Biology Reference
In-Depth Information
at random. NEWGARDEN interpolates the probability of mortality when
the difference between successively noted generations is greater than 1. For
example, the mortality statements for individual cohorts
<functionpoint x=“0” y=“0.2”/>
<functionpoint x=“2” y=“0.1”/>
<functionpoint x=“4” y=“0.1”/>
<functionpoint x=“6” y=“0.5”/>
specify that 20% of newly generated individuals aged 0 will randomly
be culled, and 15% of the cohort survivors aged generation 1, 10% of
generations 2 through 4, 30% of generation 5, and 50% of remaining
members of generation 6 for that cohort will die.
Note that a given cohort may produce new cohorts in each of many
years. Thus, the yearly reproductive schedule of individuals belonging to
different cohorts, reproducing in a particular year, with rates of reproduction
for different cohorts reproducing in the same year, etc., can become quite
complex, which is probably more realistic for numerous species as opposed
to more commonly used discrete generation models. This is one reason
output statistics for NEWGARDEN trials are given both for the different
episodic new cohorts of a developing population (i.e., only the offspring
newly produced for each new total population generation being one cohort)
and for the population as a whole, which may be composed of the new
cohort plus surviving members of several past cohorts of different ages.
Mortality: Some Further Theoretical Considerations
Varying amounts of relevant information concerning age-specifi c rates of
mortality exist for certain organisms or types of organisms (e.g., forest trees
of horticultural importance), and reference to such information concerning
relatively similar organisms might provide fi rst best estimates for trial
runs concerning species for which there is a total lack of information. For
example, if cohorts are expected to progress according to a type 3 curve,
then higher probabilities of mortality will be assigned to earlier ages. Since
the effects of mortality compound with increasing age, several experimental
trial runs may be necessary to arrive at a set of realistic age-specifi c mortality
values.
For some species, the timing of the end of reproductive activity and
death, or at least the ability to interfere with the establishment of the next
cohort, may not coincide. As an example, consider long-lived trees that
senesce, and then die standing with decay and deconstruction occurring
over several years. Such species can be modeled in NEWGARDEN by
setting reproduction to cease before death occurs (with death, an individual
is completely removed from the data set and no longer interferes with
Search WWH ::
Custom Search