Central place foraging by an ant (Cataglyphis bicolor Fab.): a model of searching

A computer model of the searching activity of Cataglyphis bicolor (Fab.), based on quantitative data obtained in the field in Greece, was investigated. This ant searches for individual items of food (mainly dead arthropods) in the open on flat ground, on which its paths can be followed and mapped. The model was based on an analogy with molecular diffusion from a centre, suggested by the fact that the average distance of ants from the nest increased in proportion to the square root of time, up to a distance more than half the radius of a circle enclosing 90% of the search area. Actual behaviour was well described by a model in which individual ants went out for the first time to search in a direction determined at random. Subsequently they went out in a straight line in a direction and to a distance related to that of the previous find before commencing a semi-random search, on a path consisting of straight portions branching at random angles, with restriction on turns in a backward direction. Individual real ants search in restricted areas, commonly sectors centred on the nest. This behaviour was reproduced in the model as were quantitative aspects of the nest behaviour. Communication between individuals was not required in the model.     

Central place foraging in the white-fronted bee-eater

Orians & Pearson (1979) proposed a series of models of optimal central place foraging. I tested their model for single-prey loading species (those that carry items singly) with a natural population of white-fronted bee-eaters (Merops bullockoides) in Kenya. These insectivorous birds breed in colonies but defend nearby foraging territories from which they gather food for their nestlings. Qualitatively, two predictions of the model were upheld: as travel time increased, birds carried larger insects to their nests and spent longer periods of time foraging. Also, as distance increased, birds were increasingly selective of which insects they ate versus carried to the colony. Quantitative comparisons were also made using observed travel times and rates of insect capture. As distance increased, (1) the observed sizes of insects carried approached the values predicted by the Orians-Pearson model, (2) observed foraging times diverged from the predicted values, and (3) birds spent more time foraging between round trips in a relatively unprofitable area near the colony. These results are examined in light of the theory of central place foraging.     

The effect of color preferences on the foraging behavior of the green-veined white butterfly (Pieris napi L.)

The color preferences of the green-veined white butterfly Pieris napi (Linnaeus, 1758) that are associated with its foraging behavior were studied in experiments with artificial flower models. It was found that newly emerged inexperienced butterflies that are searching for food prefer flower models that are blue or red and select yellow ones at a considerably lower rate. With repeated visits on artificial flowers, P. napi individuals display are highly consistent in their preference for the first chosen color. Males and females of this species display similar color preferences.     

Central place foraging in the Eastern chipmunk, Tamias striatus

Orians & Pearson (1979) considered the optimal foraging strategies of ‘central place foragers’, animals that repeatedly return with their food to a fixed location. We tested some of their predictions on eastern chipmunks, Tamias striatus. The rate of cheek pouch loading declines as the pouches fill; thus the optimal load size may vary, depending on the time required to travel between the feeding site and burrow. This ‘travel time’ may also affect the choice of feeding site. A method was developed to test this, and preliminary results confirm the hypothesis. Methodological and theoretical implications of these empirical results are discussed.     

Central place foraging by swallows (Hirundinidae): The question of load size

Some predictions of Orians & Pearson's (1979) models for central place foragers (CPF) were tested with three species of swellows (Hirundinidae). House martins (Delichon urbica) and sand martins (Riparia riparia) brought larger food loads to the nest mainly when foraging distances were great, whereas swallows (Hirundo rustica) gathered large loads when food was plentiful. For all three species the outcome conformed qualitatively with the predictions of the CPF models. Overall, house martins were the most sensitive to travel time effects, but in a quantitative test the predicted load size was 20–40% less than the observed size for a range of realistic travel times. Additional models are presented which emphasize the significance of foraging techniques and foraging costs for optimal load size in multiple prey loaders.     

In situ management options to improve crucian carp (Carassius carassius,L.) and brown trout (Salmo trutta,L.) population status in Central Europe: A case study from the Czech Republic

The crucian carp (Carassius carassius, L.) and the brown trout (Salmo trutta, L.) are vanishing from freshwater ecosystems of central Europe. To conserve both species, tailor‐made conservation management of habitats and populations of both species was implemented and tested in the Czech Republic (central Europe). This management was adjusted to reflect the ecological needs of both species. This study aimed to describe the results of a tested in situ management and to analyze the population growth of brown trout and crucian carp under ideal conditions. An experiment was performed at 14 small gravel pit lakes. Seven of them were adjusted to fit the crucian carp habitat requirements while the other seven were treated as a control group. The same experiment was done on 14 smaller streams and with brown trout. The occurrence and growth of crucian carp and brown trout were surveyed over 2 years. A significantly faster growth of both crucian carp and brown trout was observed on the adjusted lakes and streams in comparison to the control group ones. Trout and carp prospered on small streams and gravel pit lakes (respectively) that were free of angling, fish stocking, pollution, piscivorous predators, and competition with hybridizing species like Prussian carp (Carassius auratus, L.) or hatchery‐reared brown trout.     

