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<>The study of stage-structured populations sheds
light on the fundamental question of why mortality rate at age *x*,* **μ**(x)
= - *log [ *l(x+1)/l(x)*],
does NOT always increase monotonically with age as predicted by theory. As previously known, in organisms where
demographic rates are recorded for observable, discrete stages,
stage-structured matrix projection models of population dynamics contain
information about age-specific rates.
Here we provide new insights by tracking dynamic stage structure and
one-period stage-specific survival across ages for both constant and variable
environments. The underlying process
constitutes a “killed” Markov process, where the mass of the system changes
state as it decreases over time. At each
age, the stage structure may change and total cohort survival to the next age
is given by a weighted average of stage-specific survivals. Some stages may eventually drop out; at later
ages individuals are reshuffled among the remaining stage classes. For a cohort, this means that at early ages,
transient dynamics rule and anything can happen, meaning that the age pattern
of mortality can rise, fall or rise and fall before reaching the asymptotic
dynamics as the stage structure approaches a quasi-stationary distribution. Over the lifetime, mortality may start out
higher or lower than the late age plateau and it may overshoot the
plateau. Later, asymptotic dynamics rule
and a constant rate of mortality, a plateau, is approached. We find that in variable environments, an expected
long run stochastic sequence of environments has a long run stochastic
mortality rate which has not previously been described. We illustrate these points employing examples
of a pine tree, two African grasses and a temperate forest herb using constant
environment models and an understory shrub inhabiting
forests characterized by hurricane-driven canopy dynamics using a variable
environment model.
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See more of OOS 27 - Matrix population models: Theory and applications

See more of Organized Oral Session

See more of The ESA/SER Joint Meeting (August 5 -- August 10, 2007)

See more of Organized Oral Session

See more of The ESA/SER Joint Meeting (August 5 -- August 10, 2007)