Seasonal, discharge-driven patterns of mayfly assemblages in an intermittent Neotropical stream

1. Streams in the seasonal wet and dry tropics have highly dynamic discharge regimes. Our study stream, located in mid-western Brazil, drains into the Pantanal, South America's largest wetlands, and is characterized by frequent spates in the rainy season and several weeks of interrupted flow in the dry season.
2. In order to understand how these seasonal flow patterns influence the aquatic fauna, floating litter was studied because: (i) this habitat is exposed to the current, and thus is likely to be most affected abiotically and biotically by changes in flow; and (ii) this habitat is abundant in unaltered tropical streams. Studies were conducted in a third- and a fourth-order reach. Mayflies were chosen as study organisms because they were frequent and species-rich on floating litter, and because they should to be responsive to changes in current velocity.
3. In the course of 15 months, covering one rainy and two dry seasons, mayflies showed pronounced seasonal patterns at family and genus level, which were evidently driven by discharge. Two periods of high mayfly densities were observed in the course of one year. One maximum coincided with the peak of the rainy season, the other with the peak of the dry season, and both were distinct in faunistic composition. At high current velocities the leptophlebiid Farrodes sp. was dominant and Leptohyphes sp., Acerpenna sp. and Paracloeodes sp. were frequent. In the dry season, when the river was reduced to isolated standing waters, 86–93% of all mayflies were Caenis sp.
4. Altogether sixteen mayfly genera from the families Baetidae, Caenidae, Leptohyphidae, Leptophlebiidae and Oligoneuriidae were recorded. Two genera are new to science, the baetid Aturbina was recently described (among others, from material from our study river), Acerpenna and Paracloeodes are new records for South America, and Miroculis and Terpides are recorded for the first time south of the Amazon.     

Influence of season on leaf litter ant (Hymenoptera: Formicidae) diversity in the locality of Minko'o (Southern,Cameroon)

Seasonality is known to influence ant activity in many tropical rain forests in the world such as South America and Africa. We surveyed ant fauna in the leaf litter in the locality of Minko'o. The work aimed to evaluate the effect of seasonal variation on the diversity and composition of litter ants. Ants were sampled from November 2015 to June 2017, using four sampling methods: visual capture, bait, pitfall trap and extraction. Species richness, Shannon diversity index and analysis of similarities were used to characterise diversity of ant communities between seasons. We collected 306 ant species, shared out between 56 genera and 11 subfamilies. Subfamilies Myrmicinae, Ponerinae, Dolichoderinae, Formicinae, Dorylinae, Cerapachyinae and Pseudomyrmecinae occurred in all the seasons. Species richness was highest in major dry season with 243 species followed by minor rainy season with 188, major rainy season with 177 species and finally minor dry season that recorded the lowest with 155 species. Kruskal–Wallis test showed that ant species richness did not differ between seasons (p > 0.05). Species diversity index indicated that diversity was the highest during minor dry season (H′ = 4.24), followed by the major dry season (H′ = 4.23), minor rainy season (H′ = 4.21) and lowest during major rainy season (H′ = 4.06). Eight most frequents ants have been recorded: Axinidris sp.1, Camponotus flavomarginatus, Monomorium guineense, Myrmicaria opaciventris, Odontomachus troglodytes, Carebara perpusilla, Paltothyreus tarsatus and Pheidole megacephala. Assessment of the seasonal effect on diversity reveals that dry season is richer and more diverse than rainy season and the season significantly influence the diversity of litter ants.     

The sizes, maturity stages and biomass of mayfly assemblages colonizing disturbed stream bed patches in central Kenya

