Use of space and habitats by meadow voles at the home range,patch and landscape scales

Using capture/recapture methods, we examined the spatial usage patterns of Microtus pennsylvanicus within and between experimentally created habitat patches of three sizes (1.0, 0.25 and 0.0625 ha) and between a 20-ha fragmented and a 20-ha continuous habitat landscape. We tested the prediction that home ranges near patch edges would be qualitatively different from those in patch interiors, and that the edge:interior habitat ratio could be used to make predictions concerning the dispersion and spatial use of individuals occupying different sized patches and between landscapes with different habitat structure. We found adult females on patch edges to have larger and more exclusive home ranges, larger body sizes, longer residence times, and to reproduce at a higher frequency than those in patch interiors. These edge effects also appeared to be largely responsible for the greater proportion of larger, reproductive females we found in small than larger patches and in the fragmented than in the continuous habitat (control) landscape. The selection of higher quality edge habitats by dominant females and the relegation of sub-dominants to patch interiors provides an explanation for the observed differences in the distribution and performance of females over patches and between landscapes.     

An approach to the edge effect in proof of the validity ofDice's assessment lines in small-mammal censusing

A second fieldwork for the sake of solving the edge-effect subject was carried out in almost the same ways and plans in summer of 1971 in succession to that of 1970. It was found out that the population density was reduced to two-thirds, but the data were sufficient to form the subsequent conclusions:

1. The initial population estimated by the removal census method turned out to be well compatible with the numbers of survivals and emigrants of marked voles calculated byJolly 's method.
2. The natural, entire home ranges of both sexes reached by determining observed range length and width with 24 voles, selected on rigid conditions, agreed with those of the range-conservative type in 1970 in both acreage and elliptic shape.
3. In the majority of the select specimens, considered to reveal the natural ranges, the random distribution in number of captures per station within range was proved by means of I_σ so far as such capture density as treated here is concerned. On the ground of the empirical evidence, the above range size approached by the routine observational method could be made surprisingly accordant with the range size in terms of r-values calculated byWierzbowska 's method.
4. From these proofs, the validity ofDice 's assessment lines makes evident, and besides, it could be further substantiated by use ofMarten 's notion of mouse-equivalents through the mediation ofWierzbowska 's method.
5. Consequently, I have largely come to the conclusion thatDice 's assessment lines stand on justifiable basis from theoretical and empirical angles.

     

A field study of the effect of prebaiting on censusing by the capture-recapture method in a vole population

Populations of the vole, Clethrionomys rufocanus, in a lowland woodlot of Hokkaido were studied for the presence of effects of prebaiting on censusing by the capture-recapture method. A grid of 121 live-traps, spaced 5 m apart, was laid out on each of two plots, one of which alone was prebaited three days long. Owing to very high densities and great trap-efficiency, sufficient and favourable samples could be available for statistical analysis, except the trend of delayed catch for young in sampling. The population on either plot, however, proved to be markedly variable in catchability of unmarked animals in the course of trapping; while the probability of recapture was counted as invariable on the average from day to day, the recapture frequency was different between juveniles, subadults and adults. Needless to say, the catchability was distinctly greater for marked voles than for unmarked ones, whether prebaited or not, through the trapping period, except that the first-day catchability for unmarked ones on the prebaited plot seems not to be significantly lower than that for marked ones. Consequently, it turns out that the prebaiting has almost never helped to eliminate the important bias induced by differential trap-response of marked and unmarked animals; its contribution is only that the catchability for unmarked ones is slightly higher on the part of the prebaited plot on earlier days of the period. In accordance with the heterogeneous catchability, the Γ-form distribution analogous to the geometric could be applied with thorough fitness to the capture frequency in order to estimate the whole populations. The fact that the estimates are reliable, being not at any rate underestimates, was further confirmed by the result of a follow-up work conducted by means of the removal method with wider trap-spacing which brought forth distinct underestimation chiefly referable to unexposure to traps of the partial populations. The subject of unexposure was discussed by laying stress on the relation between minimum range length and trap-spacing.     

