Specimen student abstracts (note: these were the abstracts given out before the
presentation; I am looking for a draft at this stage).
EFFECTS OF THE INVASIVE ARGENTINE ANT ON RODENTS AND PLANT
SPECIES COMPOSITION IN COASTAL SAGE SCRUB HABITAT
In the coastal sage scrub (CSS) habitat of southern California, granivorous native ants
and rodents are important dispersers of seeds. Whereas rodents cache and predate the
large seeds of exotic grasses, native ants disperse the small seeds of native shrubs.
Where the invasive Argentine ant is introduced into CSS habitat, it competitively
displaces native ants. If the Argentine ant prefers eating large seeds to small seeds, it
may compete with rodents for food resources. Furthermore, changes in dispersal
dynamics caused by the displacement of native ants by the Argentine ant, as well as any
subsequent competition with rodents for food resources, may lead to changes in CSS
plant species composition. In this study I will use combinations of rodent exclosures and
ant repellant to establish sites with (1) Argentine ants only, (2) rodents only, (3)
Argentine ants and rodents, and (4) neither Argentine ants or rodents. To examine
whether Argentine ants compete with rodents for food resources, I will test for increases
in abundance and reproduction in each in the absence of the other. Additionally, I will
survey vegetation on all sites before and after prescribed fires to examine how Argentine
ant and rodent presence affects CSS plant species composition.
MECHANISM FOR SUCCESS OF A NON-NATIVE PERENNIAL C3 GRASS IN
NATIVE PRAIRIE
Bromus inermis is a cool season perennial grass that is a common invader of native
prairies. It is a persistent problem for land management and once established can greatly
reduce native species diversity. The proposed research will determine the mechanisms
that allow B. inermis to infiltrate native prairie and subsequently outcompete its
neighbors. Three hypotheses and predictions are proposed to explain this succession of
events: (1) If vegetative growth accounts for the majority of B. inermis expansion, its
success is dependent on the production of new tillers supplemented with photosynthate
from established plants. To determine which reproductive mode accounts for the
majority of the expansion, belowground barriers will be placed along leading edges of B.
inermis invasion to stop the advance of tillers, but allow for seed dispersal. (2) If B.
inermis can produce enough shade to disrupt natural photosynthesis, then seeds and
seedlings under a canopy of B. inermis will have a low likelihood of recruitment. This
same prediction holds true for existing native vegetation, resulting in lower biomass in
the presence of B. inermis. The effects of shading and aboveground biomass on native
species germination and growth will be tested in experiments using artificial shade
structures and applications of B. inermis leaf litter. A field complement to this will be
conducted in native prairies being taken over by B. inermis where thatch will be removed
to test for growth responses. (3) Finally, if this cool season invader can successfully tie
up limiting nutrients in its aboveground biomass, then a reduced amount of nutrients
would be available to warm season grasses. The change in microhabitat availability of
nutrients will be assessed by comparing nutrients inside and outside the leading edge of
B. inermis invasions. Sampling will occur during multiple seasons to coincide with warm
and cool season growth periods.