Finite Rate Of Population Increase Research Articles

THE ROLE OF DENSITY DEPENDENCE IN THE POPULATION DYNAMICS OF A TROPICAL PALM

The role of density dependence in the population dynamics of tropical trees has been a subject of considerable debate. Here, we present data on the demography of the edible palm Euterpe edulis, classified into seven size categories and monitored over three years. On average, each adult palm contributed 98 seedling recruits per year into the population. The pattern of mortality was similar to that of other palms, with mortality being highest among the smallest plants. Those plants with a diameter at soil level >20 mm had an annual mortality <7%. Density dependence was found to act only on the seedling stage of the life cycle. The probability of survival and transition of seedlings to the next size class were affected both by the density of seedlings and the presence of conspecific adults. Matrix modeling indicated that the true finite rate of population increase (λ) was 1.28 and that the observed reverse “J”-shaped size distribution of plants was a consequence of the density dependence operating in the population. Elasticity analysis showed that the survival elements in the matrix contributed most to the value of λ, and that the position of the transition matrix in growth–survival–fecundity (G–L–F) space was influenced by density. The matrix model incorporating density dependence predicted size distributions and densities approximating the maximum observed in the field. Spatial simulations indicated that the predictions from the matrix model relating to the size structure of plants are robust, but that the predictions of densities are sensitive to the precise spatial dynamics of the population.

Demography of the invasive woody perennial Prosopis glandulosa (honey mesquite)

Summary 1 To assess the effect of annual environmental variability on the long‐term population dynamics of the invasive woody perennial Prosopis glandulosa var. torreyana (honey mesquite), we employed elasticity analyses of annual, mean and periodic matrix models. Growth, survival and reproduction were recorded for 1306 individuals in a 1‐ha plot over a 4‐year period. The volume of each individual was estimated, and transition matrices with nine size classes were constructed. Standard matrix analysis was performed, and the relative importance of individual life‐cycle components to changes in the finite rate of population increase (λ) was determined. 2 Periodic matrix analysis projected a 29% annual increase in population size (λ= 1.29), while annual projection λ‐values varied between 0.99 and 1.44. For both methods, elasticity of seedling recruitment was always very low in all 4 years, and the highest elasticities were generally associated with permanence in the same size class. 3 Periodic and annual projections predicted similar elasticity patterns, with the relative contribution to a change in λ of different demographic processes changing between ‘good’ and ‘bad’ years. However, annual matrices identified two bad years, with fecundity and growth elasticity decreasing relative to survival, whereas periodic analysis identified only one such year, and elasticity changes were seen only in fecundity and survival.

Vulpia ciliata Dumort. ssp. ambigua (Le Gall) Stace &amp; Auquier (Vulpia ambigua (Le Gall) More, Festuca ambigua Le Gall)

<i>Vulpia ciliata</i> Dumort. ssp. <i>ambigua</i> (Le Gall) Stace &amp; Auquier (<i>Vulpia ambigua</i> (Le Gall) More, <i>Festuca ambigua</i> Le Gall)

Association of Within-Territory Vegetation Characteristics and Fitness Components of California Gnatcatchers

-Correlations among habitat characteristics and fitness components of California Gnatcatchers (Polioptila californica californica) were examined using within-territory vegetation and life-history data for 41 pairs of gnatcatchers at four sites from 1993 through 1995. Gnatcatchers nested earlier, had more successful nests, produced more fledglings, had a longer nesting period, and had lower fledgling costs when their territories were associated with increased grass and forb cover, increased perennial structure, increased horizontal perennial homogeneity, decreased vertical perennial homogeneity, and decreased perennial diversity. Within-territory vegetation variables, derived from the correlation of vegetation and life-history variables, were able to discriminate among gnatcatcher pairs grouped by site. Survival of adult gnatcatchers was significantly higher in the gnatcatcher group that had average within-territory vegetation characteristics associated with maximization of other life-history variables and was significantly lower in the gnatcatcher group that had average within-territory vegetation characteristics associated with minimization of other life-history variables. Survival of juveniles was not associated with within-territory vegetation. The finite rate of population increase (X) was >1 for the gnatcatcher group where within-territory vegetation and life-history variables were maximized, approximately equal to 1 for gnatcatcher groups where within-territory vegetation and life-history variables were moderate, and <1 for the gnatcatcher group where within-territory vegetation and life-history variables were minimal. Our study suggests that within-territory vegetation characteristics are associated with adult survival and X, but site characteristics independent of vegetation also could have contributed to such an association. Received 3 September 1996, accepted 1 April 1997. SPECIES ABUNDANCE can be a misleading indicator of habitat quality and reproductive success (Van Horne 1983, Pulliam 1988, Martin 1992, Vickery et al. 1992a). Assuming that habitat features associated with fitness components (i.e. increased reproductive output and survival) will be chosen more often over time, preservation of (or management for) such features should increase fitness and promote short-term increases in abundance (Martin 1992). For most bird species, however, specific habitat features associated with increased fitness are poorly understood (but see Vickery et al. 1992b). Most studies have taken a qualitative approach to linking fitness components with habitat or nest location (e.g. Walkinshaw 1953, Graber 1961, Nolan 1963, Thompson and Nolan 1973, Stewart et al. 1977, Knapton 1978, Middleton 1979, Fischer 1980, Zimmerman 1982). 3E-mail: gbraden@co.san-bernardino.ca.us Although these studies provide valuable information on life history, they lack quantitative assessments of the association between habitat and fitness. This study focuses on identifying the association between habitat features and fitness components for the California Gnatcatcher (Polioptila californica californica), a small, sedentary passerine endemic to the coastal sage scrub community of southern California and northern Baja California (Atwood 1991). The California Gnatcatcher is listed as a threatened species. The current population estimate for the United States is approximately 2,000 pairs (Atwood 1992). The decline of this species has been concomitant with the disappearance and degradation of the coastal sage scrub habitat throughout southern California (Atwood 1993). The coastal sage scrub community is a Mediterranean habitat characterized by facultatively drought-deciduous, mesophilic shrubs from

