Comparative evolutionary ecology of seed size

A seedling's chances of establishing successfully are likely to be affected by the quantity of metabolic reserves in the seed. Seed size is thought to evolve as a compromise between producing numerous smaller seeds, each with few resources, and fewer larger seeds, each with more resources. Seed size varies 10(11)-fold across plant species, so the compromise has been struck at very different levels. These basic ideas have been accepted for 50 years, and many studies have interpreted seed size differences between species by reference to larger seed size being adaptive under a variety of hazards. However, experimental tests of the benefits of large seed size in relation to particular hazards have been rare. More experiments are now being reported, but a consistent picture has yet to emerge. There is typically at least a 10(5)-fold range of seed mass between species even within a single area, suggesting that much seed size variation is evolutionarily associated with other plant attributes.     

The ecology of seeds. * Fenner M, Thompson K. 2005. Cambridge: Cambridge University Press. {pound}26 (softback) {pound}55 (hardback) 260 pp.

This volume is a timely updateand considerable expansion of the small book Seed Ecology, publishedby the first author twenty years ago, and long out of print. Is it useful to separate a particular branch of study such as‘seed ecology’ from the wider field of plant ecology?Aren't seeds just a particular packaged form of the sporophyte,at a certain stage in its life cycle? While some may ask thosequestions, a major strength of this book is the care that theauthors take throughout to set their review in the context ofcurrent ecological     

Regeneration of Cyperaceae, with particular reference to seed ecology and seed banks

Cyperaceae (sedges) are an important component of many ecosystems. To understand better their regeneration, we examined seed ecology, including dispersal, seed characteristics, and germination behavior that relate to seed bank development and persistence. We also evaluated sedge seed banks from 104 studies, representing a wide array of habitats. Sedge seed bank development and persistence were associated with germination and dormancy traits, namely: dormancy level, seasonal dormancy patterns, and requirement for light, alternating temperatures, and aerobic conditions. Interplay of traits appears to have resulted in low-risk germination strategies adapted to exploit infrequent occurrence of gaps and facilitate formation of persistent seed banks. A variety of dispersal modes and morphological adaptations occurred, but many species had no apparent specialized structures. The main dispersal vectors were water and then animals. About 216 species, in 21 genera, were recorded in the seed bank survey. High densities (>50,000 m⁻²) occurred occasionally in wet habitats, but generally values were low (<500 m⁻² in 70% of entries). Species richness was also generally low (mean 4.8 species study⁻¹), but ranged from 10 to 33 species in certain wetlands. Our studies showed varied reproductive strategies within habitats, persistence, and ability of many species to colonize disturbed habitats. Overall, seed banks tended to be persistent (>1 year). Maximum longevity ranged between 10 and 295 years, but for certain species viability was lost in <3 years. Seeds of many sedges occurred in deeper soil layers to depths >1 m. Seed production, low in rhizomatous species, ranged between 0 and 345,000 seeds m⁻² year⁻¹. Amphicarpy or pseudo-viviparous plantlets occurred in limited numbers of species. The relation between seed production, seed rain, and seed bank is largely obscure and awaits further investigation. For successful restoration and species conservation projects, seed banks (or a source of seeds) are necessary, combined with suitable germination and establishment conditions. Future seed bank studies are considered.     

Contribution to the ecology and seed germination ofCucumis callosus

Ecology and germination behaviour of the seeds of two categories ofCucumis callosus Cogn. has been studied here. The seeds were found to be rigid in their requirement of light and temperature for germination. Red and far-red lights were found to affect germination and a phytochrome system appeared to be present. Temperature was found to have a significant effect on seed germination.     

Germination ecology and seed population dynamics of Digitalis purpurea

Summary The germination ecology and the dynamics of the generative reproduction in populations of Digitalis purpurea L. were investigated in the field as well as in experiments. Germination of fresh seeds in the dark on moist filter paper appeared to differ between populations. These differences were eliminated when a moist natural soil functioned as germination substrate. An interaction between the spectral composition of light and the germination substrate was present. Germination in gradients of light, temperature and soil moisture revealed some clear-cut results. Germination proved to be strongly dependent on the percentage of vegetation cover. During two years of burial in litter bags, the number of buried viable seeds did not decrease. From one generation of seeds produced in a natural population, 18% was introduced into the buried seed bank, 10% germinated in autumn and 24% was present as a enforced dormant surface seed bank in late autumn.The results are discussed in relation to secondary succession. can be derived from Milton (1936), Salisbury (1942) and Thompson and Grime (1979). Soil disturbance and germination seem to be correlated in D. purpurea (Grime 1979). The purpose of this study is to analyse the dormancy and germination behaviour of D. purpurea in relation to the relevant environmental factors in order to explain the mechanisms of entry into, and the escape of D. purpurea seeds from a seed bank. Furthermore, an attempt will be made to quantify seed rain as well as the fate of different germinating and non-germinating seed rain fractions in space and time per unit area, in different stages of succession.     

