Ontogenetic constraints and diet shifts in Perch (Perca fluviatilis): mechanisms and consequences for intra‐cohort cannibalism

1. In many populations, sufficient size variation to allow for cannibalism may develop not only among age cohorts but also within them. Here, we used data on resource dynamics, consumer body size distribution and gape size limitation to unravel mechanisms promoting cannibalism within cohorts of young‐of‐the‐year (YOY) perch (Perca fluviatilis). 2. Perch are strongly gape limited when feeding on large zooplankton during early ontogeny. As a consequence, only initially large fish were able to shift to feeding on abundant large invertebrates, necessary to sustain fast growth. 3. We suggest that a combination of high initial size variation and exclusive access to resources for individuals with an initial size advantage is a prerequisite for the development of a size distribution sufficient for intra‐cohort cannibalism to occur. 4. During the time when cannibalism was observed, growth of the largest individuals in YOY perch cohorts was faster than that of smaller individuals. However, the energy gain from cannibalism did not increase growth rate enough to reach a size necessary to feed on more abundant size classes of victims, and therefore, the effect of cannibalism on overall cohort density was minor. 5. In addition to a high energy gain from cannibalism allowing for fast growth, strong resource limitation and slow growth rates of small individuals (i.e. potential victims) are a prerequisite not only for the development of intra‐cohort cannibalism but also for its persistence.     

Influence of predator density,diet and living substrate on developmental fitness of Orius laevigatus

Mass rearing of Orius laevigatus on non‐insect foods could substantially increase the cost‐effectiveness of the production of this biological control agent which is largely based on the use of expensive eggs of the Mediterranean flour moth Ephestia kuehniella. In this study, the effect of substrate quality and predator density on nymphal development of O. laevigatus fed on E. kuehniella eggs, honeybee pollen or an egg yolk based artificial diet was assessed using several types of substrates as shelter materials in the rearing containers (wax paper, bean pod or no extra substrate). In general, E. kuehniella eggs proved to be a nutritionally superior food compared to pollen and artificial diet. Pollen supported nymphal development of O. laevigatus better than the artificial diet. Overall, increasing nymphal density resulted in higher mortality, which may be due in part to cannibalism. The addition of a bean pod compensated for the nutritionally suboptimal artificial, but had a negative effect when O. laevigatus was fed on pollen. The non‐insect foods tested could not adequately replace lepidopteran eggs as a food source for O. laevigatus but they may be useful as an alternative food or in a part of the rearing process.     

Social wasps and bees captured in carrion traps in a rainforest in Brazil

Information is presented on social wasps and bees caught in carrion traps in ‘terra firme’ rainforest in Caxiuanã, PA, Brazil. Six species of epiponine wasps were captured. Angiopolybia pallens was the most frequent species, being caught in approximately 43.5% of the trials, followed by Angiopolybia paraensis (15.8%), Agelaia fulvofasciata (5.6%) and Agelaia angulata (3.3%). Agelaia pallipes and Agelaia cajennensis both had only a single individual captured. Twelve species of social bees were captured. The genera Trigona, Partamona and Melipona had similar numbers of species, but frequencies varied considerably. One individual of Apis mellifera was captured.     

Diet of spiny dogfish, Squalus acanthias Linnaeus, on the east coast, South Island, New Zealand

Stomach content data from 7283 spiny dogfish, Squalus ucunthius Linnaeus, from east coast South Island of New Zealand are presented. The major dietary components based on occurrence were 60% crustaceans and 15% fish. The principal food items were the post-larval phase of the squat lobster, Munida greguria Fabricius (30%), and the euphausiid, Nyctiphanes australis Sars (20%). Commercial fish species contributed to less than 5% of the diet. Diet of dogfish varied with dogfish size and sex. Compared to northern hemisphere studies, spiny dogfish in this study area had (1) a high proportion of crustaceans in their diet, (2) a relatively low percentage of empty stomachs, (3) a relatively high incidence of cannibalism.     

