Showing papers in "Journal of Animal Ecology in 1976"

The Energetics of Feeding, Metabolism and Growth of Brown Trout (Salmo trutta L.) in Relation to Body Weight, Water Temperature and Ration Size

Abstract: C is the total energy content of the food consumed by the fish, F is the energy value of the faeces, U is the energy value of the excretory products, AB is the total change in the energy value of body materials (growth or loss in energy content) and includes any reproductive products released by the fish, R is the total energy of metabolism which is subdivided into three components: R. is the energy equivalent to that released in the course of metabolism in unfed and resting fish (standard metabolism), Ra is the energy required for swimming and other activity, Rd is the energy required for the processes of digestion, movement and deposition of food materials (including specific dynamic action). The extensive literature on energetics in fish has recently been reviewed by Beamish, Niimi & Lett (1975). Few workers have published complete energy budgets and have studied the effects of varying body size, temperature and ration size. The chief purpose of the present paper is to provide this information for brown trout and to develop equations to estimate the various components of the energy budget. Previous papers have dealt with various aspects of feeding and growth in brown trout (Elliott 1972, 1975a,b,c,d, 1976a,b) and the information in these papers is used extensively in the construction of the energy budgets. All the methods used in the experiments are described in detail in these previous papers. The methods used in the construction of the energy budgets are described in the appropriate part of the results.

Field Experiments on the Drifting, Colonization and Continuous Redistribution of Stream Benthos

Abstract: Invertebrate drift is a phenomenon of prime importance to the benthic community of streams (see review papers by Elliott 1967; Hynes 1970a, b; Muller 1966, 1974; Ulfstrand 1968; Waters 1969, 1972). The downstream movement in stream currents of large numbers of invertebrates profoundly influences benthic community dynamics in two ways. Firstly, the continuous loss of animals into the water column reduces benthic density, and since some species and size classes are more prone to drift than others, the composition of the local community is affected. Secondly, the continuous settling out of animals from the drift plays an important colonizing role. Thus, the twin influences of drift contribute to a continuous redistribution of benthos. The extent and rate of these two dynamic processes are among the most basic of ecological parameters in the stream ecosystem, and yet very little study has been specifically directed to their measurement. The phenomenon of drift is one which lends itself to experimentation in the field, and it is surprising that so little has been made of this opportunity. Studies involving field experiments have, however, been carried out into the question of the distance of drift (Waters 1965; McLay 1970; Elliott 1971a), the relationship between drift and density of the benthos (Waters 1965; Dimond 1967), the influence of light on drift rates (e.g. Elliott 1965a; Holt & Waters 1967), and the influence of temperature on drift rates (Wojtalik & Waters 1970). In the present study, we distinguish between movements of invertebrates brought about by crawling over the substrate, as opposed to drifting, and evaluate the role that drift plays in the colonization of new areas of stream bed exposed both experimentally and naturally. Colonization of unpopulated areas of stream bed, whether exposed by erosion, excavation of new channels, or denuded by pollution, has often been reported to be initiated by the drifting of invertebrates from upstream (Moffett 1936; Surber 1937; Laurie & Ericksen Jones 1938; Leonard 1942; Muller 1954; Patrick 1959; Chutter 1968; Crisp & Gledhill 1970). Colonization of experimentally exposed substrates has been studied by Moon (1940), who never mentioned drift, and more quantitatively by Waters (1964), Cairns & Ruthven (1970), Dickson & Cairns (1972), Glime & Clemons (1972), Nilsen & Larimore (1973) and Ulfstrand, Nilsson & Stergar (1974). However, none of these workers specifically attempted to measure the role of drift in colonization as opposed to movements across the substrate. We also performed concurrent experiments on the spatial and temporal variability of drift in the stream, and estimated the rate and extent of drift mediated losses and gains by all the principal taxa of the benthic community.

Energy Losses in the Waste Products of Brown Trout (Salmo trutta L.)

Abstract: The total energy content of the food intake of a fish is either lost in the faeces and the excretory products or used for metabolism, growth and any reproductive products released during the period concerned. Winberg (1956) first proposed that about 15% of the total energy intake is lost in the faeces and about 3% in the excretory products. He suggested that a slightly higher value of 20% probably represents the total energy losses in the waste products and this value has been used by many workers. Few workers have measured energy losses in salmonids. Brocksen, Davis & Warren (1968) obtained a value of 14'5%o for cutthroat trout Salmo clarki (Richardson) at 10? C, and and Brocksen & Bugge (1974) obtained values ranging from 28-2% at 5? C to 15-2% at 20? C for rainbow trout S. gairdneri Richardson. None of these values include energy losses in the excretory products: ammonia and urea. Ammonia is the chief excretory product in freshwater teleosts and is excreted primarily from their gills. Kleerekoper & Mogensen (1959) found that 98%0 of amino-derived nitrogen was excreted as ammonia in brown trout S. trutta L. and brook trout Salvelinus fontinalis (Mitchill). Except for the work of Burrows (1964) on chinook salmon Oncorhynchus tschawytcha (Walbaum), only small quantities of urea have been recorded in the excreta of teleosts (Black 1957; Brett 1962; Forster & Goldstein 1969). Other excretory products appearing in very small quantities in the urine are uric acid, creatine, creatinine, amines and amino acids. The present paper is one of a series dealing with feeding and growth in brown trout (Elliott 1972, 1975a, b, c, d, 1976). Its chief purpose is to examine energy losses in the faeces and excretory products of brown trout and to develop equations to estimate these losses.

