Rotifer occurrence in relation to water colour

Information on the distribution of 223 species of planktic, periphytic and benthic rotifers from diverse waters in south and central Sweden was analyzed to reveal their relationships to the content of humolimnic substances, measured as mg Pt/l. Most rotifers have a very wide tolerance range against this factor. The majority of the planktic species prefer a low content of humolimnic substances, and the non-planktic rotifers mainly occurring in brown-coloured water show, in addition, a preference for low pH. No connection with trophic degree could be traced.     

On limnic micro-crustaceans and trophic degree

A large material of planktic and semiplanktic microcrustaceans from different types of waters in south and central Sweden was computerized. The more frequent species were ranked according to phosphorus content (tot-P), electrolytic conductivity and content of suspended matter, searching for correlations with the trophic degree. With few exceptions, species indicating oligotrophy are found at lower factor values and those indicating eutrophy at higher values concerning all the abiotic factors considered.     

Rotifer occurrence in relation to oxygen content

Information on the distribution of 204 species of planktic, periphytic and benthic rotifers from diverse waters in south and central Sweden was analyzed for details on relationships to the oxygen content of the environment. No sign of truly anoxybiontic appearance was traced, although some species may be encountered in high abundance at low O₂-values. Most cold-stenothermal species prefer an environment rich in oxygen, but there are a few exceptions. For the warm-stenothermal species no really close connections with oxygen exist. Several species combine a tolerance of low oxygen content with a preference of high Pt-values. No such connections were traced between oxygen content and trophic degree.     

The microbial loop in the planktonic communities in lakes with various trophic status

The structure of planktic trophic chains was studied in eight lakes of European Russia and five lakes in Central Asia. The lakes differed in the level of productivity, morphometric parameters, and the type of agitation and mineralization. It is found that the microbial loop of picophototrophic organisms, bacteria, heterotrophic flagellates, infusoria, and viruses constitutes 12.3-64.7% of the total plankton biomass. Positive correlation between the biomass of microbial community and the primary production of phytoplankton is observed, whereas no relation is revealed between the share of microorganisms in the plankton biomass and the trophic status of the water body. The presence of a great number of cladocerans decreased the role of the microbial loop in the structural organization of the planktic community. Heterotrophic flagellates consuming 3-81% of daily bacterial production were the principal cause of bacteria elimination only in some of the studied water bodies.     

Microalgal plankton composition in shallow coastal inlets in contrasting trophic and alternative community states

As the trophic state of the environment changes, communities develop into divergent states. These community states are conventionally reflected through primary producers, because they are directly affected by nutrient availability. Studies of submerged macrophytes often focus on community composition to decipher the vegetative (community) state of the environment, while planktic microalgae are usually viewed more cursorily. Although microalgal plankton composition has been related to the trophic state of shallow temperate lakes, corresponding qualitative knowledge is lacking for shallow inlets in the sea. We assessed the composition of microalgal plankton in relation to that of submerged macrophytes in shallow inlets in the northern Baltic Sea during one ice-free season. Microalgal plankton composition varied distinctively among inlets in different trophic and vegetative states especially during early and mid-season, before becoming comparably uniform. These patterns were consisted both inside and outside of macrophyte beds and during day and night. Local and diurnal variation was comparably high in eutrophic and charophyte-dominated inlets, but only during early season. Microalgal plankton composition not only reflects the state of littoral communities in varying trophic conditions, but it may also be important for the whole trophic structure of those communities.     

