Feeding Biology Research Articles

Effects of Food Availability and Predation on a Marine Zooplankton Community — a Study on Copepods in the Baltic Sea

AbstractThe importance of food resources versus predatory effects in determining the abundance pattern of zooplankton varies over time and space. Here, we evaluate the population dynamics of dominant calanoid copepods (Acartia spp. bifilosa/A. longiremis and Eurytemora affinis) in a reference area and a eutrophied area in the northern Baltic Sea Proper. We base the paper on a combination of statistical analyses of a long term (12 years) data set on population biomass dynamics, laboratory experiments on the feeding biology of these species and literature data of their susceptibility to predation. Overall, copepods were equally abundant at both sites, but Eurytemora was more abundant in the eutrophied area while Acartia spp. dominated in the non‐eutrophied reference area. There was, however, no significant difference between the two areas in biomass dynamics (biomass specific rate of change) of the two groups of copepods. However, in spring and early summer the population biomass increased faster for Eurytemora as compared to Acartia spp. This is consistent with our findings from feeding and respiration experiments. Eurytemora exhibited generally higher ingestion rates and had a higher growth efficiency (ratio of ingestion to respiration rates), which suggests an advantage over Acartia spp. when food availability increases. Both species generally showed a rapid population decline starting in late summer, most likely caused by intensive predation by fish and mysid shrimps. In late autumn and winter, biomasses of both genera continued to decrease, but the decline was fastest for Eurytemora. During this period of the year, when the food availability is sparse, Acartia spp. may have an advantage over Eurytemora, as we found that the former ingests a broader size range of food particles and it has also been reported to be able to switch from filter feeding to raptorial feeding. This study shows that dominant copepods in the net‐zooplankton community in our study area were structured both by food availability and predation. The relative importance of these effects varied seasonally.

The food and feeding behaviour of Limnothrissa miodon (Boulenger, 1906) in Lake Kariba, Zimbabwe

The feeding biology of the Lake Tanganyika sardine, Limnothrissa miodon (Boulenger, 1906) was studied to assess the quality and quantity of food items taken. Fish samples were collected at two hour intervals during a series of twenty-four hour trawling surveys in the Sanyati basin of Lake Kariba. The diurnal and nocturnal consumption trends for each food item were determined. Fish stomach contents were first analysed under a dissecting microscope and subsequently on an inverted regular high power Nikon microscope. Food items were identified and quantified for frequency of occurrence and percentage composition. Limnothrissa miodon feeds mainly on the cladocerans Bosmina longirostris, Ceriodaphnia cornuta and Bosminopsis deitersi and the copepods Mesocyclops sp., Tropodiaptomus sp. and Thermodiaptomus sp. Aquatic insect larvae, rotifers and ostracods also occur infrequently in the diet. Several feeding peaks exist during a twenty-four hour cycle with an overall tendency to ingest food during the daytime. Limnothrissa miodon therefore mostly feeds on crustacean zooplankton and it is mainly a visual feeder that depends on availability of adequate light to locate its prey.

The abundance and trophic biology of Clarias albopunctatus Nichols & LaMonte, 1953 (Osteichthyes: Clariidae) in a tropical floodriver basin

The abundance, food and feeding biology of Clarias albopunctatus was studied over a period of 17 months in the lower River Anambra, Nigeria. The catfish was more abundant in late dry season (January–March) and early rainy season (April–June) than in other periods of the year in the small-sized Akwu pond than in other habitats. Feeding intensity was higher at night and at dawn (20.00–05.00 h) than during the day (08.00–17.00 h) in the 151–200 mm TL size class and during the rainy season (April–September). There was no sex-dependent variation in feeding intensity. Insects were the predominant food, followed by crustaceans. Of primary importance were Chironomidae (mainly Chironomus spp. and Tanypus sp.), Odonata nymphs, Dytiscus sp., mosquito larvae and pupae, Gyrinus sp., Daphnia sp., Ostracoda and Tilapia fry. Qualitative food composition and food richness were size, but not sex – or season-dependent. Diet breadth increased with catfish size and during the rainy season. The feeding behaviour of the catfish include foraging, shovelling and surface feeding. Abundant food and ability to switch to more available items enable C. albopunctatus to maintain its abundance in the River Anambra.

