Dynamics - Matrix models

14 important questions on Dynamics - Matrix models

What are transient dynamics?

  • Matrix projection
  • Population development
  • For years or decades
  • Starting pop structure important

What are asymptotic dynamics?

  • Lambda
  • Elasticity
  • After many decades/centuries
  • Assumes stable stage distribution was reached

How is exploitation implemented in the matrix?

  • Individuals removed => increase mortality
  • Seed harvested => reduce reproduction rate
  • Leaf harvest affects growth => reduce growth rate
  • Indirect effect on other stages => change transitions
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How is exploitation implemented in the vector?

  • Seed harvested => remove seeds
  • Whole individuals harvested => remove individuals
  • Plant part harvested => NOT!

How can matrix models be made sustainable?

  • Population continues to grow: λ ≥ 1 (asymptotic)
  • Exploitation does not strongly affect population growth: elasticity (asymptotic)
  • Absolute population size stays the same: population projection (transient)
  • Availability of resource remains the same: population projection (transient)

What are the pros of using lambda=1 as a sustainability criterion?

  • Makes intuitive sense
  • Easy to test

What are the cons of using lambda=1 as a sustainability criterion?

  • Considers whole population, not resource
  • Considers population growth, not its size
  • Unaffected by starting conditions or disturbances
  • Estimate of λ can be uncertain

What are the characteristics of the Maximum Sustained Yield concept?

  • Departs from logistic growth model
  • All growth is sustainably harvested
  • Max at intermediate population size
  • Parameters hard to obtain
  • Is used in hunting & fisheries

What are differences between transient and asymptotic population growth?

Asymptotic: when population has reached SSD; transient: before that

Asymptotic: independent  from starting population; transient: dependent on starting distribution

What information is used to calcluate the transition to the next class in *size*-based models?

Both rates of individual growth and survival.

In size-based models the transition to the next size classe is a function of:

  • Individual growth rate
  • survival rate
  • 1/(category width)

Brazil nut tree: why does it take long to reach the stable size distribution?

  • This is a long-lived species
  • The matrix has many categories

Brazil nut tree: why can lambda be considered as an indicator for sustainable extraction?

If the exploited population is still growing, it implies that the population -- and thus likely the productivity -- will be sustained over time.

Brazil nut tree: Why would a low elasticity for reproduction indicate scope for sustainable nut collection?

Because it implies that changes in the number of seeds produced have very little impact on population growth.

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