Factors Limiting Post‐logging Seedling Regeneration by Big‐leaf Mahogany (Swietenia macrophylla) in Southeastern Amazonia,Brazil, and Implications for Sustainable Management1

Post‐logging seedling regeneration density by big‐leaf mahogany (Swietenia macrophylla), a nonpioneer light‐demanding timber species, is generally reported to be low to nonexistent. To investigate factors limiting seedling density following logging within the study region, we quantified seed production rates, germinability, dispersal patterns, and seed fates on the forest floor through germination and the first seedling growing season in southeastern Amazonia, Brazil. Fruit production rates were low by three logged and one unlogged populations compared to reports from other regions. Commercial‐sized trees (>60 cm diameter) were more fecund than noncommercial trees (30–60 cm diameter) at two sites, averaging 14.5 vs. 3.9 fruits/tree/year, respectively, at Marajoara, a logged site, over 8 yr. Fruit capsules contained an average of 60.3 seeds/fruit, 70 percent of which appeared viable by visual inspection. Sixty‐seven to 72 percent of apparently viable seeds germinated in nursery beds 2.5 mo after the dispersal period, when wet season rains began. Dry season winds blew most seeds west‐northwest of parent trees, with median dispersal distances of 28 and 9 m on west and east sides of parent trees, respectively. Nearly 100 percent of seeds fell within an area of 0.91 ha. On the forest floor beneath closed canopies, mammals, invertebrates, and fungal pathogens killed 40 percent of apparently viable seeds, while 36 percent germinated. Nine months after seedling establishment—midway through the first logging season following seed dispersal—14 percent of outplanted seeds survived as seedlings, representing 5.8 seeds/fruit. We conclude that seedlings are likely to survive in logging gaps at appreciable densities only in rare cases where previous year fruit production rates by logged trees were high (4–12.5% of commercial‐sized trees/year at Marajoara) and where tree crowns were felled in west or northwest directions.     

Recruitment of the invasive ornamental,Schinus terebinthifolius,is dependent upon frugivores

Abstract Generalist avian frugivores often play an important role in the processes of naturalization and invasion for plants introduced for ornamental and landscaping purposes. We investigated the potential role of Australian birds in the current invasion of riparian habitats and coastal wetlands by the ornamental Schinus terebinthifolius Raddi. Feeding trials in captivity predicted silvereyes (Zosterops lateralis Latham) as dispersal vectors for this weed. There were no differences in either total germination or germination rate between seeds voided by caged silvereyes and those from which exocarps had been removed manually. Germination of seeds incubated within entire fruits was minimal, as was emergence from intact fruits in a field experiment. Seed banks of S. terebinthifolius were relatively transient under field conditions, with no seeds surviving for 9 months. Since fewer than 5% of the seeds in sown whole fruits gave rise to seedlings (cf. 20–42% for sown bare seeds), we conclude that recruitment potential of S. terebinthifolius is highly dependent upon the consumption of its fruits by frugivores.     

Fruit fate,frugivory, and fruit characteristics: a study of the hawthorn,Crataegus monogyna (Rosaceae)

Summary The fate of fruits from a population of European hawthorn (Crataegus monogyna) in western Oregon, USA, was examined over a two-year period. Only one frugivore, the American robin (Turdus migratorius) foraged on the C. monogyna fruits, making this an unusually straightforward fruit-frugivore system. Dispersal efficiency was low, with an average 21% of seeds being dispersed (carried away from parent plants) each year; the most common fate of fruits was to simply fall. Robins dropped 20% of the fruits that they picked, and defecated/regurgitated 40% of the fruits (seeds) that they swallowed, beneath parent plants. One trait, gruit abundance, strongly affected the probability of bush visitation by robins, bushes with larger fruit displays being preferred. Both absolute dispersal success (number of seeds) and dispersal efficiency (proportion of seeds; success per propagule) were also found to be correlated most strongly with initial fruit abundance. Individual plant fecundity and fruit quality were found to vary little between years; as a result, dispersal efficiencies for individual plants were also annully consistent. Larger (older) plants produced more fruits and therefore had higher fitness. These results suggest that the optimal fruiting strategy for C. monogyna is therefore to get as big as possible as quickly as possible by delaying fruiting until later in life.     

Fruit removal and postdispersal survivorship in the tropical dry forest shrub Erythroxylum havanense: ecological and evolutionary implications

We studied the relationship between the removal rate and the spatiotemporal availability of ripe fruits of the tropical deciduous shrub Erythroxylum havanense in western Mexico. We also evaluated the effects of dispersal on seed survival during the first stages of establishment. Fast and early dispersal should be favored in E. havanense, since propagules have more time to grow and accumulate resources before the beginning of the severe dry season. In general, high rates of fruit removal imply faster and earlier dispersal. Thus, plants producing large crops should benefit from high removal rates, which will increase the probability of successful establishment by their progeny. To characterize both individual and population fruiting patterns, we made daily counts of fruits on 51 plants arranged in six clumps of different sizes. The daily number of fruits removed per plant was higher for plants with larger initial crop sizes and larger numbers of ripe fruits on a given day, but decreased as clump size increased. Additionally, we monitored postdispersal survival and germination in an experiment manipulating seed density, distance from adult plants, and seed predation. Early establishment was independent of density or distance, and vertebrate seed predation was the main agent of seed mortality. Our results indicate that the critical variable with respect to fruit removal is the number of fruits a plant produces, large plants having higher dispersal rates. Large plants are also more likely to have more seeds escaping postdispersal seed predation.     

High-quality seed dispersal by fruit-eating fishes in Amazonian floodplain habitats

Seed dispersal is a critical stage in the life history of plants. It determines the initial pattern of juvenile distribution, and can influence community dynamics and the evolutionary trajectories of individual species. Vertebrate frugivores are the primary vector of seed dispersal in tropical forests; however, most studies of seed dispersal focus on birds, bats and monkeys. Nevertheless, South America harbors at least 200 species of frugivorous fishes, which move into temporarily flooded habitats during lengthy flood seasons and consume fruits that fall into the water; and yet, we know remarkably little about the quality of seed dispersal they effect. We investigated the seed dispersal activities of two species of large-bodied, commercially important fishes (Colossoma macropomum and Piaractus brachypomus, Characidae) over 3 years in Pacaya-Samiria National Reserve (Peru). We assessed the diet of these fishes during the flood season, conducted germination trials with seeds collected from digestive tracts, and quantified fruit availability. In the laboratory, we fed fruits to captive Colossoma, quantified the proportion of seeds defecated by adult and juvenile fish, and used these seeds in additional germination experiments. Our results indicate that Colossoma and Piaractus disperse large quantities of seeds from up to 35% of the trees and lianas that fruit during the flood season. Additionally, these seeds can germinate after floodwaters recede. Overexploitation has reduced the abundance of our focal fish species, as well as changed the age structure of populations. Moreover, older fish are more effective seed dispersers than smaller, juvenile fish. Overfishing, therefore, likely selects for the poorest seed dispersers, thus disrupting an ancient interaction between seeds and their dispersal agents. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Big Fish are the Best: Seed Dispersal of Bactris glaucescens by the Pacu Fish (Piaractus mesopotamicus) in the Pantanal, Brazil

We studied the potential role as seed disperser of the pacu fish (Piaractus mesopotamicus, Characidae) in the Pantanal of Brazil. The most important food item in the diet of the pacu in the wet season was fruits of the palm Bactris glaucescens found in the guts of 73 percent of all fishes collected (N= 70). We found a positive relationship between fish length, weight, and gape size and the number of intact seeds in their gut. Therefore, large pacus are especially important in dispersing B. glaucescens seeds within the studied system. Since the best seed dispersers are the largest fishes, which are preferred by commercial fisheries, we predict that the ongoing over fishing in freshwater ecosystems will have major impacts on the dispersal system of fish‐dependent plants. We suggest that it is paramount to change the attitudes in fisheries management of fruit‐eating fishes and urgent to evaluate the impact of fishing on forest regeneration.     

Spatial–temporal distribution of ornithochorous seeds from an Elaeagnus umbellata community dominating a riparian habitat

The dispersal efficiency and potential distribution of ornithochorous seeds of Elaeagnus umbellata in a riparian habitat were evaluated to clarify this species' establishment site in relation to the disturbance regime of the floodplain. Fruit removal by avian frugivores was monitored using fruit bags, and the spatial distribution of excreted seeds was quantified by seed traps set randomly on a gravel bar as an isolated seed source in the Yoshino River throughout an autumn fruiting season. Although more than 45% of the fruits remained on the twigs in the fruit bags, almost all fruits on the control twigs without fruit bags were exploited by the beginning of January. The fruit removal rate and seed dispersal distance were positively correlated with an increase in wintering bird species and their abundance. Intact bird‐dispersed seeds of E. umbellata were trapped within a 400‐m range and damaged seeds were limited to traps set within 50 m from the seed source. Frugivore behavior, such as feces excretion on rocks near water drinking sites and perching on surrounding woodland, greatly influenced the spatial and temporal dispersal pattern of the seed rain. In the present study, the avian frugivores showed upstream seed dispersal; thus, in years with stochastic autumnal floods, secondary dispersal via hydrochory downstream may be facilitated. The intensive seed dispersal in E. umbellata indicates that the present distribution of parent trees in the restricted elevation range of the gravel bars is the result of survival through disturbance, rather than seed dispersal limitation.     

Black bears Ursus americanus are effective seed dispersers,with a little help from their friends

Black bears Ursus americanus are generally considered effective seed dispersal agents for fleshy‐fruited plants because they can consume hundreds of fruits at once and have large home ranges. Although seedlings can emerge from faecal piles, establishment of such seedlings seems to be infrequent. Removal of seeds from faeces by rodents is often considered seed predation. We show that removal of seeds from bear faeces by seed‐caching rodents in the Sierra Nevada, USA, represents a second phase of seed dispersal that benefits some fleshy‐fruited plants. Using Trail Master infrared cameras to photograph animals and scandium‐46, a gamma‐emitting radionuclide, to track seeds, we determined that deer mice Peromyscus maniculatus removed seeds from bear faeces and cached them in soil. Caches typically contained 1–3 seeds buried 5–10 mm deep. These seeds escaped several sources of mortality by being moved to relatively safe locations, but deer mice also eventually eat many of the cached seeds. A field germination study confirmed that seed burial increased seedling emergence. Rodents removed seeds in bear faeces more quickly than those in bird faeces in one year, but seeds in bird faeces were removed faster in another year. Results varied across two years, probably because of availability of alternative food sources or changes in deer mice population sizes. The two‐phase seed dispersal syndrome described here may be important in understanding seed dispersal by carnivores and large ungulates that produce large faecal deposits containing many relatively large seeds.     

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.     

Seed dispersal in Erythronium dens-canis L. (Liliaceae): variation among habitats in a myrmecochorous plant

Erythronium dens-canis is a geophyte which produces a single flower each season. The fruits produce small seeds with relatively large elaiosomes. We performed experiments to investigate primary and secondary seed dispersal mechanisms of this species in different habitats in the western part of the Cantabrian Range in northwest Spain. Sticky traps were used to measure primary dispersal of seeds up to 0.5 m from mother plants. Seed cafeteria experiments were performed in different habitats to examine the role of ants and rodents in secondary seed transport and seed predation. Our results indicate that: (a) primary seed dispersal is positively skewed (99% of seeds fall within 20 cm of the mother plant) and seed dispersal distances vary significantly among plants; (b) secondary dispersal is exclusively by myrmecochory, although the proportion of seeds removed by ants differs significantly among habitats; (c) ant species composition and abundances vary among habitats; and (d) freshly dropped seeds are more likely to be removed than seeds that have begun to dry out. We conclude that secondary dispersal of seeds is greatly influenced by habitat but not by small-scale microhabitat. This revised version was published online in June 2006 with corrections to the Cover Date.     

两种集合繁殖体形态及间歇性萌发特性——以蒺藜和欧夏至草为例

集合繁殖体(synaptospermy)是荒漠植物为适应恶劣环境条件而演化出的关键性特征,其作为植物生活史特性之一,有助于了解在荒漠环境下集合繁殖体植物的适应策略。蒺藜(Tribulus terrestris)和欧夏至草(Marrubium vulgare)分别为一年生及多年生草本植物,蒺藜扩散单位由一朵花发育而成的集合繁殖体组成,欧夏至草扩散单位由多朵花发育的集合繁殖体和种子组成,以这两种植物为材料,对其集合繁殖体形态、活力、吸水及萌发特性进行初步研究。结果显示:(1)蒺藜集合繁殖体依照发育成熟先后位置在质量、附属物刺的长度、附属物占质量百分比、种子数、活力、吸水量、萌发率及萌发速率均存在显著差异;欧夏至草集合繁殖体质量及吸水量明显大于种子,而活力、萌发率及萌发速率不存在显著差异。(2)萌发位置上,蒺藜集合繁殖体仅在长刺端位置的种子萌发,属非随机萌发,而欧夏至草集合繁殖体萌发不具有规律性,属随机萌发;萌发时间上,蒺藜和欧夏至草集合繁殖体在当季下均只萌发部分种子,具间歇性萌发特性。(3)对不同生活型植物而言,其集合繁殖体附属物对种子的保护、保水、扩散及萌发行为的功能相同,但一年生草本植物的萌发行为侧重于种群繁衍,因此蒺藜集合繁殖体在当季萌发率及萌发速率较高;多年生草本植物的萌发行为侧重于种群扩散,因此欧夏至草扩散单位多样化,且萌发率及萌发速率较低。     

The role of Orii’s flying-fox (Pteropus dasymallus inopinatus) as a pollinator and a seed disperser on Okinawa-jima Island, the Ryukyu Archipelago, Japan

The role of the Orii’s flying-fox (Pteropus dasymallus inopinatus) as a pollinator and a seed disperser on Okinawa-jima Island was investigated by direct observations and radio-tracking from October 2001 until January 2006. We found that Orii’s flying-fox potentially pollinated seven native plant species. Its feeding behavior and plant morphological traits suggested that this species is an important pollinator of Schima wallichii liukiuensis and Mucuna macrocarpa. The flying-fox also dispersed the seeds of 20 native plant species. The seeds of all plants eaten by the flying-fox were usually dropped beneath the parent tree, although large fruits of four plant species were occasionally brought to the feeding roosts in the mouth, with the maximum dispersal distance—for Terminalia catappa—estimated to be 126 m. Small seeds of 11 species (mostly Ficus species) were dispersed around other trees, during the subsequent feeding session, through the digestive tracts, with the mean dispersal distance for ingested seeds estimated at 150 ± 230.3 m (±SD); the maximum dispersal distance was 1833 m. A comparison of the seed dispersal of available fruits according to the size of flying-foxes and other frugivores suggested that the seed dispersal of eight plant species producing large fruits mostly depended on Orii’s flying-fox. On Okinawa-jima Island, the Orii’s flying-fox plays an important role as a pollinator of two native plants and as a long-distance seed disperser of Ficus species, and it functions as a limited agent of seed dispersal for plants producing large fruits on Okinawa-jima Island.     

Aggregated recruitment patterns under adult crowns in Photinia glabra,a bird‐dispersed tree species

To clarify recruitment patterns of Photinia glabra, which is an evergreen, broad‐leaved, bird‐dispersed tree species, we analyzed spatial distribution in P. glabra recruits at each growth stage and demography of current‐year seedlings with respect to distributions of adults in a warm‐temperate secondary forest, western Japan. Although individuals ≥ 5 cm diameter at breast height (DBH) that had nearly produced fruits showed a random distribution, seedlings (≥ 1 year old, < 10‐cm stem length [SL]), small saplings (10 ≤ SL < 30 cm) and large saplings (≥ 30‐cm SL, < 5‐cm DBH) were clumped and associated with reproductive adults at approximately 2–3‐m scales, nearly equal to their average crown radius. Based on monitoring the demography of current‐year seedlings, emerged seedling density profoundly decreased, and no seedlings survived at longer than an adult's crown scales, with distance‐dependent mortality as a result of disease and herbivory not greatly affecting the current‐year seedling mortality. Thus, aggregated seed dispersal under the crown of adult P. glabra would directly influence the distribution of recruits for P. glabra in this forest. Of the bird‐dispersed tree species in this forest, P. glabra produced the highest amount of fruits during large crop years, and their fruits ripened during the late seasonal period (early January), suggesting that birds might be strongly attracted to these species, in turn leading to seeds being deposited mostly under the tree crowns. We propose that dispersal limitation would occur, even in a bird‐dispersed tree species such as P. glabra, owing to plant–bird interactions in the forest.     

Effects of seed dispersal on Juniperus communis recruitment on a Mediterranean mountain

Abstract. The recruitment of the relict shrub Juniperus communis on a mountain in SE Spain was studied during the period 1994–1998. The main objective was to determine both the quantitative and qualitative effects of bird dispersal on seedling establishment. Seed removal by birds, seed rain, post‐dispersal seed predation, germination, and seedling emergence and survival were analysed in different microhabitats. Birds removed 53 ‐ 89% of the seeds produced by plants. Seed rain was spatially irregular as most seeds accumulated near stones used by birds as perches and below mother plants while a few seeds were dropped in wet meadows and open ground areas. Post‐dispersal seed predation by rodents affected < 10% of dispersed seeds but varied significantly among microhabitats. Only 3.6 ‐ 5.5% of dispersed seeds appeared viable, as many seeds had aborted or showed wasp damage. Seeds germinated in the second and third springs after sowing, reaching a germination percentage of 36%. Seedling emergence was concentrated in wet meadows. Seedling mortality was high (75–80%), but significantly lower in wet meadows, the only microhabitat where seedlings could escape from summer drought, the main mortality cause. Seed abortion, germination and seedling mortality proved to be the main regeneration constraints of J. communis on Mediterranean mountains. Birds exerted a strong demographic effect, although their qualitative effect was limited by abiotic factors which caused the pattern of seed rain to differ from the final pattern of recruitment between microhabitats.     

PHENOLOGY,SEED DISPERSAL,AND COLONIZATION IN MUNTINGIA CALABURA,A NEOTROPICAL PIONEER TREE

In this paper we describe the phenology, fruiting ecology, and colonization ability of a widespread neotropical pioneer tree, Muntingia calabura (Eleocarpaceae), in Costa Rican dry tropical forest. Individuals of M. calabura grow rapidly, flower at <2 yr age, and produce juicy red fruits containing thousands of tiny seeds that are eaten by a variety of frugivorous birds, bats, and monkeys. Although most individuals produce some flowers and fruit year-round, peak flowering occurs in the late dry season (April–May), and peak fruit availability occurs early in the wet season (May–June). Bats and parakeets are the major seed dispersers of M. calabura at our study site, and they concentrate their attention on this species at its fruit peak when few alternate fruits are available. Germinable M. calabura seeds accumulate in the forest soil in relatively high density in areas of high frugivore activity. M. calabura can quickly invade large disturbed areas with a high density of seedlings. Adult densities decline from thousands of individuals/ha to a few individuals/ha in a relatively few years. Clumps of M. calabura trees are replaced by later successional species in < 30 yr.     