The sizes, maturity stages and biomass of mayfly species colonizing disturbed patches on the stream bed surface of the Naro Moru River, Kenya, were determined from June 1993 to January 1994. All maturity stages I–VI⁺ were present in the pre-disturbance mayfly assemblages. Colonization of the disturbed patches by mayflies of different maturity stages was continuous, but slow or fast depending on the season and species. The overall post-disturbance maturity structure of the mayflies colonizing the disturbed patches did not demonstrate any distinct pattern. The majority of Caenis nymphs colonizing the patches in wet season II (November–January) were in emerging maturity stage VI⁺, whilst the majority of the individuals of Afronurus and Choroterpes ( Euthraulus ) populations matured from stage I in the wet seasons to stage VI⁺ in the dry season. Furthermore, the majority of the individuals of Baetis ( Nigrobaetis ) sp.1 were maturing to stages IV–VI during the wet seasons. Small-sized mayfly individuals (body length <3.0 mm) of all mayflies colonized the disturbed patches in the majority of numbers. However, although having the highest densities, they contributed a very low biomass compared with the fewer large-sized nymphs. There was no size gradation in the colonization of the disturbed patches, since all sizes were sampled at all times but in differing proportions. Colonization of the patches by mayflies was not size- or maturity stage-specific. Size distribution patterns could be useful in assessing which mayfly size-spectra are more or less susceptible to disturbance in streams.     

热带次生林、旱稻种植地和火烧迹地土壤节肢动物群落结构特征及季节变化

通过模拟刀耕火种过程 ,对刀耕火种前后的次生林、旱稻地 (第 2年 )和火烧迹地 (火烧后直接撂荒地第 2年 )土壤节肢动物群落结构特征及季节变化进行了调查研究。结果显示 :3块样地土壤节肢动物群落的优势类群组成相同 ,均为蜱螨目、膜翅目和弹尾目 ,但不同生境样地中各优势类群所占群落总数的比例不同 ,并且 3样地常见和稀有类群的组成差异较大 ;土壤节肢动物类群数、个体数和 DG多样性指数表现为次生林高于其它 2块样地 ,而旱稻地和火烧迹地则无较大差异 ,但一些类群在旱稻地、火烧迹地的数量分布与次生林具有差异 ,且在土壤层的表现较为突出 ;3块样地土壤节肢动物群落具有较好相似性 ,其中旱稻地与火烧迹地达到极相似水平 (D、DS>0 .9)。3种不同类型生境土壤节肢动物群落在类群数、个体数和多样性指数的季节变化总体呈现出雨量少的干季或雨季初末期高于雨量最大的雨季中期 ,与当地降雨量和气温变化有密切关系 ,同时各样地土壤节肢动物群落因生境条件不同及人为活动干扰强弱而形成各自的季节消长特点。研究表明刀耕火种后的旱稻种植对土壤节肢动物群落的恢复和发展在一定限制条件 (面积、周围次生林和坡度 )下无破坏性影响 ,但植被改变、农事活动等对直接撂荒地和旱稻地土壤节肢动物群落的季节消长产生     

枯落物处理对格木林土壤碳氮转化和微生物群落结构的短期影响

以我国南亚热带格木人工纯林为研究对象,采用气压过程分离(BaPS)技术和磷脂脂肪酸(PLFAs)法研究了不同枯落物处理(对照、枯落物去除、枯落物加倍)下土壤碳氮转化速率和微生物群落结构的季节变化.结果表明:不同枯落物处理土壤呼吸和总硝化速率均呈现明显的季节动态,雨季显著高于旱季.枯落物处理初期,土壤呼吸和总硝化速率均随枯落物输入量的增加呈下降趋势,但随着枯落物处理时间的延长,二者随枯落物输入量的增加而增加.旱季不同枯落物处理土壤微生物PLFAs总量和各菌群PLFAs量均显著高于雨季,而雨季真菌PLFAs/细菌PLFAs明显高于旱季.在旱季,枯落物去除处理土壤微生物PLFAs总量、细菌PLFAs量、真菌PLFAs量和丛枝菌根真菌PLFAs量分别显著提高30.9%、28.8%、44.4%和31.6%.在雨季,枯落物去除处理细菌PLFAs量和丛枝菌根真菌PLFAs量分别显著降低10.6%和33.3%.土壤微生物群落结构受枯落物输入量处理和季节的双重影响,土壤微生物群落结构主要受土壤温度和铵态氮的影响.枯落物输入量处理在短期内显著影响了格木林土壤碳氮转化速率和微生物群落结构,这种影响因季节的不同而存在差异.     

