Ecology 4 -

Question 1

Explain shortage of food and populations

Answer 1

• Limited resources
• Shortages of fod and shelter,increased competition between individuals and disease outbreaks, will eventually cause growth to slow down

Question 2

Explain logistic growth

Answer 2

• Results when the environment restricts growth
• Usually occurs in organisms with continuous breeding
• Produces an S-shaped or sigmoidal curve

Question 3

Explain the four phases of logistic growth

Answer 3

1. Lagphase - Growth is slow as the population is still small ( bottom )
2. Exponential growth phase – Growth increases as more individuals are added
3. Deceleration phase–Growth slows down
4. Stable equilibrium phase–Very little growth ( top )

Question 4

Explain carrying capacity

Answer 4

• ” K “ of a population is the maximum number of individuals that can be supported by the environment
• Population growth cannot increase indefinitely because resources are limited
• When a population reaches carrying capacity, it stops growing – the death rate matches the birth rate

Question 5

What happens at the carrying capacity

Answer 5

The population will usually fluctuate around the carrying capacity

Question 6

Explaing logistic growth formula with carrying capacity

Answer 6

• Calculate logistic population growth

The formula becomes:

G = rmaxN ((K-N) / K)

• G = change in population size
• rmax = maximum net reproduction per individual
• N = population size
• K = carrying capacity

Question 7

Explain logistic growth fully

Answer 7

• (K-N) / K represents the effect of carrying capacity on population growth
• If N is small, the term (K-N) / K is close to one and has little effect on population growth
• If N is approaching K, the term (K-N) / K is close to zero and has a strong effect on population growth

Question 8

Explain population regulation and its factors

Answer 8

• Population regulation is the control of population size
• Population regulating factors (limiting factors) limit the size of a population
• Prevent a population from increasing exponentially

Question 9

What factors play a role in regulating population size

Answer 9

Both biotic and abiotic factors

Question 10

What are the factors of population size regulation

Answer 10

1. Density-independent factors (abiotic)
2. Density-dependent factors (biotic)
3. Intrinsic factors (biotic)

Question 11

For competition to take place what ,ust there be

Answer 11

1. Resources in limited supply
2. Incr in density ( leading to reduction in fitness )

Question 12

Explain density independent factors

Answer 12

• A population regulating factor which is not influenced by the population size
• The intensity of the effect does not increase with increased population size

Examples: severe weather conditions, fires, natural disasters

Question 13

Explain density dependent factors

Answer 13

• A population regulating factor which is influenced by population size
• The percentage of the population affected does increase as the density increases

Examples: predation, competition, disease, parasites

Question 14

Explain competition

Answer 14

• When individuals compete for resources (e.g. food, light, space) that are in limited supply
• As a result, some members of the population may be unable to survive, grow, or reproduce

Question 15

Explain intraspecific competition

Answer 15

Individuals of the same species compete with each other

Question 16

Explain interspecific competition

Answer 16

Individuals of one species compete with individuals of another species

Question 17

Explain intrinsic factors

Answer 17

• Factors based on anatomy, physiology, behaviour) may also help to regulate population size
• Density-independent and some density- dependent factors are extrinsic

eg ) Territoriality and Dominance hierarchies

Question 18

What are examples of intrinsic factors

Answer 18

• Dispersal – leaving the population
• Social behaviour – co-operation and sharing of resources
• Physical characteristics – adaptations to the environment

Question 19

Explain strategies for survival

Answer 19

• Evolution acts on organisms to increase their individual genetic contributions to future generations
• To grow, survive, reproduce and thus contribute genetically to future generations, organisms must allocate their limited energy supply for maximum benefit

Question 20

Explain life history

Answer 20

• Concerns lifelong patterns of growth and reproduction and includes particulars such as:

1. Number of births per reproduction
2. Age at reproduction
3. Life span
4. Probability of living the entire lifespan

• Natural selection shapes the life history of a species to suit its environment

Question 21

Explain the two life history strategies

Answer 21

1. r-selection
   - In unpredictable environments, density- independent factors keep populations in the lag or exponential phase of growth
2. K-selection
   - Stable environments allow populations to approach the carrying capacity

Question 22

Explain r-selection fully

Answer 22

• Organisms live in unstable, unpredictable environments
• They are subject to density-independent factors
• They need to reproduce quickly, before the environment changes
• Produce many “cheap” offspring
• r-Selected organisms are called r-strategists

Question 23

What are characteristics of r-strategiests

Answer 23

• Low population density
• Produce large numbers of offspring
• Small body size
• Early maturity
• Short-lived
• No parental care
• Controlled by density-independent factors  Good dispersers and colonizers

Question 24

Explain k-selection fully

Answer 24

• Organisms live in stable, predictable environments
• The population is at or near the carrying capacity
• Organisms are subject to density-dependent factors
• Produce few “expensive” offspring
• K-selected organisms are called K-strategists

Question 25

What are characteristics of k-strategists

Answer 25

• High population density
• Produce small numbers of offspring
• Large body size
• Late maturity
• Long-lived
• Significant parental care
• Controlled by density-dependent factors
• Specialists