Species Distribution

Question 1

What is distribution?

Answer 1

Distribution of an organism is the region that it inhabits.

Question 2

How to determine distribution of plants and animals?

Answer 2

Distribution of plants- 
- large scale use plotting on a map 
- transects
Distribution of animals
- trapping or observation of tracks and droppings
- personal sightings
- plotting on the map

Question 3

How to determine the abundance of animals and plants?

Answer 3

Abundance of plants
- Using quadrats
Abundance of animals
- capture- marking- recapture technique

Question 4

What is uniform distribution?

Answer 4

• Individuals are spaced evenly
  Example- plants secrete toxins to inhibit growth of nearby individuals- called allelopathy
  Example- animal species that stake out and defend territories. (magpies and koalas)

Question 5

What is random distribution?

Answer 5

• Individuals distributed randomly (not predictable)
  Example- dandelions and other plants that have wind dispersed seeds. The seeds spread widely and sprout where they happen to fall. (good soil, water, sun)

Question 6

What is clumped distribution?

Answer 6

• Individuals clustered in groups
  Example- plants that drop their seeds straight to the ground- such as oak trees
  Example- animals that live in schools of fish or herds
• Clumped dispersal also happen in habitats that are patchy, with only some patches suitable to live in.

Question 7

What factors influence the size and number of quadrats that could be used to estimate abundance?

Answer 7

• Characteristics of the organism
• Larger organisms require large quadats than smaller organisms
• Even distribution/ consistent requires less quadrats than organisms that are scattered and erratic
• Smaller quadrats would be suitable to estimate abundance of grass
• Large quadrats would be suitable for sparsely scattered cedars in a rainforest

Question 8

Capture- recapture equation

Answer 8

N=Mn/R
M- total captured in first sample
n- total captured in 2nd sample
R- number of recapture marked in 2nd sample

Question 9

How does a negative and positive trap experience influence the population estimates?

Answer 9

• Method of collection. Example: Trap happy organisms that associate trap with food and little discomfort from humans; resulting in an increase in recapture of marked- under estimation
• Others may associate traps with shock of handling and marking. Example: Trap/shy organisms learn to avoid traps and give a decrease in recapture of marked individuals- inflation of estimation

Question 10

What are the disadvantages of the capture- recapture method?

Answer 10

• Weather conditions affecting the activity of organisms under study.
  Example: wet/dry conditions would affect the sampling of amphibians
• Marking method unreliable.
  Example: tags torn off, colour marking lost due to bird moulting
• Length of time between sampling.
  Example: Highly motile animals distribute themselves randomly in a population more quickly than if they were slowly moving.
• This approach assumes that animals don’t die, get born, leave or enter the population during the period of study.