Topic 24: Groups and Populations

Question 1

Differentiate groups and populations

Answer 1

• Groups: organisms of the same or different species occupied same area at the same time
• Populations: organisms of the same species in a defined area

Question 2

Describe features of groups organisms

Answer 2

• Can be ephemeral or consistent
• Social group (positive)
• Indirect (sharing common resource)
• Accidental (random grouping)

Question 3

What are some properties of a population? (occupied area, movement, etc.)

Answer 3

• size (abundance), occupied area, age structure and sex ratio
• Can be terrestrial or aquatic; motile or sessile

Question 4

Describe spatially structured populations

Answer 4

Aka metapopulations

• Local small populations scattered in an area, but they are still interacting.
• Demographic rates of each population vary.
• Beneficial in case 1 local population go extinct and others can help to reestablish the missing one.

Question 5

describe exponential and logistic models of population growth

Answer 5

• Exponential: populations grow exponentially in a non-depleting environment
• Logistic: no environment is non-depleting
  -> population still grows exponentially initially, but slows down and plateus at the carrying capacity

Question 6

Identify and describe 2 models of exponential growth

Answer 6

• Discrete: reproduction occurs periodically
  + seasonal reproduction -> recurring pattern of growth and decline
  + discrete ROC
• Continuous: reproduction occurs any time
  + all year round reproduction -> smooth line
  + instantaneous ROC changes constantly

Question 7

Identify main components of demographic rates

Answer 7

Births, deaths, immigration, emigration, sex ratio, growth and mature age

Question 8

Identify and describe most common method of estimating population size and the associated assumptions

Answer 8

• A sample of the population is captured, marked by tagging and released.
• When recaptured, the ratio between number of marked individuals and total number of recaptured sample is used to estimate the total population size
• Assumptions: closed system, individuals equally marked and not lost their marks

Question 9

How can birth and death rate be estimated?

Answer 9

Birth: count newly borned individuals

Death: tagging

Question 10

What rates are involved in age-/size-structured population?

Answer 10

Fecundity and survival rates

Question 11

What is population viability analysis. how is it calculated and what it is used for?

Answer 11

• A tool used model and predict population dynamics over time by taking different inputs and is very useful to determining conservation methods
• Utilizes basic population parameters including:
  
  • population size or carrying capacity
  • fecundity rate
  • mortality: adult and juveniles
  • annual variation of parameters
• Also include environmental factors and human impacts

Question 12

What are some factors influencing extinction?

Answer 12

• Genetic stochasticity - loss of genetic diversity → extremely vulnerable to environmental changes
• Demographic stochasticity - random nature of births and deaths that can result in too small of a population to maintain over a long time
• Environmental stochasticity - variability of weather and climate conditions
• Catastrophes - disasters, especially in recent years
• Human impacts

Question 13

When may the population exceed the carrying capacity?

Answer 13

Population may exceed the carrying capacity when resources are declining more quickly than the decrease of reproduction rate.
Eventually, the population still falls below carrying capacity.