Was it really the case that the beachgrass increased the pressure on Tidestrom's lupine by providing cover for the deer mice? To find out, the three biologists conducted both observational and experimental studies.
They followed 102 fruiting lupines for two seasons in the spring of 2008 and 2009, scoring plants as "consumed" (any fruiting stalks consumed) or "not consumed" (all stalks intact).
Dangremond, then an undergraduate at Washington University in St. Louis, also placed fruiting stalks at varying distances from the beachgrass and then scored the stalks four days later for consumption.
To avoid sacrificing fruits of Tidestrom's lupine, she used the fruits of the silver dune lupine (L. chamissonis) instead. This common lupine has fruiting stalks that "look fairly similar, although the fruits are slightly bigger," says Pardini. "They're a pretty good proxy for the rare species."
Both the observational and the experimental studies confirmed their hypothesis that the closer lupines are to beachgrass the more they are ravaged by deer mice.
Projecting the future of a population
The scientists then set up a mathematical model of lupine populations that consisted of the stages in the plant's life cycle (such as seeds in the seed bank, seedlings, nonreproductive plants and reproductive plants) and equations that described the annual transitions between these stages.
The equations were based on demographic data from three populations of lupines at Point Reyes in which individual survival, growth and fecundity were monitored for four years (from 2005 through 2008).
"People often don't study the entire life cycle of an organism," says Knight. They'll just study reproduction and seed consumption rate and conclude that if seed consumption rate is high it mus
|Contact: Diana Lutz|
Washington University in St. Louis