Phenology of Ficus variegata in a seasonal wet tropical forest at Cape Tribulation, Australia

Abstract. We studied the phenology of 198 mature trees of the dioecious fig Ficus variegata Blume (Moraceae) in a seasonally wet tropical rain forest at Cape Tribulation, Australia, from March 1988 to February 1993. Leaf production was highly seasonal and correlated with rainfall. Trees were annually deciduous, with a pronounced leaf drop and a pulse of new growth during the August-September drought. At the population level, figs were produced continually throughout the study but there were pronounced annual cycles in fig abundance. Figs were least abundant during the early dry period (June-September) and most abundant from the late dry season (October-November) through the wet season (December-April). The annual peak in reproduction actually reflected two staggered peaks arising from gender differences in fig phenology. In this dioecious species, female and male trees initiated their maximal fig crops at different times and flowering was to some extent synchronized within sexes. Fig production in the female (seed-producing) trees was typically confined to the wet season. Male (wasp-producing) trees were less synchronized than female trees but reached a peak level of fig production in the months prior to the onset of female fig production. Male trees were also more likely to produce figs continually. Asynchrony among male fig crops during the dry season could maintain the pollinator population under adverse conditions through within- and among-tree wasp transfers.     

Phenology of figs in Budongo Forest Uganda and its importance for the chimpanzee diet

This paper reports on the phenological patterns of figs in Budongo Forest, Uganda, and how it relates to chimpanzee food availability in different seasons. In addition, we analysed the dung of chimpanzees to understand the composition of fruits in their diet. The aim of our study was to assess Ficus phenology and how it affects chimpanzee diet. Fifteen species of figs were monitored for fruit (syconium) and leaf phenology between June 2000 and 2001. Ficus fruit production varied significantly between and within species, and also with tree trunk and crown diameters. Fig fruit production was asynchronous and individual fig trees produced crops from one to five times in a year. In addition to fruits, chimpanzees fed on young leaves of some Ficus species. Shedding of old Ficus leaves coincided with the dry season, followed by appearance of young leaves. The dry season in Budongo is a period of general fruit scarcity. The combination of fig fruits and young leaves make up the most important food in the diet of chimpanzees. From the chimpanzee dung, more than 78% of seeds comprised fig ‘seeds’ (nutlets) and the rest of the diaspores were from other tree species. Our findings suggest that chimpanzees disperse large number of diaspores in their dung, thereby serving as important agents of natural forest regeneration.     

Partitioning of soil water among canopy trees in a seasonally dry tropical forest

Little is known about partitioning of soil water resources in species-rich, seasonally dry tropical forests. We assessed spatial and temporal patterns of soil water utilization in several canopy tree species on Barro Colorado Island, Panama, during the 1997 dry season. Stable hydrogen isotope composition (δD) of xylem and soil water, soil volumetric water content (θ_v), and sap flow were measured concurrently. Evaporative fractionation near the soil surface caused soil water δD to decrease from about –15‰ at 0.1 m to –50 to –55‰ at 1.2 m depth. Groundwater sampled at the sources of nearby springs during this period yielded an average δD value of –60‰. θ_v increased sharply and nearly linearly with depth to 0.7 m, then increased more slowly between 0.7 and 1.05 m. Based on xylem δD values, water uptake in some individual plants appeared to be restricted largely to the upper 20 cm of the soil profile where θ_v dropped below 20% during the dry season. In contrast, other individuals appeared to have access to water at depths greater than 1 m where θ_v remained above 45% throughout the dry season. The depths of water sources for trees with intermediate xylem δD values were less certain because variation in soil water δD between 20 and 70 cm was relatively small. Xylem water δD was also strongly dependent on tree size (diameter at breast height), with smaller trees appearing to preferentially tap deeper sources of soil water than larger trees. This relationship appeared to be species independent. Trees able to exploit progressively deeper sources of soil water during the dry season, as indicated by increasingly negative xylem δD values, were also able to maintain constant or even increase rates of water use. Seasonal courses of water use and soil water partitioning were associated with leaf phenology. Species with the smallest seasonal variability in leaf fall were also able to tap increasingly deep sources of soil water as the dry season progressed. Comparison of xylem, soil, and groundwater δD values thus pointed to spatial and temporal partitioning of water resources among several tropical forest canopy tree species during the dry season. Received: 5 October 1998 / Accepted: 23 June 1999     