Thermal constraints to population growth of bacterial-feeding nematodes

Bacterial-feeding nematodes are important participants in decomposition pathways and nutrient cycles in soils. The contribution of each species to component processes depends upon the physiology of individuals and the dynamics of populations. Having determined the effects of temperature on metabolic rates of several species of bacterial-feeding nematodes, we now present the effects of temperature on population growth rates and relate those data to observed field dynamics. Of nine species of bacterial-feeding nematodes screened for reproductive performance at 20°C, finite rates of population increase ranged from 4.833 d −1 for Caenorhabditis elegans Dougherty to 1.160 d −1 for Panagrolaimus detritophagus Fuchs. Species in the family Rhabditidae generally reproduced more rapidly than those in the Cephalobidae. From the nine species, finite rates of population increase and instantaneous population growth rates were measured at temperatures between 10 and 35°C for Acrobeloides bodenheimeri Thorne, A. buetschlii Steiner and Buhrer, Bursilla labiata Andrássy. Caenorhabditis elegans, Cephalobus persegnis Bastian, and Rhabditis cucumeris Andrássy. Caenorhabditis elegans at 20°C had the maximum finite rate of population increase while R. cucumeris at 35°C had the minimum rate (4.540 × 10 −25 d −1). We utilize the geometric mean of the finite rates of population increase (d −1) as an integral measure of the innate capacity of a species to maintain reproduction across temperatures. The geometric mean varied from 1.03 × 10 −4 for R. cucumeris to 1.45 for Cephalobus persegnis. In the field, temperatures exceeded the upper thermal threshold of R. cucumeris for a significant portion of the 1993 growing season. Population dynamics of this nematode closely matched predicted trajectories. Differences in population growth rates may partially explain the amount of N mineralized by each species.

Compensation in individual growth rates and its influence on lake trout population dynamics in the Michigan waters of Lake Superior

The role of compensatory mechanisms in the population dynamics of lake trout in the Michigan waters of Lake Superior was explored during three time periods: the pre‐sea lamprey period, prior to 1950 when lake trout were at a relatively high abundance and the fishery was the primary source of lake trout mortality; the sea lamprey dominant period, from 1951 to 1961 when lake trout were at a very low abundance due to sea lamprey predation and overexploitation; and currently, from 1985 to 1993 when wild lake trout abundance was at a moderate level. The role of compensatory changes in growth and fecundity rates of lake trout in the Michigan waters of Lake Superior was evaluated using a life table approach. Individual growth and fecundity rates were calculated and compared between time periods. These rates were used to determine age‐specific fecundity which, along with age‐specific survival, were incorporated into a Leslie projection matrix to calculate the finite rate of population increase (λ). Individual growth rates and age‐specific fecundity rates changed in response to the different levels of lake trout abundance during each of the study periods. Lake trout during the sea lamprey dominant period, which experienced the lowest abundance and highest mortality levels, exhibited the fastest individual growth rates and the highest age‐specific fecundity. These high rates contributed to the relatively large compensatory scope exhibited by lake trout during the sea lamprey dominant period as compared to lake trout during the pre‐sea lamprey or the current periods which are associated with higher levels of abundance.