Relation to habitat in rotifers

Rotifera should be especially suited for an analysis of habitat relations because this group contains such a high number of species, inhabiting diverse environments. Furthermore, rotifers are to a large extent cosmopolitan, implying that ecological barriers, rather than geographical, are decisive of their distribution. In this review a short characterization of the rotifer fauna in different habitats is given, whereby macroenvironments and microenvironments are reported separately. The macroenvironments are classified as follows: harmonious lakes and ponds, arctic and antarctic waters, hot springs, hypertrophic-saprobic environments, mires, strongly acidic waters, saline waters, temporary water bodies, subterranean waters, running waters, oceans, terrestrial environments. The following microenvironments are distinguished: macrophytes (housing periphytic rotifers), open water (with planktic forms), minerogenous sediments (with psammon and hyporheos), organogenous sediments, other organisms (i.e. parasites and epizoans).Many rotifers are more or less euryecious, while relatively few are strongly restricted in their choice of habitat. In extreme environments a low number of species is found, but often a high number of individuals within these species. These rotifers are usually primary consumers, and for natural reasons extreme environments are characterized by a low number of trophic levels.In environments with a high species number the separate species differ very much in their morphology, making it difficult to find common traits which may be interpreted as adaptations to the respective habitats. The most apparent adaptations ought to be found among the planktic rotifers, and these adaptations seem to constitute largely a protection against predators. Rotifers in extreme environments are usually not very apart in a morphological or taxonomical respect, with their most close relatives living in normal habitats and sometimes euryecious (an apparent exception from this rule is formed by the class Seisonidea). Adaptations to deviating chemical and physical environments may develop relatively rapidly (seen from a geological perspective), while the more fundamental changes (occurring during a longer period of time) seem to be a response to biotic factors (e.g., the development of different types of trophi for facilitating food collection).     

High‐resolution food webs based on nitrogen isotopic composition of amino acids

Food webs are known to have myriad trophic links between resource and consumer species. While herbivores have well‐understood trophic tendencies, the difficulties associated with characterizing the trophic positions of higher‐order consumers have remained a major problem in food web ecology. To better understand trophic linkages in food webs, analysis of the stable nitrogen isotopic composition of amino acids has been introduced as a potential means of providing accurate trophic position estimates. In the present study, we employ this method to estimate the trophic positions of 200 free‐roaming organisms, representing 39 species in coastal marine (a stony shore) and 38 species in terrestrial (a fruit farm) environments. Based on the trophic positions from the isotopic composition of amino acids, we are able to resolve the trophic structure of these complex food webs. Our approach reveals a high degree of trophic omnivory (i.e., noninteger trophic positions) among carnivorous species such as marine fish and terrestrial hornets.This information not only clarifies the trophic tendencies of species within their respective communities, but also suggests that trophic omnivory may be common in these webs.     

Evolution of early planktic foraminifers

The evolution of Mesozoic species of planktic foraminifers, particularly the succession of their morphotypes and the variation in their diversity and their abundance, is shown to be related to the adaptation of evolutionary strategy to fluctuations in the oceanic environment.During periods of stress (“oligotaxic period”) the more primitive species tend to invade the oceanic surface waters by means of r-selection. During stable “polytaxic” conditions, the same species engage in an adaptive radiation colonizing progressively deeper water through K-selection.The succession of morphotypes from the middle Jurassic to the end of the Cretaceous is compared with living planktic foraminifers and related to the biogeographic (cold arctic, warm equatorial faunas) and bathymetric distribution. A general model for the evolution of early planktic foraminifers is made with reference to the preceding observations, and in relation to the pattern of variation of trophic resources.     

Assessing the contribution of foraminiferan protists to global ocean carbonate production

Larger symbiont-bearing foraminifera are prominent and important producers of calcium carbonate in modern tropical environments. With an estimated production of at least 130 million tons of CaCO(3) per year, they contribute almost 5% of the annual present-day carbonate production in the world's reef and shelf areas (0-200 m) and approximately 2.5% of the CaCO(3) of all oceans. Together with non-symbiont-bearing smaller foraminifera, all benthic foraminifera are estimated to annually produce 200 million tons of calcium carbonate worldwide. The majority of foraminiferal calcite in modern oceans is produced by planktic foraminifera. With an estimated annual production of at least 1.2 billion tons, planktic foraminifera contribute more than 21% of the annual global ocean carbonate production. Total CaCO(3) of benthic and planktic foraminifera together amounts to 1.4 billion tons of calcium carbonate per year. This accounts to almost 25% of the present-day carbonate production of the oceans, and highlights the importance of foraminifera within the CaCO(3) budget of the world's oceans.     

