on Lyell, and thus on Darwin.
Narration continues: Soon after this there was a revolution in geology, from a notion of catastrophic change
in the biological realm that was evident in changes in the fossil record to a concept of gradual change. The
former view was one developed by Georges Cuvier, who basically founded paleontology. Scottish geologists
developed the latter view. First, James Hutton believed that what had occurred in the past, leading to current
geological and fossil forms, was still operating as he wrote. He introduced the notion of gradualism, i.e. that
major changes are the cumulative result of many slow and small changes. Then came Charles. It was his
books that strongly influenced Darwin. He established the idea called uniformatarianism. This is the name
given the idea that geological processes have not changed in any basic way over the whole history of the
earth.
Biography (and partial bibliography) of Darwin:
Charles Robert Darwin was the first evolutionary
biologist. That comes not only from the publication
of The Origin of Species by Means of Natural Selection
(1859) and The Descent of Man (1871), but also from
his many other books that establish the effects of natural
and artificial selection on the traits of species. A list of
some of those other books ends this short essay. He
found the information that would lead to his theory of
natural selection during the five-year voyage of the Beagle.
He was selected to go on that voyage not for his abilities
as a naturalist, but because he could be an appropriate
companion for the young captain, Robert Fitzroy. The
admirals who chose him nevertheless, recognized the
opportunities for natural observations. He served as
geologist, botanist, and zoologist, as well as well-bred companion to the captain. Julian
Huxley stated Darwin's impact succinctly: "Darwin's work…put the world of life into the
domain of natural law."
The diversity in his writings is amazing. Here is a short list of some of his other books:
On the Various Contrivances by Which Orchids Are Fertilized by Insects (1862)
The Movements and Habits of Climbing Plants (1865)
The Variation of Animals and Plants Under Domestication (1868)
The Expression of the Emotions in Man and Animals (1872)
Insectivorous Plants (1875)
The Effects of Cross and Self-Fertilization in the Vegetable Kingdom (1876)
Volcanic Islands (1876)
Different Forms of Flowers (1877)
The Power of Movement in Plants (1880)
Charles Darwin did not put these ideas together with his own insights until years after his return to England
following the voyage of the Beagle. Even as a young man, he had been intensely interested in nature,
collecting insects and observing nature. His father, a physician, saw no future in becoming a naturalist, and
sent Charles to the University of Edinburgh to study medicine. He dropped out, but returned to university at
Oxford to study theology. It is not likely that Charles wanted to be a clergyman. Rather, the most common
university background for naturalists was theology. Darwin became a protégé of Reverend John Henslow, a
botany professor at Oxford. Soon after graduation he was recommended to the commander of the Beagle to
serve as a naturalist for its five year research voyage.
The voyage carried Darwin along the Atlantic and Pacific coasts of South America, to tropical forest on the
coast of Brazil, the pampas of Argentina, the barren land of Tierra del Fuego, the slopes of the Andes in
Chile and Peru, and to the Galapagos.
In all these places Darwin collected samples of plant and animal life. He noted, even as he collected, that
many specimens bore a basic similarity to species from Europe, but there were clear and evident differences.
Frequently there were unique characteristics to samples from particular places. He could tell from
characteristics of tortoise shells from the Galapagos Islands from which island a given tortoise had come.
He noted the enormous diversity of finches from the Galapagos, all similar to but differing from those of
South American mainland.
In addition to the evidence of differences in closely related species Darwin observed during the Beagle's
voyage, there was important evidence that came from some of his interests in England. He was an avid
breeder of pigeons, and was well aware of the potential to produce exotic looking patterns of feathers, their
colors, and similar character selection in other species. The evidence that careful selection of characteristics
and matings could produce cows that gave more milk, different breeds of dogs, or flowers with showier
petals and colors, which we call artificial selection, indicated the potential for inheritance of parental
characteristics, which is called descent with modification. Combined with observations of differences in
natural settings from the voyage, Darwin argued that natural selection could produce the varieties we see in
the world.
