Significance of intra-inflorescence variation on flowering time of a spring ephemeral, <Emphasis Type="Italic">Gagea lutea</Emphasis> (Liliaceae), under seasonal fluctuations of pollinator and light availabilities

I studied the relationship between seed-set patterns within inflorescences and temporal variations in light and pollinator availabilities for 2 years in the spring ephemeral species Gagea lutea in a deciduous forest. Timing of canopy closure and seasonal trend of pollinator frequency did not synchronize with the annual fluctuation in flowering phenology. In the early snowmelt year, seed-set success reflected the seasonal pollinator abundance from early to middle flowering periods. In the late snowmelt year, however, seed-set rates were independent of pollinator activity and decreased with canopy closing even after hand pollination. The restricted seed production by defoliation and the increase in seed-set rates at the forest edge suggested that seed production was supported by current photosynthetic carbon gain. Thus, annual fluctuations of reproductive success can explain the variation in flowering phenology within a population although seasonal light deterioration would serve as a selective force for flowering in the early season.     

Evidence for autonomous selfing in grassland Protea species (Proteaceae)

It has been assumed that species of the large African genus Protea have strong self‐incompatibility systems. However, this assumption was based largely on studies conducted on a clade of bird‐pollinated species that occur in the shrubby fynbos vegetation of the Cape region of southern Africa. To test whether self‐incompatibility occurs in a grassland/savanna Protea clade, which is largely insect‐pollinated, we performed controlled pollination experiments on four species, P. caffra, P. dracomontana, P. simplex and P. welwitschii. Although pollen–ovule ratios of all four species fall within the range for outcrossers, all four species are self‐compatible and capable of autonomous seed production. Using fluorescence microscopy, we found that self‐pollen tubes had the same probability of reaching ovules as cross‐pollen tubes. In the small tree P. caffra, selfed progeny had rates of germination and survivorship that were identical to those of crossed progeny. The grassland Protea spp. studied are likely to have mixed mating systems on account of being both visited by insects and capable of autonomous selfing. If one assumes previous reports of self‐incompatibility in Protea to be reliable, there have been at least five losses of self‐incompatibility and two gains of autonomous selfing in this genus. However, earlier studies in the genus were often methodologically flawed and a thorough re‐analysis of breeding systems in Protea is required. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 169 , 433–446.     

Spatial patterns of tree seedling establishment and their relationship to environmental variables in a cold-temperate deciduous forest of eastern North America

Patterns of seedling recruitment may have persistent effects on population and community processes. Assuming seed availability is not limiting, the environmental sieve (i.e., the suite of factors influencing seed germination and seedling emergence and survival) determines how many seedlings establish and, most importantly, where they do so. In this study, we identify the spatial structure of some resources and abiotic conditions known to be significant for tree seedling emergence and survival and determine how these environmental factors influence the establishment of Fagus grandifolia, Acer saccharum, Fraxinus americana, and Ostrya virginiana in a deciduous forest of southern Québec (Canada). We expect an increase from Fagus, through Acer and Fraxinus, to Ostrya in the control of environmental variables on seedling emergence and survival, because of differences in the seed size of these species. Density of newly-emerged seedlings of all four species showed positive spatial autocorrelation at distances of up to ca. 10 m. Environmental variables were also structured at the same spatial scale, except for soil moisture. Acer seedling emergence pattern was positively correlated to photosynthetic photon flux density (PPFD), and the pattern of Fraxinus to soil N and moisture. Seedling survival was not spatially autocorrelated for any of the four species, although it was positively density-dependent in Acer and Fagus. In only Ostrya was seedling survival correlated (positively) to one of the environmental variables studied, i.e., PPFD. Overall, environmental variables were spatially less heterogeneous than seedling emergence and survival. Either seed availability was not saturating or factors not considered here, such as competition and predation (the intensity of which often varies with resources and/or abiotic conditions), modified the influence that the physical environment had on patterns of seedling establishment. Our prediction of a greater environmental control on seedling emergence and survival in small-seed species was not totally confirmed.     

Seed size: phylogeny and adaptation in two closely related Proteaceae species-pairs

Summary We studied seed size, seed nutrient status and seedling growth of two closely related fynbos Proteaceae species-pairs growing on juxtaposed soils of different nutrient and moisture status. Seeds had a greater mass and higher phosphorus and nitrogen contents for species occurring on limestone (higher nutrient and moisture contents) than those on the colluvial sands (lower nutreints and moisture). This trend was found within, but not across genera, stressing the importance of phylogeny in interpreting adaptations. It would be difficult to test for the effects of either nutrients or moisture separately, since the same advantage of enhanced seedling size, and hence survival in a stressed environment, applies to both factors. The increased root: shoot ratios (using lengths) of the Leucadendron species relative to the Protea species are interpreted as an attempt to overcome a phylogenetic constraint that results in smaller seed size in the former genus.     

Bird and insect pollinators differ in specialization and potential pollination services along disturbance and resource gradients

Combined studies of the communities and interaction networks of bird and insect pollinators are rare, especially along environmental gradients. Here, we determined how disturbance by fire and variation in sugar resources shape pollinator communities and interactions between plants and their pollinating insects and birds. We recorded insect and bird visits to 21 Protea species across 21 study sites and for 2 years in Fynbos ecosystems in the Western Cape, South Africa. We recorded morphological traits of all pollinator species (41 insect and nine bird species). For each site, we obtained estimates of the time since the last fire (range: 2–25 calendar years) and the Protea nectar sugar amount per hectare (range: 74–62 000 g/ha). We tested how post-fire age and sugar amount influence the total interaction frequency, species richness and functional diversity of pollinator communities, as well as pollinator specialization (the effective number of plant partners) and potential pollination services (pollination service index) of insects and birds. We found little variation in the total interaction frequency, species richness and functional diversity of insect and bird pollinator communities, but insect species richness increased with post-fire age. Pollinator specialization and potential pollination services of insects and birds varied differently along the environmental gradients. Bird pollinators visited fewer Protea species at sites with high sugar amount, while there was no such trend for insects. Potential pollination services of insect pollinators to Protea species decreased with increasing post-fire age and resource amounts, whereas potential pollination services of birds remained constant along the environmental gradients. Despite little changes in pollinator communities, our analyses reveal that insect and bird pollinators differ in their specialization on Protea species and show distinct responses to disturbance and resource gradients. Our comparative study of bird and insect pollinators demonstrates that birds may be able to provide more stable pollination services than insects.     

Fungal endophytes of proteaceae, with particular emphasis onBotryosphaeria proteae

Fungal endophytes occurring in leaves and stems of three species of Proteaceae,Protea cynaroides, Leucospermum cordifolium andLeucadendron salignum×laureolum were investigated on farms in three locations in the Western Cape province of South Africa. The aims of this study were to determine ifBotryosphaeria proteae, a fungus that has been recorded from leaf spots ofProtea spp., was mostly restricted to leaf tissue, and whether it could occur as an endophyte in different members of Proteaceae. In this studyB. proteae was routinely isolated inProtea andLeucospermum, although it was not a dominant taxon and did not occur inLeucadendron. Botryosphaeria proteae occurred mostly in leaves, rather than stems, suggesting that it is not important as a stem canker pathogen.     

Coexistence of plant species in a biodiversity hotspot is stabilized by competition but not by seed predation

Understanding the mechanisms of species coexistence is a key task for ecology. Recent theory predicts that both competition and predation (which causes apparent competition among prey) can either promote or limit species coexistence. Both mechanisms cause negative interactions between individuals, and each mechanism promotes stable coexistence if it causes negative interactions to be stronger between conspecifics than between heterospecifics. However, the relative importance of competition and predation for coexistence in natural communities is poorly known. Here, we study how competition and apparent competition via pre‐dispersal seed predators affect the long‐term fecundity of Protea shrubs in the fire‐prone Fynbos biome (South Africa). These shrubs store all viable seeds produced since the last fire in fire‐proof cones. Competitive effects on cone number and pre‐dispersal seed predation reduce their fecundity and can thus limit recruitment after the next fire. In 27 communities comprising 49 990 shrubs of 22 Protea species, we measured cone number and per‐cone seed predation rate of 2154 and 1755 focal individuals, respectively. Neighbourhood analyses related these measures to individual‐based community maps. We found that conspecific neighbours had stronger competitive effects on cone number than heterospecific neighbours. In contrast, apparent competition via seed predators was comparable between conspecifics and heterospecifics. This indicates that competition stabilizes coexistence of Protea species, whereas pre‐dispersal seed predation does not. Larger neighbours had stronger competitive effects and neighbours with large seed crops exerted stronger apparent competition. For 97% of the focal plants, competition reduced fecundity more than apparent competition. Our results show that even in communities of closely related and ecologically similar species, intraspecific competition can be stronger than interspecific competition. On the other hand, apparent competition through seed predators need not have such a stabilizing effect. These findings illustrate the potential of ‘community demography’, the demographic study of multiple interacting species, for understanding plant coexistence.     

The influence of pollinators and seed predation on seed production in dwarf grassland Protea “sugarbushes” (Proteaceae)

Flowers of many plant species are visited by both birds and insects, making it necessary to establish their relative contributions to seed set. In Protea, available evidence points to an overwhelming preponderance of bird-pollination systems in the genus, but the scented flowers of several dwarf grassland “sugarbush” species suggest that some Protea species may be adapted for insect pollination. In this study, we used both selective exclusion of vertebrates and complete exclusion of all visitors to investigate whether the insects that visit the scented flowerheads of three Protea species (Protea dracomontana, Protea simplex and Protea welwitschii) in KwaZulu-Natal, South Africa contribute to seed production. We also performed supplemental hand pollinations to test for pollen limitation. Seed set was generally higher in inflorescences subjected to vertebrate exclusion than in those from which all visitors were excluded, suggesting that fertile cross-pollen was deposited by insects, but these differences were slight because of high levels of self-fertilization in the study species. Pollen deposition and pollen tube growth were similar for vertebrate-excluded and open-pollinated inflorescences. Supplemental hand-pollination treatments revealed that seed set in P. simplex and P. welwitschii was not pollen-limited. Overall seed set was low, typical of the family Proteaceae, and infructescences were highly predated by lepidopteran larvae. We conclude that insects are likely to contribute to seed set of the study species, but further studies using molecular markers are required to establish the actual level of insect-mediated outcrossing.     

Are Protea populations seed limited? Implications for wildflower harvesting in Cape fynbos

Abstract Little is known about the extent to which plant population growth is limited by seed production. We studied two non-sprouting Protea species, both entirely dependent on seeds for recruitment after fire, to determine how flower harvesting would affect the size of the next generation after burning. Five harvesting treatments (0, 25, 50, 75 and 100% inflorescence removal) were applied, each replicated four times in 10 × 10m plots. Seedbanks were censused before a late-summer burn for each species and each replicate. The mean proportion of seeds surviving the burn until germination the following spring was 0.46 for Protea repens and 0.57 for Protea neriifolia. Of the seedlings that emerged, 90% and 55%, respectively, survived the first summer drought. Flower production in the 9 year old stand was strongly related to population density. Optimal plant densities for maximum flower production were estimated as 150 for P. repens and 70 for P. neriifolia. These target densities were greatly exceeded by seedling populations surviving the first summer drought in unharvested stands. If future density-independent mortality is negligible, the excess represents that part of the seedbank that could have been harvested before the burn without influencing future flower production. We developed a simple static model for setting flower harvesting levels in these seed-saturated populations. The predicted harvesting levels (50% of inflorescences in P. repens and 85% in P. neriifolia) were validated against the experimental harvests. We discuss the sensitivity of harvesting levels to variation in fecundity/density relationships, seed survival through a burn and seedling survival until flowering, and the implications for flower harvesting.     

