Distribution and ecology of the pelagic hydromedusae,siphonophores and ctenophores of the Barents Sea,based on perennial plankton collections

The evaluation of more than 10,000 samples of plankton, taken at standard stations from 1953 to 1960 in the Barents Sea, made it possible to supplement considerably the species list of medusae, siphonophores, and ctenophores, and to revise some ecological and biogeographical characteristics of many of them. Quantitative data, assembled over many years, on the occurrence of the above-mentioned groups, demonstrated the impossibility of using the vast majority of representatives of this fauna as biological indicators. During the very warm year of 1960, reproductively and vegetatively cold-adapted forms produced the same population increase as the thermophilic forms. The change in thermal conditions influenced these animals indirectly via a favourable biotic situation due to a prolongation of the nutrition period. The capability to vary the number of eggs, timing, rates and types of reproduction, to withstand long periods of starvation, etc., facilitates a flexible synchronization of the population dynamics of these pelagic predators with the quantity of plankton used for nutrition. The same properties stipulate the possibility of seasonal and annual meandering in regard to the boundaries of the water areas occupied.     

Ecology of fouling bryozoans in Cochin waters

An extensive study was conducted on the settlement and seasonal succession of fouling bryozoans in and around Cochin Harbour during the period 1965 to 1966; it was the first study of its kind performed in Indian waters. A total of 14 species was recorded from localities which were ecologically dissimilar. A distinct succession of species, mainly of a seasonal character, was observed. Seasonal succession usually occurs in localities where seasons are well marked, and where different species of animals with short life spans settle during particular times of the year. The study has shown that a distinct seasonal succession of bryozoans occurs in this locality; out of the 14 species which appeared on the panels not one species settled throughout the year. This was due to seasonal differences in the ecological conditions which prevailed in the area investigated. The significant seasonal influences on the incidence of bryozoans led to a categorisation of the species into the following patterns (a) typical brackish-water forms not encountered in purely marine localities; (b) typical brackish-water forms which may occur in marine localities; (c) typical marine forms never found in localities where low salinity conditions prevail.Part of a thesis submitted by the first-named author for his degree of Doctor of Philosophy of the University of Kerala, India.     

Nutrients of the Cochin Backwater in relation to environmental characteristics

The nutrient distribution of the Cochin Backwater was studied at 6 stations throughout the year. The depth profiles of phosphorus (inorganic and organic), nitrogen (nitrate and nitrite) and silicon, showed a marked seasonal rhythm, induced by the local precipitation and land runoff. Changes in other environmental features such as temperature, salinity, dissolved oxygen, pH and alkalinity were small during the premonsoon period when the system remains marine-dominated, and large during the monsoon period when the estuary becomes freshwater-dominated. Seasonal changes in the hydrographical conditions of the adjoining coastal waters of the Arabian Sea which influence the backwater system have been discussed.     

Sperm chemotaxis in the hydromedusae. I. Species-specificity and sperm behavior

Egg extracts from 32 species of marine hydromedusae, siphonophores and sessile hydroids were tested for sperm attracting activity using the sperm of all species in both homo- and heterospecific combinations. Species-specific sperm chemotaxis could be demonstrated in nearly every species tested. Of the 1,024 possible combinations, 272 could not be attempted for lack of material. Of the 752 which were carried out, only 13 heterospecific cross-reactions were found. The bulk of these involved reactions which were either weaker in the heterospecific direction or unidirectional. The sperm behavior in response to both homospecific and heterospecific egg extracts is described. In the latter case, no changes in sperm motility or direction of movement were observed. In the former case, the sperm show turning behavior which brings them closer to the source of the extract. Since most of the Hydrozoa tested share the same habitat and are reproductively active at the same time of year, it appears that species-specific sperm chemotaxis may be a significant mechanism for both ensuring fertilization in an environment which subjects the gametes to massive dilution and preventing hybridization.     

Diversity of swimming behavior in hydromedusae as related to feeding and utilization of space

Feeding behaviors of the following 4 species of hydromedusae are described from field and laboratory observations: Probosidactyla flavicirrata, Stomotoca atra, Phialidium gregarium and Polyorchis penicillatus. Feeding efficiency of medusae has previously been considered equivalent to fishing with a given amount (combined tentacle length) of adhesive fishing line; however, detailed observation shows that behavior of medusae greatly modifies the fishing capacity of each species. It is hypothesized that in addition to (1) tentacle number and length, the following factors strongly influence feeding efficiency: (2) tentacle posture, (3) velocity of tentacles moving through water (4) swimming pattern of medusa, (5) streamlining effects of medusa bell on water flow, (6) diameter of prey, (7) swimming pattern and velocity of prey. Each species of hydromedusa utilizes the above factors in different combinations.Mailing address     

Sperm chemotaxis in the hydromedusae. II. Some chemical properties of the sperm attractants

Gel filtration on highly cross-linked molecular sieves of the sperm attractants of some hydromedusae revealed that the active agents differ in their molecular weights. These differences fall roughly along taxonomic lines, at least at the order level. Anthomedusae have attractants with molecular weights greater than 5,000, while the Leptomedusae attractants have weights less than 1,000. The Limnomedusae and Trachymedusae attractants have weights above 5,000. All the attractants are heat-stable, but only those of the Leptomedusae can pass across a dialysis membrane with a molecular weight cut-off of 14,000.     

