Co-evolution of seed size and seed predation

Using the evolutionarily stable strategy (ESS) approach in a model for the co-evolution of seed size and seed predation, I show that seed size variation within individual plants is favoured if there is a trade-off in the predator's attack rate for different seed sizes. A single seed size is not evolutionarily stable because a predator that is optimally adapted to one particular seed size cannot prevent invasion by plants with a different seed size. The model generates the following predictions. The ESS consists of a continuous range of seed sizes. Small seeds tend to be attacked more frequently than big seeds. Plants with many resources and plants with low (frequency-independent) juvenile mortality have more variable seeds than plants with few resources and a high juvenile mortality. Seed size variation is higher in fluctuating populations regulated by seed predation alone than in stable populations (partially) regulated by seedling competition. Predator searching behaviour does not directly affect the ESS seed size range, but may have an indirect effect by affecting population stability or the significance of seedling competition as a population regulating mechanism. Moreover, seed size distributions are found to be more skewed in favour of small seeds if predation is spatially non-uniform than if predation is more even. Application of the model to systems of several co-evolving plant and predator species is discussed.     

种壳厚度对鼠类种子扩散行为及种子命运的影响

种子扩散是植物更新和扩大分布区的一种重要途径。鼠类采取不同的种子扩散和贮藏策略,以应对食物短缺,同时也促进了植物种子扩散。为应对鼠类对植物种子的过度取食,种子进化出了一系列物理、化学等防御特征。其中种壳厚度作为一种物理防御策略,是影响鼠类贮藏行为和种子命运的关键因素。本研究拟通过去除天然栓皮栎（Quercus variabilis）种子的外壳,再在种仁外包被1、2、4、6不同层数的聚乙烯薄膜,模拟种壳厚度,准确控制种壳厚度。2020年10月—2021年1月,在四川都江堰森林生境中释放人工种壳包被的种子,研究人工种壳厚度对鼠类介导的种子扩散和命运的影响。结果表明：（1）鼠类优先扩散种壳较薄（1层薄膜包被）的人工种子;随着种壳厚度的增加,扩散速率逐渐降低,种壳最厚（6层薄膜包被）的种子扩散最慢（P < 0.001）;（2）鼠类喜好分散贮藏1层、2层薄膜包被的种子;当种壳厚度增加至包被4层、6层薄膜时,分散贮藏比例显著降低（P < 0.05）;（3）鼠类偏好集中贮藏4层薄膜包被的种子（P < 0.05）;（4）不同种壳厚度的种子扩散距离无显著差异（P > 0.05）;（5）种壳较薄（1层薄膜包被）的种子分散贮藏率在3 m范围内比例较高。采用聚乙烯薄膜包被是模拟种子外壳的可行方法,并可用于评估种壳厚度对鼠类种子贮藏行为和种子命运的影响等相关研究。     

Latitude, seed predation and seed mass

Aim We set out to test the hypothesis that rates of pre‐ and post‐dispersal seed predation would be higher towards the tropics, across a broad range of species from around the world. We also aimed to quantify the slope and predictive power of the relationship between seed mass and latitude both within and across species. Methods Seed mass, pre‐dispersal seed predation and post‐dispersal seed removal data were compiled from the literature. Wherever possible, these data were combined with information regarding the latitude at which the data were collected. Analyses were performed using both cross‐species and phylogenetic regressions. Results Contrary to expectations, we found no significant relationship between seed predation and latitude (log₁₀ proportion of seeds surviving predispersal seed predation vs. latitude, P = 0.63; R² = 0.02; n = 122 species: log₁₀ proportion of seeds remaining after postdispersal seed removal vs. latitude, P = 0.54; R² = 0.02; n = 205 species). These relationships remained non‐significant after variation because of seed mass was accounted for. We also found a very substantial (R² = 0.21) relationship between seed mass and latitude across 2706 species, with seed mass being significantly higher towards the tropics. Within‐species seed mass decline with latitude was significant, but only about two‐sevenths, as rapid as the cross‐species decline with latitude. Results of phylogenetic analyses were very similar to cross‐species analyses. We also demonstrated a positive relationship between seed mass and development time across ten species from dry sclerophyll woodland in Sydney (P < 0.001; R² = 0.77; Standardized Major Axis slope = 0.14). These data lend support to the hypothesis that growing period might affect the maximum attainable seed mass in a given environment. Main conclusions There was no evidence that seed predation is higher towards the tropics. The strong relationship between seed mass and latitude shown here had been observed in previous studies, but had not previously been quantified at a global scale. There was a tenfold reduction in mean seed mass for every c. 23° moved towards the poles, despite a wide range of seed mass within each latitude.     

