L5 Fundamentals of Pop ecology continued (matrices)

Question 1

how can maths help in population growth? (5)

Answer 1

• calculating effective pop size & no. of individuals, so pop isn’t going into vortex
• % of extinction
• consequence of management schemes in place
• which management action has the best effect
• projection models

Question 2

describe “sensitivity” in terms of population growth:

Answer 2

some life stages have higher fecundity rates & some stages make up more of a population. A change in survival or fecundity of these higher value stages will affect the growth rate of a pop more than other stages.

Question 3

how can you assess sensitivity and include it in a conservation decision?

Answer 3

use the population growth matrix/model i.e. increase juvenile survival from 0.33 to 0.34 and adult fecundity form 279.5 to 279.6 and conclude which stage has the biggest affect.

Question 4

What is negative density-dependence and what are the factors that lead to this? (2)

Answer 4

Where population growth declines by overcrowding.
- competition for resources i.e. space, light, mates, food
- increased disease
(carrying capacity)

Question 5

What is positive density-dependence and what are the factors that lead to this? (6)

Answer 5

Where growth rate declines due to a small population! 
- Increased predator defence
- Decreased prob of individual capture 
- Better access to food 
- Co-operative defence 
- Easier to reproduce 
- Temperature tolerance 
Not getting fitness benefits of being in a group especially if social organisms

Question 6

What is the Allee effect?

Answer 6

A graph showing a non linear but positive relationship between pop density and pop growth. Low populations are affected by this negatively and are more likely to become extinct. allee threshold -

Allee (1927) Isopods are easier to predate before population threshold is reached

Question 7

Allee effect case study

Answer 7

Vancouver Marmot. 300 individuals down to 25. decreasing in pop & growth rate.

Question 8

What are Density Independent Factors?

Answer 8

Factors effecting a population regardless of population density
BR and DR don’t change with density
Freak weather events such as hurricanes or cold will kill a population despite density