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  • Life history  (50)
  • 1
    ISSN: 1432-1939
    Keywords: Key words Microhabitat choice ; Foraging ; Safety ; Predation risk ; Life history
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  In Idotea baltica, a marine isopod that lives and feeds on the brown alga Fucus vesiculosus, microhabitat choice differs between sexes so that males are found more often than females on the light-coloured and exposed apical parts of the alga. We investigated how the requirements of avoiding visual predators and feeding were related to microhabitat choice in relation to diurnal and life-cycle stage in males and females. Faced with a choice between an apical and a basal piece of the alga, females spent more time than males on the basal piece, but this difference was not due to food choice. Faced with a choice between a dark, concealing and a light, exposing background, the preference for a dark background was stronger at day than at night, and stronger in females than in males. This suggests that a sex difference in the importance of avoiding visual predators can explain the sex difference in microhabitat choice. Further, the preference for a dark background and night feeding both increased with age, suggesting that feeding is increasingly subordinated to the need to avoid visual predators. Our experiment found no effect of the presence of the opposite sex on microhabitat choice. Our results support the hypothesis that the sexes trade off feeding against predation risk differently, presumably because growth is more important to males than to females, which have more to gain by protection and therefore spend more time on the lower parts of the alga.
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  • 2
    ISSN: 1432-1939
    Keywords: Life history ; Phenotypic plasticity ; Reproductive strategy ; Viviparus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Age specific fecundity and size of offspring were compared in two populations of Viviparus ater, one from Lake Zürich (Switzerland) and one from Lake Maggiore (Italy). Females were caged and their offspring sampled at weekly intervals. Average fecundity per female over one year was 19.6 and 14.7 offspring in Lake Zürich and Lake Maggiore, respectively. Average shell widths of offspring at birth in the two lakes were 8.5 mm and 7.4 mm. Fecundity did not change with age in Lake Zürich but decreased with increasing age of the snails in Lake Maggiore. Fecundity and offspring size were positively correlated with the size of the females in both lakes, but fecundity was higher and offspring were larger in Lake Zürich than in Lake Maggiore irrespective of the size of the females. An analysis of covariance, correcting for differences between the two lakes in the total fresh weight of the offspring produced annually, showed that females from the two lakes distributed their reproductive investment differently. Females in Lake Zürich produced relatively fewer but larger offspring than females in Lake Maggiore. This trade-off was hidden because females in Lake Zürich produced twice as much offspring biomass as females in Lake Maggiore. The possibility that different selection regimes might account for the observed differences is discussed.
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  • 3
    ISSN: 1432-1939
    Keywords: Snakes ; Locomotor ability ; Costs of reproduction ; Life history
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Recent studies suggest that lower survival among gravid squamate reptiles may be partially the result of decreased locomotor ability during gestation. In this study, we compared the speed and endurance of female garter snakes (Thamnophis marcianus), before, during, and after pregnancy. Gravid snakes had significantly lower locomotor performance than did non-gravid females, and performance varied among stages of gestation, reaching a minimum 0–6 weeks prior to parturition. Both number of offspring and relative clutch mass were inversely correlated with locomotor performance; as females increased these traits, locomotor ability decreased. If reduced locomotor performance results in greater risk of predation and/or lowered foraging ability, then natural selection (operating via differential mortality or feeding rates of gravid females) may result in important constraints on both clutch size and relative clutch mass in squamates.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 78 (1989), S. 521-532 
    ISSN: 1432-1939
    Keywords: Morethia boulengeri ; Scincidae ; Lizards ; Life history ; Population dynamics ; Resource availability ; Thermal ecology ; Australia ; Arid zone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The life history and population ecology of the skink Morethia boulengeri were studied from September 1985 to May 1987 in populations in a riverine woodland habitat and at an abandoned homestead in Kinchega National Park. The population dynamics and life histories of the two populations were remarkably similar. Yearly mortality (including emigration) ranged from 0.84–0.89. The yearly emigration rate was 0.01–0.03. Size-and body-condition-dependent mortality could be demonstrated for the population in riverine woodland. Average spring time densities were similar in both study sites but varied between years and ranged from 421-1823 individuals/ha. M. boulengeri females laid on average 2.8 eggs per clutch and usually produced three clutches per year. Egg mass was significantly correlated with female snout-vent-length, but relative clutch mass and egg size were not. All surviving juveniles reproduced for the first time in their first year. Some activity occurred throughout the year. Preferred body temperatures decreased in the cooler months. The data fit demographic models of life history evolution.