种子特征和结实量对啮齿动物取食和扩散种子行为的影响

为了深入了解啮齿动物在不同种子丰富度条件下对不同大小和单宁含量种子的觅食行为策略及其与植物种群更新的关系,在宁夏六盘山区的华北落叶松人工林,研究了不同大小和单宁含量[0%Tannin(T)、2%T、8%T和15%T]的人工种子在模拟结实小年和结实大年对啮齿动物取食和扩散行为的影响.结果表明: 啮齿动物消耗种子速度在结实小年更快,结实大年的种子消耗速度相对缓慢. 种子就地取食率(ISPR)在不同结实年份间无显著差异,扩散后取食率(PRAD)在结实小年显著高于结实大年,但前者的扩散后贮藏率(HRAD)显著低于后者;种子扩散后的取食距离(PDAD)和贮藏距离(HDAD)在结实小年均显著大于结实大年.在结实小年,大种子的PDAD和HDAD均大于小种子,前者在不同大小种子间均差异显著,而后者仅在2%T和15%T的不同大小种子间差异显著;在结实大年,除0%T外的其他单宁含量种子的PDAD和HDAD在不同大小种子间均差异显著.ISPR在中等单宁含量种子最大,高单宁含量种子最小;PRAD分别在结实小年的高单宁含量种子和结实大年的无单宁种子最大;不论在结实大年还是结实小年,HRAD均在高单宁含量种子最大,中等单宁含量种子最小.这说明结实大年可延缓啮齿动物对种子的消耗速率,提高种子的HRAD,但种子扩散距离减小;啮齿动物在结实大年和小年均表现出对大种子的扩散偏好,且大种子被扩散的距离更远;啮齿动物在不同结实年份均偏好于就地取食中等单宁含量种子,而扩散高单宁含量种子.     

昆虫种子捕食与蒙古栎种子产量和种子大小的关系

为了了解昆虫种子捕食者在栎类种群更新中的作用,于2006年秋季,在黑龙江省伊春市带岭区东方红林场研究了昆虫对蒙古栎Quercus mongolica在参园和东山两个种群的种子蛀食情况及其与蒙古栎种子产量和种子大小的关系。结果表明：(1)在参园和东山两个林分内,蒙古栎种子雨动态非常相似,种子雨成分中完好种子的平均密度仅为3.2±4.1个/m²（参园）和1.7±2.8个/m²（东山）,分别仅占种子产量的4.0％和3.2％,而虫蛀种子和败育种子的比例均在38%以上,以虫蛀种子的比例最高,分别为58.2％和57.7％;(2)柞栎象Curculio arakawai是蛀食蒙古栎种子的主要昆虫种类,在虫蛀种子中所占比例高达96.8％（参园）和97.1％（东山）,且象甲蛀食种子中所含虫卵数与种子大小有关,即种子越大,所含象甲的虫卵数就较多。本研究的结果说明2006年蒙古栎成熟种子多遭遇虫蛀,导致完好种子的数量极低,因而可能成为限制蒙古栎种群更新的重要因素。     

