Showing papers in "Biological Journal of The Linnean Society in 1978"

Spatial autocorrelation in biology: 1. Methodology

Abstract: Spatial autocorrelation analysis tests whether the observed value of a nominal, ordinal, or interval variable at one locality is independent of values of the variable at neighbouring localities. The computation of autocorrelation coefficients for nominal, ordinal, and for interval data is illustrated, together with appropriate significance tests. The method is extended to include the computation of correlograms for spatial autocorrelation. These show the autocorrelation coefficient as a function of distance between pairs of localities being considered, and summarize the patterns of geographic variation exhibited by the response surface of any given variable. Autocorrelation analysis is applied to microgeographic variation of allozyme frequencies in the snail Helix aspersa. Differences in variational patterns in two city blocks are interpreted. The inferences that can be drawn from correlograms are discussed and illustrated with the aid of some artificially generated patterns. Computational formulae, expected values and standard errors are furnished in two appendices.

Spatial autocorrelation in biology: 2. Some biological implications and four applications of evolutionary and ecological interest

Abstract: Spatial autocorrelation analysis tests whether the observed value of a variable at one locality is significantly dependent on values of the variable at neighbouring localities. The method was extended by us in an earlier paper to include the computation of correlograms for spatial autocorrelation. These show the autocorrelation coefficient as a function of distance between pairs of localities, and summarize the patterns of geographic variation exhibited by the response surface of any given variable. Identical variation patterns lead to identical correlograms, but different patterns may or may not yield different correlograms. Similarity in the correlograms of different variation patterns suggests similarity in the generating mechanism of the pattern. The inferences that can be drawn from correlograms are discussed and illustrated. Examination and analysis of variation patterns of several characters or gene frequencies for one population, or of several populations in different places or at different times, permit some conclusions about the nature of the populational processes generating the observed patterns. Autocorrelation analysis is applied to four biological situations differing in the nature of the data (interval or nominal), in the type of grid connecting the localities (regular or irregular), and the field of application (evolution or ecology). The examples comprise genotypes of individual mice, blood group frequencies in humans, gene frequency variation in a perennial herb, and the distribution of species of trees. The implications of our findings are discussed.

The decline of the otter Lutra lutra L. in Britain: an analysis of hunting records and discussion of causes

Abstract: 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 yet.

Why male butterflies are non-mimetic: natural selection, sexual selection, group selection, modification and sieving*

Abstract: Thomas Belt suggested that the frequent limitation of mimicry in butterflies to the female resulted from sexual selection. Because female butterflies store sperm they can be fully fertile after only one mating; the reproductive success of a male is proportional to the number of times he mates. Sexual selection is therefore much stronger in males than females, with selection coefficients being greater by a small multiple of the number of times a female is courted during her life (long-lived species) or of the reciprocal of the female mortality rate between courtships (short-lived species). As butterflies of both sexes respond to colour when courting, sexual selection resists colour changes especially strongly in males. As a result, genes conferring new mimetic colour patterns can often become established in a butterfly population much more readily if their expression is initially limited to females; when the population size of a Batesian mimic, its model, and its predator fluctuates, such sex-limited genes have an enhanced probability of ultimate fixation in the population, and a reduced chance of loss; this effect is accentuated by the selection of modifiers which improve the mimicry. When the establishment of unimodal mimicry (expressed in both sexes) is favoured in a Batesian mimic, the gene tends to rise to an equilibrium frequency at which modifiers suppressing the expression of the mimicry only in males and'modifiers enhancing the mimicry only in females are favoured. The outcome is female-limited mimicry, or unimodal mimicry with better mimicry in the females, the males either retaining some of their sexual colour or the selective behaviour of the females becoming altered. In a Muellerian mimic there is no such equilibrium and selection ultimately favours expression of mimicry in both sexes and an appropriate alteration in the courtship responses. Hence Muellerian mimicry is seldom female-limited. Exceptional cases appear to result from the sexes flying in separate habitats. The genetical evidence in Papilio and Heliconius favours initial limitation of expression over subsequent modification as the usual basis for female-limited mimicry. Other explanations of female-limited mimicry can be found wanting in various ways; a higher predation rate on females could produce sex-limitation, but is probably not a strong factor. But the greater variability of the female in Lepidoptera may indicate lesser developmental stability, which could result in greater penetrance of mutants in the female, and hence account for the initial female-limitation. At very high densities of a mimetic species which has no non-mimetic form, mimicry tends to deteriorate more rapidly in a unimodal than in an otherwise identical sex-limited species. Although by itself this would equally favour male-limitation, and hence cannot explain the predominance of female-limitation, this effect may over evolutionary time be causing a slight increase in the proportion of sex-limited species among mimics. The stability of some mimetic polymorphisms is investigated by linear approximation: in some instances a stable equilibrium can be changed into an oscillating equilibrium by changes in the population size.