Rainfall and labile carbon availability control litter nitrogen dynamics in a tropical dry forest

N cycling in tropical dry forests is driven by rainfall seasonality but the mechanisms involved are not well understood. We studied the seasonal variation in N dynamics and microbial biomass in the surface litter of a tropical dry forest ecosystem in Mexico over a 2-year period. Litter was collected at 4 different times of the year to determine changes in total, soluble, and microbial C and N concentrations. Additionally, litter from each sampling date was incubated under laboratory conditions to determine potential C mineralization rate, net N mineralization, net C and N microbial immobilization, and net nitrification. Litter C concentrations were highest in the early-dry season and lowest in the rainy season, while the seasonal changes in N concentrations varied between years. Litter P was higher in the rainy than in the early-dry season. Water-soluble organic C (WSOC) and water-soluble N concentrations were highest during the early- and late-dry seasons and represented up to 4.1 and 5.9% of the total C and N, respectively. NH₄⁺ and NO₃⁻ showed different seasonal and annual variations. They represented an average 23% of soluble N. Microbial C was generally higher in the dry than in the wet seasons, while microbial N was lowest in the late-dry and highest in the early-rainy seasons. Incubations showed that lowest potential C mineralization rates and C and N microbial immobilization occurred in rainy season litter, and were positively correlated to WSOC. Net nitrification was highest in rainy season litter. Our results showed that the seasonal pattern in N dynamics was influenced by rainfall seasonality and labile C availability, and not by microbial biomass. We propose a conceptual model to hypothesize how N dynamics in the litter layer of the Chamela tropical dry forest respond to the seasonal variation in rainfall.     

Life histories, production dynamics and resource utilisation of mayflies (Ephemeroptera) in two tropical Asian forest streams

SUMMARY 1. A 2‐year study of the life histories, production dynamics and resource utilisation of five mayfly species was undertaken in two forest streams in Hong Kong [Tai Po Kau Forest Stream (TPKFS) and Shing Mun River (SMR)]. Afronurus sp. and Cinygmina sp. (Heptageniidae), Procloeon sp. and Baetiella pseudofrequenta (Baetidae), and Choroterpes sp. (Leptophlebiidae) were abundant in both streams and contributed more than 50% of the total mayfly populations. 2. All species had asynchronous larval development with recruitment occurring throughout the year. Mean annual production (all mayflies combined) was 3.1 and 2.0 g dry weight m^?2 year^?1 in SMR and TPKFS, respectively – the higher value at SMR reflecting greater mayfly densities – with more than 70% of production occurring during the wet season. Mayfly production varied between years, decreasing by 5% in TPKFS and 43% in SMR during 1996–97, reflecting lower densities of heptageniids relative to 1995–96. Annual biomass turnover rates (P/B) were high in both sites ranging from 27.2 to 94.6 in TPKFS (Cinygmina sp. and Procloeon sp.) and from 31.8 to 109.8 in SMR (Cinygmina sp. and B. pseudofrequenta). 3. Patterns of daily production in both streams showed that Afronurus sp., Cinygmina sp. and Choroterpes sp. were most productive during the wet season, while Procloeon sp. maintained high production levels throughout the year. The highest daily production of B. pseudofrequenta occurred during the wet season in TPKFS, but in the dry season at SMR. Temporal overlap in production and hence resource utilisation in both streams, calculated using the proportional similarity index (PS), ranged from 0.39 to 0.81. It was highest (0.63–0.81) between pairs of species of Heptageniidae and Baetidae, and lowest between Choroterpes sp. and other mayflies (0.39–0.61). No clear temporal segregation was observed among any species. However, when using the fraction of production attributable to each food, lower PS values were obtained for all species in both sites. In SMR, trophic segregation may have occurred between the two species pairs Procloeon sp.–Cinygmina sp. and Procloeon sp.–Choroterpes sp. (PS=0.17 and 0.03, respectively). 4. A combination of production data and information on the stable isotope signature of mayflies revealed that, during both the wet and dry seasons, more than 50% of total mayfly production in TPKFS was derived from autochthonous foods. In SMR, 68% of production was supported by allochthonous foods during the wet season, and 72% by autochthonous sources in the dry season. Considering that more than 70% of the total production occurred in the wet season, the trophic basis of mayfly production in SMR is mostly allochthonous (58%) while in TPKFS it is mainly of autochthonous origin (66%). The year‐round importance of autochthonous foods in shaded streams such as TPKFS is surprising, but the wet season contribution of allochthonous foods (especially in SMR) may have resulted from depletion of algal biomass during spates.     

