G. Houle et al., Spatiotemporal dynamics of Floerkea proserpinacoides (Limnanthaceae), an annual plant of the deciduous forest of eastern North America, AM J BOTANY, 88(4), 2001, pp. 594-607
Because environmental filters are temporally and spatially heterogeneous, t
here often is a lack of significant relationship between the spatial patter
ns of successive life stages in plant populations. In this study, we determ
ined the spatiotemporal relationships between different life stages in two
populations of an annual plant of the deciduous forests of eastern North Am
erica. Floerkea proserpinacoides. Demographic surveys were done over a 4-yr
period, and experiments were performed in the field and under controlled c
onditions to test for the effects of various environmental factors on popul
ation dynamics. There was a general lock of relationship between the spatia
l patterns of seed bank and seedling density, and a lack of similarity betw
een their spatial correlograms. This was related mostly to the effects of s
patially variable environmental filters operating on germination and emerge
nce. However, environmental tilters acting on plant survival were stable th
rough time and contributed to stabilize the density and spatial patterns of
the populations. Despite density-dependent presenescence mortality, spatia
l patterns of seedlings and mature individuals were similar and their corre
lograms were alike, suggesting that mortality did not fully compensate for
density. Estimated fecundity was negatively correlated with population dens
ity over the study period. Although flower production started only 2-3 wk a
fter emergence, seed maturation mostly occurred at the end of the life cycl
e, just before the onset of plant senescence. Yet, individual fecundity was
low for an annual plant, i.e., 3.0 +/- 0.5 mature seeds/plant (mean +/- 1
SE). Seed predation by vertebrates was not significant. Low soil moisture h
ad little effect on the total number of seeds germinating, although it slow
ed down the germination process. In quadrats where leaf litter was experime
ntally doubled, seedling emergence was lower than in control quadrats: in q
uadrats where leaf litter was completely removed, emergence did not differ
from that in control quadrats. Susceptibility to drought stress was higher
for seedlings than for mature plants. Although the species does not maintai
n a long-term persistent soil seed bank, other factors, such as density-dep
endent fecundity and autogamy, may temper population fluctuations through t
ime and reduce the probability of local extinction.