Location via proxy:   [ UP ]  
[Report a bug]   [Manage cookies]                
SlideShare a Scribd company logo

Population Ecology.pptx

•Download as PPTX, PDF•
•
Y
YaminiPurohit1

This document provides an overview of key concepts in population ecology. It discusses population characteristics like density, natality, mortality, dispersal, growth curves, fluctuation, distribution, age pyramids, and equilibrium. It describes population density, natality rates, types of mortality, dispersal through emigration, immigration and migration. Growth curves can follow a J-curve or S-curve pattern. Populations can fluctuate cyclically. Distribution can be random, uniform, or clumped. Age pyramids reflect the age structure of a population.

1 of 30
By: Nandita Purohit (M.Sc. Zoology) Population Ecology
Synopsis • Introduction • Population Characteristics – Density – Natality – Mortality – Dispersal – Growth curve – Population Fluctuation – Distribution – Age pyramid – Equilibrium • Importance
introduction A population is generally a group of particular species occupying a particular area at a specific time. Some of the ecologists however recognize two types of population; • Monospecific population- a population with individuals only one species • Mixed or Polyspecific population- a population of more than one species However in Ecology, a polyspecific population is considered as a COMMUNITY, and the term POPULATION is used for a group of individuals of any kind of organism. POPULATION ECOLOGY is the study of individuals of the same species where the processes are aggregation, interdependencies between individuals etc, and the various factors governing such processes are emphasized.
• Demography is the study of human populations – their size, composition and distribution across space and the process through which populations change. • Births, deaths and migration are the ‘big three’ of demography, jointly producing population stability or change. • It is the study of human population dynamics. • Population dynamics is the branch of life sciences that studies the size and age composition of populations as dynamical systems, and the biological
density • Population density is the number of individuals per unit geographic area, for example, number per square meter, per hectare, or per square kilometer. • Density may be numerical density (number of individuals per unit area or volume) or biomass density (biomass per unit area or volume)
• Further, since the pattern of distribution of organisms in nature is different it becomes important to distinguish between crude density and ecological density. • Crude density is the density (number or biomass) per unit total space. • Ecological density (specific or economic density) is the density (number or biomass) per unit of habital space, i.e., available area or volume that can actually be colonized by the population.
Density is affected by four primary population parameters such as natality (births), mortality (deaths), immigration and emigration
Natality • Natality is a broader term covering the production of new individuals by birth, hatching, germination, or fission. • The natality rate may be expressed as the number of organisms born per female per unit time. • In human population, the natality rate is equivalent to the ‘birth-rate’. • The two essential aspects of the reproduction which forms main component of natality : – Fertility is the physiological notion which indicates that an organism is capable of breeding. – Fecundity is an ecological concept that is based on the numbers of offspring produced during a period of time
• Natality is of following two types : – Maximum natality. (absolute, potential or physiological natality). It is theoretical maximum production of new individuals under ideal conditions which simply means that there are no ecological limiting factors and that reproduction is limited only by physiological factors. – Ecological natality. (realized natality or simply natality). It refers to population increase under an actual, existing specific condition. Thus, ecological natality takes into account all possible existing environmental conditions. I’m here to contribute for density increase
• ∆ Nn/ Dt = the absolute natality rate • ∆ Nn/NDt = the specific natality rate – where N = the reproductive part (mature female) of the population or initial number of organisms or total population n = new individuals in the population t = time ∆ = delta : a change in value
mortality • Mortality means the rate of death of individuals in the population. • It is a negative factor for population growth • It is of following types – Minimum mortality (specific or potential mortality) represents the theoretical minimum loss under ideal or non- limiting conditions. It may be constant for a population. – Ecological mortality (realised mortality) is the actual loss of individuals under a given environmental condition. • Mortality can be expressed as- – number if individuals dying/ unit time.
• A survivorship curve is a graph that measures the proportion of individuals in a given species that are alive at different ages. • Typically, the number of individuals of the population is plotted on the y-axis of the graph and the age of survivorship is plotted on the x- axis of the graph. • There are three types of survivorship curves, and they are simply referred to as type I, type II, and type III.
•Type I (concave curve) survivorship curve shows individuals that have a high probability of surviving through early and middle life but have a rapid decline in the number of individuals surviving into late life. E.g. human, flies. •Type II (diagonal curve) survivorship curve shows a roughly constant mortality rate for the species through its entire life. E.g. hydra, mice, birds. •Type III (convex curve) survivorship curve depicts species where few individuals will live to adulthood and die as they get older because the greatest mortality for these individuals is experienced early in life. E.g. oyster, fishes
Dispersal • Populations have a tendency to disperse, or spread out in all directions, until some barrier is reached. • Accordingly, population dispersion is the movement of individuals into or out of the population area. • It takes three forms- – Emigration – Immigration – Migration
