Showing papers in "Journal of Animal Ecology in 1973"
TL;DR: If the simplest case where the parasite population is specific and synchronized temporally with its host population, the following generalized model for a host-parasite interaction is considered.
Abstract: where NS represents the survivors after Pt parasites have searched for Nt hosts resulting in P+ 1 parasite progenyt. All assumptions about parasite searching behaviour are here contained in the functionf[Pt,Nt]. If we consider the simplest case where the parasite population is specific and synchronized temporally with its host population, we can write the following generalized model for a host-parasite interaction:
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TL;DR: Evidence is presented in favour of the following hypotheses that non-ant-acacia are protected from herbivores by the presence in their foliage of toxic or repellant chemicals; symbiosis with ants has been evolved by antacacias as an alternative means of protection; and chemical defence has subsequently been lost in the ant-acacia, possibly because maintenance of both ant and chemical Defence places an unnecessary metabolic burden on the plant.
Abstract: On the basis of their association with ants, neotropical species of the genus Acacia may be grouped into two broad categories. 'Ant-acacias', comprising less than 10% of the species in Central America depend in varying degree on a mutualistic association with ants of the genus Pseudomyrmex. The plants provide their ants with shelter in swollen stipular spines and with nourishment from foliar nectaries and nutritive structures (Beltian bodies) at the leaf tips. The ants in turn provide for the plants' protection against mammalian and insect herbivores and against neighbouring plant competitors (Belt 1874; Brown 1960; Janzen 1966, 1967). Janzen (1967) has demonstrated that Acacia cornigera (L.) Willd. plants cannot survive after experimental removal of their associated ant colonies. The remaining species of Acacia in Central America comprise the second group, the 'non-ant-acacias'. These plants do not harbour mutualistic ant colonies, nor do they possess the various morphological features of acacias with such colonies. Survival of non-ant-acacias is presumably dependent, therefore, on other means of defence against herbivores. After noting that the foliage of non-ant-acacias was markedly bitter to human taste, whereas that of ant-acacias was mild-tasting, Janzen (1966) proposed the following hypotheses: (i) non-ant-acacias are protected from herbivores by the presence in their foliage of toxic or repellant chemicals; (ii) symbiosis with ants has been evolved by antacacias as an alternative means of protection; and (iii) chemical defence has subsequently been lost in the ant-acacias, possibly because maintenance of both ant and chemical defence places an unnecessary metabolic burden on the plant. In the present paper we present evidence in favour of these hypotheses. For experiments in the laboratory we selected A. cornigera, an ant-acacia, A. farnesiana (L.) Willd., a non-ant acacia, and A. chiapensis Saff., a species showing intermediate characteristics. A. cornigera and A. farnesiana are widely distributed through Central America, but A. chiapensis is very limited in distribution. Plants of A. chiapensis are normally found in nature in association with ant colonies, yet they can survive in the absence of ants; therefore, this species will be regarded as a non-ant-acacia for the purposes of this study. Since insects known to attack unoccupied ant-acacias in Central America were unavailable for our work, the southern armyworm, Prodenia eridania (Cramer) (Noctuidae), was selected for bioassay of the acacias. The caterpillar of this species is highly polyphagous with an outstanding ability to detoxify insecticides (Krieger 1970; Krieger & Wilkinson 1969) and, presumably, toxic compounds encountered in its wide array of food plants
TL;DR: The purpose of this study was to investigate whether the food taken by the house martin was the result of a similar selection of food items from the available resources, and to assess the influence of the abundance and quality of airborne insects and concurrent weather conditions on food selection.
