Food In Summer Research Articles

Effects of Variations in the Availability of Food and Home Sites and of Culling on Populations of House Mice Housed in Out-Door Pens

In field populations of house mice (Mus musculus) seasonal and year-to-year variation in numbers are usually attributed to variations in the availability of food and home sites, and the effectiveness of agents affecting life-spans. Variations in numbers similar to those observed in the field also occurred in a mouse population housed in an out-door pen in which the number of home sites was limited but food supplies were abundant but these variations were due to seasonal variations in the effectiveness of self-regulating mechanisms. To examine the effects of food supply, amount of shelter and of one agent affecting life-spans (culling) on mouse numbers in confined populations, numbers were monitored in a control pen and in three experimental pens in which food supply was halved, home sites were doubled and mice were culled at four weekly intervals. The effects of the treatments were followed for four and a half years. Although supplies of food and shelter remained constant throughout the study, mouse numbers in the control pen were high in summer and low in winter and the heights of the summer peaks varied from year to year. Halving the amount of food available reduced the mean size of the population by 37% by reducing numbers in summer. Doubling the number of home sites increased mean size by 13% by increasing numbers in winter. Culling about 60% of the mice at monthly intervals reduced mean size by 13%. All experimental treatments reduced the amplitude of the seasonal fluctuations and between-year differences in the heights of the summer peaks. In the control pen more young were recruited in summer than in winter. Halving the amount of food available reduced the numbers recruited in summer by increasing the number of pups dying between birth and weaning. Doubling the number of home sites and culling increased the numbers recruited in spring, summer and autumn by increasing the number of females breeding. These increases were associated with decreases in the mean sizes of the populations living in the home sites. In the control pen the mean life-spans of the males and females which survived until they were weaned were 4.9 and 6.4 months respectively. Halving the amount of food available had no effect on mean life-spans but doubling the number of home sites reduced them significantly. It was concluded that self-regulating mechanisms continued to affect numbers in all three experimental pens but that numbers were also affected by the availability of food in summer in both the pen in which food supplies were reduced and the pen in which the number of shelters was doubled. It was also concluded that although mouse numbers were reduced by culling, the indirect effects of this treatment on recruitment tended to compensate for its direct effect on numbers.

Effects of Food Quality on Isopod Population Dynamics

1 Growth and survival of juvenile Armadillidium vulgare (Latrielle) in the laboratory were greatest on a diet of an excess of freshly fallen leaves from dicotyledonous plants but decreased with decreasing supply of this food, even though alternative lower quality foods were provided in excess. Growth in the laboratory was positively related to temperature but mortality was not clearly related to temperature over the range observed in the field. 2 Growth and survivorship of a field population on a Breckland grass heath are described for a 2-year period during which density declined from 673m-2 to 102 m-2. The demand for high-quality food by the field population peaked during a period of rapid growth in spring and early summer when supply of leaf litter from dicotyledonous plants was at a minimum. Litter production peaked in autumn after isopods had finished breeding and when low temperatures reduced their consumption rates. 3 Competition for high-quality food in spring and early summer during this period could have reduced growth and survivorship sufficiently to account for the observed decline in population density. 4 A simulation model, based on laboratory observations, closely predicted the observed decline in the field population. Further simulations also predicted the higher population densities observed in the field before this study and also the lower equilibrium densities found on the site since the study. Key-words: Population dynamics, competition, food quality, woodlouse, Armadillidium vulgare, densitydependence, growth, survivorship, consumption * Present address: Dr S.P. Rushton, Department of Agricultural Biology, The University, Newcastle-uponTyne NEl 7RU, UK. Introduction The role of food quality in the population dynamics of herbivores has been intensively studied and its importance in limiting populations widely recognized (Lawton & McNeil, 1979; Crawley, 1983; Dempster, 1983). In contrast, the influence of food quality on the population dynamics of decomposers has received little attention. As most decomposers have a broad range of diet and dead organic material is relatively abundant in most ecosystems, it is often assumed that detrivores are surrounded by an abundance of suitable food. For this reason Warburg, Linsenmair & Bercovitz (1984), in a comprehensive review, suggest that food is not important in influencing population fluctuations of terrestrial isopods; instead they propose that the dynamics of isopod populations are primarily controlled by climatic variables, such as temperature and humidity, since these strongly affect growth, survivorship and reproduction of isopods. Growth and survivorship are also importantly influenced by food quality, as demonstrated for Armadillidium vulgare (Latreille) by Cromack (1967) and Merriam (1971). The quality of isopod foods in the field shows much variation (Hassall & Rushton, 1984) but this would not limit isopod populations if optimal quality foods were always present in excess. However, populations could be adversely affected by either a shortage of the best quality foods or by a temporal separation in supply and demand of optimal food as is the case for herbivores in the African savannah (Sinclair,

Food composition and zooplankton selection by smelts, Osmerus eperlanus L., in Lake Tyrifjorden, Norway

Stomach analyses were carried out on 80 - 160 mm long smelts sampled monthly from May 1976 to September 1977. The amount of food was lower from February to April than during the rest of the year. Zooplankton dominated the smelts' food from July to February, while zoobenthic insect larvae and nymphs were more important from March to June. Cladocerans were prefered to copepods during most of the year. From July to April cladocerans made up from 30 to 95% of the diet, while 10 to 60% of the smelts' food in spring and summer consisted of copepods. Benthic copepods occurred in the stomachs almost troughout the year. Daphnia galeata and Bosmina longispina were the most important species in the smelts' diet and they were positively selected, together with Leptodora kindti, Bythotrephes longimanus and Heterocope appendiculata. The most common copepods in the zooplankton, Eudiaptomus gracilis, was negatively selected by the smelts.

Comparative feeding and breeding strategies of a sympatric pair of leopard frogs (Rana pipiens complex)

AbstractOvary weight and fat body weight relative to total body weight were ascertained from samples of Rana magnaocularis and Rana forreri taken routinely from sympatric populations of the two species. Relative fat body weight reaches a maximum in R. forreri in October and November, about 2 months later than in R. magnaocularis (August and September). Relative ovary weight in R. forreri reaches a maximum in July and August, some 8 to 9 months after the fat body peak. In R. magnaocularis, in contrast, maximum relative ovary weight occurs in November, December, and January, only about 2 to 4 months later than the fat body peak. Both species may capitalize on abundant food in late summer to increase fat storage. Maturation of the ova and the laying of eggs are almost completely asynchronous for the two species, however. These differences are considered from the standpoint that they may represent an example of reproductive character displacement via temporal competitive exclusion.

A comparison of the feeding biology of Mink Mustela vison and otter Lutra lutra

The feeding habits and prey selectivity of Mink Mustela vison and otters Lutra lutra were compared in two localities in Devon: a eutrophic lake and a moorland river, in which both species occurred and had access to the same prey populations. The effects of prey availability on the predators' diets were assessed by comparing prey consumed, as revealed by scat analysis, with estimates of prey abundance and size range. Otters specialized in fish at all times of year but showed seasonal variation in species taken. Selection for slow‐moving fish and seasonal changes in behaviour of some fish species were the probable causes of this variation. Otters diversified more into non‐fish food in summer, when fish availability was reduced. The main alternative prey in the lacustrine habitat was waterfowl, but in the riverine habitat, rabbits. Mink were more generalized carnivores, taking a variety of fish, waterside and terrestrial prey in all seasons. These three prey categories were taken to an almost equal extent in the lake but terrestrial prey dominated in the riverine habitat. Fish were taken most frequently in winter and birds and mammals in summer. Neither predator showed selection in respect of prey size. In each area, about one third of the otter and Mink diets was common to both species. Fish was the principal group of the shared component, and dietary overlap in respect of them was greatest in autumn and winter. In view of the dietary preferences of each predator, the existence of alternative prey items and limited degree of dietary overlap, it is considered unlikely that the two species competed for food to any extent. Other factors must therefore be responsible for the spread of feral Mink and the decline in otter populations in many parts of Britain.

