Showing papers in "Journal of Animal Ecology in 1972"

Random search and insect population models

Abstract: Population models for host-parasite interactions attempt to describe the outcome of parasite search by making simple assumptions about the way in which parasites find their hosts. Parasite behaviour is often described by precise mathematical equations, which may or may not have any biological validity. In most models, parasites are assumed to oviposit or search at random, and their success is calculated from equations of the type:

East African mammals : an atlas of evolution in Africa

Abstract: Kingdon's remarkable seven-volume masterwork on East African mammals concludes with two volumes on the bovids, placing them in a broad comparative, ecological, and evolutionary context. Volume IIIC covers cattle, water buffalo, kudus, elands, dwarf antelopes, duikers, reedbucks, and waterbucks; IIID covers gazelles, impalas, wildebeests, oryxes, sheep, and goats. In addition to the stunning, lifelike drawings that are an integral part of the text, the volumes include a reappraisal of bovid taxonomy and original analyses of the form and function of body shape and size, horn shape, coat pattern, and tooth structure.

Feeding niches of hummingbirds in a Trinidad valley

Abstract: A number of detailed studies of the feeding ecology of tropical hummingbirds have appeared in recent years (e.g. Wolf 1970; Young 1971 ), and field work is in active progress, especially in Central America. So far, however, there seems to have been no attempt to survey the feeding habits of all the hummingbird species in an area of rich tropical forest. Wagner (1946), discussing the feeding habits of Mexican hummingbirds, concluded that in the more severely seasonal environments (such as the Mexican highlands, where he made most of his observations) hummingbirds rely to a very large extent on insect food, and that it is only in the more equable tropical regions that they depend mainly on nectar. Consonant with this, he found no close correlation between the size and shape of the beaks of the Mexican species which he studied and the flowers at which they fed, and he postulated that close matching of hummingbird beaks to flower form is to be expected only in the humid tropics. In a more recent discussion Grant & Grant (1968) were able to add little so far as tropical species were concerned, beyond citing Skutch's observation of an apparently adaptive relationship in Costa Rica between Passi.flora vitifolia* and the hummingbird Phaethornis superciliosus, * the only locally-occurring species with a beak long enough to reach its nectar. It is still mainly a plausible assump­ tion that the various sizes and shapes of hummingbirds' beaks are adapted to taking nectar from flowers of similar size and shape. While we were resident in the Arima Valley in the Northern Range of Trinidad, at latitude 10° 40' N, we kept records of the feeding behaviour of all the hummingbirds seen in the valley. Records were kept systematically from February 1959 to September 1961, with the main concentration of effort during the last 14 months of this period. Observations were made intermittently, often between spells of observing other kinds of birds. They were not recorded systematically until we had been living in the valley for eight months (B.K.S.) and two years (D.W.S.). Hence it is felt that the disadvantage of their being somewhat haphazard is compensated by the fact that we were thoroughly familiar with the valley and its vegetation, and so were unlikely to have missed any of the important food plants of the main hummingbird species. The Arima Valley, which extends for several miles from the lowlands to a pass at 1800 ft (550 m) at the watershed of the range, consists of primary forest, patches of secondary forest, small holdings, patches of citrus and other fruits and larger areas of cocoa and coffee. The cocoa is cultivated under shade trees, mainly the introduced immortelle (Erythrina micropteryx) (native to the Andes), an important source of nectar for many hummingbirds. Nearly all our records were obtained from the lower part of the valley, between about 400 and 800 ft (120-250 m). A few were from similar country

Some Factors Affecting Food Intake and Selection in White-Fronted Geese

Abstract: It has been shown that most grazing animals are selective in their feeding and that selection can be exercised at different scales. In sheep, for example, there are definite preferences, as measured by the length of time spent on each, for different sward types on hill land (Hunter 1954). On a smaller scale Stapledon (1953) showed that sheep selected particular grass species when given a choice on free range, and Arnold (1960a) demonstrated selection of certain plant parts in relation to their nitrogen and fibre content. Geese select their wintering haunts partly on the basis of their isolation from disturbance and freedom from snow cover. It has already been shown (Owen 1971) that wintering white-fronted geese (Anser a. albifrons Scopoli) select particular vegetation zones within a salting pasture. This paper examines the factors which must be taken into account when considering their selection on a smaller scale. The term 'small scale' includes the selection of particular plant species or parts of plants within a sward. The work is part of a study of feeding ecology carried out over three seasons, 1968-69, 1969-70 and 1970-71 on a flock of up to 7600 European white-fronted geese which spend the period between early November and early March at Slimbridge, on land surrounding the Wildfowl Trust enclosures. Most of the observations were made while the birds were feeding on a salting of approximately 40 ha known as the Dumbles. This area is particularly suitable for feeding behaviour studies as it is favoured by the geese throughout the winter and is overlooked by observatories on the landward edge. The vegetation of the Dumbles can be separated into zones, related to the saltmarsh succession. The Hordeum zone, on the landward (highest) side is characterized by an abundance of Hordeum secalinum Schreb. The Lolium zone, at a slightly lower level has abundant Lolium perenne L. and Agrostis stoloniera L. This gives way to the Agrostis zone with a predominance of Agrostis stolonifera and Puccinellia maritima (Huds.) Parl., which is the lowest grassed area. The Festuca zone is characterized by the abundance of Festuca rubra L. and occupies well-drained sites on the estuary side. Single clone circular patches of Juncus gerardii Lois. occur on the edge of Agrostis and Lolium areas. These make up the Juncus zone. A fuller description of the vegetation is given in Owen (1971). Food selection is a time consuming process and must be balanced against the ability of the animal to ingest sufficient food in the time available. In other words, it is inefficient to select a diet of 100/ better quality if total food intake is thereby reduced by more than 1000. Thus the factors affecting food intake are considered before selection is discussed.