Variation in the size of foxes in Scotland

Abstract: 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 discussed.

The effects of stylopisation on the sexual development of Javesella dubia (Kirschbaum) (Homoptera: Delphacidae)

Abstract: This is the first record of the entomophagous parasite Elenchus tenuicornis (Kirby) parasitizing Javesella dubia (Kirschbaum) in England. The effects of E. tenuicornis on the development of (a) the primary, secondary and tertiary sexual organs, and (b) the body characters of J. dubia are discussed in detail.

Cardenolide content of Danaus chrysippus butterflies from three areas of East Africa

Abstract: The African butterfly Danaus chrysippus, like other members of the family Danaidae, feeds as a larva on species of milkweeds (Asclepiadaceae). It has been demonstrated in a sample from a West African population that only a minority of adult D. chrysippus accumulated detectable amounts of poisonous and presumably emetic cardenolides from their larval foodplants. It has also been shown in D. chrysippus and the related monarch butterfly (D. plexippus) that the cardenolide content of adults varies with that of their respective milkweed foodplants. Three population samples of D. chrysippus from sites in East Africa are analysed for cardenolides using the spectrophotometric technique refined by Brower, Edmunds & Moffitt (1975), which allows the assay of individual butterflies. The East African samples all have a palatability spectrum with a considerably higher percentage of cardenolide-containing individuals than the West African one. This is discussed in terms of its effect on potential bird predators and the ‘automimicry’ of emetic by palatable individuals. In East Africa D. chrysippus is polymorphic and appears to act as a model in a complex mimicry ring, whereas in West Africa it is monomorphic and may have ‘shed’ most of its mimics. This latter hypothesis is discussed in the light of our results.

The ecology of the fishes in Nyumba ya Mungu reservoir, Tanzania

Abstract: Twenty species of fish were found in Nyumba ya Mungu reservoir on the River Pangani which, with two exceptions, were indigenous to the river basin. Their distribution is described and some information on their growth, reproduction and feeding habits is presented. The highest densities of fish were found in the littoral and the broad, shallow, upstream region of the lake. The lacustrine environment has favoured the endemic tilapias, Sarotherodon jipe and S. pangani, which graze periphyton, and the introduced species, S. esculentus which feeds on phytoplankton. Males of the endemic forms may grow to a large size, but the introduced species, including Tilapia rendalli, were heavier for a given length. A reduction in tilapia stocks since 1970 is reflected in experimental catches during 1972-74 and was attributed to the combined effects of heavy commercial exploitation and a loss of spawning grounds. In the same period a striking increase in the populations of small carnivores, Rhabdalestes leleupi and Haplochromis gr. bloyeti, was recorded. Kully plantivorous and piscivorous fish are absent but omnivores are represented by Barbus species and Synodontis punctulatus. Tilapias exhibited a high incidence of nematode infection and the available evidence indicates that fish-eating birds are important predators of cichlids in Nyumba ya Mungu.

The vegetation of Nyumba ya Mungu reservoir, Tanzania

Abstract: A study was made of the aquatic macrophyte ecology of Nyumba ya Mungu; a nine year old man-made lake in northern Tanzania. The vegetation is described with the aid of percentage cover histograms and standing crop estimates. Concurrent physical, chemical and biological studies helped in ecological interpretations. Distinct vegetation communities were found in the deltaic swamps of the two major inflow rivers and it is concluded that this was due to water chemical differences. The water of the more alkaline River Kikuletwa appeared to influence the greater part of the perimeter swamps as the species composition largely coincided with that reported for higher pH, higher conductivity African lakes. Typha domingensis swamp was predominant and extensive, whilst Cyperus alopecuroides and Paspalidium geminatum were also common emergent species. Floating and submerged plants were relatively unimportant in the lake with respect to cover. The major zonations of species appeared to be a function of water depth, while chemistry seemed the main factor controlling vegetation pattern. In conclusion the significance of interrelationships between the macrophytes and other aquatic organisms is discussed.