鸡嗉子榕内传粉小蜂与非传粉小蜂的繁殖稳定共存机制研究

【目的】榕-蜂系统是自然界协同进化和互利共生的典型模型,榕-蜂之间如何实现繁殖分配从而实现稳定共存一直是倍受研究者关注的问题,但对传粉小蜂和非传粉小蜂的繁殖稳定共存研究较少。【方法】本文选取分布在西双版纳地区的雌雄异株榕树鸡嗉子榕Ficus semicordata的雄果,通过对榕果内唯一的传粉小蜂Ceratosolen gravelyi Grandi以及4种非传粉小蜂Philotrypesis dunia Joseph,Apocrypta sp.,Platyneura sp.,Sycoscapter trifemmensis Joseph的产卵时序进行了观察,并对5种小蜂的种群数量进行统计,以及对每种小蜂产卵小花的空间分布、瘿花体积等特征进行了研究。【结果】发现:5种小蜂在产卵时间上存在分离,且传粉小蜂的种群数量远大于其他4种非传粉小蜂的种群数量之和。5种小蜂的瘿花特征也存在差异:瘿花的子房大小不同,且花梗长度即分布空间也有差异,传粉小蜂最接近果腔而非传粉小蜂则更多地利用中层和内层的小花。【结论】结果说明在鸡嗉子榕有限的空间内,5种小蜂通过产卵时间和生长空间的分离,实现了减少竞争以及长期共存的特征,维持了榕-蜂系统的稳定性。     

Adaptive radiation in the Afrotropical region of the Paleotropical genus Lissocephala (Drosophilidae) on the pantropical genus Ficus (Moraceae)

Abstract. Of sixty-three extant genera of Drosophilidae, the genus Lissocephala is unique in having produced a diverse radiation superimposed on a plant-insect mutualism. Lissocephala is basically Paleotropical, with twenty-three Afrotropical and eight Oriental and Australasian species, and seemingly the adaptive radiation occurred on a taxonomically restricted group of host-plants, species of Ficus (Moraceae), solely in the African floristic region. A paradox results from the consideration that only the African radiation is linked with a strict diversification on Ficus species, even though this host plant genus is more diverse in the Oriental region. The focus of the present work is to document the diversity of host-figs exploited by Lissocephala in the African mainland (twenty-two fig species have yielded twenty-three Lissocephala species, but similarities in numbers between insects and plants does not seemingly result from species specificity), and to show that the clear-cut divide between the two African strictly fig-breeding Lissocephala lineages (the juncta and sanu groups) observed from male terminalia is further supported on the basis of 28S nuclear DNA divergence. Evolutionary scenarios are discussed whereby the two African Lissocephala lineages might have diverged on the African mainland or arisen independently from Oriental ancestors. Although the possibility remains that the juncta and sanu lineages set foot independently on the African mainland, it is more likely that there was a single colonization event for a common juncta—sanu ancestor. A stepwise host-fig transfer would then have occurred on the African mainland. The African Lissocephala ancestor would have first spread among the Sycomorus figs and only secondarily among the Galoglychia figs.     

Development and characterization of microsatellite markers for a monoecious Ficus species,Ficus insipida,and cross‐species amplification among different sections of Ficus

The animal‐mediated pollination and seed‐dispersal mutualisms of Ficus species give them key roles in tropical ecosystems, but may make them vulnerable to habitat fragmentation. The development of highly polymorphic markers is needed to analyse their genetic diversity and investigate the effects of fragmentation on gene flow. Of thirteen microsatellite loci isolated from Ficus insipida, a monoecious species in French Guiana, eleven were polymorphic (two to six alleles each). High levels of variation were found among loci; expected heterozygosities ranged from 0.151 to 0.715. All markers revealed a broad cross‐species affinity when tested in 23 other Ficus species.     