Population Dynamics, Bioenergetics, and Role of Lepidostoma Quercina Ross (Trichoptera: Lepidostomatidae) in an Oregon Woodland Stream

The aim of this study was to gather quantitative field and laboratory data on the utilization of deciduous leaves as food by Lepidostoma quercina Ross (Trichoptera: Lepidostamatidae) and estimate the effect of this food processing on the stream ecosystem. Samples were taken monthly in a riffle—pool section of Berry Creek, Benton County, Oregon. Maximum larval density was 382 per m2, instantaneous growth rate was 2.7% per day, instantaneous mortality rate was 1.4% per day, and production was 0.19 g·—2·—1. The life cycle of L. quercina and its period of maximum larval growth correspond closely with the period of maximum availability of its prefered food (alder leaves) in the stream. Consumption and fecal production rates were measured gravimetrically. Rates (mg·—1·—1) increased with temperature, food quantity, and conditioning time of the leaves, and decreased with increased size of the larvae. Mean respiration rates of larvae were higher at 10°C than at 5°, but there was no significant difference in mean rates at 10, 15, or 20°C. Respiration rate decreased with increased size of the larvae. Size—specific respiration rates showed regulation of respiration with respect to temperature for small individuals (present in the field in September and October when temperatures are variable) and little or no regulation by large individuals (present in December and January). Stimulation modeling of larval growth based on laboratory data demonstrated that growth and production of L. quercina in the field may be limited by a lack of high—quality food (alder leaves) in late summer and early fall. Consumption of leaves by the simulated population was estimated as 3.1 g·—2·—1. Lepidostama quercina comprised only a small part of the secondary production in Berry Creek (0.19g·—2·—1, vs. 2.2 g·—2 for simuliids) and processed only a small portion of the allochthonous input to the stream. However, significant quantities of fecal material were produced and it was estimated that these fine particle would be sufficient to support ¼ to ½ of the production of simuliids, the dominant riffle species in Berry Creek.

Some effects of food and water deprivation on metabolism in black-tailed prairie dogs, cynomys ludovicianus

1. 1. Prairie dogs deprived of food and water at normal room temperatures can survive for long periods (without apparent ill effects after 6 weeks) with weight losses approaching 50%. 2. 2. During food and water deprivation during the summer respiratory exchange ratio drops below 0.7, oxygen consumption decreases, and rectal temperature drops slightly. Unlike winter experimental animals, prairie dogs deprived of food and water in summer became dehydrated and azotemic. Furthermore, plasma triglyceride and ketone concentrations of these animals were much lower than those of winter experimental and control prairie dogs. 3. 3. Typical mammalian responses to starvation, such as azotemia. hypoglycemia, and ketosis do not develop in winter starved prairie dogs, and their blood chemistry has many characteristics resembling that of black bears in winter sleep. Some possible metabolic adaptations are discussed. 4. 4. Similar concentrations (range: 62–180 pg/ml) of aldosterone were found in summer expetimental and control prairie dogs.

The food of emus

The results of a study of the food of emus, Dromaius novaehollandiae, in inland Western Australia show that they feed on a great variety of fruits, seeds, flowers, insects and green herbage of annual and perennial plants. Shrubs provide most of the food in spring and autumn (September to March), annuals in the autumn and winter (April to August) and insects are taken whenever they occur in abundance, usually in autumn and spring. Although shrubs provide a reliable supply of food in summer, annuals often produce little in the autumn and winter so that emus would have to move extensively to keep in contact with a supply of food. Records from other parts of Australia indicate that the type of food eaten by emus is similar throughout the continent, but the precise species eaten varies from time to time and place to place. Some incidental observations on characteristics of the digestive system of emus are reported. Large quantities of mineral material are carried in the gizzard and individual items may be retained for 3 or 4 months. The acidity of the anterior sections of the gut make bacterial action unlikely. The crude form of copography has been observed. Some food passes through the gut in 3h but other material from the same intake may be retained for at least 48 h. The emu's diet is nutrient-rich, but only a catholic taste and great mobility ensure that it is able to find a continuous supply of food.

Food and Feeding of Spiny Dogfish (Squalus acanthias) in British Columbia Waters

Stomach content data on 14,796 spiny dogfish (Squalus acanthias) from British Columbia waters are presented. The major dietary components based on occurrence were 55% teleosts, 35% crustaceans, and 5% molluscs. The principal food items were herring (22%) and euphausiids (14%). Prey was largely pelagic (80%), with fishes predominating in winter and invertebrates in summer. Fishes became more important in the diet with increasing dogfish size. Dogfish consumed twice as much food in summer as in winter. Annual consumption varied from 5 times biomass for small dogfish to 2.5 times for larger animals. Preliminary analyses suggest that dogfish consume over 5 times the current annual commercial catch of herring, but insignificant quantities of salmon. Key words: dogfish, Squalus, feeding, food, biomass, predation, metabolism, seasonality, survivorship, digestion

THE MOULT OF THE BULLFINCH PYRRHULA PYRRHULA

SUMMARYThe distribution of feather tracts and their sequence of moult in the Bullfinch is described. The adult post‐nuptial moult, which is complete, lasted 10–12 weeks, and the post‐juvenile moult, which is partial, 7–9 weeks. Adult moult began with the shedding of the first (innermost) primary and ended with the replacement of the last. Variations in the rate of moult in the flight feathers were mainly achieved, not by changes in the growth rates of individual feathers, but in the number of feathers growing concurrently. The primaries were shed more slowly, and the onset of body moult delayed, in birds which were still feeding late young.In 1962, the onset of moult in the adults was spread over 11 weeks from thc end of July to the beginning of October, and in the two following years over the six weeks, from the end of July to the beginning of September. The onset of moult was delayed by late breeding, which itself occurred in response to a comparative abundance of food in late summer, markedly in 1962. In all years, the first juveniles to moult started at the end of July, and the last, three weeks after the latest adults. Juveniles moulting late in the season retained more juvenile feathers than those moulting earlier.During moult, adult and juvenile Bullfinches produce feathers equivalent to 40% and 33% respectively of their dry weights. In both, for much of the moult, an average of nearly 40 mgm. of feather material—some 0.6% of their dry‐weight–is laid down each day. The remiges of the adult comprise only a seventh of the weight of the entire plumage, and it is suggested that their protracted moult results not so much from their energy requirements, as from the need to maintain efficient flight. Variation in the rate of moult in the remiges was much less pronounced than in the body feathers. Bullfinches were less active during moult than at other times of the year. The weights of both adults and juveniles increased during moult.The food during the moult period is described. In all years, most Bullfinches finished moulting just before food became scarce, even though this occurred at different times in different years. In one year, adults moulting latest in the season probably survived less well than those moulting earlier; the same was apparently true of the juveniles in all years. The timing of moult in the Bullfinch, and the factors initiating it, are discussed in relation to the breeding season and foodsupply near Oxford.