Enamel microstructure in lemuridae (mammalia,primates): Assessment of variability

This study describes the molar enamel microstructure of seven lemurid primates: Hapalemur griseus, Varecia variegata, Lemur catta, Lemur macaco, Lemur fulvus rufus, Lemur fulvus fulvus, and Lemur fulvus albifrons. Contrary to earlier accounts, which reported little or no prism decussation in lemurid enamel, both Lemur and Varecia molars contain a prominent inner layer of decussating prisms (Hunter-Schreger bands), in addition to an outer radial prism layer, and a thin, nonprismatic enamel surface layer. In contrast, Hapalemur enamel consists entirely of radial and, near the surface, nonprismatic enamel. In addition, for all species, prism packing patterns differ according to depth from the tooth surface, and for all species but Varecia (which also has the thinnest enamel of any lemurid), average prism area increases from the enamel-dentine junction to the surface; this may be a developmental solution to the problem of accommodating a larger outer surface area with enamel deposited from a fixed number of cells. Finally, contradicting some previous reports, Pattern 1 prisms predominate only in the most superficial prismatic enamel. In the deeper enamel, prism cross-sections include both closed (Pattern 1) and arc-shaped (Pattern 2 or, most commonly, Pattern 3). This sequence of depth-related pattern change is repeated in all taxa. It should also be emphasized that all taxa can exhibit all three prism patterns in their mature enamel. The high degree of quantitative and qualitative variation in prism size, shape, and packing suggests that these features should be used cautiously in phylogenetic studies. Hapalemur is distinguished from the other lemurids by unique, medially constricted or rectangular prism cross-sections at an intermediate depth and the absence of prism decussation, but, without further assessment of character polarity, these differences do not clarify lemurid phylogenetic relations. Some characters of enamel microstructure may represent synapomorphies of Lemuridae, or of clades within Lemuridae, but homoplasy is likely to be common. Homoplasy of enamel characters may reflect functional constraints. © 1994 Wiley-Liss, Inc.     

Phylogenetic relationships among the galaginae as indicated by erythrocytic allozymes

At least four hypotheses regarding the phylogenetic relationships within the Galaginae have been proposed, based on features of karyology, morphology, and behaviour, but these hypotheses share few common elements. Here we investigate erythrocytic allozymes as potential phylogenetic markers, and subject our results to a cladistic analysis. Our study offers little support for the previous models, but suggests instead that the greater galagos andG. alleni form a clade since they share character states for eight of the ten systems examined. The two lesser galago species could not be distinguished using these enzymes, and character states common to them and theallenicrassicaudatus-garnettii clade were found in only four systems. Our resultant cladogram accords well with the rather scant galagine fossil record. The data also show strong concordance with results obtained using highly repeated DNA sequences, which indicate that the galagos form a close-knit genetic group, while the Malagasy lemurids show considerably more inter-taxic variation.     

Habitat Exploitation by Free-ranging Saguinus niger in Eastern Amazonia

We monitored the foraging behavior of the members of a group of black-handed tamarins (Saguinus niger) at a site in eastern Amazonia. Their diet was frugivorous-insectivorous, but also included pod exudate of Parkia pendula. The focal group used all 3 types of forest—primary, logged, and secondary— in all months, but differentially between seasons. In the dry season, tamarins spent more than half of activity time in primary forest and less than a third in secondary forest whereas during the wet season, the proportions were reversed. Data on resource abundance indicated that the shift in habitat preference is related to a seasonal change in the distribution of fruit sources, with a larger number of species and individuals fruiting during the wet season. We recorded no such variation in the abundance of arthropods. While using a larger area, including more secondary forest, during the wet season, the group traveled significantly shorter distances each day, reflecting the availability of a larger number of fruit sources. Overall, the results reemphasize the ecological and behavioral flexibility of Saguinus niger and their ability to cope with habitat disturbance.