Variation In Life History Parameters Research Articles

Effects of Geographic Location and Habitat on Breeding Parameters of Great Tits

Studied variation in laying date, clutch size, and number of fledglings in Great Tits (Parus major) in relation to habitat, elevation, and latitude using data from 137 breeding areas. Laying date was not affected by habitat type but increased with elevation and showed a significant quadratic relationship with latitude. Food availability, ambient temperature, and photoperiod together can explain why laying date increases with latitude. However, more information is needed to understand why birds in northern Africa start laying later than in nearby southwestern Europe. Variation in clutch size and number of fledglings was significantly affected by habitat type, with lower values in coniferous forests. Mean clutch size decreased with elevation. Mean clutch size and mean number of fledglings of first and second broods showed a significant quadratic relationship with latitude, with the highest values at about 55 to 60 degrees N. The results suggest that latitudinal variation in life-history parameters is related to variation across marginal and central parts of the species' distribution and is influenced by factors such as daylength, temperature, and/or seasonality of food resources. Birds at southern latitudes are probably under lime constraints, whereas birds at northern latitudes are probably under energy constraints. Alternatively, Great Tits at northern latitudes might be less well adapted to these habitats because they invaded northerly latitudes during the last decades. The proportion of pairs laying a second clutch decreased with latitude. The observed pattern of a late start of laying, lower variability in laying date, and lower frequency of second clutches in northern populations likely was due to the late and short growing season for the Great Tit's main prey caterpillars.

Multiple bottlenecks, allopatric lineages and Badlands bison Bos bison: Consequences of lineage mixing

While ecological and conservation consequences of combining animals of varied genetic backgrounds have been widely discussed, the demonstration of effects that stem from lineage mixing remains elusive. Since management agencies relocate populations or supplement them with individuals regularly, the opportunity for either inbreeding or outbreeding depression may be high; still, any putative effects will go unnoticed without detailed knowledge of life-history and behaviour. Here, we report potential consequences of lineage mixing in a restored population of North American Bos bison studied for five years. In 1984 two allopatric lineages became sympatric in Badlands National Park, South Dakota; they differed in both founding population size and the number of demographic bottlenecks experienced since 1907. Measures of reproductive variance in both sexes were employed to estimate effective population size based on 261 copulations and the survivorship of calves between 1985 and 1989. We assumed that the reproductive variance and mortality documented in this study are representative of the bison's recent past and based on this assumption we calculated N e separately for each generation for which the lineages were allopatric. Four potential correlates of fitness were studied in the new sympatric population: (1) female fecundity; (2) juvenile survival; (3) growth rates; and (4) female age at puberty. Of these, neither female fecundity nor juvenile survival was associated with lineage but growth rates were more rapid and ages at puberty were lower for F 1 purebred (inbred) juveniles than for F 1 hybrid (outbred) juveniles. Possible consequences of this variation in the F 1 generation include (1) higher winter mortality in the slower growing line as well as (2) decreased lifetime production of young; both are life-history parameters that could be interpreted as long-term selection against outbreeding. However, these data by themselves do not constitute support for an outbreeding depression hypothesis. The failure of males from one lineage to mate at all prevented the possible combinations of the F 1 generation needed for the appropriate statistical contrasts. Nevertheless, these interpretations (1) substantiate a level of variation in life-history parameters stemming from lineage mixing; and (2) suggest that advice regarding prudent conservation strategies must be sought concerning the genetic histories of individuals and populations to be selected for re-introduction. This applies to both wild and captive populations. The prevalence of outbreeding and inbreeding tolerances within populations of managed and protected species needs verifiable documentation.

Toward Predictable Biological Control of Liriomyza trifolii (Diptera: Agromyzidae) Infesting Greenhouse Cut Chrysanthemums

