Trees in mature forests often show intermittent
reproduction. Intensive flowering and seed production occur only once
in several years (masting), often synchronized over a long distance.
Coupled map models have been adopted for the dynamics of individuals'
resource reserve. Here, individual tree accumulates resource every
year, and invests it to reproduction when resource reserve exceeds a
threshold. Reproductive investment depends on a key parameter k
(resource depletion coefficient). When k is large, tree invests a lot
of resources for a reproduction opportunity and needs several years
before recovery to the reproductive threshold. Hence the tree
reproduces intermittently. Trees in the forest are coupled with each
other by the need of outcross pollen, resulting in synchronized
reproduction (masting). When k is small, trees reproduce every year
(no masting).
In this talk, I discuss the evolution of resource depletion
coefficient k. Basic assumptions are as follows: a forest consists of
N individuals (constant). An individual seedling is recruited from
seedling bank when a tree falls down, seedling inherits k from one
parent in equally probability, and mutation occurs in a small
probability. I confirm that tree evolves masting (k becomes large)
when survivorship of seedlings is large to form a seedling bank in the
understory. Otherwise, tree reproduces every year (k becomes small).
Next, the effect of predation to the evolution of masting is
examined. Predators attack seeds according to type II functional
response. masting increases the amount of surviving seeds in two ways:
[1] a large amount of seed production satiates predator (functional
satiation), [2] intermittent reproduction decreases the number of
predators for an interval between reproductions (numerical satiation).
I discuss the effect of seed predators in the evolution of masting in
trees focusing on two types of satiations.
I conclude that both seedling bank and specialist seed predators
promote the evolution of masting in forest.
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