Effects of seed size on seedling size in Virola surinamensis; a within and between tree analysis

Summary We conducted a greenhouse study of the effects of initial seed mass on seedling characteristics in a Panamanian population of Virola surinamensis, a canopy tree in which mean seed mass of different individuals ranges from 1.34 to 4.04g. The system is of particular interest because birds preferentially eat fruits of small-seeded plants, leaving seedlings of large-seeded individuals under conditions of potentially severe sibling competition (Howe and Vande Kerckhove 1980).Effects of differences of mean seed mass between trees are explored using an analysis of variance, while effects of seed-mass variation within crops are demonstrated with a regression analysis. A two-way analysis of variance decisively shows effects of parental source and light condition on seedling height, leaf length, and dry shoot mass (all P<0.0001). A posteriori tests show that differences in seedling characteristics reflect differences in initial seed mass, with especially strong differences apparent in shoot mass. Regression of seedling characteristics on initial seed mass shows that variation of seed size within a crop is sufficient to influence shoot mass at 15 weeks (P<0.0001).Effects of size differences of seeds that land adjacent to each other, either under the parent or in monkey droppings, are documented with growth of pairs of seedlings in pots. Differences in shoot height and mass at 15 weeks are evident when seeds of average size differ by only 0.2 g, and dramatic differences are evident when paired seeds differ by an average of 1.5 g. Seedlings grow more when isolated than when planted with conspecifics.These experimental results offer indirect support for the hypothesis that small-seeded Virola parents secure an advantage in reproduction through differential dispersal, while large-seeded plants produce more competitive seedlings under their own crowns — an advantage most likely to be of importance when frugivores are scarce.     

Fecundity,fruiting pattern,and seed dispersal in Piper amalago (Piperaceae), a bat-dispersed tropical shrub

Summary This paper describes the nightly and seasonal production of ripe fruit by Piper amalago (Piperaceae), a patchily distributed, bat-dispersed forest shrub, at Parque Nacional Santa Rosa, Costa Rica. Phenological observations over several years indicate that individuals produce a low (usually 1–3) and variable number of ripe fruit each night for 3–4 wks in the early wet season (June and July). Observations of the disappearance rates of marked fruits and fruit manipulation experiments indicate that fruit removal probabilities are high (often nearly 1.0) and independent of nightly and seasonal ripe fruit crop size. Data from previous feeding and foraging studies of the bat Carollia perspicillata (Phyllostomidae) are used to estimate the mobility of P. amalago's seeds. Most seeds (>90%) are deposited 50 m from parent plants under night feeding roosts. Relatively few seeds move >300 m, and movements this long are more likely to occur early and late in the fruiting season when bats change feeding sites more frequently. Seed experiments indicate that P. amalago seedling establishment probabilities are higher in light gaps than under forest canopy. The dispersal quality (sensu McKey 1975) of P. amalago's chiropteran seed dispersers is directly proportional to the number of seeds they excrete in actual or incipient light gaps.     

Population ecology of an afro-tropical savanna herb,Lapeirousia rivularis,in Zambia

Detailed demographic studies of herbaceuos plants in afro-tropicalsavannas are extremely rare in published literature. I studied phenology andpopulation dynamics of a perennial herb, Lapeirousiarivularis Wanntorp, at a savanna site in Zambia over a 4-yearperiod, from 1997 to 2001, using enumeration techniques in permanent andtemporary quadrants. The age of the plants was accurately determined frompersistent annual sheaths that accumulate around the corm throughout the lifeofthe plant while the estimated survivorship of the 1998 cohort was developedfroma mathematical model based on the observed mortality of the cohort over a3-yearperiod.L. rivularis completed its annual phenological cycle in asingle rainy season. Plants sprouted from perennating corms in early December,flowered, fruited and dispersed seeds by end of January. Seeds germinatedimmediately after dispersal and seedlings produced small corms before aerialparts died early in the dry season. L. rivularis has twomorphs: a vegetative morph and a reproductive morph; the latter bears severalleaves and flower stalks. In the vegetative morph, the corm is renewed annuallywhile the corms of the reproductive morph did not appear to be renewed. Insteadcorms grew larger and produced lateral daughter corms that became independentramets the following rainy season.Most L. rivularis plants reached reproductive maturitywhen they were 6–10 years old. Reproductive success, seedlingestablishment and recruitment varied from year to year in the grassland plotperhaps because of fluctuations in weather conditions and heavy episodic insectherbivory. The survivorship curve of L. rivularis wascharacteristically concave due to high juvenile mortality (0.2–0.5) andvery low adult mortality (0.03). Although about 3% of the plants live to be upto 30–35 years, the mean age of the population in 2001 was 6.4 yearsbecause of the predominance of juvenile plants. The production of a protectivesheath at the end of the rainy season and the accumulation of old sheathsaroundthe fleshy corm are apparent adaptations against desiccation during the longdryseason drought when the topsoil remains below wilting point. The high juvenilemortality during the dry season is probably caused by inadequate protection bythe few sheaths around the corm against desiccation.Population dynamics in L. rivularis were caused byvariable annual recruitment and high juvenile mortality. Population densitydoubled in 1999 due to good fruiting success in the previous season that wasassociated with good weather conditions and negligible herbivory. Althoughcultivation had a significant negative effect on the population of L.rivularis, it increased consistency in fruiting success andproduction of fruits per plant, presumably because of improvement insoil-moisture status, reduction in plant competition and by providing temporalescape from insect herbivory through delayed flowering. The phenology and lifehistory of L. rivularis exhibit adaptations to a savannaenvironment that is characterized by disturbance and stress caused by seasonaldrought, fire, episodic herbivory and cultivation.     