Population ecology of wild sunflowers: effects of seed density and post-dispersal vertebrate seed predators

Assessing the effects of seed density on the population dynamics of wild plant species with crop relatives will be vital in determining the potential effects of introducing traits into wild populations as a result of crop-to-wild gene flow. We examined experimental sunflower (Helianthus annuus) patches in eastern Kansas to determine the effects of seed density and predation on seedling recruitment and seed production in the next generation. High seed density treatment plots had significantly more seedlings and adult plants than did low seed density treatment plots. Overwinter vertebrate seed predator exclusion treatments resulted in increases in plant density compared to plots in which vertebrates were not excluded. Control patches (no seeds added) contained virtually no plants. Head production and estimated total seed production for a patch were not statistically different among treatments (excluding control plots). Although initial seed density and vertebrate post-dispersal seed predation do appear to have effects on seedling recruitment, neither appear to be limiting seed production of competing adult plants. Therefore, variation in seed densities (over the range examined) may have limited effects on local population dynamics. It is important to note that the choice of seed densities may affect the results obtained: the seed densities used in this study may, in retrospect, be higher than in the small roadside populations typical in eastern Kansas, yet other natural sites have much larger densities. Further, the effects of increased seed density at a local site may have other important effects such as altering metapopulation dynamics through increased long-distance dispersal or increased local seed bank size.     

The ecology of the seed in Trapa natans var. Japonica in a eutrophic lake

The production, density and environment of buried seeds and the temperature response of germinating seeds in Trapa natans var. japonica Nakai were ascertained. The mechanism of high reproductivity, tolerance of the plant for eutrophication and the stability of the stand in an eutrophic lake are discussed. The mean fresh weight of seeds was about 7.2 g, and the density of liver and dead seeds in April ranged 66.7 to 80.0 m^-2 and 26.7 to 97.8 m^-2, respectively. The threshold temperature that breaks dormancy and promotes germination in the lake was the low temperature, 8°C. The dormancy of buried seeds was almost broken under the field condition in January. The rate of germination obtained by the field experiment, and the estimation from the density of buried seed and the number of seeds germinated at the stand, were 87% and 60%, respectively. It was estimated that about 30% of the seedlings died before the floating leaf reached water surface. A rosette produced less than three seeds a year, which were fewer than for another Trapa, but the size of the former was larger. The number of seeds changed year by year, but the size-distribution pattern of seeds did not change with years, nor was it affected by the density of rosettes. The reason why T. natans var. japonica could succeed in eutrophic waters was attributed to reproductive strategy. The stand could recover by increasing the number of rosettes through the great branching ability of the main stem, even when the density of buried seeds was greatly decreased in the previous year.     

Impacts of elevated nitrogen inputs on oak reproductive and seed ecology

The effects of increased anthropogenic inputs of reactive nitrogen (N) have been studied at the Harvard Forest Chronic N Experiment, where NH₄NO₃ has been applied experimentally since 1988 to increase atmospheric deposition rates ～6‐ and ～18‐fold above ambient. This paper asks whether conditions favorable to primary production also resulted in plastic increases to flower, fruit, and seedling traits, and focuses primarily on the oaks that dominate the hardwood stands of the Harvard Forest experiment. Litterfall samples collected between 1996 and 2001 revealed that flowers and fruits were significantly more abundant in N‐treated plots, and an analysis of oak tree abundance found significant variation both among and within plots. Acorn samples collected during 2003 and 2004 (a mast and a postmast year) were therefore analyzed using ancova models that included an estimate of oak tree abundance. This tree abundance estimate was the only significant driver of increased acorn production during the mast year, and in both years it was a significant factor on plots receiving the highest levels of N. In the postmast year, acorn production was increased in direct response to N‐related factors other than tree abundance. Our comparisons of control and N‐treated plots for acorn quality traits (e.g. rates of acorn damage, germination percentage, seedling growth) revealed negligible or only transient differences. Shifts in overall acorn abundance – particularly disproportionate N‐mediated increases during nonmast years – could have a wide range of ecological consequences beyond the more frequently examined impacts of N deposition on primary production and carbon sequestration.     

Further studies on seed transmission in the ecology of some aphid-transmitted viruses

A small proportion (1–4%) of the seeds of Stellaria media extracted from fallow soil from three widely separated areas contained cucumber mosaic virus (CMV). S. media seeds buried for 21 months produced 5 % infected seedlings. S. media plants from Britain, N. America and Australia were least severely affected by the CMV strain obtained from their country of origin and showed more severe reactions when infected with two alien strains. Several weed species were experimentally infected with lettuce mosaic, turnip mosaic and cauliflower mosaic viruses but, although virus was detected in the seeds of some species, it was not transmitted to any of their seedlings.