# population ecology

**Topics:**Population, Population ecology, Demography

**Pages:**21 (2211 words)

**Published:**February 17, 2014

13.0 POPULATION ECOLOGY

(2 HOURS)

Learning outcomes :

13.1 Population Growth

(a) Explain biotic potential (r) and

environmental resistance and their

effect on population growth

(b) Explain carrying capacity and its

importance

(c) Describe natality and mortality and

their effects on the rate of population

growth

Learning outcomes :

13.1 Population Growth

(d) Explain population growth curves

(state the basic forms of growth

curves)

i. Exponential growth curve (human)

ii. Logistic growth curve (Paramecium sp.)

(e) Explain the limiting factors affecting

the population size :

i. Density dependent factors

ii. Density independent factors

Population Ecology

• The study of variables

• That determine the population density

and distributions

• Of a population in time and space

Learning Outcomes :

13.1 (a): Explain biotic potential (r) and environmental resistance and their effects on population growth

Biotic Potential (r) :

The number of offspring of an

individual organism that would survive

to reproductive age under ideal

condition

Learning Outcomes :

13.1 (a): Explain biotic potential (r) and environmental resistance and their effects on population growth

FIGURE 1

Learning Outcomes :

13.1 (a): Explain biotic potential (r) and environmental resistance and their effects on population growth

Biotic Potential is influenced by :

1. The age beginning of reproduction

2. How often reproduction occurs

3. How many offspring are born at a time

Learning Outcomes :

13.1 (a): Explain biotic potential (r) and environmental resistance and their effects on population growth

Biotic Potential & its Effect on Population

Growth

• Biotic potential (r) also varies according to the age

structure of a population

• It also may influence by male : female ratios

• When conditions are optimal and there are no

limitations, a population can grow at its maximum

biotic potential (the vital index, rmax)

• However, under natural conditions, the growth rate

of a population is never at the highest possible rate

because there is environmental resistance

•Learning Outcomes : :

Learning Outcomes

23.1 c: Explain environmental resistanceenvironmental resistance and their effects on population growth 13.1 (a): Explain biotic potential (r) and and discuss its effects on population growth

Environmental

Resistance :

The sum total of the factors that

prevent populations from continually

growing and therefore tend to keep

populations at constant levels

Learning Outcomes :

13.1 (a): Explain biotic potential (r) and environmental resistance and their effects on population growth

FIGURE 2

Learning Outcomes :

13.1 (a): Explain biotic potential (r) and environmental resistance and their effects on population growth

FIGURE 3

Learning Outcomes :

13.1 (a): Explain biotic potential (r) and environmental resistance and their effects on population growth

Environmental Resistance & its Effect on

Population Growth

• If there is zero environmental resistance, the

ability to continue to survive rises and a

population then achieves its full biotic potential

• If the condition continues, individuals in a

population

will

continue

to

increase

exponentially, resulting in overcrowding

• Accumulation of toxic waste, stress, disease due

to overcrowding & poor nutrition

Learning Outcomes :

13.1 (a): Explain biotic potential (r) and environmental resistance and their effects on population growth

• This is prevented by environmental resistance to

maintain the total number of individuals in the

population

• This ensures that the rate of increase (natality

rate) is the same as the rate of decrease

(mortality rate)

• Example : an overcrowded population in a

habitat will reduce food supply or attract more

predators

• When the population size drops to a level below

the carrying capacity, the effect of environmental

resistance is cancelled...

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