Population of Ecology

Ecology

 Study of the interactions of organisms in their biotic and abiotic environments  Organism  Ecosystem  population  biophsere community 

Demographics of populations

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Demography

– statistical study of a population (density, distribution, growth rate)  

Population density

- # of individuals per unit area (can be misleading)

Population distribution

– pattern of dispersal across an area (controlled by resources and limiting factors) clumped, random, uniform

Population growth

 Rate of natural growth (r) based on birth and death rate.

 Biotic potential – highest possible growth rate with unlimited resources.

Survivorship curves

 Probability that newborn will survive to certain ages.

 Curve I – characteristic of a population in which most individuals survive well past midpoint of lifespan. Ex. Large mammals, humans

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Curve II

– survivorship decreases at a constant rate throughout the life span. Ex. Songbird, small mammals (death is usually unrelated to age) 

Curve III

– most individuals die young. Ex. Insects, fish, humans in less developing countries.

Age distribution

 Age structure diagrams 

Increasing population

 Prereproductive ages is largest, birth rate is higher than death rate.

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Stable population

(bell shape)  Reproductive ages equal prereproductive ages 

Decreasing population

(urn shape)  reproductive ages is larger than prereproductive ages, postreproductive age is largest

Population Growth Models

 2 patterns of population growth:  Discrete breeding – single reproductive event  Continuous breeding – many reproductive events  Research: not always have to be one or the other.

Exponential Growth

 Number of individuals added each generation increases as the total # of females increases.

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Lag phase

– growth is slow to start 

Exponential growth phase

– accelerated growth  J shaped curve

Logistic growth

 S-shaped curve  Lag phase, exponential growth phase  Deceleration phase – growth slows  Stable equilibrium phase – little to no growth, BR = DR

Carrying capacity

    Maximum # of individuals of a species an environment can support.

Exponential growth can not continue due to carrying capacity  Resources become scarce  Competition and predation Exponential growth occurs when population size is much lower than carrying capacity.

Population stabilizes when carrying capacity is reached.

Regulation of population size

 Density independent factors – those that are not dependent on numbers   Weather, natural disasters Density dependent factors – occur because of population of species   Competition, predation, parasitism Intrinsic factors? – anatomy, behavior have an affect on population?

Life History Patterns - Opportunistic

 r – strategists  Small individuals, short life span, fast to mature, many offspring, little/no care for offspring, early reproductive age  Bacteria, fungi, insects, rodents, annuals

Life History Pattern - Equilibrium

 K-strategists  Large individuals, long life span, slow to mature, few and large offspring, care for offspring, most live to reproductive age  Large mammals, birds of prey, long-lived plants

Human population growth

  MDC ’ s – North America, Europe, Japan, Australia, growth is slow LDC ’ s – Latin America, Africa, Asia, population rising rapidly  Ways to reduce projected population increase:  Strengthen family planning  Education, raising status of women, reduce child mortality  Delay onset of childbearing, wider spacing of births

Population Growth and Environmental Impact

 LCD = population growth in numbers  MCD = consume larger proportion of Earth ’ s resources  Average family in North America consumes the amount of resources and produces wastes of 30 people from India.