Relationships between indices of seed maturity and carrot seed quality

Carrot seeds cvs Chantenay and Amsterdam were harvested on several occasions from crops grown in 1985 and 1986, from the time they had reached or were close to their maximum dry weight and were starting to turn brown. Maximum seed dry weight occurred approximately 40–45 days after flowering (DAF) in both cultivars. Maximum germination (International Seed Testing Association 14-day count) occurred 40 and 55 DAF in cvs Chantenay and Amsterdam, respectively, but the maximum 7-day count and the minimum coefficient of variation of embryo length did not occur until 60 DAF in cv. Chantenay and 55 to 65 DAF in cv. Amsterdam. Percentage germination was negatively and linearly related to seed moisture content, chlorophyll a + b content in the seed coat and seed distortion, measured on a modified tensile-testing machine, the relationships accounting for 77, 71 and 64% of the variance in the 7-day germination count, respectively. The corresponding values for the 14-day count were 63, 61 and 50%. A simple field test for monitoring seed maturity is proposed.     

Native seed preferences of shrub-steppe rodents,birds and ants: the relationships of seed attributes and seed use

Summary This study established the preferences of shrubsteppe granivores among seeds of 6 common sagebrushsteppe plants and related the preferences observed to physical and nutritional attributes of the seeds. Seeds of big sagebrush (Artemisia tridentata), cheatgrass (Bromus tectorum), Indian ricegrass (Oryzopsis hymenoides), western wheatgrass (Pascopyrum smithii), bitterbrush (Purshia tridentata) and green needlegrass (Stipa viridula) were placed in groups of petri dishes designed such that seed removal could be ascribed to either diurnal vertebrates, nocturnal vertebrates or ants. Though absolute quantities of seeds removed varied among the 3 granivore classes, calculations of preference based on weights of each seed species removed by each granivore class indicated that all 3 ranked the seeds similarly. Preference hierarchies of the 3 granivore classes were highly positively correlated with both calories per seed and % soluble carbohydrate of the seeds. The first correlation supports a basic prediction of optimal foraging theory —that foragers should maximize energy intake per unit time spent foraging. Both correlations emphasize the role of seed nutritional qualities in granivore seed selectivity in that soluble carbohydrate is a water-efficient energy source and its percentage is a good indicator of the digestible energy available in a food item. A corollary experiment comparing granivore use of an exotic seed (millet [Panicum miliaceum]) and a preferred native seed (Oryzopsis) demonstrated a distinct preference for the exotic. Since millet seeds are particularly high in % soluble carbohydrate, this result reinforced the apparent value of this nutritional attribute as a predictor of granivore seed preference. Among many seed resource characteristics upon which granivore seed selectivity might operate, our results indicate that individual species' nutritional composition may be particularly important. Thus, inferences about seed selectivity and resource partitioning among arid-land granivores should be interpreted with caution, especially those based on experiments using seed introductions, since the influence of seed nutritional attributes has not been widely acknowledged heretofore.     

Controls on seed production and seed germinability inEriophorum vaginatum

Controls on seed production in Eriophorum vagina tum were studied at two Low Arctic sites, Latnjajaure in Sweden and Toolik Lake in Alaska. At Latnjajaure, seed production was monitored for 3 years (1993-1995) in control plants and in plants that were experimentally warmed using ITEX open-topped chambers (OTCs). At Toolik Lake, experimental treatments included a factorial greenhouse x NP fertilizer experiment and artificial shading; data collection occurred in 1995, after eight seasons of treatment. Temperature differences between sites, years, and treatments all had significant effects on components of Eriophorum seed production. Pre-flo ration and post-floration times were decreased in warmer treatments and years. Ovule number per inflorescence was greater in warm years and at the warmer site, Toolik Lake. Although seed set was reduced in the OTCs at Latnjajaure, probably due to low pollination rates, in the larger greenhouses at Toolik Lake seed set was increased. The most consistent responses to temperature were in seed weight, where treatment effects were greatest at lower temperatures, such that, for example, at Latnjajaure the increases in seed weight in the OTCs were greatest in the coldest year. Fertilizer treatment had no significant effect on seed number or weight at Toolik Lake, and in the fertilizer + greenhouse treatment there were no inflorescences because Eriophorum had been nearly eliminated from the treated plots. In the shade treatment at Toolik Lake, inflorescences were fertilized but only a single mature seed was collected. Overall, the results indicate that seed production by E. vagina tum is strongly responsive to environmental variation and that only a small increase in mean summer temperatures would result in a much larger and more stable seed production.     

