Showing papers in "Journal of Animal Ecology in 1964"

Pitfall Trapping as a Method for Studying Populations of Carabidae (Coleoptera)

Abstract: Pitfall traps provide a convenient method of investigating the ecology of adult Carabidae and have been used in studies on such topics as the seasonal incidence of adults, the spatial pattern of distribution in populations, the relative numbers of a species in different vegetation types, in describing the Carabid fauna of habitats, and in work on daily rhythms of activity (Hikimiuk 1948; van der Drift 1951; Scherney 1955, 1960; Gilbert 1956; 1958; Dawson 1957; Kabacik 1957; Skuhravy 1956; Williams 1959b; Kirchner 1960; Thiele 1960; and others). These traps suffer from the disadvantage that catches depend both on the density of the population being sampled and the activity of individuals in it. Briggs (1961) concluded that in the Carabid Harpalus rufipes (Deg.) the size of the population played a minor part in determining numbers trapped, and Morris (1960) has stressed the desirability of obtaining estimates of absolute population in sampling programmes, that is the number of individuals per unit of habitat. As pitfall catches vary with the amount of locomotor activity shown by Carabidae they are influenced by weather, and Briggs (1961) and Greenslade (1961) found a correlation between catches and temperature. The problem of the relation between catch, population size and activity is not dealt with here, but Taylor's (1963) recent discussion of temperature and insect flight and suction trap catches is relevant. There are, however, other factors which may result in variation in pitfall catches of Carabidae, the two main ones, which have not been considered by some workers, are the effect of ground vegetation in impeding Carabid movement and reducing catches, and the differential susceptibility of species to trapping according to their behaviour. Taking these factors into account the cases in which it is legitimate to draw conclusions from pitfall trapping are discussed. This is necessary for despite their drawbacks pitfall traps are often the only method available in studies on Carabid populations. Although direct quadrat counts are to be preferred they may be precluded by low density or other factors. On the Imperial College Field Station, Silwood Park, Berkshire, where the work described in this paper was carried out, quadrat counts of Carabidae were made in three habitats (Greenslade 1961), and the densities of adults were: beechwood, 1-33 per m2 (6 Carabidae in 4-46 m2 sampled); grass heath, 28 per m2 (52 in 1 86 m2); arable land, 80 per m2 (82 in 1 02 m2). With the sparse woodland population direct counts are not practicable on account of the time and labour they involve, while in other habitats quadrat sampling may result in excessive destruction of the site being studied, especially as Carabid distributions are often highly aggregated and centred on restricted favourable areas (Greenslade 1963a, 1964a, e).

A Table for Calculating the `Equitability' Component of Species Diversity

Abstract: where s is the total number of species in a sample and Pr is the observed proportion of individuals that belong to the r-th species (r = 1, 2, . .. , s). Fig. 1 (a) exemplifies the sort of sample to which H(s) might be applied; the data are drawn from experimental work in progress near Oxford on the mesofauna of beech litter. In this sample, our technique of extraction (Kempson, Lloyd & Ghelardi 1963) got out 632 individuals of forty-four species, mostly micro-arthropods. By equation (1), we have H(44) = 4-16. In general, H(s) will increase with s, but the function is also influcnced by the evenness with which the individuals are distributed among the species. The maximum possible value, for a given s, could be realized only if all the species were equally abundant. In this case, Hmax(s) log2(s), so with forty-four equally abundant species, we would have Hmax(44) = log2(44) = 5x46. This mathematical maximum is never achieved in practice, because one never finds all species equally abundant-not even among species of comparable size that are presumably using the same kinds of resources, much less in the community as a whole. If one accepts H(s) as a valid empirical measure of species diversity, then one can imagine two quite separate pathways whereby the species diversity of an existing community might be enhanced. One way would be for more species to come and live there, and the other way would be for the existing species to adjust their numbers so that the rare ones become commoner and/or the common ones rarer. There are two components of species diversity, so to speak: number of species and 'equitability'. (We choose the word 'equitability' here rather than 'evenness', since numerical equality among the species is too much to expect. For some purposes, it is highly desirable to have a parameter like H(s) which takes two such different things into account and reduces them to a common scale. (The 'intrinsic rate of natural increase' is another example of such a parameter-see Birch 1948.) For other purposes, it may be more interesting to separate them. For example, one might wish to consider, as a working hypothesis, that whereas number of species depends primarily on the structural diversity of a habitat, 'equitability' is more sensitive to the stability of physical conditions. In this case, one needs a way to measure 'equitability' per se. The Shannon-Wiener function provides a basis for such a measure, when combined with some theoretical distribution of abundances among the species, to serve as a 'yardstick'.

