Publication Date


Type of Culminating Activity


Degree Title

Master of Science in Biology



Major Advisor

Ian C. Robertson


Stephen J. Novak


Peter Koetsier


  1. (1) Seed predation can significantly restrict the reproductive output and individual fitness of plants, particular those plants that are rare or endangered. In some cases the total seed loss can reach 100%. Owyhee harvester ants, Pogonomyrmex salinus, actively remove the fruits and seeds of slickspot peppergrass, Lepidium papilliferum, a rare mustard endemic to southwest Idaho.
  2. (2) Several experiments were conducted to quantify seed predation on L. papilliferum located within the foraging distance of P. salinus. Individuals exposed to harvester ants experienced a direct loss of fruits and seeds ( > 40%), whereas plants shielded from ants suffered almost no seed loss. Harvester ants were also effective scavengers of seeds on the ground (removing > 90% of seeds from the ground).
  3. (3) All fruits and seeds collected by ants were returned to their nests and taken below ground. Of 100 successful foragers monitored all returned the fruit or seeds to the nest. A search of 30 middens revealed many empty L. papilliferum fruit husks but no intact seeds. Thus, it does not appear that the ants benefit L. papilliferum by dispersing their seeds.
  4. (4) Pogonomyrmex salinus is the main seed predator of L. papilliferum and in some cases can remove and destroy complete seed sets of individuals. Seed removal of this magnitude suggests that P. salinus may significantly limit recruitment of new individuals of L. papilliferum and lead to further decline of this rare plant species.


Winner of Boise State University's 2009 Distinguished Master’s Thesis Award.