土壤种子库的分类系统和种子在土壤中的持久性

对国际上已经发表的10个土壤种子库分类系统的内容进行了总结和阐述,并对土壤种子库分类系统进行了评述,其中Thompson ＆ Grime在1979年提出的把土壤种子库分为短暂土壤种子库（Transient soil seed bank）和持久土壤种子库（Persistent seed bank）的二元分类系统以及Thompson等人提出的把土壤种子库分为（1）短暂土壤种子库,（2）短期持久土壤种子库（Short term persistent seed bank）,（3）长期土壤种子库（Long termp ersistent seed bank）的三元分类系统在生态学文献中已被广泛采用。在此分类的基础上产生了植物种子在土壤中的持久性（Persistence）概念,持久性是指植物的一种特性,是指植物的种子在土壤中能够存活超过1a的特性;植物种子的持久性被认为是一种对环境的进化适应,它可以在多个生长季节萌发从而分担环境震荡的风险,持久土壤种子库不仅在不稳定的环境里占有优势;即使在稳定的环境里,也被认为能够减少种内和种间的竞争;造成持久性的原因可分为环境因子和种子本身的特性比如休眠等两个方面,持久土壤种子库的出现使得土壤种子库的研究与进化生物学结合起来,使得土壤种子库的研究进入一个新的领域,更易激发人们的兴趣。关于种子的大小、形状及持久性的关系问题已经引起了相当的争论,基本上有4种格局：一是种子大小和形状与种子在土壤中的持久性有关,小而圆或扁的种子在土壤易存活持久;二是种子大小与种子在土壤中的持久性有关,小种子在土壤中易存活持久,但种子形状与持久性无关;三是种子大小、形状与种子在土壤中的持久性无关;四为较大的种子在土壤易存活持久,而种子形状与种子在土壤中的持久性无关。影响种子在土壤中的持久性因子比较复杂,总结过去的文献发现主要有以下几个因子：①种子的散布方式,②捕食,③植被的物种组成,④风,⑤土壤基质,⑥火,⑦干扰等。通过比较分析和研究,提出影响种子大小和在土壤中的持久性关系格局的关键因子是气候,特别是生态系统所在地的雨量;湿润气候下容易产生前两种格局,而干旱环境下的生境容易产生后两种格局。     

Genomic regions affecting seed shattering and seed dormancy in rice

Non-shattering of the seeds and reduced seed dormancy were selected consciously and unconsciously during the domestication of rice, as in other cereals. Both traits are quantitative and their genetic bases are not fully elucidated, though several genes with relatively large effects have been identified. In the present study, we attempted to detect genomic regions associated with shattering and dormancy using 125 recombinant inbred lines obtained from a cross between cultivated and wild rice strains. A total of 147 markers were mapped on 12 rice chromosomes, and QTL analysis was performed by simple interval mapping and composite interval mapping. For seed shattering, two methods revealed the same four QTLs. On the other hand, for seed dormancy a number of QTLs were estimated by the two methods. Based on the results obtained with the intact and de-hulled seeds, QTLs affecting hull-imposed dormancy and kernel dormancy, respectively, were estimated. Some QTLs detected by simple interval mapping were not significant by composite interval mapping, which reduces the effects of residual variation due to the genetic background. Several chromosomal regions where shattering QTLs and dormancy QTLs are linked with each other were found. This redundancy of QTL associations was explained by ”multifactorial linkages” followed by natural selection favoring these two co-adapted traits. Received: 23 November 1998 / Accepted: 27 August 1999     

