Responses to the timing of damage in an annual herb: Fitness components versus population performance

The timing of damage plays an important role in plant fitness but its effect on population performance has received relatively little attention. I examined the effect of the timing of damage on nine components of fitness and population performance in four populations of the annual Melampyrum pratense by clipping plants at the vegetative stage (early clipping) or at the beginning of the flowering period (late clipping). I estimated population performance using a matrix population model that predicts the long-term population growth rate, λ. In early clipping, the plants were usually able to compensate for the damage during the growing season. In consequence, early clipping reduced λ in only one out of four populations, whereas late clipping reduced it in three populations. The elasticity analyses revealed that the relative importance of different demographic transitions to λ varied among the populations. This among-population variation in the sensitivities of λ to demographic transitions makes it difficult to use changes in specific fitness components as a measure of population performance for annual plants with a seed bank. The current study illustrates that although early-season damage may have a negligible impact on population dynamics in annual plants, the effect of the timing of damage often varies among populations.     

Conservation prospects for threatened Vietnamese tree species: results from a demographic study

Given that changes in population size are slow, information on future prospects of long-lived tree species is necessarily obtained from demographic models. We studied six threatened tree species in four Vietnamese protected areas: the broad-leaved Annamocarya sinensis, Manglietia fordiana and Parashorea chinensis, and the coniferous Calocedrus macrolepis, Dacrydium elatum and Pinus kwangtungensis. With data from a 2-year field study on recruitment, growth and survival, we constructed matrix models for each species. All species showed continuous regeneration, as indicated by annual seedling recruitment and inverse J-shaped population structures. To evaluate the future prospects of our study species, we calculated three parameters: (1) asymptotic growth rates (λ) from matrix models indicated significant population declines of 2–3%/year for two species; (2) population trajectories for 50–100 years showed slight population declines (0–3%/year) for five species; and (3) the reproductive period required for an adult tree to replace itself was excessive for three of the six species, suggesting that these species presently have insufficient recruitment. Overall agreement of the three parameters was low, showing that reliance on just one parameter is risky. Combining the three parameters we concluded that prospects are good for Dacrydium and Parashorea, worrisome for Annamocarya, Manglietia and Pinus, and intermediate for Calocedrus. We argue that conservation should involve strict protection of (pre-)adult trees, as their survival is crucial for population maintenance in all species (high elasticity). For species with poor demographic prospects, active intervention is required to improve seedling and tree growth, enrich populations with seedlings from controlled germination, and restore habitat. Finally, our study suggests that these conservation measures apply to long-lived trees in general, given that their demography is highly similar. Such measures should be taken before populations decline below critical levels, as long-lived species will respond slowly to management. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

用matK序列分析探讨木兰属植物的系统发育关系

用木兰科Magnoliaceae 57种植物的matK基因序列构建了该科的系统发育分支图。结果表明: (1)木兰属Magnolia L.是一个因为性状的趋同演化而建立的多系类群; (2)木兰亚属subgen. Magnolia和玉兰亚属subgen. Yulania (Spach) Reichenb.亲缘关系较远, 支持将后者从该属中分出建立玉兰属Yulania Spach, 木兰亚属作为木兰属保留; (3)木兰亚属的sect. Splendentes Dandy ex Vazquez组与皱种组sect. Rytidospermum Spach的两个美洲种M. macrophylla Michaux和M. dealbata Zucc.亲缘关系较近, 荷花玉兰组sect. Theorhodon Spach与常绿组sect. Gwillimia DC.的亲缘关系较近; (4)盖裂木属Talauma Juss.可以成立, 而其分布于亚洲的Blumiana Blume组可归入木兰属; (5)拟单性木兰属Parakmeria Hu &; Cheng、华盖木属Manglietiastrum Law以及单性木兰属Kmeria (Pierre) Dandy形成一个单系群, 与玉兰亚属和含笑属Michelia L.的亲缘关系较近。花的着生位置不足以作为木兰科的分族依据, 含笑族Michelieae和木兰族Magnolieae的特征及其界定应做修改。将玉兰亚属从木兰属分出后, 木兰属与含笑属无性状交叉,成为两个区别明显的属。     

Population dynamics of Mammillaria magnimamma Haworth. (Cactaceae) in a lava-field in central Mexico