Some factors involved in the selection of vegetable substrate by Atta cephalotes (L.) (Hymenoptera: Formicidae) in tropical rain forest

Abstract: The leaf-cutting and carrying activities of ants of the genus Atta have aroused considerable interest, and many authors have drawn attention to the wide range of plant material used by them (Wheeler 1907; Beebe 1921; Schomburgk 1922; Eidmann 1935; De Souza 1965; Cherrett 1968a; Cherrett & Sims 1968). Despite this seeming catholicity of taste, however, most authors have recorded some evidence of selectivity, whilst Belt (1874) and Beebe (1921) have suggested that introduced plants are more favoured by the ants than are indigenous ones, and Nelson (1951) has pointed out that the tenderest portions of the plant are the most sought after. In the light of these observations, studies were made in Guyana on the substrate being carried into a single colony of A. cephalotes (L.) in tropical rain forest, in an attempt to assess the types of materials utilized, and the physical characteristics of these when compared with the physical characteristics of the vegetation at large. The data were collected during 10 weeks of field work in 1963, and the study nest and study area have been fully described (Cherrett 1968a).

The Vertical Distribution and Feeding Relationships of Intertidal Fish on the Atlantic Coast of France

Abstract: The ecology and vertical distribution of many sessile littoral species is well known, but relatively little information is available regarding the intertidal fishes. The few papers that are wholly or partially concerned with this subject are those of Le Danois (1913) on the French coast, Gosline (1965) in Hawaii, Porumb & Porumb (1968) in the Black Sea, Zander (1967) in the Red Sea, Sasaki & Hattori (1969) on Japanese shores, and Abel (1962), Gibson (1968) and Casabianca & Kiener (1969) in the Meditterranean. The subject of the biology and behaviour of littoral fish in general has been reviewed recently by Gibson (1969). This paper presents the results of a detailed quantitative investigation into the distribution and feeding relationships of shore fish carried out in June and July 1969 in a limited area on the Atlantic coast of France.

Seasonal and Inter-Specific Variation in Major Components of the Gut Contents of Some Woodland Collembola

Abstract: The biotic relationships of organisms living in the soil have a great influence on the twin environmental processes of nutrient cycling and energy flow and have been subject to considerable study. Despite this fact many aspects of soil biology, especially the trophic interrelationships of the several hundred species of arthropods which may be found in a square metre of soil are little understood. In particular, little is known of the feeding biology of the Collembola (Insecta: Apterygota) which maintain populations of many thousands of individuals/M2 in nearly all soils. Although their total biomass is low (Hale 1966; Healey 1970) these large populations must play some part in soil processes, although perhaps a peripheral one (Macfadyen 1963). Several studies suggest that the gut contents of Collembola species living together in a habitat may have a very similar appearance (e.g. Poole 1959; McMillan & Healey 1971) and that differences in gut contents between the same species in different habitats may be greater than that between different species within one habitat (Gilmore & Raffensperger 1970; Bodvarsson 1970). This, together with the presence in the guts of many species of obviously indigestible material, such as large mineral particles (Poole 1959; B6dvarsson 1970) has suggested that the Collembola are unspecialized and indiscriminate feeders. However, this apparent ability of large numbers of detritivore species to coexist in a habitat while utilizing identical or very similar food resources is in conflict both with general ecological theory (de Bach 1966; Slobodkin, Smith & Hairston 1967) and with experience with other animal communities (e.g. Reynoldson & Davies 1970) which suggests that groups of related species sharing habitats usually evolve food differentiation. This paper describes a technique intended to provide a quantitative basis for the analysis and interpretation of collembolan gut contents and is part of a programme of work designed to investigate the basis of coexistence of detritivore species.