亚热带常绿阔叶林6个常见树种凋落叶在不同降雨期的分解特征

地处长江上游的四川盆地亚热带常绿阔叶林具有典型雨热同季的气候特点,季节性干湿交替可能显著影响凋落物分解,但迄今缺乏相应的报道。因此,采用凋落物分解袋法,研究了常绿阔叶林区最具代表性的马尾松(Pinus massoniana)、柳杉(Cryptomeria fortunei)、杉木(Cunninghamia lanceolata)、香樟(Cinnamomum camphora)、红椿(Toona ciliata)、麻栎(Quercus acutissima)等6种凋落叶在第1年不同雨热季节的分解特征。结果表明,经历1a的分解,6种凋落叶质量残留率大小顺序依次为:红椿(27.90%)柳杉(41.39%)杉木(48.93%)麻栎(49.62%)马尾松(68.82%)香樟(72.23%),6种凋落叶在不同干湿季节质量损失差异显著(P0.05)。阔叶树种在旱季(MRS、SRS和WRS)的质量损失显著高于针叶树种。雨季(ERS和LRS)对6种凋落叶质量损失的贡献率(69.73%—89.68%)均明显大于旱季(10.32%—30.27%)。6种凋落叶在不同时期中质量损失速率差异显著(P0.05),且6种凋落叶在雨季的质量损失速率明显高于旱季。相关分析结果表明,凋落叶质量损失及其速率均与降雨量和温度呈极显著(P0.01)正相关关系。凋落叶质量损失与初始C、木质素含量及C/N、木质素/N极显著(P0.01)负相关,与N含量极显著(P0.01)正相关。这些结果表明亚热带地区森林凋落物分解的质量损失主要发生在雨季,雨季温湿度的改变可显著影响凋落物分解过程。     

A seasonal survey of gastrointestinal parasites in captive wild impala antelope on a game facility south of Lusaka, Zambia

Faecal samples (n?=?1947) from captive wild impala (Aepyceros melampus melampus) were examined over a period of 14 months to determine quantitative seasonal helminth egg excretion patterns and qualitative protozoan oocyst excretion patterns. Geometric mean monthly faecal egg counts (FECs) ranged from 20 to 575 and coprocultures revealed three parasite genera, namely Trichostrongylus, Haemonchus and Strongyloides. Larvae of the Trichostrongylus spp. were most predominant from faecal cultures. No trematode eggs or lungworms were detected and eggs of the cestode Monezia were only seen in two samples during the entire study period. The nematode FECs showed a marked seasonal variation, being higher during the rainy season, moderate during the cool dry season and low during the hot dry season. The rainy season had significantly higher FECs than the dry season (P?0.05), but were significantly higher in pelleted faeces in the rainy season than the dry season (P?相似文献   

垂叶榕榕小蜂群落及种间互作网络季节动态

群落中的物种相互作用构成了复杂的生态网络。有关物种的数量和组成的季节性动态变化已有较多的研究, 但是对于生态网络的动态变化知之甚少。揭示生态网络的动态变化对于理解群落的稳定性以及群落的动态变化过程和机理具有重要意义。本研究以垂叶榕(Ficus benjamina)榕小蜂群落为研究对象, 分别在西双版纳的干季和雨季采集了榕小蜂的种类和数量信息。比较了两个季节榕小蜂群落的动态变化以及共存网络的参数(例如网路直径、连接数、嵌套性和群落矩阵温度)变化。结果显示: 雨季榕果内传粉榕小蜂Eupristina koningsbergeri所占比例高于干季, 传粉榕小蜂的种群数量也高于干季, 而在干季非传粉榕小蜂的种类增加(干季15种小蜂, 雨季14种)。从榕树-传粉榕小蜂互利共生系统的适合度来看, 干季非传粉小蜂的增加对传粉榕小蜂和榕树的适合度是不利的。在干季, 共存网络物种间的连接数(干季0.95, 雨季0.47)多于雨季, 群落矩阵温度(干季23.24, 雨季2.64)也显著高于雨季。表明干季榕小蜂群落组成及种间关系较雨季更为复杂而多样, 高的矩阵温度暗示群落受到的干扰更大。     

Differential behavioural responses of mayflies from streams with and without fish to trout odour

