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Yvette K. Ortega

Happiness atop St Mary's peak in Montana.


800 East Beckwith Avenue
Missoula, MT 59801-5801
Contact Yvette K. Ortega

Current Research

* Evaluate invader impacts at population and community levels, including underlying mechanisms. * Examine interactive impacts of drought and herbivory by biological control agents on the competitive dominance of a notorious weed. * Assess a new technique for assessing habitat quality for songbirds based on local song structure. * Measure effects of invasive plant control treatments on plants and animals and evaluate degree to which such methods mitigate target invader impacts.

Research Interests

My primary interest lies in building understandings of ecological patterns and processes in order to improve the management of natural systems. Current applications include evaluating impacts of exotic plants on native plants, cascading effects on consumers, and efficacy of weed control efforts in mitigating these impacts. Studies consider population and community level attributes, and organisms from plants and invertebrate to birds and their predators.

Past Research

My past research includes examination of disturbance effects on harbor seals, edge effects of forest roads on songbirds, and habitat use of Canada lynx.

Why This Research is Important

My work aims to develop and apply ecological principles to solve real-world problems facing managers of natural systems.


  • University of California, Berkeley, B.A., Environmental Science, 1992
  • University of Vermont, M.S., Wildlife and Fisheries Biology, 1998
  • Featured Publications


