安徽万佛山自然保护区常见植物种子大小变异

采用样方法收集了安徽万佛山自然保护区常见的206种植物的种子, 通过测量种子千粒重, 研究了种子大小(seed mass, SM)在不同分类水平及生活型间的变异规律。结果表明: 1) SM在植物种间变异较大, 从小到大分为A、B、C、D、E、F、G 7个数量级, SM平均为21.487 g; C级种子(0.1 g ≤ SM < 1.0 g)最多, 共计73种, 占35.4%; D级种子(1.0 g ≤ SM < 10.0g)次之, 共计56种, 占27.2%; 野菰(Aeginetia indica)种子最小, 仅为0.006 g; 木鳖子(Momordica cochinchinensis)种子最大, 重达1775.192 g。2) SM在科间(平均种子大小)存在极显著差异(p < 0.001), 且变异沿系统发育方向呈显著变小趋势(r = -0.079, p = 0.048)。其中, SM较大的5个科分别为葫芦科、柿树科、楝科、安息香科和金缕梅科; SM较小的5个科分别为列当科、兰科、秋海棠科、苦苣苔科和灯心草科。3)该研究中植物的生活型分为8种类型。其中, 多年生草本优势明显, 计83种, 占39.9%, SM变异包括A-E 5个数量级; 一年生草本次之, 计60种, 占28.8%, SM变异包括A-F 6个数量级; 灌木第三, 计34种, 占16.3%, SM变异包括B-F 5个数量级。SM在8种生活型间(平均种子大小)也存在极显著差异(p < 0.001); 从大到小分别为藤本、乔木、灌木、一年生草本、多年生草本、半灌木、一二年生草本、二或多年生草本; 从草本、半灌木、灌木、乔木到藤本, SM与生活型具有极显著的正相关性(r = 0.220, p < 0.001)。4)种类较多的菊科、禾本科、莎草科及蔷薇科, 各科内属间SM也存在极显著差异(p < 0.001)。本研究结果有助于加深对植物生活史对策中的种子大小对策的理解, 提高对森林植被的管理水平, 丰富保育生态学的种子恢复理论。     

Relationship between seed bank expression, adult longevity and aridity in species of Chaetanthera (Asteraceae) in central Chile

BACKGROUND AND AIMS: Broad surveys have detected inverse relationships between seed and adult longevity and between seed size and adult longevity. However, low and unpredictable precipitation is also associated with seed bank (SB) expression in semi-arid and arid areas. The relationship between adult longevity, SB formation, seed mass and aridity is examined in annual and perennial herbs of Chaetanthera (Asteraceae) from the Chilean Mediterranean-type climate and winter-rainfall desert areas over a precipitation range of one order of magnitude. METHODS: Seeds of 18 species and subtaxa (32 populations) were buried in field locations, and exhumed after two successive germination periods. Seeds not germinating in the field were tested in a growth chamber, and remnant intact seed tested for viability. Seed banks were classed as transient or persistent. The effect of life form, species, population and burial time on persistent SB size was assessed with factorial ANOVA. Persistent seed bank size was compared with the Martonne aridity index (shown to be a surrogate for inter-annual variation in precipitation) and seed size using linear regression. ANCOVA assessed the effect of life-form on SB size with aridity as covariate. KEY RESULTS: Three species had a transient SB and 15 a persistent SB. ANOVA revealed a significant effect of life-form on SB size with annuals having larger SB size and greater capacity to form a persistent SB than perennials. Significant inter-population variation in SB size was found in 64% of cases. Seed mass was negatively correlated with persistent SB size. Persistent seed bank size was significantly correlated with the Martonne aridity index in the perennial and annual species, with species from more arid areas having larger persistent SBs. However, when aridity was considered as a covariate, ANCOVA revealed no significant differences between the annual and perennial herbs. CONCLUSIONS: Persistent seed bank size in Chaetanthera appears to reflect environmental selection rather than any trade-off with adult longevity.     

Plant dispersal strategies and the colonization of Araucaria forest patches in a grassland‐forest mosaic

Questions: In a natural grassland‐forest mosaic: What is the influence of phylogeny and diaspore traits related to disperser attraction (DAT) on (1) seed size/number trade‐off (SSNT) in woody species colonizing forest patches; (2) on the frequency of the species? 3. What is the influence of forest patch area on mean seed size and number. 4. Do phylogeny and DAT expressed at the species level affect this relationship? Location: Campos grassland and Araucaria forest in São Francisco de Paula, RS, Brazil, at ca. 29°28’ S; 50° 13’ W. Methods: Forest patches of different sizes in a grassland site recovering for ten years since human disturbances were surveyed by the relative abundance of vertebrate‐dispersed woody saplings. We described colonizer species according to taxonomic phylogenetic relationships and diaspore type, size and color. We analyzed with a variation partitioning method their influence on SSNT and on species frequency in the patches. At the community level we regressed mean seed size and number on forest patch area and evaluated how these relationships were affected by phylogeny and DAT at the species level. Results: 1. Phylogeny and DAT mostly explained seed size and seed number per diaspore variation. 2. By controlling phylogeny and DAT influence the frequency of species in forest patches was positively associated with their seed number in the diaspores, and negatively associated with their seed size. 3. Mean seed size and seed number at the community level were positively associated with patch area. 4. When phylogeny and DAT influences on seed size were removed this relationship was stronger for seed size and weaker for seed number. Conclusions: 1. Energy allocation to dispersal in detriment of offspring survival increased the successful establishment of colonizer species in forest patches, despite phylogenetic relationships and DAT variation in their diaspores. 2. Although patch area exerted a selective pressure on seed size, habitat preferences of dispersers may also influence patch colonization.     

Seed mass and seed nutrient content as predictors of seed output variation between species

In patch‐occupancy models for vegetation, propagule output per area occupied is a key species trait, influencing the potential to colonize vacant patches, and hence species dynamics and coexistence. We estimated seed output across a range of species and quantified its relationship to seed dry mass, seed N and P content, and accessory costs in fruiting structures. Fruiting and seed production data were obtained for 47 woody perennial species, spanning an almost 3000‐fold range of seed mass, over a period of one year in Ku‐ring‐gai Chase National Park, New South Wales, Australia. Seed output was measured as numbers per m² canopy outline and per m² leaf area.
Of cross‐species variation in seed output per m² canopy outline per year, 72% could be predicted from seed mass alone, with a directly inverse relationship (log‐log slope not significantly different from ?1). Seed output per m² leaf area could be predicted somewhat more tightly (75%), indicating leaf area per canopy outline area accounted for some cross‐species variation. Reproductive production per m² occupied per year varied much less than seed mass and accounted for the remaining variation in seed output. Although accessory costs were about equal in magnitude to seed mass as a component of aggregate investment per seed, they were strongly correlated with seed mass, and consequently did not add substantially to the predictive power.
Total mass of N or P per seed were found to be slightly but significantly better predictors of seed output variation than dry seed mass (83% and 78%, respectively). This supports the idea that mineral nutrients are a more fundamental currency for seed production than dry mass. Seed mass, whether measured as dry mass or as N or P, appears to be the principal driver of variation in seed output per m² occupied, and consequently is among the most important dimensions of ecological variation across coexisting species.     

Assessing soil seed bank persistence in flood‐meadows: The search for reliable traits

