L7 Demographic and Environmental stochasticity

Question 1

What is the biggest culprit of extinction and why?

Answer 1

human land-use change! (Mantyka-Pringle et al., 2011)
- It causes habitat loss and habitat fragmentation
- The small populations that arise are at increased risk of extinction
Focusing on patch size and connectivity is really important because of this.

Question 2

What are the four main vital rates?

Answer 2

Birth, Death, Immigration and Emigration

Question 3

reminder of population growth equations:

Answer 3

r = b - d 
R = Nt+1/ Nt
λ  = R = Nt+1/ Nt if generation time is 1 year!

Question 4

the nature of vital rates are probabilistic, what does this mean?

Answer 4

we can expect what the rates should look like, for example, it should be roughly 50:50 for male and female. The smaller the sample size the bigger the deviation.

Question 5

define demographic stochasticity

Answer 5

“the random fluctuations in a population size that occur due to birth and death rates of an individual is discrete and a probabilistic event” (Melbourne, 2012)
or
“Demo stoch includes the inevitable deviation in birth & death rates of rising from the mean rates being probabilities across a population”
SIMPLY: randomness of vital rates in a population

Question 6

define environmental stochasticity

Answer 6

“Unpredictable spatiotemporal fluctuation in environmental conditions.” (Fujiwara & Takada, 2017)
- Arises from extrinsic factors
- Often related to the weather
These affect the mean vital rates for a population
NOT an intrinsic property of small populations
If environmental stochasticity is large, populations can become extinct even with mean positive growth rates

The numbers are generally increasing, but ‘bounce around’ a lot

Question 7

Give examples of environmental stochasticity

Answer 7

Changes in climate, availability of food, biotic environment changes, levels of comp:

• Winter flooding and bees’ hibernation sites
• Very dry summer – amphibian populations
• Freezing winters - herons

Question 8

case study examples of environmental stochasticity

Answer 8

1973 a hurricane decimated the last Laysan teal population (USFWS, 2004) & radio telemetry was used to review the success of their translocation to Midway Atoll (Reynolds et at., 2013) IMPORTANT REFERENCE. (lecture example)

based on a report (Dickman, 2007) it has been estimated that 480 million animals have been negatively affected by Australian wildfires. (own example)

Question 9

If a population undergoes high stochasticity what is more likely?

Answer 9

higher probability of extinction

Question 10

Which method to calculate mean growth rate of a pop is better?

Answer 10

Geometric (check maths notes on pop growth) not arithmetic

Question 11

What are the effects of population size with viability?

Answer 11

1) Increase in temporal variation in pop growth decreases persistence time of a pop.
2) Increase in actual growth rate decreases persistence time

3) If carrying capacity (K) decreases, the pop growth rate declines
(Reed, 2008)

Question 12

can conservation management techniques change the way a population survive through environmental stochasticity?

Answer 12

yes! example from lecture:
Gantianella campestris was grown in different conditions
1. Grazed with normal pasture
2. Mown, July 21st & Grazed, normal pasture
3. Mown, July 21st
4. Mown, October 5th
+ control
results = P[extinction] lowest for 2 & Most resistant to environmental stochasticity was 2
therefore management method affects population viability.
(Lennartson and Oostermeijer, 2001)