Feeding ecology and phylogenetic structure of a complex neotropical termite assemblage,revealed by nitrogen stable isotope ratios

1. In the current ecological classification of termites, four feeding groups (I–IV) are recognised, corresponding to a gradient of decomposition from sound wood to highly mineralised organic matter in the soil. 2. Nitrogen stable isotopes (hereafter δ¹⁵N) were used to place termites from French Guiana rainforests along a wood‐soil decomposition gradient, to test (i) whether feeding group assignation based on morphological characters was accurate and actually represented diet specialisation thresholds, and (ii) to what extent the dietary specialization of species is explained by phylogeny (phylogenetic autocorrelation). 3. δ¹⁵N values vary over a range of 13‰, suggesting that diet diversification contributes to the high species diversity in French Guiana. δ¹⁵N values span a similar interval in all Termitidae subfamilies. Ranges of different subfamilies broadly overlap, although each of them diversified preferentially on one side of the wood‐soil decomposition gradient. Congeneric species share similar feeding habits, whereas distant species tend to feed on distinct substrates. 4. Feeding groups did not completely match stable isotope data: there was no discontinuity between Groups III and IV, and no correlation between anatomical criteria used to distinguish these groups and δ¹⁵N values. Nor was there any consistent difference in δ¹⁵N values between wood feeders of the families Rhinotermitidae (Group I) and Termitidae (Group II). We also suggest that species feeding outside the wood‐soil gradient should be distinguished for their peculiar feeding requirements.     

Structure of tropical river food webs revealed by stable isotope ratios

Fish assemblages in tropical river food webs are characterized by high taxonomic diversity, diverse foraging modes, omnivory, and an abundance of detritivores. Feeding links are complex and modified by hydrologic seasonality and system productivity. These properties make it difficult to generalize about feeding relationships and to identify dominant linkages of energy flow. We analyzed the stable carbon and nitrogen isotope ratios of 276 fishes and other food web components living in four Venezuelan rivers that differed in basal food resources to determine 1) whether fish trophic guilds integrated food resources in a predictable fashion, thereby providing similar trophic resolution as individual species, 2) whether food chain length differed with system productivity, and 3) how omnivory and detritivory influenced trophic structure within these food webs. Fishes were grouped into four trophic guilds (herbivores, detritivores/algivores, omnivores, piscivores) based on literature reports and external morphological characteristics. Results of discriminant function analyses showed that isotope data were effective at reclassifying individual fish into their pre-identified trophic category. Nutrient-poor, black-water rivers showed greater compartmentalization in isotope values than more productive rivers, leading to greater reclassification success. In three out of four food webs, omnivores were more often misclassified than other trophic groups, reflecting the diverse food sources they assimilated. When fish δ¹⁵N values were used to estimate species position in the trophic hierarchy, top piscivores in nutrient-poor rivers had higher trophic positions than those in more productive rivers. This was in contrast to our expectation that productive systems would promote longer food chains. Although isotope ratios could not resolve species-level feeding pathways, they did reveal how top consumers integrate isotopic variability occurring lower in the food web. Top piscivores, regardless of species, had carbon and nitrogen profiles less variable than other trophic groups.     

Carbon sources of Antarctic nematodes as revealed by natural carbon isotope ratios and a pulse-chase experiment

δ¹³C of nematode communities in 27 sites was analyzed, spanning a large depth range (from 130 to 2,021 m) in five Antarctic regions, and compared to isotopic signatures of sediment organic matter. Sediment organic matter δ¹³C ranged from −24.4 to −21.9‰ without significant differences between regions, substrate types or depths. Nematode δ¹³C showed a larger range, from −34.6 to −19.3‰, and was more depleted than sediment organic matter typically by 1‰ and by up to 3‰ in silty substrata. These, and the isotopically heavy meiofauna at some stations, suggest substantial selectivity of some meiofauna for specific components of the sedimenting plankton. However, ¹³C-depletion in lipids and a potential contribution of chemoautotrophic carbon in the diet of the abundant genus Sabatieria may confound this interpretation. Carbon sources for Antarctic nematodes were also explored by means of an experiment in which the fate of a fresh pulse of labile carbon to the benthos was followed. This organic carbon was remineralized at a rate (11–20 mg C m⁻² day⁻¹) comparable to mineralization rates in continental slope sediments. There was no lag between sedimentation and mineralization; uptake by nematodes, however, did show such a lag. Nematodes contributed negligibly to benthic carbon mineralization.     