Abstract. To assess seed bank persistence of target species in endangered flood‐meadows (alliances Cnidion and Molinion), we investigated established vegetation and soil seed bank of 46 plots for 3 yr and 2 yr, respectively. As traits of seed persistence we calculated various continuous indices that refer to the frequency and abundance of species in above‐ground vegetation and at different soil depths. Furthermore, we tested the significance and soundness of easily observed traits such as maximum seed density per plot and seed attributes (mass, size and shape) as predictors of soil seed bank features. In linear regression, SAI, the seed accumulation index, showed the best agreement (R²= 0.64) with the seed longevity index that was derived from the database by Thompson et al. (1997) for a set of 115 species. The second best predictor (R²= 0.39) of the seed longevity index was maximum seed density per plot in the lower soil layer (5–10 cm). Depth distribution indices and seed attributes showed weaker but still significant relations. The dynamic character of flood‐meadows was reflected by a large proportion of species with a strong tendency to accumulate seeds in the soil relative to their importance in above‐ground vegetation. Most of these species have a ruderal strategy, exploiting gaps after flood disturbances, while the dominants of flood‐meadows tended to have short‐lived seed banks. Compared to other grassland types, a relatively large proportion of rare and endangered target species can be expected to form long‐term persistent seed banks. However, only under marginal conditions that facilitate seed survival in the soil (e.g. fallow) are these persistent seed banks likely to contribute to restoration. We conclude that easily observed traits of persistence such as seed weight, size and shape do not meet the accuracy needed in scientific and practical applications. Thus, there is a crucial demand for further seed bank studies in poorly investigated habitats and of rare species.     

Growth-form regulates the altitudinal variation of interspecific seed mass of woody plants in Mt. Dalaoling,the Three Gorges Region,China

Aims Seed size is one of the most important characteristics of plant seeds, and has significant implications in plant ecological functions. Exploring the altitudinal pattern of seed size would help to detect environmental constraints on species distribution and understand the linkage between plant ecological function traits Methods The present study measured the quantitative features of seed size, including weight of 1 000 grain seeds, lengths of longer and shorter axes, and analyzed the relationships between seed size and altitude, as well as the influence of growth form. Seed samples were all collected from 201 locally common woody plants (belonging to 59 families and 87 genera) in the Dalaoling Natural Reserve in Yichang City, Hubei Province.Important findings Measured values of the seed mass, the longer axis, and the shorter axis of the 201 woody plant species all follow the lognormal distribution. Measurements of seed mass vary across five orders of magnitude. Significant correlation was found between seed mass, seed length of the longer and shorter axes (R² = 0.755; 0.819; 0.630, p < 0.01). Moreover, seed mass of trees and small trees are significantly heavier than those of shrubs and woody vines. Seed mass values of evergreen broad leaved species are significantly heavier than those of deciduous broad leaved species and needle leaved species. Seed mass of all 201 species shows a slightly but statistically significant decreasing trend with the increase of altitude. In addition, altitudinal patterns of seed mass varied between species with different growth form. Our results indicated the variation of altitudinal trends of seed mass for different structural components of plant communities, implying the local community structure as a critical aspect of variation in macro-ecological patterns.     

Growth and longevity in freshwater mussels: evolutionary and conservation implications

The amount of energy allocated to growth versus other functions is a fundamental feature of an organism's life history. Constraints on energy availability result in characteristic trade‐offs among life‐history traits and reflect strategies by which organisms adapt to their environments. Freshwater mussels are a diverse and imperiled component of aquatic ecosystems but little is known about their growth and longevity. Generalized depictions of freshwater mussels as ‘long‐lived and slow‐growing’ may give an unrealistically narrow view of life‐history diversity which is incongruent with the taxonomic diversity of the group and can result in development of inappropriate conservation strategies. We investigated relationships among growth, longevity, and size in 57 species and 146 populations of freshwater mussels using original data and literature sources. In contrast to generalized depictions, longevity spanned nearly two orders of magnitude, ranging from 4 to 190 years, and the von Bertalanffy growth constant, K, spanned a similar range (0.02–1.01). Median longevity and K differed among phylogenetic groups but groups overlapped widely in these traits. Longevity, K, and size also varied among populations; in some cases, longevity and K differed between populations by a factor of two or more. Growth differed between sexes in some species and males typically reached larger sizes than females. In addition, a population of Quadrula asperata exhibited two distinctly different growth trajectories. Most individuals in this population had a low‐to‐moderate value of K (0.15) and intermediate longevity (27 years) but other individuals showed extremely slow growth (K = 0.05) and reached advanced ages (72 years). Overall, longevity was related negatively to the growth rate, K, and K explained a high percentage of variation in longevity. By contrast, size and relative shell mass (g mm^?1 shell length) explained little variation in longevity. These patterns remained when data were corrected for phylogenetic relationships among species. Path analysis supported the conclusion that K was the most important factor influencing longevity both directly and indirectly through its effect on shell mass. The great variability in age and growth among and within species shows that allocation to growth is highly plastic in freshwater mussels. The strong negative relationship between growth and longevity suggests this is an important trade‐off describing widely divergent life‐history strategies. Although life‐history strategies may be constrained somewhat by phylogeny, plasticity in growth among populations indicates that growth characteristics cannot be generalized within a species and management and conservation efforts should be based on data specific to a population of interest.     