Body composition of brown trout (salmo trutta l.) in relation to temperature and ration size

Abstract: The growth rates of brown trout, Salmo trutta L., fed on maximum and reduced rations were studied in a series of feeding experiments with trout in the weight range 5-300 g at both constant and fluctuating temperatures in the range 3.8-19'5° C (Elliott 1975a,b). Samples of fish from these experiments were used to determine water, fat, protein and ash content. This analysis of the four major constituents is often described as 'proximate analysis'. A guide to the extensive literature on proximate analysis in fish is provided by Love (1970). The purpose of the present paper is to examine changes in the relative proportions of the four major constituents in relation to body weight, water temperature and ration size. Equations are developed to estimate these constituents and also the energy value of the trout.

A synoptic population model.

Abstract: The relationships to population density of predation, intraspecific competition and female fertility are the major components in the population dynamics of many species. The way in which these relationships interact, and the resulting effect on the population, is conveniently illustrated by a comparison of densities in successive generations using a population growth curve (Ricker 1954). This may intersect the 450 line at several points, each of which corresponds to a stable or unstable equilibrium (Takahashi 1964; Holling 1973; Southwood 1975). An extension of such an approach to include habitat stability has been developed by Southwood (1975). This views a population's dynamics as a landscape along the axes of population growth, population density and habitat stability (Fig. 1).

Social Behaviour and Density Regulation in House Mice Living in Large Enclosures

Abstract: One of the important issues in the population biology of house mice (Mus musculus L.) is the extent to which social grouping influences gene flow and demographic processes. This species is territorial, at least in moderately large captive colonies (Eibl-Eibesfeldt 1950; Crowcroft 1955, 1973; Anderson 1961; Crowcroft & Rowe 1963; Anderson & Hill 1965; Reimer & Petras 1967). Evidence also suggests that territories are not necessarily individual but held by social groups (Eibl-Eibesfeldt 1950; Young, Strecker & Emlen 1950; Reimer & Petras 1967; Selander 1970; Busser, Zweep & van Oortmerssen 1974). It is still not known, however, whether this arrangement produces a static genetic structure, or it the combination of group cohesion with active dispersal leads to a constantly changing genetic situation. DeFries & McClearn (1972), for example, state that 'stable populations of house mice are comprised of small breeding units, or demes, with little genetic interchange among them'. Moreover, Ehrlich & Raven (1969) use the evidence for micro-geographical differentiation in this species to argue that species are not primarily held together by gene flow as is often assumed. On the other hand, the house mouse is well known as a very successful colonizing or 'weed' species. Social behaviour may also influence birth, death and emigration rates. It is difficult to study social behaviour and geographical structuring simultaneously; the one requires intensive observation on small captive groups (see Archer (1970) for review), whilst the other requires study of feral populations. The study reported here has been an attempt to narrow this gap between laboratory and field studies. My plan was to construct enclosures large enough for the development of spatial substructure, yet small enough to obtain direct evidence of social behaviour. The experimental design differed little from some commensal populations of Mus which live with abundant food and shelter in the midst of large areas of inhospitable habitat. The main difference was that normal dispersal was prevented, but, of course shortrange movements remained possible, and escape behaviour could be monitored. Moreover, enclosures are valuable for studying frustrated dispersal and hence the normal role of dispersal behaviour (Lidicker 1975). Supplies of food, water and shelter were provided in excess of demand, although food and water were dispersed only at fixed locations. I intended to study social and demographic behaviour in the absence of constraints by these basic resources. This arrangement stressed the cohesiveness of social units and provided a test of the potential responses of this species to extreme conditions.