Darwin was masterful in assembling evidence for his ideas, but he was very slow in putting those
ideas into print. He had constructed a manuscript expressing them by 1844, but had never submitted it for
publication. The voyage of the Beagle was completed in 1836. Publication of the theory of evolution was
delayed, possibly by the controversy that might have been expected from such a paradigm shift, until Alfred
Russell Wallace had independently achieved the same synthesis.
In 1858 Wallace sent Darwin a letter and a manuscript. His research leading to the hypothesis was
mostly about insects in the East Indies. He had sent an earlier manuscript to Darwin not because he knew of
Darwin's ideas, but because Darwin was widely respected as a naturalist. Darwin sent this new paper on to
Lyell to be published, feeling that the ideas were no longer his alone. It was Lyell, his friend, who arranged
publication of both portions of Darwin's old manuscript from 14 years earlier and Wallace's article together
in Nature.
There was an ongoing controversy about the occurrence of evolution, particularly as it relates to the origin of
humankind, for decades after. Aspects of the controversy continue today. Some states have passed
legislation requiring the teaching of creation alongside evolution in high school. Other jurisdictions permit
the teaching of evolution without mention of the creationist view, but severely restrict how much time can
be devoted to the study of evolution.
An Input from Genetics
Part of Darwin's problem in explaining the mechanism of evolution was the lack of knowledge and
understanding of genetics as he constructed the theory. It was less than a decade later that Mendel developed
the laws of inheritance, even though he, too, lacked knowledge of the sub-cellular mechanisms involved.
Short biography of Alfred Russell Wallace:
Alfred Russell Wallace was born in 1823 and died in
1913. His father had been a man of leisure until illadvised investments left the family quite poor, and
Alfred had to leave school at 14. While in London
living with his brother he learned map making and
drafting. After a time in London and exposure to both
natural history and the utopian socialism of Robert
Owen, he taught at post-secondary institutions for a
time using both his knowledge of natural history and
trades. After forming a sort of partnership with an
experienced entomologist, Henry Bates, in 1848 he
took a position as a commercial collector of insects in
the Amazon basin. Bates' observations of mimicry
among insects in the Amazon gave his name to one
form of the evolved similarity. During this period
Wallace began to observe patterns among the insect
species he collected that were the initial basis of his ideas about evolution. However, on the
return voyage a fire on the ship destroyed everything he had collected. After a time in
England, he went back to collecting, this time in the Indonesian archipelago. He traveled and
collected for eight years, adding more than 1,000 new species to science. He also developed
a theory for the evolution of new species, and published it. The more fully developed version
that forced Darwin to finally publish his work followed further studies and an attack of
malaria. Wallace's paper was titled On the Tendency of Varieties to Depart Indefinitely from
the Original Type." With the publication of Darwin's and Wallace's papers, the concept of
natural selection was made public.
Wallace did more than just collect insects. After four additional years in the Indonesian
archipelago, he also published in zoogeography, and Wallace's line established the
boundaries separating faunas identified with Australia and associated islands from those of
islands associated with Asia.
Short biography of Gregor Mendel:
Gregor Mendel (1822-1884) was an Austrian monk who taught
and studied genetics. His most famous and most successful
work was on the common garden pea plant. Until Mendel's work,
there was the common sense realization that offspring resembled
parents. Mendel quantified and predicted traits that would be
observed in offspring peas and the plants grown from them.
Mendel carefully chose traits that that are passed, whole and
intact, to offspring. He performed meticulous experiments that
permitted him to determine both male and female parents of
peas, and counted the frequencies with which different kinds
of offspring were produced. The work took him from 1857 to
1865. From it he recognized dominant and recessive traits, but
because of the traits he chose, he did not encounter measurable
recombination. In 1866 he published his results in a regional naturalists' journal, but they
were effectively lost until re-discovered in 1900 by geneticists, including de Vries, who found the
same sort of results in studies of Drosophila.