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  • 5
    ISSN: 1432-1939
    Keywords: Life history ; Countergradient variation ; Growth rate ; Seasonality ; Latitudinal variation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary How do organisms adapt to the differences in temperature and length of the growing season that occur with latitude? Among Atlantic silversides (Menidia menidia) along the east coast of North America, the length of the first growing season declines by a factor of about 2.5 with increasing latitude. Yet body size at the end of the first growing season does not decline. High-latitude fish must, therefore, grow faster within the growing season than do low-latitude fish. This geographical pattern has a genetic basis. Laboratory experiments on fish from six different locations revealed a latitudinal gradient in the capacity for growth (i.e., maximum growth potential). In two subsequent experiments using fish from Nova Scotia (NS), New York (NY) and South Carolina (SC) that had been separately reared in a common environment for several generations, differences in growth rate among populations were highly significant. The rank order was NS〉NY〉SC, but the difference among populations depended on temperature. High-latitude fish outperformed those from low latitudes primarily at the high temperatures that low-latitude fish would be expected to experience most often in nature. These results suggest that instead of being adapted for growth at low temperatures, fish from high latitudes are adapted for rapid elevation of growth rate during the brief interval of the year when high temperatures occur. Selection on growth rate results from sizedependent winter mortality: the importance to winter survival of being large increases with latitude but the length of the growing season simultaneously decreases. The end result is countergradient variation in growth rate, a phenomenon that may be much more widespread than currently recognized.
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  • 6
    ISSN: 1432-1939
    Keywords: Mollusca ; Pioneers ; Life history ; Colonizing ability ; r-selection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We examine whether pioneer species of terrestrial gastropods (snails and slugs) possess particular life history traits commonly associated with r-selection, using data on gastropod colonization in four areas in north-west Europe (the Kvarken and Tvärminne archipelagos in the Baltic, polder woods in IJsselmeer, and a rehabilitated quarry near Maastricht). Data on age at first reproduction, longevity, clutch size, egg size and lifetime fecundity were gathered from the literature. In order to control for potentially confounding effects of body size on life history traits, we compared the residuals from the allometric relations between life history traits and body size for pioneers and non-pioneers. In snails, all life history traits examined were related to body size. In slugs, all traits except age at first reproduction scaled with body size. Body sizes did not differ between pioneers and non-pioneers in any area. In all four areas, there were no significant differences between pioneers and non-pioneers in any of the life history traits examined, after body size had been taken into account. This indicates that pioneer terrestrial gastropods generally cannot be regarded as r-selected. Pioneer species may possess any of several life history strategies, and the combinations of traits shown by them may have little in common with the r-K selection concept.
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  • 7
    ISSN: 1432-1939
    Keywords: Genetic variation ; Aphididae ; Life history ; Parthenogenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Many aphid species have shown remarkable adaptability by invading new habitats and agricultural crops, although they are parthenogenetic and might be expected to show limited genetic variation. To determine if the mode of reproduction limits the level of genetic variation in adaptively important traits, we assess variation in 15 life history traits of the pea aphid, Acyrhosiphon pisum (Harris), for five populations sampled along a north-south transect in central North America, and for three traits for three populations from eastern Australia. The traits are developmental times and rates as affected by temperature, body weights as affected by temperature, fecundity, measures of migratory tendency, and photoperiodic responses. The most southerly population from North America is shown to be obligately parthenogenetic, as are the Australian populations, and the four more northerly North American populations are facultatively parthenogenetic with the number of parthenogenetic generations per year increasing from north to south. The broad-sense heritabilities of life history traits varied from 0.36 to 0.71 for nine quantitive traits based on a comparison of within-and between-lineage variances. Using these traits, 7–13 distinct genotypes (i.e. clones) were identified among each of the 18 lines sampled from the North American populations, but the number did not differ significantly among populations. The level of genetic variation differed from trait to trait. For 4 of 12 quantitative traits, the level of variation in the obligately parthenogenetic population from North America was lowest, but significantly lower than all the sexual populations for only 1 trait. The obligately parthenogenetic population had the highest level of genetic variation for two traits, and had intermediate levels for the others. The most northerly population, which was sexual and had relatively few parthenogenetic generations each year, had the lowest level of variation for 5 of 12 traits and the highest level of variation for 2 traits. There was no decline in variability from north to south correlated with the increase in the annual number of parthenogenetic generations. The Australian populations showed no less variation than the North American populations for two of three traits, although the pea aphid was introduced to Australia only 5 years prior to the study, whereas the aphid has been in North America for at least 100 years. The mode of reproduction has not had a substantial impact on the level of genetic variation in life history traits of the pea aphid, but there are population-specific factors that effect the level of variation in certain traits.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 96 (1993), S. 324-330 
    ISSN: 1432-1939
    Keywords: Ocypodid crab ; Life history ; Geographic variation ; Breeding season
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Reproductive traits of the mud crab Macrophthalmus banzai were compared in populations from Okinawa (26°13′ N) and Amakusa (32°32′ N). Crabs matured earlier and at a smaller size in Okinawa than in Amakusa, but growth rate did not differ between the two localities. Population density was much higher in Okinawa. Breeding occurred in winter in Okinawa and in summer in Amakusa. In Okinawa, females produced one brood at over 1 year of age and then died. In Amakusa, females produced one brood at over 1 year of age, and one or two broods at around 2 years of age, and then died. Egg weight in the Okinawa population was almost twice that of the Amakusa population. Furthermore, brood weight was larger in Okinawa than in Amakusa. Longevity was 16–19 months in Okinawa and 28–30 months in Amakusa. At high latitudes, the winter low temperature blocks reproduction of M. banzai. At low temperature blocks reproduction of M. banzai. At low latitudes, their short lifespan prevents iterative breeding. Thus, the difference in breeding season greatly affects other life-history traits.