The Distribution of Two Predators and their Prey in an Iron Rich Stream

Abstract: Plectrocnemia conspersa (Curtis) and Sialis fuliginosa Pict. are two well-known streamdwelling carnivores with contrasting predator strategies. The net-spinning caddis larva, Plectrocnemia conspersa, can be considered as a 'sit-and-wait' predator, while the alderfly larva, Sialis fuliginosa, is more active. Their common occurrence in a small iron-rich stream was investigated after preliminary observations indicated that the diversity and abundance of available prey in the benthos was low. Information on the role of terrestrial food for invertebrate predators appears to be lacking, although trout have been shown to take a significant proportion of terrestrial invertebrates in their diet (Elliott 1967). Attempts were made to determine and account for the abundance and distribution of Plectrocnemia conspersa and Sialis fuliginosa and their prey and to describe the factors affecting feeding by these predators. There is evidence that many herbivores and detritivores in streams respond to factors related to food supply (Ulfstrand 1967), but rather little is known about biotic factors influencing stream-dwelling invertebrate predators. Therefore, emphasis has been placed on this aspect of predator distribution. Responses of predators to the distribution of their prey are well known in other habitats, and could prove to be important as stabilizing forces in animal communities (Hassell & Rogers 1972; Hassell & May 1973). The stream is a headwater of the river Medway and is situated on the Ashdown Sands of Sussex (Nat. Grid ref. TQ 436327, altitude approx. 120 m). The study section, which is up to 1 m wide, 20 cm deep and with flow rates ranging from 0 to 25 cm s-1, runs through mixed woodland of mainly Alder (Alnus glutinosa Gaertner), with Oak (Quercus robur L.), Beech (Fagus sylvatica L.), Birch (Betulapendula Roth.), Holly (Ilex aquifolium L.) and Hazel (Corylus avellana L.). The substrate is variable, consisting of gravel, small stones and occasional rocks of up to 30 cm largest dimension and with extensive areas of fallen leaves and twigs. Except at the highest flow rates, the substrate is more or less covered with an ochre deposit of iron bacteria (probably mostly Leptothrix ochraceae Roth.) and ferric hydroxide derived from the iron bearing rocks of the area. The mean stream temperature during the study period was 13-3° C and the mean daily range 1-2° C (maximum daily range 2.0° C, minimum 0.5° C).

Interspecific Competition Experienced by South African Patella Species

Abstract: There are eleven species of Patella in South Africa, up to ten of which may coexist. Their zonation, distribution and feeding habits are sufficiently different to reduce competition between the species (Branch 1971), but it would be naive to assume that no competition occurs where niches overlap. The present paper concerns two facets of this competition: first, the effects barnacles have on P. granularis L. with respect to mean size, growth, gonad output and mortality. Secondly, consideration is given to the interactions between overlapping limpet species, particularly P. concolor Kr. and Cellana capensis (Gm.); Patella cochlear Born. and P. longicosta Lam.; and P. longicosta and P. oculus Born. One other interaction is mentioned in less detail: P. longicosta with P. tabularis Kr. The general ecology of these species has already been described (Branch 1971). Miller's review (1967) indicates the diversity of ideas on competition, and points out the confusion that has arisen from failure to define the common resource which is being competed for. His review also raises such basic questions such as: How is diversity maintained ? Is Gause's principle fundamental and inviolable or can coexistence occur between species using common resources ? Coexistence may be a temporary phase on the path to exclusion. In many ways the intertidal zone is ideal for studies on competition, for habitats are diverse but compressed into a small area. Vertical gradients allow definition of zones and delimit the fauna. Upper limits of zonation are usually determined by physical conditions, lower limits by biological interactions. The latter has been demonstrated in the field by Connell's work (1961a, b, 1970) on Chthamalus stellatus (Poli.). Dayton (1971) has also shown the dramatic effects predation, herbivorous grazing, competition and physical disturbance may have in controlling intertidal populations. Lewis & Bowman (1975) consider that the population characteristics of Patella vulgata L. are dictated predominantly by biological interactions. Grazing by limpets removes algae (Jones 1948; Lodge 1948) and recently settled barnacles (Branch 1975b). Conversely, dense barnacles depress growth of limpets (Fischer-Piette 1948; Lewis & Bowman 1975).

Diets of the shrews Sorex araneus L. and Sorex minutus L. in Wytham grassland.

Abstract: Animals were collected in an area known as Rough Common where thin soil covers the limestone cap of Wytham Hill and Brachypodium pinnatum (L.) is the dominant plant species. The area is divided by a road, one part bounded on the other sides by woodland and the second by a muddy cart track. The surrounding woodland is mixed deciduous with bramble (Rubus fruticosus agg.) hawthorn (Craetagus monogyna Jacq.), wild rose (Rosa sp. L.) and a few deciduous saplings forming a transition zone between it and the grassland. Bramble is also found in patches in the lower lying areas of the grassland and bracken (Pteridium aquilinum L.) on slight rises. The ground flora includes teasel

The adaptive significance of variation in breeding area fidelity of the blackbird (turd us merula l.)

Abstract: In species which maintain breeding territories a conflict exists between selection favouring dispersal between breeding seasons and selection operating to prevent it. Individuals that disperse are more likely to avoid the deleterious effects of inbreeding depression (see Wilson 1975). Those which do not disperse will have the advantage of being familiar with spatial and temporal variation in the availability of resources (Hinde 1956). In addition, by establishing a breeding area close to related individuals, the territory defender may be at an advantage through kin selection (Maynard Smith 1964). A comparison of age and sex variation in dispersal patterns of territorial species should help towards understanding the factors that influence dispersal in natural populations. In this paper we examine the breeding dispersal of the blackbird (Turdus merula L.) using data collected in the British Isles by members of the British Trust for Ornithology (B.T.O.) over the last twenty years. The species is strongly sexually dimorphic; the male establishes and defends the breeding territory. It is generally extremely sedentary in