8. THE NIVEN FAMILY VISITS NYASALAND

Species worldwide are threatened due to various factors including habitat transformation and degradation. The Gurney's Sugarbird Promerops gurneyi is a bird species endemic to southern Africa. It is a nectarivorous species that is highly dependent on Protea woodland areas in the eastern parts of southern Africa and makes seasonal migrations between these localities. Although many of these habitats have been destroyed by human development activities, the start of commercial Protea farms in the KwaZulu-Natal Midlands may provide alternative habitat and year-round food resources for sugarbirds. Presence/absence of Gurney's Sugarbird on seven KwaZulu-Natal Protea farms were recorded monthly for one year (2006–2007) and compared to past distributions from 1980 and 1992. Sugarbirds were found to be resident for the entire year on some farms and breeding. The total distribution of Gurney's Sugarbird has extended with the development of Protea farms, as has its seasonal distribution and its breeding range. Our results also highlight the reliance that sugarbirds have on Protea whether indigenous or exotic species. More research on the interactions between Gurney's Sugarbirds and the commercial Protea farms is needed.     

Sugar landscapes and pollinator‐mediated interactions in plant communities

Pollinator‐mediated interactions between plants can play an important role for the dynamics of plant communities. Pollination services depend on the abundance and the foraging behaviour of pollinators, which in turn respond to the availability and distribution of floral resources (notably nectar sugar). However, it is still insufficiently understood how the ‘sugar landscapes’ provided by flowering plant communities shape pollinator‐mediated interactions between multiple plant species and across different spatial scales. A better understanding of pollinator‐mediated interactions requires an integrative approach that quantifies different aspects of sugar landscapes and investigates their relative importance for pollinator behaviour and plant reproductive success. In this study, we quantified such sugar landscapes from individual‐based maps of Protea shrub communities in the Cape Floristic Region, South Africa. The 27 study sites of 4 ha each jointly comprise 127 993 individuals of 19 species. We analysed how rates of visitation by key bird pollinators and the seed set of plants respond to different aspects of sugar landscapes: the distribution of nectar sugar amounts, as well as their quality, taxonomic purity and phenology. We found that pollinator visitation rates strongly depended on phenological variation of site‐scale sugar amounts. The seed set of focal plants increased with nectar sugar amounts of conspecific neighbours and with site‐scale sugar amounts. Seed set increased particularly strongly if site‐scale sugar amounts were provided by plants that offer less sugar per inflorescence. These combined effects of the amount, quality, purity and phenological variation of nectar sugar show that nectar sugar is a common interaction currency that determines how multiple plant species interact via shared pollinators. The responses of pollinator‐mediated interactions to different aspects of this interaction currency alter conditions for species coexistence in Protea communities and may cause community‐level Allee effects that promote extinction cascades.     

Correlated evolution between climate and suites of traits along a fast–slow continuum in the radiation of Protea

Evolutionary radiations are responsible for much of Earth's diversity, yet the causes of these radiations are often elusive. Determining the relative roles of adaptation and geographic isolation in diversification is vital to understanding the causes of any radiation, and whether a radiation may be labeled as “adaptive” or not. Across many groups of plants, trait–climate relationships suggest that traits are an important indicator of how plants adapt to different climates. In particular, analyses of plant functional traits in global databases suggest that there is an “economics spectrum” along which combinations of functional traits covary along a fast–slow continuum. We examine evolutionary associations among traits and between trait and climate variables on a strongly supported phylogeny in the iconic plant genus Protea to identify correlated evolution of functional traits and the climatic‐niches that species occupy. Results indicate that trait diversification in Protea has climate associations along two axes of variation: correlated evolution of plant size with temperature and leaf investment with rainfall. Evidence suggests that traits and climatic‐niches evolve in similar ways, although some of these associations are inconsistent with global patterns on a broader phylogenetic scale. When combined with previous experimental work suggesting that trait–climate associations are adaptive in Protea, the results presented here suggest that trait diversification in this radiation is adaptive.     