Seed mass and germination in an alpine meadow on the eastern Tsinghai–Tibet plateau

In this study, we built up a database of 570 species from an alpine meadow on the eastern Tsinghai–Tibet plateau. We examined the correlation of seed mass and germination with phylogeny, habitat and altitude, and the relationship between seed mass and germination. We found that: habitats had no significant effects on seed mass and germinability, which was in accord with the former studies; there was a significant negative correlation between seed mass and altitude, as well as between germinability and altitude, which was opposite to most of the former studies; there was a significant negative correlation between seed mass and germinability, which was in contrast with other studies that have found a positive relationship, and seed mass could explain 24.1% of total variation in germinability; in GLM, family and genus accounted for 43.9% and 83.9% of total variation in seed mass, and 34.1% and 65.4% in germinability, respectively, thus, it was evident that seed mass and germinability were strongly related to phylogeny. We considered that seed mass and germination might be the result of both selective pressures over long-term ecological time and the constraints over long-standing evolutionary history of the taxonomic membership. We suggest that correlates of ecology and phylogeny should be taken into account in comparative studies on seed mass and germination among species.     

Ecological correlates of seed size in the British flora

1. The association between seed size and habitat shade within the British flora was investigated using a data set of seed masses, life histories and quantitative measures of habitat shade for 504 species; the association between seed size and seed longevity was investigated using a data set of seed masses, life histories and seed longevities for 301 species.
2. The data were analysed using the method of phylogenetically independent contrasts (PICs) calculated using the software package CAIC (Comparative Analysis by Independent Contrasts).
3. Seed mass was found to be positively correlated with habitat shade and negatively correlated with seed longevity, after variation owing to life history had been accounted for.     

Ecological niche and phylogeny explain distribution of seed mass in the central European flora

Seed size is a crucial life‐history trait determining the amount of reserves that are available to establishing seedlings. The most frequently observed patterns in seed size distribution are a higher frequency of large‐seeded species in shaded habitats and a positive correlation of seed size with plant size. We analysed to what extent realised niche dimensions, as expressed by Ellenberg indicator values and plant functional traits such as plant height and life form, explained seed mass variation in the central European flora. By including information on phylogenetic relatedness of the species, not only contemporary ecology but also the evolutionary history of plant species could be taken into account. Seed mass evolution was slow and was best explained by selection‐inertia models with multiple adaptive peaks as a function of either habitat or life form. The highest seed mass optima were observed in the deciduous forest and saltwater and seashore habitats, and in phanerophytes in case of models with optima as a function of life form. The analyses showed that Ellenberg values were more important than habitat and life form in explaining seed mass distribution in the central European flora. The often observed relation between shade and large seeds was also evident in our study, but we found an equally important relation between large seeds and drought and a positive relation between seed mass and salinity. Our results indicate that not only plant size and competition for light but a complex set of factors influence the ecology of seed size, and that a more precise delineation of species’ niches improves the understanding of seed size evolution.     

Differential seed germination responses to the ratio of red to far-red light in temperate and tropical species

