10: Populations and Species

Question 1

Three main issues with small populations

Answer 1

1. loss of genetic diversity
2. demographic stochasticity (birth and death rates, density, allee effet)
3. environmental stochasticity (e.g. predation, natural disasters)

Question 2

What is effective population size

Answer 2

Only breeding adults are ‘effective’; they contribute to population viability

Question 3

Why might there be an unequal sex ratio in populations?

Answer 3

Differential survival (e.g. human females live longer)

Environmental sex determinations (e.g. in alligators, temps of 34C or above = male, temps of 30C or below = females)

Question 4

How many individuals (Ne) are enough to avoid genetic problems?

Answer 4

50 needed to avoid issues related to inbreeding

500 is minimum to make sure genetic drift is balanced by the # of mutations

Question 5

What is the ultimate source of variation? Does this work for small populations?

Answer 5

Mutations
In small pop, loss of genetic variation via genetic drift is greater than new variation from mutations

Question 6

What is demographic stochasticity?

Answer 6

Skewed age/sex ratios, population too old, fluctuations in birth and death

Question 7

What is environmental stochasticity?

Answer 7

Variation in habitat suitability/quality, declining habitat quality, natural catastrophes

Question 8

Most important form of stochasticity in populations of moderate to small size?

Answer 8

Environmental (increases probability of extinction)

Question 9

What are the two paradigms for conserving populations (DR. Graeme Caughley)

Answer 9

1. Focus on small populations
   - estimate pop size over time
   - use theory to estimate pop viability or length oft to extinction
   - deductive approach
2. Focus on declining populations
   - identify ultimate cause of decline, try to fix
   - try to generalize to other pop/species
   - inductive approach

Question 10

What are sensitive / important locations

Answer 10

Particular behaviours occur there (e.g. calving), greater risk of mortality

Question 11

Examples of approaches to monitoring

Answer 11

• repeated census
• surveys conducted by bioindicators, biologists, citizens
• anecdote/traditional knowledge

Question 12

What are bioindicators

Answer 12

Populations that indicate ecosystem health

Question 13

Three types of survivorship curve? What are on the x and y axes

Answer 13

Type 1: long-lived
Type 2: breed for entirety of life
Type 3: short-lived

x axis = % of max lifespan
y axis = % of survivors

Question 14

What is MVP

Answer 14

Minimum viable population

Question 15

How is a good MVP estimated? What is the function?

Answer 15

Using average demographic info and includes extremes
Provides a “buffer” is the basis for the precautionary principle

Question 16

average MVP for terrestrial vertebrates

Answer 16

500-1000 (if genetics and inbreeding ignored)
- 1000s if include genetic effects

Question 17

What information is needed to estimate a decent MVP (5)

Answer 17

• environment of species
• distribution of habitat & species in it
• biotic interactions
• morphology, behaviour, physiology, genetics
• demography

Question 18

What is PVA

Answer 18

Population viability analysis
Modelling with the intent of uncovering threats to long-term persistence of populations (educated guesses of MVP)

Question 19

Three applications of PVA

Answer 19

• used to model the probability of a pop failing or prospering under a set of circumstances
• used to set size of pop required to maintain species
• find features that make pop vulnerable

Question 20

Population abundance and age structure are a result of…

Answer 20

1. extrinsic natural factors (e.g. habitat)
2. intrinsic factors (e.g. fecundity, mortality)
3. human-induced factors (e.g. hunting, fragmentation)

Question 21

Issues with PVA models

Answer 21

1. data often unavailable or incomplete
2. does not incorporate unknown variables
3. lack of ecological reality or are over simplified

Question 22

Three primary problems of PVAs

Answer 22

1. Single species techniques
2. Omit risk sources difficult to estimate
3. project long into the future, where conditions difficult to predict

Question 23

What is statistical power

Answer 23

Likelihood that a study will detect an effect when it actually (biologically) exists

Question 24

What is a type 1 error? Type 2?

Answer 24

Type 1: rejecting the null hypothesis when it is true
Type 2: not rejecting the null hypothesis when it is false

Question 25

What are patterns? Processes?

Answer 25

Pattern = change over time
Process = cause of the change