Hutchings, 2015 - thresholds for impaired species recovery

Question 1

What is are the small population & declining population paradigms concerned with?

Answer 1

SPP:

• correlates of extinction probability
• dynamics of species at such low numbers that probability of extinction is decreased
• due to demographic/environmental/genetic stochasticity

DPP:
- causes and consequences of population depletion

Question 2

What happens to depleted populations?

Answer 2

• continue to decline, stabilise, or increase
• SPP & DPP concern themselves with these
• neither concerned with recovery

Question 3

What’s an allee effect?

Answer 3

• positive correlation between population size or density and the mean individual fitness (often measured as per capita population growth rate)
• mean individual fitness/per capita population growth measured as (r realised)
• strong allee effects when r realised is negative at low abundances, leading to extinction
• weak when remaining positive

Question 4

What is a component allee effect?

Answer 4

• a positive relation between any component of individual fitness and either numbers
  or density of members of the same species (conspecifics)
• requires assumptions that increase in one component of fitness = increase in overall fitness
• focusing attention on one aspect of fitness & finding no association with population size can lead to failure detecting Allee effects from other components of fitness

Question 5

What is an Allee threshold/Allee effect threshold?

Answer 5

• Allee threshold = population size/density at which r realised becomes negative and population isn’t going to recover
• Allee threshold = population size or density below which r realised begins to decline relative to the negatively density-dependent pattern exhibited at larger population sizes

Question 6

What are temporal thresholds for impaired recovery?

Answer 6

• the longer a population remains depleted, the more likely its environment will change & become unfavourable to it persisting
• prolonged recovery times/increased uncertainty in recovery expected for depleted populations suffering Allee effects
• recovery time/uncertainty of recovery predicted to increase in presence of Allee effects

Question 7

What’s the recovering population paradigm?

Answer 7

• ultimate goal of conservation = recovery
• rather than extinction focused SPP & DPP
• effort needed to identify thresholds of abundance below which recovery is impaired
• estimating red flags for impaired recovery
• theoretical & empirical template for research on determinants, rate & probability of recovery
• might be expected to differ among broad taxonomic groups