Correlations of food distribution and patch size with agonistic interactions in female vervets (Chlorocebus aethiops) and patas monkeys (Erythrocebus patas) living in simple habitats

Food distribution is hypothesized to be important in determining the nature of female relationships within social groups of primates. When food limits female reproductive success, spatially clumped foods are expected to produce strong, linear dominance hierarchies within groups, whereas more spatially dispersed foods are expected to produce weaker or non-existent dominance hierarchies. The association between food distribution and competitive relationships presumably occurs because clumped foods are usurpable but dispersed foods are not. We examined the spatial distribution of food patches (trees) and patch size relative to feeding behavior and agonistic interactions in vervets and patas monkeys, two closely related and sympatric species that nonetheless differ in the strength of the female dominance hierarchy. Food patches of both patas monkeys and vervets were small in size and randomly distributed in Acacia drepanolobium habitat. In contrast, in A. xanthophloea woodland, the habitat type that was exclusively used by vervets, food patches were larger and more spatially clumped. These similarities and differences between and within species were correlated with similarities and differences in the strength and linearity of their dominance hierarchies. Patas monkeys and vervets in A. drepanolobium habitat had dominance hierarchies that were weakly defined because there were relatively few agonistic interactions between females. By contrast, in A. xanthophloea habitat, vervets had a stronger, linear dominance hierarchy characterized by a higher rate of agonistic interactions over food. The covariation of agonistic interactions with patch size is discussed in relation to depletion time, another characteristic that may covary with food distribution, and resource renewal rate, an important determinant of agonistic interactions in insectivorous birds, fishes, insects, and mammals. Received: 18 February 2000 / Revised: 5 September 2000 / Accepted: 26 September 2000     

Social and ecological influences on activity budgets of vervet monkeys,and their implications for group living

Summary Activity patterns were documented over a 20-month period in six groups of vervet monkeys (Cercopithecus aethiops) in Amboseli National Park, Kenya. Group size varied both among groups and within groups through time. The home ranges of two groups were located in Acacia xanthophloea habitat whereas those of four adjacent groups were located in A. tortilis habitat. Repeated measures analysis of variance, three-way analysis of variance, and meta-analysis of group size effects were carried out on feeding, moving, resting, scanning, allo-grooming, and other behavior. Time spent feeding varied seasonally, peaking during periods when A. tortilis seeds were eaten. However, time spent feeding did not vary within or among groups, or between habitats, males and females, or dominants and subordinates. Males spend more time scanning and less time allo-grooming than females, and high-ranking individuals of both sexes spent more time scanning than low-ranking individuals. Among females, subordinates spent more time moving, whereas among males, dominants spent more time moving. Groups living in A. xanthophloea habitat spent more time moving and allo-grooming than groups in A. tortilis habitat but this may have been confounded by the fact that these two groups were on average larger than the others. Significant differences in activity budgets among groups demonstrate that activity patterns observed in one group are not always readily generalized to other groups even when they come from the same population. Group size analyses examined potential costs and benefits of group living. Increased intragroup competition, measured by time spent moving and feeding, was only weakly evident in larger groups. Individuals in larger groups allo-groomed more than individuals in smaller groups. Self-grooming also increased in larger groups. Individuals in larger groups spent less time scanning than individuals in smaller groups, but there was more scanning per group in larger groups than in smaller groups. Correspondence to: L.A. Isbell     

Costs and benefits of home range shifts among vervet monkeys (Cercopithecus aethiops) in Amboseli National Park,Kenya

Summary A decline in the density of trees and the deterioration of the habitat of vervet monkeys (Cercopithecus aethiops) in Amboseli National Park, Kenya, have been accompanied by movement of vervet groups into unfamiliar areas. These home range shifts were documented over a period of 26 months. The largest group moved into the home ranges of neighboring groups and acquired more trees, a resource that had become more limited. The groups whose home ranges were encroached upon did not share their home ranges with the intruders, but instead moved into areas that were unoccupied and had a lower density of trees. The largest group was thus more successful than smaller groups in competition for limited resources. For all but one group, movement into new areas was directly associated with the disappearances of female and immature monkeys. Most of the disappearances were attributable to predation. These results suggest that the cost of predation in unfamiliar areas may contribute to the evolution of philopatry in vervets. However, under unstable conditions, resource competition forces these animals to disperse (in groups) despite the high risk of predation. Offprint requests to: L.A. Isbell     