The Law of Segregation and the Law of Independent Assortment predict the inheritance of many traits, but
not all. T.H. Morgan found white-eyed male Drosophila, and was able to discern that some traits are sexlinked, inherited from the X chromosome, which is not present in diploid condition.
Short biography of Thomas Hunt Morgan:
Thomas Hunt Morgan (1866-1945) studied the genetics
of the fruitfly, Drosophila melanogaster. He is one of the
key figures in the history of genetics, wrote, with other
geneticists, the first landmark textbook of genetics, The
Mechanism of Mendelian Heredity, and won a Nobel Prize
for his work that established the chromosomal mechanism
of inheritance. Early in this work he discovered sex-linked
inheritance. The initial phase of this discovery was an
observation that only males inherited a white-eyed condition,
then exploring the inheritance of the trait.
The chromosome that 'pairs' with the X chromosome is the Y that, in part, determines maleness. Still the
molecular mechanisms weren't known. A trait carried on the X chromosome of a male has no paired allele
on the Y. That knowledge did not develop until the 1940's and 50's. Now ecological genetics and concepts
like expression of genes dependent on environmental conditions complicate the subject, but add to our
ability to understand the importance of genetics to ecology.
Mathematical Models of Population Growth
In quantitative ecology, the basic equation for population growth and models of species interaction is the
logistic.
Logistic equation:
dN
KN
 rN (
)
dt
K
Pierre Francois Verhulst first published papers expressing the logistic equation as a measure of growth
between 1838 and 1847. At the time, scientists apparently were unsatisfied because the mathematical model
of growth lacked a physical analogy. As a result, the logistic was rediscovered and finally accepted as a
result of its use in Pearl and Reed's studies of population growth in the United States around 1920. They also
found one of the key difficulties in applying the logistic model to real data. It doesn't work well when the
carrying capacity, K, of a population in some environment changes over time.
Short biography of Pierre Verhulst:
Pierre Francois Verhulst was born in 1804 in Brussels,
Belgium and died there in 1849. He was educated at the
University of Ghent, and was, both there and afterward,
influenced by Quetelet, a foremost French mathematician
of the time. A part of that influence was to become
interested in what was termed social statistics. However,
the older and younger mathematicians differed in their views
about population growth. Quetelet believed populations grew
geometrically, but that a force proportional to the square of
the rate of growth prevents indefinite geometric increase.
Verhulst believed that the opposing force was proportional
to a ratio of the difference between a maximum supportable
population size and the current size to that maximum size.
Expressed in mathematical terms, the differential equation
that Verhulst developed is the logistic equation. The logistic
equation, like the genetics of Mendel, disappeared from
sight for an extended period. This basic equation was
re-discovered by Pearl and Reed in studying American
population growth early in the 20th century.
Biography of Raymond Pearl:
Raymond Pearl (1879-1940), with L.J. Reed, a biostatistician
also at Johns Hopkins University, re-discovered the
mathematical model of logistic growth, and published the
model in a paper titled "On the rate of growth of the
population of the United States since 1790 and its
mathematical representation." (PNAS, USA [1920] 6:275-288).
He founded one of the premier journals in biological research,
Quarterly Review of Biology, but, during the 1920s, he also
supported the eugenics movement. Apparently he rescinded
that support when eugenics was scientifically discredited.
Community Ecology
In addition to developments in population biology, early in the 20th century there were also important
developments in what we now term community ecology. One of the key questions was how communities
were assembled. Are communities much like organisms, with specific species having critical functions? Or
are communities much more random groups of species, where specific functions must be achieved, but there
are many alternative species that can do the various jobs (or fill the niches), and it doesn't matter much
which species end up filling the niches? What matters in which species we find is that they all can tolerate
the physical conditions in the place under study. These are relatively extreme statements of positions taken
by ecologists F.E. Clements and H.A. Gleason.
