Directed vertebrate-mediated seed dispersal of a fleshy-fruited amaryllid in a heterogenous habitat

Most plants with fleshy fruits have seeds that are ingested by animals, but a less well-understood mode of seed dispersal involves fleshy fruits containing seeds that are discarded by frugivorous animals because they are too large or toxic to be ingested. We studied the seed dispersal biology of Haemanthus deformis, an amaryllid lily species found in a mosaic of bush clumps in a grassland matrix in South Africa. We asked whether seed dispersal is directed in and among bush clumps and whether germination and survival are greater for seeds dispersed to bush clumps than for those dispersed into grassland. Using camera trapping, we found that fruits are consumed mainly by birds and rodents. The pulp was removed from the seeds which were then discarded without ingestion. While many seeds were dispersed close to the parent plant, most (c. 78.5%) were dispersed further than 1 m away from the parent plant. Longer distance dispersal resulted mainly from birds flying off with fruits in their bill or from rodents engaging in scatter-hoarding behavior. Seedling survival was most successful within bush clumps as compared to grasslands and shade was identified as a primary requirement for seedling survival. Seeds from which the fruit pulp had been removed germinated faster than those in intact fruits. Haemanthus deformis deploys a system of directed seed dispersal, whereby both birds and rodents contribute to the dispersal of seeds within patchy bush clumps that are favorable for seedling survival.     

Secondary seed dispersal by ants in Neotropical cerrado savanna: species‐specific effects on seeds and seedlings of Siparuna guianensis (Siparunaceae)

1. Most woody plant species in tropical habitats are primarily vertebrate‐dispersed, but interactions between ants and fallen seeds and fruits are frequent. This study assesses the species‐specific services provided by ants to fallen arillate seeds of Siparuna guianensis, a primarily bird‐dispersed tree in cerrado savanna. The questions of which species interact with fallen seeds, their relative contribution (versus vertebrates) to seed removal, and the potential effects on seedling establishment are investigated. 2. Seeds are removed in similar quantities in caged and control treatments, suggesting that ants are the main dispersers on the ground. Five ant species attended seeds. Pheidole megacephala (≈0.4 cm) cooperatively transported seeds, whereas the smaller Pheidole sp. removed the seed aril on spot. Large (> 1.0 cm) Odontomachus chelifer, Pachycondyla striata, and Ectatomma edentatum individually carried seeds up to 4 m. Bits of aril are fed to larvae and intact seeds are discarded near the nest entrance. 3. Overall, greater numbers of seedlings were recorded near ant nests than in control plots without nests. This effect, however, was only detected near P. megacephala and P. striata nests, where soil penetrability was greater compared with controls. Soil nutrients did not differ between paired plots. 4. This study confirms the prevalence of ant–seed interactions in cerrado and shows that ant‐derived benefits are species‐specific. Ant services range from seed cleaning on the spot to seed displacement promoting non‐random spatial seedling recruitment. Although seed dispersal distances by ants are likely to be shorter than those by birds, our study of S. guianensis shows that fine‐scale ant‐induced seed movements may ultimately enhance plant regeneration in cerrado.     

Composition and clumping of seeds deposited by frugivorous birds varies between forest microsites