Intra- and interspecific reproductive barriers inCrocus (Iridaceae)

The reproductive system was studied inCrocus genus (Iridaceae) following intra- and interspecific pollination, by using light and scanning electron microscopy. The results suggest that the stigma-style tract of theCrocus pistil is a mere promoter of pollen tube growth, while intra- and interspecific discrimination of compatible and incompatible pollen occurs in the ovarian tract. Here, the transmitting tissue consists of special epidermal cells, whose granular or floccular secretions provide the selective medium for the growth of pollen tubes. The ovarian self-incompatibility (SI) is widespread within the genus, resulting in a partial or complete suppression of self-fertilization. Moreover, postzygotic SI mechanisms, as well as postzygotic mechanisms of unknown nature, seem to be recurrent and both are responsible for seed abortion. The interspecific ovarian incompatibility concerns only unrelated crosses; crosses between related fertile species succeed both in fertilization and seed-set.     

Seed mass and summer drought survival in a Mediterranean-climate ecosystem

We related seed mass to summer drought survival in a Mediterranean-climate ecosystem. Previous experimental evidence linking seed mass and survival under drought is limited and at times contradictory. We tracked summer drought survival among four families/subfamilies at a restoration site in southwestern Australia. We coupled these observations with a glasshouse experiment assessing the growth and root morphology of Acacia and Eucalyptus species, with a range of seed masses, under mild and severe drought compared with a well-watered control. Summer drought survival in the field increased with seed mass across all four families/subfamilies. Seedling root biomass and length increased with seed mass consistently across five harvests over 60 days. Initial survival of seedlings in the glasshouse increased with seed mass and decreased with drought, but there was no interaction between the two. Greater absolute root investment provides a mechanism for both short and longer-term drought survival. Within-species variation in root growth may also affect the relative versus absolute survival advantage of large-seeded species. The benefits of large seed mass for establishment under environmental hazards are often considered to be temporary. Our results show that seed mass was correlated with other traits, including root length, which in turn, increased longer-term drought survival. Traits correlated with seed mass should therefore be considered in explanations of the ecological effect of seed mass variation.     

Evidence for beetle pollination in the African grassland sugarbushes (Protea: Proteaceae)

Most lineages in the African genus Protea consist of species with large unscented flowers pollinated principally by birds, and several of these lineages also show evidence of shifts to rodent pollination, associated with concealed yeasty-scented flowerheads. In this study we investigated the hypothesis that brightly coloured and fruity-scented flowerheads of four Protea species (P. caffra, P. simplex, P. dracomontana and P. welwitschii) represent a novel shift from bird to insect pollination in a grassland lineage in the genus. These species are visited by a wide range of insects, but cetoniine beetles were found to be the most important pollinators because of their abundance, size and relatively pure pollen loads. Three of the four putatively insect-pollinated Protea species have flowers presented at ground level, and experiments showed that cetoniine beetles preferred inflorescences at ground level to those artificially elevated to the height of shrubs and small trees. Relative to insects, birds were infrequent visitors to all of the study species. The nectar of all the study species contained xylose, as documented previously in bird- and rodent-pollinated Protea species, suggesting that this is a phylogenetically conserved trait. However, the very low concentration of nectar (ca. 8%), short nectar-stigma distance and the fruity scent of florets appear to be traits that are associated with specialisation for pollination by cetoniine beetles.     