Frederic E. Clements (1874-1945) did decades of
field research under the auspices of the Carnagie
Institute of Washington. He believed that his
"study of vegetation reveals that it is an organic
entity and that, like an organism, each part is
interdependent upon every other part…" This has
been phrased as the 'superorganism' view of
plant communities.
Henry Allen Gleason (1882-1975) had a very
different view of plant community structure, termed
the 'individualistic' or 'continuum' concept of
associations. "Vegetation, in its broader aspects, is
composed of a number of plant individuals. The
development and maintenance of vegetation is
therefore merely the resultant development and
maintenance of the component individuals…"
Clements believed that communities bore important similarities to organisms. His view is called the
interactive or, more usually, the organismal hypothesis for community structure. Gleason's view is termed
the individualistic hypothesis. As is usual in such conflicts, the truth lies somewhere between the extreme
views.
Neither Clements nor Gleason phrased their hypotheses for community structure in terms of the
niches occupied by species. Yet during the middle of the 20th century ecology was vitally concerned with
understanding how species pack themselves into an environment, and, thus, better ways of thinking about
their niches. G. Evelyn Hutchinson made a critical contribution to this debate by introducing the notion of
the niche as a multidimensional hypervolume.
G. Evelyn Hutchinson (1903-1991) grew up with the subdiscipline called limnology, but his contributions extended far
beyond that. Among the minor ones, he persuaded the City of
New York to cancel a construction project that would have
destroyed Belvedere Lake in Central Park. In it lived 19
different species of dragonflies. The lake is now a dragonfly
reserve. He accomplished the same end in preventing the
construction of a military base on Aldabra Island in the Indian
ocean. It is now a reserve for sea turtles. His academic career
began in South Africa at the University of Witwatersrand, but
moved to Yale University for a post-doctoral position after a
dismissal. He stayed at Yale for a long academic career, during
which he Published extensively in limnology, including a 3volume text, A Treatise on Limnology. His most lasting
contributions may well lie outside limnology, in papers such as
“Homage to St. Rosalia, or Why are there so Many Kinds of
Animals” and “Concluding Remarks” for the Cold Spring Harbor symposium of 1957, where he
introduced the concept of the multidimensional niche, as well as in a classic population biology text,
An Introduction to Population Ecology.
That complicated terminology simply means that each species occupies a range of conditions along each
niche axis. The many axes that may be important include physical variables like temperature, humidity, and
soil composition, as well as biological axes like food, frequently in the form of the size of food items, and
the abundances of the other species with which it lives. Since we usually think of a volume as involving only
three axes, height, width, and depth, Hutchinson termed the volume of this multidimensional niche a
hypervolume. With it, many different ecologists contributed ideas about how species packed into the
environment.
Species Interactions
Initially, competition among species was thought to be the principle organizing force for communities.
Probably the most important contribution to understanding competition as a structuring force was the
research, both in the field and in the development of theory, of Robert MacArthur.
He studied the use of spruce trees by a number of warbler species living together in New Jersey. All the
species fed on insects, but they lived and caught insects in different parts of the tree.
One species lived in the topmost branches of trees, another about midway up, and a third in the lower
branches; some species live in the interior, and others live on the outer branches. The species divide space
and limit the intensity of competition among them through this partitioning.
The belief that communities were structured by competition among species held sway in ecology for
many years. Eventually, ecologists recognized that in many studied examples predation was important in
determining which species survived. One of the most important of these examples is Robert Paine's studies
of the effect of the starfish Pisaster on the community of invertebrates living on the rocky shore along the
coast of Washington State.
Make Paine's name come on as a clickable object. If clicked, fade out MacArthur. Bring up a portrait of
Paine on the left. With or without the click, bring up a picture of the intertidal community on the right.
