Research Areas:
Interactive roles of predation and hybridization on population dynamics of an endangered Lupinus species


Species introductions are one of the largest threats to global biodiversity. We are studying two important mechanisms by which introduced species may harm native species that have heretofore received less attention in population viability analyses. First, introduced plants may compete with native plants by increasing the pressure of native consumers, a mechanism known as apparent competition. Second, hybridization with introduced plants may result in extinction via genetic assimilation of a native species.


The endangered plant, Lupinus tidestromii
A predator caught in the act: the deer mouse (Peromyscus maniculatus) consuming fruits of the endangered plant, Lupinus tidestromii. Steve Kroiss took this fantastic photo.
Apparent competition
Grasses that invade coastal ecosystems often provide a dense cover to native rodents, and may therefore cause increased levels of seed consumption on nearby native plant species. Our research shows that apparent competition threatens the federally endangered coastal plant, Lupinus tidestromii. Lupinus tidestromii experiences high levels of pre-dispersal seed consumption by the native rodent Peromyscus maniculatus due to its close proximity to the invasive grass, Ammophila arenaria (up to 70% of its fruits are consumed each year!). If these levels of consumption continue, we project that two of our three study populations will decline towards extinct. For one of our declining populations, a relatively small decrease in the consumption pressure should allow for persistence. Our research has important implications for the management Lupinus tidestromii. Specifically, large scale habitat restoration is necessary to protect threatened populations from Ammophila arenaria since apparent competition is high if Lupinus tidestromii is within 100 meters of this invasive grass. Currently, we are working with the National Park Service to conduct large scale habitat restorations and to test the predictions of our population viability analysis.


Eleanor Pardini with two of the largest threats to the endangered plant Lupinus tidestromii: the invasive grass Ammophila arenaria (behind her) and Lupinus chamissonis (left of her), which is the congener that Lupinus tidestromii hybridizes with.

Hybridization
Hybridization occurs frequently in plants and animals and is an important mode of speciation; it is typically considered an evolutionarily constructive process. However, hybridization can jeopardize the viability of rare and endemic species through outbreeding depression and the loss of locally adapted genotypes and through introgression and genetic assimilation. The endangered plant, Lupinus tidestromii has been historically separated from its congener, Lupinus chamissonis throughout most of its range. Lupinus chamissonis has been recently introduced to the Monterey Peninsula for horticulture; hybridization does occur and may pose a significant threat to Lupinus tidestromii. To assess extinction risk, we are quantifying the frequency of intermating using Allozyme genetic markers (in collaboration with Jim Hamrick at the University of Georgia) and the relative fitness of Lupinus tidestromii, Lupinus chamissonis and hybrid individuals. Hybridization is a frequency-dependent phenomenon; intermating with Lupinus chamissonis is expected to increase as the frequency of the Lupinus tidestromii decreases. Intermating is even more likely for Lupinus tidestromii because Lupinus chamissonis is reproductively more vigorous (i.e., it produces more flowers) than Lupinus tidestromii.


The California research team (left to right): Zach Marine, Tiffany Knight, Steve Kroiss, Eleanor Pardini and Emily Dangremond