Variation in vegetation density creates a range of red to far-red ratios of irradiance (R:FR) potentially permitting fine-scale discrimination of light conditions for seed germination. However, remarkably few studies have explored whether R:FR responses of germination vary among species that differ in distribution and life-history traits. In this study, we explored the relationships between R:FR requirements and four species characteristics: seed mass, latitudinal distribution (tropical vs. temperate), seed dormancy (dormant vs. nondormant), and plant growth form (woody vs. nonwoody). We obtained data on germination response to R:FR of 62 species from published literature and added new data for ten species from aseasonal tropical forests in Borneo. First, we analyzed whether species characteristics influenced overall light dependency of germination using phylogenetic logistic regression. We found that seed mass had a strong negative effect on light dependency, but that the seed mass at which tropical taxa had a 50 % probability of light dependency was 40 times that of temperate taxa. For light-dependent species, we found that the threshold R:FR that stimulates 50 % of maximum germination (R:FR₅₀) was also related to seed mass and latitudinal distribution. In agreement with an earlier study, we found that for temperate taxa, the R:FR₅₀ was significantly negatively correlated with seed mass. In contrast, for 22 tropical taxa, we found a significant positive correlation. These opposing relationships suggest contrasting selection pressures on germination responses of tropical taxa (mostly trees) and temperate herbaceous plants, and which are likely related to differences in seed longevity, seed burial rates, and reproductive output.     

Growth-form regulates the altitudinal variation of interspecific seed mass of woody plants in Mt. Dalaoling,the Three Gorges Region China北大核心CSCD

Aims: Seed size is one of the most important characteristics of plant seeds, and has significant implications in plant ecological functions. Exploring the altitudinal pattern of seed size would help to detect environmental constraints on species distribution and understand the linkage between plant ecological function traits. Methods: The present study measured the quantitative features of seed size, including weight of 1 000 grain seeds, lengths of longer and shorter axes, and analyzed the relationships between seed size and altitude, as well as the influence of growth form. Seed samples were all collected from 201 locally common woody plants (belonging to 59 families and 87 genera) in the Dalaoling Natural Reserve in Yichang City, Hubei Province. Important findings: Measured values of the seed mass, the longer axis, and the shorter axis of the 201 woody plant species all follow the lognormal distribution. Measurements of seed mass vary across five orders of magnitude. Significant correlation was found between seed mass, seed length of the longer and shorter axes (R2 = 0.755; 0.819; 0.630, p > 0.01). Moreover, seed mass of trees and small trees are significantly heavier than those of shrubs and woody vines. Seed mass values of evergreen broad leaved species are significantly heavier than those of deciduous broad leaved species and needle leaved species. Seed mass of all 201 species shows a slightly but statistically significant decreasing trend with the increase of altitude. In addition, altitudinal patterns of seed mass varied between species with different growth form. Our results indicated the variation of altitudinal trends of seed mass for different structural components of plant communities, implying the local community structure as a critical aspect of variation in macro-ecological patterns.     

REEXAMINING THE RELATIONSHIP BETWEEN BODY SIZE AND TONAL SIGNALS FREQUENCY IN WHALES: A COMPARATIVE APPROACH USING A NOVEL PHYLOGENY

A negative relationship between cetacean body size and tonal sound minimum and maximum frequencies has been demonstrated in several studies using standard statistical approaches where species are considered independent data points. Such studies, however, fail to account for known dependencies among related species—shared similarity due to common ancestry. Here we test these hypotheses by generating the most complete species level cetacean phylogeny to date, which we then use to reconstruct the evolutionary history of body size and standard tonal sounds parameters (minimum, maximum, and center frequency). Our results show that when phylogenetic relationships are considered the correlation between body size (length or mass) and minimum frequency is corroborated with approximately 27% of the variation in tonal sound frequency being explained by body size compared to 86% to 93% explained when phylogenetic relationships are not considered. Central frequency also correlates with body size in toothed whales, but for other tonal sound frequency parameters, including maximum frequency, this hypothesized correlation disappears. Therefore, constraints imposed by body size seem to have played a role in the evolution of minimum frequency but alternative hypotheses are required to explain variation in maximum frequency.     