FOOD AND FEEDING HABITS OF THE MOUNTAIN HARE LEPUS TIMIDUS SCOTICUS, HILZHEIMER

The food of the mountain hare Lepus timidus scoticus Hilzheimer was studied by means of stomach analysis, and the use of hare‐proof enclosures on moorland; and grazing habits by regular visits to a study area in Banffshire. The main grazing period is at night, varying seasonally in relation to sunset and sunrise. During the day grazing may occur sporadically, or intensively if before rain or during heavy snow cover. Refection, that is the production of soft faeces which are swallowed directly from the anus, occurs during the period between the end of morning grazing and the start of the next evening's grazing. On ground covered with young ling Calluna vulgaris, mountain hares removed 27 per cent of the vegetation (dry weight) from the control plot, and on cotton grass Eriophorum spp. ground, 20 per cent and 24 per cent from control plots. In three of the eight enclosures used, on various herbage complexes, there was no appreciable difference from the control plots. Analysis of the dried stomach contents of forty‐seven mountain hares, collected at monthly intervals over a period of a year, showed that ling formed 90 per cent of the winter and about half the summer diet. Cotton grass made up about a tenth of the winter and a fifth of the summer diet, while grass species, present as a trace in winter stomachs, increased to a quarter of the total food in summer. Food plants of particular importance during storms and complete snow cover may be missed by the method of sampling or the use of enclosures. The extent to which hares grazed these plants was verified by visits during snow. Gorse Ulex europaeus, juniper Juniperis communis and soft rush Juncus effusus, are among the chief food plants in storms and snow cover.Summary1. The grazing habits of the mountain hare are described. The main grazing period is at night, varying seasonally in relation to sunset and sunrise. Sporadic grazing, or intensive grazing before rain or during snow cover, may occur during the day.2. Refection, the production of soft faeces which are swallowed directly from the anus, occurs during the day, beginning with the end of intensive grazing and ceasing with its resumption.3. The use of hare‐proof enclosures on moorland showed that on ground covered with young ling Calluna vulgaris mountain hares removed 27 per cent of the vegetation (dry weight), and on cotton grass Eriophorum spp. ground 20 per cent and 24 per cent. In three out of eight enclosures used, covering various herbage complexes, there was no appreciable difference from the control plots.4. Analysis of the dried stomach contents of forty‐seven mountain hares, collected at approximately monthly intervals over a period of a year, showed that ling formed almost 90 per cent of the winter and about half the summer diet. Cotton grass made up about a tenth of the winter and a fifth of the summer diet, while grass species present as a trace in winter stomachs, increased to a quarter of the total food in summer.5. Food plants of particular importance during storms and complete snow cover may be missed by the method of sampling or the use of enclosures. The extent to which hares grazed these plants was verified by visits during snow. Gorse Ulex europaeus, juniper Juniperus communis and soft rush Juncus effusus are among the chief food plants in storms and snow cover.

FOOD, FEEDING HABITS AND TERRITORY OF THE ROCK PIPIT ANTHUS SPINOLETTA.

Summary. This paper describes the food and ecology of a few Rock Pipits, mainly in Cornwall in winter. Rock Pipits prefer exposed to sheltered coasts. Their average density in favourable habitats was ca. 8 pairs per mile of coast. Rock Pipits fed chiefly on the shore in winter and just inland in summer. Rock Pipits fed more intently in mid‐winter than in spring and autumn; and, at any one season, most intently when food was scarce. Also, they fed more intently in the afternoon than in the morning in mid‐winter (correlated with the long winter nights), and vice versa in spring and autumn. Whenever food was scarce they fed hard all day. There were four common littoral foods in winter:the periwinkle Littorina neritoides, chironomid midge larvae, dipteran larvae (Coelopa spp.), and isopods (Idotea spp.). Amphipod hoppers (Talitridae) were sometimes an important food in late summer. The availability of these foods and the predation of the Rock Pipit upon them are described; rates of feeding and defaecation were measured. The total food consumption of one Rock Pipit was estimated for a number of days in December, 1950 and 1951. The dry weight of food eaten daily averaged ca. 26 gms. when periwinkles, and ca. 12‐5 gms. when chironomid larvae were the main food. The dry weights of organic material consumed daily were ca. 6 gms. (calorific value 30 Calories) in December 1950 and ca. 4 gms. in December 1951. When periwinkles were the main food the bird digested only 40% of the organic intake; hence its energy intake was ca. 12 Cals. daily. These results are compared with similar data for three other bird species. No other bird species seriously competed with the Rock Pipit for food. Intra‐ and inter‐specific fighting (chiefly for food), and the Rock Pipit's response to predators are described. Rock Pipits are intensely territorial; they defend individual territories in winter. The possible functions of territory are discussed:winter territories are primarily concerned with food. Conclusions: (i) since winter territories were just, but only just, big enough to provide sufficient food, their size was probably determined by their food resources; (ii) since Rock Pipits were sometimes apparently short of food and competed for it in winter, food shortage could limit their density.

The Significance of the Presence of Pollen in the Food of Worker Larvae of the Honey-bee

ABSTRACT 1. From a study of the quantity of undigested shells of pollen grains in the gut of worker honey-bee larvae it is concluded that the larvae receive a variable quantity of pollen in their food in summer and sometimes none at all in winter. 2. Probably less than one-tenth of the nitrogen requirements of growing larvae are obtained from the pollen in their food.