Critical appraisals allow the analytical review of existing knowledge on current topics of significance in ecological entomology. They should assess the worth or quality of the work in the field and suggest areas for investigation.

Summary. Previous studies have synthesized life‐table data from herbivore species to identify general trends in the demography of herbivorous insects. Frequency‐based analyses were used to ascertain which of five mortality sources (enemies, plant factors, competition, weather, intrinsic developmental failure) and which of five ecological characteristics of herbivores (feeding biology, invasion status of the herbivore, latitude, cultivation, and successional status of the habitat) had important influences on mortality patterns.Here these results are reinforced with a quantitative analysis that relies on actual numbers of herbivores killed at different developmental stages by each of the five mortality sources in different ecological settings. We also examine the relationship between taxonomic category (Coleoptera, Diptera, Lepidoptera, and Hymenoptera) and mortality.The analysis identified developmental changes of herbivores as having an important influence on sources of mortality; feeding biology, latitude, and cultivation status also influenced the distribution of mortality sources. Other aspects of the herbivores’ ecology and taxonomy had limited effects.Natural enemies were identified as the most important mortality source overall, and their importance increased from the early larval stages to the pupal stages. They also kill more exophytic insects than endophytic insects, and kill a higher proportion of insects in cultivated habitats than in natural habitats.Weather kills more temperate‐zone immatures than tropical/subtropical immatures.The results of the quantitative analysis generally confirm the earlier frequency‐based tests.Several predictions that can serve as the foundation of an empirically‐based theory of herbivore demography are offered: (1) natural enemies are the dominant cause of mortality in exophytic herbivore populations and may compete more intensely than on endophytics; (2) plant factors and enemies play a more balanced role in endophytic populations; (3) exophytic species should be particularly susceptible to top‐down effects, especially in agroecosystems; (4) plant defences will often have sublethal effects, but when they are lethal they will be most important as the hatchling larva is just getting established on the plant.These predictions should be viewed as a challenge to engage in a broader way of thinking about herbivore demography.

Feeding rates and carbohydrate metabolism by Bemisia tabaci (Homoptera: Aleyrodidae) on different quality phloem saps

Abstract.The effects of water stress on phloem sap quality of the melon, Cucumis melo, and how this, in turn, has an impact on the sweet potato whitefly, Bemisia tabaci were studied. Melon plants were grown under watering regimes that produced plants with or without water stress. Plants showed strong developmental responses to the treatments; water‐stressed plants were shorter, with fewer, smaller leaves than those without stress. There was, however, no effect of plant water stress on the development period of whiteflies feeding on these plants, or on the weights of male or female adults. Honeydew production was used as an indirect measure to test whether the absence of insect developmental or behavioural effects was due to differential phloem sap ingestion. Feeding rates on the stressed plants were almost half those on unstressed plants, and there was also variation in the daily pattern of honeydew production. Phloem sap and honeydew were analysed to determine why the feeding behaviours differed. Amino acid composition of the phloem sap was similar in both groups of plants, but carbohydrate concentrations were greater in water‐stressed plants, indicating that lower feeding rates may have been due either to the physical or nutritional quality of the phloem sap. The honeydew of insects that were feeding on water‐stressed plants contained a greater concentration of carbohydrate than those on unstressed plants, and was composed of a significantly greater proportion of glucose and the disaccharide, trehalulose. This isomerization of more complex sugars from those in the diet suggests that B. tabaci uses a mechanism of osmoregulation to actively maintain its internal water status. It is concluded that transient conditions of water stress in this host plant do not affect the development of B. tabaci, due to physiological and behavioural changes in response to diets with different nutritional and physical properties. The implications of this finding for the feeding biology of B. tabaci on desert‐grown crops are discussed.