More frequent deposition of seeds by frugivores beneath plants in fruit could impose spatial limits to the distribution of plants dispersed by animals and contribute to species coexistence. Also, differences in diet and use of microhabitats by seed dispersers could promote spatial variation in the combination of seed species deposited. We investigated patterns of seed deposition of Miconia fosteri and Miconia serrulata (Melastomataceae) by birds in the Amazon. The goal was to determine how distribution and abundance of fruiting plants, both con‐ and hetero‐specifics, affect the spatial variability in clumping and composition of multi‐specific seed deposition. We established two 9‐ha plots in undisturbed terra‐firme understory in the Ecuadorian Amazon. Seed rain was sampled with seed traps located in four microsites: below plants of the focal species, below Anthurium eminens (Araceae), and in randomly selected microsites. We examined seed deposition in these microsites in relation to habitat, fruiting neighborhood (fruit abundance, and distance to and density of plants of the target species), and crop size of M. fosteri or M. serrulata to determine if microsites differed in abundance and species composition of seeds. Seed traps below plants in fruit received more seeds than did randomly located traps. Seeds of the target species were, moreover, more commonly deposited below con‐ rather than hetero‐specific plants. Seed aggregation below fruiting plants increased in forest neighborhoods where the abundance of fruits and the combination of fruiting plant species contributed to the arrival of seeds. Microsites differed notably in the combination of seeds deposited by frugivores, and differences were less pronounced among microsites that received seeds of M. fosteri and M. serrulata than among all microsites where at least some seed species were deposited by birds. We demonstrate that two closely related, ecologically similar species possess many similarities in their patterns of seed deposition and in the factors that affect those patterns. The combination of seed species deposited below foci of dispersal depended on the fruiting plant species, and the spatial patterns of seed deposition varied with the location of the microsite and the combination of co‐dispersed species in the neighborhood. Similar species that share the same dispersers were confronted with different combinations of seeds depending on the microsite where they arrived, which could promote forest heterogeneity in the combination of plant species.     

High salinity impacts germination of the halophyte Cakile maritima but primes seeds for rapid germination upon stress release

Seed germination recovery aptitude is an adaptive trait of overriding significance for the successful establishment and dispersal of extremophile plants in their native ecosystems. Cakile maritima is an annual halophyte frequent on Mediterranean coasts, which produces transiently dormant seeds under high salinity, that germinate fast when soil salinity is lowered by rainfall. Here, we report ecophysiological and proteomic data about (1) the effect of high salt (200 mM NaCl) on the early developmental stages (germination and seedling) and (2) the seed germination recovery capacity of this species. Upon salt exposure, seed germination was severely inhibited and delayed and seedling length was restricted. Interestingly, non‐germinated seeds remained viable, showing high germination percentage and faster germination than the control seeds after their transfer onto distilled water. The plant phenotypic plasticity during germination was better highlighted by the proteomic data. Salt exposure triggered (1) a marked slower degradation of seed storage reserves and (2) a significant lower abundance of proteins involved in several biological processes (primary metabolism, energy, stress‐response, folding and stability). Yet, these proteins showed strong increased abundance early after stress release, thereby sustaining the faster seed storage proteins mobilization under recovery conditions compared to the control. Overall, as part of the plant survival strategy, C. maritima seems to avoid germination and establishment under high salinity. However, this harsh condition may have a priming‐like effect, boosting seed germination and vigor under post‐stress conditions, sustained by active metabolic machinery.     

Deposition of exotic bird-dispersed seeds into three habitats of a fragmented landscape in the northeastern United States

Dispersal by frugivorous birds facilitates invasion by many exotic plants. We measured the seed rain of ornithochorous native and exotic plants at three habitats of a fragmented landscape of the northeastern United States for 1 year. We studied maple-beech forests, old fields, and abandoned conifer plantations. Across all sites we collected 2,196 ornithochorous seeds, including seeds from six exotic species and 10 native species. The majority (90%) of collected seeds were from exotic species. Seed dispersal was broadly similar among habitats, though seed rain of exotic species was higher in old fields than forested habitats. Seed rain was not strongly influenced by artificial perches for most species. However, seeds of exotic species were more commonly found in traps under an artificial perch in old fields. Seed rains for the exotic Elaeagnus umbellata, Rhamnus cathartica, and Rosa multiflora were positively associated with local density of mature plants. Seed rain of R. cathartica was positively associated with abundance of seedlings but not saplings, suggesting that post-dispersal mortality was important. Seed dispersal of the exotic Lonicera spp. was high in all habitats, accounting for 66% of all seeds collected. With the exception of Lonicera spp., seed rain of common exotic invaders was affected by the abundance of seed sources, and these species might be effectively controlled by elimination of local fruiting plants. Fruits of Lonicera morrowii, which has extensively invaded our area, are apparently a common component in the diet of frugivores.     

