Sunday, July 15, 2012

The Good, the Bad, and the Odd




Good plant. Bad pun. And oddness.

Four out of six flower heads miserably drooping and brown.

We had noticed compass plants like this and assumed that they were aborting their flowers because of drought. 

But on a tour with ultimate botany guru Floyd Swink, and we saw such plants.

When we asked about them, he said, “A weevil does that. It’s a problem for the plant, but not a bad one. Compared to the devastation caused by the boll weevil in the South, this one is the lesser of two weevils.”

It turns out that the weevil bug cuts the stem and then lays its eggs in the hanging flower-head. Apparently, young weevils like to eat dying greens.

Compass plant roots look like giant multiple carrots and go deep into the subsoil. You’d think these fat roots would have adequate reserves for most anything, but they don’t gamble on blooming every year. One summer there’ll be lots of leaves but few or no flower stalks in the whole prairie. The next summer it seems like every plant is putting up a forest of higher-than-our-heads massive hairy stalks and happy flowers.

Why? One possibility is the “periodic cicada principle” – in which a species overwhelms predators and pests by having few individuals, or seeds, or eggs most years. Then, with pest numbers down, it blasts forth with so-many-all-at-once that the sparse pests just can’t eat them all.

It’s one of the most satisfying things about conservative plants. Do they worry about pests? Doughts? Ho hum. 

They’re in no hurry and take what comes. Compass plants have reserves and confidence (and tricks when needed) to kick butt in their own quiet way.  

6 comments:

orchidartist said...

I think they affect prairie dock too - have not yet seen them on rosinweed but perhaps that's because I haven't looked closely enough?

Stephen Packard said...

Oh, yes. Weevils "prey" on the seeds of a great many species. So do other beetles, moths, flies and other groups. That's part of the balance. Their approach to compass plant and prairie dock is just a bit more "in our faces."

Stefan Johnsrud said...

The cicada principle you mentioned is called "masting" in community ecology. Some plants have been observed to grow large amounts of leaves at once to combat predation. Of course insects are best known for that kind of behavior.

Stephen Packard said...

Stefan, thanks for the helpful word - masting. I wonder if the Silphiums communicate by chemicals to help them "mast" at the same time. Or if they're just responding to seasons and resource build-up in such a way that they tend to bolt and seed together.

Steve Halm said...

I assume the two flowers not infested by the weevils will bloom and be healthy, or is the plant eventually going to die because of the weevils?

Stephen Packard said...

Yes, the flowers that the weevils leave alone will typically set good seeds. These plants live a long time and reproduce well, despite the "tax" imposed by the weevils.