Compensation in individual growth rates and its influence on lake trout population dynamics in the Michigan waters of Lake Superior

The role of compensatory mechanisms in the population dynamics of lake trout in the Michigan waters of Lake Superior was explored during three time periods: the pre-sea lamprey period, prior to 1950 when lake trout were at a relatively high abundance and the fishery was the primary source of lake trout mortality; the sea lamprey dominant period, from 1951 to 1961 when lake trout were at a very low abundance due to sea lamprey predation and overexploitation; and currently, from 1985 to 1993 when wild lake trout abundance was at a moderate level. The role of compensatory changes in growth and fecundity rates of lake trout in the Michigan waters of Lake Superior was evaluated using a life table approach. Individual growth and fecundity rates were calculated and compared between time periods. These rates were used to determine age-specific fecundity which, along with age-specific survival, were incorporated into a Leslie projection matrix to calculate the finite rate of population increase (λ). Individual growth rates and age-specific fecundity rates changed in response to the different levels of lake trout abundance during each of the study periods. Lake trout during the sea lamprey dominant period, which experienced the lowest abundance and highest mortality levels, exhibited the fastest individual growth rates and the highest age-specific fecundity. These high rates contributed to the relatively large compensatory scope exhibited by lake trout during the sea lamprey dominant period as compared to lake trout during the pre-sea lamprey or the current periods which are associated with higher levels of abundance.

Estimating population growth of grizzly bears from the Flathead River drainage using computer simulations of reproduction and survival rates

Using survival and reproduction data obtained from radio-tracking 23 adult female, 24 subadult female, 49 yearling, and 44 cub grizzly bears (Ursus arctos) in the Flathead River drainage of British Columbia and Montana, we estimated the finite rate of population increase [Formula: see text] from 1979 to 1994 at 1.085 ± 0.026, with ≈95% confidence limits of 1.032–1.136. Estimated annual survival rates were 0.946 ± 0.026 for adult females, 0.931 ± 0.038 for subadult females, 0.944 ± 0.039 for yearlings, and 0.867 ± 0.050 for cubs (rates for cubs and yearlings represented both sexes). The estimated annual reproduction rate and age at first parturition were 0.422 ± 0.042 female cubs per female and 6.44 ± 0.45 years, respectively. We found that uncertainty in [Formula: see text] was mostly attributable to uncertainty in survival rates (76.7%), with subadult (47.5%) and adult (21.9%) survival contributing the largest portions. These results indicated that to reduce uncertainty in [Formula: see text], further research on grizzly bears in our study area should focus on improving estimates of adult and subadult female survivorship. Other demographic variables are not as important in estimating the grizzly bear population trend in the North Fork of the Flathead River drainage.

A comparison of the demographies of pesticide susceptible and resistant strains of Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae) on kibbled wheat

Oryzaephilus surinamensis (L.) is becoming a serious pest of grain storages in Australia and this is partly due to an increase in the number of strains that are resistant to the commonly used pesticides. The purpose of this study was to investigate whether varying degrees of pesticide-resistance to fenitrothion, pirimiphos-methyl and chlorpyrifos-methyl affected the demographic performance of this species at different temperatures and relative humidities, and to estimate the degree of biological variability within a diversity of populations. Finite rates of population increase (λ) of six pesticide-susceptible and resistant strains, living in kibbled wheat, were obtained at 22.5 and 30 °C at 30 and 50% relative humidity (r.h.). Variability in survivorship, fertility, egg to adult development, and immature mortality rates was assessed. A method of estimating equations was employed to determine if population growth rates differed significantly. The degree of variation in the value of λ between strains was greater at cooler conditions. Values ranged from 0.8535 to 1.1961 at 22.5 °C/30% r.h., 0.9643 to 1.2609 at 22.5 °C/50% r.h., 1.4941 to 1.7092 at 30 °C/30% r.h. and 1.6285 to 1.8607 at 30 °C/50% r.h. There was evidence to suggest that resistance to fenitrothion and pirimiphos-methyl has little effect on demographic performance whereas resistance to chlorpyrifos-methyl does have a detrimental effect.

Optimal Resource Allocation to Seeds and Vegetative Propagules in the Understory Herb Syneilesis palmata (Compositae)

Abstract The aim of the present study was to evaluate the fitness consequences of resource allocation balance between seeds and vegetative propagules in an understory herb, Syneilesis palmata. Based on field censuses, transition matrices were constructed to compare the fitness of hypothetical S. palmata populations with different allocation balances (from seeds alone to vegetative propagules alone). We obtained the dominant eigenvalue (λ) of each matrix, which gives the finite rate of population increase, i.e. a fitness measure for a population with overlapping generations. The value of λ was highest when the relative allocation to seeds (P) was zero and decreased as P increased, indicating that the optimal strategy was to reproduce only vegetatively. Seed reproduction was favored only under quite unrealistic situations such as production of 500–1000 times more seeds per unit investment than those observed in the real plants, or seedling growth under full sun light. The majority of fertile plants, however, produced seeds in addition to vegetative propagules in the natural habitats. The results of our simulations provide quantitative, though indirect, evidence for important roles of seeds in dispersal and/or sexual reproduction.