Seed to seedling transitions in successional habitats across a tropical landscape

Recognition that tree recruitment depends on the balance between seed arrival and seedling survival has led to a surge of interest in seed‐dispersal limitation and seedling‐establishment limitation in primary forests. Virtually unaddressed are comparisons of this balance in mature and early successional habitats. We assessed seed rain and seedling recruitment dynamics of tree species in primary forest, secondary forest and pasture released from grazing in a tropical agricultural landscape. Seed to seedling ratios (seed effectiveness; Φ_i) for 43 species in southern Mexico determined differences in the extent to which seeds produced seedlings by habitat, life history, and dispersal mode. Reproductive potential as estimated by the transition from seed rain to seedling recruitment, differed by habitats, and varied dramatically by life history and dispersal mode. Expected recruit densities (E_it) were higher for animal‐dispersed than wind‐dispersed species, and for non‐pioneer than pioneer species. Non‐pioneers and animal‐dispersed species had higher expected relative recruit abundance (ε_it) in primary forest (median of 4 seeds recruit^?1) whereas in secondary forest wind‐dispersed pioneers had the highest expected relative recruit abundance (median of 16 seeds per recruit). In pastures, wind‐dispersed pioneer species were most successful with many more seeds per recruit (median of 291) than both forest habitats. Seeds per recruit (Φ_i) appeared to decrease with increase in seed mass for 43 species for which data were available (r = –0.55, P < 0.001). This was associated with a negative correlation of Φ_i with seed size in primary forest (r = –0.50, P = 0.08 for 13 species); Φ_i was not correlated with seed size in secondary forest (n = 16) or pasture (n = 14). Metrics of seeds per recruit, expected recruit density and expected relative recruit abundance dramatically illustrate differences in barriers to recruitment in successional habitats.     

Polyploidy affects the seed,dormancy and seedling characteristics of a perennial grass,conferring an advantage in stressful climates

• Polyploidy (the state of having more than two genome copies) is widely distributed in flowering plants and can vary within species, with polyploid races often associated with broad ecological tolerances. Polyploidy may influence within‐species variation in seed development, germination and establishment. We hypothesized that interactions between polyploidy and the seed developmental environment would affect subsequent dormancy, germination and early growth traits, particularly in stressful environments.
• Using seeds developed in a common garden under ambient and warmed conditions, we conducted germination trials under drought and temperature stress, and monitored the subsequent growth of seedlings. The study species, Themeda triandra, is a widespread, keystone, Australian native grass and a known polyploid complex.
• Tetraploid plants produced heavier, more viable seeds than diploids. Tetraploids were significantly more dormant than diploids, regardless of seed developmental environment. Non‐dormant tetraploids were more sensitive to germination stress compared to non‐dormant diploids. Finally, tetraploid seedlings were larger and grew faster than diploids, usually when maternal plants were exposed to developmental temperatures atypical to the source environment.
• Seed and seedling traits suggest tetraploids are generally better adapted to stressful environments than diploids. Because tetraploid seeds of T. triandra are more dormant they are less likely to germinate under stress, and when they do germinate, seedling growth is rapid and independent of seed developmental environment. These novel results demonstrate that polyploidy, sometimes in interaction with developmental environment and possibly also asexuality, can have within‐species variation in seed and seedling traits that increase fitness in stressful environments.

     

The “Trojan horse” strategy: Seed fungal endophyte symbiosis helps to explain the invasion success of the grass,Poa annua,in Maritime Antarctica

Aim

Poa annua L. (annual bluegrass) is presently the sole invasive vascular plant species to have successfully established in Maritime Antarctica, where it poses a significant conservation threat to native plant species. However, the reasons for its success in the region have yet to be established. Here, we determined whether the invasiveness of P. annua, and its competitiveness with the native Antarctic hairgrass Deschampsia antarctica, is influenced by symbioses formed with seed fungal endophytes, and whether plants derived from seeds from four global regions differ in their performance.

Locations

Four regions (Maritime Antarctica, sub-Antarctica, South America and Europe).

Methods

Endophyte frequency was measured in P. annua seeds collected from the four regions. The germination, survival, biomass accumulation, flowering and competitiveness with D. antarctica of P. annua plants grown from endophyte-uncolonised and uncolonised seeds was determined in the laboratory. The effects of endophytes on P. annua seed germination and survival and seedling osmoprotection were also assessed in the Maritime Antarctic natural environment using locally-sourced seeds.