Biomass and carbon dynamics of a tropical mountain rain forest in China

Biometric inventories for 25 years, from 1983 to 2005, indicated that the Jianfengling tropical mountain rain forest in Hainan, China, was either a source or a modest sink of carbon. Overall, this forest was a small carbon sink with an accumulation rate of (0.56±0.22) Mg C ha⁻¹yr⁻¹, integrated from the long-term measurement data of two plots (P9201 and P8302). These findings were similar to those for African and American rain forests ((0.62±0.23) Mg C ha⁻¹yr⁻¹). The carbon density varied between (201.43±29.38) Mg C ha⁻¹ and (229.16±39.2) Mg C ha⁻¹, and averaged (214.17±32.42) Mg C ha⁻¹ for plot P9201. Plot P8302, however, varied between (223.95±45.92) Mg C ha⁻¹ and (254.85±48.86) Mg C ha⁻¹, and averaged (243.35±47.64) Mg C ha⁻¹. Quadratic relationships were found between the strength of carbon sequestration and heavy rainstorms and dry months. Precipitation and evapotranspiration are two major factors controlling carbon sequestration in the tropical mountain rain forest.     

Changes in stable nitrogen and carbon isotope ratios of plants and soil across a boreal forest fire chronosequence

Background and Aim

Nitrogen (N) and carbon (C) isotopic signatures (δ¹⁵N and δ¹³C) serve as powerful tools for understanding temporal changes in ecosystem processes, but how these signatures change across boreal forest chronosequences is poorly understood.

Methods

The δ¹⁵N, δ¹³C, and C/N ratio of foliage of eight dominant plant species, including trees, understory shrubs, and a moss, as well as humus, were examined across a 361 years fire-driven chronosequence in boreal forest in northern Sweden.

Results

The δ¹³C and C/N ratio of plants and humus increased along the chronosequence, suggesting increasing plant stress through N limitation. Despite increasing biological N fixation by cyanobacteria associated with feather mosses, δ¹⁵N showed an overall decline, and δ¹⁵N of the feather moss and associated vascular plants diverged over time from that of atmospheric N₂.

Conclusions

Across this chronosequence the N fixed by cyanobacteria is unlikely to be used by mosses and vascular plants without first undergoing mineralization and mycorrhizal transport, which would cause a change in δ¹⁵N signature due to isotopic fractionation. The decreasing trend of δ¹⁵N suggests that as the chronosequence proceeds, the plants may become more dependent on N transferred from mycorrhizal fungi or from N deposition.     

Forest savanna ecotone dynamics in India as revealed by carbon isotope ratios of soil organic matter

Linear programming models of diet selection (LP) have been criticized as being too sensitive to variations in parameter values that have not been or may not be able to be measured with a high degree of precision (small standard error). Therefore, LP's predictions have been questioned, even though the predicted diet choices agree very well with observations in 400 published tests. The philosophical and statistical aspects of this criticism of LP are reviewed in light of the ability to test any nontrivial ecological theory. It is argued that measures of error in field data may not meet simple statistical definitions, and thereby, may make sensitivity analyses that use the error measures overly conservative. Furthermore, the important issue in testing ecological theory may not be the statistical confidence in a single test, but whether or not the theory withstands repeated tests.     