The Determinants of the Distribution and Abundance of the Winter Annual Grass Vulpia Ciliata ssp. Ambigua

1 Vulpia ciliata ssp. ambigua is a winter annual grass that occurs primarily in southern and eastern England. A model is constructed which relates this distribution to three climatic factors: the total number of sunshine hours in the spring quarter of the year (March-May), the temperature of the winter quarter (December-February), and the temperature of the autumn quarter (September-November). 2 The species is primarily limited to sandy soils and shingle. A map of Great Britain is created to indicate where the suitable soils on which the species can exist are to be found. The resolution of current databases is such that field verification of soil types on which the species is occasionally found is essential. 3 The density and size of four populations, along a 100-km transect from the heart of the species range in eastern England to the most northerly population, suggest that populations become smaller towards the northern edge of the distribution. 4 The primary reason for the decline in abundance towards the margins of populations and towards the edge of the range is a decline in the fecundity of individuals, which is strongly correlated with the finite rate of population increase. There was a slight increase in mortality towards the margin of populations.

The demography of Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae) on kibbled wheat

Finite rates of population increase (λ) of a pesticide susceptible strain of Oryzaephilus surinamensis (L.) living in kibbled wheat were determined at 20, 22.5, 25, 30, 32.5 and 35°C at 30, 50 and 70% relative humidity (r.h.) using survivorship and fertility schedules, i.e. observed numbers of adult offspring produced by cohorts of insects over a physiological time frame of twice the immature development period at each condition. Population growth rate increased with temperature up to 30°C at 30% r.h. and up to 32.5% at 50 and 70% r.h. Populations subjected to drier conditions grew slower than those subjected to moister conditions. The greatest value of λ (2.4122) was observed at 32.5° C 70% r.h. The rate of population increase declined rapidly after a maximum value was reached and at 35° C 30% r.h. a negative rate of increase was observed. The value of λ at low temperatures was little affected by relative humidity with a minimum theoretical population growth threshold varying from 19.0 to 19.4°C between 30 and 70% r.h. Egg to adult development and immature age-specific mortality were examined in detail at 20, 30 and 35°C at 30, 50 and 70% r.h. Minimum mortality occurred at 30 and 35°C at 70% r.h. and maximum mortality occurred at 20 and 35°C at 30% r.h. Maximum mortality accounted for almost complete extinction of the immature population and occurred mainly during the egg stage. At increasingly suboptimum conditions, a larger proportion of surviving immatures required an extra instar before pupation. Demographic data for O. surinamensis were compared with other available data for the species, as well as with similar data for Sitophilus oryzae and Rhyzopertha dominica. Concerns were raised about relating estimates of population growth of O. surinamensis to wet bulb temperature. It was considered that relating population growth to dry bulb temperature and relative humidity or equilibrium grain moisture content, in the conventional manner, was more appropriate for this insect.

A Demographic Interpretation of Grime's Triangle

1.The CSR theory of life-history strategies of Grime, and demographically based theories of life history represent strongly contrasting approaches that have yet to be reconciled. 2. It is argued that there are a priori grounds for analogy between Grime's three primary strategies of the established phase in plants and the demographic processes of growth (≈C), survival (≈S), and fecundity (≈R). 3. The contribution of growth, fecundity and survival to the finite rate of population increase λ was calculated for populations of 18 plant species that have also been classified according to Grime's CSR scheme. The match between the demographic classification of species based on these data and their CSR status was determined using a randomization test, and no significant match between the two was found. The reasons for this result are discussed, and it is concluded that it would be premature to abandon attempts to reconcile these two important approaches to plant life history.

Competition and the Local Distribution of the Grass Stipa Neomexicana

Within a grassland in southern Arizona, Stipa neomexicana occurs only on dry ridge crests with low total grass cover, while total grass cover is greater below the ridge crests in moister, low—lying areas. I hypothesized that Stipa neomexicana was limited to these dry ridges by competitive exclusion. This hypothesis was tested by removal experiments conducted at three positions along the topographic gradient. The responses of Stipa were compared with those of Aristida glauca and other neighboring species. The predictions made under the hypothesis were confirmed; competitors limited seedling establishment, seeding survival, flower production, and the growth of mature plants. The response to the removal of competitors increased from the ridge crest to the downslope positions. Competition depressed estimated finite rates of population increase for Stipa neomexicana, particularly on the lower slope. Thus, increasing competition from neighboring grasses along the topographic gradient was responsible for restricting Stipa neomexicana to the unfavorable ridge crest sites.