# Demography of the Perennial Herb Lathyrus Vernus. II. Herbivory and Population Dynamics

Johan Ehrlen
Journal of Ecology
Vol. 83, No. 2 (Apr., 1995), pp. 297-308
DOI: 10.2307/2261568
Stable URL: http://www.jstor.org/stable/2261568
Page Count: 12

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## Abstract

1 The population dynamics of the perennial forest herb Lathyrus vernus were studied in six populations during 4 years. The main objective was to examine the influence of three types of herbivory (meristem damage by molluscs, vertebrate grazing and predispersal seed predation) through effects on different stages of the life-cycle. 2 Transition population matrix analyses indicated that L. vernus exhibits stable dynamics with small variations in $\lambda$ among years although transition probabilities differed among years and populations. Stochastic simulations yielded $\hat{\lambda}$-values ranging from 0.95-1.19. Extinction risk within 100 years was close to zero in five of the six investigated populations. 3 One population which suffered from a high level of meristem damage and seed predation and one which suffered from intense grazing were selected to study the effects of the three types of herbivory. Transition probabilities of severely damaged individuals (more than half the meristems or half above-ground volume removed) differed from less damaged individuals for both meristem damage and grazing. Different damage levels were simulated by assigning transition probabilities of damaged and less damaged individuals different weights. In stochastic simulations meristem damage reduced population growth rate more than grazing or seed predation. 4 Very small, small and intermediate individuals accounted for the majority of individuals in all populations. Meristem damage and grazing increased the proportion of small and dormant individuals while seed predation increased the proportion of large individuals. 5 Population growth rate was most sensitive to changes in the probability of individuals remaining in the same class, whereas transitions that involved seed production had very little effect on $\lambda$. The effects of meristem damage and grazing on $\lambda$ were therefore mainly due to a decreased probability of established individuals maintaining or increasing their size rather than to their very large reduction in seed production.

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