摘要:

Hypolimnas misippus, a sexually dimorphic, nymphalid butterfly with a very variable female, was sampled for 41 consecutive months, along with its supposed model,Danaus chrysippus(Danaidae), at Dar es Salaam, Tanzania.Hypolimnaslarvae collected in the field were reared to compare their range of variation with that of the wild adult population. Some breeding data are presented.Although I show that the colour variations inDanausandHypolimnasare remarkably similar, the frequency rankings of the analogous forms within each species differ markedly in the long term. Moreover, 24% ofHypolimnasare transitional forms which are poor mimics. As the range of variation at Dar es Salaam is similar to that reported from Ghana, where the “model” is of quite different appearance, I conclude that mimetic resemblance is not of over‐riding importance to its maintenance and perpetuation.The continuous variation in both fore‐ and hindwing coloration in the field is reflected in reared broods which fail to segregate into discontinuous phenotypes so thatH, misippusis not truly polymorphic at Dar es Salaam.Females with transitional forewings have white on their hindwings more often than do the two extreme phenotypes,misippusandinaria.Transitional or white winged females are abundant only at times of high population density, whereasinarialarvae seem to have an advantage in crowded conditions. The extreme rarity of association between theinariaforewing and white hindwing suggests disruptive selection, the former being associated with the conditions ofKselection and the latter withrselection. The calculation of selection coefficients supports this interpretation.Phenotypic diversity is greatest at high population density when the proportion of poor mimics is also maximal. At these times, apostatic selection may be important. At low density, diversity is minimal.Recent evidence concerning the efficiency ofD. chrysippusas a model is discussed. The origin of colour variation inH. misippusprobably owed much to mimicry but other selective forces such as apostatic selection or perhaps sexual selection are now of greater importance in maintai

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1976.tb00245.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Laysan Island, a low atoll in the Leeward Hawaiian Islands, exhibits a biota that contains nine genera of upland and montane lineages of animals and plants usually of restricted range and occurrence and adapted to high island habitats. The geological history of Laysan Island, interpreted in terms of plate tectonic theory and recent ideas on the formation of linear island chains, shows that Laysan existed as an active high volcanic island approximately 15 million years ago. Since that time subaerial erosion and tectonic subsidence have combined to reduce the height of the island. During the past 250,000 years glacioeustatic sea level changes have resulted in Laysan Island fluctuating, geomorphologically, between a high limestone island and an atoll status. Laysan is viewed as a refugium for upland and montane lineages able to keep pace, via great adaptive flexibility, with drastic habitat changes. The thesis that plants of Laysan are recent arrivals is considered unlikely, as regards the upland contingent, in view of the geological history of the island.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1976.tb00246.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

The natural enemies ofBathycoelia thalassinain Ghana are surveyed and their effect and suitability as natural controls of the pest in the field and in the insectary assessed. Mass rearing methods in the insectary for the most common parasites,Trissolcusspp. andCylindromyia cribrataare described.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1976.tb00247.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Species ofDichromothripsare shown to be widespread on Orchidaceae in the Old World Tropics from Africa to New Zealand. The centre of diversity appears to be the Malaysian Region but this may be an artefact resulting from poor collections. The genus is redefined, its relationships discussed and a key provided to the 14 species [australiaesp. nov.,borneensis(Pr.);corbetti(Pr.);dendrobiiSaki.;indicussp. nov.;maorisp. nov.;nakaharisp. nov.;nigeriaesp.nov.;orchidis Pr.;phalaenopsidisSaki. (=sakimuraiBhatti syn.nov.);priesneri(Hood);semicognitusSaki.;smithi(Zimm.)jvia torussp. nov.|.EugeneothripsHood is synonymised withDichromothrips.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1976.tb00248.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

The diet and feeding interrelationships of ten species of Mugilidae were studied over a two‐year period in the St. Lucia lake system of South Africa. Qualitative stomach analyses were performed on over 1000 fish of more than 5 cm (standard length). All are soft bottom substrate feeders ingesting inorganic particles mixed with food items. The food of most species is the same and consists ofAssiminea bifasciata, foraminifera, the large centric diatomAptinoptychus splendens, small centric and pennate diatoms, and filamentous algae. Individual species of mullet however, differ, in the size of inorganic particles ingested and exhibit marked sand grain size preferences. The consumption of the various food items may depend upon their occurrence on substrates of the preferred particle size. There is no apparent change in diet and particle size preference according to age in any of the species and no seasonal variation was recorded in the diet. It is suggested that interspecific competition for food is reduced by substrate particle size selection and perhaps by differences in feeding periodicity. Where there is an apparent overlap in diet, as in the case ofAssiminea bifasciata, on substrates of the same size then there is a superabundance of the food organism which serves to minimize competitive interaction

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1976.tb00249.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY

摘要:

Food selectivity by the common freshwater carp,Esomus danricus(Ham.) was studied through Ivlev's equation of electivity. The selective feeding seemed to be influenced by many factors, including the accessibility, abundance and taste, of the food items, the mechanical and physiological adaptations on the part of the fish to capture and digest those food organisms, as also the inherent and instinctive property of the fish to prefer certain types of food over the others. The absence of strong specific selectivity by the fish for a variety of planktonic food organisms was found to be a phenomenon compensatory to stenophagism, in order to make use of whichever food items remained in the habitat at the time when the preferred genera of plankton were not available, due to the process of succession.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1976.tb00250.x

出版商:Blackwell Publishing Ltd    

年代:1976

数据来源: WILEY