The effect of supplementary food on a population of wood mice(Apodemus sylvaticus).

Abstract: Previous work at Oxford has shown that the amount of natural food available to wood mice (Apodemus sylvaticus (L.)) influences their quality and survival. Smyth (1966) showed that breeding in winter often followed a good acorn crop, and Watts (1970) demonstrated that the provision of food for a field population could advance the start of the breeding season by at least 2-3 weeks. Populations of Apodemus are known to exhibit a high density over winter which declines over summer and then increases through the autumn (e.g. Miller 1958; Bergstedt 1965; Crawley 1970). Watts (1969) analysed these changes over a period of 18 years from trapping records in one area of woodland and concluded the following.

Chick Survival in Terns (Sterna Spp.) with Particular Reference to the Common Tern

Abstract: The differential survival of young birds within a brood prior to fledging occurs in many bird species. This phenomenon is particularly common in raptors, storks and corvids where it has been well documented (e.g. Schmaus 1938; Schuiz 1942, 1957; Lockie 1955), but it also occurs in various other species. This differential survival within a brood reflects the asynchronous hatching of the eggs which occurs when the parent bird commences incubation before the clutch is complete. It has been suggested that this asynchronous hatching is an adaptation to a variable food supply (Lack 1954, 1966), so that if the parents find difficulty in obtaining food for all their brood, food will go to the first hatched and largest nestlings which are higher in the peck order. Only when food is plentiful and the first chicks become satiated do the smaller and weaker chicks obtain food. When the food supply is limited, the last hatched chicks soon starve to death, so that food goes only to the survivors and is not wasted. Asynchronous hatching occurs in terns, and differential survival of chicks within a brood was found during a study of the breeding biology of the common tern (Sterna hirundo L.), Arctic tern (S. paradisaea Pontopp.), roseate tern (S. dougallii Montague) and the sandwich tern (S. sandvicensis Latham). In all four species, the survival of single chicks and first chicks from broods of two or three tended to be similar within a species. However, second chicks from broods of two and three had a lower fledging success and this was much lower still in third chicks. Since differential fledging success was most marked in broods of three, it was decided to examine chick mortality in the common tern where this brood size was most frequent. During this investigation carried out on Coquet Island, 55038' N, 01037' W, from 1965 to 1967, inclusive, about 59?4 of the common terns laid three eggs, 37Y/. two eggs and 4XO one egg. Normally, the second egg in a clutch of two hatches half a day after the first, but in a clutch of three the first and second eggs hatch closer together whilst the third egg hatches about 2 days later. The demands of the brood and the parental care were examined to detect the method by which this differential mortality occurs in common tern chicks.

Dispersal and quality in populations of cicadulina species (cicadellidae)

Abstract: Cicadulina species are found in grasses in many parts of the tropical and warm temperate parts of the world. Ruppel (1965) recognizes thirteen different species and most of these are of economic importance, either confirmed or suspected of being vectors of plant diseases. Five species have been shown to be vectors of miaize streak, a disease which is a cause of crop losses in eastern and southern Africa (Nielson 1968). Three of these, C. mbila (Naude), C. parazeae Ghauri, and C. storeyi China are the principal vectors of the disease in Rhodesia (Rose 1963). Field observations have indicated that Cicadulina leafhoppers fly two very different kinds of distances. Many fly only a few metres and there is a sharp fall in numbers captured on trap plants with distance from the edge of a breeding source. During the main flight season, however, Cicadulina are captured in suction traps 20 m above the ground and there is widespread invasion of cereal crops by leafhoppers dispersing from low density populations in drying grasses. These two levels of dispersal are also indicated by the differences in the patterns of streak disease which are found during the main flight period in the dry season and on irrigation areas in the summer (Rose 1971). Although these patterns are partly explained by increases in numbers of Cicadulina emerging from grasses at the end of the summer, they may also be due to changes in quality of populations within the grasses. Changes in qualities such as size, wing length, colour and activity are known to be caused in populations of many different insects as responses to effects produced by the environment (Uvarov 1921; Faure 1932, 1943). The mass of information that has been collected on morphological and behavioural polymorphism is thoroughly discussed by Johnson (1969) who stresses its significance as it affects the dispersal of insects. He concludes that it 'seems that the proportion of migrants in a population may be determined not only by ontogenetic effects produced by adverse changes or associated token stimuli in the environment but also by selection from particularly vigorous females from one generation to another'. A laboratory method was required in order to find out more about the conditions that affect flight and flight duration in the three Cicadulina species. Flying Cicadulina tethered to pins proved to be satisfactory.