Alpine species seed longevity in the soil in relation to seed size and shape – A 5-year burial experiment in the Central Alps

Long-term persistent seeds are generally expected to be small and spherically shaped. In contrast, transient seeds are often large, flattened and elongated. We hypothesized that alpine species follow these trends, and that most species of unstable alpine habitats have the potential to form long-term persistent seed banks. The latter would enable them to delay germination until favourable conditions are present in their environment thereby increasing the likelihood for establishment of seedlings. We selected nine alpine species of more or less unstable habitats (i.e. Achillea moschata, Artemisia genipi, Anthyllis vulneraria ssp. alpicola, Geum reptans, Linaria alpina, Oxyria digyna, Saxifraga aizoides, Saxifraga oppositifolia, and Trifolium pallescens) for this study. Seed longevity was estimated by a 5-year burial experiment in the field with seed excavations after 1 winter, 2 years and 5 years. Germination experiments in the growth chamber and viability tests were performed after each excavation. We detected longevity patterns ranging from transient to long-term persistent. Two species were classified as transient. All other species have the potential to form persistent seed banks, with almost half of the investigated species showing a trend for long-term persistence. Despite contradictory reports, long-term persistent seed banks are an important life history trait of species of unstable alpine habitats. We found that seed shape and hard-seededness are good predictors of seed persistence of alpine species. Seed size seems to be less important. The data from this study support the general hypotheses describing the relationship among seed size, seed shape and seed persistence in the soil.     

古尔班通古特沙漠植物种子大小变异的空间格局

在古尔班通古特沙漠70个固定样地中采集了87种植物种子,通过测量种子百粒重,分析了种子大小在不同分类群中的变异规律,并调查了样地中不同类型种子总数目的空间格局。结果发现:1)古尔班通古特沙漠植物种子大小可分为:A(0.1—1 mg)、B(1—10 mg)、C(10—100 mg)、D(100—1000 mg)、E(1000—5000 mg)5种类型。拥有不同类型物种数量差异较大,其中D型种子物种最多,含41种占总物种数目的 47.1%,其次C型种子30种占总物种数目的 34.5%,E型种子占总物种数的13.8%,B型种子总物种数的3.5%,A型种子占总物种数的1.1%。沙漠植物中中等种子大小物种占多数,与以色列特拉维夫以北的Poleg自然保护区地中海沿岸沙漠地区相似。由于本地属、种为地中海区、西亚至中亚分布,所以认为本沙漠种子大小主要受系统演化影响。2)科间种子大小存在极显著差异,百粒重最大科是蓼科(29315 mg)、最小的是列当科(0.3 mg)。藜科,菊科,紫草科的属间种子大小差异显著。3)生活型间种子大小差异显著,种子大小从大到小排序为:灌木类短命植物多年生草本短命植物半灌木1年生草本。4)种子大小与物种相对分布频度相关性不显著,但将相对分布频度小于1.4%的环境特化物种去除后,种子大小与物种相对分布频度呈指数型极显著负相关。5)B型、C型、D型三类种子在样地中的总数目随海拔、经度和降水的增加而极显著增加,随纬度的增加而极显著降低,E型种子则与之相反。表明古尔班通古特沙漠未来随着降水的增加,B型、C型、D型种子的植物优势性逐渐增加,而E型种子的灌木类等物种优势性逐渐减少,注意加以保护。     

Seed size, shape and vertical distribution in the soil: indicators of seed longevity

1. We investigated the vertical distribution of seeds in the soil, using data from nine studies in five European countries. We discovered significant correlations between seed shape and distribution in the soil.
2. The classification of the longevity of seeds of plant species has been improved by the introduction of a 'longevity index', expressing on a continuous scale the most recent information on seed longevity represented as the proportion of non-transient seed bank records in the database of Thompson et al. (1997 ). Remarkably, no difference in seed longevity was found if the index was based on direct observations only when compared with the index based on the complete data set where indirect, 'depth-derived' observations were included.
3. Seed longevity was best estimated using a multiple regression model with an integrated measure of seed size and shape and depth distribution of seeds.
4. The shape of seeds, known to be a consistent character of species, was shown to be constant within species, whereas depth distribution of seeds was highly variable among sites. This is consistent with the variability of seed longevity found in published seed bank data.     

