1. Question of the day
All of the following are examples of abiotic factors except
temperature pH
wind
salinity
vegetation

2. Population Dynamics & Carrying Capacity
NOTES Chapter 9-1
Population Dynamics & Carrying Capacity

3. Core Case Study: Southern Sea Otters: Are They Back from the Brink of Extinction?
Sea otters are an important keystone species for sea urchins and other kelp-eating organisms.
They were over-hunted to the brink of extinction by the early 1900’s and are now making a comeback.
Figure 8-1

4. Key Terms & Concepts (1 of 2)
Population- the number of individuals of a species that inhabit a particular area.
Population structure- the density and spacing of individuals within a landscape.
Spacing (or dispersion) refers to the dispersion pattern of individuals in a population.
Geographic distribution – a species’ range; the range can change with changing population dynamics.
Population dynamics- population changes over time.
Reasons for caring:
Aesthetics
Keystone species
Ethical

5. Population Spacing or Dispersal
Spacing is dependent on the availability of resources
Clumped Spacing - individuals are clustered in groups, most common.
Uniform spacing – regular spacing or dispersal
Random spacing - no spacing pattern is apparent

6. Key Terms & Concepts (2 of 2)
Natality
Number of individuals added through reproduction
Crude Birth Rate - Births per 1000
Total Fertility Rate – Average number of children born alive per woman in her lifetime
Mortality
Number of individuals removed through death
Crude Death Rate Deaths per 1000
Age Structure - proportion of individuals in each age group in population

7. Population Growth Population growth depends upon
birth rates (+)
death rates (-)
immigration rates (+ into area)
emigration rates (- exit area)
Population = Pop0 + (b + i) - (d + e)
Zero Population Growth (ZPG)
(b + i) = (d + e)

8. Age Structure: Young Populations Can Grow Fast
How fast a population grows or declines depends on its age structure.
Prereproductive age: not mature enough to reproduce.
Reproductive age: those capable of reproduction.
Postreproductive age: those too old to reproduce.
What factors influence the growth of a population?

9. Age Structure Diagrams
Positive Growth Zero Growth Negative Growth
(ZPG)
Pyramid Shape Vertical Edges Inverted Pyramid

10. Limits on Population Growth
Biotic potential is a population’s capacity for growth.
Biotic potential is limited by environmental factors.
Thus no population can increase its size indefinitely.
Environmental resistance: all the factors that act to limit the growth of a population.
Biotic factors: reproductive rate, niche, food supply, disease resistance, etc.
Abiotic factors: light, temperature, chemical environment (i.e. pH)

11. Limits on Population Growth
The intrinsic rate of increase (r) is the rate at which a population would grow if it had unlimited resources.
Carrying capacity (K): the maximum population of a given species that a particular habitat can sustain indefinitely without degrading the habitat.
Determined by the interaction of biotic potential and environmental resistance.
Growth rate (r) decreases as its size nears the K. Why?

13. Population Growth Populations show two types of growth Exponential
J-shaped curve
Growth is independent of population density
Logistic
S-shaped curve
Growth is not independent of population density

14. Exponential and Logistic Population Growth: J-Curves and S-Curves
Populations grow rapidly with ample resources, but as resources become limited, its growth rate slows and levels off.
Figure 8.3
Natural capital: no population can continue to increase in size indefinitely. Exponential growth (lower part of the curve) occurs when resources are not limited and a population can grow at its intrinsic rate of increase (r) or biotic potential. Such exponential growth is converted to logistic growth, in which the growth rate decreases as the population becomes larger and faces environmental resistance. Over time, the population size stabilizes at or near the carrying capacity (K) of its environment, which results in a sigmoid (S-shaped) population growth curve. Depending on resource availability, the size of a population often fluctuates around its carrying capacity, although a population may temporarily exceed its carrying capacity and suffer a sharp decline or crash in its numbers.
Figure 8-4

15. Logistic Growth
Because of Environmental resistance, population growth decreases as density reaches carrying capacity
Graph of individuals vs. time yields a sigmoid or S-curved growth curve
Reproductive time lag causes population overshoot
Population will not be steady curve due to resources (prey) and predators

17. Population Dynamics and
Carrying Capacity (K)
Over time, populations of species in an ecosystem are usually in a state of equilibrium (balance between births and deaths)
There is a dynamic balance between biotic potential and environmental resistance
Exponential curve is not realistic due to carrying capacity of area