Results

Endophytes were at least twice as frequent in seeds from Maritime Antarctica than in those from other regions. A higher proportion of endophyte-colonized seeds germinated and survived than did uncolonised seeds, but only when they originated from Maritime Antarctica. Seed endophytes increased the competitiveness of P. annua with D. antarctica, but only for plants grown from Maritime Antarctic seeds. In the field, endophyte-colonized seeds from Maritime Antarctica germinated and survived more frequently than uncolonised seeds, and osmoprotection was higher in seedlings grown from colonized seed.

Main Conclusions

The findings indicate beneficial effects of seed endophytes on invasion-related traits of P. annua, such as survival, germination success and flowering. Together with vegetative and reproductive traits facilitating the colonization process, the seed-fungal endophyte symbiosis can be invoked as an important factor explaining the invasiveness of P. annua in Maritime Antarctica.     

Switching roles from antagonist to mutualist: a harvester ant as a key seed disperser of a myrmecochorous plant

1. Harvester ants are major seed predators in arid environments. However, given that many harvester ants are partly omnivorous and therefore potentially attracted to the elaiosomes of myrmecochorous seeds, it is unclear if these ants act as predators or dispersers when removing myrmecochorous seeds. 2. We describe the outcomes of interactions between the harvester ant, Pogonomyrmex naegelii, and myrmecochorous plant, Microstachys serrulata, in a Brazilian savanna. We: (i) evaluated the role of elaiosome in seed removal by P. naegelii; (ii) investigated the fate and viability of removed seeds; (iii) tested if soils associated with P. naegelii nests are nutrient-enriched; (iv) compared seedling survival; and (v) the density of seedling and adult M. serrulata nearby to P. naegelii nests compared with those away from these nests (i.e. controls). 3. Rates of removal of M. serrulata seeds were two-fold higher with elaiosomes than without. The ant attractant oleic acid was the dominant fatty acid in elaiosomes, but it was absent from seeds. Removed seeds are taken into nests, and Tetrazolium tests indicated that 95% of seeds remain viable. Soils associated with P. naegelii nests were not nutrient-enriched, and seedling survival was similar nearby to P. naegelii nests compared with control areas. However, densities of both seedling and adult M. serrulata were higher nearby to P. naegelii nests than in control areas. 4. Our findings show that P. naegelii switches its role from seed predator for most plant species to be the dominant seed disperser for M. serrulata, playing a key role in the distribution of adult plants.     

Influence of temporal fluctuations in seed abundance on the diet of harvester ants (Pogonomyrmex spp.) in the central Monte desert,Argentina

Harvester ants usually go through temporal fluctuations in environmental seed abundance and composition which could influence their behaviour and ecology. The aim of this study was to evaluate how these fluctuations influence the diet of Pogonomyrmex rastratus, P. pronotalis and P. inermis (Hymenoptera, Formicidae) in the central Monte desert during three consecutive growing seasons. Although seeds were the main item in the diet, these ants turned more generalist when seed abundance of the most consumed species (grasses Aristida spp., Trichloris crinita, Pappophorum spp., Digitaria californica and Stipa ichu) was low. Accordingly, diversity of items in the diet decreased with seed abundance in a logarithmical fashion, showing higher foraging efficiency for seeds at higher seed abundance. Seed diversity, however, was not related to seed abundance as ants always included several species in their diet, with alternating prevalence. The proportion of the most consumed species increased logarithmically in the diet of P. rastratus and P. pronotalis along with their abundance in the environment probably as a consequence of diet switching (from forb and shrub seeds to grass seeds) and by an increase in foraging efficiency at higher seed densities. In contrast, foraging activity of P. inermis was very low at low seed abundance and its diet included only the five grasses. Among the most consumed species, proportion in the diet was not associated with relative abundance in the environment. Aristida spp., Pappophorum spp. and D. californica were overall highly selected. However, the flexibility in the diet of P. pronotalis and P. rastratus and the low foraging activity of P. inermis during periods of low resource abundance could attenuate potential top‐down effects in the central Monte desert. This study shows that bottom‐up effects are important in ant‐seed interactions and should be considered when predicting and evaluating ants' effects on seed resources.     

