DEMOGRAPHY OF ASTRAGALUS-SCAPHOIDES AND EFFECTS OF HERBIVORY ON POPULATION-GROWTH

Losses in fecundity due to predispersal herbivory can be large; howeve r, the effects of this loss on longterm population viability have rare ly been investigated. I conducted a demographic study of Astragalus sc aphoides (Fabaceae), a long-lived perennial endemic to east central Id aho and adjacent Montana, by following mapped individuals at two sites from 1986 to 1993. Astragalus scaphoides suffers losses of predispers al fecundity averaging nearly 50% from insect seed predation and inflo rescence predation by insects and livestock. Cattle reduced fecundity by 0-85%. Nonetheless, estimates from matrix projection models indicat e that both sample populations had positive growth in most years. Elas ticity analyses revealed that population growth occurred in spite of r elatively small contributions by recruitment compared to growth and su rvival of nonreproductive plants. Results suggest that populations of this long-lived perennial depend little on reproduction and recruitmen t for growth and can persist in association with seasonal-rotation liv estock grazing.