Robert MacArthur (1930-1972) was one of the key fathers of modern ecology. G. Evelyn
Hutchinson supervised his graduate studies. It was MacArthur’s work, both in field
observations and in the development of mathematical theory, that gives us much of our
modern view of species interactions and community ecology. He came by his interest in
nature from observations on birds, mammals and trees in Ontario and rural Vermont. He
switched from mathematics to biology in graduate school, and his Ph.D. thesis, supervised
by G. Evelyn Hutchinson, resolved the mechanism of coexistence of a number of warbler
species living in the same trees in New Jersey pine forests: niche partitioning. Later he
developed core theoretical ideas in species diversity, the relative abundance of species in
communities, species (niche) packing, competition, and, finally, island biogeography. In all
these sub-disciplines his work is seminal to our modern view of how communities, and
nature in general, are structured.
Robert Paine retired in 1999 from a long career at the
University of Washington. For most of his career he studied
the ecology of the rocky intertidal along the coast of
Washington. He studied the impact of wave disturbance and
the impact of biological interactions on intertidal community
structure. One of his most lasting contributions was recognizing
that a single species could have a major impact on a whole
trophic level with which it interacted. The concept of a keystone
species came from Paine's studies of the starfish, Pisaster, and
its effects on the community of invertebrates on which it fed. With
Pisaster present, that community was diverse, since the dominant
species, a mussel, Mytilus, was preferentially removed by feeding.
When the starfish was absent, the community was severely
reduced in diversity, and Mytilus occupied most of the shoreline
space in the intertidal zone.
In the absence of the predatory starfish, a mussel, Mytilus, dominated the community through its success in
competing for space. Being a 'smart' predator, the starfish fed most intensively on this mussel, opening space
for other species to colonize the shoreline. The difference in the number of species living on the shoreline
with and without the starfish was dramatic. After a decade in a test area where Paine had removed all
starfish there were only 2-3 species present, while in areas where starfish had been allowed to feed naturally
approximately 20 species coexisted. Where the effect of a single species on the structure of a community is
so dramatic, that species is called a keystone.
Island Biogeography and Non-Equilibrium Ideas
In addition to achieving a balance in considering interactions among species as critical in understanding how
communities are assembled, over the last two decades ecology has come to recognize the importance of
disturbance and colonization of sites in determining what we observe. When a habitat is bare, it is those
species that successfully colonize the site that we will observe there. It may be a newly formed site from
volcanic eruption or it may have been cleared as a result of some catastrophe like a hurricane, tornado, flood,
or tidal wave. The colonization process and the kinds of species we will observe on the site are similar
whatever has caused the habitat to be empty. Robert MacArthur and E.O. Wilson developed a theory of
island biogeography to quantify the number of species that should be found on these islands of habitat
during the colonization process.
Short biography of E.O.Wilson
E.O.Wilson (1930 -) has worked from a laboratory at
the Museum of Comparative Zoology at Harvard for
many years. Much of his research has been concerned
with the sociobiology of ants. However, from that
research arose a seminal and controversial book,
Sociobiology: A New Synthesis. Some took that book
to be racist, and read the text to suggest that genetic
variation among humans left some superior to others.
In what is now the middle term, the concepts presented
in the book are recognized to represent a 20th century
Darwinian approach, and not an advocacy of eugenics
or other ill-conceived notions. With Robert MacArthur,
he 'invented' island biogeography, which was also
seminal to the development of a sub-discipline we now
call conservation biology. The two books about biodiversity and its conservation that he in part
wrote and also edited have been extremely important in making the call for biodiversity
conservation the subject of major international conventions. He has never avoided
controversy, and sees a need for genetically modified organisms (GMOs) to protect
humankind from starvation. One writer, Ed Douglas in the Guardian, has placed Wilson
intellectually at Darwin's right hand, and that is not a bad place, given the many major
contributions Wilson has made to modern views of evolution, genetics, and conservation.
How isolated an island is and the dispersal capabilities of potential colonists determine the rate of
immigration, and the number of species already present determines the rate at which resident species should
go extinct.
