Food searching decisions in four cyprinid species

Synopsis Four species of cyprinids (vimba, bream, Danubian bleak and roach) which had been incubated and reared under identical conditions differed qualitatively as well as quantitatively in the use of prey search strategies during comparative experiments. While bream and vimba prefer to use sampling techniques under conditions of reduced visibility of benthic prey, roach favor almost exclusively directed search methods. Vimba and Danubian bleak, in contrast to bream and roach, rapidly increase their total search activity in response to successive presentations of novel prey. These results have several ecological implications which are confirmed by field data. It is concluded that food searching cyprinids follow decision rules which are species specific both in the amount of sampling and in the responsiveness to rapidly changing conditions.     

Incidental nest predation in freshwater turtles: inter- and intraspecific differences in vulnerability are explained by relative crypsis

There has long been interest in the influence of predators on prey populations, although most predator–prey studies have focused on prey species that are targets of directed predator searching. Conversely, few have addressed depredation that occurs after incidental encounters with predators. We tested two predictions stemming from the hypothesis that nest predation on two sympatric freshwater turtle species whose nests are differentially prone to opportunistic detection—painted turtles (Chrysemys picta) and snapping turtles (Chelydra serpentina)—is incidental: (1) predation rates should be density independent, and (2) individual predators should not alter their foraging behavior after encountering nests. After monitoring nest survival and predator behavior following nest depredation over 2 years, we confirmed that predation by raccoons (Procyon lotor), the primary nest predators in our study area, matched both predictions. Furthermore, cryptic C. picta nests were victimized with lower frequency than more detectable C. serpentina nests, and nests of both species were more vulnerable in human-modified areas where opportunistic nest discovery is facilitated. Despite apparently being incidental, predation on nests of both species was intensive (57% for painted turtles, 84% for snapping turtles), and most depredations occurred within 1 day of nest establishment. By implication, predation need not be directed to affect prey demography, and factors influencing prey crypsis are drivers of the impact of incidental predation on prey. Our results also imply that efforts to conserve imperiled turtle populations in human-modified landscapes should include restoration of undisturbed conditions that are less likely to expose nests to incidental predators.     

Beobachtungen zum Nahrungserwerb des Schuhschnabels(Balaeniceps rex)

Zusammenfassung In einer 1977 durchgeführten Freilandstudie in verschiedenen Sumpfgebieten Ugandas wurde das Nahrungsverhalten von ca. 60 Schuhschnäbeln beobachtet. Insbesondere während der Nahrungssuche meidet der Schuhschnabel die Nachbarschaft von Artgenossen. Der Nahrungserwerb findet tagsüber statt mit deutlicher Bevorzugung der Morgen- und Abendstunden.Zwei Beutefangmethoden sind zu unterscheiden: Lauern und Pirschen. Bei der Pirsch ruht der Kopf ca. 60% der Zeit in einem Raumpunkt. Eine dadurch verbesserte Wahrnehmung wird diskutiert. Als Beutetiere werden in der Hauptsache größere Fische genommen, in geringem Umfang auch Reptilien und Amphibien. Beim Beutefang liegt die Erfolgsquote über 50%.

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Observations on the feeding behaviour of the Whale-headed Stork(Balaeniceps rex)

Summary During a field study in different swamps of Uganda, 1977, about 60 Whale-headed Storks were observed with regard to their feeding behaviour. In particular when searching for food, the birds avoid the neighbourhood of members of their own species. Food searching takes place during the day, with peaks in morning and evening. Two types of food searching can be distinguished: lurking and stalking. While stalking the head remains stationary about 60% of the time. In this way a better perception of prey might be possible. The Whale-headed Stork preys mainly on bigger fishes, to a less account on reptiles and amphibians. More than 50% of the attempts to catch prey are successful.

     

14j?hrige Beobachtungen zur Vermehrung des Waldkauzes (Strix aluco L.)

