Ecological energetics of Chaoborus in a tropical lake

Summary Ecological energetics of Chaoborus brasiliensis from Lake Valencia, Venezuela, were studied between February 1979 and February 1980. Direct measurements were made of the respiration rate, assimilation efficiency, and growth rate of all 4 larval instars and of the pupae. For the larval stages, respiration increased as the 0.67 power of body mass. Respiration rates of the larvae, when corrected for body size and temperature, were extraordinarily low by comparison with the rates for most aquatic insects. The respiration rates of pupae were 3 times as high as those of larvae the same size. Assimilation rates increased significantly with body size for the larvae and differed slightly but significantly among food types. Assimilation efficiencies fell within the expected range for carnivores. The growth efficiencies were exceptionally high for instars II-IV by comparison with other small aquatic organisms. High growth efficiency for Chaoborus brasiliensis, and possibly for Chaoborus generally, is explained by a very low maintenance cost and may be a significant explanation for the wide distribution and high degree of ecological success in this primary carnivore of plankton communities.     

Temperature affects selectivity of Chaoborus larvae-eating Daphnia

In ponds, a chemical produced by predaceous Chaoborus (Insecta, Diptera) larvae changes the development of juvenile Daphnia pulex (Crustacea, Branchiopoda) so the juveniles grow spines (neckteeth) on the back of their head. It is generally assumed that the spined phenotype is (or is an indicator of) a morphological predator defense. The research reported here tests the hypothesis that the induced neckteeth do in fact increase Daphnia survivorship, over a range of temperatures. Predation experiments were conducted over a range of temperatures from 6 to 22 °C using fourth instar Chaoborus americanus larvae as the predator. The prey were a mixture of spined (induced necktooth phenotype) and unspined (uninduced) juvenile Daphnia pulex. At 6 and 11 °C, Chaoborus selected the unspined phenotype over the spined phenotype, as expected. However, at 22 °C, the selectivity was reversed: significantly fewer on the spined survived compared to the unspined phenotype. These results suggest that the spined phenotype may either increase or decrease Daphnia pulex survival, depending on temperature and clone.     

Feeding efficiency of Chaoborus flavicans (Insecta, Diptera) under turbulent conditions

Turbulence can affect predator–prey interactions. The effect of turbulence on the feeding efficiency of an ambush predator was tested with laboratory experiments. The experiments were conducted in 100-L aquaria in which ten individuals of fourth instar Chaoborus flavicans larvae were placed as predators. Two prey densities (3 and 10 ind. of Daphnia pulex L^?1) and two durations (30 and 120 min) were tested in a nonturbulent treatment and five different turbulence levels [average root-mean-square (RMS) velocities ranging from 0 to 7.3 cm s^?1, corresponding dissipation rates from 7.2 × 10^?7 to 1.3 × 10^?3 m² s^?3]. We hypothesized that the feeding rate of C. flavicans would be enhanced by turbulence due to increasing encounter rates up to a turbulence level above which a disturbance in post-encounter processes would lead to reduced feeding efficiency. However, the results showed no significant increase in the feeding rate of C. flavicans at intermediate turbulence. At high turbulence we found the expected significant negative response in the feeding rate of Chaoborus larvae. The feeding rate declined below the rates at nonturbulent and intermediate turbulence conditions as the average RMS velocity exceeded 3.1 cm s^?1 (dissipation rate 9.9 × 10^?5 m² s^?3, respectively).     

Feeding rates of planktonic copepods from a tropical sea

The feeding rates of the marine planktonic copepods, Eucalanus subcrassus Giesbrecht, Tortanus gracilis (Brady), Calanopia elliptica (Dana) (both male and female), Temora turbinata (Dana), and Paracalanus aculeatus Giesbrecht (only female) from tropical inshore waters have been studied. Newly hatched Artemia nauplii (for Eucalanus, Tortanus, and Calanopia), Dunaliella (for Temora), and Skeletonema (for Paracalanus) were used as food.Feeding rates were measured for a single individual through successive incubations once or twice a day until death to determine changes in feeding rate after collection. Copepods survived from a few days to three weeks. In general, feeding rates varied from day to day, but were less variable than the differences between day and night rates. In some cases, feeding rate consistently decreased up to the death of the copepod. Daily ration, estimated in terms of percentage body weight, was in the range of 28–329 ‰ Using the results together with the those of other workers, gives the relation between daily ration (Y, % body weight) and body weight of copepods (X; μg dry weight) at 20 °C as, logY = 2.531?0.377 logX.Copepods given Artemia nauplii as food killed more nauplii than were eaten. This phenomenon, tentatively called ‘over-hunting’, is possibly an important feeding behaviour for carnivorous copepods.     

