Variability in the dynamics of northern peripheral versus southern populations of two clonal plant species, Helianthus divaricatus and Rhus aromatica

Citation
P. Nantel et D. Gagnon, Variability in the dynamics of northern peripheral versus southern populations of two clonal plant species, Helianthus divaricatus and Rhus aromatica, J ECOLOGY, 87(5), 1999, pp. 748-760
Citations number
53
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Environment/Ecology
Journal title
JOURNAL OF ECOLOGY
ISSN journal
0022-0477 → ACNP
Volume
87
Issue
5
Year of publication
1999
Pages
748 - 760
Database
ISI
SICI code
0022-0477(199910)87:5<748:VITDON>2.0.ZU;2-L
Abstract
1 The clonal perennial herb Helianthus divaricatus and the clonal shrub Rhu s aromatica reach the northern limit of their distribution in southern Queb ec (Canada), where both are rare, but they are more common southwards in th e adjacent province of Ontario. We tested whether peripheral populations of these species maintain themselves by having highly variable individual gro wth and survival rates. Their annual rates of population growth, lambda, wo uld then vary more, from year to year, than those of more southern populati ons in neighbouring Ontario, where the species are common. 2 Demographic analyses compared, over two transition intervals, size-based transition matrices for two northern (Gatineau Park, southern Quebec) and t wo southern populations (Pinery Park, southern Ontario) of each species. Co mparisons used log-linear analyses, bias-corrected lambda-values with 95% c onfidence intervals, and elasticity values. 3 For both species, the northern populations showed a larger variation betw een transition intervals and local populations in some of their vital rates and in lambda-values. For H. divaricatus, elasticity values combined with log-linear analyses indicated that differences in the growth and survival o f medium-sized ramets contributed most to the differences in lambda-values between northern and southern populations. For R. aromatica, they indicated that differences in the fate of both medium and large ramets contributed t o variation in lambda. 4 Most of our data indicated a greater demographic variability in the north ern populations of H. divaricatus and R. aromatica. At the northern periphe ry, these species grow in very few of the numerous habitat patches that app ear to be suitable for them, whereas the two species together present a nea r continuous cover in all suitable habitats further south. High demographic variability therefore appears to contribute to determining the distributio n of plant species, by increasing the extinction probabilities of local pop ulations at the distribution limit.