Zusammenfassung Von 1958 bis 1971 wurde die ca. 20 Paare zählende Waldkauzpopulation eines Westberliner Waldgebietes kontrolliert. In diesen 14 Jahren hatten von 232 Paaren 107 (46,1%) Junge; über 50% brüteten demnach erfolglos.Pro erfolgreiches Paar ergaben sich 2, pro Paar überhaupt nur 0,92 Junge. Der Bruterfolg war in den einzelnen Jahren sehr unterschiedlich (Tab. 1).Unter 13 359 in Gewöllen nachgewiesenen Wirbeltieren betrafen 34,9% Vögel, 29% die 3Apodemus-Arten, 16,7%Microtus, 12,7% Insektivoren, 7,6% Amphibien. Keine der vielen Beutetierarten hatte einen dominierenden Anteil in der Gesamtbeute. In der Winternahrung bildeten jedoch über 50% der Beute Kleinvögel, in Spitzenjahren sogar 67%.Die jährlichen Unterschiede in der Vermehrungsrate des Waldkauzes scheinen vor allem auf die wechselnde Bestandsdichte der Gelbhalsmaus(Apodemus flavicollis), des Hauptbeutetieres, zurückzuführen zu sein (Abb. 2). Eine Berliner Stadtpopulation (17 Paare), die sich zu 70% von Vögeln, vor allem Haussperlingen, ernährte, zog 3,2 Junge pro erfolgreiches Paar auf.Bei den Eulen scheint im Gegensatz zu den Greifvögeln eine Regulation der Vermehrung in Abhängigkeit vom Nahrungsangebot nicht nur durch Reduktion der Gelegegröße, sondern vor allem auch durch totalen Brutausfall zu erfolgen.

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Fourteen Years observations on the reproduction of a Tawny Owl population

Summary From 1958–1971 the Tawny Owl(Strix aluco) population in the Grunewald Pine forest of Berlin (West) was observed. About 20 pairs breed yearly in this wood (31 km²). A total of 232 pairs was checked during these 14 years; 107 pairs (46,1%) had fledged 214 young (2 young per successfull pair). In many years most of the pairs did not rear any young, for instance in 1968 only 4 (=21%) out of 20 pairs had young. 13 359 vertebrates were found in the pellets of the owls: 34,9% birds; 29%Apodemus (most of themA. flavicollis), 16,7%Microtus (4 species), 12,7% shrews and other small mamals, 7,6% toads and frogs, 0,09% fishes. Of the numerous prey species none showed a preponderance while in wintertime the proportion of birds was more than 50%.The breeding rate seems to be due to the yearly changing density of the main prey: in years of a high density ofApodemus flavicollis the reproduction of the Tawny Owls was high, in years of low density a great number of the owls did not rear young (figure 2). Another factor of high or low reproduction is perhaps the quantity of food available during the time immediately before laying (fig. 3). The low breeding results of this woodland population are in contrast to the reproduction figures of another Berlin population living in parks and cemeteries inside of the city. 17 pairs were observed; they had 54 young (3,2 young per pair). Here the food situation is much better: 70% of the prey were birds, most of them House Sparrows(Passer domesticus) and Greenfinches(Carduelis chloris).

     

Effects of vertical prey distribution on the food-searching behaviour of Danube bleak Chalcalburnus chalcoides mento

Planktivorous fishes frequently have to cope with spatial dynamics of their prey and should be flexible in their vertical food search position. In two experiments Danube bleak Chalcalburnus chalcoides mento, a planktivorous cyprinid, was conditioned to forage on chironomid larvae within the bottom zone and on the cladoceran Leptodora kindtii in the open water of experimental tanks. The fish responded to the presence of chironomids by orienting their snapping behaviour towards the bottom. After most of the prey were depleted, the fish shifted their search position to the open water. Fish were offered L. kindtii at higher densities than the chironomids in the second experiment. With one exception all fish snapped at a high rate into the open water with no observed vertical spatial shifts. One highly active individual showed a clear shift from the open water towards the bottom after depleting most of the L. kindtii. After previous conditioning with chironomids, Danube bleak responded to the presentation of a conditioned stimulus by searching at a deeper position than during control recordings of spontaneous snappings and during a conditioned response test after training with L. kindtii. These results provide preliminary evidence that Danube bleak can detect variation in vertical prey distribution and can build up internal spatial representations.     