Use of carbon and nitrogen isotope ratios in termite research

In this paper, I review carbon and nitrogen isotopic (natural abundance levels) studies of termites. The carbon isotope ratio of CH₄ emitted from termites, together with the emission rates of CO₂, CH₄ and H₂, showed several trends corresponding to the kinds of symbiotic microbes and feeding habits. The fraction of methane oxidized in the nest structure was estimated by comparing carbon isotope ratio of CH₄ emitted from the nest with that produced by termites in the nest. Symbiotic nitrogen fixation in the gut of termites has been shown to have a significant contribution to the nitrogen economy in some wood-feeding termites. The carbon isotope ratio distinguishes between C4 from C3 plants, and the fractional contribution of grass in the diet can thereby be estimated. The carbon and nitrogen isotope ratios in termites are discernible among soil-feeders, fungus cultivators and wood-feeders. Wood/soil-interface feeders have intermediate values between wood- and soil-feeders, and thus carbon and nitrogen stable isotope ratios are assumed to characterize the degree of humification of the material consumed by termites. It is suggested that carbon and nitrogen isotope ratios are useful indicators of the functional position of termites in the decomposition process. A similar isotope pattern has been obtained in earthworms, suggesting that isotope signatures might be useful parameters in investigating detritivorous animals in general.     

Seed rain and advanced regeneration in a tropical rain forest

By comparing seed rain, seedling and sapling community structures we assessed the possible role played by vertebrate seed dispersal as a structuring factor in advanced regeneration of closed-canopied sites in the tropical rain forest of Los Tuxtlas, Mexico. Seed weight, initial morphology of seedlings and species abundance were also analyzed to determine if these traits influenced the probability of establishment in the shade.About half of the seed species falling in five closed forest sites (25×25 m) during one year came from fruiting trees growing within the sites (local seeds) and half from fruiting trees found outside the sites (immigrant seeds). Seeds of liana and upper-canopy species were over-represented among immigrant seeds compared with seeds of understory tree species. This probably reflects the activity of frugivorous arboreal mammals, bats, and birds. Species with immigrant seeds had both a lower abundance and a narrower spatial distribution than locally produced seeds. Therefore, immigrant seeds showed higher diversity values than locally produced seeds.Average seed size and the proportion of epigeous seedlings were similar in local and immigrant species. Under closed-canopied sites, factors affecting community organization seem to operate selectively, favoring the establishment of large-seeded, local abundant species in the advanced regeneration. However, the fact that some saplings of immigrant species were found in the plots suggest that a slow species infiltration may be occurring leading to a slow shift in the advanced regeneration species composition. We propose that the influence of seed dispersal on advanced regeneration structure depends on the disturbance history of the patches where seeds land.     

Leaf carbon isotope ratios of plants from a subtropical monsoon forest

Summary Carbon isotope ratios were used to survey the distribution of photosynthetic pathways among taxa, the relationship between photosynthetic pathway and habitat light levels, and the relationship between intercellular CO₂ levels of C₃ plants and habitat light levels within a subtropical monsoon forest in southern China. Of 128 species, most (94) possessed the C₃ photosynthetic pathway; 33 species possessed the C₄ pathway and all of these were restricted to high light locations. There was one epiphytic CAM species. The C₃ species were classified as occurring in open, intermediate, and closed canopy sites. Among C₃ species, carbon isotope ratios tended to become more negative with decreasing light availability in the habitat.C.I.W.D.P.B. Pub no 931     

Nitrogen conservation in a tropical rain forest

Summary A series of plots in an Amazonian Rain Forest were trenched and treated with calcium to determine the effects of perturbation on numbers and activity of nitrifying bacteria. Although treatment resulted in between 2 and 26% of the nitrogen being lost from the humus layer, virtually all of it was in the NH ₄ ⁺ form. Numbers of nitrifying bacteria in the plots were relatively low. The low numbers and low activity of nitrifying bacteria is attributed to the low pH and high concentration of tannins in the root mat. It is hypothesized that the suppression of nitrifying bacteria results in nitrogen conservation in the rain forest.     