Shrub emergence and seedling growth in microenvironments created by Prosopis glandulosa

Abstract. Facilitation of the establishment of certain plant species by nurse plants is a common phenomenon in arid and semiarid ecosystems. The most commonly reported mechanisms of facilitation include cooler temperatures and increased soil nutrients beneath the nurse plant canopy, which favor establishment of other plant species. During conversion of upland grasslands to thorn woodland in southern Texas, Prosopis glandulosa appears to facilitate establishment of other woody plants, including Celtis pallida, whereas Acacia smallii occurs only in habitats between P. glandulosa canopies. We tested the hypothesis that light intensity and soils under P. glandulosa canopies facilitate seedling emergence and growth of C. pallida but inhibit seedling emergence and growth of A. smallii. In the field, C. pallida and A. smallii seeds were planted under P. glandulosa canopies and in adjacent interspaces. Percent emergence of C. pallida seedlings was greater under the canopy of P. glandulosa, whereas percent emergence of A. smallii seedlings was greater in interspaces. In a greenhouse experiment, seeds of each species were planted in pots filled with soil from under P. glandulosa canopies or from adjacent interspaces. Two treatments, shade and sunlight, were imposed and plants harvested seven weeks later. Seedling mass of both species was greater in canopy soil than in interspace soil in sunlight but mass of the two species did not differ between soil sources in shade. Canopy soils contained more total and available nitrogen than interspace soils. These results suggest that light is more limiting than nutrients under shaded conditions and so neither species can take advantage of the high nutrients beneath P. glandulosa. Shade and greater soil nutrients beneath P. glandulosa do not appear to be the major factors that facilitate C. pallida or inhibit A. smallii. Aggregation of C. pallida beneath P. glandulosa canopies appears to be a complex process that involves both passive facilitation (seed dispersal by birds) and active facilitation (reduction of seed dormancy by under-canopy temperatures) operating only during the seed germination stage with successional mechanisms other than facilitation operating during later stages of shrub establishment and growth.     

Population dynamics of the shrub Acacia suaveolens (Sm.) Willd.: Survivorship throughout the life cycle,a synthesis

Survivorship in Acacia suaveolens was assessed through seedling and adult stages. Moisture stress was found to be the critical factor limiting early seedling survival. Both seedling and adult populations were characterized by periods of low mortality interspersed with pulses of high mortality. A composite survivorship curve for A. suaveolens based on nine sites predicts that some 20–25 years after afire, established plants should disappear from the above-ground flora if another fire does not occur. Fecundity and survivorship data were used to estimate the flux of seed in the soil over time in a hypothetical A. suaveolens population. From this it was predicted that, following establishment of plants after a fire, the seed-bank would rapidly reach a maximum after 6 years and thereafter slowly decline, until after 60 years there would be only as many seeds as there were original parental plants. The situation would vary with predispersal seed predation, seed predation on the soil surface, seed dispersal by ants to ‘unsafe sites’ and the size of the initial seed-bank prior to establishment. Only after a very long inter-fire period would A. suaveolens be eliminated from a site. Elimination of the species is also possible under very frequent fires. A 2–5 year fire-free period is needed for plants to reach maturity and another 6 years are needed to maximize seed input into the soil seed-bank. In addition, seedling recruitment following cool burns is low to non-existent as dormancy is not broken for most seeds in the soil during such burns.     

