INTERACTIONS
— The simulation is designed to study the effects of "winner-loser"
interactions, so they are the default. However, one can also remove
species interactions (leaving everything else the same) and compare
the behavior of species abundances under random walks. Instead of
there being winners and corresponding losers, winners simply gain
or lose a small amount of energy. Extinction and replacement of
species occurs as usual. There are two possible modes, depending
on the ENERGY CAP setting.
ENERGY CAP
— (Used ONLY if the INTERACTIONS are set to "NONE").
When "ON", the gain or loss to any focal species is immediately
portioned out (as a loss or gain, respectively) to all other species
equally. The total amount of energy remains fixed, and the gain
or loss by the focal species does not change the population sizes
of any of the other species relative to each other. When "OFF",
winner species simply lose or gain energy without any regard to
other species. In this case, the total amount of energy used by
all species of the fauna can change, and increase without limit.
Simulation behavior under both modes is very similar, and differs
radically from that seen under winner-loser interactions.
MINIMUM —
Simply a toggle that determines whether the criterion for species
extinction is the result of low population size ("Density";
how low a population is determined by the Extinction Limit slider
[10]), or the result of relatively low energy. In the latter case
the species becomes extinct when it reaches one half of the lowest
energy observed for any species in the initial regression.
POOL VARIANCE
— Indicates the variance used to generate new species from
"outside" the community. If CONSTANT, it is always the
value of Initial Y-Variance (9). If VARIABLE, the variance
about the current timestep's regression is used. Note: New species
are assigned a random body mass, and the slope for making new species
is always the current slope exhibited by the community.The Pool
Variance is the variance about that slope. The effect of changing
this state is negligible.
E VALUE —
Determines whether the amount of energy demanded in an evolutionary
advance has a small random component added. The effect of changing
this state is negligible. |