1. In streams, mayflies (Order Ephemeroptera) are at risk from fish feeding visually in the water column. The effect of fish odour on the behaviour of Baetis bicaudatus from a fishless stream and a trout stream was investigated in four large oval tanks supplied with water from the fishless stream.
2. For each mayfly population, mayfly positioning on the substratum and movement in the water column (drift) were measured during the day and night, over 3 days. Brook trout ( Salvelinus fontinalis ) odour was added to two tanks to test the effect of a threat from fish.
3. Throughout the experiment more mayflies from the trout stream were observed on the substratum surface and in the water column during the night than the day, but the magnitude of night drift was less in tanks with fish odour.
4. Baetis from the fishless stream also displayed a nocturnal periodicity in drift and positioning, but their night-time drift was not affected by the presence of fish odour. On the first day of the experiment, however, more mayflies were observed on the substratum surface and drifting in tanks without fish odour during the day.
5. Sensitivity to fish odour may enable mayflies to alter their behaviour according to the risk of predation from fish.     

Differential behavioural responses of mayflies from streams with and without fish to trout odour

1. In streams, mayflies (Order Ephemeroptera) are at risk from fish feeding visually in the water column. The effect of fish odour on the behaviour of Baetis bicaudatus from a fishless stream and a trout stream was investigated in four large oval tanks supplied with water from the fishless stream.
2. For each mayfly population, mayfly positioning on the substratum and movement in the water column (drift) were measured during the day and night, over 3 days. Brook trout ( Salvelinus fontinalis ) odour was added to two tanks to test the effect of a threat from fish.
3. Throughout the experiment more mayflies from the trout stream were observed on the substratum surface and in the water column during the night than the day, but the magnitude of night drift was less in tanks with fish odour.
4. Baetis from the fishless stream also displayed a nocturnal periodicity in drift and positioning, but their night-time drift was not affected by the presence of fish odour. On the first day of the experiment, however, more mayflies were observed on the substratum surface and drifting in tanks without fish odour during the day.
5. Sensitivity to fish odour may enable mayflies to alter their behaviour according to the risk of predation from fish.     

Reproductive phenology, life-forms, and habitats of the Venezuelan Central Plain

Reproductive phenology of 171 plant species belonging to 57 families of angiosperms was studied according to life-forms in four habitat types in a savanna-forest mosaic on the Venezuelan Central Plain. Flowering, unripe fruit, and mature fruit patterns were affected significantly according to life-forms and habitats respectively. Production of flowers, unripe fruits, and mature fruits showed marked seasonality for all habitats except for the forest. Flowering peaked during the rainy season, and fruiting peaked toward the end of the rainy season. The savanna and the disturbed area had similar proportions of species that flowered over the year. The percentage of species with unripe fruits produced throughout the year was more seasonal for the disturbed area than for the other habitats. Mature fruit patterns showed an increase during the late rainy season for the ecotone and savanna. A large number of herbaceous (annual and perennial) and liana species flowered during the wet season, and a smaller fraction flowered during the dry season; and trees, shrubs, and epiphytes increased flowering activity during the dry season. Unripe fruit patterns were similar to those of flowering for all life-forms, however, tree species were less seasonal. Mature fruit production by shrubs peaked in the period of maximum rainfall, while the peak for perennial herbs was in the late rainy season and the peak for annual herbs was during the transition between the rainy season and the dry season. The largest proportion of tree and liana species with ripe fruits occurred during the dry season. Differences among phenological patterns in habitats were caused mainly by life-forms and promote a wider distribution of reproductive events in habitats and overall community in the Venezuelan Central Plain.     

Organic Matter Dynamics in a Tropical Gallery Forest in a Grassland Landscape

The high biodiversity of tropical forest streams depends on the strong input of organic matter, yet the leaf litter decomposition dynamics in these streams are not well understood. We assessed how seasonal litterfall affects leaf litter breakdown, density and biomass of aquatic invertebrates, and the microbial biomass and sporulation of aquatic hyphomycetes in a South American grassland ‘vereda’ landscape. Although litter production in the riparian area was low, leaf litter breakdown was high compared with other South American systems, with maximum values coinciding with the rainy season. Fungal biomass in decomposing leaves was high, but spore densities in water and sporulation rates were very low. Invertebrates were not abundant in litter bags, suggesting they play a minor role in leaf litter decomposition. Chironomids accounted for ~70 percent of all invertebrates; only 10 percent of non‐Chironomidae invertebrates were shredders. Therefore, fungi appear to be the drivers of leaf litter decomposition. Our results show that despite low productivity and relatively fast litter decomposition, organic matter accumulated in the stream and riparian area. This pattern was attributed to the wet/dry cycles in which leaves falling in the flat riparian zone remain undecomposed (during the dry period) and are massively transported to the riverbed (rainy season).     