The impact of thermal seasonality on terrestrial endotherm food web dynamics: a revision of the Exploitation Ecosystem Hypothesis

Many terrestrial endotherm food webs constitute three trophic level cascades. Others have two trophic level dynamics (food limited herbivores; plants adapted to tackle intense herbivory) or one trophic level dynamic (herbivorous endotherms absent, thus plants compete for the few places where they can survive and grow). According to the Exploitation Ecosystems Hypothesis (EEH), these contrasting dynamics are consequences of differences in primary productivity. The productivity thresholds for changing food web dynamics were assumed to be global constants. We challenged this assumption and found that several model parameters are sensitive to the contrast between persistently warm and seasonally cold climates. In persistently warm environments, three trophic level dynamics can be expected to prevail almost everywhere, save the most extreme deserts. We revised EEH accordingly and tested it by compiling direct evidence of three and two trophic level dynamics and by studying the global distribution of felids. In seasonally cold environments, we found evidence for three trophic level dynamics only in productive ecosystems, while evidence for two trophic level dynamics appeared in ecosystems with low primary productivity. In persistently warm environments, we found evidence for three trophic level dynamics in all types of ecosystems. The distribution of felids corroborated these results. The empirical evidence thus indicates that two trophic level dynamics, as defined by EEH, are restricted to seasonally cold biomes with low primary productivity, such as the artic–alpine tundra and the temperate steppe.     

Echinoderms display morphological and behavioural phenotypic plasticity in response to their trophic environment

The trophic interactions of sea urchins are known to be the agents of phase shifts in benthic marine habitats such as tropical and temperate reefs. In temperate reefs, the grazing activity of sea urchins has been responsible for the destruction of kelp forests and the formation of 'urchin barrens', a rocky habitat dominated by crustose algae and encrusting invertebrates. Once formed, these urchin barrens can persist for decades. Trophic plasticity in the sea urchin may contribute to the stability and resilience of this alternate stable state by increasing diet breadth in sea urchins. This plasticity promotes ecological connectivity and weakens species interactions and so increases ecosystem stability. We test the hypothesis that sea urchins exhibit trophic plasticity using an approach that controls for other typically confounding environmental and genetic factors. To do this, we exposed a genetically homogenous population of sea urchins to two very different trophic environments over a period of two years. The sea urchins exhibited a wide degree of phenotypic trophic plasticity when exposed to contrasting trophic environments. The two populations developed differences in their gross morphology and the test microstructure. In addition, when challenged with unfamiliar prey, the response of each group was different. We show that sea urchins exhibit significant morphological and behavioural phenotypic plasticity independent of their environment or their nutritional status.     

A form-function analysis of photon capture for seaweeds

A large material of planktonic and semiplanktonic micro-crustaceans from various type of waters in south and central Sweden was computerized. The more frequent species were listed according to pH-preference and relation to humic content measured as mg Pt/l. Species indicating oligotrophy have their optima just below the neutral point, eurytopic ones around this level, while the eutrophic species Daphnia cucullata and D. magna were closely correlated with higher pH-levels. No really extreme pH-preference was observed. There is no link between trophic indication and the ranking list for humic content. Most planktic species occur at lower humic contents and semiplankters at higher.     

The structure of the planktic microbial community in the lower reaches of the Ob River near Salekhard

We studied the distribution of the main components of planktic food web: bacteria, heterotrophic flagellates, and ciliates in the lower reaches of the Ob River near the town of Salekhard. In the early summer, the abundance, biomass, and diversity of protozoans were low; the plankton community was dominated by heterotrophic bacteria whose biomass was higher than that of phyto- and zooplankton. Downstream of Salekhard, biomass and abundance of bacterioplankton were increased due to household and industrial wastewater. The data obtained showed the importance of heterotrophic organisms in trophic dynamics and self-purification of the lower reaches of the Ob River.     

