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Small mammals effect seedling progression to an adult plant surplus. Rosemary Crebs University of Montana, Project IBS-CORE Undergraduate Research Fellow Results Actual Lupinus germination Abstract This project is still in the early stages of field work and will include several different methods to obtain any final conclusive data. 80 Small mammal consumption of seedlings, could limit seedling recruitment and eventual adult plant abundance, in the Blackfoot Vally of two western Montana grassland forbs: Lithospermum ruderale, Lupinus sericeus. Previous observations of research suggest several rodent species affect productivity, through flower destruction and seed consumption. Plants have many ways to interact with other species, understanding the significance of these interactions is central to the field of ecology. Little is known about how reductions in plant performance, translate into change of plant abundance or population dynamics. Materials and Methods •Small mammal consumers include: deer mice, montane voles, northern pocket gophers, Columbian ground squirrels, and yellow-pine chipmunks. •7 10 x 10 meter rodent exclosers, with .625 cm welded wire fencing. Buried 30 cm in the ground and extended 60 cm above ground, with additional 20 cm of aluminum flashing over the top. •Each of these exclosures are paired with nearby 10 x 10 meter control plot, where there was no fence. •A stage-based matrix model will be used to predict population sizes and growth rates of the two plant species in the absence and presence of small mammals. •Each spring, winter survival for each plant is recorded: size, summer survival and reproduction. •In the late summer live plants are individually tagged and measured: plant size, number of stems, plant height and canopy diameter. •Estimates of plant fecundity are derived by averaging the number of seeds per pod for Lupinus, and seeds per plant for Lithospermum. Number Seedlings Introduction Three times through summer and fall, seed removal experiments will take place to get an idea of the seed predation intensity at each site. This will help identify what types of predators and describe temporal variation is seed predation over the growing season. Seeds in sand filled petri dishes will be set out, both inside and outside of the exclosures, how many seeds are removed will be recorded. The ones inside will tell if they were removed by birds or ants, and give and index of rodent activity. Rodent Exclosure Control 70 Estimates of seed predation intensity: 60 50 40 30 20 10 Seed Addition: 0 0 In September 2004, a seed addition experiment was initiated to determine how seed predation influences seedling recruitment. Seeds of each species were added to 0.5 by 0.5 m subplots within each rodent exclosure and control plots. They were placed free from adults of each species. Lupinus seeds were added at densities of 0, 25, 50, 100, and 200 seeds per subplot, and Lithospermum at 0, 50, 100, 200, and 300 seed per subplot. From 2005 to 2007, in the early summer of each year a census will be taken of the seed addition plot for emerging seedlings, mark new seedlings, and follow their survival through time. At the end of the season those still alive will receive permanent numbered tags, and their growth, survival, and reproduction will be monitored through subsequent years. Seed bank longevity: Seed dormancy can buffer plant populations from negative impacts of consumers, but understanding the role of seed dormancy in plant population is limited. To investigate what happens to un-germinated seeds, six bags of thirty seeds at each of the three sites were buried, for each species. Bags were 5 cm x 5 cm, made of fiberglass window screen sewn at edges with nylon monofilament thread. Bags were encased in wire mesh and buried 2 cm deep, inside rodent exclosures. Each summer the packets will be dug up and the number of seeds still present will be determined. This will provide an estimate of the rate of decline of seeds in the seedbank. A new cohort of seeds will be buried each year to examine year-to-year variation in rates of seed dormancy in the soil. 50 100 150 200 250 Seed Density Seed density: F1,115= 67.231, P<.001 Treatment: F1,115 = 12.371, P=0.001 Discussion and Conclusions Seedling recruitment is limited by seed input. Seed predation is affecting rates of seedling recruitment. This will be used in demographic models to assess the importance of seed predation to overall population dynamics. Inference strength: medium Inference scope: western Montana grasslands •This research will evaluate the role small mammal’s play in plant population dynamics. The study of consumer impacts provides information about community-level changes in other systems. Population modeling: Demographic data from monitoring naturally occurring plants and from seed addition and seed bag experiments, will be used to construct stage-based models for each species. Stages will comprise seed, seedling, juvenile (nonflowering), adult (flowering), and dormant size classes. Density dependence will be incorporated into the model using measures either from varying densities in the seed addition plots, or from measures in naturally established populations of varying densities. These density-dependent models will yield predictions of the long-term equilibrium population densities. By building models incorporating seed to seedling transition rates from within the rodent exclosures, it will be able to predict population growth rates and population densities with and without small mammal granivores. Acknowledgments Research Mentor: Mary Bricker Funding: Project IBS-CORE Undergraduate Research Fellowship, provided by a grant from the Howard Hughes Medical Institute to the University of Montana. Literature Cited Crawly, M. J. 1989. Insect herbivores and plant population dynamics. Annual Review of Entomology 34:531-564. Crawly, M. J. 2000. Seed Predators and Plant Population Dynamics. Pg 410 in M. Fenner, editor. Seeds: the Ecology of Regeneration In Plant Communities. CABI, New York.