Showing papers in "Journal of Applied Ecology in 1972"

Solar radiation and productivity in tropical ecosystems

Abstract: In thermodynamic terms, ecosystems are machines supplied with energy from an external source, usually the sun. When the input of energy to an ecosystem is exactly equal to its total output of energy, the state of equilibrium which exists is a special case of the First Law of Thermodynamics. The Second Law is relevant too. It implies that in every spontaneous process, physical or chemical, the production of 'useful' energy, which could be harnessed in a form such as mechanical work, must be accompanied by a simultaneous 'waste' of heat. No biological system can break or evade this law. The heat produced by a respiring cell is an inescapable component of cellular metabolism, the cost which Nature has to pay for creating biological order out of physical chaos in the environment of plants and animals. Dividing the useful energy of a thermodynamic process by the total energy involved gives a figure for the efficiency of the process, and this procedure has been widely used to analyse the flow of energy in ecosystems. For example, the efficiency with which a stand of plants produces dry matter by photosynthesis can be defined as the ratio of chemical energy stored in the assimilates to radiant energy absorbed by foliage during the period of assimilation. The choice of absorbed energy as a base for calculating efficiency is convenient but arbitrary. To derive an efficiency depending on the environment of a particular site as well as oil the nature of the vegetation, dry matter production can be related to the receipt of solar energy at the top of the earth's atmosphere. This exercise was attempted by Professor William Thomson, later Lord Kelvin, in 1852. 'The author estimates the mechanical value of the solar heat which, were none of it absorbed by the atmosphere, would fall annually on each square foot of land, at 530 000 000 foot pounds; and infers that probably a good deal more, 1/1000 of the solar heat, which actually falls on growing plants, is converted into mechanical effect.' Outside the earth's atmosphere, a surface kept at right angles to the sun's rays receives energy at a mean rate of 1360 W m-2 or 1f36 kJ m-2 s-1, a figure known as the solar constant. As the energy stored by plants is about 17 kJ per gram of dry matter, the solar constant is equivalent to the production of dry matter at a rate of about 1 g m-2 every 12 s, 7 kg m-2 per day, or 2 6 t m-2 year-'. The annual yield of agricultural crops ranges from a maximum of 30-60 t ha-' in field experiments to less than I t ha-' in some forms of subsistence farming. When these rates are expressed as a fraction of the integrated solar constant, the efficiencies of agricultural systems lie between 0-2 and 0 004%, a range including Kelvin's estimate of 0-1%. Conventional estimates of efficiency in terms of the amount of solar radiation incident at the earth's surface provide ecologists and agronomists with a method for comparing plant productivity under different systems of land use and management and in different * Opening paper read at IBP/UNESCO Meeting on Productivity of Tropical Ecosystems, Makerere University, Uganda, September 1970.

The transport of pollen on the body hairs of honeybees (Apis mellifera L.) and bumblebees (Bombus spp. L.)

Abstract: A honeybee has difficulty in grooming some parts of its body, such as the back of its head, the central dorsal part of its first thoracic segment and the first and second abdominal segments (Lukoschus 1957). Consequently, some pollen often remains on the bodies of honeybees while in their hives, and enough of this is viable to pollinate flowers visited during their next foraging trip (Free & Durrant 1966) although any pollen remaining on their bodies during the night, or other long period in the hive, probably dies (Butler & Haigh 1956; Kraai 1962). It has been suggested that pollen is transferred from bee to bee as they brush against each other in the hive between foraging trips (Karmo & Vickery 1954; Lukoschus 1957; Karmo 1961) so that bees leaving their hives may carry pollen of a type other than the one they are working. If true, this would have important practical implications. However, the evidence supporting this hypothesis is meagre. Lukoschus (1957) found that the bodies of eight comb-building bees had a mean of ninety-one grains each (range 28-209) and two other bees he thought might have foraged had 378 and 827 grains respectively; however, these amounts resembled those on ten bees (mean of 85 grains; range 30-264) he collected during winter when they were not foraging. We have, therefore, determined the amount and distribution of pollen on the bodies of bees caught: (a) within their hive; (b) leaving their hive; (c) foraging on flowers.

The Relationship Between the Presence of Larval Anisakine Nematodes in Cod and Marine Mammals in British Home Waters

Abstract: The infestation of cod, Gadus morhua (L.), from Scottish waters with larvae of parasitic anisakine nematodes was studied by Rae (1960, 1963). The final hosts of marine species of this subfamily are normally fish-eating vertebrates. In fish, their larvae are commonly found in the internal organs, but two of those occurring in cod, Terranova decipiens (Krabbe) and an undetermined species of Anisakis, are also found in the body musculature where their presence is of concern to the fish food industry and consumers. Previous authors have shown that these two nematodes have, as their final hosts, a wide variety of fish-eating mammals, thus Terranova decipiens is reported from at least eighteen species of Pinnipedia, five species of Cetacea and one species of Mustelidae, whilst species of Anisakis have been recorded from at least twenty-five species of Cetacea and eight species of Pinnipedia. Scott & Martin (1957, 1959) and Templeman, Squires & Flemming (1957) examined the muscles of cod off Eastern Canada for larval nematodes and concluded that the larvae mostly belonged to the species Porrocaecum decipiens (= Terranova decipiens) but between 3 and 6% were Anisakis sp. The distribution of larvae within the cod populations was related to the known distribution of harp seals (Pagophilus groenlandicus), harbour seals (= common seals, Phoca vitulina) and grey seals (Halichoerus grypus). Scott & Fisher (1958a, b) examined these three seal species, common porpoises (Phocaena phocaena (L.) and one white whale (Delphinapterus leucas) for adult nematodes. They considered that only common and grey seals were significant in transmitting larval Terranova decipiens to cod. Mansfield (1968) examined the same three species of seal from the Gulf of St Lawrence and calculated that in this area the relative importance of common seals, grey seals and harp seals to the infestation of cod was 2%, 45% and 53% respectively. In British home waters, Rae (1960) examined cod from the northern areas and related the numbers of larvae that he found to the known breeding sites of grey seals but although he suggested (1963) that all the nematodes he found in a sample of seventeen grey seals from Scotland were Porrocaecum decipiens (= Terranova decipiens), Van Theil (1966) found Porrocaecum decipiens and also Anisakis sp. and Contracaecum sp. in a sample of eighteen seals from the same area. The present study was started because of the marked disparity between the reported number of adult nematodes in seals from Canada and the United Kingdom and to extend the survey done by Rae (1960). In it the distribution of anisakine larvae in British home water stocks of cod was examined further, and the normal populations of gut nematodes