Rather than limiting the model to oceanic islands, ecologists quickly recognized that the same ideas
should apply to isolated areas of habitats on mainland. These isolates might be lakes, forests isolated by
farmed areas on all sides, or, of greater impact, parks. Though the basic model is so simplified that
application to real world situations was difficult and dangerous, it formed a key basis for the development of
the field known as conservation biology. It was also used to construct an early set of guidelines for designing
parks and preserves to conserve the largest number of species possible. Research into 'island' biology led to
the recognition that their edges are altered by incursion of species from surrounding areas and changes in the
climate (temperature, humidity, etc.) in edge areas. Since the island biogeography models had also pointed
to the importance of island isolation, the idea of connecting 'islands' by corridors was introduced.
Developing corridors has become a controversial subject, and the balance between benefit and cost is still
under intense study.
More modern evolution of these ideas has led to an approach called metapopulation biology, in
which a continuous flow individuals among islands of habitat leads to the preservation of a species, even if
individual sub-populations on particular islands may not long persist. The metapopulation view seems closer
to real world conditions, where individual parks are rarely large enough to ensure long term persistence of a
population, but a number of smaller parks close enough together for dispersal among them to be a
reasonable expectation may together conserve the species.
Models of island biogeography and the ideas that have developed from them are among the first ecological
models to recognize that the real world does not persist in equilibrium. The very events that lead to loss of
species from communities are themselves now recognized as important. Disturbances take many forms.
They include those that damage communities, like floods, overgrazing, and other human activities, as well
as some events that may be important in the survival of species and communities. Fire, for example, is
necessary for the success of seeds of some pine species, and is critical to the persistence of a number of
prairie plants. Disturbances provide openings for species to become established. However, disturbances can
occur at different frequencies. If they occur too frequently, only 'weedy' species can complete their life
cycles and successfully reproduce. If they occur too infrequently, there is little open space, and competitively
dominant species will come to occupy most space, preventing the existence there of other species. This led,
in the 1970s, to the proposal of an intermediate disturbance hypothesis. Joseph Connell proposed that the
maximum diversity or richness of species would persist at an intermediate frequency and intensity of natural
disturbance.
Other ecologists have had a lasting impact on the direction and approach research in ecology has taken.
Among them, six who contributed in very different ways to the current views of the subject are Ronald
Lindeman, whose paper on “The trophic-dynamic aspect of ecology” underlies our view of the way energy
moves among organisms in communities, Robert H. Whittaker, who showed the way out of the conflict
between Clements and Gleason, as well as applying statistical methods to the analysis of community
structure, C.S. Holling, who neatly categorized the different ways predators may relate to the densities of
their prey, E.P. Odum, who instituted a larger view of ecological processes that drew in some of the methods
of analysis more traditionally seen in engineering, an approach called systems ecology, Charles Elton, who
developed the concept of trophic structure that we still call an "Eltonian pyramid", as well as anticipating the
importance of invading species, and John L Harper, who is the progenitor of applying demographic tools to
studies of plant populations. Short biographies of each of these eminent ecologists are available by clicking
on their names. The ecologists whose biographies are presented represent an idiosyncratic list from among
many others that different authors might have felt more important.
Joseph Connell has made two vitally important contributions to ecology. In the 1960s he published a
series of studies of the rocky intertidal zone on the coast of Scotland. His study of interactions between
the barnacles Balanus balanoides and Chthalmalus stellatus are the classic example in every text. Later
he studied the impact of disturbance on community diversity. A figure reflecting the pattern he found,
that led to the intermediate disturbance hypothesis, is shown on the right.
Crawford S. (Buzz)
Holling is still active
as an emeritus scholar
at the University of
Florida. Canadian by
birth and training, he
took his degrees at the
University of Toronto
and the University of
British Columbia. For
many years he worked in a government of
Canada lab. During that time he published
papers recognizing different kinds of predatorprey interactions. Type I is a filter-feeding
animal. Type II hunts and feeds on specific
prey species. Type III is an adaptive predator
that shifts the prey taken based on the relative
abundances of its prey species. Holling's work
is also important in the development of
adaptive management strategies for
conservation, and in integrating economic,
social and cultural factors into management
within a framework he terms "resilience".