Development of 17 microsatellite markers for Ceratosolen constrictus, the pollinating fig wasp of Ficus fistulosa

The obligate mutualism between figs (Ficus) and fig pollinating wasps (Agaonidae) is regarded as a classic example of mutualism. Seventeen polymorphic microsatellite loci were developed for Ceratosolen constrictus, the pollinating wasp of the dioecious fig Ficus fistulosa. The number of alleles per locus ranged from two to 15 and the observed and expected heterozygosities ranged from 0.040 to 0.846 and from 0.040 to 0.916, respectively. These microsatellite loci offer a powerful tool for evolutionary and population genetic studies in C. constrictus, and gene flow of F. fistulosa.     

Mast fruiting of large ectomycorrhizal African rain forest trees: importance of dry season intensity, and the resource-limitation hypothesis

Mast fruiting is a distinctive reproductive trait in trees. This rain forest study, at a nutrient-poor site with a seasonal climate in tropical Africa, provides new insights into the causes of this mode of phenological patterning. At Korup, Cameroon, 150 trees of the large, ectomycorrhizal caesalp, Microberlinia bisulcata, were recorded almost monthly for leafing, flowering and fruiting during 1995-2000. The series was extended to 1988-2004 with less detailed data. Individual transitions in phenology were analysed. Masting occurred when the dry season before fruiting was drier, and the one before that was wetter, than average. Intervals between events were usually 2 or 3 yr. Masting was associated with early leaf exchange, followed by mass flowering, and was highly synchronous in the population. Trees at higher elevation showed more fruiting. Output declined between 1995 and 2000. Mast fruiting in M. bisulcata appears to be driven by climate variation and is regulated by internal tree processes. The resource-limitation hypothesis was supported. An 'alternative bearing' system seems to underlie masting. That ectomycorrhizal habit facilitates masting in trees is strongly implied.     

Disturbance effects on community structure of Ficus tinctoria fig wasps in Xishuangbanna, China: Implications for the fig/fig wasp mutualism

Abstract  Fig trees are important components of tropical forests, because their fruits are eaten by so many vertebrates, but they depend on pollinating fig wasps to produce mature fruits. Disturbance to habitat structure can have a major impact on insect diversity and composition, potentially reducing fruit yields. We investigated the impact of habitat disturbance on the fig wasp community associated with male figs of Ficus tinctoria in Xishuangbanna, China. The community comprised one pollinator species Liporrhopalum gibbosae and six non-pollinating wasp species: Sycoscapter sp.1, Philotrypesis ravii , Philotrypesis sp.1, Neosycophila omeomorpha , Sycophila sp.1, and Walkerella sp.1. More disturbed areas were characterized by higher temperatures, less shade, and more vehicle noise. The response of the fig wasp community was complex, with no simple relationship between intensity of disturbance and pollinator abundance. However, the sex ratios (proportion of male progeny) of pollinators increased significantly in more disturbed areas. We conclude that potential changes in fig wasp community composition brought about by disturbance, are unpredictable, with unclear consequences for tropical rainforest biodiversity.     

Respiration acclimation contributes to high carbon-use efficiency in a seasonally dry pine forest

Predictions of warming and drying in the Mediterranean and other regions require quantifying of such effects on ecosystem carbon dynamics and respiration. Long‐term effects can only be obtained from forests in which seasonal drought is a regular feature. We carried out measurements in a semiarid Pinus halepensis (Aleppo pine) forest of aboveground respiration rates of foliage, R_f, and stem, R_t over 3 years. Component respiration combined with ongoing biometric, net CO₂ flux [net ecosystem productivity (NEP)] and soil respiration measurements were scaled to the ecosystem level to estimate gross and net primary productivity (GPP, NPP) and carbon‐use efficiency (CUE=NPP/GPP) using 6 years data. GPP, NPP and NEP were, on average, 880, 350 and 211 g C m^?2 yr^?1, respectively. The above ground respiration made up half of total ecosystem respiration but CUE remained high at 0.4. Large seasonal variations in both R_f and R_t were not consistently correlated with seasonal temperature trends. Seasonal adjustments of respiration were observed in both the normalized rate (R₂₀) and short‐term temperature sensitivity (Q₁₀), resulting in low respiration rates during the hot, dry period. R_f in fully developed needles was highest over winter–spring, and foliage R₂₀ was correlated with photosynthesis over the year. Needle growth occurred over summer, with respiration rates in developing needles higher than the fully developed foliage at most times. R_t showed a distinct seasonal maximum in May irrespective of year, which was not correlated to the winter stem growth, but could be associated with phenological drivers such as carbohydrate re‐mobilization and cambial activity. We show that in a semiarid pine forest photosynthesis and stem growth peak in (wet) winter and leaf growth in (dry) summer, and associated adjustments of component respiration, dominated by those in R₂₀, minimize annual respiratory losses. This is likely a key for maintaining high CUE and ecosystem productivity similar to much wetter sites, and could lead to different predictions of the effect of warming and drying climate on productivity of pine forests than based on short‐term droughts.     