Contrasting responses to ectomycorrhizal inoculation in seedlings of six tropical African tree species

Five caesalpinioid legumes, Afzelia africana, Afzelia bella, Anthonotha macrophylla, Cryptosepalum tetraphylum and Paramacrolobium coeruleum, and one Euphorbiaceae species, Uapaca somon, with a considerable range in seed sizes, exhibited different responses to inoculation by four species of ectomycorrhizal (ECM) fungi, Scleroderma dictyosporum, S. verrucosum, Pisolithus sp. and one thelephoroid sp. in greenhouse conditions. Thelephoroid sp. efficiently colonized seedlings of all of the five caesalpinioid legumes except U. somon, but provided no more growth benefit than the other fungi. Thelephoroid sp. and S. dictyosporum colonized seedlings of U. somon poorly, but stimulated plant growth more than the other fungi. The relative mycorrhizal dependency (RMD) values of the caesalpinioid legumes were never higher than 50%, whilst U. somon had RMD values ranging from 84.6 to 88.6%, irrespective of the fungal species. The RMD values were negatively related to seed mass for all plant species. Potassium concentrations in leaves were more closely related than phosphorus to the stimulation of seedling biomass production by the ECM fungi. Our data support the hypothesis that African caesalpinioid legumes and euphorbe tree species with smaller seeds show higher RMD values than those with the larger seeds.     

Seedling emergence and survival in contrasting soil microsites in Patagonian Monte shrubland

Abstract. The potential of two perennial species (Larrea divaricata and Stipa tenuis) to colonize different soil microsites was analyzed in the Patagonian Monte shrubland. We hypothesize that the short-lived grass S. tenuis is more able to colonize the soil of microsites beneath vegetation patches where N-fertility is higher than those in bare soil, while the long-lived shrub L. divaricata colonizes different soil microsites irrespective of their N fertility. A greenhouse experiment was carried out to evaluate the emergence and survival of both species in different soil microsites at different water, inorganic N and seed densities. In all cases soil microsites were seed limited since the addition of viable seeds increased seedling emergence. Both species showed, however, different abilities to emerge and survive in different soil microsites. Microsites of bare soil were more favourable for seedling emergence and survival of L. divaricata than those beneath vegetation patches, independent of their water status. This ability of L. divaricata can not be explained on the basis of increased water or N availability, but probably because of lower salt content of bare soil. The addition of inorganic N reduced the survival of L. divaricata in both microsites but increased individual plant performance. The emergence and survival of S. tenuis was not different in both types of soil microsites but the addition of inorganic N increased seedling emergence and plant biomass. According to these results, emergence and plant performance of S. tenuis may be promoted during humid years by increased concentration of inorganic N. Since N mineralization occurs at a higher rate in soil microsites beneath vegetation patches than in those of bare soil, higher plant performance and probably establishment of S. tenuis is to be expected. These results are consistent with an existing conceptual model of plant dynamics under various grazing intensities in the Patagonian Monte shrubland based on previous field observations.     

Temporal patterns of seed use and availability in a guild of desert ants

ABSTRACT.

• 1 Temporal patterns of seed use were studied from late winter to autumn in three species of seed-harvesting ants in the Sonoran Desert. Measures of effective foraging activity, dietary niche breadth and dietary niche overlaps were obtained each month and were tested for correlation with estimates of the available seed resource.
• 2 Seeds were the only numerically important type of food in the diets of all species.
• 3 The ants partitioned the resource according to both seed species and seed size, although there was considerable overlap.
• 4 Pheidole xerophila had the smallest forager body size and is a specialist on small seeds because it harvested them in greater proportion than their rank in the soils and expanded its diet to larger seeds only when the abundance of small seeds declined.
• 5 When the abundance of the small seeds of Bouteloua barbata decreased, the middle-sized ant, Veromessor pergandei, showed a decrease in foraging activity, increase in niche breadth, and a decrease in overlap with P.xerophila.
• 6 Seed size preferences of V.pergandei did not vary seasonally, except that during the month of highest seed abundance, V.pergandei showed no size preference.
• 7 Pogonomyrmex rugosus was the largest ant; it preferred larger seeds and was inactive when small seeds were most abundant. Seasonal foraging activity and niche parameters were random in relation to seed abundance.
• 8 We suggest that nocturnal foraging by P.rugosus during the summer months was a response to interference with diurnal foraging by either predation frorn horned lizards or competition from V.pergandei.
• 9 Seasonal abundance of small seeds explains most of the seasonal foraging patterns of P.xerophila and V.pergandei. The summertime abundance of larger seeds during years of adequate precipitation may account for the seasonal activity patterns of P.rugosus.

