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Chapter 6 POPULATION BIOLOGY

Chapter 6 POPULATION BIOLOGY. OUTLINE. DYNAMICS OF POPULATION GROWTH FACTORS THAT INCREASE OR DECREASE POPULATIONS FACTORS THAT REGULATE POPULATION GROWTH CONSERVATION BIOLOGY. OPTION 1 = $_______________________. OPTION 2 = $_______________________. BIOTIC POTENTIAL.

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Chapter 6 POPULATION BIOLOGY

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  1. Chapter 6 POPULATION BIOLOGY

  2. OUTLINE • DYNAMICS OF POPULATION GROWTH • FACTORS THAT INCREASE OR DECREASE POPULATIONS • FACTORS THAT REGULATE POPULATION GROWTH • CONSERVATION BIOLOGY

  3. OPTION 1 = $_______________________ OPTION 2 = $_______________________

  4. BIOTIC POTENTIAL • BIOTIC POTENTIAL refers to unrestrained biological reproduction. Biological organisms can produce enormous numbers of offspring if their reproduction is unrestrained. • ENVIRONMENTAL RESISTANCE refers to the total of all factors that limit population growth. These are also known as LIMITING FACTORS • As population increases so does environmental resistance!!

  5. DYNAMICS OF POPULATION GROWTH • POPULATION - all the members of a single species living in a specific area at the same time • EXPONENTIAL GROWTH - growth at a constant rate of increase per unit time; has no limit dN/dt = rN The change in the Number of individuals (dN) per change in time (dt) equals the rate of growth (r) times the number of individuals in the population (N). r is often called the INTRINSIC CAPACITY FOR INCREASE.

  6. EXPONENTIAL GROWTH • Number of individuals added to a population at the beginning of exponential growth is relatively small. But numbers increase quickly because a % increase leads to a much larger increase as the population grows. • J CURVE when the equation is graphed • Exponential growth is a simple, idealized model. In the real world there are limits to growth.

  7. EXPONENTIAL GROWTH

  8. ***RULE OF 70 YOU MUST KNOW THIS • RULE OF 70 is used to determine the approximate doubling time of a population Doubling Time = 70 % growth rate 1. If a country was doubling its population every 35 years what would its growth rate be? 2. Currently, human pop growth rate is 1.2% In what year do you predict the world population will have doubled?

  9. CARRYING CAPACITY • CARRYING CAPACITY - limit of sustainability that an environment has in relation to the size of a species population • OVERSHOOT - population exceeds the carrying capacity of the environment and death rates rise as resources become scarce • POPULATION CRASH - growth becomes negative and the population decreases suddenly • BOOM AND BUST - population undergoes repeated cycles of overshooting followed by crashing

  10. BOOM & BUST OR J CURVE

  11. GROWTH TO A STABLE POPULATION • LOGISTIC GROWTH - growth rates regulated by internal and external factors until coming into equilibrium with environmental resources • dN/dt = r N (1 - N/K) • Terms have the same definitions as previous slide, with K added to indicate carrying capacity. • Growth rate slows as population approaches carrying capacity. • S CURVE when the equation is graphed

  12. LOGISTIC GROWTH CURVE OR S CURVE

  13. J vs S POPULATION CURVES

  14. r AND K SELECTED SPECIES • r SELECTED SPECIES rely upon a high reproductive rate to overcome the high mortality of offspring with little/no parental care. ie: A clam releases a million eggs in a lifetime but the larva are so small that few survive. • K SELECTED SPECIES have few offspring but more parental care so most young survive. ie: An elephant reproduces every 4 or 5 years.

  15. REPRODUCTIVE STRATEGIES r-selected species 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. K-selected species 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

  16. FACTORS AFFECTING POPULATION GROWTH • EXTERNAL FACTORS include habitat quality, food availability and interaction with other organisms. • INTERNAL FACTORS include physiological stress due to overcrowding, maturity, body size, and hormonal status. • These factors are DENSITY DEPENDENT, meaning as population size increases the effect intensifies. • DENSITY INDEPENDENT effects (drought, an early frost, flooding, landslides, etc.) also may decrease population size.

  17. FACTORS THAT INCREASE POPULATION • NATALITY – birth rate • FECUNDITY - physical ability to reproduce • FERTILITY - measure of actual number of offspring produced • IMMIGRATION - organisms introduced into new ecosystems • Dispersal of organisms by wind or water currents over long distances. Sometimes carried by animals or on rafts of drifting vegetation.

  18. FACTORS THAT DECREASE POPULATION • EMIGRATION – individuals leaving an area • MORTALITY - death rate • SURVIVORSHIP - percentage of cohort surviving to a certain age • LIFE EXPECTANCY - probable number of years of survival for an individual of a given age • Increases as humans age. By older age, most individuals destined to die early have already done so. • Has risen in nations/areas with good nutrition, sanitation and medical care • Women live longer than men.

