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Lesson Ten

The Ecology of Population

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populations

(Ecology) All the organisms that constitute a specific group or occur in a specified habitat.

【生态学】 种群，族群

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ecology

The science of the relationships between org

anisms and their environments. Also called

bionomics([]).生态学

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Ecology is the scientific study of the distribution and abundance of life and the interactions between organisms and their natural environment.. The environment of an organism includes physical properties, which can be described as the sum of local abiotic factors such as insolation (sunlight), climate, and geology, and biotic ecosystem, which includes other organisms that share its habitat.

The term ecology was coined by the German biologist Ernst Haeckel in 1866, when he defined it as "the comprehensive science of the relationship of the organism to the environment.“

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Thomas Robert Malthus

The first significant contribution to the theory of population

ecology was that of Thomas Malthus, an English clergyman, who

in 1798 published his Essay on the Principle of Population.

The English political economist and demographer Thomas

Robert Malthus FRS (1766–1834) analyzed population growth

and noted the potential for populations to increase rapidly, often

faster than the food supply available to them.

Commentators may refer to such a runaway scenario, as outlined

in Malthus's treatise An Essay on the Principle of Population, as

a "Malthusian catastrophe".

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The Principle of Population Between 1798 and 1826 Malthus published six editions of

his famous treatise, An Essay on the Principle of Population, updating each edition to incorporate new material, to address criticism, and to convey changes in his own perspectives on the subject.

Malthus regarded ideals of future improvement in the lot of humanity with scepticism, considering that throughout history a segment of every human population seemed relegated to poverty. He explained this phenomenon by pointing out that population growth generally preceded expansion of the population's resources, in particular the primary resource of food.

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The Principle of Population

Malthus also saw that societies through history had experienced at one time or another epidemics, famines, or wars: events that masked the fundamental problem of populations overstretching their resource limitations.

To give a mathematical perspective to his observations, Malthus proposed the idea that population, if unchecked, increases at a geometric rate (i.e. 1, 2, 4, 8, 16, etc.), whereas the food-supply grows at an arithmetic rate (i.e. 1, 2, 3, 4, 5 etc.).

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The major problem in population ecology is

to derive population characteristics from

characteristics of individuals and to derive

population processes from the processes in

individual organisms.

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Thomas Malthus

Malthus introduced the concept that at some point in time an expanding population must exceed supply of prerequisite natural resources, i.e., population increases exponentially resulting in increasing competition for means of subsistence, food, shelter, etc. This concept has been termed the "Struggle for Existence".

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Charles Darwin

Malthus's theories profoundly influenced

Charles Darwin 1859,

On the Origin of Species, e.g., the concept of

"Survival of the Fittest". Mortality of this type

can be termed "facultative mortality" (as

opposed to catastrophic mortality, e.g.,

weather, insecticides).

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Harry Smith, pioneering biological control

worker with the University of California

(1935), proposed the equivalent and now

accepted terms density-dependent and density-

independent. Density-dependent mortality

factors are those that are facultative in effect,

density-independent mortality factors are those

that are catastrophic in effect.

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Royal N. Chapman, Univ. Minnesota, in the 1930s proposed the concept of a balance between biotic potential and environmental resistance.

Chapman`s model was a mathematical representation of the Malthusian concept, illustrated by the logistic growth of a laboratory population of some species.

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Human populations represent another example of exponential growth. Magnitude of the problems posed by human population growth can be seen from the fact that it took more than 1 million years for the human population to first reach 200,000.

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The human population is estimated to have first reached 1 billion persons in 1830, and 2 billion in 1930, a doubling time of 100 years. In 1960, thirty years later, the population edged past 3 billion, and a mere 15 years later, 4 billion. In 1986, we exceeded 5 billion for the first time.

Despite a slowing of the growth rate, it is expected that the human population will exceed 6 billion in early 1999. To feed this population, only as well as we presently do, it will be necessary to increase food production 20% over the next 10-15 years.

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glossary

age structure

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allelopathy[]

Allelochemics []

[ 生态 ] 种间化学物质 allo- 其他的 -pathy 后缀 表“感情”；“痛苦”“感知” ; 表

“疾病” telepathy. 心灵感应 neuropathy. 神经病 Meristem []. 分生组织

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allelopathy

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carrying capacity

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character displacement

Character displacement among Darwin's Finches

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density-dependent factorsdensity-independent factors

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exponential growth curve

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interspecific competition

intra-

intraspecific competition

inter-

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logistic growth curve

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mortality [] 死亡率

natality [] 　出生率

population density

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survivorship curve

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Text

Malthus(1766-1834 )

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Human Population Growth

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The end

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