A Preliminary Survey of the Possile Contamination of Lake Nakuru in Kenya with Some Metals and Chlorinated Hydrocarbon Pesticides

Abstract: In many parts of the world the release of persistent chemicals into the natural environment has given rise to various, often serious, detrimental effects on the fauna. Excessive mortality in fish and birds due to pesticides present in industrial effluents, mortality in seed eating birds and birds of prey following the application of chlorinated hydrocarbon insecticides and organomercurials as fungicides in seed dressing operations, and interference with the process of reproduction in birds due to the wide-spread occurrence of certain persistent chlorinated hydrocarbons have been well documented. The amount of information dealing with tropical parts of the world is still rather limited. So far attention has been given primarily to the possible side-effects of chlorinated hydrocarbon pesticides used in tsetse control (Graham 1964; Koeman & Pennings 1970, Koeman et al. 1971) and cotton culture (Everaarts, Koeman & Brader 1971). Aware of the mounting world-wide concern over the environment, a few Kenyan scientists have considered the possible contamination particularly of the 'closed system' Rift Valley Lakes of their country. In many areas, including the catchment basins of these lakes, urban, industrial and agricultural activities have shown a marked increase, which increases the dangers of pollution to the aquatic environments, a danger which could be cumulative as the lakes have no outlet. In the first instance a preliminary study was made of Lake Nakuru.

Aspects of the population dynamics of the weed alopecurus myosuroides huds. in winter cereal crops

Abstract: The winter annual weed Alopecurus myosuroides Huds. (blackgrass) has become prominent in some parts of Britain where continuous winter cereals are grown. Though it is present over much of south-eastern England it is especially prevalent on the heavy soils of Cambridgeshire and Bedfordshire. The distribution does not, however, seem to be correlated directly with soil type but rather with the system of cropping (Brenchley 1913). A. myosuroides has proved resistant to many selective herbicides at concentrations that are not harmful to crop species. A summary of the biological characteristics of this species will appear (Naylor 1972); the present paper is concerned with its population dynamics.

The estimation of the dispersal rate of the adult cabbage root fly (erioischia brassicae (bouche)) in the presence of a brassica crop

Abstract: Dispersal has been defined as any movement away from an aggregation or population (Southwood 1966) and it can result from migration or the 'trivial' movements associated with appetitive behaviour. Migration is usually considered to be a long distance, 'straightened-out' movement which, if successful, results in the arrival of the animal at a new habitat, and the term 'trivial' is applied to short meandering movements limited to one habitat. Greater dispersal is therefore likely to occur as a result of migration than from 'trivial' movements. A behavioural difference distinguishes migrants from non-migrants (Kennedy 1961); the temporary inhibition of the responsiveness of migrants to the 'vegetative' stimuli which finally arrest them separates migratory from 'trivial' movements which are readily interrupted by responses to such stimuli. Only some species of insects show migratory behaviour (see Southwood 1962) and thus there is variation in the innate tendencies of species to disperse. The dispersal of an insecticide-resistant strain of the cabbage root fly (Erioischia brassicae (Bouche)), was studied by Mowat & Coaker (1968). Their first observations indicated that considerable dispersal had occurred and this was attributed to an abnormally dense population and the destruction of the host-crop at the site of origin of resistance. In two subsequent years, the distribution of resistant flies changed only slightly and it was concluded that E. brassicae had little innate tendency to disperse. The assessment of the dispersal rate of a gene for resistance is an indirect method of measuring the dispersal of a wild population of flies and such estimates may be influenced by interfering factors such as the densities of populations in the area under study and the relative fitness of the strains. Experiments were, therefore, undertaken to measure the dispersal of E. brassicae more directly by the release and recapture of marked flies. The results of experiments to estimate its dispersal rate in the presence of a brassica crop are described in this paper.

Ecological regionalization of poplar cultivating in Tonghva rt~Oll of Jiling Province．

Abstract: Hyparrhenia rufa (Nees) Stapf, a grass of African origin, is the only herbaceous plant that prospers under annual burning in the most prevalent type of derived savanna in northwestern Costa Rica. The present account summarizes observations and experiments on the autecology of the grass in this locality. All field records not otherwise specified were made at an annually burned site approximately 8 km north-west of the city of Cailas, in the Province of Guanacaste. The