  19. LIFE SPAN • LIFE SPAN - longest period of life reached by a given type of organism • Bristlecone pine lives 4,600 years. • Human maximum lifespan is 120 years. • Microbes may live a few hours. • Differences in relative longevity among species are shown as survivorship curves.

  20. SURVIVORSHIP CURVES • FOUR GENERAL PATTERNS: (NOTE THE #’s) I. Full physiological life span if organism survives childhood • Example: top consumers, Humans II. Probability of death unrelated to age • Example: Sea gull, rodents IV. Mortality peaks both early and late in life. • Example: Deer, crabs III. Mortality peaks early in life. • Example: oysters, sea turtles, oak tree

  21. SURVIVORSHIP CURVES

  22. FACTORS THAT REGULATE POP. GROWTH ENVIRONMENTAL RESISTANCE • DENSITY DEPENDENT FACTORS • Have more influence as the population density increases • They slow population growth • Impact large % of population • Disease, competition, predation, stress and stress related issues – aggression, decreased fertility and immunity, pathological behaviors due to high density

  23. FACTORS THAT REGULATE POP. GROWTH ENVIRONMENTAL RESISTANCE • DENSITY INDEPENDENT FACTORS • Not influenced by the size of the population • All organisms are affected equally regardless of population density • Fire, floods, weather, natural disasters, human-caused habitat disruption, etc.

  24. FACTORS THAT REGULATE POP. GROWTH ENVIRONMENTAL RESISTANCE • INTRINSIC FACTORS - operate within or between individual organisms in the same species • competition, territoriality, stress, etc • EXTRINSIC FACTORS - imposed from outside the population • predation, climate, natural disasters, etc.

  25. FACTORS THAT REGULATE POP. GROWTH ENVIRONMENTAL RESISTANCE • ABIOTIC FACTORS - Caused by non-living environmental components. Tend to be density independent, and do not really regulate population although they may be important in increasing or decreasing numbers. ie: climate, weather, natural disasters, fire • BIOTIC FACTORS - Caused by living organisms. Tend to be density dependent. They regulate population size by decreasing natality or increasing mortality.

  26. DENSITY DEPENDENT FACTORS(biotic factors) • INTERSPECIFIC INTERACTIONS (between different species) • predator/prey, mutualism, commensalism, etc • Resource partitioning, invasives, etc Predator-Prey Oscillating Cycles

  27. DENSITY DEPENDENT FACTORS (biotic factors) • INTRASPECIFIC INTERACTIONS - competition for resources by individuals within a population • As population density approaches the carrying capacity, resources become limited. • Control of access to resources by territoriality; owners of territory defend it and its resources against rivals. • STRESS-RELATED DISEASES occur in some species when conditions become overcrowded. • DISEASES – tend to spread faster with a higher population density

  28. CONSERVATION BIOLOGY • Critical question in conservation biology is the minimum population size of a species required for long term viability. • SPECIAL CASE OF ISLANDS • ISLAND BIOGEOGRAPHY • MacArthur and Wilson proposed that species diversity is a balance between colonization and extinction rates. • Small islands vs Large islands • Far from mainland vs closer to mainland

  29. CONSERVATION GENETICS • In a large population, genetic diversity tends to be preserved. A loss/gain of a few individuals has little effect on the total gene pool. • However, in small populations small events can have large effects on the gene pool. • GENETIC DRIFT • Change in gene frequency due to a random event • FOUNDER EFFECT • Few individuals start a new population.

  30. CONSERVATION GENETICS • DEMOGRAPHIC BOTTLENECK - just a few members of a species survive a catastrophic event such as a natural disaster • Founder effects and demographic bottlenecks reduce genetic diversity. There also may be INBREEDING due to small population size. Inbreeding may lead to the expression of recessive genes that have a harmful effect on the population.

  31. GENETIC DRIFT

  32. POPULATION VIABILITY ANALYSIS • MINIMUM VIABLE POPULATION is the minimum population size required for long-term survival of a species. ie: • The number of grizzly bears in North America dropped from 100,000 in 1800 to 1,200 now. The animal’s range is just 1% of what is once was and the population is fragmented into 6 separate groups. Biologists need to know how small the bear groups can be and still be viable in order to save the grizzly.

  33. METAPOPULATIONS • METAPOPULATION - a collection of populations that have regular or intermittent gene flow between geographically separate units • SOURCE HABITAT - Birth rates are higher than death rates. Surplus individuals can migrate to new locations. • SINK HABITAT - Birth rates are less than death rates and the species would disappear if not replenished from a source.

  34. METAPOPULATION

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