"But that's not necessarily true.
"The rate limiting step could easily be somewhere else in the life cycle. Maybe seedling survivorship is very low. If that's the case, it doesn't matter how many seeds you produce or consume, survivorship will drive population growth."
Running the model
Once they built the lupine population model, they could experiment digitally to better understand what might cause a population to grow or shrink.
"Suppose the consumption rate in the field was 70 percent," Knight says, "as it was in the case of one population. The model then allows us to ask what would happen if it were 60 percent, or 50 percent. What if it were zero? What if none of the seeds were consumed; how would this population perform?"
According to the model, all three of the lupine populations will eventually disappear. On the other hand, the simulations also offer some room for optimism.
"Abbotts Lagoon was the biggest population we were modeling," says Pardini. "And the model says only a small reduction in consumption would result in a stable population size."
Will the lupines make it?
That's a tantalizing prediction because Point Reyes is about to undertake a dune restoration project that should remove some of the pressure on the Abbotts Lagoon lupines.
"All along the West Coast," say Pardini, people are trying to take out the European beachgrass and restore the native dune structure and plant and animal communities. Point Reyes National Seashore is conducting a large restoration at Abbotts Lagoon. They're taking out about 110 acres of beachgrass in a 300-acre area."
The biologists will know in a few years whether their prediction is accurate and the restoration removes enough consumption pressure to allow the Abbotts Lagoon lupines to recover.
In the meantime, the biologists have begun to monitor other populations of lupine
|Contact: Diana Lutz|
Washington University in St. Louis