Distribution and occurrence of myxomycetes on agricultural ground litter and forest floor litter in Thailand

The ecological distribution and seasonal patterns of occurrence of myxomycetes associated with the microhabitats represented by agricultural ground litter and forest floor litter were investigated in six study sites in northern Thailand during Oct 2004-Oct 2005. Both specimens that developed under natural conditions in the field and specimens obtained in moist chamber cultures were considered. Agricultural study sites were a banana plantation, a mango orchard and a sweet corn farm, whereas forest study sites consisted of a lowland forest, a midelevation forest and a highland forest. Seventy species of myxomycetes representing 20 genera were collected, with 34 species recorded during the dry season and 58 species recorded during the rainy season. Distinct differences were apparent for numbers of positive moist chambers, numbers of species recorded from moist chambers, numbers of species recorded as field collections and numbers of field collections when data obtained for the two seasons were compared. In the dry season only three species were collected in the field, but the percentage of positive moist chamber cultures (129/180 or 72%) and number of species recorded (33) from these cultures were high. In contrast, during the rainy season, 52 species of myxomycetes were collected in the field but only 15 species were recorded from the much lower percentage (75/180 or 42%) of positive moist chambers cultures.     

Evolutionary divergence in freshwater insects with contrasting dispersal capacity across a sea of desert

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Characteristics of floor litter and soil arthropod community in different types ot subtropical forest in Ailao Mountain of Yunnan, Southwest China

By using line transect method, an investigation was conducted on the floor litter and soil arthropod community in a mid mountain wet evergreen broad-leaved forest, a mossy dwarf forest, and a Populus bonatii forest in Ailao Mountain of Yunnan in April (dry and hot season), June (rainy season), and December (dry and cold season), 2005. In both dry and rainy seasons, the existing floor litter mass, C storage, and C/N ratio in the three forests all increased in the order of mossy dwarf forest > P. bonatii forest > evergreen broad-leaved forest, but the N storage had less difference. In the floor litter layer of the forests, Acari and Collembola were the dominant groups of soil arthropod community, while Diptera larvae, Coleoptera, ants, and Homoptera were the common groups. The Sorenson coefficients of soil arthropod community in the three forests were extremely great. No significant differences were observed in the soil arthropod density (ind x m(-2)) in the floor litter layer among the three forests, but the relative density (ind x g(-1)) of soil arthropods was higher in the evergreen broad-leaved forest and P. bonatii forest than in the mossy dwarf forest. In the three forests, the density of soil arthropods was significantly higher in dry season than in rainy season, but the Shannon diversity index had less difference. There were significant positive correlations between the existing floor litter mass and the individual density (ind x m(-2)) and dominant groups of soil arthropod communities in dry and hot season (April), but negative correlations between the existing floor litter mass and the relative density (ind x g(-1)) of soil arthropod communities and Acari in dry and cold season (December). The individual densities of Collembola and Coleoptera also had positive correlations with the N storage of the existing floor litter mass in the three forests. It was considered that the floor litter and the development of soil arthropod community in the litter layer of the subtropical forests in Ailao Mountain had a close relation with the vegetation structure of the forests, and the individual density and the diversity of the soil arthropod community were controlled by the floor litter, whereas the environmental factors such as temperature and moisture in the forests also had obvious effects on the seasonal dynamics of the individual density of the soil arthropods.     