An energy–distance trade-off in a central-place forager,the Antarctic fur seal (<Emphasis Type="Italic">Arctocephalus gazella</Emphasis>)

We tested the prediction that lactating fur seals (Arctocephalus gazella) at South Georgia will take prey of greater energy density with increasing distance of foraging from the colony. The study investigated the differences in diet of fur seals foraging within two regions, one near the breeding colony and the other at greater distance. Diet varied significantly in relation to foraging location. Dietary items of low quality were eaten in both regions but more food items with a high-energy content appeared in the diet of seals travelling to distant oceanic waters. We conclude that there is likely to be a trade-off between energy gain and distance travelled which enables female fur seals to maintain a relatively constant rate of energy delivery to their offspring irrespective of the distance travelled to find food.     

Sex differences in the movement patterns of free-ranging chimpanzees (<Emphasis Type="Italic">Pan troglodytes schweinfurthii</Emphasis>): foraging and border checking

Most social primates live in cohesive groups, so travel paths inevitably reflect compromise: decision processes of individuals are obscured. The fission–fusion social organisation of the chimpanzee, however, allows an individual's movements to be investigated independently. We followed 15 chimpanzees (eight male and seven female) through the relatively flat forest of Budongo, Uganda, plotting the path of each individual over periods of 1–3 days. Chimpanzee movement was parsed into phases ending with halts of more than 20 min, during which individuals fed, rested or engaged in social activities. Males, lactating or pregnant females and sexually receptive females all travelled similar average distances between halts, at similar speeds and along similarly direct beeline paths. Compared to lactating or pregnant females, males did travel for a significantly longer time each day and halted more often, but the most striking sex differences appeared in the organisation of movement phases into a day's path. After a halt, males tended to continue in the same direction as before. Lactating or pregnant females showed no such strategy and often retraced the preceding phase, returning to previously visited food patches. We suggest that female chimpanzee movements approximate an optimal solution to feeding requirements, whereas the paths of males allow integration of foraging with territorial defence. The ‘continually moving forwards’ strategy of males enables them to monitor their territory boundaries—border checking—whilst foraging, generally avoiding the explicit boundary patrols observed at other chimpanzee study sites.     

Nutritional constraints on mountain baboons (Papio ursinus): Implications for baboon socioecology

Summary Populations of baboon (Papio sp.) at geographic and climatic extremes for the genus show a tendency to one-male organization, whereas most baboons live in multimale social groups; this effect has been attributed largely to limitation of food supply, but baboons' complex diet has hindered proper nutritional analyses. To test these optimal-diet explanations of social variation, we quantified intake and used phytochemical analysis of foods to compare the nutrition, during seasonal changes, of two groups of mountain baboons (P. ursinus) living at different altitudes of a continuous grassland habitat. The majority of plant foods were eaten uniquely by one or other group, though their altitudinal separation was only 400 m, and the time budget of feeding choices varied with age-sex class as well as season. Converting to a common currency of nutrients reveals that baboons gained the same yield from a unit time spent foraging (whether this is measured in edible dry weight, or simply protein) in both groups, despite their differing mean altitude, whereas seasonal variation was large and statistically significant. Increased feeding time at the winter bottleneck made no effective compensation for the poorer food yields: in late winter there was a minimum for daily nutrient gain at both altitudes. Apparently this population is already at an extreme for the time animals devote to foraging in winter, when they rely on inconspicuous and slow-to-harvest swollen shoot bases and underground plant storage organs. Since an individual's nutrient yield does not vary with altitude, we conclude that socioecological parameters are effectively optimized for feeding. Since contest competition is absent, this adjustment of foraging efficiency is largely through the effect of differential density on scramble competition. Differences in social structure are considered to be a secondray consequence of optimal foraging, mediated through altitudinal variation in either population density or in day range limits.     

Nest defense and central place foraging: A model and experiment

Summary A graphical model presented here indicates that a nest-defending forager should stay closer to its nest, forage for shorter times per patch, and deliver smaller loads than predicated for delivery rate maximization. The effect is more pronounced farther from the nest, so that if nest defense is especially important, the predator should leave far patches sooner than near ones, and deliver smaller loads from farther away. Moreover, if the attack rate at the nest is increased, the defending forager should move closer and deliver smaller prey.Experimental attacks with stuffed specimens at Gila woodpecker (Melanerpes uropygialis) nests produced the predicted changes in the foraging behavior of males, but not of females.Mated pairs may work as a team to pursue simultaneously two conflicting goals—food delivery and nest protection—both of which affect the survivorship of the young. Sexual dimorphism in monogamous species may result in part from specialization in these roles.     