Immature stages of the butterfly Magneuptychia libye (L.) (Lepidoptera: Nymphalidae, Satyrinae)

The immature stages of the butterfly Magneuptychia libye (L.) are described, and their morphology is compared with other Neotropical Satyrinae.     

Density‐dependent,central‐place foraging in a grazing herbivore: competition and tradeoffs in time allocation near water

Optimal foraging theory addresses one of the core challenges of ecology: predicting the distribution and abundance of species. Tests of hypotheses of optimal foraging, however, often focus on a single conceptual model rather than drawing upon the collective body of theory, precluding generalization. Here we demonstrate links between two established theoretical frameworks predicting animal movements and resource use: central‐place foraging and density‐dependent habitat selection. Our goal is to better understand how the nature of critical, centrally placed resources like water (or minerals, breathing holes, breeding sites, etc.) might govern selection for food (energy) resources obtained elsewhere – a common situation for animals living in natural conditions. We empirically test our predictions using movement data from a large herbivore distributed along a gradient of water availability (feral horses, Sable Island, Canada, 2008–2013). Horses occupying western Sable Island obtain freshwater at ponds while in the east horses must drink at self‐excavated wells (holes). We studied the implications of differential access to water (time needed for a horse to obtain water) on selection for vegetation associations. Consistent with predictions of density‐dependent habitat selection, horses were reduced to using poorer‐quality habitat (heathland) more than expected close to water (where densities were relatively high), but were free to select for higher‐quality grasslands farther from water. Importantly, central‐place foraging was clearly influenced by the type of water‐source used (ponds vs. holes, the latter with greater time constraints on access). Horses with more freedom to travel (those using ponds) selected for grasslands at greater distances and continued to select grasslands at higher densities, whereas horses using water holes showed very strong density‐dependence in how habitat could be selected. Knowledge of more than one theoretical framework may be required to explain observed variation in foraging behavior of animals where multiple constraints simultaneously influence resource selection.     

Pupal polymorphism in the butterfly Danaus chrysippus (L.): environmental, seasonal and genetic influences

The pupae of the tropical butterfly Danaus chrysippus are either green or pink the switch being operated by a ‘greening’ hormone produced in the larval head. Both environmental and genetic cues are involved in controlling the endocrine mechanism. The environmental factors identified are of two distinct kinds: proximate factors influence pupal colour after the larva has selected its pupation site, whereas ultimate factors are effective at an earlier stage, either prompting choice of pupation site by the larva or priming pupation physiology in a particular direction. Genetic factors preadapt the larva to form a pupa which will be cryptic in the normal or average conditions, climatic or biogeographical, anticipated in its environment. The proximate factors demonstrated are background colour, darkness, light quality (wavelength) and humidity. There is some evidence that substrate texture may also be relevant. Ultimate factors are temperature, humidity and species of larval foodplant. Two closely linked gene loci which govern the phenotype of adult morphs and races either have a pleiotropic effect on pupa colour or are closely linked with other genes which do so. Moreover, the two loci interact epistatically with respect to their pupation effects. Factors producing predominantly green pupae are plant substrates, yellow background, darkness, yellow light, high humidity, high temperature, the b allele at the B locus when homozygous and, on non-plant substrates, the C allele at the C locus. High frequencies of pink pupae result on non-plant substrates, red backgrounds, in blue light, low humidity, low temperatures and in B- and cc genotypes. The C locus alleles, C and c, interact epistatically with the B alleles, their effect on choice of pupation site being determined by linkage phase. Of the two foodplants tested, Calotropis produced a high frequency of green pupae and Tylophora of pinks. The seasonal cycling of rainfall, temperature, availability or condition of foodplant, and gene frequencies are all correlated with oscillations in the frequencies of green and pink pupae. Though genotype influences pupa colour, all genotypes are capable of forming pupae of both colours. The variation can therefore be attributed to an environmental polyphenism superimposed upon a genetic polymorphism. The hormone producing green pupae emanates from the head during the prepupal period. Denied hormonal influence, the pupa is pink. Pupal colour is judged to be aposematic at close range and cryptic at distance.     

