共查询到20条相似文献，搜索用时 15 毫秒
1.
2.
Recent studies have shown that simplistic measures of toxicity such as the LC50 do not provide enough information about the actual effects that may occur in pesticide-exposed populations over longer time
periods than a few days. In this paper we discuss the use of demography and population modeling for estimation of pesticide
effects on pest and beneficial species and argue that these new approaches are essential to further our understanding of the
potential impacts that pesticides might have on both pest and beneficial species such as biological control agents. 相似文献
3.
Biological invasions are inherently demographic processes, but trait differences between native and introduced genotypes are rarely linked to population growth rates. Native European Centaurea stoebe occurs as two cytotypes with different life histories (monocarpic diploids, polycarpic tetraploids); however, only tetraploids have been found in its introduced range in North America. In a common garden experiment using artificial populations, we compared the demographic performance of the three geo-cytotypes in the presence and absence of a specialist herbivore using periodic matrix models. We found no difference in population growth rate between the two European cytotypes and no significant effects of herbivory in all geo-cytotypes. However, there was a pronounced increase in population growth rate for North American compared with European tetraploids due to increased seed production and juvenile establishment. These results suggest that genetic drift or rapid evolution, rather than pre-adaptation through polyploidy may explain the invasion success of tetraploids. 相似文献
4.
利用生命表理论与人口统计资料 ,模拟台闽地区人口至 2 0 50年的增长。模拟结果显示台闽地区总人数将于 2 0 2 0年至 2 0 2 5年间达到高峰 ,约为 2 3 50～ 2 4 0 0万人。其后则逐渐减少 ,到 2 0 50年可能减少为 2 1 0 0余万至 2 2 0 0余万人。预测出生率逐年显著下降 ,至 2 0 50年时 ,每年每 1 0 0 0人约仅生育 1 0人。男性与女性人口总数的差距有减少的趋势 ;性比率将于 2 0 2 0年至 2 0 3 0年间更接近 1∶ 1。年龄结构的变化趋势显示台闽地区人口逐渐老化 ;65岁以上的老年人口数逐年增加 ,2 0 50年时将超过 1 8%。扶养比于 1 985至 2 0 0 5年间下降 ,2 0 1 0年后则上升。若分别考虑老年人口与幼年人口 ,老年扶养比自 1 985起持续增加 ,而幼年扶养比则先逐年下降 ,至 2 0 1 0年后逐渐趋于稳定 相似文献
5.
6.
Julio Arrontes 《Population Ecology》2021,63(1):123-132
This report explores how the heterogeneity of variances affects randomization tests used to evaluate differences in the asymptotic population growth rate, λ. The probability of Type I error was calculated in four scenarios for populations with identical λ but different variance of λ: (1) Populations have different projection matrices: the same λ may be obtained from different sets of vital rates, which gives room for different variances of λ. (2) Populations have identical projection matrices but reproductive schemes differ and fecundity in one of the populations has a larger associated variance. The two other scenarios evaluate a sampling artifact as responsible for heterogeneity of variances. The same population is sampled twice, (3) with the same sampling design, or (4) with different sampling effort for different stages. Randomization tests were done with increasing differences in sample size between the two populations. This implies additional differences in the variance of λ. The probability of Type I error keeps at the nominal significance level (α = .05) in Scenario 3 and with identical sample sizes in the others. Tests were too liberal, or conservative, under a combination of variance heterogeneity and different sample sizes. Increased differences in sample size exacerbated the difference between observed Type I error and the nominal significance level. Type I error increases or decreases depending on which population has a larger sample size, the population with the smallest or the largest variance. However, by their own, sample size is not responsible for changes in Type I errors. 相似文献
7.
We analyzed the effect of competition on survival‐ and reproduction‐related parameters under two (0.5 · 106 and 1.5 · 106 cells ml—1 of Chlorella) food densities between Moina macrocopa and Ceriodaphnia dubia using the life table demography approach. In general, regardless of the presence of Moina, the average lifespan and generation time were higher for C. dubia. However, rate of population increase (r) and values of reproductive effort were higher for M. macrocopa. The net reproductive values of C. dubia grown alone varied from 7.6 to 36.6 offspring female—1 lifetime—1, depending on Chlorella density. Corresponding values for Moina varied little (16.4 and 17.4 offspring female—1 lifetime—1). Values of gross reproductive rate, net reproductive rate and the generation time of both cladoceran species were higher in mixed cultures than when grown alone. The negative effect of competition was evident for both the cladoceran species, not in their reproductive rates, but in their generation times, and thus population growth rates. The role of competition and facilitation occurring between the two species was discussed in relation to different algal food levels. 相似文献
8.
