Saturday, May 23, 2009
. . . how plants maintain their niche in the desert environment by evolving to accept only certain pollinators and then only at particular times of the year. Bees, birds, bats and nearly everything small and mobile in the desert play a part in this ongoing drama.
The first hints come when you approach a flower and see that nearly always there is some form of life scrambling through the anthers, stamen, corolla and calyx. Fortunately, most are so intent on their occupation they don't notice that a giant w/camera has approached.
I go through this scenario frequently when taking photos for Cactus PhotoGraphics or for my website, www.cactusphotographics.com.
Flower petals and sepals are shaped to encourage and accept certain pollinators and reject others. Shape doesn't affect the spiders, for example, but it has a marked affect on whether bees, hummingbirds, bats and moths get in on the action. The Thurber gilia is a good example. Its pale lavender flowers are the wrong color to be noticed by hummingbirds and its tubes are too long for the hummingbirds to feed effectively. But this flower is an ideal food source for night fliers such as hawkmoths.
The evolutionary tricks are endless. The wild bean, for example, sports two-sided petals which serve as a convenient landing pad for bees that need to perch when they gather pollen. In contrast, the scarlet penstemon provides no such foothold and is a color that bees can't see...but alternately provides a perfect food source for hummingbirds that quickly distinguish reds and hover while feeding.
Cactus flowers, in particular, bloom when specific pollinators are seasonally abundant and active either nocturnally or during the daytime. Bats and hawkmoths aren't active during daylight hours but there are, nonetheless, cactus flowers open at night just for them. By opening for only a few hours early in the day, certain other flowers encourage bees...which have a well developed sense of time...to arrive faithfully for nectar and pollen.
Probably the "largest" of these adapters is the saguaro cactus which has flowers that stay open for only about 36 hrs. (including the night following daytime bloom) and is pollinated by birds, bees and nectar-feeding bats. Timing for these desert giants is critical. Pollination and later seed dispersal is timed for the summer rains which follow shortly thereafter.
Pollination takes place either actively or passively. While some common pollinators are actively looking for pollen, others are seeking only nectar, pollinating passively as they search for the nectar. Flowers are selective, however, about which they allow.
Bees, for example, don't have a chance in hell of reaching the nectar in some flowers because they have short or non-existent tongues. Hawkmoths and certain butterflies, in contrast, have probosces which extend a full 1 1/2 to 2 in. to reach the nectar in other flowers such as columbine, gilia, and others.
What does all this go to show?...probably nothing of significance except that when you set out to take pictures of the sex organs of plants, you meet the strangest creatures. Sex and cameras have always gone together so I'm never surprised at what I see. Often it's only in photographic "post production", as the journals call it, when cactus flowers are enlarged to two or three times life-size that I see the bees, bugs and spiders that have crept into the camera's frame.