Implementation of augmentative biological control is often hindered by the inability to obtain accurate information on natural enemy release rates that will ultimately yield a salable crop within economic constraints. The purpose of this study was to develop and evaluate a computer model that attempts to predict augmentative releases of the parasitoid Diglyphus begini (Ashmead) (Hymenoptera: Eulophidae) to use for biological control against the serpentine leafminer Liriomyza trifolii (Burgess) (Diptera: Agromyzidae) infesting greenhouse-grown cut chrysanthemums. The model attempts to determine the appropriate release rate necessary to reduce leafminer densities below 1 larvae per 1,000 chrysanthemum leaves within 40 d after planting, after which time aesthetically important foliage forms on chrysanthemums. In the construction of this deterministic model, three simplifying assumptions have been made: (1) there is no insect movement between the greenhouse and outside, (2) greenhouse temperatures are a constant 27°C, and (3) the greenhouse represents a homogeneous environment. Model simulations indicated that successful biological control was unlikely when parasitoid releases are initiated later than 14 d after planting regardless of the release rate. The simulations also demonstrated that D. begini release rates are not linearly related to L. trifolii densities, and that a parasitoid release strategy is not simply the determination of a proper wasp/leafminer ratio. Validation studies of the model's predictions provided mixed results. Following the release rates generated by the model, L. trifolii larval densities were not significantly greater than I per 1,000 leaves 40 d after planting. However, the model did not always track the succession and magnitude of leafminer population fluctuations with statistical accuracy. Two factors probably contributed to these errors in prediction: (1) the assumptions inherent to the model were not met during the validation trials, and (2) the leafminer subroutine of the model could not accurately predict L. trifolii densities in the absence of D. begini . In spite of these errors, leafminer damage to the harvested foliage was significantly lower in the treatments receiving D. begini releases than in the control treatments. In addition, when the model was tested in a commercial cut chrysanthemum greenhouse, L. trifolii was successfully controlled by releases of D. begini , resulting in the production and harvest of a salable cut chrysanthemum crop without the use of any pesticides. Finally, postvalidation reconstruction of the model, to include temperature-dependent variation in life history parameters, increased the predictive power of the model.

Managing beaver to benefit waterfowl: J. K. Ringelman, Fish & Wildlife Leaflet - US Fish & Wildlife Service, 13.4.7, 1991, 7 pp

While ecological and conservation consequences of combining animals of varied genetic backgrounds have been widely discussed, the demonstration of effects that stem from lineage mixing remains elusive. Since management agencies relocate populations or supplement them with individuals regularly, the opportunity for either inbreeding or outbreeding depression may be high; still, any putative effects will go unnoticed without detailed knowledge of life-history and behaviour. Here, we report potential consequences of lineage mixing in a restored population of North American Bos bison studied for five years. In 1984 two allopatric lineages became sympatric in Badlands National Park, South Dakota; they differed in both founding population size and the number of demographic bottlenecks experienced since 1907. Measures of reproductive variance in both sexes were employed to estimate effective population size based on 261 copulations and the survivorship of calves between 1985 and 1989. We assumed that the reproductive variance and mortality documented in this study are representative of the bison's recent past and based on this assumption we calculated Ne separately for each generation for which the lineages were allopatric. Four potential correlates of fitness were studied in the new sympatric population: (1) female fecundity; (2) juvenile survival; (3) growth rates; and (4) female age at puberty. Of these, neither female fecundity nor juvenile survival was associated with lineage but growth rates were more rapid and ages at puberty were lower for F1 purebred (inbred) juveniles than for F1 hybrid (outbred) juveniles. Possible consequences of this variation in the F1 generation include (1) higher winter mortality in the slower growing line as well as (2) decreased lifetime production of young; both are life-history parameters that could be interpreted as long-term selection against outbreeding. However, these data by themselves do not constitute support for an outbreeding depression hypothesis. The failure of males from one lineage to mate at all prevented the possible combinations of the F1 generation needed for the appropriate statistical contrasts. Nevertheless, these interpretations (1) substantiate a level of variation in life-history parameters stemming from lineage mixing; and (2) suggest that advice regarding prudent conservation strategies must be sought concerning the genetic histories of individuals and populations to be selected for re-introduction. This applies to both wild and captive populations. The prevalence of outbreeding and inbreeding tolerances within populations of managed and protected species needs verifiable documentation.

Intraspecific variation of life history parameters in the terrestrial isopod, Armadillidium vulgare.