Foraging behavior in early Atlantic cod larvae (Gadus morhua) feeding on a protozoan (Balanionsp.) and a copepod nauplius (Pseudodiaptomussp.)

Food limitation is likely to be a source of mortality for fish larvae in the first few weeks after hatching. In the laboratory, we analyzed all aspects of foraging in cod larvae (Gadus morhua Linnaeus) from 5 to 20 d post-hatching using protozoa (Balanion sp.) and copepod nauplii (Pseudodiaptomus sp.) as prey. A camera acquisition system with two orthogonal cameras and a digital image analysis program was used to observe patterns of foraging. Digitization provided three-dimensional speeds, distances, and angles for each foraging event, and determined prey and fish larval head and tail positions. Larval cod swimming speeds, perception distances, angles, and volumes increased with larval fish size. Larval cod swam in a series of short intense bursts interspersed with slower gliding sequences. In 94% of all foraging events prey items were perceived during glides. Larval cod foraging has three possible outcomes: unsuccessful attacks, aborted attacks, and successful attacks. The percentage of successful attacks increased with fish size. In all larval fish size classes, successful attacks had smaller attack distances and faster attack speeds than unsuccessful attacks. Among prey items slowly swimming protozoans were the preferred food of first-feeding cod larvae; larger larvae had higher swimming speeds and captured larger, faster copepod nauplii. Protozoans may be an important prey item for first-feeding larvae providing essential resources for growth to a size at which copepod nauplii are captured. Received: 20 April 1999 / Accepted: 12 January 2000     

Towards an ecological solution to the folivore paradox: patch depletion as an indicator of within-group scramble competition in red colobus monkeys (Piliocolobus tephrosceles)

A number of socioecological models assume that within-group food competition is either weak or absent among folivorous primates. This assumption is made because their food resources are presumed to be superabundant and evenly dispersed. However, recent evidence increasingly suggests that folivore group size is food-limited, that the primates prefer patchily distributed high-quality foods, and display some of the expected responses to within-group scramble competition. To investigate this apparent contradiction between theoretical models and recent empirical data, we examined the foraging behaviour of red colobus monkeys (Piliocolobus tephrosceles) in Kibale National Park, Uganda. We found that red colobus monkeys foraged in a manner that suggests they deplete patches of preferred foods: intake rate slowed significantly during patch occupancy while movement rate, an index of foraging effort, increased. Furthermore, patch occupancy was related to the size of the feeding group and the size of the patch. These results suggest that within-group scramble competition occurs, may limit folivore group size, and should be considered in models of folivore behavioural ecology.     

Post-nesting migrations of green turtles (Chelonia mydas) at Wan-An Island, Penghu Archipelago, Taiwan

 During the summers of 1994 to 1997, eight green turtles (Chelonia mydas) nesting at Wan-An Island, PengHu Archipelago, Taiwan, were equipped with satellite-telemetry transmitters. Using the Argos-linked satellite system, the turtles' migration routes were tracked until the transmissions stopped. The turtles migrated widely on the continental shelf to the east of Mainland China. The migration distances ranged from 193 to 1909 km, and the migration speeds from 1.2 to 2.8 km h⁻¹. The turtles apparently utilize several coastal areas as temporal residential foraging sites, and their migrations consist of both trans-oceanic and coastal legs. The wide distribution of the foraging sites of the turtles comprising this rookery reflects the extent to which the green turtle migrates in northeast Asia; regional and international cooperation will therefore be needed to conserve this declining population. Received: 14 December 1998 / Accepted: 8 May 2000     

Heritability of the algal-foraging ability: an indirect benefit of female mate preference for males' carotenoid-based coloration in the guppy, Poecilia reticulata