Abstract: This paper describes part of a 3-year study in southern England of the breeding biology of the house martin (Delichon urbica (L.)). The food of house martin nestlings and the relationship between the prey taken and the food available to the aerial feeding adult martins is discussed. Lack & Owen (1955) investigated the food and feeding habits of the common swift (Apus apus (L.)) in southern Britain. The diet of the house martin in Germany has been examined by von Gunten (1961). The study of Johnson (1967) on the food of the purple martin (Progne subis (L.)) in North America notably compared the stomach contents of feeding birds with samples of flying insects. In a fundamentally similar study of the feeding of the brown trout (Salmo trutta (L.)), the stomach contents showed a high correlation with the occurrence of invertebrates in freshwater drift samples (Elliot 1970). This study also demonstrated the phenomenon of diel variation in the predator's diet associated with diel changes in the composition of the available food. The analogous phenomenon of diel changes in the composition of the aerial fauna, associated with differences in flight periodicity of the constituent insects (Lewis & Taylor 1965), results in different food availabilities at different times of day to aerially feeding birds. This emphasizes the necessity for a continuous diurnal sample of both the available food and the diet. Such a sample was collected in this study, which consequently differs in this respect from earlier work on the diet of swallows (Hirundinidae) and swifts (Apodidae). Hespenheide (1971) described the food preferences of a number of insectivorous birds, including several hirundines. He concluded that the average size of prey taken is always larger than that available. Gibb & Betts (1963) also demonstrated selection of larger prey than those generally available by tits (Parus spp.) feeding on lepidopterous larvae in a pine forest. The purpose of this study was to investigate whether the food taken by the house martin was the result of a similar selection of food items from the available resources, and to assess the influence of the abundance and quality of airborne insects and concurrent weather conditions on food selection.
TL;DR: This paper attempts to assess the searching capacity and survival of the predator on lime, and to evaluate the role of the two-spot coccinellid in the regulation of the numbers of the lime aphid.
Abstract: The two-spot coccinellid (Adalia bipunctata (L.)), will feed on a variety of aphid species but is usually associated with those living on trees or shrubs greater than 2 m in height (Putnam 1964; Iperti 1966; Hodek 1966). In Glasgow, larvae of this predator are common on lime (Tilia x vulgaris Hayne), where they feed mainly on the aphid Eucallipterus tiliae and less often on the cicadellid Alnetoidea alneti Dahlbom. A. bipunctata occurs less frequently on sycamore (Acer pseudoplatanus L.), where its effects on populations of the aphid Drepanosiphum platanoides (Schr.) were described by Dixon (1970). The numbers of the lime aphid fluctuate markedly within a season and from year to year (Dixon 1971), but the role of coccinellid predation in these changes is unknown. This paper attempts to assess the searching capacity and survival of the predator on lime, and to evaluate the role of the two-spot coccinellid in the regulation of the numbers of the lime aphid.
TL;DR: The food of gadfly petrels (and shearwaters, Puffinus spp.) was known only by generalizations until Ashmole &Ashmole (1967) examined the feeding ecology of Procellariidae, Phaethontidae (tropic-birds) and Sterninae (terns and noddies) on Christmas Island in the central Pacific Ocean.
Abstract: Although the ecology of several species of Procellariidae (petrels, shearwaters and fulmars) has been studied by many ornithologists, of the eleven genera only Fulmarus, Puffinus and Pachyptila have received much critical attention; Pterodroma, which comprises more species than any other genus in the family, has been little studied. This is because Pterodroma is an oceanic genus breeding in the tropics, sub-tropics and southern hemisphere in places difficult of access such as remote islands. In common with most pelagic birds the food and feeding habits of gadfly petrels (Pterodroma spp.) are known only vaguely (see Ashmole 1971). A number of authors have recorded food remains obtained from petrels they handled. Often stomachs were empty but for digestion-resisting fragments of cephalopod beaks and eye lenses, fish bones, crustacean exoskeleton or pieces of stone or pumice. This situation seems to result from rapid digestion combined with infrequent feeding. The following information applies to Pterodroma only; comparisons with some other genera are made in the discussion. Cephalopods have been reported in the diet of P. m. macroptera (Smith), P. m. gouldi (Hutton), P. cooki (Gray), P. leucoptera (Gould), P. neglecta (Schlegel), P. cahow (Nichols & Mowbray), P. lessoni (Garnot), P. solandri (Gould), P. brevirostris (Lesson), P. mollis (Gould) and P. phaeopygia (Salvin) (Sladden & Falla 1928; Oliver 1930, 1955; Falla 1934, 1937; Palmer 1962; Mougin 1969; Harris 1970; Serventy, Serventy & Warham 1971; Wingate 1972). Fish are eaten by P. inexpectata (Forster), P. phaeopygia, P. solandri and P. mollis (Kuroda 1955; Pocklington 1967; Harris 1970; Serventy et al. 1971). Crustacea are taken by P. macroptera gouldi, P. neglecta, P. phaeopygia, P. brevirostris and P. cahow (Sladden & Falla 1928; Oliver 1930; Larson 1967 per Harris 1970; Mougin 1969; Wingate 1972); those eaten by P. cahow include a small scarlet shrimp (Palmer 1962). Other pelagic organisms have been noted among food of P. macroptera gouldi and P. phaeopygia which took pteropods (Oliver 1930; Loomis 1918 per Harris 1970). But none of these workers was able to analyse the composition of the food or to identify food items to a lower level. Thus the food of gadfly petrels (and shearwaters, Puffinus spp.) was known only by generalizations until Ashmole & Ashmole (1967) examined the feeding ecology of Procellariidae, Phaethontidae (tropic-birds) and Sterninae (terns and noddies) on Christmas Island in the central Pacific Ocean. The petrels they studied were the phoenix petrel (Pterodroma alba (Gmelin)) and the Christmas Island shearwater (Puffinus nativitatis Streets). Detailed comparisons of their findings with mine are made in the discussion. In their analysis of samples from Pterodroma alba they identified several
TL;DR: This paper quantifies certain aspects of the interaction between B. hebetor and Cadra cautella (Walker) and examines the importance of these factors in the population dynamics of the parasite.
Abstract: Studies of the dynamics of insect populations are often concerned with the interaction between a host and its parasite or predator, potential agents of biological control that may contribute significantly to host mortality in a natural population. Early attempts at modelling the host-parasite inteiaction were confined to simplified situations where other host mortality was neglected; Nicholson(1 933) and Nicholson & Bailey (1935) emphasized the importance of parasite searching efficiency, and Thompson (1922, 1939) considered the fecundity of the parasite to be most important; models have recently been reviewed by Royama (1971). Life tables are often prepared for the host population (Harcourt 1969) but only rarely for the parasite; Varley (1970) stressed the need for these. While the ability of the parasite to find the host may be important for the host population, so is the effect of the host on the dynamics of the parasite population. Three aspects of these relationships have been extensively studied: (1) the parasite's ability to detect and accept a suitable host; (2) the degree of synchronization between host and parasite life cycles (Fisher 1971); and (3) the ability of the host to resist attack by the parasite and the ability of the parasite to escape the defence reactions of the host (Salt 1970). The majority of studies, however, have been confined to endoparasites where often only one parasite can develop to maturity in a single host. In gregarious parasites, varying numbers of progeny are able to survive in a single host and parasitism may be internal (e.g. Apanteles glomeratus (L.)) or external (e.g. Bracon hebetor Say). More parasite progeny per host can lead to their increased mortality, reduced size, and changes in their sex ratio. The effects of superparasitism on mortality, size and sex ratio (Narayanan & Subba Rao 1955; Chacko 1964; Wylie 1966a, b; Shiga & Nakanishi 1968a, b) have been studied but not from the point of view of population dynamics. This paper quantifies certain aspects of the interaction between B. hebetor and Cadra cautella (Walker) and examines the importance of these factors in the population dynamics of the parasite.
TL;DR: This study compares the two colony structures of obligate acacia-ants and discusses some of the ways in which such a difference influences the mutualistic interaction between ants and acacias.
Abstract: Central American obligate acacia-ants (Pseudomyrmex spp.) have either monogynous (single-queen) or polygynous (multiple-queen) colonies, depending on the species of ant. This study compares the two colony structures and discusses some of the ways in which such a difference influences the mutualistic interaction between ants and acacias. I also examine some of the selective pressures for the evolution of polygynous colonies from monogynous ones. Polygyny has not been previously recorded for obligate acacia-ants (but the Pseudomyrmex in Tachigalia is polygynous (Wheeler 1921)) and, as an ecological phenomenon, has received almost no attention. Ant and acacia obligatory mutualism has been discussed by Janzen (1966, 1967a, b, 1969, 1973), Hocking (1970) and Monod & Schmitt (1968), and is not the primary focus of this study.
