摘要:

A new mode of speciation, competitive speciation, is suggested. It assumes that fitness is depressed by the density of a phenotype's competitors, and that the adaptive landscape of phenotypes is complex. From this it follows that some intermediate forms may be fit if and only if some extreme forms are rare or absent. Subsequent to the evolution and population growth of both extreme forms, the intermediate may disappear and homogamy evolve among each of the extremes because of disruptive selection If so, sympatric speciation has occurred and niche space has been rendered into discrete segments.The limitations of the forces leading to competitive speciation are explored. Competitive speciation is discussed in relation to stasipatric speciation and host race formation. It may be responsible for both. Finally the rates of geographical speciation and polyploidy are compared to those of competitive speciation. The latter should be almost as fast as polyploidy and may be at the root of adaptive radiation. Unlike either polyploidy or geographical speciation, competitive speciation accelerates when species diversity declines.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1978.tb00016.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Foxes become larger from south to north in Scotland, independently of the climate, the prey taken or the productivity of the areas in which each population lives. In areas where fluctuating vole populations are important as food, foxes born in high vole years are no larger than those born in poor years. However foxes became smaller after a severe winter in north‐east Scotland, followed by a gradual increase in the size of each year class through a series of years with mild winters and expanding rabbit populations. It is suggested that food availability is determining the average size of foxes through selection, and the north/south cline in size is the result of increased hunting hours at higher latitudes during winter. The selective advantage of different size animals under conditions of different food availability is discusse

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1978.tb00017.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

The records of one pack of Otter Hounds hunting in southwest England are examined for the period 1907 to 1971 as well as the records of all packs active in Britain between 1950 and 1976. The hunting success per unit effort varies from year to year depending on changes in hunting conditions but longer term changes can also be identified. The hunting success of the Culmstock Otter Hounds (hunting in parts of south‐west England) increased steadily from 1907 to 1956 but in most of England and south Wales the success rate of the hunts declined rapidly after 1957. There was also a decline in success in northern England and southern Scotland but to a lesser extent, while in north Wales and Eire, there is no evidence for a decline.These changes are considered to reflect changes in otter populations but the extent of the decline in hunting success (to between 37% and 55% of previous levels in the southern hunts) is probably less than the actual decline in otter numbers. There are no signs of a recovery in the population but indications of a continuing decline up to 1976.The reason for the increasing population in the first half of the century in south‐west England is probably the decrease in persecution since the nineteenth century. A variety of causes for the crash in the late 1950s are considered and the factor most likely to be responsible is the introduction of the dieldrin group of insecticides in 1956. Use of these compounds has been increasingly restricted since 1963 and the possible reasons for the failufe of the otter population to recover are listed but no firm conclusions can be drawn as

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1978.tb00018.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

The metabolism of photosynthetically fixed14C by isolated chloroplasts fromCodium fragileis compared with that byElysia viridis(which containsC. fragilechloroplasts). There are marked differences between the two in the formation and subsequent metabolism of both soluble and insoluble products. Less than 6% of the carbon fixed by the isolated chloroplasts during a 15 min pulse of14C‐bicarbonate in the light is released into the medium over the succeeding 24 h. During photosynthesis glycollate and glucose monophosphate are the only labelled compounds released; after the pulse very little glycollate is released and over 24 h only glucose monophosphate and an unidentified compound are found in the medium. InE. viridisphotosynthetically fixed carbon can be recovered from compounds of all major classes found in animals. Soon after the pulse, hexoses are the most heavily labelled compounds, but two hours later amino acids are more heavily labelled than hexoses. The unidentified compound is not found in the animals.E. viridiscan absorb and metabolize exogenous glycollate and glucose. Earlier authors' suggestions that glucose is the compound which moves from the chloroplast to the animal cell are discussed, and it is proposed that both glucose monophosphate and glucose are formed outside the chloroplast from triose phosphate exported from i

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1978.tb00019.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Data are presented showing the number of butterfly species present in areas of different size. The species, area curve for South America starts at a higher value than that for Africa, indicating a greater species richness in a small area. It is also steeper, which indicates that there are more allopatric species. The relation for south‐east Asia is more like that for South America than Afric

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1978.tb00020.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Samples of butterflies were collected along the Zaire River from its source to Kisangani and in the Ituri region. The number of species flying in the same area has been estimated wherever possible, and the degree of faunal similarity at different sites. The number of species increases as one proceeds north from 50–100 to 100–150, and the fauna is separable into two groups. The difference in faunal composition and diversity is related to the southern boundary of the rain forest. The comparative poorness of the butterfly fauna in tropical Africa compared to tropical South America is discussed, with reference to the parallel difference in the bird faunas of the two contine

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1978.tb00021.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY