CH 08 Population & Carrying Capacity

Section 01

A. POPULATION DYNAMICS AND CARRYING CAPACITY

1. Three general patterns of population distribution occur in a habitat: clumping, uniform distribution and random dispersion.

a) Most species live in clumps b) Uniform pattern distribution may occur where a resource

such as water c) In random distribution members of a species are placed in

seemingly random placement.

Distribution Patterns

PLAYANIMATION

Which pattern is this?

Fig. 8-2c, p. 162

Fig. 8-2b, p. 162

Which pattern is this?

Fig. 8-2a, p. 162

Which pattern is this?

2. Four variables influence/govern population size: births, deaths, immigration, and emigration

a) Populations increase through births and immigration

b) Populations decrease through deaths and emigration

3. How fast a population grows or declines depends on its age structure.a) Prereproductive age: not mature enough to

reproduce.b) Reproductive age: those capable of

reproduction.c) Postreproductive age: those too old to

reproduce.

A Population’s Age Structure Determines its Potential for Growth

PLAYANIMATION

Age Structure Diagram

Populations with a pyramid-shaped age structure will grow explosively.

Populations with a rectangular age structure will grow much slower.

4. No population can increase its size indefinitely due to limited resources such as light, water, and nutrients and because of competitors or predators

a) The biotic potential is the population’s capacity for growth

b) The intrinsic rate of increase (r) is the rate at which a population would grow if it had unlimited resources.

5. Environmental resistance consists of factors

that limit population growtha) Carrying capacity (K): the maximum population of

a given species that a particular habitat can sustain indefinitely without degrading the habitat

b) Populations grow rapidly with ample resources, but as resources become limited, its growth rate slows and levels off.

Figure 8-4Figure 8-4

Fig. 8-3, p. 163

EnvironmentalResistance

Time (t)

Pop u

lati o

n si

ze ( N

)

Carrying capacity (K)

ExponentialGrowth

BioticPotential

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6. A population can grow rapidly with ample resources

a) With few resource limitations, This population will have a fixed rate of growth that will take be a J-shaped growth curve

b) This represents its intrinsic rate of increase (r) or biotic potential

Animation: Exponential Growth

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7. This exponential growth is converted to logistic growth when the populations face environmental resistance

a) In logistic growth, the growth rate levels off as population size reaches or nears carrying capacity

b) The sigmoid (s-shaped) population growth curve shows that the population size is stable

8. As a population levels off, it often fluctuates slightly above and below the carrying capacity

a) Overshooting an environment’s resources often is a result of a reproductive time lag

b) The reproductive time lag can produce a dieback/crash of organisms unless the organisms can find new resources or move to an area with more resources

c) If the carrying capacity of an area is exceeded, changes in the area itself can reduce future carrying capacity

Fig. 8-4, p. 164

Carrying capacity

Year

Num

ber o

f she

ep (m

illio

ns)

Overshoot

9. Exceeding Carrying Capacity: Move, Switch Habits, or Decline in Size

a) Over time species may increase their carrying capacity by developing adaptations.

b) Some species maintain their carrying capacity by migrating to other areas.

c) So far, technological, social, and other cultural changes have extended the earth’s carrying capacity for humans.

Fig. 8-6, p. 165

Num

ber o

f rei

ndee

r

Populationovershootscarryingcapacity

Carryingcapacity

Year

PopulationCrashes

Population Crash

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10. The density of a population may or may not affect how rapidly it can grow

a) Population density: the number of individuals in a population found in a particular area or volume.

b) Density-independent population controls affect a population’s size regardless of its density (abiotic factors: weather)

c) Density-dependent factors population controls have a greater affect on the population as its density increases (biotic factors:disease)

11.Population sizes may stay the same, increase, decrease, vary in regular cycles, or change erratically.a) Stable: fluctuates slightly above and below carrying

capacity because species are living under fairly constant environmental conditions

b) Irruptive: populations explode and then crash to a more stable level which is characteristic of short-lived, rapidly reproducing species

c) Cyclic: populations fluctuate and regular cyclic or boom-and-bust cycles.

d) Irregular: erratic changes possibly due to chaos or drastic change.

12. Interaction between predators and their prey change in cycles

a) Hypothesis of top-down control of prey by predators may not be only explanation for cycling

b) Bottom-up control hypothesis is that plants consumed too rapidly by herbivores for replacements to keep up

Fig. 8-7, p. 166

Popu

latio

n si

ze (t

hous

ands

)

Year

LynxHare