Apparent competition with an invasive plant hastens the extinction of an endangered lupine

• Published in: Ecology (Durham) 2010-08, Vol.91 (8), p.2261-2271
• Main Authors: Dangremond, Emily M., Pardini, Eleanor A., Knight, Tiffany M.
• Format: Article
• Language: English
• Subjects: Ammophila arenaria; Animal and plant ecology; Animal, plant and microbial ecology; Animals; apparent competition; Biological and medical sciences; biotic homogenization; California; coastal dune ecosystems; Conservation biology; Demography; Ecological competition; Ecological invasion; Economic competition; Ecosystem; ecosystems; Extinction; Feeding Behavior - physiology; Flowers & plants; Fundamental and applied biological sciences. Psychology; General aspects; grasses; Habitats; homogenization; indigenous species; Inflorescences; Invasive species; life-table response experiment; Lupinus; Lupinus - physiology; Lupinus tidestromii; matrix population model; Nonnative species; northern California; Peromyscus - physiology; Peromyscus maniculatus; Plant ecology; Plants; Poaceae - physiology; Point Reyes National Seashore; population growth; Population growth rate; population viability analysis; pre-dispersal seed consumption; Rodents; Seed banks; Species extinction; Stochastic models; stochastic population model; Synecology; USA
• ISSN: 0012-9658; 1939-9170
• DOI: 10.1890/09-0418.1

Invasive plants may compete with native plants by increasing the pressure of native consumers, a mechanism known as "apparent competition." Apparent competition can be as strong as or stronger than direct competition, but the role of apparent competition has rarely been examined in biological invasions. We used four years of demographic data and seed-removal experiments to determine if introduced grasses caused elevated levels of seed consumption on native plant species in a coastal dune system in California, USA. We show that the endangered, coastal dune plant Lupinus tidestromii experiences high levels of pre-dispersal seed consumption by the native rodent Peromyscus maniculatus due to its proximity to the invasive grass, Ammophila arenaria . We use stage-structured, stochastic population models to project that two of three study populations will decline toward extinction under ambient levels of consumption. For one of these declining populations, a relatively small decrease in consumption pressure should allow for persistence. We show that apparent competition with an invasive species significantly decreases the population growth rate and persistence of a native species. We expect that apparent competition is an important mechanism in other ecosystems because invasive plants often change habitat structure and plant-consumer interactions. Possible implications of the apparent-competition mechanism include selective extinction of species preferred by seed consumers in the presence of an invasive species and biological homogenization of communities toward non-preferred native plant species.