Investigation into the edge effect by use of capture-recapture data in a vole population

A substantial explication of the edge effect has been attempted by use of capture-recapture data for a vole population (Microtus montebelli), gathered intwo plots of 100×100 m or less during 12 days, cheked twice daily, in August 1970; the sample was quite sufficient for the aim. The edge effect as guessed by increased catch per trap is usually suspected to ensue from range-settlers in the outside boundary strip of a plot and immigrants. But by a theoretical analysis I could attain a tentative conclusion that no increased catch per trap will occur unless any invasion takes place. Then it follows that, apart from the effect of invasion, the role of the adjoining outside settlers in the edge effect is essentially required to be studied in the light of knowledge on the truth of size and shift in home range. The variation in range behavior for 183 adult voles, captured 6 times or more, could be grouped into eight types, of which the range-conservative type possessed 52% of the sample and the group of the type was justly utilized for giving averages of range size. Besides, it was seen from the observed frequency of types that a considerable number of immigrants onto the census plot were induced perhaps being allured by trap baits, but the majority of them proved to be assigned to the voles that have their ranges inside the assessment line ofDice ; the rest referable to effective immigrants was only a few (7%). I could perceive no reason such as disproves the idea ofDice 's additional boundary strip. Viewed from maps of ingress shift of ranges, the effect of ingress must have been greater in the outer trap rows than in the inner within the plot, so that it might well be called edge effect in general; such effect, however, is seen gradually diminishing toward the center, and hence it is almost unlikely that one should find any clear-cut intra-plot assessment lines demarcating such an inner square as quite free from edge effects. Averages of observed range length and width (ORL and ORW), as reliable measures for the true range size, were determined from the above group of specimens; as a result, the remarkable concept of elliptic range shape was established by regarding ORL as long axis and ORW as short one, and, directly from these averages, the mean range sizes worked out at 0.04 for females and 0.09 for males in acreage which proved to be surprisingly well agreeable with those of isotope-revealed ranges for voles given byGodfrey (1954) andAmbrose (1969). The catchability for marked voles () was estimated by the maximum likelihood method by use ofJolly 's formulae (1965), but that for unmarked ones () was made by the regression census formula; as a result it was shown that the population was clearly of π>p type and that the trap-experience that voles underwent one month or more ago can make them retain as high catchability as π.     

Utilization of fruiting trees by monkeys as analyzed from feeding traces under fruiting trees in the tropical rain forest of Cameroon

Individual trees of the food species of monkeys were identified by placing plastic tapes with an identification number on them in the tropical rain forest of Cameroon, West Africa. In order to determine the use of the feeding trees by monkeys, the ground under each of the trees was checked at least once a week to see if there were any fallen fruits or traces of feeding on fruits. Some fruit species were not fed on by either monkeys or large arboreal squirrels. Among the food species common to both the monkeys and large squirrels, a larger proportion in terms of quantity in each species was mainly eaten by the monkeys except in the case of super-abundantly fruit producing species. The monkeys and large arboreal squirrels were well segregated in their diets. Larger proportions (more than 85% for most of the monkeys' major foods) of fruits of larger sizes were made to fall on the ground by the monkeys and squirrels. The monkeys displayed a tendency to visit fruiting trees rather evenly (even rate of visit = even frequency of visit/duration of fruiting) not ignoring any area of the home range, although a small difference in this tendency was observed between the two study periods, one an abundant season and the other a poor fruiting season. On average, one associated polyspecific group of monkeys encountered only 14 fruiting trees per day. On the other hand, fruits were available all around the year, as the fruiting periods of different tree species were widely distributed around the year, or the fruiting periods of some species were very long. Although the monkeys are able to depend heavily on fruits, the quantity of fruits is not so great. The population size of monkeys is well balanced with the available food supply in the tropical rain forest of West Africa.     

