## Program LIFETIME: explanations and documentationThe - Introduction and installation
- Parameters
- Output
- Illustrations
- Documentation and definitions
- About the program
## Introduction and installationThe ·
·
After you have installed and started
· write
· use
your browser to navigate to
http://www.evol.no/hanno/12/lifetime.rtx
and save this file to your harddisk;
later, write ·
Now you can run the script by writing
lifetime(N0=50,
lambda=0.96, envvar=0.01)Parameter names can be omitted if they are provided in the precise order
N0/lambda/demvar/envvar/C: lifetime(1000,
1.05, 0.9)is thus identical to lifetime(N0=1000,
lambda=1.05, demvar=0.9)Some more parameters can be used if desired (r, K, ndis,
pdis,
theta, varK, rho),
although this may not often be needed.Please note that this ## ParametersThe function
· Definition: The number of individuals that currently make up the population. ·
Significance: The larger · Default: none. The parameter must be specified with a number ≥ 1.
·
Definition: λ = _{+1} / N, where _{t}t is time (year).·
Significance: The larger λ, the ·
Default: none. Either
·
Definition: Demographic variance is the variance in fitness
·
Significance: The larger · Default: Exact knowledge of alien species' demographic variance will rarely be available from their novel environments. If the parameter is omitted, it is set to 0.5. This is a realistic assumption for several vertebrates, but can be strongly misleading for other taxa. It should be attempted to specifiy a realistic value at least for the larger taxon to which the species belongs.
·
Definition: ·
Significance: The larger ·
Default: The estimation of environmental variance requires
several years of population estimates for the species in question. This information will often
be unavailable for alien species. If the parameter is omitted, it will be set to 0.05.
This is a realistic assumption for several vertebrates, but can be strongly misleading for other taxa.
It should be attempted to specifiy a realistic value at least for the larger taxon to which the
species belongs. If environmental variance is mainly caused by relatively rare "disasters"
characterised by unusually high mortality, an alternative way of specifying environmental variance
is by using the parameters
· Definition: The largest number of individuals that is sufficiently small to effectively prevent reproduction (e.g., because the inability to find potential mates). ·
Significance: The larger · Default: If the parameter is omitted, it will be set to 10. Potentially, it can be both lower (down to 1, e.g. in species with vegetative reproduction) and larger (e.g. under strong Allee effects).
·
Definition: ·
Significance: The larger ·
Default: none. See
· Definition: The population size at which density regulation balances the growth rate. ·
Significance:
The effect of ·
Default: Exact knowledge of alien species' carrying capacity
will rarely be available from their novel environments. If the parameter is omitted, it is set to
100 times
· Definition: The mean or expected number of "disaster years" within a 50-year period, where disaster year is defined as a year with unusually high mortality that is caused by an environmental factor common to the entire or large parts of the population. ·
Significance: The larger ·
Default: none. The figure must be ≥
1 (one disaster per 50 years) and < 50 (one disaster each year).
Disasters, defined as episodes during which an unusually large proportion of the population
dies through a common environmental effect (such as frosts, fires, droughts),
are an alternative way of specifying environmental variance. It is based on the
assumption that environmental variance is in its entirety caused by such disasters.
Note that the population growth rate (
·
Definition: The proportion of the population dying in a
disaster year ·
Signficance: The larger ·
Default: none. The value must be a fraction larger than 0
(no additional individuals dies during a disaster year than during a normal year)
and less than 1 (all individuals die during a disaster year). See Further parameters are available, although they may rarely be needed. The ones that are implemented thus far are: ·
·
·
·
·
## OutputThe output of the function is a number, representing
the population's median lifetime in years. Some additional information
is displayed on the screen only (provided you didn't specify
Estimation may take several
minutes (especially when the population size is high). If you get unexpectedly
high or low estimates, this ## IllustrationsThe following figures are meant to illustrate how sensitive the estimate of expected lifetime is to variation in the different parameters. (For the time being, the figures are in Norwegian.)
## Documentation and definitionsA population's expected
lifetime is the
where
See Leigh ( If environmental variance can
be assumed to due to the occurrence of disaster years alone, growth rate and environmental
variance can be estimated using the following equations (based on a 50-year period and with
Derivation of equation 6 (where μ is the
arithmetic mean annual growth rate, i.e.
## About the programThe Its present version number is 1.6 (April 2017). In case of questions or comments, please contact Hanno Sandvik. |