Effects of water quality on habitat use by lesser scaup (Aythya affinis) broods in the boreal Northwest Territories, Canada

The dynamics of Rhizophora mangle litter production and decomposition were studied in a tropical coastal lagoon on the Gulf of Mexico in Veracruz, Mexico over a year (October 2002–October 2003). This region is characterized by three seasons: northerly winds (called ‘nortes’), dry, and rainy. Annual litter production (1116 g m⁻²) followed a seasonal pattern with leaf litter as the main fraction (70%) with two peaks in the dry and one in the rainy season. Leaf decomposition was evaluated with two types of litter bag in each season: fine mesh (1×1 mm) and coarse mesh (3×7 mm). Decomposition data were adjusted to a single negative exponential model. The results indicated faster decomposition rates in the coarse litter bag and significant differences among seasons. However these differences occurred after the 60th day of decomposition, indicating that leaching and microbial action were responsible for more than 50% of mass loss. After this period, the effects of aquatic invertebrates were evident but depended on climatic conditions. In the rainy season, the gastropod Neritina reclivata was associated with increasing leaf decomposition rate. In the ‘nortes’ season, the effect of aquatic invertebrates was smaller, and there were no differences in the decay constants calculated for the two litter bag types. High litter production represents an important input of organic matter which, through decomposition, may represent an important source of C, N, and P in this aquatic system.     

热带雨林林内小生境对木奶果和染木种子萌发与幼苗存活的影响

森林生态系统中小生境的差异可能影响种子萌发与幼苗的建立,并形成物种不同的分布格局。为探讨生境异质性对植物分布的影响,该研究在西双版纳热带季节性雨林中选取5个具有不同海拔和地形的小生境,人工散布木奶果与染木种子,定期监测种子萌发与幼苗存活,同步记录小生境的近地面（距地面3 cm）温度、近地面(3 cm)空气湿度和表层土壤(5 cm)含水量变化,并在实验室开展种子脱水和不同水势条件下的种子萌发实验。结果表明：（1）实验所选的5个小生境中,沟底地带的土壤水分含量在一年中始终都高于其他小生境;5个小生境的空气相对湿度在雨季与雾凉季都接近饱和,只有在干热季出现明显的差别,即随海拔的升高,空气湿度下降。同时,在旱季,近地面温度随海拔的升高而升高, 出现1~2个月的山地逆温现象。（2）木奶果与染木具有不同的种子传播与萌发规律,而且染木种子在不同生境下,其种子萌发率和幼苗存活率有显著的差异。其中：木奶果种子在雨季成熟散布并快速萌发,以幼苗的形式度过干热季,其种子可以在相对较低的水势下萌发;染木种子在雨季末期成熟并进入休眠期,以种子的形式度过干热季,其种子相对较抗脱水。研究认为,地形是决定西双版纳热带季节性雨林生境异质性的重要因子,小生境在温度和水分方面的差异在干热季时尤为明显,并对木奶果和染木种子的萌发或幼苗存活产生了重要影响, 而木奶果与染木种子自身的特性使其对于西双版纳季节性的干旱具有不同的适应对策。     

Species Richness and Abundance of Cerambycidae (Coleoptera) in Huatulco,Oaxaca, Mexico; Relationships with Phenological Changes in the Tropical Dry Forest

Cerambycidae have an important ecological role in initiating the degradation process of dead wood, but few studies have evaluated Cerambycidae community attributes in relation to ecosystem phenology. We surveyed the cerambicid fauna of the tropical dry forest in Huatulco, Oaxaca, Mexico, and explored the relationship of Cerambycidae species richness and abundance with phenological changes in vegetation. We applied three collecting methods of light traps, direct collection, and Malaise traps to survey Cerambycidae throughout 2005. To determine seasonal variations, we collected samples in the dry season month of February in the rainy season of May–July and August–September, and in the transition months of October and November through. We collected and identified 145 species, 88 genera, 37 tribes, and four subfamilies. The subfamily with the highest number of species was Cerambycinae (100 species), and the tribe with the highest number of genera and species was Elaphidiini with 13 genera and 33 species. The ICE non-parametric estimator determined an overall expected richness of 373 species, while the overall Shannon Diversity Index was 4.1. Both species richness and abundance varied seasonally, with the highest values recorded in the rainy season and the lowest in the dry season. Overall species abundance was not significantly correlated to monthly rainfall or EVI neither, only for “direct collecting” the EVI vs Richness and EVI vs Shannon Diversity Index were significantly correlated. We propose that the seemingly contradictory relationships between seasonal richness patterns of Cerambycidae and the greening/senescence of vegetation (EVI) may be explained by the seasonal availability of dead organic matter, flowers, or leafy vegetation that may be synchronized with the behavior of different cerambycid species.