Feeding ecology of the lanternfish Benthosema pterotum from the Indian Ocean

The feeding ecology of lanternfish Benthosema pterotum (Alcock) from the north Arabian Sea, Mozambique and the Bay of Bengal was studied. Samples were collected on cruises carried out by R.V. Dr. Fridtjof Nansen during the period 1978 to 1983. A wide variety of zooplankton organisms were identified in the diet of B. pterotum with crustanceans dominating the diet. Copepods constituted ca. 40 to 90% of the diet. Dry weight analyses of the stomach contents from the Gulf of Oman in February 1983 showed copepods to be 35 to 55% in weight (average in samples). Ontogenetic differences were observed in the diet. Prey size increased as the fish length increased, but the largest fish did not exclude the smaller prey organisms from their diet. Regional variation in diet was also shown in B. pterotum. The degree of filling and the state of digestion of stomach contents revealed that this species feeds intensively at night in the epipelagic layer. All copepods indentified were epipelagic species, providing additional evidence of diurnal pattern in the feeding chronology of B. pterotum. Identification of copepods from the Gulf of Oman in February 1983, revealed that herbivorous species dominated in biomass. Quantitative analyses show that B. pterotum probably have a daily food intake of ca. 4.5% of the body weight.     

Growth,reproduction and nutrition of some Barents Sea hydromedusae in natural aggregations

Mass aggregations of the hydromedusae Tiaropsis multicirrata and Rathkea octopunctata have been studied in the Jarnyshnaya Fjord on the Kola Penninsula during the period of domination of the summer neritic plankton complex. The mass aggregations persist at least over periods of 2 months. No hyrometereological parameters could be established that would conceivably favour such aggregations. The factor most likely responsible for creating the aggregations is assumed to be related to the stable level of the summer zooplankton, production in the study area. The vast individual numbers of hydromedusae as well as their polyphageous feeding behaviour and high growth rates suggest that the medusae represent the most substantial consumers of plankton in inshore waters. The low and highly variable percent of medusae individuals which reveal food in their intestinal system lead the authors to assume additional food sources: nannoplankton, bacteria, and dissolved organic matter.     

A comparison of the efficiency of the bottom samplers used in benthic studies off Cochin

The efficiency of the van Veen and Foerst Petersen grabs used in sampling the bottom fauna near the Cochin Harbour area has been compared in two selected stations having different hydrographic and substratic conditions. The results indicate that the heavier grab is generally more efficient than a lighter one, especially when the substratum is sandy. An examination of the quantity of the sediment and the total number of species brought by the two grabs showed that the design of the van Veen is superior to the Petersen type grab used in the present study. However, due to the highly patchy distribution of the organisms the superiority of the van Veen was less evident when a comparison was made of the total number of animals sampled by the two grabs. When the distribution is bunched it is suggested that samples are drawn, as far as possible, from the same sampling position. The grabs should also be of the same weight and biting area.     

Interference from ants alters foraging ecology of great tits

In a field experiment, great tits Parus major foraged on a pair of artificial trees that were supplied with equal amounts of food. Wood ants Formica aquilonia were excluded from one tree, but foraged on the other. Great tits visited the tree without ants more frequently, and for longer periods of time, than the tree with ants. The time of foraging visits by tits in the tree with ants decreased as ant activity there increased. These results are the first to show that interference competition from ants can influence a bird’s choice of microhabitat in which to forage, as well as alter the time it spends foraging there. Received: 10 March 1995/Accepted after revision: 9 September 1995     

Advances in pollination ecology from tropical plantation crops

Although ecologists traditionally focus on natural ecosystems, there is growing awareness that mixed landscapes of managed and unmanaged systems provide a research environment for understanding basic ecological relationships on a large scale. Here, we show how tropical agroforestry systems can be used to develop ideas about the mechanisms that influence species diversity and subsequent biotic interactions at different spatial scales. Our focus is on tropical plantation crops, mainly coffee and cacao, and their pollinators, which are of basic ecological interest as partners in an important mutualistic interaction. We review how insect-mediated pollination services depend on local agroforest and natural habitats in surrounding landscapes. Further, we evaluate the functional significance of pollinator diversity and the explanatory value of species traits, and we provide an intercontinental comparison of pollinator assemblages. We found that optimal pollination success might be best understood as a consequence of niche complementarities among pollinators in landscapes harboring various species. We further show that small cavity-nesting bees and small generalist beetles were especially affected by isolation from forest and that larger-bodied insects in the same landscapes were not similarly affected. We suggest that mixed tropical landscapes with agroforestry systems have great potential for future research on the interactions between plants and pollinators.     