Linking lakes? The population genetic structure of Chaoborus flavicans

Larvae of Chaoborus flavicans (Diptera: Chaoboridae) are commonin various lakes and are important members of plankton communities.To assess gene flow between lakes, we sampled several populationsthroughout Europe. To explicitly test whether gene flow is higherwithin regions than between regions, we examined four regionseach containing several populations. For a detailed analysisof regional gene flow, 12 populations within a region in NorthGermany were analysed. Allozymes and mitochondrial restrictionfragment length polymorphism (RFLP) were used to estimate therelative amounts of gene flow. Results indicate that most ofthe dispersal in C. flavicans takes place between lakes withinregions. Therefore, the population genetic structure of C. flavicanssets this species apart from other planktonic organisms, whichare mainly passive dispersers and display low gene flow betweenlakes within regions. Consequently, these data are the firstevidence that C. flavicans may form an important link betweenlakes within regions. Local adaptation within lakes may be decreasedbecause of these processes, and the role of C. flavicans asa biomonitor of local lake conditions needs to be carefullyreinvestigated.     

Feeding and reproductive biology of eleotrid fishes in a tropical estuary

Five species of eleotrid fishes ( Gobiomorus dormitor, Dormitator maculatus, Eleotris amblyopsis, Eleotris pisonis and Leptophilypnus fluviatilis ) are known from the Tortuguero estuary of Costa Rica. One, E. amblyopsis , appears tightly linked to the presence of mats of macrophytes and two others, E. pisonis and D. maculatus , are largely limited to this habitat in the lower estuary. All three of these species feed on hyacinth roots. Despite certain food and habitat specializations among the forms, there is evidence of competition and predation among four species. Individuals of breeding size have never been found in the system for D. maculatus and L. fluviatilis . Alternative means of establishing and maintaining eleotrid populations are suggested.     

Zooplankton populations and the diets of three Chaoborus species (Diptera, Chaoboridae) in a tropical lake

SUMMARY. 1. Zooplankton populations in a small, natural, tropical lake are dominated by a few, small-sized taxa including the copepod Thermo- cyclops consimilis , the cladoceran Moina micrura and several rotifer species.
2. Moina micrura and adults of Thermocyclops consimilis undergo diel vertical migrations within the water column. Population densities of T. consimilis show marked intra-annual variations which may to some extent be related to variations in rainfall and to lunar periodicities In predator abundance.
3. The diets of Chaoborus lavae include other Chaoborus , Cladocera, Copepoda. Rotifera and the dinoflagellate Peridinium. The diets of late instars of the largest species, edulis , were dominated by Crustacea, while those of the two smaller species. C, ceratopogones and C. anomalus , were dominated by Rotifera and the dinoflagellate alga Peridinium , as were the diets of early instars of all species. Algae have not been previously reported to be a large component of the diet of Chaoborus populations in nature.
4. Some of the dietary differences among Chaoborus instars and species are related to the size of each prey species in relation to the mouth gape of each instar. However, there are also important differences in electivity among instars of different species of the same size.     

Feeding selectivity in relation to territory size in a herbivorous reef fish

Summary Territory size in the herbivorous reef fish, Parma victoriae, (Pisces: Pomacentridae) is primarily determined by local density patterns and is independent of changes in food levels (Norman and Jones 1984). However, while individual readily expand territories in response to having their neighbours removed, they appear not to increase total food consumption. Individuals with large territories may benefit from improved food quality. Here we test the hypothesis that expanded territories increase access to preferred food types.A preliminary comparison of the relative proportions of algal species consumed and those present in the field indicated that feeding was highly selective. Strong feeding preferences were indicated by a field cafeteria experiment, in which algal species were presented to individuals in equal amounts. Selectivity indices calculated from diet and availability measures were positively correlated with the feeding preference rankings.Individuals examined from two territory size categories (<10 m² and > 10 m²) did not exhibit significant differences in feeding prefernces. However, they differed greatly in terms of the makeup of their diets. Higher ranking algae such as Champia zostricola and Rhodoglossum sp. were consumed in greater proportions on large territories. Algal abundances within territories also differed for the two groups. Some of the less abundant, high ranking food species were found in greater quantities per unit area on large territories. The differences in diet were not solely explained by changes in availability. The appropriate comparison showed that whereas individuals on large territories fed in a highly selective manner, those on small territories consumed algae in proportion to their availability. A neighbour removal experiment supported the hypothesis that territory expansion results in an increase in the consumption of preferred algal species.     