Selection of food patches by sympatric herbivores in response to concealment and distance from a refuge

Small herbivores face risks of predation while foraging and are often forced to trade off food quality for safety. Life history, behaviour, and habitat of predator and prey can influence these trade‐offs. We compared how two sympatric rabbits (pygmy rabbit, Brachylagus idahoensis; mountain cottontail, Sylvilagus nuttallii) that differ in size, use of burrows, and habitat specialization in the sagebrush‐steppe of western North America respond to amount and orientation of concealment cover and proximity to burrow refuges when selecting food patches. We predicted that both rabbit species would prefer food patches that offered greater concealment and food patches that were closer to burrow refuges. However, because pygmy rabbits are small, obligate burrowers that are restricted to sagebrush habitats, we predicted that they would show stronger preferences for greater cover, orientation of concealment, and patches closer to burrow refuges. We offered two food patches to individuals of each species during three experiments that either varied in the amount of concealment cover, orientation of concealment cover, or distance from a burrow refuge. Both species preferred food patches that offered greater concealment, but pygmy rabbits generally preferred terrestrial and mountain cottontails preferred aerial concealment. Only pygmy rabbits preferred food patches closer to their burrow refuge. Different responses to concealment and proximity to burrow refuges by the two species likely reflect differences in perceived predation risks. Because terrestrial predators are able to dig for prey in burrows, animals like pygmy rabbits that rely on burrow refuges might select food patches based more on terrestrial concealment. In contrast, larger habitat generalists that do not rely on burrow refuges, like mountain cottontails, might trade off terrestrial concealment for visibility to detect approaching terrestrial predators. This study suggests that body size and evolutionary adaptations for using habitat, even in closely related species, might influence anti‐predator behaviors in prey species.     

Food supply and prey selection in planktivorous cyprinidae

Summary In small Bavarian lakes, the gut contents of the Cyprinid fish roach (Rutilus rutilus), rudd (Scardinius erythrophtalamus), bream (Abramis brama) and bleak (Alburnus alburnus), and the actural food supply during the fish's feeding period were examined in relation to the species composition of zooplankton. Accompanied by feeding experiments in the laboratory, the selective effect of fish predation could be attributed to the distribution patterns of prey and predator in time and space, to the prey's specific visibility and escape ability and, to some extent, to the fish's active choice. The possibility that the species composition of zooplankton is regulated was indicated only in the fish's positively abundance-dependent preference for the prey types and restricted to only a few plankter species.     

黑龙江省完达山东部林区东北虎猎物生物量

研究一个地区猎物种群生物量能否满足捕食动物种群数量的需求,这对于了解濒危大型食肉动物是否受到来自于食物缺乏的威胁和制定相应的保护措施极其重要。为了掌握黑龙江省完达山东部林区东北虎食物需求与猎物生物量之间的关系,于2008年冬季至2009早春积雪覆盖期采用随机布设样线,通过收集有蹄类动物在雪地上留下的足迹等活动的方法,在东方红林业局和迎春林业局管辖境内3 692.06 km²的区域布设大样方48个,并在大样方里共布设样线240条开展有蹄类动物种群数量调查,确定东北虎猎物生物量。调查结果表明:研究地区野猪(成体502 606只,亚成体209 210只)、马鹿(成体331 357只,亚成体67 72只)和狍子(成体810 815只,亚成体202 203只)的生物量分别为74 767.50 87 825.00 kg、79 744.50 85 984.50 kg 和 31 337.00 31 525.50 kg,3种有蹄类动物生物量共计1 85 849.00 205 335.00 kg。研究地区猎物总生物量为209 619.89 231 598.24 kg。如果按8%的生物提供给东北虎,3种主要猎物生物量可满足5.22 6.92只东北虎个体的食物需求,研究地区猎物总生物量则可满足5.89 7.81只东北虎个体的食物需求。此外,对足迹遇见率与抽样强度、抽样强度与足迹遇见率的均值标准误差之间关系的分析表明,在完达山东部林区布设120条样线(抽样距离600 km)、150条样线(抽样距离750 km)和115条样线(抽样距离675 km)能满足野猪、马鹿、狍子种群数量调查准确性的最低需求。     