广州市不同城市化发展区域蝶类多样性

2005～2006年,对广州地区4个不同城市化发展区域(森林区、农田区、城市区、沿海湿地区)的蝶类进行6次调查,共统计到10科46属73种.森林区科、属、物种和个体数目都最多,沿海湿地区各项数量指标都最小,农田区的个体数量大于城市区,但科、属和物种数却与城市区差异不大.多样性分析结果表明,森林区的种类丰度、多样性指数最高,沿海湿地区的种类丰度和多样性指数最低;均匀度大小依次为沿海湿地区﹥农田区﹥森林区﹥城市区;优势度指数大小依次为沿海湿地区﹥城市区﹥农田区﹥森林区.相似性分析结果表明,森林区和农田区具有的相同物种数最多,相似性系数最高;沿海湿地区和森林区、农田区、城市区具有的相同物种数都较少,相似性系数也较低.     

The SLOSS dilemma: a butterfly case study

Butterfly species richness is examined on simulated archipelagoes of 2, 3, 4 and 5 holm oak forest fragments in the Guadalajara Province (central Spain). It is shown that there are more species on several small islands than on a single island. Also, species number increases with the number of fragments that form the archipelago, and with the average distance between islands within the archipelago. Thus, we conclude, at least for butterflies in a system of fragmented holm oak forests in central Iberia, that the best strategy in order to maximize the conservation of species richness is the creation of a net of some small and scattered reserves.     

Thoracic temperature,shivering, and flight in the monarch butterfly,Danaus plexippus (L.)

Summary Monarch butterflies, Danaus plexippus (L.), display a warm-up behavior characterized by wingstrokes of small amplitude. Thoracic temperature during this shivering and during fixed flight was measured by means of a smallbead thermistor inserted into the thorax. At ambient temperatures of 15–16°C, once shivering is initiated the thoracic temperature rises at a maximum rate of 1.3°C/min, and a thoracic temperature 4.0°C greater then ambient is produced (Table 1). Fixed flight at these low ambient temperatures results in a similar rate of increase in thoracic temperature, and a similar temperature excess is produced (Fig. 3). At ambient temperatures between 22 and 35°C the thoracic temperature of an animal starting to fly rises at a faster rate, 3.6°C/min, and reaches a greater excess, 7.9°C (Fig. 4). The wingbeat frequency of animals in fixed flight increases with increasing thoracic temperature (Fig. 2). In the absence of direct solar radiation, shivering typically occurs prior to flight at low ambient temperatures (13–17°C), and the resulting increase in thoracic temperature allows monarch butterflies to fly at these cool temperatures.I thank Miss Janice Ruppert and Mr. C. J. Doughty for their valuable technical assistance. The co-operation of the administrators of New Brighton Beach State Park in permitting me to collect in the park is appreciated. Financial support for this study was provided in part by a faculty research grant from the University of California.     

Visual mate-searching behaviour in the evening brown butterfly, Melanitis leda (L.) (Lepidoptera: Nymphalidae)

Abstract As in most animals, male butterflies are generally the more proactive sex with respect to seeking out mating opportunities. In most cases, males conduct their search sometime between mid-morning and mid-afternoon, but a few species are active only before dawn or after sunset. These crepuscular species offer a good opportunity to study how males deal with markedly different visual and thermal conditions. Here, I present data from a 5-month behavioural study of male Melanitis leda (Nymphalidae) at a mate-encounter site in tropical Australia. Males of this species defended perching locations along a forest edge in a similar manner to other diurnally active territorial nymphalids. They generally arrived at these sites after sunset and arrived earlier on evenings that darkened earlier. Actively mate-locating males were only seen at the site during a 25−35 min evening period, during which ambient light levels ranged between 50 and 2600 lux. Only 27% of marked territory residents were recorded again at their location of capture, but fidelity in this 'resighted' group ranged up to 23 days. A sample of males, captured under ambient temperatures of 24.0−27.2°C, maintained a mean thoracic excess of 8.25 ± 0.73°C, but did not appear to 'shiver' in the manner of other crepuscular species. Males courted conspecific females and one mating was observed. This species is an excellent candidate for further research into the evolution of mating tactics in crepuscular butterflies.     