• Emigration (one-way outward movement) under natural conditions occurs when there is overcrowding in the migratory locust, lemming, grouse, snowy owl, snowshoe rabbit. • This is generally regarded as an adaptive behavior that regulates the population on a particular site and prevents over-exploitation of the habitat. • Further, it leads to occupation of new areas elsewhere • By dispersing into new localities, there is opportunity gained for interbreeding with other populations leading to more genetic heterozygosity and adaptability. • Immigration (one-way inward movement) leads to a rise in population level, causing an overpopulation which may lead to an increase beyond the carrying capacity. • These immigrations result in increased mortality among the immigrants or decreased reproductive capacity of the individuals
• Migration (periodic departure and return) is a peculiar kind of population dispersion which involves the mass movement of entire population. • This can occur only in mobile organisms and best developed in insects such as desert locust(Schistocerca gregaria), migratory locust(Locusta migratoria), butterfly (Danaus plexippus) • In most cases, it may occur for food, shelter, or reproduction. • Better utilization of uninhabited untouched habitats and their resources are the greatest benefits of migratory movements.
Population Ecology.pptx
Growth Curves • Population growth is the increase in the number of individuals in a population. • Two types of population growth patterns may occur depending on specific environmental conditions: – An exponential growth pattern (J curve) occurs in an ideal, unlimited environment. – A logistic growth pattern (S curve) occurs when environmental pressures slow the rate of growth.
J- Curve • In J-shaped curve there is a rapid increase in density with the passage of time (called exponential growth). • The density values when plotted against time give a J- shaped growth curve. • If 1000 bacteria are placed in a large flask with an unlimited supply of nutrients, after an hour there will be one round of division, resulting in 2000 organisms. In another hour, each of the 2000 organisms will double, producing 4000, and so on. • The bacteria example is not representative of the real world where resources are limited, and ultimately competition for food would result in deaths and population decline.
S- curve • The population growth curve in human populations and growth of yeast, Drosophila and rabbit under laboratory conditions show an initial slow rate and then it accelerates and finally slows giving the growth curve which is sigmoid or S- shape. • The peak constant level represented by K or upper level (called asymptote) of the sigmoid curve is called the maximum carrying capacity. It marks the limit to which the environment can support the population
Population fluctuation • Populations are said to be cyclic when they alternatively errupt and subside in a more or less uniform manner between high and low levels of density. • Different animals exhibit population cycles different times. • Population ecologists commonly divide the factors that affect the size of populations into – Density-dependent factors (regulating factors), intensify as the population increases in size, and has a potential for maintaining population density within a narrow range of values. – Density-independent factors (limiting factors), such as weather and climate, exert their influences on population size regardless of the population’s density.
Cyclical fluctuations in the population density of the snowshoe hare and its effect on the population of its predator, the lynx.
Distribution • Individuals of a population arrange themselves in a manner that is specific for each population. • In nature, due to various biotic interactions and influence of abiotic factors, the following three basic population distributions can be observed : – Random distribution – Uniform or regular distribution – Clumped distribution
I. Regular Dispersion: here the individuals are spaced at equal distance from one another. This is rare in nature but common in managed systems (croplands). Animals with territorial behavior tends towards this dispersion II. Random Dispersion: the position of one individual is unrelated to the position of its neighbor. This us also relatively rare in nature. III. Clumped Dispersion: most population exhibit this dispersion to some extent, with individuals aggregated into patches interspersed with no or few individuals.
Age pyramid • In most types of populations, individuals are of different age. • The proportion of individuals in each age group is called age structure or age distribution of the population. • Age distribution of the population influences natality and mortality. • A model representing geometrically the proportion of different age groups in the population of any organism is called age pyramid (or age-sex pyramid)
Population Ecology.pptx
• According to Bodenheimer (1938), there are following three basic types of age-sex pyramids: 1. Pyramid with broad base (or Triangular structure) indicates a rapidly expanding population with a high percentage of young individuals and only few old individuals.  Thus, in rapidly growing young population, birth rate is high and population growth may be exponential as in yeast, housefly, Paramecium, etc. 2. Bell-shaped polygon indicates a stationary population having an equal number of young and middle-aged individuals.  As the rate of growth becomes slow and stable, i.e., the pre- reproductive and reproductive age groups become more or less equal in size, post-reproductive group remaining as the smallest.
3. Urn-shaped structure indicates a low percentage of young individuals.  It shows a declining population.  Such an urn-shaped figure is obtained when the birth rate is drastically reduced, the pre- reproductive group dwindles in proportion to the other two age groups of the population.
importance • The study of human population is of immense importance to an economy. • Population studies help us to know how far the growth rate of the economy is keeping pace with the growth rate of population. • Data relating to the present trend in population growth help the planners in formulating policies for the economic plan of the country.
Population Ecology.pptx