Food selectivity and diel vertical distribution of Chaoborus edulis (Diptera, Chaoboridae) in Lake Malawi

1. Diel diet and vertical distribution patterns of the larval instars of Chaoborus edulis were studied in deep water near the central part of Lake Malawi, Africa.
2. First instar larvae contained very little food in their crops and probably depended on reserves from the egg. Second, third and fourth instars fed on zooplankton and were size-selective in their feeding. The mean size of prey eaten by the three instars was significantly different from each other, with larger instars feeding on larger prey. Smallest available prey was selected against and the upper size of prey was probably constrained by larval gape. Nauplii were not found in any of several thousand larvae examined. Phytoplankton did not form a significant part of the diet.
3. There was a progressive and related increase in diel periodicity in feeding and vertical migrations of successive instar stages. Fourth instars migrated particularly large distances. Such migrations removed them from their zooplankton food supply but avoided predators. A refuge from predators is probably found in or near the permanent zero oxygen boundary, at depths greater than 200 m.     

The Feeding of Chaoborus flavicans Meigen (Diptera,Chaoboridae). and its Predation on Lake Zooplankton

In a study of Chaoborus feeding in a eutrophic lake, selectivity was found to be positive with Crustacea (especially copepodit stages). and negative with Rotatoria. Daily food rations were about 20% for most of the feeding period, but higher (106%). during the month of intensive growth after hatching. Feeding intensity correlated positively with amount of food an temperature, and negatively with Chaoborus concentration. Elimination of Crustacea (in the epilimnion of the central zone of the lake). equalled about 30–40% of Crustacea production in June and September and slightly exeeded the August production (it was almost zero in the remaining months because Chaoborus larvae stayed at the bottom). This applies, however, only in the central zone – about 50% of the lake volume. Chaoborus probably influences both the density of zooplankton and the quantitative relations between zooplankton species.     

Feeding ecology of a population of GoshawkAccipiter gentilis

Summary 1. The food of a goshawk population was studied by means of collecting and identifying remains of their prey.2. Prey items found included almost any medium-sized bird and mammal species regularly occurring in the study area. However, the bulk of the diet consisted of five species only.3. There is considerable difference in the diet composition between winter and nesting season as well as among breeding pairs. This is considered to be due to divergence in food supply.4. As compared with populations studied in other parts of Europe, diet is poorly diverse. Main prey species are man-dependant herbivorous animals.5. It is concluded that the high density of the goshawk population studied is possible thanks to modern human agriculture and breeding of homing pigeons.6. Factors are discussed which are thought to be responsible for differences in the vulnerability of some prey species.

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Nahrungsökologie einer Habichtspopulation

Zusammenfassung 1. Die Nahrungszusammensetzung einer Habichtspopulation wurde auf Grund der Analyse von Beuteresten ermittelt.2. Die gefundenen Beutereste enthielten fast alle mittelgroßen Vögel und Säugetiere, die im Untersuchungsgebiet regelmäßig vorkommen. Die Masse der Beute bestand jedoch nur aus 5 Arten.3. Sowohl zwischen Winter- und Brutzeit als auch zwischen einzelnen Paaren bestehen bemerkenswerte Unterschiede in der Nahrungszusammensetzung. Dies wird auf unterschiedliches Nahrungsangebot zurückgeführt.4. Im Vergleich zu anderen europäischen Populationen ist die Diversität in der Nahrungszusammensetzung der untersuchten Population gering. Herbivore Arten des Kulturlandes bilden die Hauptbeute.5. Die hohe Siedlungsdichte der untersuchten Habichtspopulation wird auf die Agrarwirtschaft und Taubenzucht zurückgeführt.6. Faktoren, die möglicherweise für unterschiedlichen Feinddruck verantwortlich sind, den der Habicht auf einzelne Beutetierarten ausübt, werden diskutiert.

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From department of Animal Ecology, University of Nijmegen.     