Gall Morphology and Community Composition in Asphondylia flocossa (Cecidomyiidae) Galls on Atriplex polycarpa (Chenopodiaceae)

Asphondylia flocossa Hawkins (Diptera: Cecidomyiidae) and its associated community of natural enemies were sampled in galls on Atriplex polycarpa (Torrey) Watson (Chenopodiacedae) at 3 locations north of Phoenix, AZ, between October 1994 and March 1995. Galls collected in the autumn had dramatically smaller diameters and shorter trichomes than galls collected in the spring. Asphondylia flocossa were more likely to emerge from larger than average galls with a thick trichome layer in both the autumn and winter samples. The different species of natural enemies each emerged from galls with different characteristics. There was significant variation among taxa of natural enemies for both gall diameter and trichome depth in both the spring and autumn samples. The community of natural enemies also varied significantly among populations and more markedly between seasons. Both Asphondylia flocossa and Rileya tegularis Gahan (Hymenoptera: Eurytomidae) were much more abundant in spring samples than in autumn samples. In contrast, Torymus cappilaceus (Hüber) (Hymenoptera: Torymidae) and an undescribed species of Galeopsomyia (Hymenoptera: Eulophidae) were abundant in the autumn samples but almost non-existent in the spring samples. The first 2 species tended to emerge from relatively large galls while the latter 2 species tended to emerge from small galls. Torymus umbilicatus (Gahan) (Hymenoptera: Torymidae) was the only parasitoid abundant in samples from both seasons. This species emerged from galls with the widest range of diameters and trichome depths of any species, both within and between seasons. The feeding biology of the individual species coupled with seasonal and temporal covariation in gall morphology makes natural enemy control of gall size unlikely. The data is consistent with the hypothesis that gall morphology influences insect community composition.

Investigations on the feeding habits of the rocky-shore miteHyadesia fusca (Acari: Astigmata: Hyadesiidae): diet range, food preference, food quality, and the implications for distribution patterns

Within the food web of estuarine and marine rocky shore ecosystems phytophagous mites of terrestrial and marine origin constitute an important part as grazers on algae and as a food source for certain arthropods, especially zoophagous mites. This investigation deals with the feeding biology ofHyadesia fusca taking as an example a population located on an artificial rocky shore of the middle Weser estuary in Northern Germany. The species is characterized by a broad diet range; in feeding experiments diatoms, lichens, detritus as well as blue, red and green algae were accepted. Even analyses of faecal pellets produced by field specimen suggest a non-specific feeding habit. However, the influence of certain diets on mortality, offspring number and rearing success showed that the food quality differs significantly. The most suitable food, the UlvaceaeBlidingia, was clearly preferred in a series of pairwise choice tests. These findings correlate with the vertical zonation of the field population i.e.: higher population densities in the vegetation zone dominated byBlidingia. It can be concluded that in addition to abiotic factors food supply could play an important role for distribution patterns of phytophagous mites.

Physiological constraints in shrimp cultures

The biological requirements of animals change considerably during development from the egg to the (early) adult stage. Some basic physiological requirements (respiration, excretion of metabolic end products, space requisites, aspects of feeding biology) of cultured animals are considered in relation to design (surface area, depth) and maintenance (water refreshment) of shrimp (and fish) culture units. From general relations between respiration and food intake with body weight, the required changes in medium dimensions or animal density can be derived. It follows that water volume of a rearing system should be kept approximately proportional to biomass, surface area, food and water supply and should remain proportional to the metabolic weight ( W b) of the biomass. Depth and water refreshment should be proportional to, respectively, W 1−b and W b−1 ( b ∼ 0.74). The increase of body weight requires a reduction of animal density proportional to the reciprocal of metabolic weight. This can be achieved, for instance, by stepwise increasing the available surface area of the culture enclosure by 10 0.735 (∼5.4) times and depth by 10 0.265 (∼1.8) times at each 10-fold increase in biomass.

Suppression of nematophagous fungi by enchytraeid worms: a field exclosure experiment.

