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Conservation Biology - 10. PVAs

Course Code
BIOL 3130
Andrew Mac Dougall

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Conservation Biology: Lecture Notes
10. PVAs
- Key question: How small a population size is too small?
- Small populations can go extinct even if the expected (b-d) > 0, there is safety in
Conservation Planning
- Quantitative methods are needed to assess viability of threatened and endangered
populations in these plans
- Population viability analysis is a set of tools for quantifying the current and future
status of populations of conservation interest
Population Viability Analysis
- Used to understand the persistence of populations over time.
- Requires long-term data sets and an in-depth understanding of the species’ biology:
dormancy, survival rates, seed bank dynamics, reproductive rates, age of
reproductive maturity, impacts of stochastic events, mortality
- Synthesis of knowledge about a species, its environment, and human actions in a
model of population dynamics.
Population size (N)
- Restoration implications [based on PVA simulations]:
What size is needed for a founder population?
Is a restored population or a rare population sustainable over the long term?
Vital Rates
- Like most demographic analyses, PVAs focus on key birth and death processes
- Simpler models ignore immigration and emigration (although more complicated
ones can include multiple populations with migration)
-Survival refers to remaining in an stage class (age class)
-Growth refers to going from one stage class (age class) to another
-Reproduction refers to number of offspring per individual (usually female)
- We can measure some demographic characteristics (Pop size, brood size, proportion
of young), and use them do infer other characteristics (breeding ratio, survival rates
Estimating Population Growth
- Vital rates determine rate of population growth
- The growth or decline of the population is expressed Nt+1=λtNt, where λ describes the
annual population growth rate
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