Distribution of the monarch butterfly, Danaus plexippus (L.) (Lepidoptera: Nymphalidae), in western North America

The standard model for the migration of the monarch butterfly in western North America has hitherto been movement in the autumn to overwintering sites in coastal California, followed by a return inland by most individuals in the spring. This model is based largely on observational and limited tagging and recovery data. In this paper we test the model by plotting many years of museum and collection records on a monthly basis on a map of the region. Our plots suggest a movement of Oregon, Washington and other north-western populations of summer butterflies to California in the autumn, but movement of more north-easterly populations (e.g. from Idaho and Montana) along two pathways through Nevada, Utah and Arizona to Mexico. The more westerly of these two pathways may follow the Colorado River south as indicated by museum records and seasonal temperature data. The eastern pathway may enter northern Utah along the western scarp of the Wasatch Mountains and run south through Utah and Arizona. Further analysis of distributions suggests that monarch butterflies in the American West occur primarily along rivers, and there are observations indicating that autumn migrants often follow riparian corridors. More data are needed to test our new model; we suggest the nature of the data required.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 85 , 491–500.     

Heterosis, epistasis and linkage disequilibrium in a wild population of the polymorphic butterfly Danaus chrysippus (L.)

The colour polymorphism of the Danaus chrysippus population at Dar es Salaam, East Africa, is controlled at three major loci, each with two alleles. Two of the loci, one governing ground colour and the other forewing pattern, are closely linked. The third locus, determining hindwing pattern, assorts independently. Thirty-eight broods raised from wild mated pairs, Fl and F2 generations gave 857 offspring of 23 genotypes (out of 27 possible). The forewing length, taken as an index of size, was investigated in relation to the genotype. Heterosis is evident at all three loci. The two linked loci show epistatic interaction of an unexpected kind: double heterozygotes are smaller than heterozygotes at only one locus but larger than double homozygotes. The heterotic effect at the third, unlinked locus is the most pronounced and is additive to that at the other two. Heterosis is more marked in males than females. The possibility that body size has importance in connexion with sexual selection, food resources and mimetic relationships is discussed. Analysis of gene and chromosome frequencies in the wild parents of 61 broods suggests that double heterozygotes for the two linked loci may have heterozygous advantage. Seventy-eight per cent of chromosomes are repulsion phase: thus, there is pronounced linkage disequilibrium which must be maintained by selection as crossing over is almost 296. In particular, the chromosome carrying both dominant alleles in coupling is rare. Consideration of the centres of distribution and present ranges of the alleles at all three loci suggests that three geographical races, aegyptius, dorippus and alcippus, were isolated by forest barriers, during wet periods in the Pleistocene, in south-west, north-east and north-west Africa respectively. They have probably expanded their ranges in the post-glacial period to overlap and interbreed in central and east Africa. Either heterozygous advantage or seasonal (directional) selection or a combination of both is responsible for the persistence of the polymorphism.     

The growth of Bibio johannis (L.) and Dilophus febrilis (L.) (Diptera: Bibionidae) larvae in the field

Bibionid larvae were extracted from soil samples collected from June 1985 to March 1987. Each larva was identified, weighed and measured for maximum head capsule width. Both Bibio johannis and Dilophus febrilis have six larval instars. Bibio johannis grew slowly in late summer and early autumn but rapidly from October to January. Early and late instar larvae of D. febrilis occurred simultaneously and it was concluded that this species was not bivoltine but may exist as two separate cohorts with distinct flight periods.     

Evidence of protease in the saliva of the butterfly Heliconius melpomene (L.) (Nymphalidae, Lepidoptera)

Butterflies of the genus Heliconius are well known for their peculiar habits of utilizing pollen as a source of amino acids. Saliva plays a major role in the process of extracting amino acids and proteins from the pollen grains. In this investigation, we obtained samples of saliva from adult Heliconius melpomene by placing pumpkin pollen or fine glass-beads on the proboscis, which stimulates the butterflies to release saliva. Proteolytic activity was determined in the saliva by an insoluble protein-dye that turns blue when cleaved by proteases. Its extinction value was measured with a spectrophotometer at 595 nm. Both the saliva sampled with pollen and the saliva obtained from inert glass-beads exhibit proteolytic activity demonstrating that the saliva contains proteases. The proteolytic activity of the pollen/saliva samples was higher than that of the glass-bead/saliva samples, which we attribute to the stimulating effects of pollen, such as taste, smell, and texture, and not to proteases which might have been liberated from the pollen. This is indicated by the fact that pollen samples without saliva showed only a negligible indication for proteolytic activity. In general, females exhibit higher proteolytic activities than males, presumably due to their greater amino acid investment in reproduction. We present here first evidence for the existence of proteases in the saliva of a butterfly species and suggest that these enzymes are crucial for the use of amino acids and proteins from pollen in Heliconius butterflies.