This study compares demographic parameters and population dynamics for high disturbance (maquis) and low disturbance (rain forest) environments of the montane conifer, Araucaria laubenfelsii, in New Caledonia. The establishment, growth, survival and reproduction of ca 2500 individuals were followed in permanent plots over 10 yr. Growth and survival rates for A. laubenfelsii show that it is a long-lived, slow growing tree, with evidence of suppression in the sapling size classes in mature rain forest. Growth rates for all size classes are generally faster in maquis than rain forest. Transition matrix analyses estimated positive rates of population increase (λ values>1), with populations expanding in maquis, and stable in mature forest. Araucaria laubenfelsii is able to regenerate continuously in maquis and early successional rain forest, but recruitment is limited in older stands. Life table response experiment analyses showed that reproduction, and transitions from sapling to mature tree stage, contributed positively to λ in maquis, but negatively in forest. Araucaria laubenfelsii on Mont Do can be considered a long-lived pioneer, with early maquis colonizers helping to drive succession from maquis to forest. While opportunities for recruitment decline with time as rain forest sites develop a closed canopy, occasional gap phase recruitment, combined with disturbance by cyclones, landslides and fire, provide opportunities to ensure species persistence. Understanding contrasting population dynamics of A. laubenfelsii in maquis and rain forest will better facilitate conservation management of this species, particularly given current high rates of land conversion and degradation in New Caledonia. Abstract in French is available at http://www.blackwell-synergy.com/loi/btp 相似文献
9.
This study used computer models to investigate two different strategies for assessing risk in the development of age‐based life‐tables from studbook data sets. One methodology is similar to that currently employed in American Zoo and Aquarium Association population management, which prorates animals at risk within age‐classes. The other follows the method used in human life‐tables that assumes animals are at risk for the entire age‐class. This study concludes that prorating risk may invalidate population growth projections by significantly and unequally over‐estimating fecundity and mortality rates. This effect is most pronounced in species that have distinct breeding seasons (birth pulse populations), seasonal mortality, and small data sets. Recommendations include using a non‐prorated methodology, tabulating life‐tables using only completely known age‐class data, and combining population parameters for emigrations, releases, and deaths for population growth projections. Zoo Biol 20:279–291, 2001. © 2001 Wiley‐Liss, Inc. 相似文献
10.
Orchids (Orchidaceae) are a family of flowering plants with a high proportion of threatened taxa making them an important focus of plant conservation. Orchid conservation efforts are most effective when informed by reliable demographic research. We utilized transition matrix models to examine the population dynamics and demography within sympatric populations of a species pair of terrestrial round-leaved orchids, Platanthera macrophylla and P. orbiculata. The models were parameterized from a large data set spanning 9 years from field observations of over 1,000 orchids. Life table response experiments (LTRE) were used to identify which life history transitions, and which vital rates within those transitions, most contributed to observed differences between the two species and most contributed to interannual variation within each species. Results from mean transition matrices projected finite rates of population growth that were not significantly different between the two species, with P. macrophylla near the replacement rate and P. orbiculata below it. LTRE revealed that the difference in population growth rates between the two species was mostly due to differences in fecundity (flowering adult to protocorm transition) driven by differences in fruit set and seed germination into protocorm, which were much greater for P. macrophylla. The two primary contributors to interannual variation in population growth rates for both orchids were adult survival and fruit set, respectively. These findings indicate that any environmental disturbances harming adult survival or fecundity will have a disproportionately negative effect on the orchid populations. 相似文献
11.
利用生命表技术对连续3个世代暴露于不同浓度(20、40、80、160、320μg/L和640 μg/L)艾试剂(aldrin)溶液中的多刺裸腹溞(Moina macrocopa)生命表统计学参数进行了研究.结果表明:艾试剂对3个世代多刺裸腹溞所有生命表统计学参数均有显著性影响(P<0.05).与空白对照组相比,浓度高于80 μg/L的艾氏剂使多刺裸腹溞母代的生命期望和净生殖率显著降低;浓度高于160 μg/L的艾氏剂使母代的世代时间显著缩短,种群内禀增长率显著降低.浓度高于40 μg/L的艾氏剂使多刺裸腹溞F1代的生命期望显著缩短,20μg/L和80～640 μg/L的艾试剂使F1代的净生殖率显著降低,320μg/L和640 μg/L的艾氏剂使F1代的世代时间显著缩短,所有浓度的艾试剂均使F1代的种群内禀增长率显著降低.160～640 μg/L的艾氏剂使多刺裸腹溞F2代的生命期望和世代时间显著缩短,160 μg/L和640 μg/L的艾氏剂使F2代的净生殖率显著降低;除40和320 μg/L外,所有浓度的艾试剂均显著提高了F2代的种群内禀增长率.在实验设置的艾试剂浓度范围内,除F2代种群内禀增长率外,3个世代多刺裸腹溞的所有生命表统计学参数均与艾试剂浓度呈曲线相关.在慢性毒性试验中,污染物对多刺裸腹溞生命表统计学参数的影响因其暴露时所处发育时期和持续暴露世代数的不同而存在着重要的差异. 相似文献
12.
