Stage projection (Lefkovitch) matrices for 21 species of woody plants and 45 herbaceous perennials were extracted from the plant demographic literature or compiled from published data. Each matrix was divided into six regions representing: recruitment of seeds to the seed pool; recruitment of seedlings or juveniles from current seed production; clonal growth; retrogression, due to plants decreasing in size or reverting in stage; stasis, (survival from one year to the next in the same stage class); progression to later stage classes. Matrix analysis was used to calculate the finite rate of increase λ for each population and to calculate the elasticities of each transition coefficient in the matrices (...)

comparative plant demography - relative importance of life-cycle components to the finite rate of increase in woody and herbaceous perennials

Genetics and Conservation of Rare Plants

To investigate some of the factors that determine the fate of a seedling, censuses of seedlings of two native grasses, Aristida longiseta and Bouteloua rigidiseta, were made at frequent intervals in a Texas grassland for 2 yr. Seedlings of both species with neighboring seedlings or juvenile plants of either species within 2 cm had higher rates of survival and growth than those without such neighbors, implying that the effects of aggregation in favorable microsites outweighed the effects of competition among these plants. Neighboring adults of these species, and neighboring juveniles of other species, had positive effects in some instances, negative in others. Litter, even in amounts too small to cover the surface, reduced the survival rates of seedlings of both species, while surface rocks may have increased them. Overall, seedlings that germinated earlier in the autumn were more successful. The rank order of quadrat favorableness for seedlings varied in a complex fashion between species, between years, among census intervals, and among germination cohorts. This variation in patch favorableness must prevent these populations from reaching a stable spatial distribution and from reaching a stable age distribution in any given patch.

What is a Safe Site?: Neighbor, Litter, Germination Date, and Patch Effects

Monocarpic plants, which flower once then die, are ideal systems for testing evolutionary ideas because the cost of reproduction is easily quantified and the timing of flowering is a key determinant of darwinian fitness. Monocarps should flower at the size that maximizes fitness, enabling models of life-history evolution to be tested. These models are becoming increasingly sophisticated and accurate, making a review of the techniques and underlying theory timely. Here, we review the long-term demography of monocarpic species, focusing on how demographic rates vary with size and age. We then examine the broad array of evolutionary models, and question what aspects of the demography are crucial for the successful prediction of the size and age at flowering, shedding light on both the important aspects of monocarp demography and current advances in life-history modelling.

Evolutionary demography of monocarpic perennials.

Certain seed dispersers may benefit plants by depositing seeds in specific microsites favorable for survival or growth. This has been called "directed dispersal." We examine the effects of seed dispersal by ants on the demography of two seed cohorts of Corydalis aurea: one relocated to ant nests by undisturbed ant foragers, and a control cohort of equal numbers planted by hand in the vicinity of each nest. The ant-treated cohort produced 90% more offspring than the control cohort and had a higher finite rate of increase: a finite rate of increase of 2.83 per year versus a rate of 2.05 per year for the control. The higher rate for the ant-treated cohort was the result not of an increase in the fecundity of reproductive plants, which did not differ significantly from that of the control, but of a significant increase in survival to reproduction. The benefit to the ant-handled plants was determined by the specific end point of dispersal, not by the removal of seeds from the parent plant per se or the distanc...

Directed dispersal: demographic analysis of an ant-seed mutualism

Population Ecology of Melilotus Alba in a Limestone Quarry

SUMMARY (1) A population of the summer annual Erucastrum gallicum (Brassicaceae) colonizing an abandoned limestone quarry near Syracuse, New York, U.S.A., was monitored for five consecutive years and its demographic performance was interpreted in relation to rainfall patterns. (2) Survival and percentage reproduction of plants that emerged in the spring varied markedly depending upon rainfall. Deevey survivorship curves, Types I, II, and III were observed in cohorts from a year with abundant rainfall, a year with intermittent rainfall and drought, and a year with spring drought, respectively. Growth and the number of seeds produced by the population were also influenced by rainfall. (3) The number of seeds produced per plant ranged from 24 to 1675. The latter value is similar to or greater than that recorded in many other annual species. (4) Several lines of evidence suggest that less than half the viable seeds in the soil germinate in any one year and that a substantial proportion of seeds survive from one year to the next. (5) Unlike some annual plants, that persist in variable habitats by exhibiting phenotypic plasticity in growth coupled with high seedling survival, E. gallicum persists in the quarry through a suite of traits including high seed output by those plants that survive to reproduce, germination by a small proportion of the seeds in the seed bank in any one year, and viability of seeds that remain in the soil for at least 1 year.

Population biology of an annual plant in a temporally variable habitat

SUMMARY character: the 'sparse' and 'dense' sites. The number of seeds produced were also estimated on the two sites. (2) The demography of P. hieracioides differed greatly on the two sites. On the dense site, more seedlings emerged and a greater proportion established, probably due to the higher water retention than on the sparse site. Conversely, a lower proportion of plants at the dense site survived to maturity, reproduction was delayed, and there was reduced seed output by mature plants, possibly due to competition. Survival and reproduction was highest in 1976, the year with the most rainfall during the growing season. Populations of P. hieracioides declined during the study on both sites, apparently because of low survival and establishment of seedlings during 4 subsequent years of drought. Populations persisted through the dry years by reproductive delay coupled with comparatively high survival of established plants. (3) Most aspects of Echium vulgare demography appeared unaffected by site conditions; only reproduction was delayed longer on the dense site. Moreover, the rates of survival from seedling emergence to maturity were as l gh during years of drought as when rainfall was abundant. Echium vulgare plants survived better during drought than those of Picris hieracioides. Populations of Echium vulgare increased even during 4 years of drought, suggesting that the species may have only recently begun colonizing the quarry. Echium vulgare appears to tolerate better the dry, infertile quarry habitat than Picris hieracioides, indicating that there is substantial between-species variability among facultative biennials in their ability to colonize unproductive sites. (4) Unlike old-field populations of facultative biennials that typically become extinct after one or two generations due to successional changes, P. hieracioides and Echium vulgare showed no decline resulting from competitive displacement. The populations will probably continue to persist in the quarry for many years.

Demography of two facultative biennial plant species in an unproductive habitat

Populations of the polycarpic perennial Asclepias tuberosa L. growing in a 50-year-old abandoned limestone quarry near Syracuse, New York, were studied from 1976-1981. Plants were mapped on two sites that differed in density and substrate. Population size increased during 1976, a year of abundant rainfall, because recruitment and survival were both relatively high. During 4 drought-prone years that followed, rates of both seedling recruitment and survival were much lower, causing a marked decline in population size on both sites. The low rates of seedling emergence appeared to result mainly from low survival rates of seeds in the soil. The density of A. tuberosa seedlings that emerged was much lower than those of co-occurring monocarpic species. Fewer seedlings of A. tuberosa emerged because percentages of seeds surviving to produce seedlings were much lower and because the number of seeds produced per crop was lower. Seedling survival was much higher in A. tuberosa than in the monocarps.

Dudley J. Raynal

Papers

Population Ecology of Melilotus Alba in a Limestone Quarry

Population biology of an annual plant in a temporally variable habitat

Demography of two facultative biennial plant species in an unproductive habitat

Demography of the polycarpic herbaceous perennial Asclepias tuberosa (butterflyweed) in a chronically unproductive site.