R.H. Whittaker (1920-1980) was a distinguished
professor at Cornell University in Ithaca, New
York for most of his professional career. During
that career he advocated a 5-kingdom classification
of life to replace the earlier 3 kingdom view. More
recently, a six-kingdom system has replaced his
advance. He was a major force in the acceptance of
Gleason’s view of an individualistic species
continuum through studies on the spatial
distribution of species in the Siskyou Mountains of
northern California, the Great Smoky Mountains
of Tennessee and the Santa Catalina Mountains of
Arizona in a series of classic papers. He developed
the tools of ordination to assess plant community
spatial structure that made it possible to quantify
community structure. He was the author of a
classic ecology text titled Communities and
Ecosystems. In addition to these contributions to
ecology, he was active in Mycology and other
areas of Microbiology and plant biology.
Joseph Connell has made two vitally important
contributions to ecology. In the 1960s he published a series of studies of the rocky intertidal
zone on the coast of Scotland. His study of
interactions between the barnacles Balanus
balanoides and Chthalmalus stellatus are the
classic example in every text. Later he studied
the impact of disturbance on community
diversity. A figure reflecting the pattern he found,
that led to the intermediate disturbance hypothesis, is
shown on the right.
Eugene P. Odum is
also still active as an
emeritus scientist at
the University of
Georgia, where he
spent the largest part
of his career. He is the
author of one of the
first modern texts in
ecology, Fundamentals
of Ecology, and the
intellectual father of large scale ecology, sometimes called systems ecology. He studied
wetland ecology in Georgia and the energy
flows through food chains in these systems.
More recently he has been involved in
assessment of the relations between society and
environmental and environmental conditions.
Charles Elton taught at Oxford, and established
its Bureau of Animal Populations. At many
points in this text we will refer to research
done by scientists who became associated with
that institution. His recognition of the
numerical and biomass relationships among
the trophic levels comprising and ecosystem
led to that structure being called an Eltonian
pyramid. He also anticipated the importance
and impact of invasions by non-native species,
and wrote the seminal book on that subject,
The Ecology of Invasions by Animals and
Plants.
Raymond Lindeman (1915-1942) died before his
critical paper, initially rejected as being “too
theoretical”, was published in Ecology. That paper
was titled “The Trophic-Dynamic Concept in
Ecology”, and forms the basis for ecological
limnology and the modern methods for studying
aquatic food chains. In it he studied the
relationships among nutrient cycling, productivity,
energy flow, and nutritional efficiency. He could
well be considered the father of ecosystem
ecology, in part because he coined the term
ecosystem to describe the system of species he
studied in Cedar Bog Lake. He, too, was a student
supervised by G. Evelyn Hutchinson, and it was
Hutchinson’s belief in Lindeman’s work that led
him to persuade the editors of Ecology to publish
what became a seminal work in fields as widely
divergent as aquatic ecology, ecosystem ecology,
and ecological energetics.
John L. Harper can reasonably be given credit for
beginning the study of plant demography. He
taught a large number of the first generation of
plant demographers at the University of North
Wales at Bangor. For plant population biologists,
his 1977 book, The Population Biology of Plants,
is the bible of all that was known at the time it was
written. Later in his career he was a co-author of
texts in ecology and introductory biology that were
widely used and appreciated.
Broadening the Base: Landscape Ecology
Landscape ecology is a recent offshoot of ecologists' attempts to integrate the real world into answers for
important questions in conserving species and habitats. Landscape ecology recognizes that the artificial
division of large areas into separate ecosystems is ineffective in designing strategies for conservation.
Borders between habitats and ecosystems are inherently fuzzy. Human land use patterns are critically
important in both political and ecological decision making. Landscapes cross the ecological boundaries,
integrating what has happened, what is happening, and what we predict will happen over regions, rather than
ecosystems. It is, therefore, an important element in the goal of preserving species, biodiversity, and
communities in all parts of the earth.