Lecture 13


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Lecture 13

  1. 1. Lecture 13: Population Growth Covers Chapter 26
  2. 2. Some Definitions* • Population: all of the members of a particular species that live within an ecosystem • Community: a group of interacting populations • Ecosystem: all of the living and non-living components of a defined geographic area • Biomes: Large land areas with similar environmental conditions and characteristic plant communities • Biosphere: all living and non-living components covering Earth’s surface • Ecology: the study of interrelationships of organisms with each other and with their non-living environment
  3. 3. Population Change • *Populations change through – Births – Deaths – Migration: net migration depends on • Immigration (entering the population) • Emigration (leaving the population) • The natural increase in population is difference between births and deaths. • The total change in a population size is births minus deaths plus net migration.
  4. 4. births immigration deaths (births − deaths) + (immigrants − emigrants) = change in population size emigration Population Change Fig. 26-1
  5. 5. 2 opposing factors affect population change* • Biotic Potential: maximum rate at which a population could increase assuming ideal conditions • Carrying Capacity: maximum population size that can be sustained – for an extended period of time* – without damage to the ecosystem*
  6. 6. Biotic Potential stimulates population growth • Factors influencing biotic potential: – Age at which organism first reproduces* – Frequency of reproduction* – Average number of offspring produced each time an organism reproduces* – Length of organism’s reproductive lifespan* – Death rate of individuals under ideal conditions*
  7. 7. Carrying Capacity limits population growth • If population exceeds carrying capacity, surrounding resources cannot feed all of the members of the population…then – the population will stop growing (and eventually begin to shrink) – the carrying capacity will shrink (because resources cannot renew themselves quickly enough)*
  8. 8. Fig. 26-6a (a) An S-shaped growth curve stabilizes at carrying capacity Growth stops and the population stabilizes close to the carrying capacity Population grows rapidly Growth rate slows
  9. 9. Carrying Capacity Adjusts Fig. 26-6b (b) Consequences of exceeding carrying capacity High damage; the carrying capacity is permanently lowered Low damage; resources recover, and the population fluctuates Extreme damage; the population dies out The population overshoots the carrying capacity; the environment is damaged
  10. 10. Environmental Resistance* • Degree to which the living and non-living environment limits population growth. • A way to quantify environmental resistance is to divide factors that limit population growth into – density-dependent factors – density-independent factors
  11. 11. Density dependent and density independent factors: overview* • Density Dependent: factors that limit population size more when populations are larger – Competition – Predation – Parasitism – Availability of Nutrients – Availability of Space – Availability of Energy • Density Independent: factors that limit population size regardless of how large/concentrated the population is – Climate and Weather – Human activities: pesticides, pollution
  12. 12. Density Dependent* • These factors become more effective at limiting growth as the population grows/becomes more dense: – Competition: interactions among individuals who attempt to use the same resources-harms both species involved – Predation: organisms kill/eat other organisms – Parasitism: one organism (parasite) feeds off of a larger one (host)-harms the host only
  13. 13. Fig. 26-11 bean weevils (prey) A high predator population reduces the prey population The prey population peaks when the predator population is low braconid wasp (predator)
  14. 14. More next lecture • Next lecture will be a more in depth look at competition, predation, etc…..community interactions. • Today we are talking more about how these factors affect population growth.
  15. 15. Density Independent* • Climate and weather • Human activity – Some populations evolve adaptations to survive climate/weather • thick coats for winter that are shed in spring/summer • Migration to warmer climate or one with more resources for a period of time • Plants have dormant period during winter
  16. 16. Population Distribution* • Populations show characteristic spacing, which may vary with time: • Clumped: members live in groups (herds, packs, prides, flocks and schools) – Many eyes to see food – Protection from predators – Some species clump near resources (trees near water) • Uniform: members maintain a relatively constant distance between each other – Territorial behavior: stay farther apart from others because of limited resources (plants, birds, etc) • Random: rare – Resources equally available – Trees and other plants mostly
  17. 17. Populations Distribution • Great pacific media (You Tube)
  18. 18. Clumped Distribution Fig. 26-14a
  19. 19. Uniform Distribution Fig. 26-14b
  20. 20. Random Distribution Fig. 26-14c
  21. 21. What about the human population? • Demography: study of the changing human population – Measure populations in different countries/regions – Track population changes – Make comparisons between developed and third world countries – Examine birth/death rates among different sexes & races – Attempt to estimate future population changes – Evaluate the impact of these changes
  22. 22. Humans • Human population growth used to be exponential: continually accelerating increase. Now it seems we may be leveling off…..at least some think so. • It took 200,000 years to get to 1 billion (1804), but now in 2012 we are at 7 billion – 1.4 million born each week – What about environmental resistance? – Are we at carrying capacity?
  23. 23. 7 billion: Nat Geo Magazine • You Tube
  24. 24. Humans and Environmental Resistance • Humans have encountered resistance, but we have developed ways to overcome it: – Discovered fire* – Tools & weapons to kill food* – Shelter and clothing to live in cold areas* – Domesticated crops and animals for food* – Industrial and medical advances* – Scientific advances (discovery of bacteria)*
  25. 25. Population Growth is different in developed & developing countries • Many factors determine population growth in different countries
  26. 26. Developed countries • High standard of living • Access to modern technology • Access to medical care, including contraception • Education/employment opportunities • Decreased death rates, increased life span, more stable birth rates • US is fastest growing developed country
  27. 27. Developing countries • Higher birth rates (less access to contraception) • More poverty • Lack of education
  28. 28. Europe: 0.0% Latin America/Caribbean: 1.5% Asia (excluding China): 1.5% Developing countries average: 1.5% Africa: 2.4% N. America: 0.6% World average: 1.2% Developed countries average: 0.2% China: 0.5% Fig. 26-21