Sunday, July 15, 2012

The Good, the Bad, and the Odd


A little story about, among other things, an evil weevil.

Four out of six flower heads, miserably drooping and brown.

"Who cares?" you might ask. But we were trying to restore health to nature, and we needed the seeds.

We had noticed distressed compass plants like this and assumed that they were aborting their flowers because of drought. Good plant. Bad weather. 

But we saw them again on a tour with botany guru Floyd Swink.

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. Young weevils like to eat dying greens. Odd.

Compass plants have strategies. Their roots look like giant forked carrots and go deep into the subsoil. You’d think these fat roots would have adequate reserves for most anything, but they don’t use their energy to bloom 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 reduces numbers of predators and pests by having few individuals, or seeds, or eggs most years. Then one year, with few pests left, it blasts forth with huge numbers of babies, flowers, or seeds all-at-once. The sparse pests just can’t eat them all.

Such strategies are an impressive feature of rare conservative plants in healthy habitats.

Unlike weeds, do these conservatives worry about pests? Doughts?

Ho hum.
No hurry.

Compass plants have reserves and confidence
(and odd 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."

Unknown 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.

Unknown 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.