One of the habitats occupied by Mammillaria magnimamma is a 2000-year old lava-field, in Mexico City. The great ecological interest on this lava-field and the little knowledge there is regarding cacti population ecology have compelled us to analyse the demography of this species to evaluate its present conservation status at this site. We studied two populations of this species within the lava-field: one in a disturbed site (i.e., recently burned) and another one in a well preserved site. For each population we built two size-based population projection matrices (1996/97 and 1997/98). Demographic data were gathered directly from observations of plant fates from one year to the next. Additionally, seed germination and seedling establishment experiments were carried out in the field to estimate fecundity values and seedling survival probabilities. The four matrices built were used to perform numerical analyses simulating yearly stochastic demographic variation to project the overall population's long-term behaviour under these changing conditions. Three of the four matrices showed λ values slightly below unity. In these cases elasticity values were highest for matrix entries corresponding to plants remaining in their same category. The matrix that showed a λ value above unity (well preserved site, 1997/98) had higher elasticity values for entries referring to seedling survival and growth. The numerical simulations of demographic stochasticity showed that the population appears to be growing at a slow rate. According to the simulation results, the variation in overall population size over time may be accounted for by yearly variation in seed germination and seedling survival. Population persistence probability might decrease significantly if fire frequency increases. This revised version was published online in August 2006 with corrections to the Cover Date.     

Variation in the components of relative growth rate in 10 Acacia species from contrasting environments

In this study we assessed the inherent relative growth rate (RGR) under controlled environment conditions of 10 contrasting Acacia species from semi-arid and mesic environments. For several of the species, compound pinnate leaves produced early in the seedling stage, were gradually replaced by phyllodes (expanded petioles that form simple lamina). Other species either did not form phyllodes, or only did so to a minor degree by the end of the study. Phyllode production was dominant in the four slow-growing Acacia species from semi-arid environments (A. aneura, A. colei, A. coriacea and A. tetragonophylla), with leaf production being exclusive or dominant in five (A. dealbata, A. implexa, A. mearnsii, A. melanoxylon and A. irrorata) of the six faster-growing species from mesic environments. The exception was A. saligna which was fast growing but did produce phyllodes. From a carbon economy perspective, slow growth in the semi-arid species was not associated with lower net assimilation rates or less plant mass allocated to foliage. Rather, the primary factor associated with their slow growth was a smaller foliage area per unit foliage mass. This was true for comparisons based on the mean over all harvests or at set plant masses. The production of phyllodes by the semi-arid species substantially reduced foliage area per unit foliage mass, as this was lower for phyllodes than leaves in all species. To assess the impact that phyllode production had on ontogenetic changes in RGR, we modelled the situation where only leaves were formed. This analysis showed that changing from leaves to phyllodes substantially reduced the RGR. There was little difference in plant nitrogen concentration or the ratio of foliage nitrogen to plant nitrogen between the species. This resulted in foliage nitrogen productivity (dry mass gain per unit foliage nitrogen and time) being directly proportional to foliage area per unit foliage mass between species. We concluded that a smaller foliage area per unit foliage mass and phyllode production are the primary factors associated with lower RGR in contrasting Acacia species.     

Nucleotide diversity and demographic history of Pinus bungeana,an endangered conifer species endemic in China

Orographic and climatic oscillations have played crucial roles in shaping the nucleotide diversity and evolutionary history of many species across the Northern Hemisphere. In this study, based on 10 nuclear loci and a chloroplast DNA marker, we analyzed the nucleotide polymorphisms and demographic history of the endangered conifer species Pinus bungeana in Northwest China and investigated the phylogenetic relationships between P. bungeana and two related species, that is, Pinus gerardiana and Pinus squamata. We found that P. bungeana exhibited an extremely low level of nucleotide diversity (π_sil = 0.00159). Demographic simulations based on DIYABC analysis showed that P. bungeana underwent demographic expansion and contraction during the Miocene. According to ecological niche modeling, we found that this species survived in situ during the glacial period and was not restricted to southern refugia. We speculate that P. bungeana may have experienced widespread population shrinkage from the Last Interglacial to the Last Glacial Maximum due to geological or climatic events. Isolation‐with‐migration analysis revealed that the divergence (~2.4–4.2 Ma) among P. bungeana and its related species was significantly associated with the Qinghai–Tibetan Plateau uplift events in the mid‐to‐late Tertiary period. Species tree analyses suggested that these three related Pinus species formed a monophyletic clade with high bootstrap support. These results suggest that the Miocene–Pliocene and Pleistocene geological and climatic fluctuations might have profoundly affected the nucleotide diversity and demography of this psychrotolerant conifer species in western China.     