The importance of the littoral epiphyton as food for commercial fish in the recent African man-made lake, Nyumba ya Mungu reservoir, Tanzania

Abstract: Nyumba ya Mungu reservoir is a man-made lake in the Kilimanjaro region of northern Tanzania. The commercial fisheries are principally based on the cichlids, Sarotherodon pangani Lowe, S. jipe Lowe, S. esculentus Graham, and Tilapia rendalli Boulenger. Examination of gut contents revealed that the dominant species, S. pangani and S. jipe, fed on the epiphyton attached to the vegetation in the littoral zone, S. esculentus was a phytoplankton filter feeder, and T. rendalli consumed macrophytes and associated epiphytes. A fish exclosure quantitatively demonstrated that the epiphyton community was appreciably depleted by the grazing of fish. After 35 days the mean epiphyton density on the submerged surfaces of Cyperus articulatus L. within the exclosure was 285 times 103 individuals cm-2 shoot, but only 181 times 103 individuals cm-2 shoot on grazed surfaces outside the exclosure. The differences were statistically significant, and corresponded to a difference in biomass of about 6.5 g organic dry weight m-2 lake surface. Vertical profiles of periphyton density on Cyperus indicated that fish grazed mainly below a depth of 100 mm from the water surface. The littoral epiphyton commercial fish food chain, which may be unique, is considered to predominate in Nyumba ya Mungu, and is compared with the major food chains of commercial fish in some other African natural and man-made lakes.

Re-curation of the Linnaean Hymenoptera (Insecta), with a reassessment of the taxonomic importance of the collection.

Abstract: The history of acquisition and maintenance of the Linnaean insect collections is briefly summarized. Curatorial details (such as kinds of label) are discussed, chiefly with reference to Hymenoptera. Some misleading opinions concerning the taxonomic value of the collections and the nature of Linnaean type-material are examined and a practical approach is recommended. The rationale governing re-curation of the collections is detailed, and the present contents of the collection of Hymenoptera are listed in order to inform interested specialists.

The metabolism of photosynthetically fixed carbon by isolated chloroplasts from Codium fragile (Chlorophyta: Siphonales) and by Elysia viridis (Mollusca: Sacoglossa)

Abstract: The metabolism of photosynthetically fixed 14C by isolated chloroplasts from Codium fragile is compared with that by Elysia viridis (which contains C. fragile chloroplasts). 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 of 14C-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. In E. viridis photosynthetically 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. viridis can 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 it.

The periphyton communities of Nyumba ya Mungu reservoir, Tanzania

Abstract: The periphyton communities established in Nyumba ya Mungu were investigated between July and September 1974. One hundred and ninety-two taxa were identified. One hundred and fifteen taxa were collected in the southern end of the lake, where 97 taxa were non-selectively distributed in the littorine epiphytic, epilithic, and epixylic environments. The offshore epixylon supported only 53 taxa. The epipelon and epipsammon were poorly developed at the southern end of the lake but were well developed in the northern inflow regions. Diatoms and cyanophytes were the dominant phyla which contributed over 80% of the algal numbers. Chlorophytes were not common. Taxonomic compositions of periphyton on artificial and natural surfaces were similar, but artificial substrata accumulated greater proportional representations of diatoms. The mean net production rates of periphyton on artificial substrata located at depths from 0-0.65 m for 28 days ranged from 140 mg organic dry weight m-2 day-1 on shoots in the macrophyte zone to 820 mg organic dry weight m-2 day-1 on glass surfaces on a rocky shore. The epiphytic environments produced the least standing crops of less than 250, 000 individuals cm-2, but maximum densities of over 2,000,000 individuals cm-2 were recorded in the epilithon.

Observations on the zooplankton and littoral macroinvertebrates of Nyumba ya Mungu reservoir, Tanzania

Abstract: Eight species of Crustacea and 28 species of Rotifera were identified in zooplankton samples from Nyumba ya Mungu reservoir. In all localities the dominant organism was the copepod Thermocyclops hyalinus. Cladocerans and rotifers made a variable contribution. Insects, among which the Chironomidae were pre-eminent, formed the major component of littoral macroinvertebrate communities. Oligochaetes, crustaceans and gastropods, including vectors of Schistosomiasis, were rare or restricted in distribution. In contrast to the deep end of the lake, where submerged trees were the poorest substrate, those at the shallow end supported a high biomass of invertebrates, since prolonged exposure had accelerated rotting and facilitated colonisation by the burrowing nymphs of Povilla. The variety of invertebrates on stony and muddy shores was increased when rooted emergent plants were present. The richest benthic community was found in submerged beds of Ceratophyltum. It is suggested that drawdown and the restricted development and movement of floating vegetation, have limited the spread of gastropods in the lake. Zooplankton, chironomid larvae and pupae, and ephemeropteran nymphs were shown to be important in the diet of small carnivorous and omnivorous fish species.