Population growth and life table demography of the predatory rotifer A. girodi using spineless Brachionus calyciflorus and spined Brachionus havanaensis as prey at densities of 1, 2, 4 and 8 ind. ml–1 at 25°C were studied. Regardless of the prey species, the population of A. girodi increased with increasing availability of Brachionus in the medium. At any given prey density, A. girodi fed B. calyciflorus showed consistently better growth than when fed B. havanaensis. The maximum population densities of A. girodi varied from 0.28 to 1.8 ind. ml–1 depending on the prey species and the density. The rate of population increase observed in population growth studies varied from 0.17 to 0.43 day–1 when fed B. calyciflorus and 0.09 to 0.27 day–1 when fed B. havanaensis. Male population of A. girodi was closely related to female density. The lowest average lifespan was observed for A. girodi when fed B. havanaensis at 1 ind. ml–1, while the converse was the case when fed B. calyciflorus at comparable prey concentration. Net reproductive rates varied from 16 to 26 offspring female–1 lifespan–1 depending on the prey species and concentration. Generation time of A. girodi decreased with increasing food concentrations for both the prey species. The rates of population increase obtained from life table demography were lower for A. girodi when fed B. havanaensis than when fed B. calyciflorus. 相似文献
13.
Gene flow in crop–wild complexes between phenotypically differentiated ancestors may transfer adaptive genetic variation that alters the fecundity and, potentially, the population growth (λ) of weeds. We created biotypes with potentially invasive traits, early flowering or long leaves, in wild radish (Raphanus raphanistrum) and F5 crop–wild hybrid (R. sativus × R. raphanistrum) backgrounds and compared them to randomly mated populations, to provide the first experimental estimate of long‐term fitness consequences of weedy life‐history variation. Using a life table response experiment design, we modeled λ of experimental, field populations in Pellston, MI, and assessed the relative success of alternative weed strategies and the contributions of individual vital rates (germination, survival, seed production) to differences in λ among experimental populations. Growth rates (λ) were most influenced by seed production, a trait altered by hybridization and selection, compared to other vital rates. More seeds were produced by wild than hybrid populations and by long‐leafed than early‐flowering lineages. Although we did not detect a biotype by selection treatment effect on lambda, lineages also exhibited contrasting germination and survival strategies. Identifying life‐history traits affecting population growth contributes to our understanding of which portions of the crop genome are most likely to introgress into weed populations. 相似文献
14.
Abstract In this work we report on the seasonal trends of abundances in terms of temperature exposure for four coexisting cladoceran species (Daphnia ambigua (Daphniidae), Ceriodaphnia dubia (Daphniidae), Diaphanosoma chilense (Sididae) and Moina micrura (Moinidae)) from a Chilean temperate lake. In order to compare the demographic response to temperature, we used life table experiments to parameterize matrix models for the four species at four fixed temperatures. From these life table response experiments we assessed the effects of temperature, species and their interaction on the variation in growth rate, as well as the contribution of juvenile survival, adult survival, fertility and age at first reproduction to the changes in growth rate. Our results showed interspecific differences in the effect of temperature on the growth rate. Species that present higher field abundance at lower temperature also exhibited, under controlled experiments, higher growth rates at low temperature and lower growth rates at high temperature, relative to the additive model. Conversely, species with higher abundances during the warmer seasons exhibited higher growth rates at higher experimental temperatures and lower growth rates at lower temperatures, relative to the additive model. The vital rates that most contributed to the variation in growth rate were age at first reproduction and fertility. Our growth rate estimates matched predictions of the metabolic ecology model. 相似文献
15.
Ryan D. O'Connell;Daniel F. Doak;Carol C. Horvitz;John B. Pascarella;William F. Morris; 《Ecology letters》2024,27(3):e14417
Life table response experiments (LTREs) decompose differences in population growth rate between environments into separate contributions from each underlying demographic rate. However, most LTRE analyses make the unrealistic assumption that the relationships between demographic rates and environmental drivers are linear and independent, which may result in diminished accuracy when these assumptions are violated. We extend regression LTREs to incorporate nonlinear (second-order) terms and compare the accuracy of both approaches for three previously published demographic datasets. We show that the second-order approach equals or outperforms the linear approach for all three case studies, even when all of the underlying vital rate functions are linear. Nonlinear vital rate responses to driver changes contributed most to population growth rate responses, but life history changes also made substantial contributions. Our results suggest that moving from linear to second-order LTRE analyses could improve our understanding of population responses to changing environments. 相似文献
16.