Primary and secondary settlement in Mytilus edulis L.(Mollusca).

Abstract: In 1942 Maas Geesteranus postulated that the annual spatfall of mussel larvae in the vicinity of Den Helder, Holland, was scattered over a wide area, that these young mussels subsequently detached themselves from the substrate and that they then entered upon a migratory phase during which further attachment and detachment occurred many times. Eventually the mussels made contact with a substrate suitable for the adult way of life and then final attachment occurred. Verwey (1952) restated this view and stressed the importance of water currents and current-velocity in transporting the young mussels and in determining the site of final attachment. De Blok & Geelen (1958), also working at Den Helder, showed that the larvae of Mytilus edulis attached preferentially to artificial filaments which simulated the naturally occurring filamentous algae on which young mussels were found. They also observed that these young mussels subsequently disappeared from the filaments. Up to the present, however, it has not been demonstrated that the mussel larvae pass successively from the plankton to temporary sites of attachment and thence to their final place of settlement. Population studies therefore have been made to follow the sequence of young stages in the field to confirm that the observed settlement on filamentous algae was the natural prelude to permanent settlement and not a wasteful settlement of larvae on unsuitable substrata. The incidence of various age-groups of M. edulis in the Menai Straits, North Wales, was studied by observing the distribution of (a) the planktonic larvae, (b) the first settlement stages, and (c) the final settlement stages. The first settlement stages will be called early plantigrades and the final settlement stages late plantigrades, after the terminology of Carriker (1961).

The Distribution of Some Woodland Herbs in Relation to the Supply of Nitrogen and Phosphorus in the Soil

Abstract: One of the earliest experimental studies of the ecological requirements of a single species to be published in The Journal of Ecology was contributed by Olsen and is devoted to an investigation of the distribution of nettle (Urtica dioica) in Danish woodlands in relation to soil conditions (Olsen 1921). U. dioica was one of several plants which had been shown by Molisch (1883) to contain free nitrate in its tissues and this was confirmed by Olsen, who also showed that in sites where nettle colonies were adjacent to vegetation dominated by Deschampsia caespitosa, little or no nitrate could be detected in the leaves of the grass. Using an incubation technique, Olsen demonstrated this difference to be related to the intensity of nitrification in the respective soils, but where Urtica grew luxuriantly there was not only high nitrification, but also a high concentration of most plant nutrients including for example, calcium, magnesium, phosphate and in most cases potassium. Olsen also investigated the growth of Urtica in water culture and demonstrated that the species responds over a wide range to increases in nitrogen supply. In these experiments there was no comparison with the response of such species as Deschampsia caespitosa, so that the claim that Urtica dioica has an unusually high nitrogen requirement may seem unjustified. In spite of this criticism, the conclusion that the natural distribution of U. dioica is primarily controlled by nitrogen supply has found wide acceptance. The distribution of U. dioica in Britain has been summarized by Greig-Smith (1948). The species is widespread on disturbed soils around human habitations, farm buildings and at the foot of walls and hedges, especially along roadsides. It is also frequent in many types of woodland and grows luxuriantly in woods of Alnus glutinosa on alluvial soils and in woods of Fraxinus excelsior and Ulmus glabra in the north and west of Britain. In the limestone dales of the Pennines, Urtica dioica is one of several tall perennial herbaceous species which commonly occur together and form the characteristic vegetation along the foot of cliffs and screes, and on moist ungrazed ledges. In many of the wooded Derbyshire dales, this vegetation of tall herbs occurs in a narrow and discontinuous belt on deep mull along the foot of scree slopes, where the whole of the upper part of the scree is occupied by an almost continuous sward of Mercurialis perennis, or a mixture of this species with either Brachypodium silvaticum or Deschampsia caespitosa. This arrangement is illustrated in Fig. 1 by a transect in Monk's Dale, where a colluvial loam fills the bottom of the dale and is occupied by D. caespitosa. The composition of the three types of vegetation in comparable sites in Cressbrook Dale is summarized in Table 1. Both Urtica dioica and Mercurialis perennis are perennials, which die down in winter and produce a fresh crop of photosynthetic shoots each year. Deschampsia caespitosa