The Distribution and Habitat Range of the Brackish Water Cockle (Cardium (Cerastoderma) glaucum) in the British Isles

Abstract: The distribution of the most common cockle Cardium (Cerastoderma) edule (L): of the British particulate shores is well known and is extensively documented (Wright 1926; Stephen 1931; Newell 1954; Cole 1956; Plymouth Marine Fauna 1957; Millport Marine Fauna 1962; Dale Fort Marine Fauna 1966; Hancock 1967, etc.). Factors which restrict the occurrence of this cockle, however, have received little attention. Even less detailed information is available concerning the habitats occupied by its sibling C. (C.) glaucuml for it is only recently that the specific status of this latter cockle has been fully recognized. Initial separation between C. edule and C. glaucum on morphological grounds (H0pner Petersen 1958; Tebble 1966; Boyden 1971a; Russell 1972) has been vindicated by evidence of reproductive isolation (Boyden 1971b), by differences in behaviour and physiology (Boyden 1972) and from studies of the geographical distribution of the two cockles (Russell 1971). In this paper we have investigated the ecology and distribution of C. glaucum in the British Isles and have compared its habitat preferences with those of C. edule.

The Effects of the Variability of Cattle Dung on the Multiplication of the Bushfly (Musca vetustissima Walk.)

Abstract: During the summer months bushflies are found over most of Australia, but in winter they disappear from the cooler (southern) third of the continent (Hughes 1970). Norris (1966) described the seasonal cycle of the bushfly in the Canberra district, in S.E. Australia. In this region there is generally a more or less unimodal population curve from October to May, but the abundance of the flies decreases markedly in late January and remains lower thereafter throughout a period of apparently still favourable temperatures. As Norris was able to show that cattle dung was the most important breeding site for the bushfly, he discussed the possibility that seasonal changes in the quantity and quality of forage in late summer would affect the dung and so have an important effect on bushfly breeding. Profound effects on the success of bushfly breeding were found in experiments using dung from different pasture and management regimes during the 1967 drought (Hughes & Walker 1970). In the field, changes in cattle dung consistency and texture are readily discernible through the spring and summer. When grazing pastures consisting predominantly of new spring growth, cattle 'scour', voiding dung that is very liquid, rich, and homogeneous. When the new growth emerges through standing winter grass the dung is thicker but is still amorphous, moist and rich. As pastures mature and vegetation becomes more fibrous, dung becomes less uniform in texture and has a stiffer consistency. On 'hayedoff' pasture, dung is composed mostly of undigested plant fibre. Being stiff and dry in consistency it forms high mounds on the ground that may persist for several years (Bornemissza 1960). The present paper reviews the composition and formation of cattle dung, indicating possible causes of the variation. It then describes the collection and analysis of dung from different localities and times of year, and assays of the effect of dung variations on bushfly population biology.

Control and significance of the seasonal development of colour forms in the sycamore aphid, drepanosiphum platanoides (schr.)

Abstract: In spring and summer alate virginoparae of the sycamore aphid are present but with the onset of autumn apterous oviparae and alate males appear. These mate, and the oviparae lay the overwintering eggs. This polymorphism is controlled by the aphid's response to changes in its environment (Dixon 1971). In addition to this polymorphism there are changes in the background colour of the aphid. Adult aphids of the spring and autumn generations have black bands on their abdomen and are generally darker in colour. In addition to this pigmentation of bands of the cuticle the body fluids and tissues range in colour from green to red. As the abdominal sclerites are transparent, except in the areas that are melanized, the aphid has a green or reddish ground colour. Aphids with a reddish ground colour are the rarer and they first appear in summer. The aim of this paper is to determine what factors in the sycamore aphid's environment regulate the appearance of the reddish and melanic forms and to discuss the adaptive significance of these forms.

Distribution Patterns and Population Dynamics of the Micro-Arthropods of a Desert Soil in Southern California

Abstract: Work on the soil fauna of hot deserts has been primarily of an autecological or physiological nature up to the present. Emphasis has been placed on animals of relatively large body size, such as burrowing rodents (Missone 1959; Kirmiz 1962; Schmidt-Nielsen 1964; MacMillen & Lee 1967), woodlice (Edney 1968; Warburg 1968) and insects (Bodenheimer 1953; Leouffre 1953; Cloudsley-Thompson & Chadwick 1964; Edney 1967). Apart from the work of Krivolutski (1968) in U.S.S.R. and Wood (1971) in Australia, very little information is available about the ecology of desert micro-arthropods, or about the way in which the various species populations are integrated into a community system. Such a system is likely to be a simple one in view of the severe limitations imposed by the physical factors in the environment, and the present study was designed not only to identify the principal faunal components of a desert soil community, but also to investigate distribution patterns and population dynamics in relation to certain welldefined factors, such as temperature, moisture, shade and food supply.