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  • 9
    ISSN: 1432-1939
    Keywords: Life history ; Coadapted traits ; Clone Daphnia ; Diurnal vertical migration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract To test the hypothesis of co-adaptation of life histories and daytime vertical distribution (vertical migration behaviour) in Daphnia, life history characteristics were analysed for two positively, three negatively, and four intermediately phototactic Daphnia magna clones. Clones with different phototactic behaviour were found to have divergent life history strategies, with positively phototactic clones being good exploiters under the non-limiting conditions provided in the laboratory, i.e. low density (1 ind./1), high food concentration (6,5–7 105 Scenedesmus cells/ml, restored daily) and high temperature (20° C). They realized a high intrinsic rate of increase at a small adult body size through rapid development, at a cost of producing small neonates. Negatively and intermediately phototactic clones had larger adult body sizes, and produced larger neonates that were more starvation-resistant than those of positively phototactic clones. Selection for high intrinsic rate of increase in intermediately phototactic clones was mediated through the production of large clutches.
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  • 10
    ISSN: 1432-1939
    Keywords: Alpine ; Colubridae ; Life history ; Reproduction ; Reptile
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A 5-year mark-recapture study of smooth snakes (Coronella austriaca) in the Carnic Alps (1100 m above sea level) of north-eastern Italy provided extensive information on the biology and life-history of these small viviparous snakes. Offspring were relatively large (mean=15 cm total length, 2.9 g) when they were born in late summer, and females grew to maturity (44 cm, 50 g) in approximately 4 years. Larger neonates retained their size advantage for at least 12 months, but did not have a higher probability of survival. Although sexual size dimorphism (at birth and at mean adult body sizes) was minor, the sexes differed significantly in several respects. Females grew faster than males during juvenile life, and adult females diverged in dietary habits from the rest of the population. Whereas juveniles (of both sexes) and adult males fed primarily on lizards, larger females shifted to feeding less frequently, but taking larger prey (mammals and snakes). Reproductive output increased strongly with maternal body size: larger females reproduced more frequently, produced larger litters of larger neonates, had higher relative clutch masses (RCMs), and had a lower proportion of stillborn off-spring. Most females produced a litter every 2nd or 3rd year. We did not detect significant year-to-year variation in reproductive traits over the 5 years of our study. Females were consistent from one litter to the next in several traits (e.g., litter sizes, offspring sizes and shapes, proportions of stillborn neonates, RCMs), but this consistency was due to differences in body size among females rather than to size-independent maternal effects. Overall litter sex ratios averaged 50/50, but sex ratios tended to be more male-biased in litters that were unusually large relative to maternal body size, and in litters containing a high proportion of stillborn offspring. “Costs” of reproduction appear to be high in this population, in terms of both energy allocation and risk. Reproduction reduced growth rates, and females that recovered condition more quickly in the year after reproduction were able to reproduce again after a briefer delay. Mortality was highest in reproducing females with high RCMs, and in females that were very emaciated after parturition. The marked increase in reproductive output with increasing maternal body size in C. austriaca may reflect a reduction in “costs” as females grow larger, and the dietary shift to larger prey may enhance the rate that females can accumulate energy for reproduction.
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