试论生态学的一门分支学科:环境耐性生态学

针对目前对生态学的学科分支情况,及生态学的发展趋势和环境灾害的启示,提出了"环境耐性生态学"这一生态学的分支学科.初步明确了这一分支学科的概念,提出了它的3个研究层次的研究框架,即耐性特征、耐性规律及提高耐性的方法与途径,指出了它的核心思想是:把自然环境看成是具有"生命"的系统,有一定的耐性能力和自我恢复能力,也具有自然免疫的特征和能力.同时,指出了当前急需确定的3个生态环境耐性指标,即容许侵蚀量、容许施肥量和容许承载量.     

Coexistence of species of Acartiidae (Copepoda) in the Cochin Backwater,a monsoonal estuarine lagoon

A study was made of copepods of the family Acartiidae which form the dominant component of the plankton in the Cochin Backwater (Kerala, India). At least nine species inhabit the backwater at one time or another, more than have been recorded for any other area. Reasons were sought for this diversity. The surface plankton was sampled from the head of the estuary to the mouth and from one season to another. There were large seasonal changes in salinity (0 to 35 ), due to monsoonal flooding, and associated changes in species composition. Species diversity was highest during the dry season and lowest in the wet. It is suggested that this annual catastrophic flooding leads, in the long run, to high species diversity by imposing a regular check on interspecific competition.     

The arcsine is asinine: the analysis of proportions in ecology

The arcsine square root transformation has long been standard procedure when analyzing proportional data in ecology, with applications in data sets containing binomial and non-binomial response variables. Here, we argue that the arcsine transform should not be used in either circumstance. For binomial data, logistic regression has greater interpretability and higher power than analyses of transformed data. However, it is important to check the data for additional unexplained variation, i.e., overdispersion, and to account for it via the inclusion of random effects in the model if found. For non-binomial data, the arcsine transform is undesirable on the grounds of interpretability, and because it can produce nonsensical predictions. The logit transformation is proposed as an alternative approach to address these issues. Examples are presented in both cases to illustrate these advantages, comparing various methods of analyzing proportions including untransformed, arcsine- and logit-transformed linear models and logistic regression (with or without random effects). Simulations demonstrate that logistic regression usually provides a gain in power over other methods.     

Estimating the complexity of bird song by using capture-recapture approaches from community ecology

Repertoire size, the number of unique song or syllable types in the repertoire, is a widely used measure of song complexity in birds, but it is difficult to calculate this exactly in species with large repertoires. A new method of repertoire size estimation applies species richness estimation procedures from community ecology, but such capture-recapture approaches have not been much tested. Here, we establish standardized sampling schemes and estimation procedures using capture-recapture models for syllable repertoires from 18 bird species, and suggest how these may be used to tackle problems of repertoire estimation. Different models, with different assumptions regarding the heterogeneity of the use of syllable types, performed best for different species with different song organizations. For most species, models assuming heterogeneous probability of occurrence of syllables (so-called detection probability) were selected due to the presence of both rare and frequent syllables. Capture-recapture estimates of syllable repertoire size from our small sample did not differ significantly from previous estimates using larger samples of count data. However, the enumeration of syllables in 15 songs yielded significantly lower estimates than previous reports. Hence, heterogeneity in detection probability of syllables should be addressed when estimating repertoire size. This is neglected using simple enumeration procedures, but is taken into account when repertoire size is estimated by appropriate capture-recapture models adjusted for species-specific song organization characteristics. We suggest that such approaches, in combination with standardized sampling, should be applied in species with potentially large repertoire size. On the other hand, in species with small repertoire size and homogenous syllable usage, enumerations may be satisfactory. Although researchers often use repertoire size as a measure of song complexity, listeners to songs are unlikely to count entire repertoires and they may rely on other cues, such as syllable detection probability.Communicated by A. Cockburn     

The contribution of community wisdom to conservation ecology

Scientists have traditionally collected data on whether a population is increasing, decreasing, or staying the same, but such studies are often limited by geographic scale and time frame. This means that for many species, understanding of trends comes from only part of their ranges at particular periods. Working with citizen scientists has the potential to overcome these limits. Citizen science has the added benefit of exposing citizens to the scientific process and engaging them in management outcomes. We examined a different way of using citizen scientists (instead of data collection). We asked community members to answer a question directly and thus examined whether community wisdom can inform conservation. We reviewed the results of 3 mail‐in surveys that asked community members to say whether they thought koala populations were increasing, decreasing, or staying the same. We then compared the survey results with population trends derived from more traditional research. Population trends identified through community wisdom were similar to the trends identified by traditional research. The community wisdom surveys, however, allowed the question to be addressed at much broader geographical scales and time frames. Studies that apply community wisdom have the benefit of engaging a broad section of the community in conservation research and education and therefore in the political process of conserving species.