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Abundance declines of a native forb have nonlinear impacts on grassland invasion resistance
Author(s) -
Hulvey Kristin B.,
Zavaleta Erika S.
Publication year - 2012
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1890/11-0091.1
Subject(s) - abundance (ecology) , ecology , biology , species richness , invasive species , grassland , ecosystem , resistance (ecology) , introduced species , biodiversity
The effects of declining plant biodiversity on ecosystem processes are well studied, with most investigations examining the role of species richness declines rather than declines of species abundance. Using grassland mesocosms, we examined how the abundance of a native, resident species, Hemizonia congesta (hayfield tarweed), affected exotic Centaurea solstitialis (yellow starthistle) invasion. We found that progressive H. congesta abundance declines had threshold effects on invasion resistance, with initial declines resulting in minor increases in invasion and subsequent declines leading to accelerating increases in invader performance. Reduced invasion resistance was explained by increased resource availability as H. congesta declined. We also found evidence that resident abundance might indirectly affect invasion by mediating invader impact on resident competitors; C. solstitialis disproportionately reduced H. congesta biomass in low‐abundance rather than high‐abundance populations. H. congesta 's direct and indirect effects on invasion resistance illustrate that an individual species' declining abundance can have accelerating, deleterious effects on ecosystem functions of conservation value.