     

Plant recruitment bottlenecks in temperate forest fragments: seed limitation and insect herbivory

Numerous studies have documented declines in plant diversity in response to habitat loss in fragmented landscapes. However, determining the mechanisms that lead to species loss is challenging using solely a correlative approach. Here we link correlative assessments of plant community composition with seed additions for a focal species to test the hypothesis that distributions of forests plants within a fragmented landscape are limited by seed dispersal. Woody plant species richness of fragments declined as fragments (n=26) became more isolated by agricultural fields. We predicted that if these isolation effects were driven by poor dispersal rather than other effects associated with habitat loss, then plants should vary in their response to isolation in relation to their seed size (i.e., stronger effects for plants with larger seeds). As predicted under this dispersal limitation hypothesis, sensitivity of bird-dispersed shrubs to isolation was related to their seed mass, with species with heavy seeds (e.g., Lindera benzoin) exhibiting stronger declines in presence across isolation gradients than species with light seeds. Seed addition experiments were performed for Lindera benzoin in two high isolation forest fragments (nearest neighbor mean distance=803 m) where Lindera was naturally absent, and two low isolation fragments (nearest neighbor mean distance=218 m) with naturally occurring Lindera populations. Seed addition and control plots (n=50 1 m² plots per fragment) were monitored for 13 censuses over 3 years. Across all four fragments, seed additions resulted in significant increases in Lindera seedling recruitment with no differences in final seedling establishment among fragments. However, insect herbivory was higher on Lindera seedlings in high isolation compared to low isolation fragments and was negatively correlated with seedling survival over some years. Consistent with prior work, our results confirm that seed dispersal plays a significant role in affecting plant diversity in fragmented landscapes. However, results also suggest the need for a better understanding of how additional processes, such as herbivory, may be altered as habitat is lost and what effects such changes have for forest plants.     

棕榈科植物种子内生细菌群落多样性的高通量测序分析

【目的】探究棕榈科种子内生细菌群落组成及其随物种的差异。【方法】运用MiSeq高通量方法测定蒲葵、棕榈、加拿利海枣、山棕、软叶刺葵、短穗鱼尾葵及三药槟榔7种棕榈科种子内生细菌群落16S rRNA基因V3–V4区序列并进行生物信息学分析。【结果】7种测试种子中获得的V3–V4区有效序列数在2341–40671条之间,聚成97–590个操作分类单元(OTU),Shannon指数计算为1.35–2.94,以加拿利海枣种子最高,山棕种子最低;种群归类结果显示不同种子中测得的各级细菌分类阶层总数及组成不同,总丰度以厚壁菌门的肠球菌属最高,同为厚壁菌门的芽孢杆菌属次之;属级水平上,第一优势细菌属分别为:蒲葵种子(芽孢杆菌属,45.8%),棕榈种子(肠球菌属,51.2%),山棕种子(肠球菌属,12.1%),短穗鱼尾葵种子(肠球菌属,32.6%),三药槟榔种子(肠球菌属,42.9%),软叶刺葵种子(肠球菌属,28.3%),加拿利海枣种子(糖多孢菌属,31.2%)。各种子中次优势细菌属分别为:蒲葵种子(乳球菌属),棕榈、山棕及三药槟榔种子(类芽孢杆菌属),加拿利海枣种子(戈登氏菌属),软叶刺葵和短穗鱼尾葵种子(鞘脂单胞菌属);PICRUST基因预测显示各种子均包含多个与人体器官及人类疾病相关的KEGG功能模块。此外,各种子中均产生了丰度较高的外源物质降解、萜和聚酮合成、多糖合成等有益功能信息。【结论】棕榈科植物种子内生细菌群落多样性较为丰富,群落组成随物种不同而异。各种子内生细菌群体中普遍含多个与人和动物体相关的种群和功能信息,也定殖多种具有益功能性状的细菌类群,值得进一步研究。     