Several sexual selection theories assume certain benefits of female mate preference. The direct benefit, i.e., the direct contribution from males to their offspring and females, has been well tested empirically. However, the indirect benefit, i.e., the male's genetic contribution to their offspring, has been poorly demonstrated. Female preference for males' carotenoid-based coloration is known in some animals. Since animals must acquire carotenoids through foods, it is often hypothesized that the brightness of the carotenoid-based coloration is a reliable indicator of the male's foraging ability. Hence, females' indirect benefits, such as greater foraging ability in their offspring, through mate preference for the carotenoid-based coloration are assumed. However, the heritability of the foraging ability for foods that serve as carotenoid resources has not been tested. In this study, a maze experiment was performed in guppies (Poecilia reticulata) to examine the heritability of the foraging ability for algae, carotenoid resources in nature. The latency for completing algal-foraging tasks in this experiment showed high individual variation. Heritable estimates of the foraging ability were substantial (h ² = 0.57 – 0.66) and significant, suggesting a genetic contribution to the foraging ability from fathers to their offspring. This result may support the hypothesis that indirect benefits influence the evolution of female choice.     

Size and seasonal influences on the foraging range of female grey seals in the northeast Atlantic

Evidence of segregation in foraging habitat has been demonstrated in some top marine predators, including cetaceans, pinnipeds and seabirds. However, most data are not adequate to assess differences relating to body size or seasonal influences. This has implications for quantitative modelling of population-level predator–prey interactions and ecosystem structure. We examined potential influence of body size and ‘fatness’ on the foraging trip characteristics of a top marine predator, the Atlantic grey seal (Halichoerus grypus), in southwest Ireland within the framework of optimal foraging theory to examine how female grey seals foraging behaviour varied with size, and across the period between moult and breeding. Larger seals undertook trips of greater duration and travelled further from haul-out sites than smaller seals. However, body fat was negatively associated with trip duration and extent. Seals spent more time at sea during the summer, but trips were shorter in extent, suggesting more localized foraging during this season.     

The function of polydomy: the ant <Emphasis Type="Italic">Crematogaster torosa</Emphasis> preferentially forms new nests near food sources and fortifies outstations

Many ant species are polydomous, forming multiple spatially segregated nests that exchange workers and brood. However, why polydomy occurs is still uncertain. We investigated whether colonies of Crematogaster torosa form new polydomous nests to better exploit temporally stable food resources. Specifically, we tested the effect of food presence or absence and distance on the likelihood that colonies would form a new nest. Because this species also forms little-known structures that house only workers without brood (outstations), we also compared the function of this structure with true nests. Laboratory-reared colonies were connected to a new foraging arena containing potential nest sites with or without food for 4 months. When food was present, most colonies formed polydomous nests nearby and the remainder formed outstations. When food was absent, the behavior of colonies differed significantly, frequently forming outstations but never polydomous nests. Distance had no effect on the type of structure formed, but when food was present, a larger proportion of the workforce moved shorter distances. Workers often fortified the entrances to both structures and used them for storage of dried insect tissue (“jerky”). In an investigation of spatial fidelity, we found that workers on the between-nest trail were associated with the original nest, whereas workers collecting food were more likely to be associated with the new nest or outstation. C. torosa appears to have a flexible colony structure, forming both outstations and polydomous nests. Polydomous nests in this species were associated with foraging and were only formed near food resources.     

A patch use model to separate effects of foraging costs on giving-up densities: an experiment with white-tailed deer (<Emphasis Type="Italic">Odocoileus virginianus</Emphasis>)

The giving-up density of food (GUD), the amount of food remaining in a patch when a forager ceases foraging there, can be used to compare the costs of foraging in different food patches. But, to draw inferences from GUDs, specific effects of foraging costs (predation risk, metabolic and missed opportunities costs) on GUDs have to be identified. As high predation risk, high metabolic costs and abundant food all should produce high GUDs, this does not allow us to infer directly the quality of a habitat. In order to separate the effect of each foraging cost, we developed an optimal foraging model based on food supplementation. We illustrate the use of our model in a study where we assessed the impact of a power line right-of-way in a white-tailed deer (Odocoileus virginianus) winter yard by determining whether the negative effects of cover loss outweigh the positive effects of browse regeneration.     

