摘要:

The land snailArianta arbustorumis polymorphic for colour and banding of the shell. This paper reports the results of a survey of natural populations of the species in the valley of the River Dove in Derbyshire and Staffordshire. There is some evidence of climatic selection in non‐woodland populations such as has been observed elsewhere in Britain.The woodland sites can be divided into several classes depending upon the tree species present. The morph‐frequencies are significantly different between class, but homogeneous within. It is argued that the greenness of the ground cover depends upon the trees growing overhead, and that the morph‐frequency is related to this. It is suggested that visually discriminating predators may be partially responsible for this correlation.SUMMARYArianta arbustorum(L.) is a terrestrial land snail which is polymorphic for colour and banding. Brown shell colour is dominant to yellow, and banded is dominant to unhanded. The two loci are closely linked.Communities of larger helicid snails were sampled along the valley of the River Dove in Derbyshire and Staffordshire. The samples were scored for species composition, and the proportions of the various morphs ofA. arbustorumwere determined.Outside the woodland areas,A. arbustorumshows slight evidence of micro‐climatic selection similar to that found elsewhere in Britain.There is little evidence of differences in the ecological genetics ofA. arbustorumbetween woodland and non‐woodland habitats despite fairly heavy predation. It is argued that predation may be lower outside the woods allowing climatic effects to become detectable.The woodland samples are heterogeneous with respect to morph frequency. The heterogeneity can be partitioned between three classes of woodland which are internally homogeneous. It is argued that birch woodland may be lighter in background than hazel, with the elm‐ash‐beech woods being darker than either. The proportion of unhanded yellowA. arbustorumis highest in the first of the classes, and lowest in the last. It is argued that this result could be due to the actions of visually discriminating predators upon these populations of

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1973.tb00703.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

A study was made on a freshwater planktonic population of centric diatoms, mainlyStephanodiscus rotula(Kütz.) Hendey, in Loch Leven, Kinross, Scotland. The observations were analyzed in relation to changes in water temperature and chemistry, parasitism by a chytridiaceous fungus, grazing by a recently described protozoan and competition from another alga (Synechococcuxsp.). Each of these factors is thought to have affected the recorded rise and fall in diatom population density, in particular, silica limitation, fungal parasitism and protozoan grazing.The protozoan involved (Asterocaelum algophilumCanter) forms digestion cysts, the predominantly diatomaceous contents of which suggested very selective feeding but laboratory experiments with dual cultures did not confirm this. They indicated that both the size and quality of algae affected their suitability as food. Feeding activities ofAsterocaelumseemed to be more or less confined to a solid surface; grazing rates in cultures shaken to maintain the animals and algae in suspension were low relative to those observed in unshaken cultures. This suggests that much of the grazing occurred on diatoms that had sunk onto the sediments

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1973.tb00704.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

Investigation by light and electron microscopy was carried out using clonal material ofRhynchomonasisolated from freshwater. Parallels were found withBodospecies, but the formation of the proboscis seems to be unique. The latter is not a modification of the short flagellum, as had been previously supposed, but is completely separate from it. The occurrence of the organism in the wild is commented upon.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1973.tb00705.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

Ecologists are increasingly in demand to provide both background information to development and to conduct validatory studies prior to funding. This paper describes an advisory study conducted on the Caribbean island of Mustique prior to development for tourism. It is argued that the ecologist uses biological as well as physical indicators to assess suitability of different areas for development and to anticipate possible problems. In this study the primary environmental determinants and biological and human factors have been interpreted to identify the distribution and degree of seriousness of exposure, erosion potential and water yield and quality. The compatibility of physical and ecological factors with different categories of proposed development have been assessed, and maps of vegetation, soil and exposure transferred onto gridded overlays. The use of these overlays combined with a consideration of the compatibilities permitted the degree of restraint to the various categories of development to be presented in map form. The problems that are likely to be encountered as a result of development are discussed, and finally it is suggested that the development be subjected to regular ecological monitoring.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1973.tb00706.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

The medium and large ground finches of the Galapagos archipelagoGeospiza fortisandG. magnirostrisare distinguished by their different body size and bill dimensions on most of the islands where they both occur. On the island of Indefatigable this distinction is not complete and a group of birds with intermediate bill dimensions is present. The origin of this group could be explained by sympatric divergence ofG. fortisor by hybridization, between this species andG. magnirostris. Although the conditions for sympatric divergence are severe it seems likely that strong disruptive selection for different optimal bill sizes may be operating onG. fortis, due to the presence of several ecological niches, separate categories of size and hardness of seeds the birds eat. It is suggested that islands in the Galapagos archipelago, and perhaps other oceanic islands, may provide conditions extremely conducive to sympatric divergence, or even sympatric speciation.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1973.tb00707.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY