Seed size selection by olive baboons

Seed size is an important plant fitness trait that can influence several steps between fruiting and the establishment of a plant’s offspring. Seed size varies considerably within many plant species, yet the relevance of the trait for intra-specific fruit choice by primates has received little attention. Primates may select certain seed sizes within a species for a number of reasons, e.g. to decrease indigestible seed load or increase pulp intake per fruit. Olive baboons (Papio anubis, Cercopithecidae) are known to select seed size in unripe and mature pods of Parkia biglobosa (Mimosaceae) differentially, so that pods with small seeds, and an intermediate seed number, contribute most to dispersal by baboons. We tested whether olive baboons likewise select for smaller ripe seeds within each of nine additional fruit species whose fruit pulp baboons commonly consume, and for larger seeds in one species in which baboons feed on the seeds. Species differed in fruit type and seed number per fruit. For five of these species, baboons dispersed seeds that were significantly smaller than seeds extracted manually from randomly collected fresh fruits. In contrast, for three species, baboons swallowed seeds that were significantly longer and/or wider than seeds from fresh fruits. In two species, sizes of ingested seeds and seeds from fresh fruits did not differ significantly. Baboons frequently spat out seeds of Drypetes floribunda (Euphorbiaceae) but not those of other plant species having seeds of equal size. Oral processing of D. floribunda seeds depended on seed size: seeds that were spat out were significantly larger and swallowed seeds smaller, than seeds from randomly collected fresh fruits. We argue that seed size selection in baboons is influenced, among other traits, by the amount of pulp rewarded per fruit relative to seed load, which is likely to vary with fruit and seed shape.     

The role of chemical cues in host finding and acceptance by Callosobruchus chinensis

We studied the response of female Callosobruchus chinensis to chemical cues emitted by cowpea seeds at different stages of bruchid infestation (uninfested, egg carrying, L1-, and L4-infested). Olfactory attractiveness was determined in Y-tube olfactometer assays by testing individual seed categories against either clean air or uninfested seeds. Oviposition preferences between uninfested and infested seeds were determined in petri-dish choice-experiments. The olfactometer assays revealed that weevils discriminate between seeds containing different stages of developing bruchids on the basis of olfactory cues. While odors from uninfested and egg-carrying seeds acted as attractants, odors from L1- and L4-infested seeds failed to induce a positive response by the bruchids. When given a choice between uninfested and infested seeds in the olfactometer, weevils preferred uninfested seeds over L1- and L4-infested seeds, but failed to distinguish between uninfested and egg-carrying seeds. In the oviposition experiment as well, bruchids showed a distinct preference for uninfested seeds when offered in combination with L1- and L4-infested seeds. This experiment further showed a reduced acceptance of egg carrying seeds. Our results indicate that C. chinensis females use chemical information during both host searching and host acceptance. Volatiles from uninfested or egg carrying seeds act as attractants, while deterrence increases as development of bruchid immature stages progresses.     

Patterns and kinetics of water uptake by soybean seeds

Soybean [Glycine max (L.) Merr.] plants produce some seeds (called stone or impermeable seeds) that do not take up water for long periods of time. The present investigation confirmed that the stone seed trait is a feature of the seed coat: isolated embryos from both stone and permeable seeds took up water equally quickly. A whole, permeable seed typically imbibed water initially through its dorsal side, forming wrinkles in the seed coat and delivering water to the underlying cotyledons. Later, some lateral movement of water through the coat occurred, presumably through the air spaces of the osteosclereid layer. Imbibition by seeds was a two-phase process, the first dominated by hydration of the seed coat and the second by hydration of the cotyledons, which was rate-limited by the coat. When hydrated, coats of stone seeds were permeable to water but their hydraulic conductivity, as measured with a pressure probe, was smaller than that of coats from permeable seeds by a factor of five. Hydrated coats of both permeable and stone seeds showed weak osmometer properties.     

Mucilage secretion by seeds doubles the chance to escape removal by ants

Post-dispersal seed predation is a risk for plants in semiarid environments, leading to strategies to protect their propagules from seed collection by animals. In this study, we evaluated the importance of mucilage secretion in seeds as a mechanism to reduce seed collection by ants. We selected three Mediterranean species with strong mucilage secretion on their seeds which become sticky upon wetting. Seeds of Rosmarinus officinalis, Fumana ericoides, and Fumana thymifolia were exposed to ants and survival was compared between dry loose seeds and seeds glued to the soil with previously secreted mucilage. The study site was in the Sierra Calderona, 25?km north of Valencia (Spain). The ant?Cplant interaction was analyzed by scrutinizing seed collection by ants and by analyzing the waste piles of ant nests. To test survival, groups of 10 seeds were placed on the ground. Each group consisted of five control (dry) and five?mucilaginous seeds (previously mucilage secreted) and was covered by the cover of a Petri dish modified to permit only the entry of ants. Seeds were inspected weekly for seed disappearance and the survival function (Kaplan?CMeier estimator) was calculated. Seeds of the target species were important food items for ants and were actively collected, and more than 50?% of the experimental seeds that were glued to the ground with their own mucilage survived at the end of the study period but only 0?C20?% of the control seeds survived after the same time of exposure. The implications for plant establishment of these findings are discussed.     

山杏的种子雨及鼠类的捕食作用

山杏(Prunus armeniaca)是一种灌木状小乔木,在北京山区较为贫瘠、干旱的阳坡地带广泛分布。于2002年7月和2003年7～9月,采用种子收集筐估计了山杏种子的产量、种子雨的动态变化过程;在2003年的研究中,把收集筐中所获得的种子转入扣网之中以排除鸟类的影响,并设置了地表对照样方,调查和比较了扣网内和对照样方中、扣网和对照样方之间山杏种子被取食、搬离的动态变化及其差异性。研究表明,山杏种子的下落高峰发生于7月下旬至8月上旬,败育种子的下落早于完好种子且数量极少;在扣网内和对照样方中,被取食和被搬运的种子数量之间存在显著性差异,在扣网和对照样方之间．被取食和被搬运的种子数量的差异均未达到显著性水平;鼠类是种子雨期间取食山杏种子的主要动物．鸟类的作用可以忽略。     

鸟类对山黄麻种子的传播及其生态作用

在云南西双版纳的勐宋和勐仑地区观察和研究了传统山黄麻种子的鸟类。在野外持网捕获摄食山黄麻果实的鸟类,称量后分别放在布袋内,让其自然排泄,然后标志释放,观察和网捕共记录到摄食山黄麻果实的鸟类36种,其中26种挂网捕获并从排泄物得到种子。用鸟类排泄物中的山黄麻种子、山黄麻树上采摘的成熟果实及人工分离山黄麻种子播种,进行萌发对比实验,实验结果表明,直接播种成熟果实,在阳光充足的空旷地、林冠下或用树叶覆盖遮光等条件下都未萌发,种子容易霉烂或被虫蚀;从山黄麻果肉中分离出来的种子具有萌发能力;而经鸟类摄食、消化后从果肉中分离的种子,具有较好的萌发活力。在不同条件下山黄麻种子萌发情况差异明显,林冠下条件对种子有抑制作用,阳光作用下种子显示出很好的萌发及成活率。鸟类排泄物种子放在林上或用树叶覆盖遮光,经过较长时间便可萌发,而人工分离种子不能萌发。鸟类摄食及消化过程对山黄麻种子的处理表现出很好的生态互惠关系,观察萌发后的山黄麻幼苗的生长情况还表明,幼苗生长也需要光照和较开阔的生境条件,鸟类取食山黄麻果实及其将种子远距离传播适宜生境,正好具有这样的生态作用。     

Cheek-pouch dispersal of seeds by Japanese monkeys (Macaca fuscata yakui) on Yakushima Island, Japan

Seed dispersal by Japanese monkeys (Macaca fuscata yakui) via cheek-pouch was studied in a warm temperate evergreen forest on Yakushima Island. Plant list was compiled based on a study during 1986–1995, of which troops of monkeys have been habituated without artificial feeding. We followed the well-habituated monkeys in 1993 and 1994 to observe the feeding behavior and their treatments of fruits and seeds, and collected seeds dispersed by monkeys to record the distance carried from the mother trees. We checked the difference of germination ratio between seeds dispersed via cheek-pouch and seeds taken from mother trees by sowing experiments. Seeds and acorns of 22 species were observed to be dispersed via cheek-pouch of monkeys. Among them, three species with acorns were never dispersed via feces, and 15 species with drupes were seldom dispersed via feces. Plant species of which seeds are dispersed only via cheek-pouch had larger seeds than those of dispersed both via cheek-pouch and via feces, and typically had only one or two seeds in a fruit. As for one of cheek-pouch dispersal species,Persea thunbergii, the mean distance when seeds were carried from the mother trees via cheek-pouch was 19.7 m, and the maximum distance was as long as 105 m although more than 80% of seeds were dispersed within 30 m from mother trees. And 82% of seeds dispersed via cheek-pouch germinated. The easy separation of seeds from other parts of the fruit seems to facilitate cheek-pouch dispersal more than dispersal via feces. Cheek-pouch dispersal by monkeys has possibly enhanced the natural selection for larger seeds which bring forth larger seedlings with high shade-tolerance. In conclusion, cheek-pouch dispersal by monkeys is quite an important mode for trees in the mature stand in a warm temperate evergreen forest on Yakushima Island.     

Diversity of seeds captured by interception exceeds diversity of seeds deposited in traps

Seed dispersal, a key process in terrestrial landscapes, is increasingly important in the face of habitat fragmentation and global climate change. Seed dispersal is also notoriously difficult to characterize, especially in species rich and spatially complex tropical forests. We contrasted assemblages of biotically dispersed seeds collected from four sites using two methods: deposition into seed traps and interception by the capture of frugivorous birds. We also compared seed deposition and interception with local fruit production. Species accumulation curves for seeds deposited in seed traps began to level off sooner than curves for seeds collected from birds captured in mist nets, and extrapolation showed significantly greater estimated species richness for seeds collected from birds than for those deposited in traps. Assemblages from birds and from traps at each site were quite different, with an abundance‐based similarity index of 0.64; this dissimilarity increases if bat‐dispersed seeds are included in the analysis. Common bird‐dispersed species were retrieved from both mist‐netted birds and from seed traps, but numerous locally fruiting understory species were recovered only from birds. We conclude that the sampling of seeds carried by birds provides a valuable complement to other methods of studying seed dispersal in species‐rich tropical forests by revealing relationships between specific dispersers and their seed plants and by creating a more complete account of species diversity of seeds being transported at a given site.     

Single seed viability checked by delayed luminescence

Time resolved spectral components of delayed luminescence (DL) from single dry soybean seeds were measured using a device with single photon sensitivity. The seeds were aged by a thermal treatment to change their viability. A correlation was observed between the seeds viability and some DL parameters, i.e. the total number of photons emitted and the relative decay probability of excited states. This relevant result confirms the close connection between the state of biological systems and their DL, and it can allow the development of a quick selection technique for single dry seeds, a goal impossible up today.     

Seed dispersal by carnivores in temperate and tropical dry forests

The seed dispersal mechanisms and regeneration of various forest ecosystems can benefit from the actions of carnivores via endozoochory. This study was aimed to evaluate the role of carnivores in endozoochory and diploendozoochory, as well as their effect on seed viability, scarification, and germination in two forest ecosystems: temperate and tropical dry forest. We collected carnivore scat in the Protected Natural Area of Sierra Fría in Aguascalientes, Mexico, for 2 years to determine the abundance and richness of seeds dispersed by each carnivore species, through scat analysis. We assessed seed viability through optical densitometry using X‐rays, analyzed seed scarification by measuring seed coat thickness using a scanning electron microscope, and evaluated seed germination in an experiment as the percentage of seeds germinated per carnivore disperser, plant species, and forest type. In the temperate forest, four plant species (but mainly Arctostaphylos pungens) were dispersed by four mammal species. The gray fox dispersed the highest average number of seeds per scat (66.8 seeds). Bobcat dispersed seeds through diploendozoochory, which was inferred from rabbit (Sylvilagus floridanus) hair detected in their scats. The tropical dry forest presented higher abundance of seeds and richness of dispersed plant species (four species) than in the temperate forest, and the coati dispersed the highest number of seeds (8,639 seeds). Endozoochory and diploendozoochory did not affect viability in thick‐testa seeds (1,480 µm) in temperate forest and thin‐testa seeds (281 µm) in tropical dry forest. Endozoochory improved the selective germination of seeds. Nine plant species were dispersed by endozoochory, but only one species (Juniperus sp.) by diploendozoochory. These results suggest that carnivores can perform an important ecological function by dispersing a great abundance of seeds, scarifying these seeds causing the formation of holes and cracks in the testas without affecting viability, and promoting the selective germination of seeds.     

Endozoochory by beetles: a novel seed dispersal mechanism

Background and Aims

Due in part to biophysical sized-related constraints, insects unlike vertebrates are seldom expected to act as primary seed dispersers via ingestion of fruits and seeds (endozoochory). The Mediterranean parasitic plant Cytinus hypocistis, however, possesses some characteristics that may facilitate endozoochory by beetles. By combining a long-term field study with experimental manipulation, we tested whether C. hypocistis seeds are endozoochorously dispersed by beetles.

Methods

Field studies were carried out over 4 years on six populations in southern Spain. We recorded the rate of natural fruit consumption by beetles, the extent of beetle movement, beetle behaviour and the relative importance of C. hypocistis fruits in beetle diet.

Key Results

The tenebrionid beetle Pimelia costata was an important disperser of C. hypocistis seeds, consuming up to 17·5 % of fruits per population. Forty-six per cent of beetles captured in the field consumed C. hypocistis fruits, with up to 31 seeds found in individual beetle frass. An assessment of seeds following passage through the gut of beetles indicated that seeds remained intact and viable and that the proportion of viable seeds from beetle frass was not significantly different from that of seeds collected directly from fruits.

Conclusions

A novel plant–animal interaction is revealed; endozoochory by beetles may facilitate the dispersal of viable seeds after passage through the gut away from the parent plant to potentially favourable underground sites offering a high probability of germination and establishment success. Such an ecological role has until now been attributed only to vertebrates. Future studies should consider more widely the putative role of fruit and seed ingestion by invertebrates as a dispersal mechanism, particularly for those plant species that possess small seeds.     

Seed consumption and dispersal of ant-dispersed plants by slugs

In beech-dominated forests in Central Europe, many spring geophytes show adaptations to seed dispersal by ants (myrmecochory). Ants, however, can be rare in such moist forests. Motivated by observations of slug feeding on seeds we investigated the seed consumption of two plant species, Anemone nemorosa and Asarum europaeum, by slugs, in a series of experiments. In a seed predation experiment in a beech forest, we found that seed removal was strongly reduced when gastropods were excluded from the seed depots. The contribution of insects, including ants, and rodents to seed removal was relatively less but differed between May and July. In the laboratory, slug species, in particular Arion sp., consumed seeds of both plant species. Slugs either consumed the elaiosomes of seeds or swallowed seeds intact. Swallowed seeds were defecated undamaged and germinated as well as control seeds when buried overwinter, indicating the potential for seed dispersal by slugs. We also recovered seeds of myrmecochores in the faeces of several slugs caught in forests. In a slug release experiment in the forest, slugs moved up to 14.6 m (mean 4.4 m) in 15 h, which is the median gut passage time of seeds based on measurements made in the laboratory. We also found that when slug-defecated seeds were offered to rodents, these were less attractive than control seeds, suggesting that passage through the slug gut reduces seed predation risk. Our results demonstrate that slugs are significant consumers of elaiosomes or entire seeds of ant-dispersed plants and that they can function as seed dispersers of these plants.     

贮藏种子的啮齿动物对油茶种子沉积形式的影响

种子沉积的质量常常涉及种子扩散作用者(如鸟类和小型啮齿动物)对生境和微生境的选择以及种子沉积的形式(如种子埋藏)。然而,很少的研究涉及到种子在离开母树后被这些动物沉积在何处。在四川省都江堰一个实验林场的2个林分(次生林和原生林)内,通过追踪用带编号的金属薄片标记的油茶(CamelliaoleiferaAbel.)种子的命运,研究了贮藏种子的啮齿动物对种子沉积的影响。研究发现在2个林分内,80%以上的种子被很好地埋藏在0~60mm深的土壤中,而小部分种子则被放置在地表(但有少量落叶遮盖)。小型啮齿动物喜好在灌丛下或灌丛边缘贮藏和取食种子,可能是在这样的微生境下它们在觅食时将遭遇较小的捕食风险。研究还发现,贮藏点的微生境分布随贮藏点等级而逐渐变化在两个林分内较高等级的贮藏点(如次贮藏点和三级贮藏点)比初级贮藏点有更多的种子被贮藏在灌丛下或灌丛边缘。这表明,啮齿动物对油茶种子的埋藏可能更有益于种子的存活、萌发以及幼苗的建成。啮齿动物将散落在母树下或其附近的油茶种子扩散到不同的微生境,这可能有利于他们遭遇到更多的适宜环境而萌发,实现幼苗补充。     

The Effect of Dung and Dispersal on Postdispersal Seed Predation of Attalea phalerata (Arecaceae) by Bruchid Beetles1

Low postdispersal mortality of palm seeds in tapir dung is hypothesized to result from the mechanical barrier provided by dung against bruchid infestation and/or from the distance to adult palms at which seeds are dispersed. We tested these hypotheses by distributing endocarps of Attalea phalerata Mart. ex Spreng. in experimental dung piles in Beni, Bolivia. Predation rates were significantly lower for seeds covered by dung than for exposed or partially covered seeds, but did not differ between seeds placed below and 50 m away from palms. Thus, dung, not short‐distance dispersal, protects seeds against bruchid beetles, and may ultimately promote survival of palm seeds.     

Granivory rates by rodents, insects, and birds at different microsites in the Patagonian steppe

We studied the rates of seed removal by different granivores, in different microsites, at different times, in a Patagonian shrub steppe in South America. Granivory rates of exotic ( Phalaris canariensis ) and native ( Mulinum spinosum ) seed species were an order of magnitude lower than those reported for another cool desert from North America with comparable climatic conditions. Insects and rodents removed the greatest amount of seeds in comparison to birds. In general, there were no differences in seed removal across microsites, except at one sampling time (when rodents and insects removed more seeds from bare soil and beside tussocks in comparison to positions beside shrubs, while birds took similar amounts of seeds from all microsites). The length of the experiment differentially affected the granivory rate of different groups. Removal rates (per day) were significantly greater, and exhibited lower variability, when seeds were left for a longer period of time in the field (a month) than for a few days. Insects were more efficient at finding the seeds rapidly and rodents at depleting them; birds could not find or deplete many seeds in short periods of time. Rates of granivory decreased slightly but significantly as the summer progressed mainly due to a reduction of seed removal by birds and rodents but not by insects. Granivores removed an order of magnitude less native seeds than exotic seeds. These differences seemed to be related to palatability as M. spinosum seeds have more phenols, toxic concentrations of iron and copper, and lower dry matter digestibility, phosphorous, and nitrogen content, in comparison to P. canariensis seeds.     