Water uptake and transport in lianas and co-occurring trees of a seasonally dry tropical forest

Water uptake and transport were studied in eight liana species in a seasonally dry tropical forest on Barro Colorado Island, Panama. Stable hydrogen isotope composition (D) of xylem and soil water, soil volumetric water content (_v), and basal sap flow were measured during the 1997 and 1998 dry seasons. Sap flow of several neighboring trees was measured to assess differences between lianas and trees in magnitudes and patterns of daily sap flow. Little seasonal change in _v was observed at 90–120 cm depth in both years. Mean soil water D during the dry season was –19 at 0–30 cm, –34 at 30–60 cm, and –50 at 90–120 cm. Average values of xylem D among the liana species ranged from –28 to –44 during the middle of the dry season, suggesting that water uptake was restricted to intermediate soil layers (30–60 cm). By the end of the dry season, all species exhibited more negative xylem D values (–41 to –62), suggesting that they shifted to deeper water sources. Maximum sap flux density in co-occurring lianas and trees were comparable at similar stem diameter (DBH). Furthermore, lianas and trees conformed to the same linear relationship between daily sap flow and DBH. Our observations that lianas tap shallow sources of soil water at the beginning of the dry season and that sap flow is similar in lianas and trees of equivalent stem diameter do not support the common assumptions that lianas rely primarily on deep soil water and that they have higher rates of sap flow than co-occurring trees of similar stem size.     

Diversity of flowering and fruiting phenology of trees in a tropical deciduous forest in India

BACKGROUND AND AIMS: In the dry tropics, vegetative phenology varies widely with tree characteristics and soil conditions. The present work aims to document the phenological diversity of flowering and fruiting with reference to leafing events in Indian dry-tropical tree species. METHODS: Nine tree species, including one leaf-exchanging and eight deciduous showing varying leafless periods, were studied. Monthly counts of leaves, flowers and fruits were made on 160 tagged twigs on ten individuals of each species for initiation, completion and duration of different phenological events through two annual cycles. KEY RESULTS: Variation in flowering relative to leaf flushing (which occurred just prior to or during a hot, dry summer) revealed five flowering types: summer flowering (on foliated shoots), rainy-season flowering (on foliated shoots following significant rains), autumn flowering (on shoots with mature leaves), winter flowering (on shoots undergoing leaf fall) and dry-season flowering (on leafless shoots). Duration of the fruiting phenophase was shortest (3-4 months) in dry-season and winter-flowering species, 6-9 months in rainy-and autumn-flowering species, and maximum (11 months) in summer-flowering species. A wide range of time lag (<1 to >8 months) between the start of vegetative (first-leaf flush) and reproductive (first-visible flower) phases was recorded in deciduous species; this time lag was correlated with the extent of the leafless period. A synthesis of available phenological information on 119 Indian tropical trees showed that summer-flowering species were most abundant (56 % of total species) amongst the five types recognized. CONCLUSIONS: The wide diversity of seasonal flowering and fruiting with linkages to leaf flush time and leafless period reflect the fact that variable reproductive and survival strategies evolved in tree species under a monsoonic bioclimate. Flowering periodicity has evolved as an adaptation to an annual leafless period and the time required for the fruit to develop. The direct relationship between leafless period (inverse of growing period) and time lag between onset of vegetative and reproductive phases reflects the partitioning of resource use for supporting these phases. Predominance of summer flowering coupled with summer leaf flushing seems to be a unique adaptation in trees to survive under a strongly seasonal tropical climate.     