The feeding biology of Enchytraeus crypticus and other enchytraeids is poorly understood as is their effect on nematophagous fungi. Because enchytraeids had been associated with nematophagous fungi in the field and had suppressed these fungi in soil microcosms, we tested the hypothesis that exclusion of enchytraeids, largely E. crypticus, would improve establishment of certain nematophagous fungi in field plots. The fungi, Hirsutella rhossiliensis and Monacrosporium gephyropagum, are being studied as potential control agents of plant-parasitic nematodes and were formulated as hyphae in alginate pellets. The pellets were mixed into soil without enchytraeids and placed in cages (PVC pipe, 80 cm3 volume) with fine (20 μm) or coarse (480 μm) mesh; cages were buried 15 cm deep in field plots and then recovered after 6-52 days. When fine mesh was used, enchytraeids were excluded and the fungi increased to large numbers. When coarse mesh was used, enchytraeid numbers in cages increased rapidly and the fungi did poorly. Although mesh also affected other potential fungivores, including collembolans and large dorylaimid nematodes, we suspect that enchytraeids were more important because large numbers were consistently found in cages with coarse mesh soon after the cages were placed in soil. Organisms smaller than enchytraeids (bacteria, fungi, and protozoa) also appeared to be important because the fungi did better in heat-treated soil than in non-heat-treated soil, regardless of mesh size. The rapid increase in enchytraeid numbers in cages with hyphal pellets and coarse mesh was probably caused by movement of enchytraeids toward the pellets with hyphae: increase in enchytraeid numbers was minimal when movement into cages was blocked (or when cages contained pellets without hyphae). Overall, the data were consistent with the hypothesis that enchytraeids, or other meso- or macrofauna, contributed to suppression of nematophagous fungi in our field plots.

PREDATORS, PARASITOIDS, AND PATHOGENS AS MORTALITY AGENTS IN PHYTOPHAGOUS INSECT POPULATIONS

We compiled life tables for 78 holometabolous herbivorous insect species to quantify levels of apparent enemy-induced mortality of immature insects. Enemies were classified by type (predator, parasitoid, or pathogen), and mortalities caused by each type in each herbivore immature stage were tested with Analysis of Deviance for differences associated with four ecological characteristics of preadult herbivores: feeding biology, invasion status, and the cultivation status and latitudinal zone of the habitat. Total enemy-induced mortality is higher in the late developmental stages, and overall, parasitoids kill more herbivores than do either predators or pathogens. Among the ecological variables, both feeding biology and latitude showed significant enemy effects in at least one late developmental stage, whereas neither cultivation status nor invasion status was associated with enemy-induced mortality in any stage. Bonferroni adjustment of probabilities for multiple comparisons resulted in few significant interactions between enemy type and the ecological variables. However, raw probabilities and comparisons across herbivore immature stages suggest several patterns that deserve attention in future studies: (1) endophytic herbivores suffer lower mortality by predators and pathogens than exophytics, and endophytic leaf miners suffer the greatest parasitoid-induced mortality, while endophytic gallers/borers/root feeders suffer the least; (2) overall enemy-induced mortality is similar in natural and cultivated habitats; (3) exotic insects do not suffer lower enemy-induced mortality rates than natives; and (4) predation and disease may be greater in tropical/subtropical habitats, whereas parasitism is greater in the temperate zone. These results identify several general patterns in insect demographics that should be useful for hypothesis testing.

Feeding Behavior of Dipolydora commensalis (Polychaeta: Spionidae): Particle Capture, Transport, and Selection

Feeding Behavior of Dipolydora commensalis (Polychaeta: Spionidae): Particle Capture, Transport, and Selection

Laboulbeniales on beetles: host utilization patterns and species richness of the parasites

Fungi of the order Laboulbeniales are obligate ectoparasites that are easy to detect on the integument of their arthropod hosts. This apparency, and other characteristics that suit them for the role of ‘model’ group in the exploration of parasite biodiversity patterns, are discussed. Salient features of the general biology of these organisms are summarized and past patterns of species description reviewed. In recent years, much as in the fungi as a whole, roughly equal proportions of new species have been described from tropical and temperate regions. Comparison of the known Laboulbeniales mycobiotas of Europe, Asia and ‘tropical Asia’ reveals that most of the more significant parasite genera are more or less equally well represented in each region. Patterns of host utilization are also largely similar, with more than 50% of host species recorded from each region belonging to the two beetle families Carabidae and Staphylinidae. However, there are indications that parasite species that are not confined to a single host species have significantly broader geographical ranges than any of their hosts. The pattern of host utilization in the relatively fully-inventoried assemblage of beetles of a tropical forest in North Sulawesi is described, in terms of the taxonomic group membership, habitat affiliation and feeding biology of recorded hosts. On the basis of the Sulawesi dataset and other available data on host exploitation patterns at various spatial scales, we suggest that between 2 and 5%, i.e. between ca 40000 and ca 100000 of an estimated 2 million extant beetle species, are hosts of one or more species of Laboulbeniales. Known and predicted levels of host specificity imply that a global figure for Laboulbeniales species exploiting Coleoptera is likely to be between 10000 and 50000 species. A smaller number of Laboulbeniales species, probably no more than half the number associated with beetles, are to be found on other arthropod hosts. Ways in which these estimates might be refined are discussed.