Seed Dispersal of a High Quality Fruit by Specialized Frugivores: High Quality Dispersal?1

Dispersal quality, as estimated by the cumulative effects of dispersal, germination, seed predation, and seedling survival, was examined for Beilschmiedia pendula (Lauraceae) in Monteverde, Costa Rica. I determined the pattern of dispersal by finding seeds deposited by birds, protected the seeds from seed predators with cages to assess germination and seedling survival, and examined seed predation rates with marked seeds. Seed predation, germination, and seedling survival were compared between seeds naturally dispersed by birds and seeds placed at randomly located sites. Approximately 70 percent of seeds dispersed by birds (N= 244) were deposited <10 m from crown edges of fruiting B. pendula trees, although some seeds were dispersed at least 70 m away. Larger seeds were more likely to be dispersed under or close to the parent trees, and larger seeds produced larger seedlings. Seed size was not correlated directly with seedling survival, but larger seedlings at three months were most likely to survive one year. Seed predation by mammals and insects and seedling mortality due to fungal pathogens were concentrated beneath the crowns of parent trees. Seedlings and saplings were more abundant beneath fruiting B. pendula trees, but individuals farther away were taller on average. Thus, dispersal is beneficial for B. pendula, but such benefits appear most pronounced at a small spatial scale; seeds dispersed >30 m from the crown edges actually had a lower probability of survival than those dispersed 10–20 m. Only 10 percent of B. pendula. seeds received high‐quality dispersal in terms of landing in the zone with the highest per seed probability of seedling survival 10–20 m from parental crowns.     

Distance and non-randomness of seed dispersal by the dwarf cassowary Casuarius bennetti

To determine the sources of dispersed seeds I inserted unique tags in fallen Aglaia aff flavida seeds before dwarf cassowaries (Casuanus bennetti) ate the fruits containing the seeds Thirty naturally-dispersed, marked seeds were re-located in cassowary droppings m a 400 ha study area The distribution of seed dispersal distances did not differ significantly from a normal distribution with a mean dispersal distance of 388 m, SD= 196 8 Mean distance of dispersed seeds to nearest mature conspecific tree was 170 m, SD= 108 4, dispersed seeds usually landed closer to other conspecifics than their parent The estimated distribution of all seeds (including many undispersed seeds) was leptokurtic, creating high densities near source trees (>0 035 seeds m^-2 within 100 m of bole) that quickly tapered off (<0 002 seeds m^-2 > 100 m from the bole), any density dependent effects are liable to be manifest only near parent trees
Cassowary movement patterns and resting behavior caused non-random dispersal of seeds Seeds were preferentially moved to level sites uphill from their source trees along routes that did not cross.steep terrain Undispersed seeds generally landed downhill from source trees This population of Aglaia would probably contract downhill into smaller, fragmented populations m the absence of cassowary-mediated dispersal     

贮藏种子的啮齿动物对油茶种子沉积形式的影响

种子沉积的质量常常涉及种子扩散作用者(如鸟类和小型啮齿动物)对生境和微生境的选择以及种子沉积的形式(如种子埋藏).然而,很少的研究涉及到种子在离开母树后被这些动物沉积在何处.在四川省都江堰一个实验林场的2个林分(次生林和原生林)内,通过追踪用带编号的金属薄片标记的油茶(Camellia oleifera Abel.)种子的命运,研究了贮藏种子的啮齿动物对种子沉积的影响.研究发现:在2个林分内,80%以上的种子被很好地埋藏在0～60 mm深的土壤中,而小部分种子则被放置在地表(但有少量落叶遮盖).小型啮齿动物喜好在灌丛下或灌丛边缘贮藏和取食种子,可能是在这样的微生境下它们在觅食时将遭遇较小的捕食风险.研究还发现,贮藏点的微生境分布随贮藏点等级而逐渐变化:在两个林分内较高等级的贮藏点(如次贮藏点和三级贮藏点)比初级贮藏点有更多的种子被贮藏在灌丛下或灌丛边缘.这表明,啮齿动物对油茶种子的埋藏可能更有益于种子的存活、萌发以及幼苗的建成.啮齿动物将散落在母树下或其附近的油茶种子扩散到不同的微生境,这可能有利于他们遭遇到更多的适宜环境而萌发,实现幼苗补充.     

