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 = $_______________________

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 =
% 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?
DT = 70/r = 70/r r = 70/ r = 2%
DT = 70/ DT = 58 years = 2075

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
Oscillating Cycles of growth and decline

10. BOOM & BUST OR J CURVE
Why does carrying capacity go down over time? Degradation of habitat over time
Sometimes referred to Irruptive growth / Malthusian Growth
Aside from dying – what else might individuals do in response to overshoot? Migrate, spread to new areas

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
Population grows rapidly BUT slows as it nears CC

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.
r – weeds, insects, mice, herbaceous plants,
K – whales, apes, trees, top carnivores, elephant, bald eagle

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
Is known as TYPE I – “late-loss” curve – K strategists
Is known as TYPE II – “constant loss” curve
Is known as TYPE IV -
Is known as TYPE III – “early-loss” curve – r-strategists

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
Behaviors – locusts in swarms, lemmings,

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

30. 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.

31. 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.

32. GENETIC DRIFT

33. 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.

34. 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.

35. METAPOPULATION