The Oxygen Content of Interstitial Water in Sandy Shores

Abstract: Several field investigations have been made into the nature and variations of environmental factors in the beach, both physical and chemical. The classical survey of such factors was made by Bruce (1928a, b). Other authors, for example Reid (1932), Perkins (1957), Chapman (1949) and Webb & Hill (1958), have studied specific factors in more detail than Bruce, such as salinity, the black layer, thixotropy, and the relationships between sand grain size, pore space, and drainage. Investigations into the oxygen content of the interstitial water, however, are rare. The scarcity of data concerning the oxygen content of the interstitial water is clearly demonstrated by the fact that Deboutteville (1960) in his extensive volume on the fauna and ecological factors of both freshwater and marine beaches, is compelled to deal with the oxygen content of the latter in one sentence: 'Le taux d'oxygene dissous dans les eaux interstitielles ou souterraines littorales est encore fort mal connu.' The oxygen regime existing in lakeside beaches is rather better understood, chiefly as a result of the studies by Wiszniewski (1934), Pennak (1940, 1951) and Angelier (1953). Unfortunately these workers gave few details of their methods of analysis. Nor did they report other features such as the grain size distributions of the beaches studied. A summary of studies on the oxygen content of marine beaches is given in Table 1. All except those of Jones (1955) are rather imperfect, either because the method of collecting the water sample was such that atmospheric oxygen was allowed to invade the sample, so causing errors of unknown size, or because the method of analysis failed to take into account the sources of error arising from the possible presence of chemical pollutants in the beach. The temperature of the samples was not always given. Jones (1955) used a reliable method, but a rather lengthy and cumbersome one. He gave few details of the physical characteristics of the beaches. Consequently it was considered necessary in the present work on the oxygen content of the interstitial water of marine beaches to attempt three main objects. Firstly, to devise a reliable method whereby samples of interstitial water could be collected without exposing them to the air at any stage. Secondly, to establish a reliable method of determining the amount of dissolved oxygen in an interstitial water sample. Such a method, which takes due account of all the potentially disturbing factors, was devised and used in nearly all the studies undertaken. Thirdly, using these methods of collection and oxygen determination, to make accurate investigations of the oxygen content of a number of beaches under differing conditions, in an attempt to discover the relative importance of the various factors which affect the oxygen content and control its level.

The Distribution of Spiders on the Moor House National Nature Reserve, Westmorland

Abstract: Systematic ecological studies on the British spider fauna are still few in number, the more important of these being an account of the spiders of Limestone grassland and oak woodland near Oxford by Duffey (1956, 1962a, b) and Turnbull (1960a) respectively, the spiders of an oak wood in Devon by Gabbutt (1956), those of sand dunes in the Gower Peninsula by Cooke & Cotton (1961), and studies on the activity of spiders in three contrasting lowland habitats by Williams (1962). With the exception of casual collecting, little seems to be known of the spiders inhabiting high moorlands, and the present investigation was undertaken as part of a continuing series of studies on the ecology of the British uplands (see Cragg 1961). This project is being carried out on the Moor House National Nature Reserve (N.R. 80) and involves qualitative and quantitative studies on the distribution and interrelations of the fauna in the wide range of habitats to be found in Pennine moorland. The present paper represents part of the studies on spiders undertaken from 1957 to 1960.

The Distribution of Invertebrates on Submerged Aquatic Plants in a Chalk Stream

Abstract: Studies of animal populations in various aquatic habitats have usually included some reference to the animals present on the vegetation (Carpenter 1927; Whitehead 1935; Moon 1936; Jones 1949; Smyly 1957) but few quantitative surveys of the animals on the plants have been attempted. There is a certain amount of evidence from the studies of vegetation in ponds and lakes, that different plants shelter different animals (Krecker 1939; Edmondson 1944; Bryden 1952; Smyly 1952; Rosine 1955). The quantitative investigations by Krecker and Rosine showed in addition, that plants with very finely divided leaves possessed larger and more varied animal populations than those with simple entire leaves. There is less evidence that different plants in streams possess different faunas. To date, observations have been of a qualitative nature (Butcher, Pentelow & Woodley 1931; Whitehead 1935). The following paper describes a quantitative investigation of the distribution and abundance of animals on four aquatic plants in a small chalk stream. The stream arises from the River Test below Romsey, Hampshire (Map reference: Ordnance Survey sheet 180, ref. 350170). An area of stream approximately 9 m long, containing beds of Ranunculus fluitans Lam., Callitriche platycarpa Kutz., Veronica beccabunga L. and a Carex sp.t was chosen as the site for the survey. The plants did not die down during the winter months.