Evaluation of terminal-restriction fragment length polymorphism analysis in contrasting marine environments

Terminal-restriction fragment length polymorphism (T-RFLP) analysis is widely used in microbial ecology studies. In the present study, T-RFLP analysis of PCR products digested by five restriction enzymes (AluI, HaeIII, MspI, Sau3AI and TaqI) was applied for 20 samples from three contrasting coastal environments to assess the biases associated with the choice of enzyme digestion and T-RF analysis. The five enzyme digestions produced highly variable species richness (in terms of number of T-RFs). Analysis of peak areas with a threshold of 0.5% of the total peak area, which recovered 92-96% of the total peak area, revealed different diversity indexes from the five enzyme digestions. Multidimensional scaling, based on matrices that were generated by scoring peak presence/absence and area, revealed similar bacterial community structure patterns among the 20 samples, regardless of the choice of restriction enzymes. Our results strongly argue that the choice of different digestion enzymes in the T-RFLP technique generated valid and consistent bacterial community structures but highly variable species richness and diversity indices. The biases associated with the choice of digestion enzymes needs to be evaluated carefully or at least to be addressed when using T-RFLP analysis.     

The plasticity of the germinative response in the populations of two xeric species inhabiting two contrasting environments of central Mexico

The species' germination response evolves based on its population environment; therefore, the responses of each local population evolve independently. We investigated two xeric species from central Mexico, Echeveria gibbiflora and Penstemon campanulatus, the populations of which inhabit two localities (Reserva Ecológica del Pedregal de San Ángel [REPSA] and Parque Ecológico de la Ciudad de México [PECM]) that differ in environmental conditions. For both species and populations, final germination, cardinal temperatures, thermal time and range of temperature for germination (RTG) were determined in seeds that were (a) collected recently, (b) stored in a laboratory for 2 months and (c) reciprocally buried in field conditions for 2 months. The results indicated that for both species, seed population, laboratory storage and temperature were significant for final germination. These responses indicated differences in germination based primarily on the site in P. campanulatus (PECM seeds germinated at higher percentages than REPSA seeds) and the burial site in the REPSA seeds of E. gibbiflora. Cluster and discriminant analyses were conducted for both species, identifying the following significant variables for group treatments: base temperature between the stored and buried seeds of E. gibbiflora and the ceiling temperature between the recently collected, stored and buried seeds of P. campanulatus. The results suggest that instead of seed population, burial (in both species) and laboratory storage (in P. campanulatus) narrowed the RTG. These responses could indicate plasticity in both germination and dormancy in response to environmental conditions experienced in the different habitats, which are crucial for understanding species' adaptive capacity.     

不同种源厚朴苗期性状变异及主成分分析

基于厚朴（Magnolia officinalis）作为一种传统中药植物及分布区域广、环境异质化程度明显的现象,采用田间种源实验,对分布在中国7个省的14个种源厚朴苗期的生长性状进行了观测分析。结果表明,不同种源厚朴的苗期生长性状差异显著。种源遗传力分析表明,苗高和单株叶面积两个性状的遗传力较高,分别为0.93、0.79,可认为以苗高和单株叶面积为主的种源多性状综合选择改良潜力巨大。相关性分析表明各性状间遗传相关、表型相关、环境相关均存在一定的相关关系,单株叶面积和地上部生长性状的遗传相关程度高于地下部生长性状,表型显著相关的性状组合数量和程度低于遗传相关。厚朴苗期种源选择的首选因子为各生物量及单数叶面积性状,辅助因子为苗高和地径。通过系统聚类分析,初步选定景宁、武夷山、龙胜、开县、城固、宁强及洋县的种源为优良厚朴种源。     

A demographic analysis of skeletons from the Larson site (39WW2) Walworth County,South Dakota: Vital statistics

A life table methodology was used for paleodemographic analysis of skeletons from the Larson site (39WW2), an Arikara village and cemetery dated to circa A.D. 1750–1785. Vital statistics on mortality, survivorship, age-specific probability of death, life expectancy and crude mortality rate were derived from skeletal data. The population had an extremely high infant mortality rate and high rates of childhood mortality. The lowest probability of death was for adolescents. Mortality increased for young adults, ages 15–19. This increase was especially marked for females, the actual peak of adult female mortality was during ages 15–19. A second mode in the female mortality curve occurred at ages 35–39. The greatest percentage of male deaths was observed in the fourth decade, ages 30–34. Only 4.0% of the population attained the age of 50. The population crude death rate was 76 per thousand per year. This estimate, although high, is congruent with archaeological and historical sources which report a rapid Arikara population decline during the Post-Contact period. Causes of specific deaths appear to be linked to childbirth (affecting mother and infant), starvation, diseases especially tuberculosis, and intertribal warfare.     