基于碳、氮稳定同位素的厦门筼筜湖两种优势端足类食性分析

测定了厦门市筼筜湖(内、外湖)大型海藻群落两种优势端足类(强壮藻钩虾Ampitheoe valida和上野蜾蠃蜚Corophium uenoi)及其潜在食源的碳、氮稳定同位素比值(δ~(13)C和δ~(15)N),分析研究了这两种端足类摄食习性的空间变动特征。研究发现,端足类的潜在食源包括悬浮颗粒有机物(Particulate organic matter:POM),沉积有机物(Sedimentary organic matter:SOM),石莼(Ulva lactuca:Ulva)及其表面的附生生物(Epiphytes:Epi),它们的δ~(13)C和δ~(15)N值分别介于-24.0‰(POM)—-11.8‰(Ulva)和-1.7‰(POM)—4.7‰(Ulva)之间。其中,Ulva和POM的δ~(13)C值的内、外湖差异不显著;而外湖SOM和Epi的δ~(13)C值则明显高于内湖。采样区SOM有机质来源的空间差异是其δ~(13)C内、外湖差异的主要原因。除POM外,外湖有机碳源的δ~(15)N明显高于内湖,这与它们利用氮源的δ~(15)N的差异有关。潜在食源稳定同位素组成的空间差异,使得筼筜湖端足类的稳定同位素组成,尤其是δ~(15)N值表现出显著的空间变动特征(强壮藻钩虾和上野蜾蠃蜚δ~(15)N的内、外湖差异高达1.6‰和4.2‰,变幅约1个营养级),但2种端足类食性的空间差异却不尽相同:强壮藻钩虾的食性相对稳定,其δ~(13)C值介于Ulva和Epi之间,表明它主要从Ulva及其表面的Epi获取碳源;而上野蜾蠃蜚的食性内、外湖差异较大:内湖从石莼表面的Epi获取碳源,约20%是来自POM的贡献,而外湖则主要以Ulva及其表面的Epi为食。分析显示,筼筜湖内、外湖端足类δ~(15)N的空间差异并不是端足类的营养级发生了变化,而是由于端足类食源δ~(15)N的空间差异引起的,而不同端足类食性的内、外湖差异则可能与环境中饵料的丰度和生物量密切相关。     

Phenology of a tropical rain forest in Malaya

During 1960-69, observations were made of flowering, fruiting and foliar activity of 61 canopy trees (representing 45 species) in a largely undisturbed tract of Hill Dipterocarp Forest. Rainfall was measured by an accumulating gauge and, at a nearby station, the number of rainy days recorded. Annually recurrent floral cycles were displayed by only ten species. In these and in 11 additional species, foliar cycles were also circannual. Gregarious flowering, apparently in response to drought, occurred in many species in 1963 and 1968. In other years, interspecific differences in periodicity maintained a minimal incidence of flowering at 44%, and fruiting at 27% of species in the sample. Despite specific variations in phenology, the community as a whole exhibited regular seasonality, with single annual peaks of flowering and fruiting and a double peak of leaf production.     

基于碳、氮稳定同位素研究胶州湾普氏栉虾虎鱼的摄食习性

普氏栉虾虎鱼属于小型暖温性底层鱼类,是胶州湾鱼类群落中的优势种之一,在胶州湾食物网和生态系统中发挥着重要作用.本文应用碳、氮稳定同位素技术,基于胶州湾渔业资源底拖网调查采集的样品,对普氏栉虾虎鱼的摄食习性进行了研究.结果表明: 胶州湾普氏栉虾虎鱼的δ¹⁵N值范围为11.24‰～13.99‰,平均值为(12.70±0.70)‰,δ¹³C值范围为-20.67‰～-18.46‰,平均值为(-19.08±0.36)‰;各体长组的营养级范围为3.49～3.76,平均营养级为(3.62±0.21),其δ¹⁵N值和营养级与体长呈显著负相关,δ¹³C值与体长无显著相关性.普氏栉虾虎鱼摄食的主要饵料生物类群为多毛类、虾类和软体动物,浮游动物和颗粒有机物(POM)的饵料贡献率较小.聚类分析结果表明,普氏栉虾虎鱼各体长组食物组成的相似性均在92%以上,相似性较高,说明其摄食习性随体长变化无明显差异.普氏栉虾虎鱼在胶州湾生态系统中属于中级消费者,其摄食各饵料生物类群比例的变化可能是其营养级与体长呈负相关关系的主要原因.     

