Demography of Astragalus scaphoides and effects of herbivory on population growth

Authors

Peter Lesica, University of Montana, Missoula, Montana

Abstract

Losses in fecundity due to predispersal herbivory can be large; however, the effects of this loss on long-term population viability have rarely been investigated. I conducted a demographic study of Astragalus scaphoides (Fabaceae), a long-lived perennial endemic to east central Idaho and adjacent Montana, by following mapped individuals at two sites from 1986 to 1993. Astragalus scaphoides suffers losses of predispersal fecundity averaging nearly 50% from insect seed predation and inflorescence predation by insects and livestock. Cattle reduced fecundity by 0–85%. Nonetheless, estimates from matrix projection models indicate that both sample populations had positive growth in most years. Elasticity analyses revealed that population growth occurred in spite of relatively small contributions by recruitment compared to growth and survival of nonreproductive plants. Results suggest that populations of this long-lived perennial depend little on reproduction and recruitment for growth and can persist in association with seasonal-rotation livestock grazing.

Recommended Citation

Lesica, Peter (1995) "Demography of Astragalus scaphoides and effects of herbivory on population growth," Great Basin Naturalist: Vol. 55: No. 2, Article 6.
Available at: https://scholarsarchive.byu.edu/gbn/vol55/iss2/6