The pollination of Ficus vogelii in Ghana

Ficus vogelii is a primitive monoecious species, in which staminate and pistillate flowers are distributed throughout the syconium without localization. There is no bimodal structural distinction between seed flowers and gall flowers, and any pistillate flower is capable of seed production. Each syconium follows a development cycle lasting approximately 45 days. The chief pollen vector is the agaonid wasp Allotriozoon heterandromorphum , which is an obligate symbiont. Adult females of this species have mesothoracic pockets in which pollen is carried. Adult males do not display the anther-cutting activity reported in other species. The life cycle of the pollinator is described in relation to the developmental cycle of the syconium.     

Species diversity of lepidopteran stem borer parasitoids in cultivated and natural habitats in Kenya

Field surveys were conducted during 2005 to 2007 to assess the species diversity of stem borer parasitoids in cultivated and natural habitats in four agroecological zones in Kenya. In total, 33 parasitoid species were recovered, of which 18 parasitized six stem borer species feeding on cereal crops, while 27 parasitized 21 stem borer species feeding on 19 wild host plant species. The most common parasitoids in cultivated habitats were Cotesia flavipes Cameron, Cotesia sesamiae (Cameron), Pediobius furvus Gahan and the tachinid Siphona sp., whereas in natural habitats, Siphona sp. was the most common. The majority of parasitoids were stenophagous species; only five species –Cotesia sp., Enicospilus ruscus Gauld and Mitchell, Pristomerus nr. bullis, Sturmiopsis parasitica (Curran) and Syzeuctus ruberrimus Benoit – were monophagous. In both cultivated and natural habitats, parasitoid species diversity was highest on the most dominant stem borers Busseola spp. and Chilo spp. On cereal crops, parasitoid diversity was highest on maize and among wild host plants, it was highest on Setaria spp. The ingress‐and‐sting attack method was the most common strategy used by parasitoids in both habitats. In all agroecological zones, parasitoid species diversity was significantly higher in natural than in cultivated habitats. Furthermore, the majority of parasitoid species were common to both cultivated and natural habitats. It was concluded that natural habitats surrounding cereal crops serve as refugia for sustaining the diversity of stem borer parasitoids from adjacent cereal fields.     

榕树在西双版纳热带雨林生态系统中的作用

榕树是西双版纳热带雨林中的关键植物类群之一,能够为多种生物提供栖息地和食物,从而维持该地区热带雨林生态系统的物种多样性。一些种类的榕树有绞杀特性,在森林更新演替中能够起到积极的作用;还有些种类的榕树是先锋物种,在植被恢复中起重要作用。但是,近些年对西双版纳的过度开发已经使热带雨林片断化,榕树种群数量大量减少,榕果内的寄生蜂、食榕果动物也受到了不同程度的影响。保护好西双版纳热带雨林中关键植物类群榕树,是保护和恢复热带雨林生态系统的重要措施之一。     

Pollinating fig wasps: genetic consequences of island recolonization

The levels of genetic diversity and gene flow may influence the long-term persistence of populations. Using microsatellite markers, we investigated genetic diversity and genetic differentiation in island (Krakatau archipelago, Indonesia) and mainland (Java and Sumatra, Indonesia) populations of Liporrhopalum tentacularis and Ceratosolen bisulcatus, the fig wasp pollinators of two dioecious Ficus (fig tree) species. Genetic diversity in Krakatau archipelago populations was similar to that found on the mainland. Population differentiation between mainland coastal sites and the Krakatau islands was weak in both wasp species, indicating that the intervening 40 km across open sea may not be a barrier for wasp gene flow (dispersal) and colonization of the islands. Surprisingly, mainland populations of the fig waSPS may be more genetically isolated than the islands, as gene flow between populations on the Javan mainland differed between the two wasp species. Contrasting growth forms and relative 'immunity' to the effects of deforestation in their host fig trees may account for these differences.