Effects of seed morphology and orientation on secondary seed dispersal by wind

传播体形态与方位对二次种子风力传播的影响     

Pre-dispersal seed predation and seed limitation in an annual legume

The basic idea of the source simulation technique is to replace the scatterer (or radiator by a system of simple sources located within the envelope of the original body. The extent to which the simulated field reproduces the original field depends on the degree of correspondence between the simulated and the given boundary conditions. Numerical simulations have shown that: (1) the shape of the auxiliary surface, (2) the number of sources, and (3) the way the sources are distributed are the most relevant parameters to ensure an accurate solution for the problem. In the case of the single-layer method, sources should not be positioned close to the center of the body, because the problem becomes ill-conditioned. The auxiliary surface and the scatterer should be as similar as possible in order to minimize the boundary error. With respect to the number of sources (N), there are two opposite effects: (1) if (N) is too small, the sound field is not reproduced accurately; (2) if (N) is too large, computing time increases and solution accuracy decreases. The method beaks down when excitation frequency coincides with the eigenfrequencies — a narrow range of frequencies — of the space formed by the auxiliary surface. As the auxiliary surface is frequently represented by simple surfaces (cylinder, sphere), one can easily calculate the eigenfrequencies and therefore avoid them.

Pollen and seed analogies

Abstract

The dispersal units of plants are seeds but pollen is also dispersed and there are many similarities to be found between these two types of diaspores, especially in their environmental interactions. The economy of natural processes suggests that Nature would not “re-invent the wheel” and indeed there are many similarities, if not identical types of mechanisms, in the metabolic activities of seed and pollen responses to environmental conditions. The main differences regard scale and the responses/mechanisms available to bi-or tri-cellular systems compared to those operating at cytological or organ level. Intriguing parallels are highlighted in this paper without implying homologies.     

Parsnip (Pastinaca sativa) seed production: effects of seed crop plant density, seed position on the mother plant, harvest date and method, and seed grading on embryo and seed size and seedling performance

Parsnip seeds from four years of seed production (1980–83) were used to examine the effects of position of the seed on the parent plant and several cultural factors on seed and embryo growth and seedling performance. Maximum seed dry weight was reached c. 50 days after flowering (DAF) but embryos continued to grow for a further 7–15 days. The coefficient of variation (C.V.) of seed weight fell from c. 35–40% at 40 DAF, to about 20–25% at maturity. The corresponding figures for C.V. of embryo length were 25–35% at the early harvest and 12–15% at maturity. The effects of seed position, plant density, harvest method, seed grading after harvest on seedling emergence and weight characters were small. Harvesting seeds c. 60 DAF gave, on average, 3.3 days earlier emergence, c. 3.6 days lower ‘spread’ of emergence time and c. 9% higher seedling emergence than harvesting 2 wk earlier. Late harvesting of the seed crop reduced the C.V. of seedling weight from 53 to 46%, on average, but there were variations in response from year to year. Seedling emergence and seedling weight characters were more closely related to embryo length than to seed weight characters.     

Telomeres and seed banks

We have found that a progressive loss of telomeric sequences occurs in high molecular weight DNA with an increasing appearance at a low molecular weight as the period of storage in the dry state was extended in time to provide seed germination loss from 98 to 0%. Telomere distribution would appear to follow the general pattern of DNA random fragmentation, which occurs in the embryos of seeds stored in a dry state; however, there are also indications of an overall telomere loss from DNA as a consequence of storage. There is a need for a convenient quality marker for the seeds that can be monitored over time. Having reviewed the implications of our results very carefully, we believe that there is considerable potential for the use of telomere sequences to mark the embryo ageing of seeds held in seed banks. The text was submitted by the authors in English.     

Interspecific patterns of seed selection among granivorous passerines: effects of seed size, seed nutritive value and bird morphology

The relationships between seed characteristics (size and nutrient contents) and bird morphology were investigated in ten species belonging to three specialized families of granivorous passerines. Wild-caught birds were exposed in captivity to a fixed mixture of thirteen seed types before measuring their consumption rates and seed preferences. A multivariate analysis of seed characteristics showed two principal and independent gradients of covariation, namely seed nutritive value and seed size. The smaller the birds, the more nutritive the seeds they selected, this result being largely independent of the family the bird belonged to. The selected seed size was directly related to both the body and bill sizes of the birds, hut these relationships varied between families, most probably as a consequence of interfamilial differences in the structure of the ramphotheca and the associated seed handling method.     