Dopaminergic modulation of visual responses in toads I. Apomorphine-induced effects on visually directed appetitive and consummatory prey-catching behavior

This study confirms for a phylogenetically basal terrestrial vertebrate that dopaminergic modulations interfere with the visually directed appetitive and consummatory feeding behaviors orienting and snapping, respectively. (1) In common toads Bufo bufo, intralymphatic administration of the dopamine D₂/D₁-receptor agonist apomorphine led to a dose-dependent facilitation of prey-snapping in response to moving objects. The snapping activity reached a maximum 15–35 min after apomorphine injection. (2) To changes in configurational stimulus features, the basic pattern of discrimination was maintained; however, the acuity of discrimination was reduced due to the high snapping response level. (3) The apomorphine-induced facilitation of snapping was accompanied by a suppression of prey-oriented lunging and turning. Toads snapped only if prey occurred frontally in the visual field at a relatively short distance. The snapping behavior was fixed in its form and stereotyped regarding its immediate release. (4) About 90 min after apomorphine administration, prey-oriented turning behavior was restored and displayed a facilitatory rebound. (5) In comparative experiments with the species B. marinus, both prey-oriented turning and snapping responses were suppressed by apomorphine in a dose-dependent manner. (6) After pre-treatment with the dopamine antagonist haloperidol, apomorphine showed no measurable effect on the visual release of prey orienting or snapping. (7) The results contribute to the sensorimotor and the motivation hypothesis of dopamine function proposed for higher vertebrates and stimulate a comparative discussion of anatomic homologies and functional analogies. Accepted: 10 July 1996     

Cover Caption

It is often assumed that learning improves foraging, but its direct benefits are not often examined. We demonstrate the contribution of learning to the foraging success of desert ants when a trained colony successfully competes against a naïve one. The outcome also depends on the relative group size. Desert Cataglyphis ants search individually for food (mostly dead prey) without laying pheromone trails (see pages 241-250). The cover photo shows a Cataglyphis niger worker searching for food in its typical sandy habitat. Photo provided Arik Dorfman.     

Territorial aggressiveness and predation: two possible origins of snapping in the ant Plectroctena minor

Plectroctena minor workers have long mandibles that can snap and deliver a sharp blow to intruders or prey, stunning or killing them. Encounters between homocolonial P. minor workers separated for 24 h or 15 days never resulted in snapping, while this behaviour was always noted during encounters between heterocolonial workers on neutral arenas or on the territory of a colony. In the latter case, only the aliens, that generally tried to escape, were snapped at. Snapping also occurred during encounters with workers belonging to sympatric ponerine species. During predation, the percentages of snapping varied according to prey nature, suggesting prey discrimination. Termite soldiers were always snapped at, while other prey were more often snapped close to rather than far from the nest entrances, indicating an intermingling of territorial aggressiveness and predatory behaviour. We discuss the adaptive value of snapping for hunting in galleries.     