More Related Content

Population Ecology.pptx

  • 2. Synopsis • Introduction • Population Characteristics – Density – Natality – Mortality – Dispersal – Growth curve – Population Fluctuation – Distribution – Age pyramid – Equilibrium • Importance
  • 3. introduction A population is generally a group of particular species occupying a particular area at a specific time. Some of the ecologists however recognize two types of population; • Monospecific population- a population with individuals only one species • Mixed or Polyspecific population- a population of more than one species However in Ecology, a polyspecific population is considered as a COMMUNITY, and the term POPULATION is used for a group of individuals of any kind of organism. POPULATION ECOLOGY is the study of individuals of the same species where the processes are aggregation, interdependencies between individuals etc, and the various factors governing such processes are emphasized.
  • 4. • Demography is the study of human populations – their size, composition and distribution across space and the process through which populations change. • Births, deaths and migration are the ‘big three’ of demography, jointly producing population stability or change. • It is the study of human population dynamics. • Population dynamics is the branch of life sciences that studies the size and age composition of populations as dynamical systems, and the biological
  • 5. density • Population density is the number of individuals per unit geographic area, for example, number per square meter, per hectare, or per square kilometer. • Density may be numerical density (number of individuals per unit area or volume) or biomass density (biomass per unit area or volume)
  • 6. • Further, since the pattern of distribution of organisms in nature is different it becomes important to distinguish between crude density and ecological density. • Crude density is the density (number or biomass) per unit total space. • Ecological density (specific or economic density) is the density (number or biomass) per unit of habital space, i.e., available area or volume that can actually be colonized by the population.
  • 7. Density is affected by four primary population parameters such as natality (births), mortality (deaths), immigration and emigration
  • 8. Natality • Natality is a broader term covering the production of new individuals by birth, hatching, germination, or fission. • The natality rate may be expressed as the number of organisms born per female per unit time. • In human population, the natality rate is equivalent to the ‘birth-rate’. • The two essential aspects of the reproduction which forms main component of natality : – Fertility is the physiological notion which indicates that an organism is capable of breeding. – Fecundity is an ecological concept that is based on the numbers of offspring produced during a period of time
  • 9. • Natality is of following two types : – Maximum natality. (absolute, potential or physiological natality). It is theoretical maximum production of new individuals under ideal conditions which simply means that there are no ecological limiting factors and that reproduction is limited only by physiological factors. – Ecological natality. (realized natality or simply natality). It refers to population increase under an actual, existing specific condition. Thus, ecological natality takes into account all possible existing environmental conditions. I’m here to contribute for density increase
  • 10. • ∆ Nn/ Dt = the absolute natality rate • ∆ Nn/NDt = the specific natality rate – where N = the reproductive part (mature female) of the population or initial number of organisms or total population n = new individuals in the population t = time ∆ = delta : a change in value
  • 11. mortality • Mortality means the rate of death of individuals in the population. • It is a negative factor for population growth • It is of following types – Minimum mortality (specific or potential mortality) represents the theoretical minimum loss under ideal or non- limiting conditions. It may be constant for a population. – Ecological mortality (realised mortality) is the actual loss of individuals under a given environmental condition. • Mortality can be expressed as- – number if individuals dying/ unit time.
  • 12. • A survivorship curve is a graph that measures the proportion of individuals in a given species that are alive at different ages. • Typically, the number of individuals of the population is plotted on the y-axis of the graph and the age of survivorship is plotted on the x- axis of the graph. • There are three types of survivorship curves, and they are simply referred to as type I, type II, and type III.
  • 13. •Type I (concave curve) survivorship curve shows individuals that have a high probability of surviving through early and middle life but have a rapid decline in the number of individuals surviving into late life. E.g. human, flies. •Type II (diagonal curve) survivorship curve shows a roughly constant mortality rate for the species through its entire life. E.g. hydra, mice, birds. •Type III (convex curve) survivorship curve depicts species where few individuals will live to adulthood and die as they get older because the greatest mortality for these individuals is experienced early in life. E.g. oyster, fishes
  • 14. Dispersal • Populations have a tendency to disperse, or spread out in all directions, until some barrier is reached. • Accordingly, population dispersion is the movement of individuals into or out of the population area. • It takes three forms- – Emigration – Immigration – Migration