Foraging areas and foraging behavior in the notch-eared bat,Myotis emarginatus (Vespertilionidae)

Summary Field observations in a maternity colony of Myotis emarginatus (Vespertilionidae) were made during the summers of 1986 and 1987 in southern Germany. The nursery colony consisted of about 90 adult and 30 juvenile bats which roosted in a dimly lit and relatively cool church attic. Telemetry data from six adult M. emarginatus disclosed that some individuals also use secondary day roosts in trees or small buildings located close to their foraging areas. During the night, radiotagged individuals spent most of the time on the wing in forested areas (Fig. 2). Stationary bouts lasted no longer than 63 min. Individual bats returned to the same foraging areas on consecutive nights. All major foraging areas were situated in or at the fringes of forests, at distances as far as 10 km from the nursery roost. During commuting flights to the forests, M. emarginatus avoided open fields and preferred flight paths which offered cover such as orchards, hedges, overhanging foliage along creeks, etc. On the way to the forests, the bats started to forage within buildings, in open spaces where aggregations of insects were present, and around or within the foliage of various types of trees at the level of tree tops or the upper third of the foliage. At these transient foraging areas close to the maternity roost, M. emarginatus displayed flexible foraging strategies: (1) They gleaned prey (mainly flies and spiders) from the substrate, (2) seized insects in aerial pursuit, and (3) occasionally hovered in front of foliage and walls.Our observations confirm the conclusion from morphometric data on the wings that M. emarginatus is a predominantly gleaning bat and contradict the suggestion that it makes only brief flights of short distances. On the contrary, our field data suggest that M. emarginatus spends most of the night on the wing and commutes over distances of at least 10 km. Offprint requests to: D. Krull     

Individually different foraging methods in the desert ant Cataglyphis bicolor (Hymenoptera,Formicidae)

Summary Observations and field experiments on the foraging behaviour of individual workers of Cataglyphis bicolor in a Southern Tunisian shrub desert are reported. The workers search singly for their food (mostly animal carcasses) and are singleprey loaders. The individuals differ to a great extent in their persistence to re-search the place of a find on a previous foraging excursion. The differences range continuously from thoroughly researching a place to just walking by. If, in an experiment, the same reward is offered farther from the nest, each ant persists more in re-searching the place than if food is offered close to the nest. In a further experiment, some individuals persisted less in searching near the former finding site if they had collected a fly than after collecting a piece of cheese. There is, however, evidence that individuals do not differ in their food preference. Persistent individuals, which re-search the place of a former find, are faster than non-persistent ones in retrieving food that is experimentally arranged in an aggregated manner. The experiment failed to demonstrate the (reverse) superiority of non-persistent individuals foraging on homogeneously distributed food. The observations of unmanipulated foraging excursions in the field suggest such an advantage for non-persistent foragers under natural conditions where food in general occurs widely dispersed. The colony as a whole retrieves more food within the same time from an experimental lay-out that is homogeneous than from an aggregated one. The behavioural differences between individuals could be caused by a training bias of the short-lived foragers, leading to a different assessment of the profitability of a searching method which implies returning to a formerly rewarding place. Thus, each worker uses the most promising behaviour according to its individual experience. Alternatively, the individually different searching methods could mainly contribute to the welfare of the colony as a whole rather than leading to a maximal short-term efficiency of each individual. In particular, the colony, disposing of only a few highly persistent foragers, could quickly exploit occasional short-lived, but unpredictible, clumps of food within its foraging range.     

Female mimicry and resource defense polygyny by males of a tropical rove beetle,Leistotrophus versicolor (Coleoptera : Staphylinidae)

Summary Adults of the staphylinid beetle Leistotrophus versicolor Grav. aggregate at vertebrate dung and carrion where males and females forage for adult Diptera. Some males aggressively exclude others from dung and carrion. Winners in male combat gain access to many females, which are often receptive at these foraging sites. The mating system can be categorized as resource defense polygyny. Males vary greatly in size, are larger than females on average, and have allometrically enlarged mandibles that they use in fighting. Large males consistently defeat smaller ones. Some males employ female mimicry in order to avoid aggression, remaining at dung where they forage and even obtain copulations while being courted by rival males. Female mimicry is most often practiced by males that are smaller than their rivals or by males that are unable to use their jaws aggressively because they are feeding or courting females when encountered by an opponent. Female mimicry is a conditional tactic of mature males; some individuals behave like females toward larger males but attack smaller rivals. Offprint requests to: J. Alcock     

Natal dispersal in Belding's ground squirrels (Spermophilus beldingi)

