The role of small mammals in the population dynamics of two native grassland forbs: Lupinus sericeus and Lithospermum ruderale

Although post-dispersal seed predators are common and often reduce seed density, their influence on plant abundance remains unclear. We examined the impact of seed predation by small mammals, primarily deer mice (<i>Peromyscus maniculatus</i>), on seedling recruitment and plant establishment of two perennial grassland forbs: <i>Lupinus sericeus</i> (Fabaceae) and <i>Lithospermum ruderale</i> (Boraginaceae), using experimental seed addition and rodent exclusion treatments. For both species, small mammal exclusion increased the total number of seedlings that emerged, and these effects were still significant three years after seed addition, resulting in greater numbers of established plants inside exclosures than in control plots.</p> To shed light on how these relatively short-term rodent-driven reductions in seed abundance and recruitment might influence longer-term patterns of <i>L. ruderale</i> population growth, we combined experimental results with demographic data in stage-based population models. Model outputs revealed that rodent seed predation had a significant impact on <i>L. ruderale</i> population growth rate. These results demonstrate that rodent granivory can be a potent force limiting the abundance of a perennial forb.<p> In the third chapter, we examined the effects of multiple consumers on <i>L. sericeus </i>populations. We combined the experimental evidence of rodent-driven reduction in seedling recruitment in with the impacts of two other consumers, folivorous ground squirrels (<i>Spermophilus columbianus</i>), and herbivorous insects (Lepidopteran and Coleopteran larvae) on <i>L. sericeus</i> fecundity, with stage-based matrix models. We examined how these consumers, individually and in concert, influence the population growth of <i>L. sericeus </i>at three sites. Because consumers sequentially attack flowers, pre-dispersed seeds and then post-dispersed seeds, the opportunities for any given species to influence the population growth rate of <i>L. sericeus</i> is contingent on the impacts of the preceding consumer. We found that release from all consumers caused significant, and sometimes dramatic, increases in the population growth rate. These results suggest that despite high rates of asexual reproduction, consumers impose strong limits to the population growth and therefore the abundance of this long-lived forb.</p> The final chapter reflects outreach to the public school community, bringing scientific content and methods to an elementary school classroom in an inquiry demonstrating the importance of seed dispersal in plants.

Name thesis:degree_name

Doctor of Philosophy (PhD)

Grantor dc:publisher

University of Montana

Year

2009

Author dc:creator

• Bricker, Mary Carolyn

• Lithospermum ruderale
• Lupinus sericeus
• plant-consumer interactions
• population dynamics
• demography
• seed predation

Repository record dc:identifier

https://scholarworks.umt.edu/etd/1073

OAI identifier oai:identifier

oai:scholarworks.umt.edu:etd-2092