The species of “Ichneumon” (Hymenoptera) described by Linnaeus

Abstract: Ichneumonidae in the Linnaean and other collections have been critically assessed with regard to their status as type-specimens of species described by Linnaeus. The generic placements of the 56 nominal species of Ichneumonidae (54 originally in Ichneumon and two in Mutilla) described by Linnaeus are established after study of the extant type-material. Lectotypes are designated for eleven of the species and one new synonymy is established. Notes are given on the 33 species originally described by Linnaeus in Ichneumon but now placed in other families.

Limnochemical and phytoplankton studies on Nyumba ya Mungu reservoir, Tanzania

Abstract: This publication reports on the chemical and phytoplankton aspects of a three month biological survey of Nyumba ya Mungu reservoir, Tanzania. The lake had a total salt concentration of about 8 meq dm-3 and specific conductivity of 900 μS cm-1. The main salt in solution was sodium bicarbonate, and when the lake level fell it sometimes formed a crust on the exposed shore. The concentrations of major nutrient ions were probably not limiting to algal growth and good nutrient replenishment was provided by the two inflow rivers. Nyumba ya Mungu supports a rich phytoplanton dominated by Melosira and blue-green algae. Acetone extractions gave chlorophyll ‘a’ concentrations ranging from 20–40 mgm-3 in the vertical profiles, and light and dark bottle experiments indicated a maximum gross photosynthesis of about 800 mg O2 m-3h-1. There was evidence of chemical stratification in the open water and diurnal stratification in the sheltered bays, but discontinuities were short-lived and the Trade Winds ensured regular mixing of the water. The lake appeared to have a higher primary production than the larger Rift Valley lakes and it was considered that this level of production would continue.

Nyumba ya Mungu reservoir, Tanzania: The general features

Abstract: Nyumba ya Mungu reservoir was completed in 1965 in northern Tanzania. By 1970 there was a thriving tilapia fishery but it declined catastrophically in subsequent years. A team of biologists surveyed the lake in 1974, and this paper outlines their hydrological, geographical, and climatic findings. The dam, constructed across a north/south Neogene fault-trough 80 km south of Mt. Kilimanjaro, has produced a reservoir about 180 km2 with a mean depth of 6 m. The catchment area is extensive but the main source of water is from Mt. Kilimanjaro. The lake is situated in an arid area, and over one quarter of the input water evaporates from the lake's surface. The outflow is regulated by a hydro-electric power station and is practically constant. At full capacity the retention time of the lake is one year but due to abnormally low rainfall, the reservoir was not full, and the retention time was nearer nine months. The lake is polymictic and a deep wind-driven current is maintained by the Trade Winds for most of the year. The general features of Nyumba ya Mungu are briefly compared with other man-made and natural lakes in Africa.

Zaire butterflies and faunal diversity in the tropics

Abstract: 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 continents.

An unpublished letter by Richard Spruce on the theory of evolution

Abstract: The unparalleled plant explorations of the British botanist Richard Spruce in the Amazon Valley and the northern Andes from 1849 to 1864 are now well known in scientific circles. What is not so widely recognized, however, is the depth of philosophy characteristic of this man, a depth of philosophy nurtured especially during his many years of living alone in closest association with nature in the forests of South America.

A note on the diversity of World Lepidoptera (Rhopalocera)

Abstract: 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 Africa.

The 1974 biological survey of Nyumba ya Mungu reservoir, Tanzania: Concluding remarks

Abstract: Hydrobiological events in Nyumba ya Mungu reservoir, a recent man-made lake in Tanzania, are reviewed in the light of those described for larger impoundments in other parts of Africa. An initial phase of rapid eutrophication and of high fish production has been replaced by a slower stabilization phase. At present the inflowing rivers supply a nutrient rich water and the level of primary production remains high. In spite of the risk of an encroachment of Typha domingensis across the shallow end and events associated with overfishing, the lake retains most of the essential requirements to continue as a useful tilapia fishery. The introduction of new fish into the reservoir, to fill gaps in the trophic structure of the fish community is not recommended.