动物与植物种子更新的关系Ⅱ．动物对种子的捕食、扩散、贮藏及与幼苗建成的关系

植物的繁殖体总是面临来自各类生物（如昆虫、脊椎动物、真菌）的捕食风险。因动物捕食引起的种子死亡率影响植物的适合度、种群动态、群落结构和物种多样性的保持。种子被捕食的时间和强度成为植物生活史中发芽速度、地下种子库等特征的主要选择压力,而种子大小、生境类型等因素也影响动物对植物种子的捕食。捕食者饱和现象被认为是植物和种子捕食者之间的高度协同进化作用的结果,是限制动物破坏种子、提高被扩散种子存活率的一种选择压力。大部分群落中的大多数植物种子被动物扩散。种子扩散影响种子密度、种子被捕食率、病原体攻击率、种子与母树的距离、种子到达的生境类型以及建成的植株将与何种植物竞争,从而影响种子和幼苗的存活,最终影响母树及后代植物的适合度。种子被动物扩散后的分布一般遵循负指数分布曲线,大多数种子并没有扩散到离母树很远的地方。捕食风险、生境类型、植被盖度均影响动物对种子的扩散。植物结实的季节和果实损耗的过程也体现了其对扩散机会的适应。许多动物有贮藏植物种子的行为。动物贮藏植物繁殖体的行为,一方面调节食物的时空分布,提高了贮食动物在食物缺乏期的生存概率;另一方面也为种子萌发提供了适宜条件,促进了植物的扩散。于是,植物与贮食动物形成了一种协同进化关系,这种关系可能是自然界互惠关系（mutualism)的一种。影响幼苗存活和建成的因子包括种子贮蒇点的微生境、湿度、坡向、坡度、林冠盖度等。许多果食性动物吃掉果肉后,再将完好的种子反刍或排泄出来。种子经动物消化道处理后,发芽率常有所提高。     

Post-dispersal predation of Acacia farnesiana seeds by Stator vachelliae (Bruchidae) in Central America

Summary Post-dispersal seed predation by the bruchid beetle Stator vachelliae was investigated in Santa Rosa National Park, Costa Rica. This insect finds the seeds of the leguminous Acacia farnesiana in the feces of horses, deer, and ctenosaur lizards, the current major dispersers. Patterns of oviposition and pre-adult survival of beetles in the seeds were investigated in a series of experiments using fresh horse dung. S. vachelliae never minded into the dung balls, attacking only those seeds located on the surface. Fresh horse dung did not attract insects more readily than dry dung. The proportion of seeds attacked was not related to their density in a defecation, and was similar in three areas with different densities of the host plant. In a fourth area with no fruiting A. farnesiana shrubs all seeds survived insect predation. Bruchids attacked a greater proportion of seeds at 1 m than at 5 m from the edge of the shrub's crown. Seeds were mainly removed from horse dung by rodents with similar intensity in all areas and at both distances; this seed removal interfered with bruchid oviposition and probably with bruchid survival. S. vachelliae oviposited less frequently on seeds in dung fully exposed to sun. When oviposition on a dung pile was high, the distribution of eggs on the seeds was clumped, suggesting that some seeds were preferred to others. By the end of the dry season, bruchids stopped attacking the seeds. The results show that the fate of both seeds and bruchids is greatly influenced by the location and time of defecation.