Spatial variability of stable carbon and nitrogen isotope ratios in a Mediterranean coastal lagoon

Exploring the trophic pathway of organic matter within the Mauguio lagoon (southern France, western Mediterranean), we found spatial differences in the isotopic composition (both δ¹³C and δ¹⁵N values) of organic matter sources (primary producers, particulate and sedimentary organic matter), which were mirrored in the upper trophic levels (invertebrates and fish). On average, δ¹³C was heavier by about 1.5–2‰ in the location under marine influence than in the sites influenced by freshwater discharge. The opposite trend was found for δ¹⁵N, which attained maximum values in the north-central zone influenced by freshwater delivery. For both C and N stable isotope ratios, the highest spatial variability was found in organic matter sources (2–3‰), while invertebrates and fish exhibited less variability (\~1–2‰). The differences observed may be related to both anthropogenic (wastewater input) and natural (marine vs. terrestrial inputs) factors. Discharge of wastewater, which affects the innermost location, generally determines an increase in the relative abundance of ¹⁵N. In addition, terrestrially derived nutrients and organic matter, which also affect the innermost location, are known to determine a shift towards ¹³C-depleted values. Our results substantiate the finding that the analysis of carbon and nitrogen stable isotopes can help in elucidating origin and fate of organic matter in coastal lagoons, which are characterised by a great spatial variability and complexity.     

Stable carbon and nitrogen isotope signatures of decomposing tropical macrophytes

The Pantanal of Mato Grosso, Brazil, is a large, seasonal wetland, which exhibits high macrophyte productivity at the beginning of the rainy season, when the floodplain becomes flooded. During inundation, from December through May, there is rapid turnover of decomposing macrophyte litter, which is subsequently colonized and consumed by various organisms. In this paper, the variation in the carbon and nitrogen isotope signatures of decomposing macrophytes and detritus was determined to provide an isotopic baseline for the elucidation of higher trophic levels. Seven abundant macrophyte species, Cyperaceae sp., Pontederia lanceolata, Cabomba furcata, Salvinia auriculata, Eichhornia crassipes, Nymphaea amazonum and Paspalum repens, were exposed in mesocosm decomposition experiments lasting 21 or 100 days. Stable isotope ratios of carbon and nitrogen and the atomic C/N ratios were determined for decomposing plant material, particulate organic matter (POM), the microbial film, and aquatic invertebrate larvae. The ¹³C values for the macrophytes did not change during decomposition. However, the variability of ¹⁵N was high (range of ± 6 ) due to microbial activity. There was no consistent difference in the isotopic signatures of macrophytes and POM. C/N ratios decreased from 17 to 50 in macrophytes, to 7 to 12 in POM. The isotopic signatures and C/N ratios of the microbial film were the same as those of POM. We concluded that heterotrophic processes did not fractionate stable carbon isotopes but caused an increase in the variability of stable nitrogen ratios and a change in the C/N ratios in our experimental system. Therefore, it was not possible to distinguish fresh and senescent material or even POM when used as a food source. The ¹³C values of the aquatic larvae were closely coupled to those of the carbon source provided.     