    Pearson, Dean E.; Valliant, Morgan; Carlson, Chris; Thelen, Giles C.; Ortega, Yvette K.; Orrock, John L.; Madsen, Matthew D., 2019. Spicing up restoration: Can chili peppers improve restoration seeding by reducing seed predation?
    Pearson, Dean E.; Eren, Ozkan; Ortega, Yvette K.; Villarreal, Diego; Senturk, Muhyettin; Miguel, M. Florencia; Weinzettel, C. Miguel; Prina, Anibal; Hierro, Jose L., 2018. Are invasive plants more abundant in the introduced versus native range?
    Pearson, Dean E.; Ortega, Yvette K.; Eren, Ozkan; Hierro, Jose L., 2018. Community assembly theory as a framework for biological invasions
    Pearson, Dean E.; Valliant, Morgan; Carlson, Chris; Thelen, Giles C.; Ortega, Yvette K.; Orrock, John L.; Madsen, Matthew D., 2018. Spicing up restoration: Can chili peppers improve restoration seeding by reducing seed predation?
    Pearson, Dean E.; Ortega, Yvette K.; Villarreal, Diego; Lekberg, Ylva; Cock, Marina C.; Eren, Ozkan; Hierro, Jose L., 2018. The fluctuating resource hypothesis explains invasibility, but not exotic advantage following disturbance
    Maron, John L.; Smith, Alyssa Laney; Ortega, Yvette K.; Pearson, Dean E.; Callaway, Ragan M., 2016. Negative plant-soil feedbacks increase with plant abundance, and are unchanged by competition
    Waller, Lauren P.; Callaway, Ragan M.; Klironomos, John N.; Ortega, Yvette K.; Maron, John L., 2016. Reduced mycorrhizal responsiveness leads to increased competitive tolerance in an invasive exotic plant
    Pearson, Dean E.; Ortega, Yvette K.; Butler, Jack L., 2015. Invasive Species Science Update (No. 8)
    Pearson, Dean E.; Ortega, Yvette K.; Butler, Jack L., 2014. Invasive Species Science Update (No. 7)
    Pearson, Dean E.; Ortega, Yvette K., 2013. Biogeography of plant invasions
    Zwolak, R.; Pearson, Dean E.; Ortega, Yvette K.; Crone, E. E., 2012. Mechanisms driving postfire abundance of a generalist mammal
    Maron, John L.; Pearson, Dean E.; Potter, Teal; Ortega, Yvette K., 2012. Seed size and provenance mediate the joint effects of disturbance and seed predation on community assembly
    Pearson, Dean E.; Ortega, Yvette K., 2011. Invasive Species Science Update (No. 5)
    Zwolak, Rafal; Pearson, Dean E.; Ortega, Yvette K.; Crone, Elizabeth E., 2010. Fire and mice: Seed predation moderates fire's influence on conifer recruitment
    Ortega, Yvette K.; Pearson, Dean E., 2009. Factors influencing plant invasiveness
    Zwolak, Rafal; Foresman, Kerry; Crone, Elizabeth; Pearson, Dean E.; Ortega, Yvette K., 2008. Are mice eating up all the pine seeds?
    Ritter, Sharon; Jones, Greg; Watson, Alan E.; McCaughey, Ward; Harrington, Mick; Zwolak, Rafal; Foresman, Kerry; Crone, Elizabeth; Pearson, Dean E.; Ortega, Yvette K.; Loeffler, Dan, 2008. ECO-Report - Finding common ground: Montana Forest Restoration Committee
    Ritter, Sharon; Canton-Thompson, Janie; Ruggiero, Leonard F.; Jones, Greg; Sullivan, Janet; McCaughey, Ward; Ortega, Yvette K.; Christensen, Neal; Harrington, Mick; Page-Dumroese, Deborah S., 2007. ECO-Report - Scientific independence: A key to credibility
    Sturdevant, Nancy; Kegley, Sandy; Ortega, Yvette K.; Pearson, Dean E., 2006. Evaluation of establishment of Cyphocleonus achates and its potential impact on spotted knapweed
    Schwartz, Michael K.; Mills, L. S.; Ortega, Yvette K.; Ruggiero, L. F.; Allendorf, F. W., 2003. Landscape location affects genetic variation of Canada lynx (Lynx canadensis)
    Pearson, Dean E.; Ortega, Yvette K.; Ruggiero, Leonard F., 2003. Trap-induced mass declines in small mammals: Mass as a population index
    Ortega, Yvette K.; Capen, David E., 2002. Roads as edges: Effects on birds in forested landscapes
    Pearson, Dean E.; Ortega, Yvette K.; McKelvey, Kevin S.; Ruggiero, Leonard F., 2001. Small mammal communities and habitat selection in Northern Rocky Mountain bunchgrass: Implications for exotic plant invasions
    McKelvey, Kevin S.; Ortega, Yvette K.; Koehler, Gary M.; Aubry, Keith B.; Brittell, J. David., 2000. Canada lynx habitat and topographic use patterns in north central Washington: A reanalysis [Chapter 10]
    Canton-Thompson, Janie; Smith, Jane Kapler; Jones, Greg; Brown, Perry J.; Arno, Stephen F.; Daniels, Orville L.; Burk, Dale A.; Hardy, Colin C.; Silvieus, Dave; Pflug, Kristi D.; Winhorst, Bruce; Thompson, Brooke; Ortega, Yvette K.; McKelvey, Kevin S.; Thompson, Tom; Pearson, Dean E.; Stewart, Cathy; Sullivan, Janet, 1999. ECO-Report - 1999 Symposium highlights five years of learning
    Wildflowers on the Uinta-Wasatch-Cache National Forest
    It has been suggested that exotic plants will be more successful than native plant species as a result of climate change. This is because exotics often exhibit stronger responses to disturbance, faster growth rates, and greater plasticity. In this study, we show that climate change can actually shift the balance in favor of natives when it creates conditions that favor the slower more "tortoise-like" strategies of some natives.
    Herbicide treatment targeting the invasive plant, spotted knapweed, in Montana.
    A rapidly emerging problem is that of secondary invasion – an increase in non-target exotics following efforts to suppress targeted invasive plants. Researchers conducted a global literature review and meta-analysis directed at quantifying the magnitude of secondary invasion effects and identifying possible causes in order to improve management outcomes. 
    Spotted knapweed
    Invasive plants such as spotted knapweed (Centaurea maculosa) have overrun vast areas of the United States to the detriment of native plants and wildlife. Managers increasingly use broadleaf herbicides to suppress plant invaders, assuming that suppression will relieve the impacts of invasion. Rocky Mountain Research Station scientists evaluated the effects of a common herbicide treatment on grassland plants in western Montana to determine if and when suppression of spotted knapweed may relieve impacts of this notorious invader.
    We quantified and ranked invasiveness and impact for 48 exotic plant species based on surveys over 20,000 km2 of grasslands in western Montana. These data provide a valuable tool for managers to determine the relative impacts of invaders for prioritizing exotic plants for control in the bluebunch wheatgrass habitat type.
    Invasive plant impacts on native plants can ripple through native food webs from plants to insects all the way to birds. We observed that the invasion of spotted knapweed into grasslands of western Montana affects not only breeding success of songbirds but also the way song is passed between generations. 
    For over 10 years, Rocky Mountain Research Station scientists and their partners have engaged in research to 1) determine the causes underlying plant invasions, 2) identify invader impacts in native systems, and 3) improve the efficacy of invasive plant mitigation efforts.