  • 15. • Emigration (one-way outward movement) under natural conditions occurs when there is overcrowding in the migratory locust, lemming, grouse, snowy owl, snowshoe rabbit. • This is generally regarded as an adaptive behavior that regulates the population on a particular site and prevents over-exploitation of the habitat. • Further, it leads to occupation of new areas elsewhere • By dispersing into new localities, there is opportunity gained for interbreeding with other populations leading to more genetic heterozygosity and adaptability. • Immigration (one-way inward movement) leads to a rise in population level, causing an overpopulation which may lead to an increase beyond the carrying capacity. • These immigrations result in increased mortality among the immigrants or decreased reproductive capacity of the individuals
  • 16. • Migration (periodic departure and return) is a peculiar kind of population dispersion which involves the mass movement of entire population. • This can occur only in mobile organisms and best developed in insects such as desert locust(Schistocerca gregaria), migratory locust(Locusta migratoria), butterfly (Danaus plexippus) • In most cases, it may occur for food, shelter, or reproduction. • Better utilization of uninhabited untouched habitats and their resources are the greatest benefits of migratory movements.
  • 18. Growth Curves • Population growth is the increase in the number of individuals in a population. • Two types of population growth patterns may occur depending on specific environmental conditions: – An exponential growth pattern (J curve) occurs in an ideal, unlimited environment. – A logistic growth pattern (S curve) occurs when environmental pressures slow the rate of growth.
  • 19. J- Curve • In J-shaped curve there is a rapid increase in density with the passage of time (called exponential growth). • The density values when plotted against time give a J- shaped growth curve. • If 1000 bacteria are placed in a large flask with an unlimited supply of nutrients, after an hour there will be one round of division, resulting in 2000 organisms. In another hour, each of the 2000 organisms will double, producing 4000, and so on. • The bacteria example is not representative of the real world where resources are limited, and ultimately competition for food would result in deaths and population decline.
  • 20. S- curve • The population growth curve in human populations and growth of yeast, Drosophila and rabbit under laboratory conditions show an initial slow rate and then it accelerates and finally slows giving the growth curve which is sigmoid or S- shape. • The peak constant level represented by K or upper level (called asymptote) of the sigmoid curve is called the maximum carrying capacity. It marks the limit to which the environment can support the population
  • 21. Population fluctuation • Populations are said to be cyclic when they alternatively errupt and subside in a more or less uniform manner between high and low levels of density. • Different animals exhibit population cycles different times. • Population ecologists commonly divide the factors that affect the size of populations into – Density-dependent factors (regulating factors), intensify as the population increases in size, and has a potential for maintaining population density within a narrow range of values. – Density-independent factors (limiting factors), such as weather and climate, exert their influences on population size regardless of the population’s density.
  • 22. Cyclical fluctuations in the population density of the snowshoe hare and its effect on the population of its predator, the lynx.
  • 23. Distribution • Individuals of a population arrange themselves in a manner that is specific for each population. • In nature, due to various biotic interactions and influence of abiotic factors, the following three basic population distributions can be observed : – Random distribution – Uniform or regular distribution – Clumped distribution
  • 24. I. Regular Dispersion: here the individuals are spaced at equal distance from one another. This is rare in nature but common in managed systems (croplands). Animals with territorial behavior tends towards this dispersion II. Random Dispersion: the position of one individual is unrelated to the position of its neighbor. This us also relatively rare in nature. III. Clumped Dispersion: most population exhibit this dispersion to some extent, with individuals aggregated into patches interspersed with no or few individuals.
  • 25. Age pyramid • In most types of populations, individuals are of different age. • The proportion of individuals in each age group is called age structure or age distribution of the population. • Age distribution of the population influences natality and mortality. • A model representing geometrically the proportion of different age groups in the population of any organism is called age pyramid (or age-sex pyramid)
  • 27. • According to Bodenheimer (1938), there are following three basic types of age-sex pyramids: 1. Pyramid with broad base (or Triangular structure) indicates a rapidly expanding population with a high percentage of young individuals and only few old individuals.  Thus, in rapidly growing young population, birth rate is high and population growth may be exponential as in yeast, housefly, Paramecium, etc. 2. Bell-shaped polygon indicates a stationary population having an equal number of young and middle-aged individuals.  As the rate of growth becomes slow and stable, i.e., the pre- reproductive and reproductive age groups become more or less equal in size, post-reproductive group remaining as the smallest.
  • 28. 3. Urn-shaped structure indicates a low percentage of young individuals.  It shows a declining population.  Such an urn-shaped figure is obtained when the birth rate is drastically reduced, the pre- reproductive group dwindles in proportion to the other two age groups of the population.
  • 29. importance • The study of human population is of immense importance to an economy. • Population studies help us to know how far the growth rate of the economy is keeping pace with the growth rate of population. • Data relating to the present trend in population growth help the planners in formulating policies for the economic plan of the country.