Ergebnis für URL: http://alexei.nfshost.com/PopEcol/lec7/modif.html7.5. Modifications of the Leslie model
1. Variable matrix elements. Survival and reproduction rate of organisms may
depend on a variety of factors: temperature, habitat characteristics, natural
enemies, food, etc. To represent these dependencies, the elements of Leslie model
can be replaced by equations that specify survival and reproduction rates as
functions of various factors. Equations can be obtained from experimental data.
2. Distributed delays. Age and time are equivalent in the original Leslie model,
and thus, all organisms develop synchronously with constant rate. However,
development rate of invertebrates and plants is not constant: it depends on
temperature and may vary among individuals. Individual variation of development
rates is called "distributed delay" because there is a distribution of time when
organisms reach maturity. Transition matrix can be modified to incorporate these
features.
[eqtab1.gif]
[eqtab2.gif]
This matrix has non-zero diagonal elements, and thus, some proportion of
organisms remain in the same age class when time increases. As a result,
development goes slower than it would be in the original Leslie model. The rate
of development can be adjusted by changing relative values of diagonal and
sub-diagonal elements This matrix allows organisms to leap over several age
intervals in one time step. As a result, development goes faster than it would be
in the original Leslie model. The rate of development can be adjusted by changing
the length of age leaps.
3. Partitioning the life cycle into stages. Many invertebrate species have a
complex life cycle that includes several stages. For example, holometabolous
insects usually have 4 stages: egg, larvae, pupae, and adult. Each of these
stages may include several age intervals: In these models, age is no longer
measured in calendar time units (e.g., days or years). Instead, it is measured in
independent units which can be interpreted as "physiological age". The concept of
physiological age will be discussed in details in the next chapter. It can be
used to define "rate of development" as the average increment of physiological
age per calendar time unit.
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[4]Alexei Sharov 1/12/96
References
1. http://alexei.nfshost.com/PopEcol/lec7/agedist.html
2. http://alexei.nfshost.com/PopEcol/lec7/leslie.html
3. http://alexei.nfshost.com/PopEcol/lec8/tempdev.html
4. http://alexei.nfshost.com/~sharov/alexei.html
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Errormessages are in German, sorry ;-)