Telomeres and seed banks

We have found that a progressive loss of telomeric sequences occurs from high molecular weight DNA with an increasing appearance at low molecular weight as the periods of storage in the dry state were extended in time to provide seed germination loss from 98 to 0%. Telomere distribution would appear to follow the general pattern of DNA random fragmentation that occurs in the embryos of seeds stored in the dry state, but there are also indications of an overall telomere loss from DNA as a consequence of storage. There is a need for a convenient "equality marker" for the seeds that can be monitored over time. Reviewing the implications of our results very carefully we believe that there is considerable potential in the use of telomere sequences to mark embryo ageing of seeds held in Seed Banks.     

Allometric scaling of seed retention time in seed dispersers and its application to estimation of seed dispersal potentials of theropod dinosaurs

Seed retention time (SRT), the time interval between seed ingestion and defaecation, is a critical parameter that determines the spatial pattern of seed dispersal created by an animal, and is therefore, an essential component of trait‐based modelling of seed dispersal functions. However, no simple predictive model of SRT for any given animal exists. We explored the linkage between animal traits and SRT. We collected previously published data on mean SRT for 112 species of birds, mammals, reptiles and fishes and investigated the general allometric scaling of mean SRT with body mass for each taxon. Moreover, we analysed the effects of food habit and digestive strategy on mean SRT for birds and mammals. In general, mean SRT increased with body mass in all four taxa, whereas the pattern of allometric scaling varied greatly among the taxa. Birds had a smaller intercept and larger slope than those of mammals, whereas reptiles had a much larger intercept and smaller slope than those of either birds or mammals. For birds, food habit was also detected as an important factor affecting SRT. We applied the allometric scaling that was obtained for birds to estimate mean SRT of extinct Mesozoic dinosaurs (Theropoda) – few of which are assumed to have acted as seed dispersers. SRT for large carnivorous theropods was estimated to be 4–5 days, when considering only body mass. The present study provides allometric scaling parameters of mean SRT for a variety of seed‐dispersing animals, and highlights large variations in scaling among taxa. The allometric scaling obtained could be a critical component of further trait‐based modelling of seed dispersal functions. Further, the potential and limitations of the scaling of animal SRT with body mass and a future pathway to the development of trait‐based modelling are discussed.     

Pollination, seed set and seed predation on a landscape scale

We analysed the combined effects of pollination and seed predation on seed set of Centaurea jacea in 15 landscapes differing in structural complexity. In the centre of each landscape, a patch of Centaurea plants was established for standardized measurements of flower visitation, seed predation and seed set. Both the number of flower-visiting bees and the proportion of flower heads damaged by seed predators increased with landscape complexity, which was measured as the proportion of semi-natural habitats. The mean number of seeds per flower head did not increase with the proportion of semi-natural habitats, presumably because of the counterbalancing effects of pollination and seed predation. For a subset of undamaged flower heads, the number of seeds per flower head was positively correlated with the number of flower visits. Further reasons for the unexpected failure to detect a correlation between landscape complexity and seed set appeared to be changes in flower-visitor behaviour and the contrasting responses of honeybees and wild bees to habitat context. Landscape analyses at eight spatial scales (radius of landscape sectors, 250-3000 m) showed that different groups perceived the landscape at different spatial scales. Changes in pollinator numbers could be explained only at small scales (up to 1000 m), while the seed predators also responded to large scales (up to 2500 m).     

The role of seed coats in seed viability

The seed coat is the seed’s primary defense against adverse environmental conditions. A hard seed coat protects the seed not only from mechanical stress but also from microorganism invasion and from temperature and humidity fluctuations during storage. Phenolic compounds in the seed coat contribute to seed hardness and inhibition of microorganism growth. During germination, the seed coat protects the seed from hydration stress and electrolyte leakage.