Regeneration filters in post-agricultural fields of Puerto Rico and Ecuador

To better understand how rainforest regenerates after agriculture I sampled the seed rain and seed bank, and set out seeds and seedlings, on microsites defined by distance to the forest in fields both in Puerto Rico and Ecuador. I found that (1) total seeds, species richness and life-form richness were twice as great in the Ecuador seed rain compared to Puerto Rico but Puerto Rico seeds were more evenly distributed among species and (2) total seedlings from the seed bank were similar between Puerto Rico and Ecuador, (3) the majority of seeds were lost to predation among all species and study sites, (4) seed disease was absent in P. aduncum and Miconia prasina, and no seeds germinated for Gonzalagunia spicata and P. riparia, (5) in Ecuador pathogenic disease claimed more seeds than germinated for all species, and Solanum ovalifolium was the only species that had seeds germinate but did not lose seeds to disease, (6) also in Ecuador, insect predation was significantly lower in the forest border for P. aduncum, and seed disease was significantly greater at the 10 m micro site for S. ovalifolium, (7) distance has a significant effect on seedling height and basal diameter, (8) losses of leaf area due to herbivory and pathogens were always low and (9) biomass and leaf specific mass were significantly reduced in the border and forest microsites. I conclude that Ecuador fields had more seeds, species, and life-forms than Puerto Rico fields, predation was the most severe post-dispersal seed filter in all fields, seeds that survived predation on Puerto Rico were lost either to disease or germination but to both mechanisms in Ecuador, all three seed mechanisms in Ecuador fields showed distance effects of seedling growth but not survivorship.     

Initial regenerative processes ofDistylium racemosum andPersea thunbergii in an evergreen broad-leaved forest

We studied the initial regenerative processes ofDistylium racemosum andPersea thunbergii, major canopy species, in an old-growth evergreen broad-leaved forest, Kagoshima, southwestern Japan. Although the two species coexisted, the patterns of seed production, seedling emergence, and sapling survival were different between them. During the observation (1989–1991),P. thunbergii produced large numbers of seeds in alternate years, whileD. racemosum had no mast year. The density of established seedlings was high and increased with mass seed production forP. thunbergii, but was fairly low forD. racemosum. The mortality of seedlings and saplings ofP. thunbergii was higher than that ofD. racemosum. In a closed stand, the sapling bank was maintained by dense seedling supply forP. thunbergii, and by extremely low mortality of individuals germinated before the beginning of observation forD. racemosum. Since saplings ofD. racemosum showed continuous height growth beneath the closed canopy, the possibility of recruitment into the upper layer seems to be high. The strategy ofP. thunbergii might be to wait for suitable conditions favoring sapling growth on various site by means of frequent and large seed productivity and wide dispersal of seeds. Thus both species might be able to coexist through environmental heterogeneity.     

Ecological longevity of Polaskia chende (Cactaceae) seeds in the soil seed bank,seedling emergence and survival

• Soil seed banks are essential elements of plant population dynamics, enabling species to maintain genetic variability, withstand periods of adversity and persist over time, including for cactus species. However knowledge of the soil seed bank in cacti is scanty. In this study, over a 5‐year period we studied the seed bank dynamics, seedling emergence and nurse plant facilitation of Polaskia chende, an endemic columnar cactus of central Mexico.
• P. chende seeds were collected for a wild population in Puebla, Mexico. Freshly collected seeds were sown at 25 °C and 12‐h photoperiod under white light, far‐red light and darkness. The collected seeds were divided in two lots, the first was stored in the laboratory and the second was use to bury seeds in open areas and beneath a shrub canopy. Seeds were exhumed periodically over 5 years. At the same time seeds were sown in open areas and beneath shrub canopies; seedling emergence and survival were recorded over different periods of time for 5 years.
• The species forms long‐term persistent soil seed banks. The timing of seedling emergence via germination in the field was regulated by interaction between light, temperature and soil moisture. Seeds entered secondary dormancy at specific times according to the expression of environmental factors, demonstrating irregular dormancy cycling.
• Seedling survival of P. chende was improved under Acacia constricta nurse plants. Finally, plant facilitation affected the soil seed bank dynamics as it promoted the formation of a soil seed bank, but not its persistence.