A keystone ant species promotes seed dispersal in a “diffuse” mutualism

In order to understand the dynamics of co-evolution it is important to consider spatial variation in interaction dynamics. We examined the relative importance of ant activity, diversity and species identity in an ant seed dispersal mutualism at local, regional and continental scales. We also studied the determinants of seed dispersal rates and dispersal distances at eight sites in the Eneabba sandplain (29.63 S, 115.22 E), western Australia to understand local variation in seed dispersal rate and distance. To test the generality of the conclusions derived from the eight local sites, we established 16 sites along a 1650-km transect in western Australia, covering 11° of latitude and a six-fold increase in rainfall, at which we sampled the ant assemblage, estimated ant species richness and ant activity and observed the removal rate of myrmecochorous seeds. We also assessed the importance of ant species identity at a continental scale via a review of studies carried out throughout Australia which examined ant seed dispersal. Among the eight sandplain shrubland sites, ant species identity, in particular the presence of one genus, Rhytidoponera, was associated with the most dispersal and above average dispersal distances. At the landscape scale, Rhytidoponera presence was the most important determinant of seed removal rate, while seed removal rate was negatively correlated with ant species richness and latitude. Most ant seed removal studies carried out throughout Australia reinforce our observations that Rhytidoponera species were particularly important seed dispersers. It is suggested that superficially diffuse mutualisms may depend greatly on the identity of particular partners. Even at large biogeographic scales, temporal and spatial variation in what are considered to be diffuse mutualisms may often be linked to variation in the abundance of particular partners, and be only weakly – or negatively – associated with the diversity of partners.     

Effect of three mound-building ant species on the formation of soil seed bank in mountain grassland

The effect of three ant species (Lasius flavus, Formica spp., Tetramorium caespitum) on soil seed bank formation was studied in temperate mountain grassland. Seed removal experiments, analysis of soil seed content and seed survival experiments were carried out to evaluate the influence of ground ants on the seed fate. In the seed removal experiment seeds of 16 species, including 5 species with elaiosome-bearing seeds (myrmecochores), were exposed and their removal followed for 39 h. On average, ants removed 63.8% of myrmecochorous seeds and 10.9% of seeds without adaptation to ant dispersal. Analysis of soil seed content revealed that myrmecochores, in spite of expectations that they would accumulate in nests of seed dispersing ants, were most abundant in the soil of control plots. Evidence on seed relocation to the ant nests was obtained from a comparison of mounds of seed dispersing and seed non-dispersing ant species, as more seeds were found in the mounds of Formica spp. and Tetramorium caespitum (seed dispersers) in comparison with the mounds of Lasius favus (non-disperser).The soil seed bank of the compared microhabitats (control plots and mounds of 3 ant species) differed in their species composition, seed abundance and vertical distribution. The most distinct qualitative differences were between seed flora of control plots and mounds of Tetramorium caespitum. Control plots had approximately 30,000 propagules per m², which was double the number of seeds found in the ant mounds. In control plots, abundance and diversity of seeds steeply declined with depth; this trend was not observed in the mounds probably due to bioturbation. In the seed survival experiment, more seeds (2 out of 3 species) survived in control plots, which may also contribute to the higher seed abundance in this microhabitat.This study showed that seed relocation by ants does not contribute significantly to seed bank build-up at this study site. Ants may, however, increase the regeneration success of myrmecochores, mainly by dispersal for distance and placement in a larger spectrum of microsites, in contrast to species not adapted for myrmecochory.     

贵州省野生皂荚种实表型性状多样性分析

为深入了解贵州省野生皂荚(Gleditsia sinensis)荚果表型性状的遗传多样性及其变异类型,为皂荚的遗传改良、种质鉴定、亲本选择以及品种培育奠定理论基础。该研究以贵州省7个野生皂荚群体70个个体为研究对象,采用方差分析、主成分分析、相关性分析及多性状综合评价等方法对皂荚群体的10个种实表型性状进行系统分析和综合评价。结果显示：(1)所测皂荚的表型性状差异在群体内均达到极显著水平(P＜0.01);在群体间,除每荚粒数、种子宽、种子长宽积以及种子长宽比之外,其余表型性状的差异均达极显著水平(P＜0.01)。(2)7个居群野生皂荚各性状平均变异系数为21.16%,其中凯里市(P4)居群的变异系数最高(24.44%);居群间荚果的变异(29.22%)高于种子的变异(11.04%),且变异主要来自于群体内。(3)相关分析显示,皂荚种实各性状之间存在不同程度的关联性;主成分分析显示,前4个主成分(皂荚种子大小、单个荚果出籽数量、种子形态指数因子、与荚果长和种子厚相关的因子)的累积贡献率达69.783%,可基本反映皂荚表型性状的大部分信息;以10个种实性状对皂荚野生群体进行综合评价发现,来自于惠水县(P7)群体的皂荚种实性状综合评价最高。研究表明,贵州省野生皂荚在群体间及群体内具有丰富的表型变异,且群体内的变异大于群体间的变异,变异主要来自于群体内。     