FRUIT TRAITS,AND SEED CONSUMPTION BY RODENTS,OF CRESCENTIA ALATA (BIGNONIACEAE) IN SANTA ROSA NATIONAL PARK,COSTA RICA

The pulp in the large hard fruits of Crescentia alata (Bignoniaceae: jicaro) are eaten by horses, surrogate Pleistocene dispersal agents, and the seeds pass through the horse to germinate in dung. I hypothesize that the distribution of jicaro has probably changed dramatically with the introduction of the horse. Two samples of ripe jicaro fruits weighed an average of 210 and 390 g, and contained an average of about 400 and 600 seeds. There was strong variation within and between two trees in the number of seeds per fruit. Mature live seeds weighed an average of 36 and 40 mg, but varied strongly in weight between and within fruits. The seeds were found to be highly edible to a small terrestrial native rodent (Liomys salvini, Heteromyidae) and this rodent avidly harvests the seeds from horse dung but cannot open the hard fruits by itself. The interaction between horses, jicaro fruits, and Liomys mice is probably representative of that which used to occur between Pleistocene megafauna and a number of contemporary Central American trees.     

Population dynamics of the shrub Acacia suaveolens (Sm.) Willd.: Dispersal and the dynamics of the soil seed-bank

Genet survival in seeds of Acacia suaveolens was examined through both dispersal and dormancy in the soil in populations near Sydney. Following initial passive seed-fall, the majority of seeds lie within a 1 m radius of the stem of the parent. Further dispersal is predominately mediated by ants. A. suaveolens seeds possess an elaiosome which attracts ants. When elaiosomes are removed, the potential for further dispersal of seeds is greatly reduced. Three species of ant disperse seeds of A. suaveolens and the fate of seeds following ant dispersal was observed to depend on the particular species of ant involved. Ants of both Iridomyrmex sp. and Pheidole sp. B are too small to drag seeds and, instead, ants of these species usually remove the elaiosome in situ, with little dispersal of the-seed resulting. Ants of Pheidole sp. A are larger and disperse seeds further, frequently taking them into their nests where the elaisosome is removed. Seeds are retained inside the nests and incorporated into the floors and walls of passageways and chambers. Several supposed ‘advantages’ of myrmecochory were examined but none were verified. Instead, two distinct ‘disadvantages’ were identified. These were: burial of seeds by ants of Pheidole sp. A into ‘unsafe sites’; and too deep a burial of seeds in nests for seeds to receive a stimulus to germinate during fires, and for seedlings to emerge successfully. Outside nests of Pheidole sp. A. seeds are concentrated in the top 5 cm of the soil, whilst within nests of these ants, seeds are found up to 15 cm deep. The dynamics of various components of the soil seed-bank were examined using seeds buried in nylon mesh containers. The seed-bank is persistent without annual recruitment to seedlings, enabling a population to persist as seeds after all above-ground plants have perished.