Lupinus
lepidus var. lobbii on Mount St. Helens 
Above: Large lupine patch, 1997, ~12 yrs old.
Left: Two year old lupine. Stem is sheathed in lupine aphids.
In southern Washington, you'll find L. lepidus on volcanos, at around 6000-8000 feet in elevation (but only 3000-6000 feet at Mount St. Helens). I have found it growing on Mount Rainier, the Goat Rocks, and Mt. Adams, and nowhere in betweeen. If you find it somewhere west if Mt. Adams and South of Mount Rainier, please contact me!
Still, in 1981 it was a big surpise when scientists, flown to the Pumice Plains by Army Corp helicopters, found a single lupine plant in flower far out on the Pumice Plains. What a surprise! These plants were several kilometers from the nearest surviving vegetation, and lupine seeds were thought too big to be wind-blown (now we know that strong winds can easily move them- that is probably how these arrived). Charlie Crissafulli who has carefully monitored the resulting population for 18 years, recorded the rapid growth of an enormous lupine patch, apparently springing entirely from this one plant. Within 4 years, there were 16,000 plants! By 1991, this patch contained millions of plants covering several hectares, and had given rise to numerous sattelite patches downslope, some of them already very large in their own right. Here is the original patch in August 1999.
In 1990, when I first visited Mount St. Helens, the landscape uphill of the original patches was still mostly barren. Exploring it more carefully, I found a handful of small lupine patches scattered at wide intervals. All had been founded in the last 1-3 yrs. The pattern of widely scattered, newly-founded and relatively isolated patches provided a great opportunity to study the evolutionary genetic consequences of colonization. Recent population genetic models of patch formation and extinction demonstrate that such metapopulation systems exhibit very interesting evolutionary dynamics that depend on the details of founding and migration between patches. However, these models could not include all the complex biology exhibited by these lupines (or most other organisms) - how would the population genetic patterns found in these lupines relate to metapopulation genetic theory? To read about my population genetic and evolutionary study of L. lepidus on Mount St. Helens, click here.
Currently, my collaborator Bill Fagan and I are investigating how spatially-structured trophic interactions can change patterns of lupine colonization. Lupines were expected to strongly affect successional trajectories through facilitative effects. However, their effects remain localized because initially high rates of reinvasive spread were short-lived, despite widespread habitat availability. During the period 1990-95, population growth rates in newly formed patches was far below that in the initial colonizing patches, suggesting some factor is decreasing population growth and spread.
Detailed observational data indicate that insect herbivory in edge region patches and at the margin of high density core patches is strongly correlated with decreased lupine survival, seed production, and population growth and has caused the local extinction of entire lupine patches (see photo at left). Lupines at Mount St. Helens endure a suite of native insect herbivores, chiefly lupine-specific lepidopterans that are divisible into two functional groups. The first group, which consists of univoltine folivorous leaf-miners (Gelechiidae: Filatima spp.), caudex-borers (Tortricidae: Hystricophora nr. roessleri and Grapholita lana), and cut-worms (Noctuidae: Euxoa spp.), causes plant damage that is immediately obvious upon visual inspection, presenting as either a complete yellowing of leaves bound up in webbing and then mined out, or as a distinctive gray pallor on plants whose vascular tissues have been attacked. The evidence of such herbivory persists throughout the growing season. The second important group of herbivores destroys lupine seeds prior to explosive dehiscence of the fruits. This second group includes larvae of several species (Lycaenidae: Plebejus icariodes montis; Noctuidae: Schinia sueta; Anthomyiidae: Crinurina sp.). Impacts of these species on lupines are subtle and must be assessed through careful examination of lupine fruits for holes and hollowed-out seeds.
Experimental removal of these insects results in a several fold increase in lupin population growth in the low-density edge regions of the lupine population, but has no effect in the high-density core areas. The lack of effect in core areas has two causes: 1) density dependent seedling mortality is very high, and 2) leaf-mining and stem-boring herbivores are uncommon.
Currently we are investigating why herbivory is concentrated in the low density edge areas. We have two hypotheses: 1) edge area lupines may be a lower quality food source for herbivores, and 2) parasite and predator populations suppress herbivores in core areas but not at margins or edges.
Leaf-Mining Gelechiid
Lupinus lepidus infested with a gelechiid leaf miner, Filatima sp.
Top: caterpillars weave armored retreats, hear hanging from edge of plant.
Bottom: Leaf miners on a 1 yr old plant.
Tortricid Root-Borer
Left: L. lepidus killed by root-boring Tortricids, including, Hystricophora nr roessleri and Grapholita lana. The caterpillars essentially girdle the upper root and caudex.
Left: Whole patches can be driven extinct by the root-borer. Here about 1000 plants were killed simultaneously.
Insects severely affect other colonizing plants.
Willow (Salix spp.) and alder (Alnus sinuata) are attacked by stem-boring weevil larva (Cryptorhynchus latvia).
Weevil larva often kill whole plants.
