10: Populations and Species Flashcards
Three main issues with small populations
- loss of genetic diversity
- demographic stochasticity (birth and death rates, density, allee effet)
- environmental stochasticity (e.g. predation, natural disasters)
What is effective population size
Only breeding adults are ‘effective’; they contribute to population viability
Why might there be an unequal sex ratio in populations?
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)
How many individuals (Ne) are enough to avoid genetic problems?
50 needed to avoid issues related to inbreeding
500 is minimum to make sure genetic drift is balanced by the # of mutations
What is the ultimate source of variation? Does this work for small populations?
Mutations
In small pop, loss of genetic variation via genetic drift is greater than new variation from mutations
What is demographic stochasticity?
Skewed age/sex ratios, population too old, fluctuations in birth and death
What is environmental stochasticity?
Variation in habitat suitability/quality, declining habitat quality, natural catastrophes
Most important form of stochasticity in populations of moderate to small size?
Environmental (increases probability of extinction)
What are the two paradigms for conserving populations (DR. Graeme Caughley)
- Focus on small populations
- estimate pop size over time
- use theory to estimate pop viability or length oft to extinction
- deductive approach - Focus on declining populations
- identify ultimate cause of decline, try to fix
- try to generalize to other pop/species
- inductive approach
What are sensitive / important locations
Particular behaviours occur there (e.g. calving), greater risk of mortality
Examples of approaches to monitoring
- repeated census
- surveys conducted by bioindicators, biologists, citizens
- anecdote/traditional knowledge
What are bioindicators
Populations that indicate ecosystem health
Three types of survivorship curve? What are on the x and y axes
Type 1: long-lived
Type 2: breed for entirety of life
Type 3: short-lived
x axis = % of max lifespan
y axis = % of survivors
What is MVP
Minimum viable population
How is a good MVP estimated? What is the function?
Using average demographic info and includes extremes
Provides a “buffer” is the basis for the precautionary principle
average MVP for terrestrial vertebrates
500-1000 (if genetics and inbreeding ignored)
- 1000s if include genetic effects
What information is needed to estimate a decent MVP (5)
- environment of species
- distribution of habitat & species in it
- biotic interactions
- morphology, behaviour, physiology, genetics
- demography
What is PVA
Population viability analysis
Modelling with the intent of uncovering threats to long-term persistence of populations (educated guesses of MVP)
Three applications of PVA
- 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
Population abundance and age structure are a result of…
- extrinsic natural factors (e.g. habitat)
- intrinsic factors (e.g. fecundity, mortality)
- human-induced factors (e.g. hunting, fragmentation)
Issues with PVA models
- data often unavailable or incomplete
- does not incorporate unknown variables
- lack of ecological reality or are over simplified
Three primary problems of PVAs
- Single species techniques
- Omit risk sources difficult to estimate
- project long into the future, where conditions difficult to predict
What is statistical power
Likelihood that a study will detect an effect when it actually (biologically) exists
What is a type 1 error? Type 2?
Type 1: rejecting the null hypothesis when it is true
Type 2: not rejecting the null hypothesis when it is false
What are patterns? Processes?
Pattern = change over time
Process = cause of the change