Floristic diversity of sabal palmetto woodland: an endemic and endangered vegetation type from Mexico

The sabal palmetto woodland is a tropical plant formation dominated by Sabal mexicana, with restricted distribution to southeast Mexico. Sabal palms grow on poor soils but accumulate large quantities of organic substrate in their crowns, harboring a contingent of plants that use it as phorophyte. Although it is a threatened formation, basic information on its biodiversity is scant. We examined the floristic diversity of recruited (diameter at breast height, DBH, ≥1 cm) and understory (DBH ≤ 1 cm) plants, and its variation with anthropogenic disturbance. We also examined the floristic diversity of plants that use the sabal palms as phorophytes, and assessed its variation with human impact. All plants present in transects within a conserved and an adjacent perturbed area were sampled. The list of observed taxa shows that this vegetation has a clear affinity with tropical dry and wet forests of Mexico, with a small representation of taxa from desert ecosystems. The floristic contingent included a total of 81 species in 2000 m². Richness, composition and diversity were affected by disturbance. Recruited and understory vegetation in the disturbed site were 5- and 1.6-times less diverse than in the conserved site, and species of mature, conserved vegetation were substituted by heliophytes in the disturbed site. In contrast, abundance of palms and diversity and identity of epiphytic/hemiepiphytic plants were not affected by disturbance. We show that even monodominated tropical ecosystems growing on poor soils have a high floristic diversity and that current anthropogenic impact threatens not only species and populations but also entire plant formations.     

Detecting and managing an overgrazing-drought synergism in the threatened <Emphasis Type="Italic">Echeveria longissima</Emphasis> (Crassulaceae): the role of retrospective demographic analysis

Echeveria longissima, a threatened herb whose habitat has been severely overgrazed and eroded, was studied for three years in a currently grazed and a fenced area. Matrix population models were used to assess if livestock elimination provides a proper management strategy. The merits of retrospective perturbation analyses in terms of management planning have been debated. Nevertheless, they may prove useful when applied in combination with exclosures because they may detect the effects of anthropogenic disturbance on population dynamics. Thus, the results of retrospective and prospective methods were compared. A rapid decrease in population size was projected in both areas, even though it was faster in the exposed one. The demographic processes that were favourable or detrimental in a given year were magnified outside of the fence, but buffered in the exclosure, showing a strong drought-disturbance synergism. Thus, the largest difference in the population growth rate λ between areas was observed in the driest year. Higher nurse-plant density inside the fence seems to alleviate drought effects. The use of prospective analysis alone may lead to erroneous management decisions, since the highest elasticities corresponded to transitions that were favoured by human activities. While allowing for an increased λ in the short term, intervention aimed at increasing these transitions further without attending others that are lessened by disturbance may introduce large changes in the population dynamics, with negative long-term consequences. Retrospective methods can detect which processes have been altered by disturbance and its synergisms, so we may more efficiently restore healthy population dynamics.     

An analysis of species response curves and of competition from field data: Some results from heath vegetation

The variation in species composition of plant communities has been described by means of the Gaussian distribution (relations between plant populations and environmental variables) and by linear equations (mutual interference between mixed populations). An important presupposition is the existence of a theoretical population, covering 100% of the soil surface. A numerical approximation of the parameters can be obtained by means of an iterative procedure. This technique has been applied to heath vegetation. A small sample has been used to demonstrate the algorithm. The cover ofCalluna vulgaris, Erica tetralix andMolinia caerulea could be explained to a large extent from phosphate and ground water table. A comparison of the results with those of experiments by other authors showed a reasonable similarity. The linear coefficients of interference as means to describe relations between mixed plant populations in a local area have been evaluated by means of dynamic simulation.     

Root system analysis of seedlings of seven tree species from a tropical dry forest in Mexico

Summary Root attributes of tree seedlings of seven species from the tropical deciduous forest along the Pacific Coast of Mexico are described using morphometirc root system analysis. Mean relative growth rate, root/shoot ratios, specific root length, root density, mean number of roots tips and root length/leaf area ratio were determined in seedlings grown for 35 days inside growth chambers. All the species had low relative growth rates, low root/shoot ratios and low root densities (<0.5 cm/cm³). The species associated with disturbed habitats, in contrast to the species characteristic of undisturbed areas, presented small seeds, a dichotomous root branching pattern and large specific root length. No relationship was found between seed size and mean relative growth rate among the species studied.     

A life‐history perspective on the demographic drivers of structured population dynamics in changing environments

Current understanding of life‐history evolution and how demographic parameters contribute to population dynamics across species is largely based on assumptions of either constant environments or stationary environmental variation. Meanwhile, species are faced with non‐stationary environmental conditions (changing mean, variance, or both) created by climate and landscape change. To close the gap between contemporary reality and demographic theory, we develop a set of transient life table response experiments (LTREs) for decomposing realised population growth rates into contributions from specific vital rates and components of population structure. Using transient LTREs in a theoretical framework, we reveal that established concepts in population biology will require revision because of reliance on approaches that do not address the influence of unstable population structure on population growth and mean fitness. Going forward, transient LTREs will enhance understanding of demography and improve the explanatory power of models used to understand ecological and evolutionary dynamics.