Williams AL Wills KE Janes JK Vander Schoor JK Newton PC Hovenden MJ 《The New phytologist》2007,176(2):365-374
Species differ in their responses to global changes such as rising CO(2) and temperature, meaning that global changes are likely to change the structure of plant communities. Such alterations in community composition must be underlain by changes in the population dynamics of component species. Here, the impact of elevated CO(2) (550 micromol mol(-1)) and warming (+2 degrees C) on the population growth of four plant species important in Australian temperate grasslands is reported. Data collected from the Tasmanian free-air CO(2) enrichment (TasFACE) experiment between 2003 and 2006 were analysed using population matrix models. Population growth of Themeda triandra, a perennial C(4) grass, was largely unaffected by either factor but population growth of Austrodanthonia caespitosa, a perennial C(3) grass, was reduced substantially in elevated CO(2) plots. Warming and elevated CO(2) had antagonistic effects on population growth of two invasive weeds, Hypochaeris radicata and Leontodon taraxacoides, with warming causing population decline. Analysis of life cycle stages showed that seed production, seedling emergence and establishment were important factors in the responses of the species to global changes. These results show that the demographic approach is very useful in understanding the variable responses of plants to global changes and in elucidating the life cycle stages that are most responsive. 相似文献
17.
SUMMARY 1. Temporary ponds are inhabited by a variety of invertebrates, of which anostracans are an important group. We studied the lifetables of male and female anostracan Streptocephalus mackini at 3 algal concentrations (0.5 × 106 , 1.0 × 106 and 1.5 × 106 cells mL−1 ).
2. Regardless of sex, S. mackini showed better survivorship at lower food levels. The longest average lifespan observed was 85 ± 2 days for males fed Chlorella at 0.5 × 106 cells mL−1 .
3. Both net reproductive rate and generation time decreased with increasing food level. The highest net reproductive rate was about 120 cysts per female. The longest generation time of about 40 days, observed at 0.5 × 106 cells mL−1 , was more than three times that at 1.5 × 106 cells mL−1 .
4. The rate of population increase ( r ) was nearly the same (0.31 ± 0.06) at high (1.5 × 106 cells mL−1 ) and intermediate (1.0 × 106 cells mL−1 ) food levels. The r -value at low food level (0.5 × 106 cells mL−1 of Chlorella ) was 0.20 ± 0.01 per day. 相似文献
2. Regardless of sex, S. mackini showed better survivorship at lower food levels. The longest average lifespan observed was 85 ± 2 days for males fed Chlorella at 0.5 × 10
3. Both net reproductive rate and generation time decreased with increasing food level. The highest net reproductive rate was about 120 cysts per female. The longest generation time of about 40 days, observed at 0.5 × 10
4. The rate of population increase ( r ) was nearly the same (0.31 ± 0.06) at high (1.5 × 10
18.
19.
百草枯和草甘膦对多刺裸腹溞的毒性效应 总被引：2，自引：0，他引：2
采用急性毒性实验方法研究了两种常见除草剂百草枯和草甘膦对多刺裸腹溞(Moina macrocopa)的48hLC50值,应用生命表实验方法研究了亚致死浓度的百草枯(0、0.01和0.04mg·L-1)和草甘膦(0、0.4和1.6mg·L-1)对多刺裸腹溞生命表统计学参数的影响。结果表明:百草枯和草甘膦对多刺裸腹溞的48hLC50值分别为0.626和26.287mg·L-1;百草枯浓度对多刺裸腹溞的生命期望、世代时间、净生殖率和种群内禀增长率有显著影响(P<0.01),草甘膦浓度对多刺裸腹溞的生命期望、世代时间和种群内禀增长率有显著影响(P<0.01),百草枯和草甘膦的交互作用对多刺裸腹溞的世代时间和种群内禀增长率有显著影响(P<0.01)。多重比较显示:当忽略草甘膦的影响时,0.01mg·L-1的百草枯使多刺裸腹溞的生命期望显著延长,而0.04mg·L-1的百草枯则相反,0.04mg·L-1的百草枯使多刺裸腹溞的净生殖率显著降低;当忽略百草枯的影响时,0.4和1.6mg·L-1的草甘膦均使多刺裸腹溞的生命期望显著缩短;与空白对照组相比,0.01mg·L-1的百草枯和1.6mg·L-1的草甘膦混合液使多刺裸腹溞的世代时间显著延长;而0.04mg·L-1的百草枯和0、0.4、1.6mg·L-1的草甘膦混合液均使多刺裸腹溞的世代时间显著缩短,种群内禀增长率显著降低。随着草甘膦浓度的升高,0.04mg·L-1的百草枯对多刺裸腹溞的毒性显著降低,表现出明显的拮抗作用。 相似文献