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Population ecology
Population ecology is the study of how population sizes change over time and the factors influencing these changes. Key points include: - Population dynamics examines population growth, stability, and decline through measuring factors like birth rate, mortality, survivorship, and migration. - Population size, density, dispersion, immigration, and emigration all shape population characteristics and are influenced by interactions with the environment. - Population growth rates are determined by birth rate, death rate, immigration, and emigration and can follow exponential or logistic growth curves depending on environmental constraints.
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Population ecology
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- 2. • Population ecology: - Science that deals with measuring changes in population size and composition - Identify the factors that cause the changes
- 3. What is population? A group of individual of the same species of organisms that occupy the same area, using the same resources and acted upon by the same environmental factors
- 4. Population dynamics • Studyhow and why population size changes over time • Study the factors affecting growth, stability and decline of populations (birth rate, mortality, survivorship, migration) • All populations undergo 3 phases in life cycle : - growth, stability, decline
- 5. Population Dynamics •Characteristics of Dynamics •Size •Density •Dispersal •Immigration •Emigration •Births •Deaths •Survivorship
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- 7. The characteristics ofpopulations are shaped by the interactions between individuals and their environment • Populations have size and geographical boundaries. – The density of a population is measured as the number of individuals per unit area. – The dispersion of a population is the pattern of spacing among individuals within the geographic boundaries – The size of a population Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
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- 9. MEASURING DENSITY Density Number of individuals per unit of area at a given time • Expressed in terms of items or organisms per unit area • Ex : the number of paddy plants per square meter of a paddy field • Population density varies due to limiting factors
- 10. • Measuring densityof populations is a difficult task. – We can count individuals; we can estimate population numbers. Fig. 52.1 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
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- 12. PATTERN OF DISPERSION UNIFORM CLUMPED RANDOM
- 13. Clumped dispersion • Alsoknown as aggregated distribution • Individuals aggregate in patches • Caused by : environment where the resources concentrated in patches • Other factors : mating, limited seed dispersal • Importance : for protection, reducing competition, increasing feeding efficiencies
- 14. Clumped Dispersion Copyright ©2002 Pearson Education, Inc., publishing as Benjamin Cummings
- 15. Uniform dispersion • Patternof equally spaced individuals • Caused by the ability to survive anywhere in the habitat • Used the resources found immediately around them • Importance : able to set up the zone of territories for feeding, nesting, breeding
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- 17. Random dispersion • Spacingpattern based on total unpredictability • Individual in a population are spaced all over an area in a way that in unrelated to the presence of others • Caused by the ability to live anywhere in a given area except, they are limited to grow wherever they are first set root (for plants)
- 18. Random Dispersion Fig. 52.2c Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
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- 20. • Population oforganism able to change over time • Increase in population size usually due to natality (birth rate) • Decrease in population size as a result of mortality
- 21. Do you know? •For human, natality is expressed as the number of births per 1000 people per year • Mortality can be defined as : - the rate at which individual die - expressed as the number of deaths per 1000 people per year
- 22. How to determinethe rate of changes in population? • Changes in time must take into consideration ΔN / Δt = N (b-d) Δ = change in equations N = number of individuals t = time b = natality d = mortality
- 23. • The growthrate or rate of changes (increase or decrease) of population is expressed by r r=b-d
- 24. Immigration and emigration •Immigration (individual enter a population) and emigration (individual leave a population) also affects the growth rate of a population r = (b - d) + (i – e ) i = immigration e = emigration
- 25. Parameters that effectsize or density of a population: Immigration Birth Population (N) Death Emigration Figure 1. The size of a population is determined by a balance between births, immigration, deaths and emigration
- 26. FACTORS INFLUENCING POPULATION GROWTH
- 27. • Population growthcan be describe by using a growth curve - exponential growth curve - logistic growth curve
- 28. Exponential growth curve •Mode of population that assume birth rate and death rate remain constant over time • Describing an idealized population in an unlimited population • Ignoring immigration and emigration • The result in exponential growth is that if b > d, r > 0
- 29. Exponential growth • The growth rate is always positive • NO upper limit to population size
- 30. Logistic population growth •Referred as a ‘S – shaped’ curve or sigmoidal growth curve • The growth start with a slow rate, followed by growth rising rapidly and enter a stabilized constant population size • The population stops increasing when it reach its carrying capacity (K)
- 31. The logistic modelof population growth incorporates the concept of carrying capacity • Typically, unlimited resources are rare. –Population growth is therefore regulated by carrying capacity (K), which is the maximum stable population size a particular environment can support. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
- 32. POPULATION GROWTH RATE LOGISTICGROWTH RATE Assumes that the rate of population growth slows as the population size approaches carrying capacity, leveling to a constant level. S-shaped curve CARRYING CAPACITY The maximum sustainable population a particular environment can support over a long period of time.
- 33. Example of ExponentialGrowth Kruger National Park, South Africa
- 34. Factors influencing population density Population density can be affected by the interaction of density-dependent factors and density-independent factors
- 35. Density-dependent factors • Factorsthat limit population growth by
- 36. Density-Dependent Factors • limiting resources (e.g., food & shelter) • production of toxic wastes • infectious diseases • predation • stress • emigration
- 37. Density-Independent Factors • severe storms and flooding • sudden unpredictable severe cold spells • earthquakes and volcanoes • catastrophic meteorite impacts