Trophic partitioning in tropical rain forest birds: insights from stable isotope analysis

Bird communities reach their highest taxonomic and trophic diversity in tropical rain forest, but the use of different foraging strategies to meet food requirements in such competitive environments is poorly understood. Conventional dietary analyses are poorly suited to investigate dietary patterns in complex systems. We used stable carbon (¹³C/¹²C) and nitrogen (¹⁵N/¹⁴N) isotope analysis of whole blood to examine avian trophic patterns and sources of diet in the tropical rain forest of Los Tuxtlas, Veracruz, Mexico. We used stable nitrogen isotope analysis to delineate trophic levels, and stable carbon isotope analysis to distinguish the relative contribution of C-3 and CAM/C-4 ultimate sources of proteins to diets. There was large inter- and intraspecific variation in whole blood ¹³C and ¹⁵N values in 23 species of birds. Stable nitrogen isotope analysis separated birds into several trophic levels, including species that obtained their dietary protein mostly from plants, insects or a combination of both food sources. Stable carbon isotope analysis showed that most birds fed on C3-based foods but Stub-tailed Spadebills (Platyrinchus cancrominus) included C-3- and C-4/CAM-specialist individuals. Our analyses provided insights into the nutritional contribution of plant and animal sources of protein and distinguish their photosynthetic origin over relatively long average time periods.     

Sandfly distribution and abundance in a tropical rain forest

1. The distribution patterns of sandflies (Diptera: Psychodidae) upon tree buttresses were studied in tropical rain forest at Finca la Selva in the Caribbean lowlands of Costa Rica. 2. Four species of sandfly, Lutzomyia shannoni Dyar, L. trapidoi F. & H., L. ylephiletor F. & H. and L. vespertilionis F. & H. comprising 97% of those caught, used tree buttresses as diurnal resting sites. Their distribution on the buttresses was aggregated. 3. During the dry season tree species had no significant effect upon the distribution of the sandflies. However, during the wet season the distributions of two of the species, L. trapidoi and L. ylephiletor, were significantly affected by the species of tree; it is suggested that some species of tree may provide greater protection from rainfall than others. 4. L. vespertilionis was restricted to a single buttress on each positive tree. Distribution of this species is evidently determined by the distribution of its host animal, the bat (Emballonuridae). Female flies feed upon the bat's blood and male flies may be attracted to the bat as it provides a source of female sandflies. It is suggested, therefore, that tree buttresses serve as sandfly swarming sites. 5. Within a large buttress the sandflies are not randomly distributed but are aggregated in particular areas. Within these aggregations, the sandflies are vertically zoned upon the buttress with a shift in species composition with height. Two hypothesis were suggested to account for this distribution pattern: a response to an environmental gradient or an interaction between the four species of fly.     

Stable carbon and nitrogen isotope ratios in muscle and epidermis of arctic whales

Collection of minimally invasive biopsy samples has become an important method to establish normal stable isotopes reference ranges in various wildlife species. Baseline data enhance the understanding of feeding ecology, habitat use, and potential food limitation in apparently healthy, free‐ranging cetaceans. Epidermis and muscle were collected from subsistence‐hunted northern Alaskan bowhead (n= 133 epidermis/134 muscle) and beluga whales (n= 42/49) and subsistence‐hunted Russian gray whales (n= 25/17). Additional samples were obtained from gray whales stranded in California (n= 18/11) during mortality events (1999, 2000). Both δ¹⁵N and δ¹³C are trophic position and benthic/pelagic feeding indicators, respectively, in muscle and epidermis. Epidermis is generally enriched in ¹⁵N over muscle, while epidermal ¹³C is more depleted. Lipid extraction does not alter δ¹⁵N in either tissue, but affects epidermal δ¹³C. Nitrogen‐15 is enriched in muscle, but not epidermis of stranded compared to subsistence‐hunted gray whales, indicating probable protein catabolism and nutritional stress in stranded whales. Similarly, epidermal δ¹³C of harvested whales is lower than in stranded whales, suggesting depleted lipid stores and/or food limitation in stranded animals. Epidermal isotope signatures are similar in both present‐day bowheads and in an ancient sample from the Northern Bering Sea region. Although only one specimen, this suggests trophic level of the ancient whale compares to modern bowheads after a millennium.