Prey diversity as a driver of resource partitioning between river‐dwelling fish species

Although food resource partitioning among sympatric species has often been explored in riverine systems, the potential influence of prey diversity on resource partitioning is little known. Using empirical data, we modeled food resource partitioning (assessed as dietary overlap) of coexisting juvenile Atlantic salmon (Salmo salar) and alpine bullhead (Cottus poecilopus). Explanatory variables incorporated into the model were fish abundance, benthic prey diversity and abundance, and several dietary metrics to give a total of seventeen potential explanatory variables. First, a forward stepwise procedure based on the Akaike information criterion was used to select explanatory variables with significant effects on food resource partitioning. Then, linear mixed‐effect models were constructed using the selected explanatory variables and with sampling site as a random factor. Food resource partitioning between salmon and bullhead increased significantly with increasing prey diversity, and the variation in food resource partitioning was best described by the model that included prey diversity as the only explanatory variable. This study provides empirical support for the notion that prey diversity is a key driver of resource partitioning among competing species.     

Species‐level predation network uncovers high prey specificity in a Neotropical army ant community

Army ants are among the top arthropod predators and considered keystone species in tropical ecosystems. During daily mass raids with many thousand workers, army ants hunt live prey, likely exerting strong top‐down control on prey species. Many tropical sites exhibit a high army ant species diversity (>20 species), suggesting that sympatric species partition the available prey niches. However, whether and to what extent this is achieved has not been intensively studied yet. We therefore conducted a large‐scale diet survey of a community of surface‐raiding army ants at La Selva Biological Station in Costa Rica. We systematically collected 3,262 prey items from eleven army ant species (genera Eciton, Nomamyrmex and Neivamyrmex). Prey items were classified as ant prey or non‐ant prey. The prey nearly exclusively consisted of other ants (98%), and most booty was ant brood (87%). Using morphological characters and DNA barcoding, we identified a total of 1,103 ant prey specimens to the species level. One hundred twenty‐nine ant species were detected among the army ant prey, representing about 30% of the known local ant diversity. Using weighted bipartite network analyses, we show that prey specialization in army ants is unexpectedly high and prey niche overlap very small. Besides food niche differentiation, we uncovered a spatiotemporal niche differentiation in army ant raid activity. We discuss competition‐driven multidimensional niche differentiation and predator–prey arms races as possible mechanisms underlying prey specialization in army ants. By combining systematic prey sampling with species‐level prey identification and network analyses, our integrative approach can guide future research by portraying how predator–prey interactions in complex communities can be reliably studied, even in cases where morphological prey identification is infeasible.     

Advantages of social foraging in crab spiders: Groups capture more and larger prey despite the absence of a web

Among group‐living spiders, subsocial representatives in the family of crab spiders (Thomisidae) are a special case, as they build protective communal leaf nests instead of extensive communal capture webs. It could thus be inferred that antipredator benefits (e.g., enhanced protection in larger nests) rather than foraging‐related advantages (e.g., capture of more and larger prey) promote sociality in this family. Nonetheless, subsocial crab spiders do share prey, and if this behaviour does not reflect mere food scramble but has a cooperative character, crab spiders may offer insights into the evolution of social foraging applicable to many other cooperative predators that hunt without traps. Here, we performed a comparative laboratory feeding experiment on three of the four subsocial crab spider species—Australomisidia ergandros, Australomisidia socialis and Xysticus bimaculatus—to determine if crab spiders derive advantages from foraging in groups. In particular, we tested artificially composed groups of five sibling spiderlings vs. single siblings in terms of prey capture success and prey size preference. Across species, groups had higher prey capture success (measured in terms of capture rates and capture latency) and were more likely to attack large, sharable prey—dynamics leading to reduced food competition among group members in favour of living and foraging in groups. Within groups, we further compared prey extraction efficiency among the three applied social foraging tactics: producing, scrounging and feeding alone. In A. ergandros, individuals were exceptionally efficient when using the non‐cooperative scrounger tactic, which entails feeding on the prey provided by others. Thus, our multispecies comparison confirms foraging advantages in maintaining a cooperative lifestyle for crab spiders, but also demonstrates the relevance of research into exploitation of cooperative foraging in this family.     