On choice of substrate and habitat in brachionid rotifers

Information on the distribution of 28 rotifers of the family Brachionidae from diverse waters in south and central Sweden was analyzed to reveal their relationships to substrate and habitat. Some brachionids are preferably planktic, others periphytic and/or benthic. Some non-planktic habitats are utilized more than others, but there is no evidence of a chemical attraction from any substrate. Instead, some substrates seem to be avoided, possibly depending on a poorer flora of periphytic algae. Besides substrate type, the following factors are found to be important for creating separate ecological niches in the brachionid family: temperature, oxygen content, trophic degree, chemical environment, food choice and sensitivity to predation. It is possible to delineate separate ecological niches for all brachionid rotifers, implying that Hutchinson's ideas about the plankton paradox are contradicted. Some species are specialists, other are generalists, the latter being characterized by a great morphological variation. The species are adapted in different ways to their preferential habitats, as regards foot, egg-carrying, protrusions and other lorical structures etc. Longer spines, for instance, are generally found in more transparent water, being a supposed protection against visual predators.     

Birds help plants: a meta-analysis of top-down trophic cascades caused by avian predators

The tritrophic interactions between plants, herbivores and avian predators are complex and prone to trophic cascades. We conducted a meta-analysis of original articles that have studied birds as predators of invertebrate herbivores, to compare top-down trophic cascades with different plant responses from different environments and climatic areas. Our search found 29 suitable articles, with a total of 81 separate experimental study set-ups. The meta-analysis revealed that plants benefited from the presence of birds. A significant reduction was observed in the level of leaf damage and plant mortality. The presence of birds also positively affected the amount of plant biomass, whereas effects on plant growth were negligible. There were no differences in the effects between agricultural and natural environments. Similarly, plants performed better in all climatic areas (tropical, temperate and boreal) when birds were present. Moreover, both mature plants and saplings gained benefits from the presence of birds. Our results show that birds cause top-down trophic cascades and thus they play an integral role in ecosystems.     

Exploring the drivers of variation in trophic mismatches: A systematic review of long‐term avian studies

1. Many organisms reproduce in seasonal environments, where selection on timing of reproduction is particularly strong as consumers need to synchronize reproduction with the peaked occurrence of their food. When a consumer species changes its phenology at a slower rate than its resources, this may induce a trophic mismatch, that is, offspring growing up after the peak in food availability, potentially leading to reductions in growth and survival. However, there is large variation in the degree of trophic mismatches as well as in its effects on reproductive output.
2. Here, we explore the potential causes for variation in the strength of trophic mismatches in published studies of birds. Specifically, we ask whether the changes in the degree of mismatch that have occurred over time can be explained by a bird''s (a) breeding latitude, (b) migration distance, and/or (c) life‐history traits.
3. We found that none of these three factors explain changes in the degree of mismatch over time. Nevertheless, food phenology did advance faster at more northerly latitudes, while shifts in bird phenology did not show a trend with latitude.
4. We argue that the lack of support in our results is attributable to the large variation in the metrics used to describe timing of food availability. We propose a pathway to improve the quantification of trophic mismatches, guided by a more rigorous understanding of links between consumers and their resources.

     

The genetic diversity of planktic foraminifera and the global distribution of ribosomal RNA genotypes

Fossil planktic foraminifers in the ocean sediments play an unparalleled role in our understanding of the oceanographic environment in the past. An in depth knowledge of their diversity, ecology and biogeography in the modern ocean lies central to the interpretation of the fossil assemblages. In comparison with their benthic counterparts, planktic foraminifera have a very limited diversity of around fifty extant morphospecies. Their morphospecies diversity peaks in the sub-tropics and decreases steeply towards the poles. Traditional species concepts have partitioned morphological types into distinct species (morphospecies) based on test shape, but genetic studies show that individual morphospecies are actually complexes of several discrete genetic types (genotypes). Many of these genotypes have distinct ecologies and novel adaptations that are consistent with species-level classification, indicating that the true diversity of planktic foraminifers has been greatly underestimated. Although planktic foraminifera are clearly capable of long-distance dispersal, they may be constrained by both physical and ecological barriers that vary according to the evolutionary history and ecology of the individual genotypes within a morphospecies. These differences lead to diverse biogeographies. Here, we provide an overview of the genetic and biogeographic data available to date for the planktic foraminifera and present global biogeographies highlighting the distribution of genetic types in the eight planktic foraminiferal morphospecies for which detailed molecular evidence is available.     