Seed limitation of woody plants in Neotropical savannas

The failure of seeds to arrive at all suitable sites (seed limitation) greatly affects plant distribution and abundance. In contrast to tropical forests, the degree of seed limitation in Neotropical savannas is unclear because empirical studies at the community level are scarce. We estimated seed limitation of 23 woody species from annual seed rain measurements along a tree density gradient in the savannas of Central Brazil. These savannas differ in tree density and canopy cover, from closed to open savannas, and are located along shallow topographic gradients. We also studied post-dispersal seed predation and removal of 17 representative woody species, and seed viability loss over time of 12 common woody species under dry-storage conditions. Annual seed rain was lower in open (410 seeds/m²) than in closed savannas (773 seeds/m²). Average seed limitation across woody species was higher than 80% along the tree density gradient. More than 60% of seeds of the studied woody species were predated or removed within 30–45 days in all savannah types. Seeds of most common woody species (66%) lost their viability in less than 12 months of dry storage. This study shows that Neotropical savannah woody plants are strongly seed-limited because of low and poor distribution of seeds among sites, post-dispersal seed removal, and short seed longevity. The high seed limitation of tree species in Neotropical savannas, particularly in open savannas, also may contribute to maintain their relatively low tree densities and help to explain the spatial variation of tree abundance along topographic gradients.     

Variation in relative growth rate and its components in the annual Polygonum aviculare in relation to habitat disturbance and seed size

Polygonum aviculare is an annual weedy species showing extensive genetic variation in seed and leaf size and colonizing various types of man-disturbed habitats. A growth analysis was conducted on 12 genotypes representative of three regimes of disturbance of natural habitat (trampling, weeding, and no disturbance in the course of the growing season), grown under productive conditions in order to test whether relative growth rate (RGR) varies at the intraspecific level and, if so, which growth parameters may explain its variation. RGR showed significant genotypic variation (0.355–0.452 g g^-1 day^-1), positively correlated with specific leaf area (SLA) and leaf mass ratio (LMR) and negatively correlated with unit leaf rate per unit leaf area (ULR_A). Thus, the paramount importance of leaf area ratio (LAR=SLA×LMR) in determining growth rate variation between different herbaceous species is confirmed at the intraspecific level in this species. Genotypes originating from trampled habitats had smaller seeds and smaller leaves than genotypes from habitats subject to other disturbance regimes. Additionally, they showed a lower LAR, not entirely compensated for by a higher ULR_A, which resulted in a positive allometric relationship between seed size and RGR. It is hypothesized that their lower SLA, correlated with a higher leaf dry matter content (possibly a consequence of a higher cell wall content per unit leaf area) and their lower LMR have been co-selected with small leaf size as adaptations promoting resistance to trampling stress. It is suggested that variation in cell size and/or gibberellin content might be the mediators of the correlation found between seed size, leaf size and growth parameters within this species.     

Optimal age of sexual maturity and limitations of juvenile survival in mammals

Although the life history evolution of small- and large-bodied mammals seems to be governed by different factors, the both shows relative neonate size and juvenile survival to be slightly dependent on body mass. I propose a hypothesis that natural selection simultaneously maximizes a time to maturity (minimizes somatic growth rate) and a number of newborn survived to reproduction. In this case optimal juvenile survival of large-bodied mammals must be close to e-beta and that of small-bodied approximately e-(1 + beta), where beta is the slope of the regression of log annual fecundity on log annual juvenile mortality. Analysis of vital characters for 71 mammal species revealed the slope to be close to unity. As a result frequency distribution of log juvenile survival shows bimodality which coincides well with predicted optimal survival for large- and small-bodies species. It is shown that the relative neonate size can be directly proportional to the juvenile survival and inversely proportional to the lifetime offspring production irrespective of mortality factors.     

Comparative radiosensitivity in the class insecta.

A “radiosensitivity index” (LT₅₀/mean longevity) was correlated with the mean longevity and dry weight of 37 insect species (both sexes of 12 species) representing eight orders. Curvilinear regression analysis relating radiosensitivity to mean longevity and mean dry weight indicated that 46·3% of the observed variation could be attributed to longevity and 32·6% to the dry weight of the species. In general, large long-lived adults were more radiosensitive than small short-lived adults. Correlation of the phylogeny of insect orders and order groupings with the radio-sensitivity index was found to be poor. However, when the index was related to longevity, there was a tendency for species comprising the major orders investigated to occur in groups along the predicted curve.