Diving beetle offspring oviposited in amphibian spawn prey on the tadpoles upon hatching

In highly ephemeral freshwater habitats, predatory vertebrates are typically unable to become established, leaving an open niche often filled by macroinvertebrate predators. However, these predators are faced with the challenge of finding sufficient food sources as the rapid rate of desiccation prevents the establishment of extended food chains and limits the number of prey species present. It could therefore be advantageous for predators to synchronize their phenology with that of their prey within sites of extreme ephemerality. We report the first case of adult diving beetles (Hydaticus parallelus) ovipositing their eggs within spawn of an amphibian species (sandpaper frog, Lechriodus fletcheri). This behavior was found among several pools used by L. fletcheri for reproduction. Beetle eggs oviposited in frog spawn were found to hatch within 24 h of the surrounding L. fletcheri eggs, with the larvae becoming voracious consumers of the hatched tadpoles. Although it has yet to be established experimentally whether this is an adaptive behavior, the laying of eggs among potential future tadpole prey in this instance should confer significant fitness benefits for the offspring upon hatching, ensuring that they are provided an immediate source of food at the start of their development and potentially throughout. This oviposition behavior might be common among diving beetles and could form a significant predatory threat for amphibians with a free‐swimming larval stage in ephemeral freshwater habitats.     

Food selectivity versus prey availability: a study using the marine fish Pomatoschistus microps

Summary The food selection of the common goby, Pomatoschistus microps Krøyer, was studied in the field and in laboratory experiments on the Swedish west coast. The three most important prey organisms for P. microps in the study area were Corophium volutator, chironomid larvae and Nereis spp. Corophium was consumed more than any other prey, even when it was not the most abundant prey species in the bottom. One reason may be the higher activity of Corophium above the sediment surface, which may increase its visibility and consequently its vulnerability to visual predators. When P. microps was offered Corophium and chironomid larvae with similar exposure in laboratory experiments, it showed no preference for either of the prey items. It always took the closest mobile prey, regardless of species and size.     

Intrinsic prey suitability in specialist and generalist Harmonia ladybirds: a test of the trade‐off hypothesis for food specialization

The trade‐off hypothesis posits that increased performance on a given resource comes at the cost of decreased performance on other resources, and that this trade‐off is a driving force of food specialization in both predators and herbivores. In this study, we examined larval survival and performance in two sibling ladybird species, Harmonia yedoensis Takizawa and Harmonia axyridis Pallas (Coleoptera: Coccinellidae), fed on one of four prey species. Harmonia yedoensis is a specialist predator that preys mostly on pine aphids in the field, whereas H. axyridis is a generalist predator with a broad prey range. We experimentally showed in the laboratory that larval survival and performance were not higher when H. yedoensis was fed on pine aphids, compared with the other prey species. Rather, prey suitability was similar in both ladybird species, and H. yedoensis larvae developed as well or even better on prey species that they never utilize in nature. These results suggest that the host range in H. yedoensis may not be limited by the intrinsic suitability of the aphid species per se. Moreover, as shown by our previous study, the pine aphid is a highly elusive prey that is difficult for small ladybird hatchlings to capture, which means that the cost of utilizing this prey is high. Therefore, we conclude that some factor other than prey suitability is responsible for the observed food specialization in H. yedoensis.     

The reaction time of leech and triclad species to crushed prey and the significance of this for their coexistence in British lakes