The Distribution, Dispersal and Size of a Population of Nebria brevicollis (F.), with Comparative Studies on Three Other Carabidae

Abstract: The main purpose of the work described in this paper was to investigate the spatial distribution of populations of Carabidae, and the amount of movement by individuals within and between them. The term population is used loosely to include both its usual meanings, that is the sum total of individuals in a given area, and alternatively a group of individuals communicating more among themselves than with other similar groups of the same taxon. In the latter sense population is synonymous with gamodeme in Gilmour & Gregor's (1939) terminology. A secondary purpose of this study was to investigate the probability of different factors limiting numbers in different parts of a population. Elton (1949) pointed out that populations commonly consist of centres of varying density, and Wellington (1957) showed that there may be important seasonal and spatial variation in behaviour and physiology among individuals within a population. Richards (1961) suggested that at the climatically optimal centre of a species' geographical distribution, Nicholsonian controls maintain steady populations with only minor year-to-year fluctuations due to weather, while at the limits of the range, climate may cause more drastic variation. It is possible that Richards's suggestion can be applied also to local populations, Nicholson (1958) stating that at the fringes of a population there may be a gradient of favourability in an environmental factor over which 'density-governing reaction' does not occur. Some information is available on the effect of climate on Carabidae, and this is a factor in which gradients may occur at the edge of population areas. Briggs (1961) and Greenslade (1961), found a correlation between Carabid activity and temperature, while several workers, reviewed by Greenslade (1964b) have observed that Carabid adults, and more especially the larvae, are susceptible to desiccation; in some cases the habitats of species have been related to microclimate factors. Greenslade (1964b) concluded that although open habitats with high temperatures may be the most favourable for Carabidae, many species are excluded from them by low humidities. Tipton (1960) investigated the water and temperature relations of Nebria brevicollis (F.), one of the species studied here. The effect of weather on insect numbers may be simple and direct or delayed, Edwards (1960) for example correlating grasshopper abundance and aspects of climate over the previous three years.

Substrate Selection by Corophium Species: The Particle Size of Substrates

Abstract: Marine invertebrates which live in sand or mud are often limited to sediments or 'substrates' having a particular range of particle size (Pirrie, Bruce & Moore 1932; Thamdrup 1935; Yonge 1953; Steven 1953; Anon. 1957; Wieser 1959; Aldrich 1961). The amphipods Corophium arenarium Crawford and C. volutator (Pallas) are no exception to this rule: the former lives in sand and the latter in mud (Hart 1930; Thamdrup 1935; Crawford 1937; Beanland 1940; Watkin 1941; Holme 1949; Segerstrale 1959; Stock & de Vos 1960; Gee 1961; Anon. 1963). Both species inhabit permanent U-shaped burrows. The experiments reported below are concerned with why the two species are found in markedly different substrates. They form part of a series which were designed to elucidate the factors affecting substrate selection by C. arenarium and C. volutator (Meadows 1964a, b). Their subject is the influence of particle size. Other characteristics of the substrate which Corophium react to include substrate depth (Meadows 1964b), and the nature of naturally occurring films on substrate particles (Meadows 1964a).

Field study of the mobility of oribatei (acari), using radioactive tagging*

Abstract: To some extent, it is possible to check the validity of these hypotheses by following the movements of individuals in the field. Taking into account 'the size of the animals, the only practicable method for this purpose is by radioactive tagging. After labelling, the animals are returned to the field and their daily movements are observed with a Geiger counter. Two methods were used to label the animals. The first, proposed by Davis & Nagel (1956) consists of immersing the individuals in a radioactive solution, by ion exchange, some radioactive salts remain on the cuticle. The animals were immersed three to six times for 1 min every 2 h in a solution of Na2Ir192Cl6 (2 mc/ml) or of Sc46Cl (8 mc/ml). One day after the last immersion, the animals were washed in distilled water, to remove any salt not fully bound on the cuticle. Generally, forty animals were treated simultaneously and at the end of the labelling, twenty were selected whose radioactive level was adequate for detection in the field. Unfortunately, this simple method does not suit many Oribatids, most of which have an unwettable cuticle. For such animals, I used a different method consisting of mixing a small amount (250 nrc) of Ce144Cl in a little Students' oil Colour, and putting a tiny drop of this paint on the hysterosoma. Cerium-144 is an isotope with quite a long half-life, and gives by disintegration a daughter isotope, Praseodymium-144, which is a very strong beta emitter. Thus, the detection of the animals is easy with a Geiger-Muller tube (laboratory portable monitor M.B.L.E., PN 282/A equipped with a Geiger tube, ASDAM 18505). The amount of radioactive material that was used for these experiments was 10 mc of iridium, 40 mc of scandium and twice 5 mc of cerium. The radioactivity of these solutions was sufficiently high to require the precautions usually associated with a properly equipped radioisotope laboratory (lead bricks, laboratory monitor, pocket dose-meter .) and a special training of the experimenter.