19. Exceeding Carrying Capacity: Move, Switch Habits, or Decline in Size
Members of populations which exceed their resources will die unless they adapt or move to an area with more resources.
Figure 8.6
Exponential growth, overshoot, and population crash of reindeer introduced to the small Bering Sea island of St. Paul. When 26 reindeer (24 of them female) were introduced in 1910, lichens, mosses, and other food sources were plentiful. By 1935, the herd size had soared to 2,000, overshooting the island’s carrying capacity. This led to a population crash, with the herd size plummeting to only 8 reindeer by 1950.
Figure 8-6

20. Exceeding Carrying Capacity: Move, Switch Habits, or Decline in Size
Over time species may increase their carrying capacity by developing adaptations.
Some species maintain their carrying capacity by migrating to other areas.
So far, technological, social, and other cultural changes have extended the earth’s carrying capacity for humans.

21. Population Density and Population Change: Effects of Crowding
Population density: the number of individuals in a population found in a particular area or volume.
Density depends upon social/population structure, mating relationships, time of year
A population’s density can affect how rapidly it can grow or decline. e.g. biotic factors like disease
Some population control factors are not affected by population density.
e.g. abiotic factors like weather

22. Types of Population Change Curves in Nature
Population sizes may stay the same, increase, decrease, vary in regular cycles, or change erratically.
Stable: fluctuates slightly above and below carrying capacity.
Irruptive: populations explode and then crash to a more stable level.
Cyclic: populations fluctuate and regular cyclic or boom-and-bust cycles.
Irregular: erratic changes possibly due to chaos or drastic change.

23. Types of Population Change Curves in Nature
Figure 8.7
Population cycles for the snowshoe hare and Canadian lynx. At one time scientists believed these curves provided circumstantial evidence that these predator and prey populations regulated one another. More recent research suggests that the periodic swings in the hare population are caused by a combination of top-down population control—predation by lynx and other predators—and bottom-up population control. In the latter, changes in the availability of the food supply for hares help determine hare population size, which in turn helps determine the lynx population size. (Data from D. A. MacLulich)
Population sizes often vary in regular cycles when the predator and prey populations are controlled by the scarcity of resources.
Figure 8-7

24. Question of the day
When a population’s growth rate changes to match local conditions, it is known as
Exponential growth
Density-independent growth
natality
Logistic growth
Pioneer growth

25. NOTES Section 9-2 Reproductive Patterns & Survival

26. REPRODUCTIVE PATTERNS
Some species reproduce without having sex (asexual).
Offspring are exact genetic copies (clones).
Others reproduce by having sex (sexual).
Genetic material is mixture of two individuals.
Disadvantages: males do not give birth, increase chance of genetic errors and defects, courtship and mating rituals can be costly.
Major advantages: genetic diversity, offspring protection.

27. Reproductive Patterns: Opportunists and Competitors
Large number of smaller offspring with little parental care (r-selected species).
Fewer, larger offspring with higher invested parental care (K-selected species).
Figure 8-9

28. r - Strategists Most of their time is in
exponential growth. High growth rate (r)
Max. reproductive life
Minimum life span
Pop. size fluctuates
wildly above & below carrying capacity – (K)
Generalist niche K

29. K - Strategists Maintain population at carrying capacity (K)
Maximize lifespan
Lower population growth rate (r)
Specialist niche K

30. Reproductive Patterns
r-selected species tend to be opportunists while K-selected species tend to be competitors.
Figure 8-10

31. Survivorship Curves
Survivorship curves represent the age structure of a population.
Type 1: Late loss population live to an old age. Usually K-strategists
Type 2: Constant loss population die at all ages. Usually intermediate reproductive strategies
Type 3: Most members of early loss population, die at young ages. Usually r-strategists

32. Survivorship Curves
The populations of different species vary in how long individual members typically live.
Figure 8-11

33. NOTES Section 9-3 Effects of Genetic Variations on Population Size

34. EFFECTS OF GENETIC VARIATION
Small, isolated populations are most vulnerable
Founder Effect – a few individuals colonize a geographically isolated habitat. Ex.
Limited genetic diversity may threaten the survival of the population.
Demographic Bottleneck: a few individuals survive a catastrophe.
Lack of genetic diversity limits the ability to rebuild the population
Genetic Drift: random changes in the gene frequencies lead to unequal reproductive success.