Variation In Ingestion Rates Research Articles

In situ feeding rates and grazing impact of Mesopodopsis africana O. Tattersall in the St Lucia Estuary, South Africa

Mesopodopsis africana is an important mysid in southern African coastal zooplankton and a key species in the St Lucia estuarine lake, which is currently undergoing severe desiccation owing to freshwater deprivation. M. africana populations through much of the system are consequently under severe environmental stress. This study investigates the grazing dynamics of this mysid species, in relation to autotrophic food availability and other environmental constraints in two contrasting areas of the St Lucia Estuary, Charters Creek, heavily affected by the desiccation process and the Mouth, virtually under unchanged conditions. Gut evacuation experiments were conducted once each during the day and the night. Evacuation rates were consistently higher during the night, ranging from 0.27 to 0.33 h -1 at Charters Creek and from 1.13 to 1.24 h -1 at the Mouth. Ingestion rates were, therefore, higher at the Mouth resulting in population grazing impacts of 2.5% of the total microalgal biomass, while the grazing impact at Charters Creek was only 0.5%. The spatial variation in ingestion rates could be attributed to seasonal differences in gut evacuation rates, differences in the mean size of mysids used, or the physicochemical conditions present at the two stations. It is suggested that mysid populations at Charters Creek are predominantly driven by bottom-up forces, initiated by the harsh environmental conditions. Despite the lower ingestion rates exhibited at Charters Creek, results indicate that these mysids are capable of meeting all their energetic requirements from a microalgal diet alone, although they may also utilise a heterotrophic diet.

The importance of ingestion rates for estimating food quality and energy intake

Testing ecological or socioecological models in primatology often requires estimates of individual energy intake. It is a well established fact that the nutrient content (and hence the energy content) of primate food items is highly variable. The second variable in determining primate energy intake, i.e., the ingestion rate, has often been ignored, and few studies have attempted to estimate the relative importance of the two predictors. In the present study individual ingestion rates were measured in two ecologically very different populations of Hanuman langurs (Semnopithecus entellus) at Jodhpur, India, and Ramnagar, Nepal. Protein and soluble sugar concentrations in 50 and 100 food items. respectively, were measured using standardized methods. Variation in ingestion rates (gram of dry matter per minute) was markedly greater among food items than among langur individuals in both populations, but did not differ systematically among food item categories defined according to plant part and age. General linear models (GLMs) with ingestion rate, protein, and soluble sugar content explained 40-80% of the variation in energy intake rates (kJ/min). The relative importance of ingestion rates was either similar (Ramnagar) or much greater (Jodhpur) than the role of sugar and/or protein content in determining the energy intake rates of different items. These results may impact socioecological studies of variation in individual energy budgets, investigations of food choice in relation to chemical composition or sensory characteristics, and research into habitat preferences that measures habitat quality in terms of abundance of important food sources. We suggest a definition of food quality that includes not only the amount of valuable food contents (energy, vitamins, and minerals) and the digestibility of different foods, but also the rate at which the food can be harvested and processed. Such an extended definition seems necessary because time may constrain primates when feeding competition is intense and foraging is risk-prone.

Temporal variability in functional responses and prey selectivity of the pelagic mysid, Mysis mixta , in natural prey assemblages

Predation rates and prey selection of the pelagic mysid shrimp, Mysis mixta, were studied experimentally in the northern Baltic Sea in 1998 during their most intensive growth period, from June to October. Functional responses during 5 months were determined by providing the mysids with a natural zooplankton assemblage, diluted to several different concentrations. The results show that ingestion rate increased, along with mysid growth, from early summer to autumn and that saturation level was reached between 400 and 500 μg C l−1. Ingestion rates increased with increasing prey concentration, and sigmoidal curves explained mostly the variation in ingestion rates (explanatory levels of 86–97%). Prey selection was evident in June, July and August, though weaker during the latter 2 months. Selection differed between the studied months but, generally, copepods were more positively selected than cladocerans. Rotifers were the main prey during June and July, when mysids were small, while larger mysids fed on copepods and cladocerans. Of the copepods, Eurytemora affinis was a truly selected species. This study shows that mysids feed on many zooplankton taxa and that they undergo ontogenetic diet shifts.

Feeding Behavior and Assimilation Efficiency of the Rufous-Tailed Plantcutter: A Small Avian Herbivore

We examined the feeding behavior and nutritional ecology of one of the smallest species of avian herbivores (ca. 44 g), the Rufous-tailed Plant cutter Phytotoma rara (Phytotomidae). This species inhabits forests and scrublands, as well as crop fields and orchards in central Chile. Field and laboratory data revealed that P. rara is a herbivorous bird with marked preferences for leaves in comparison to fruits and insects. When P. rara eats a highly diluted plant material (such as lettuce), a shorter digesta retention time and a lower apparent digestibility was observed in comparison to a high-quality diet. Wet-mass daily intake of plant material was 5.4 times body mass, two times higher compared with the high-quality diet. The larger proportion of water and refractory materials in lettuce diet may explain the variation in ingestion rates. Feeding bouts were longer with lettuce diet, because birds spent more time handling and chewing previous in gesta. Chewing may increase overall digestibility through physical breakdown of cell walls, making available the highly digestible cell contents. These strategies may allow P. rara to maintain body mass balance when feeding on highly diluted plant material.

