1. population dynamics
A look at the factors that tend to increase or decrease the size of a population.

2. POPULATION DYNAMICS AND CARRYING CAPACITY
Most populations live in clumps although other patterns occur based on resource distribution.
Figure 8-2

3. (a) Clumped (elephants)
Figure 8.2
Natural capital: generalized dispersion patterns for individuals in a population throughout their habitat. The most common pattern is clumps of members of a population throughout their habitat, mostly because resources are usually found in patches.
(a) Clumped (elephants)
Fig. 8-2a, p. 162

4. (b) Uniform (creosote bush)
Figure 8.2
Natural capital: generalized dispersion patterns for individuals in a population throughout their habitat. The most common pattern is clumps of members of a population throughout their habitat, mostly because resources are usually found in patches.
(b) Uniform (creosote bush)
Fig. 8-2b, p. 162

5. (c) Random (dandelions)
Figure 8.2
Natural capital: generalized dispersion patterns for individuals in a population throughout their habitat. The most common pattern is clumps of members of a population throughout their habitat, mostly because resources are usually found in patches.
(c) Random (dandelions)
Fig. 8-2c, p. 162

6. The population size of a species in a given space at a given time is determined by the interplay between BIOTIC POTENTIAL and ENVIRONMENTAL RESISTANCE.
Biotic potential = growth rate with unlimited resources.
Environmental resistance = all the factors acting jointly to limit population growth.

7. (environmental resistance)
POPULATION SIZE
Growth factors
(biotic potential)
Favorable light
Favorable temperature
Favorable chemical environment
(optimal level of critical nutrients)
Abiotic
Biotic
High reproductive rate
Generalized niche
Adequate food supply
Suitable habitat
Ability to compete for resources
Ability to hide from or defend
against predators
Ability to resist diseases and parasites
Ability to migrate and live in other
habitats
Ability to adapt to environmental
change
Decrease factors
(environmental resistance)
Too much or too little light
Temperature too high or too low
Unfavorable chemical environment
(too much or too little of critical
nutrients)
Low reproductive rate
Specialized niche
Inadequate food supply
Unsuitable or destroyed habitat
Too many competitors
Insufficient ability to hide from or defend
Inability to resist diseases and parasites
Inability to migrate and live in other
Inability to adapt to environmental

8. Population characteristics
Density~ # of individuals per unit of area •counts •sample size estimate •indirect indicators •mark-recapture
Dispersion~ pattern of spacing •random~ unpredictable, patternless spacing (a) •clumped~ patchy aggregation (b) •uniform~ even spacing (c)

9. Four variables change population size:
NATALITY = birth rate
MORTALITY = death rate
IMMIGRATION = rate of organisms moving in
EMIGRATION = rate of organisms moving out

10. Changes in Population Size: Entrances and Exits
Populations increase through births and immigration
Populations decrease through deaths and emigration

11. Demography: factors that affect growth & decline of populations
Birthrate (natality, fecundity)~ # of offspring produced
Death rate (mortality)
Age structure~ relative number of individuals of each age
Survivorship curve~ plot of numbers still alive at each age

12. Limits on Population Growth: Biotic Potential vs
Limits on Population Growth: Biotic Potential vs. Environmental Resistance
No population can increase its size indefinitely.
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.

13. 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 8-4

14. Environmental Resistance
Carrying capacity (K)
Population size (N)
Biotic
Potential
Exponential
Growth
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.
Time (t)
Fig. 8-3, p. 163

15. 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

16. Population overshoots carrying capacity Number of reindeer Population
Crashes
Number of reindeer
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.
Carrying
capacity
Year
Fig. 8-6, p. 165

17. 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.

18. Population life history “strategies”
r-selected (opportunistic)
Short maturation & lifespan
Many (small) offspring; usually 1 (early) reproduction; no parental care
High death rate
K-selected (equilibrial)
Long maturation & lifespan
Few (large) offspring; usually several (late) reproductions; extensive parental care
Low death rate

19. Opportunistic or r-Selected Species
cockroach
dandelion
Many small offspring
Little or no parental care and protection of offspring
Early reproductive age
Most offspring die before reaching reproductive age
Small adults
Adapted to unstable climate and environmental
conditions
High population growth rate (r)
Population size fluctuates wildly above and below
carrying capacity (K)
Generalist niche
Low ability to compete
Early successional species

20. Competitor or K-Selected Species
elephant
saguaro
Fewer, larger offspring
High parental care and protection of offspring
Later reproductive age
Most offspring survive to reproductive age
Larger adults
Adapted to stable climate and environmental
conditions
Lower population growth rate (r)
Population size fairly stable and usually close
to carrying capacity (K)
Specialist niche
High ability to compete
Late successional species

21. REPRODUCTIVE STRATEGIES
Number of individuals
Time
Carrying capacity
K species;
experience
K selection
r species;
r selection K

22. Survivorship Curves: Short to Long Lives
The way to represent the age structure of a population is with a survivorship curve.
Late loss population live to an old age.
Constant loss population die at all ages.
Most members of early loss population, die at young ages.

23. Percentage surviving (log scale)
SURVIVORSHIP CURVES
Percentage surviving (log scale)
100 10 1
Age

24. Type I: high survivorship until late in life
Survivorship Curves
Type I: high survivorship until late in life
Type II: constant death rate at all ages
Type III: death rate is highest early in life

25. Population Density and Population Change: Effects of Crowding
Population density: the number of individuals in a population found in a particular area or volume.
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

26. Population density affects population growth.

27. 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.

28. Population limiting factors
Density-dependent factors
•competition •predation
•stress/crowding •waste accumulation
Density-independent factors
•weather/climate
•periodic disturbances

29. R-strategists populations are most affected by these.
DENSITY INDEPENDENT FACTORS = affect a populations’ size regardless of its population density.
Weather
Earthquakes
Floods
Fires
. . . Natural disasters
R-strategists populations are most affected by these.

30. DENSITY DEPENDENT FACTORS = affect a populations’ size depending on its population density.
Predation
Disease
Availability of food and water
Space
Negative Feedback!!

31. INTERNAL FACTORS = might include density-dependent fertility or size of breeding territory.
EXTERNAL FACTORS = might include predation and disease.

32. Limiting Factors on Growth
Essential resources
Food
Minerals
Water
Refuge
Carrying capacity
Logistic growth

33. For some additional info click here…..Great website on populations.