Feeding ecology of thirteen syntopic species of anurans in a seasonal tropical environment

Summary Thirteen species of anurans belonging to three families forage diurnally for arthropods in the leaf litter of the lowland rainforest at the Río Llullapichis in Amazonian Perú. This paper investigates the diets and patterns of coexistence in this group of ecologically similar species. All thirteen species use the forest floor habitat without apparent differentiation. Most species take prey in proportions significantly different from those occurring in the leaf litter and comprise two specialist guilds: dendrobatids and bufonids that eat hard-bodied, slow-moving arthropods such as ants and mites; and leptodactylids that eat soft-bodied, mobile arthropods, primarily orthopterans and large spiders. Dendrobates femoralis (Boulenger) is a generalist, taking prey in proportions not significantly different from those in the leaf litter. Within specialist guilds, body sizes of species vary and are correlated with the size of prey taken. Foraging behavior and predator defense also correlate with the type and sizes of prey taken. Ant specialists tend to be poisonous and active searchers, taking many small prey per day. Non-ant specialists are cryptic, sit-and-wait foragers that take few large prey per day. Similarity in diet within guilds tends tobe lowest in the dry season when food is less abundant, suggesting that food is in short supply in the dry season.     

Characterization of a Chromobacterium haemolyticum population from a natural tropical lake

Aim: To study genetic diversity of Chromobacterium haemolyticum isolates recovered from a natural tropical lake. Methods and Results: A set of 31 isolates were recovered from a bacterial freshwater community by conventional plating methods and subjected to genetic and phenotypic characterization. The 16S ribosomal RNA (rRNA) gene phylogeny revealed that the isolates were related most closely with C. haemolyticum. In addition to the molecular data, our isolates exhibited strong β‐haemolytic activity, were nonviolacein producers and utilized i‐inositol, d ‐mannitol and d ‐sorbitol in contrast with the other known chromobacteria. Evaluation of the genetic diversity in the 16S rRNA gene, tRNA intergenic spacers (tDNA) and 16S‐23S internal transcribed spacers (ITS) unveiled different levels of genetic heterogeneity in the population, which were also observed with repetitive extragenic palindromic (rep)‐PCR genomic fingerprinting using the BOX‐AR1 primer. tDNA‐ and ITS‐PCR analyses were partially congruent with the 16S rRNA gene phylogeny. The isolates exhibited high resistance to β‐lactamic antibiotics. Conclusion: The population genetic heterogeneity was revealed by 16S rRNA gene sequence, ITS and BOX‐PCR analysis. Significance and Impact of the Study: This study provides for the first time an insight into the genetic diversity of phylogenetically close isolates to C. haemolyticum species.     

Vertical migration of Chaoborus flavicans in a Scottish loch

The pattern of diel vertical migration of Chaoborus flavicans larvae in a shallow Scottish loch varies according to the instar and, in third and fourth instars, according to the season. The planktonic phase of the migration is not exclusively concerned with predation, the larvae feeding at least equally actively in the benthos. Although there is no conclusive evidence as to the role of vertical migration in Chaoborus flavicans, it has some of the characteristics of an epideictic display. Upward and downward locomotion can be induced experimentally in a plankton wheel by manipulating light intensity alone. However, the responses are complex and there is a great deal of individual variation, suggesting that additional factors are involved.     

Determinants of intra-annual population dynamics in a tropical soil arthropod

Studies on inter-annual dynamics of populations from temperate regions have shown that density dependence and climate effects are relatively common, albeit weak. Yet, for short-lived organisms, intra-annual variation may be at least as important. Furthermore, tropical species commonly experience temperatures close to their upper thermal limit and thus may be more likely to experience heat stress. Here, we used the soil mite Rostrozetes ovulum to investigate the drivers of intra-annual population dynamics in an Amazonian rain forest. We sampled 3,600 soil cores from 20 transects during 13 months, obtaining 180 mite counts. Next, we built a dynamic N-mixture model accounting for different detection probabilities between soil types. In a Bayesian framework, we used this model to estimate (a) the strength of density dependence and (b) per capita growth rates, which were then tested against environmental variables. We found that the intra-annual population dynamics of R. ovulum were weakly density dependent. Further, per capita growth rates increased with resource supply (litterfall) and decreased with maximum temperature over much of the observed thermal range, although these effects explained relatively little variance. Yet, the seasonal correlation between these factors created a trade-off, so that realized population growth was highest when neither resource supply nor thermal suitability was optimal. Overall, our results suggest that the mechanisms shaping soil animal population dynamics may be surprisingly similar across latitudes. Our model offers a starting point for analyses of soil animal counts when extraction from soil samples is imperfect.     

Relationships of nitrogen and phosphorus to a tropical phytoplankton population

Summary The relationships of nitrogen and phosphorus in the plankton of tropical Lake George (Uganda) have been investigated. The data used are from analyses of samples collected from mid-lake areas during one year, and along transects of increasing plankton concentration, at various times when conditions allowed, and also from results of nutrient uptake experiments. These data are discussed in relation to previously reported information about general limnological conditions in Lake George, and in relation to physiological effects of nutrient enrichments. The features are compared with other waters.The peculiarities of the lake make difficult the precise calculations of long term primary production using oxygen exchange techniques, so that the determination of nutrient turnover rates based upon metabolic activity measured in this way could be misleading. Nevertheless, reasonable overall assessment of nitrogen and phosphorus turnover might be obtained from the proportions of these elements in the plankton. This could be done mainly due to the low variability of the limnological conditions, the apparent limitation of both nitrogen and phosphorus nutrients and the extreme predominance of algal metabolism over the remaining biota.It was also considered that the multiplicity of growth limiting factors which the nitrogen and phosphorus conditions impart contribute to an inherantly stable biomass.

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Zusammenfassung Die Beziehungen zwischen Stickstoff und Phosphor im Plankton des tropischen Sees Lake George (Uganda) wurden untersucht. Die benutzten Daten stammen aus Analysen vom Proben, die über ein Jahr hinweg aus einem Gebiet in Seemitte entnommen wurden. Des weiteren wurden Proben entlang von Profilen mit steigender Planktonkonzentration untersucht. Ferner wurden Ergebnisse von Nährstoffaufnahme-experimenten benutzt. Die Daten wurden mit denen verglichen, die bereits über die algemeinen limnologischen Bedingungen des Sees veröffentlicht wurden. Auch wurden sie in Bezug auf die physiologischen Einflüsse einer erhöhten Nährstoffzufuhr diskutiert. Die Merkmale des Sees wurden mit denen anderer Gewässern verglichen.Die charakteristischen Besonderheiten des Sees machen eine genaue Berechnung von lang anhaltender Primärproduktion unter Anwendung der Sauerstoffaustausch-Methode schwierig, so dass die Bestimmung der Raten des Nährstoffwechsels, basiert auf gemessener metabolischer Aktivität, ein falsches Bild geben könnte. Immerhin konnten annehmbare allgemeine Werte von Stickstoff und Phosphorstoffwechsel aus der Verteilung dieser Elemente im Plankton gewonnen werden. Diese Werte konnten vor allem durch die geringen Schwankungen in den limnologischen Bedingungen, durch die auffallende Beschränkung im Auftreten von Stickstoff und Phosphor und durch das extreme Überwicht vom Algenmetabolismus über die übrige Biota, gewonnen werden.Es wird angenommen, dass die Vielfalt der wachstumbegrenzenden Faktoren, die mit dem Stickstoff- und Phosphorhaushalt zusammenhängen, zu einer von Natur aus stabilen Biomasse führen.

     

Feeding selectivity of Corbicula fluminea (Bivalvia) on natural phytoplankton

Phytoplankton in water samples from the lower delta of the Paraná river (Argentina) and in the gut contents of a local populaton of the Asiatic clam Corbicula fluminea was identified and counted monthly between April 1992 and March 1993. Relative abundances of algal species were generally similar in the medium and in the stomachs of clams, suggesting the absence of feeding selectivity on the basis of taxonomic group or size-class. Diatoms made up a slightly but consistently larger (yet not significantly different) proportion of the diet of C. fluminea than of the plankton; this pattern is attributed to enhanced preservation of algal siliceous frustules, rather than to feeding selectivity. It is suggested that non-selective feeding by the bivalve is a response to the overall scarcity of food and, probably, to food collection by a combination of deposit and filter feeding.     

Feeding behaviour in a population of domestic fowls in the wild

In 1976 the diet of adult feral fowls on a Scottish island consisted mainly of grass from January to July and oats from August to December. Juveniles ate many invertebrates in their first two months of life, but otherwise their diet was similar to that of the adults. In contrast to the non-breeding adults, broods and their dams showed two distinct types of feeding behaviour, called “sporadic” and “intensive” feeding. These were directed towards scattered and concentrated food sources, and the type shown depended mainly on the dam's behaviour. The significance of these and other aspects of feeding behaviour is discussed.