Relationship between feeding time and food intake in hamadryas baboons (Papio hamadryas) and the value of feeding time as predictor of food intake

The relationship among time spent feeding, number of feeding bouts, feeding bout length, and the amount of food ingested was determined in a study of 18 hamadryas baboons (Papio hamadryas) at the German Primate Center (DPZ). There was considerable within- and between-subject variation in all four variables. Feeding time and number of feeding bouts could explain only 30% and 40%, respectively, of the variation in the ingested amount of food. No relationship was found between feeding bout length and amount of food ingested. The reason for these weak relationships is the high within- and between-subject variation in ingestion rate. If the amount of ingested food is estimated by multiplying mean ingestion rates of various subject categories by feeding time, deviations from true amounts range from 8% to 50%. A prediction of feeding success solely by measuring feeding time or number of feeding bouts is therefore not recommended and an estimation of food intake from ingestion rates and feeding time has to be treated with caution. Zoo Biol 18:495–505, 1999. © 1999 Wiley-Liss, Inc.

Determinants of ingestion rates in filter‐feeding larval blackflies (Diptera: Simuliidae)

SUMMARY 1. The functional response of the filter‐feeding blackfly larva Frosimulium mixtum/fuscum was examined in laboratory experiments. We focused on the relationship between a component of the particle handling process (the cephalic fan flick rate) and ingestion rate, to determine whether ingestion rate is limited by handling‐time. The influence of food deprivation on ingestion rate and feeding efficiency also was assessed.2. Ingestion rate rose asymptotically with increasing food availability, leveling off at a concentration of about 100 mg1−1. Satiation did not account for this plateau. Flick rate (the frequency with which larvae open and close their cephalic fans) increased in a similar fashion, though flick rate only accounted for about two‐thirds of the variation in ingestion rate.3. A simple equation describing the components of the feeding process in blackfly larvae was developed to investigate alternate flick rate ‘decision rules’ capable of predicting relationships between food concentration, flick rate and ingestion rate. The flick rate did not follow a fixed time rule, in which larvae allow particles to accumulate in the fan for a fixed amount of time prior to retraction. For most food densities, flick rate patterns more closely approximated a fixed number rule, in which fans are retracted after a fixed number of particles accumulate.4. Flick rate rose with increasing food concentration even after the ingestion rate had levelled off, whereas several optimal filter‐feeding models predict that filtering rate should decline as food concentration increases above this level. This predicted behavior was not observed because the number of particles ingested per flick failed to increase with increasing food concentration.5. The efficiency of particle ingestion (number ingested × number available−1× 100) was very low (<0.1%), and declined with increasing food concentration.6. An increase in food deprivation time prior to a feeding trial produced a significant increase in flick rate, ingestion rate and feeding efficiency. This adjustment of feeding behaviour allowed animals to replace their gut contents more quickly following longer periods of food deprivation, which agrees with the qualitative predictions of optimal digestion‐time models.

In situ predatory behavior ofMysis relicta in Lake Michigan

Selectivity coefficients (W′) and predation rates on Lake Michigan zooplankton were determined forMysis relicta during spring through fall using anin situ method. W′ values indicated the following ranked order of prey preference: Cladocera > copepod copepodites and copepod nauplii > adult diaptomids and cyclopoids. With few exceptions, W′ values for different prey categories remained fairly constant despite greatly changing relative abundances of prey. Predation rates and prey selectivity were similar in most cases to those determined in laboratory studies. Ingestion rates (percent dry body weight · day−1) were correlated to total prey biomass (r = 0.38) and to effective prey biomass (r = 0.85), where the weighting factors were overall mean selectivity coefficients for the different prey categories. This result suggested that seasonally varying composition of prey caused much of the variation in ingestion rates among experiments. Feeding trials performed at the same depth with daytime and nighttime assemblages of zooplankton indicated that Cladocera may escape heavyMysis predation at night by migrating from the metalimnetic-hypolimnetic interface into the epilimnion.

The Influence of Moulting on the Ingestion Rate of an Isopod Crustacean

The variation in ingestion rate throughout one entire instar of the isopod Idotea baltica (Pallas) is described and compared with that suggested by Duncan and Klekowski for a generalized continuous feeder. Feeding is greatly inhibited during ecdysis, enhanced directly afterward, and diminishes slightly for the latter half of the moulting cycle to a level that corresponds to the mean daily ingestion rate for the entire cycle. This fluctuation accounts for 86% of the residual variation in ingestion rate remaining after the influence of body length is removed. It is thought that an increased ingestion rate immediately following ecdysis ensures that sufficient minerals are available for rapid calcification of the new integument.