Importance of fragmentation-tolerant species as seed dispersers in disturbed landscapes

Forest fragmentation can negatively affect plants if animal seed-dispersers become locally extinct in fragments. We conducted a 2-year experiment to evaluate the importance of tree squirrels (Sciurus) as seed dispersers for Quercus, Carya, and Juglans, and to assess dispersal consequences in patches where fragmentation-sensitive eastern gray squirrels (Sciurus carolinensis) are absent. We accounted for fates of ∼15,700 seeds from five tree species in four exclosure treatments at 18 fragments during a high (2003–2004) and low seed (2004–2005) year. Two treatments excluded Sciurus to mimic disperser loss. We sampled nut-tree seedling density at 259 sites across eight watersheds, half of which were too fragmented to support S. carolinensis, but supported fragmentation-tolerant fox squirrels (Sciurus niger). Autumn-to-spring seed survival was low (∼1%) for all species during low seed production. During high seed production, survival was higher for Juglans nigra (20%) and Carya ovata (16%) than for three Quercus species (∼4% for Quercus palustris and Quercus rubra in two exclosure types; ∼1% for Quercus alba in all treatments). Survival of J. nigra, C. ovata, and Q. rubra was ≥2.1–7.7 times higher for seeds in exclosures that Sciurus could access. Seed displacement distance was higher in the low seed than the seed-rich year, but the proportion of seeds surviving to greater distances was higher in seed-rich years for all seed types except Q. rubra. This affirms the importance of masting to seed survival and dispersal, but also suggests an advantage to trees of producing seed in non-mast years. Seedling densities were comparable in watersheds with and without S. carolinensis. These results demonstrate the importance of tree squirrels as dispersers of nut-bearing trees, but suggest that fragmentation may not disrupt dispersal of certain species if losing S. carolinensis from disturbed landscapes is compensated for by fragmentation-tolerant fox squirrels (S. niger).     

Seed size variation in the palm Euterpe edulis and the effects of seed predators on germination and seedling survival

Intraspecific variation in seed size is common in wild plant populations and has important consequences for the reproductive success of individual plants. Multiple, often conflicting evolutionary forces mediated by biotic as well as abiotic agents may maintain such a variation. In this paper we assessed seed size variation in a population of the threatened, commercially important palm Euterpe edulis in southeast Brazil. We investigated (i) how this variation affects the probability of attack by vertebrate and invertebrate post-dispersal seed predators, and (ii) if seed size influences the outcome of seeds damaged by beetles in terms of seed germination and early survival of seedlings. Euterpe edulis seeds varied in diameter from 8.3 to 14.1 mm. Neither insects nor rodents selected the seeds they preyed upon based on seed size. Seed germination and total, shoot and root biomasses of one-year seedlings were significantly and positively affected by seed size. Root biomass and seedling survival were negatively affected by seed damage caused by a scolytid beetle (Coccotrypes palmarum) whose adults bore into seeds to consume part of the endosperm, but do not oviposit on them. Seed size had a marginally significant effect on seedling survival. Therefore, if any advantage is accrued by E. edulis individuals producing large seeds, this is because of greater seed germination success and seedling vigor. If this is so, even a relatively narrow range of variation in seed size as observed in the E. edulis population studied may translate into differential success of individual plants.