1. Three species of leeches, Erpobdella octoculata, Glossiphonia complanata and Helobdella stagnalis, and four species of triclads, Polycelis nigra, P. tennis, Dugesia polychroa and Dendrocoelum lacteum, commonly coexist on stony shores in productive British lakes. All species are food limited and there is much overlap in their diet. For both leech and triclad communities, coexistence of species is through the occurrence of food refuges. Leeches are more successful than triclads at capturing live prey, whereas both groups feed on damaged prey, comprising incapacitated, live or dead animals that are leaking body fluids. If triclads are better than leeches at exploiting damaged prey, this could be a mechanism for their coexistence. 2. Laboratory experiments investigated the comparative speeds at which leeches and triclads responded to crushed prey. Young and adult predators were offered a crushed specimen of the oligochaete Tubifex tubifex, the snail Lymnaea peregra, the crustacean Asellus aquaticus or the chironomid Chironomus sp., and their reaction times recorded. These four prey groups constitute the main diet of the predators in the field. Only D. polychroa and D. lacteum showed a significantly different reaction time between young and adults to crushed prey, and the reason for this is unclear. All predators, except H. stagnalis and D. polychroa, showed a difference in reaction time to the four types of prey, presumably a consequence of differences in both the ‘quality’ and ‘concentration’ of the different prey fluids, and there were some differences between predators in their speed of reaction to the same prey type. The following sequence, from fastest to slowest, in general reaction time to prey was obtained: E. octoculata, D. polychroa, P. tenuis, D. lacteum, P. nigra, H. stagnalis and G. complanata. 3. The location of the damaged food by the predators can be explained partly in terms of their foraging behaviour, with E. octoculata, D, polychroa and P. tenuis exhibiting a more seek-out strategy than other species which have a more sit-and-wait behaviour, and partly on the level of sophistication of their chemosensory system used to detect leaked prey fluids. This system is highly developed in triclad species but poorly developed in leeches. 4. In a second type of experiment in which prey, L. peregra, A. aquaticus or Chironomus sp., were offered at different time intervals after crushing to H, stagnalis and P. tenuis, few predators fed on food crushed for 24 h or longer, although a few leeches fed on Chironomus crushed for up to 72 h. 5. It is concluded that coexistence of leech and triclad species on stony shores in lakes is assisted by partitioning of food on a damaged or live basis.     

ZUR SUCHFÄHIGKEIT DER EILARVEN VON APHIDOLETES APHIDIMYZA (DIPTERA: CECIDOMYIIDAE)

Zusammenfassung Die Eilarven der aphidophagen Gallmücke Aphidoletes aphidimyza tasteten auf der Suche nach ihrer ersten Beute im Schnitt nur 0.76 cm² der Blattfläche ab, bevor sie verhungerten. Aus dem Sucherfolg bei unterschiedlicher Blattlausdichte ergab sich aber, daß sie die Beute auf einem Areal von 2,70 cm² erfaßten, also offenbar bereits auf kurze Entfernung wahrnahmen. Durch Festkleben von Blattläusen in verschiedener Richtung und Entfernung von schlupfreifen Eiern ließ sich zeigen, daß die Attraktivität der Beute für die schlüpfenden Larven von Größe und Distanz abhängig ist. Dabei traten jedoch Unterschiede im Verhalten der Larven auf, deren Ursache noch unbekannt ist. Die populationsdynamischen Folgen der Wahrnehmung von Beute auf Distanz werden diskutiert.

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Summary Fecundity and mortality of the aphidophagous midge Aphidoletes aphidimyza are dependent in various ways on prey density. The first period of life is the most crucial one: Without food the newly hatched larvae covered only an average distance of 63 mm. Consequently, the larvae could find their prey within an area of 0.76 cm², if aphids were recognized only by touch. From the percentage of successful searching with different aphid densities, however, it was calculated that the larvae discovered their prey within an area of 2,70 cm². Hence, prey is already perceived at a short distance and the probability of survival is correspondingly enhanced.In the absence of prey nearly two-thirds of the newly hatched larvae crawl from the start toward the direction indicated by the anterior pole of the egg, the others go sidewards or backwards. If single peach aphids (Myzus persicae) are glued to the leaf surface near the egg, some larvae turn toward them. But only the number of larvae crawling forward is correspondingly reduced; crawling in other directions is not markedly influenced.The attractiveness of prey is dependent on its size and distance. At a distance of 5 mm young peach aphids had only a weak influence. On the other hand, a considerable part of the newly hatched larvae appeared to be not influenced at all by the prey.The causes of the different behaviour and the mode of perception are the objects of further investigation.