Descriptions of the pupae and larvae of Stenopsyche siamensis martynov, 1931 (Trichoptera: Stenopsychidae) with notes on larval biology

Detailed descriptions are given of the pupae and larvae of Stenopsyche siamensis Martynov, and comparisons are made with the immature stages of other Stenopsyche species previously described from Asia. The larval feeding biology of S. siamensis and its position in stream communities are briefly discussed.

Differences in Diet, Population Size and Reproductive Performance between Two Colonies of Audouin's Gull Larus audouinii Affected by a Trawling Moratorium

discards caused by the moratorium and the likely decrease of clupeiform populations have affected both the feeding and breeding biology of the species. However, the effects of a reduced food supply were greater in the Columbretes Is., probably because of the lack of alternative food resources. When trawlers operated, the gulls' diet was very similar in the two colonies, but when the moratorium started, significant differences were found at both taxonomic and typologic levels. Prey from rice fields acted as a buffer for the Ebro Delta colony, whereas in the Columbretes Is. the gulls were forced to fish actively, probably at greater energy costs. In the moratorium years, breeding success was always significantly lower in the Columbretes Is. than in the Ebro Delta; extremely, no young fledged in the Columbretes Is. in 1993. Clutch size was also significantly lower in the Columbretes Is. colony, even when the moratorium did not coincide with the laying stage, suggesting that predation by Yellow-legged Gull Larus cachinnans could be an additional limiting factor at this locality, where the ratio of breeding pairs of Yellow-legged to Audouin's Gulls is much higher than in the Ebro Delta. In contrast to previous studies, the larger colony (Ebro Delta) had better breeding performance than the smaller colony (Columbretes Is.), suggesting that density-dependent effects may not operate in the Ebro Delta colony because of the large variety of foraging habitats (rice fields, lagoons, dunes, beaches) and the high productivity of the sea off this colony. While population size in the Ebro Delta colony suggested the absence of limiting factors until the establishment of the trawling moratorium, the size of the Columbretes Is. colony indicated a breeding site limitation, and probably competition with the Yellow-legged Gull.

Ecological Explanation through Functional Morphology: The Feeding Biology of Sunfishes

Researchers have been using simple morphological measures as indicators of ecological features for some time. The utility of morphological variables as ecological indicators depends upon our understanding of how the variable effects the ability of the organism to perform a particular task. Functional morphological analyses identify those features that can be directly related to behavioral performance and help to distinguish causal functional relationships from spurious correlations. The behavioral abilities of the individual, in turn, shape patterns of resource use and fitness by placing limits on the range of resources that can be utilized and by shaping the cost/benefit curve for resource choices. Examples from research on the feeding biology of North American sunfishes are discussed to illustrate how functional morphology can be used to provide explanations for differences between species in patterns of prey use, patterns of habitat use, ontogenetic diet switches, and population size. Trends from analyses of the evolution of fish feeding mechanisms suggest specific functional features that are most likely to vary among taxa and underlie differences in feeding performance and diet. Included in this group of predictive variables are the organization of lever arms in the jaw opening and closing systems, the size of the mouth, and the size of muscles used in prey—crushing behaviors. The link between morphology and ecology will be made most firmly when variables are chosen that clearly reflect the ability of the organism to perform relevant behaviors.

Aspects of Common Loon (Gavia immer) feeding biology on its breeding ground

Field studies and experiments with hand-reared loons found loons to be facultative predators, foraging on a variety of fishes, crustateans and other aquatic animals. Loons selected certain species and size of prey when present, favoured fusiform shapes and atypical, erratic swimming behavior, but took the most readily available and susceptible to capture, often yellow perch. Chick feeding behaviour developed during the first 8 wks after which physical maturity permitted independent feeding. Juveniles resembled adults in size and shape by wk-11, and were capable of catching all of their own food. Evidence suggests that loons are not harmful to sport fisheries and may ba beneficial by supressing species competing with game fish. Territories averaged 72 ha, and food may be a determinant for maximum size. Based on the average amount of food required by a chick for its first 15 wks (53 kg), plus the daily consumption of older birds (960) g, a pair of loons rearing 2 chicks could remove about 423 kg of food during 5.5 months on territory.

Density independent growth of Haliotis iris Martyn (Mollusca: Gastropoda)

The growth rate and nutritional status of abalone ( Haliotis iris) exposed to low (~ 0.3 m −2) and high densities of conspecifics (~ 15 m −2) was measured in 5 × 5 m experimental enclosures. Over the duration of the experiment (15 months), estimates of the percent cover of macroalgae revealed no significant difference attributable to density except for crustose coralline algae which had significantly greater cover in high density enclosures. Drift seaweed, the preferred food of Haliotis iris was always present in low abundance (< 5% cover). There was no significant effect of density on the relative gut fullness or growth of H. iris, but significant variation in the dry weight of pedal muscle was due to density. Measurements of the dry weight of gonad and the ash-free dry weight of pedal muscle or gonad were otherwise similar between low and high density treatments for H. iris. Shell growth was similar among high density and low density treatments but high in relation to other populations of H. iris. Density independent growth is consistent with the feeding biology of H. iris and may apply to other species of abalone.

The reproductive and feeding biology of Schilbe intermedius Rüppell in the Okavango Delta, Botswana

The reproductive and feeding biology of 314 Schilbe intermedius Ruppell 1832 collected in the Okavango Delta, Botswana, between April 1985 and February 1986 during low, intermediate and high water level were investigated. S. intermedius matures at 130 mm standard length and is a monocyclic spawner. Females predominate in the population and have an average fecundity of 27107 eggs. In the northern riverine floodplain of the Delta fish spawn in mid-summer during the peak flood. In the southern drainage rivers fish spawn in spring, which is two to three months after the arrival of the winter flood waters. S. intermedius is an opportunistic predator with a diet consisting largely of fish 41%, aquatic larvae 25%, terrestrial insects 14%, aquatic insects 7% and crustacea 5%. Juvenile S. intermedius feed predominantly on insect larvae, while adults are largely piscivorous.

Phylogeny of the Euhirudinea: Independent evolution of blood feeding by leeches?

The phylogenetic relationships of leeches were investigated by examining 22 species representative of the 10 euhirudinean familes in a cladistic analysis. Forty-five characters relating to internal and external morphology as well as cocoon deposition characteristics were used. Polarization of character states was accomplished using Acanthobdella peledina as the sister-taxon to the Euhirudinea. Two equally parsimonious solutions resulted. One was chosen as a preferred tree on the basis of defensible character state transformations. Previous speculations as to evolutionary branching patterns are largely consistent with the results obtained by cladistic analysis. Similarly, contemporary taxonomic groupings of leeches into higher taxonomic categories were found to be largely consistent with monophyletic groups identified in the analysis. The family Piscicolidae was found to be paraphyletic; elevating the constituent piscicolid subfamilies to the level of family is proposed. The origin of sanguivory as a life-history mode was investigated by optimizing this characteristic on the phylogenetic hypothesis, indicating the possibility of at least two origins of blood-feeding in the evolutionary history of leeches, depending largely on how the feeding biology of acanthobdellids is interpreted. Sanguivory is seen to have been lost at least twice.

Diel periodicity of spawning activity in a permanently territorial damselfish: a test of adult feeding hypotheses

Among species of damselfish in which both sexes defend individual feeding territories, spawning nearly always begins at first light and is completed within 2 h. According to the anti-competitor hypothesis, such dawn spawning occurs because it minimizes the rate of intrusion by diurnally active food competitors while the female is away from her territory. An alternative hypothesis pertaining to adult feeding biology is that dawn spawning minimizes interference with the female's own feeding activity. Diel patterns of spawning and mate-searching activity were documented for a population of garibaldi damselfish, Hypsypops rubicundus, and compared with their diel feeding patterns and those of their food competitors. Female garibaldi spawned at approximately constant levels from dawn through late afternoon and showed peaks in mate-searching activity in the late morning or in the afternoon. However, feeding activity of both female garibaldi and their food competitors increased significantly from dawn to early afternoon. Thus, there was no inverse relationship between garibaldi spawning activity and feeding activity as predicted by these hypotheses.