Fish predation regimes modify benthic diatom community structures: Experimental evidence from an in situ mesocosm study

Diatoms are important primary producers in shallow water environments. Few studies have assessed the importance of biological interactions in structuring these communities. In the present study, benthic diatom community structure in relation to manipulated food webs was assessed using in situ mesocosms, whereby predator‐free environments and environments comprising two different fish species were assessed. Zooplankton abundance, settled algal biomass and the diatom community were monitored over a 12‐day period across each of the three trophic scenarios. Differences among treatments over time were observed in zooplankton abundances, particularly copepods. Similarly, the benthic diatom community structure changed significantly over time across the three trophic treatments. However, no differences in total algal biomass were found among treatments. This was likely the result of non‐diatom phytoplankton contributions. We propose that the benthic diatom community structure within the mesocosms was influenced by trophic cascades and potentially through direct consumption by the fish. The study highlights that not only are organisms at the base of the food web affected by predators at the top of the food web, but that predator identity is potentially an important consideration for predator–prey interaction outcomes with consequences for multiple trophic levels.     

Dictyonema Hall and its importance for the evolutionary history of the Graptoloidea

Dictyonema retiforme has been regarded as the benthic ancestor to the planktic Graptoloidea, represented by the earliest planktic Rhabdinopora flabelliformis and its descendants. The revision of the type material of Dictyonema retiforme, the type species of the genus Dictyonema, from the Silurian of New York State shows compound stipes formed by the complexly growing and overlapping tubular thecae of acanthograptid type. The connections between adjacent stipes are formed by thecal tubes or thecal bridges and not by dissepiments. Thus, the species has to be transferred to the Acanthograptidae and cannot be regarded as being related to the early planktic Graptoloidea. The tubarium meshwork of Dictyonema is phylogenetically unrelated to the meshwork of the planktic Rhabdinopora, and represents a case of convergent evolution. The origins of the planktic graptoloids lie among members of middle to upper Cambrian Dendrograpidae, as can be seen from the thecal style and the triad budding patterns with regularly developed bithecae in this group.     

Effect of nutritional condition on photosymbiotic consortium of cultured <Emphasis Type="Italic">Globigerinoides sacculifer</Emphasis> (Rhizaria,Foraminifera)

Several foraminifers found in warm and low-nutrient ocean surface water have photosynthetic algae as endosymbionts (photosymbiosis). To understand the trophic interactions, we studied Globigerinoides sacculifer, a spinose planktic foraminifer that has a dinoflagellate endosymbiont. We controlled two nutritional factors, feeding and inorganic nutrients in the seawater. The growth of the host and the symbionts and the photophysiological parameters were monitored under four experimental conditions. The results demonstrated that the holobionts primarily relied on phagotrophy for growth. The foraminifers grew considerably, and the chlorophyll a content per foraminifer, which is an indicator of the symbiont population, increased in the fed groups, but not in the unfed groups. The nutrient-rich seawater used for some of the cultures made no difference in either the growth or photophysiology of the holobionts. These observations indicated that the symbionts mainly utilized metabolites from the hosts for photosynthesis rather than inorganic nutrients in the seawater. Additionally, we observed that the symbionts in the starved hosts maintained their photosynthetic capability for at least 12 days, and that the hosts maintained at least some symbionts until gametogenesis was achieved. This suggests that the hosts have to retain the symbionts as an energy source for reproduction. The symbionts may also play an indispensable role in the metabolic activities of the hosts including waste transport or essential compound synthesis. Overall, our results revealed a novel mode of photosymbiosis in planktic foraminifers which contrasts with that found in benthic photosymbiotic foraminifers and corals.