Individual populations of the terrestrial isopod, Armadillidium vulgare, were studied in three Texas coastal prairie habitats: Chinese tallow forest, oak forest, and a Baccharis-grassland area. Time-specific life tables were compared for each population to determine intraspecific variation in life history parameters. Survivorship was greatest in the Baccharis area but density was lower and fluctuated less in this area than in the tallow or oak forests. Density in the oak forest was higher than in the tallow or Baccharis habitat. Density in the tallow and oak forests increased sharply during spring and summer and declined throughout the winter. Reproductive capacity of females in all three areas increased directly with body length but did not differ significantly between habitats. Density and reproductive performance of isopods in the tallow and oak forests was asynchronous with autumn leaf fall; this asynchrony may be a response to tannins leached from fallen leaves of these trees. Density and reproductive potential of isopods in the Baccharis-grassland, however, did not exhibit such marked fluctuations. Isopods in this latter habitat responded moderately to annual input of detritus during the fall.

Reproductive Strategies in Flatfish: A First Synthesis

This paper examines the factors determining the age and size at maturity of temperate species of flatfish. In some species maturity is governed by size, not age. I propose that the most likely determinant of this size is size-dependent predation. Many species fast during the winter months and rely upon reserves stored in the body tissues to provide energy for gonad maturation. The stress placed upon a fish by the breakdown of body tissues may be very substantial and could significantly affect the predation function. Under these conditions selection may favor the deferment of maturity until a size is achieved at which predation is relatively low. I suggest that such a mechanism may account for the extreme geographic variation in life history parameters of American plaice, Hippoglossoides platessoides, and witch flounder, Glyptocephalus cynoglossus. The generality of winter cessation of feeding suggests that the above hypothesis may also be applicable to a wider range of species. By contrast, in several species, age has been shown to be more important than size in determining the onset of maturity. I suggest that age is likely to be more important than size in early maturing species; in these a decrease in the age at maturity may be, temporarily at least, prevented by genetic/physiological constraints imposed by the time required for oocyte development. This hypothesis is tested and supported by historical data on several European species. Finally, I examine the intra- and inter-specific patterns of allocation to fecundity. Interspecific differences in allocation to reproduction are greatly reduced but not eliminated when egg volume is taken into consideration. Factors influencing the observed allocation patterns are examined.Key words: pleuronectiformes, life history, reproduction, fecundity, maturity

Size, life history and ecology in mammals

SummaryAllometric laws which scale numerous biomechanical and physiological processes to size in mammals have long been recognized and widely used in biology. There is now sufficient evidence to suggest that those life history parameters such as growth and maximum rates of reproduction, which depend in part on metabolic rate, are also scaled to size. Data are presented which, coupled with a literature review, show that gestation time, growth rates, age at first reproduction, lifespan, the intrinsic rate of natural increase, birth rate, net reproductive rate and litter weight are allometrically scaled to size and are, in consequence, inter‐related. The exponents of the scaling functions are similar in all mammalian orders but in some taxa such as the primates, the species grow slower, live longer and reproduce at a lower rate. For these taxa the differences in life history parameters can be explained by differences in brain size and an existing hypothesis that the maximum rate of neural tissue growth constrains the maximum rate of growth and development of the entire organism.It is then argued that because size scales the main life history parameters of mammals it should also be a central theme in ecology from the individual to the community level of organisation. Examples are presented to show that size is ubiquitous in ecology and accounts for most of the variation in life history parameters between species. Size scaling offers a method of reducing species of varying size to similar dimensions of time, space and rates of action. It is therefore fundamental in distinguishing those life history parameters which arise as a consequence of size, the first order strategies, from those that vary between populations and according to environmental circumstances, the second order strategies. From this approach should develop a broader biological synthesis in which genetic and physiological determinants will inevitably feature more centrally than they do in ecological and behavioural theory.RésuméLes lois allométriques unissant les processus biomécaniques et physiologiques avec la taille chez les mammifères ont été reconnues depuis longtemps et largement utilisées en biologic Il y a maintenant assez de certitude pour suggérer que les paramètres biologiques tels que croissance et taux maximal de reproduction, qui dépendent partiellement du rendement métabolique, sont aussi fonctions de la taille. Les données présentées ici, couplées avec une revue de la littérature, montrent que la durée de gestation, le taux de croissance, l'âge à la première reproduction, la durée de vie, le taux intrinsèque d'accroissement naturel, le taux de natalité, le taux de reproduction net et le poids de la portée sont en relation allométrique avec la taille et, par conséquent, sont en interrelation.