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Re: pollinators

After reading the many contributions to the grass/pollinator
discussion I got the impression that some conclusions were being drawn
that weren't entirely justified, similar to hearing someone remark that
they thought the temperature of the previous summer was unusual, and
thus global warming must or must not be occuring. I consulted
some textbooks, class notes and Dr. Ted Barkely of the Kansas State
Herbarium and decided to add my two (or slightly more) cents: 

Floral structures of grasses are designed/arranged in a manner that
facilitates wind pollination and/or self pollination.  Sepals and petals 
are reduced (lodicules) or absent and thus are not usefull for attracting
animal pollinators.  Anthers may be exserted from the floral bracts to
enable wind to easily remove pollen, and stigmas may be large and feathery
to enable the capture of pollen that drifts aimlessly throught the air.
Conversely, anthers and stigmas may be tightly enclosed within bracts to
prevent the release or input of pollen.  The classic
plant/pollinator scenario hinges on the plant using a "reward" to induce 
the pollinator to visit floral structures.  A reward can be nectar, pollen
or even floral structures that are shaped in a way that induces an insect
to attempt to copulate with the flower.  Pollen consuming insects that
visit grass flowers surely inadvertantly transfer pollen from one plant to
another, but the classic notion of an intimate plant/pollinator
interaction probably does not apply to grasses.  Classifying a a pollen
consuming insect as a pollinator may be tricky.  I think there should be
verification that the plants fitness is enhanced above what it would be in
the absence of the pollen consumption.  In the absence of such
verification, I think it would be safer to assume that consumption of
grass pollen by an insect is simply a cost that the plant incurs. 

A characteristic of perennial plants such as the dominant prairie grasses
is the strategy of investing little in the production of seeds
and instead investing in maintenence/long life and reproduction by asexual
means (rhizomes, stolons, tillering).  This low investment in production
of seeds may manifest itself in the absence/reduction of seed production
or in the production of mostly non-viable seeds.  The dominant perennial
prairie grasses are apparently well served by asexual reproduction, to the
extent that any given tract of prairie may be composed of hundreds -
thousands of stems belonging to a much smaller number of individual
plants, many of which may be clones of each other.  My concept of a
prairie is that of a "closed" community, where plants have established and
occupied space, monopolize resources and do not allow new plants to become
established.  Given this scenario, it makes sense that perennial prarie
plants would be typified by poor seed production.  

A couple of subscribers noted a relationship between
stressfull environmental conditions and increased seed production, and
I think this is a common observation.  A fair amount of research has
demonstrated the role of disturbance (by pocket gophers, badgers, large
herbivores) in facilitating the colonization of new plants or the
increased vigor/abundance of sub-dominants.  The following may be a
usefull model for predicting seed production by plants that normally are
not inclined to not invest much in seed production (such as long lived
perennials): In the absence of disturbance, seedlings will not survive
in the competitive vegetative matrix, so invest little in seed production.
When disturbance occurs, and the plants recognize this because they are
stressed by the disturbance, there should be an increased chance of
seedlings surviving, so invest a lot in seed production.

Finally, I thought I would share some information that I gleaned from
class notes about plant/pollinator interactions that I find very
provocative and thought some of you might enjoy pondering.  It is in the
plants best interest to invest as little as possible in the reward that
is given, and to have the pollinator(s) be under-fed or
under-rewarded in order to maximize the number of flower visits.
It is in the pollinators best interst to recieve the maximum amount
of reward per visit, and to visit as few flowers as possible.  I find it
really amazing that this obvious conflict of interests can be fine tuned
through co-adaptation to the point that both players may become
highly dependent on each other even though both players are acting in
purely selfish ways.

Steve Winter

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