TL;DR: Measurements of the pepsin-soluble content of several grasses at different times of year are presented, in parallel with changes in weight, body composition and breeding condition of voles from isolated populations in two types of habitat-ungrazed limestone grassland and a young plantation.
Abstract: The short-tailed vole, Microtus agrestis (L.), is found primarily in grassland, where it feeds chiefly on the green leaves and stems of various grasses (Godfrey 1953; Hansson 1971). Its population dynamics have been studied in detail in Britain by Chitty and his co-workers (Chitty 1952; Godfrey 1955; Chitty & Chitty 1962a; Chitty & Phipps 1966) and quantitative estimates have been made of its food supply (Chitty, Pimentel & Krebs 1968; W. N. Charles unpublished). Hitherto, however, little attention has been paid to the qualitative changes which occur during each year in the various grasses eaten by Microtus. This paper presents measurements of the pepsin-soluble content of several grasses at different times of year, in parallel with changes in weight, body composition and breeding condition of voles from isolated populations in two types of habitat-ungrazed limestone grassland and a young plantation. It will be shown that grasses have maximum pepsin solubility for only a short period in the year, and that most growth and reproduction of M. agrestis occurs outside this period; that the pepsin solubility of the grasses has little direct effect on the timing of changes in weight of different body components (except that the spring weight increase in males coincides with the spring flush of grass), and that in the area studied Microtus carries no appreciable energy reserve at any time of year.
TL;DR: It has been shown that there is a change in the feeding habits of Leptopterna dolabrata (L.) during the later part of its life-cycle, apparently correlated with the maturation of the gonads, a period when nitrogen demand is high.
Abstract: Recent studies on insect herbivores have increasingly shown the effects of food quality on insect populations (e.g. Feeny 1970; Dixon 1966, 1970; Way & Cammell 1970; van Emden 1966). The problems facing herbivores in utilizing plant materials as food have been reviewed by Morowitz (1968) and Southwood (1972). It has been shown (McNeill 1971) that there is a change in the feeding habits of Leptopterna dolabrata (L.) during the later part of its life-cycle, apparently correlated with the maturation of the gonads, a period when nitrogen demand is high. The rOle of food in the population dynamics of this population was therefore further examined. The life-cycle of the insect and a description of the experimental area have already been published (NcMeill 1971). The life-cycle of the nymphal parasite Leiophron pallipes Curtis (Hymenoptera: Braconidae) has been studied by Loan (1965), and is shown in Table 1.
TL;DR: Measurements and experiments on air flow through mounds of Macrotermes subhyalinus (Rambur) (formerly known as M. bellicosus), were done on the Serengeti Plains, Tanzania, during the months of September and October 1969, and the effect of this air flow on the thermal, mineral and water budgets of the mounds is assessed.
Abstract: Accumulations of mineral salts such as calcium carbonate in certain African termite mounds (Hesse 1955; Milne 1947; Watson 1962,1967; Weir 1969,1972; Wild 1952) are of considerable ecological and agricultural importance in savanna grasslands and other areas, though the mechanisms which lead to them remain uncertain. In some cases the mound is a mass of subsoil raised above ground level by the termites (Hesse 1955), and if the subsoil is mineral-rich the mounds will be also. The chemical composition of termites and of fungus gardens has been analysed and discounted as a source of minerals (Hesse 1955), though it has since been shown that fungus comb may be consumed and replaced by termites very rapidly (Grasse & Noirot 1958a; Sands 1969). The upward movement of water through the soil (Milne 1947) was shown not to be primarily responsible for mineral accumulation in two mounds in Rhodesia (Watson 1969). Measurements and experiments on air flow through mounds of Macrotermes subhyalinus (Rambur) (formerly known as M. bellicosus), were done on the Serengeti Plains, Tanzania, during the months of September and October 1969, and the effect of this air flow on the thermal, mineral and water budgets of the mounds is assessed.