Summary Dispersal from the natal site was documented in two populations of Belding's ground squirrels (Spermophilus beldingi) living at different altitudes in the Sierra Nevada of North America. Distance dispersed and age at dispersal were monitored by a combination of observation, trapping, radio telemetry, and examination of road kills. Dispersal was sexually dimorphic in both populations (Tables 1 and 2). All surviving males emigrated before they were 55 weeks of age, with most dispersing midway through the juvenile summer (Fig. 1). By contrast, most females remained within the boundaries of their mothers' home range (Fig. 2 and 3). Those very few females that did emigrate moved distances from their natal burrows similar to those travelled by dispersing males (200–450 m; Table 2), but females tended to disperse at a slightly older age. Significant differences between the study populations were found in distances moved by juveniles of both sexes (Fig. 2). Body weights of juvenile male dispersers were significantly greater than were those of juvenile males of equivilent ages that had not yet dispersed (Fig. 4). The results were considered in light of Shields' (1982) discussion of dispersal and inbreeding. I concluded that if dispersal is related to reproductive success, then dispersal distances selected for use in tests of evolutionary hypotheses should be measured just prior to the subject animals' first reproduction. Finally, although not tested in the present study, the evolutionary hypothesis most consistent with my data suggests that dispersal in S. beldingi may function to minimize nuclear family incest.     

Foraging and homing behaviour in the high-shore, crevice-dwelling limpet Helcion pectunculus (Prosobranchia: Patellidae)

The foraging activity of the high-shore, crevice-dwelling limpet Helcion pectunculus (Gmelin, 1791) (Prosobranchia: Patellidae) from an exposed shore on the eastern Cape coast of South Africa was monitored. Activity was compared during spring and neap tides and between spring, summer, autumn and winter. Rhythms of activity in this limpet varied depending upon microhabitat; individuals inhabiting both east- and west-facing rock surfaces were active during nocturnal low tides, but limpets on west-facing rock surfaces were also active during daytime low tides, whilst in the shade. Individuals travelled further during foraging excursions in winter (xˉ=85.53 cm) than in either spring (xˉ=55.7 cm) or summer (xˉ=48.8 cm) and also during spring low tides (xˉ=89.8 cm) compared with neaps (xˉ=40.9 cm). H. pectunculus exhibited rigid homing to a fixed scar within a crevice, and feeding excursions were found to consist of three distinct phases: a relatively rapid outward phase, a much slower foraging phase and a rapid homeward phase. Whether or not these limpets graze throughout an excursion is not known. Foraging was always highly directional, with a mean vector which took limpets onto an area of the rock face with the highest microalgal biomass. The fact that H. pectunculus took advantage of optimal feeding areas and memorized their location to enable return visits suggests a learning component in herbivorous gastropod foraging behaviour. Received: 29 December 1997 / Accepted: 8 May 1998     

Fecundity studies on Acartia tonsa (Copepoda: Calanoida) in standardized culture

Acartia tonsa Dana longevity and egg production data were studied over a 4-year period under standardized culture conditions. Egg-laying patterns and daily rates were evaluated as bioassay tools for measuring the nutritional value of various copepod foods, as well as assessing other aspects of environmental quality. Altogether, 337 females were observed in various aspects of this work. Experiments were performed with newly matured females in loosely covered crystallizing dishes. Fresh water and a standard concentration of algae were supplied daily, and a running daily tally was kept of the eggs produced. The effects of male copepods on egg production were analyzed. Males were either removed after the first eggs were observed or they remained with the female throughout her life span. Daily egg-laying rates of this latter group of females appeared to be more stable, but abnormal embryo development occurred if the males were not removed after fertilization. Likewise, the results of females which were not mated were studied. Life spans were shorter and egg production rates were lower than those of contemporary mated females. Unmated females were subjectively observed to be less active than their mated counterparts. The effects of continuous and temporary starvation on egg-laying were also observed. Under both normal and starved conditions, males appeared to have shorter life spans than either mated or unmated females. During starvation there were no real differences between the life spans or egg productions of mated or unmated females. Non-nutritional particulate matter was evaluated as a food source. It was ingested by the females, but did nothing to prolong the egg-laying period. Finally, the three algal components of the standard ration were evaluated. Females produced equally well with a mixed diet or with Thalassiosira pseudonana (100 m³) or Chroomonas salina (140 m³), the two larger species of this diet, but when Isochrysis galbana (40 m³) was fed, females reacted as if in a starved situation.