The influence of habitat and behavioural interactions on the local distribution of the wrasse,Pseudolabrus celidotus

Synopsis The temperate wrasse, Pseudolabrus celidotus (Labridae), was studied in a shallow rocky reef habitat to asses how ecological and behavioural factors influence its within habitat patterns of distribution. Emphasis was placed on examining the mechanisms underlying size/age related changes in dispersion and habitat use. Juveniles (< 100 mm SL) were found to be aggregated whereas adults tended to be more randomly dispersed. This pattern appeared to be a product of both (a) ecological, and (b) behavioural factors. (a) Juveniles were closely associated with shelter (macro-algae) which was located in patches throughout the habitat. Their local distribution was probably not related to the distribution of their major prey items. Shelter dependence appears to decrease with growth and fish switched from feeding on micro-crustaceans present in macro-algae to those associated with bare rock — coralline turf areas. Adults foraged throughout larger home ranges, but fed preferentially in microhabitats where their prey items (e.g. bivalves) were most abundant. (b) Juveniles tended to aggregate into loose foraging schools. This tendency declined with age and was associated with a corresponding increase in the rate of aggressive interactions among individuals of a cohort. Consequently, individuals of the same size became more spaced out as they grew. Between cohort association or aggression was rare and apparently unimportant in determining local patterns of distribution. Many interspecific foraging associations and aggressive interactions were recorded. However, with the probable exception of interspecific territoriality by the blenny Forsterygion varium, these behaviours probably had only a transitory influence on the distribution of the wrasse.     

Evaluation of movement parameters in insects – bias and robustness with regard to resight numbers

Because of the low number of observation points per animal attainable in insect movement studies, linear parameters are frequently used to quantify the data. These linear parameters are evaluated, as well as several home range estimators, by means of an empirical study of the bush cricket Phaneroptera falcata (Insecta: Ensifera) and a Monte Carlo simulation model. The examination of differences between complete and artificially reduced data sets, as well as between the “real” (i.e. simulated) data set and the data recorded by a simulated observer, allows us to quantify robustness and bias of the evaluated parameters. We show that nearly all tested methods are strongly influenced by the resight number of the investigated individuals. Hence, those parameters should be used cautiously in studies with few resights, i.e. in insect studies as well as studies on vertebrates. Results of earlier studies should be reconsidered and some comparisons between different studies are questionable. Estimates of home range using a 95% ellipse with fewer than five locations are extremely unreliable (overestimation). The minimum convex polygon leads to a clear underestimation. The robustness of both parameters is low. Among the home range parameters the kernel method is most robust, but it leads to an overestimating bias. The harmonic mean method is the only home range parameter whose results are comparable to the area actually used. However, this method requires a minimum number of 11 observation points per individual. Evaluating the linear parameters, the mean daily movement and the total recorded movement are inappropriate for statistical analyses, because of their high sensitivity to the resight number. Maximum activity radius and dispersal range are much more robust. They are not as sensitive to sample size and deviate little from the “real” values of the parameters. However, this bias is statistically significant. The mean activity radius of an individual is the most useful linear parameter. This measure is very robust down to a sample size of four individual locations and compares well with the real parameter values. Received: 12 March 1996 / Accepted: 30 September 1996     

Plasma cortisol and metabolite level profiles in two isogenic strains of common carp during confinement

A rapid increase in common carp Cyprinus carpio plasma cortisol levels was noted, in two experiments, after 30 mins of a 3 h net confinement, which was sustained while the fish were held in the nets. After release from the nets, cortisol levels returned to control values in 1 h. Plasma glucose and free fatty acid levels were elevated by the confinement. Glucose was increased after 30 min but returned to basal levels after 22 h of recovery while free fatty acids were not elevated until 3 h of confinement and remained high for the duration of the recovery period. After confinement for 3 h, plasma lactate levels were reduced and remained low for a further 1 h. No change in either plasma triglyceride or cholesterol levels were found during the study. Confinement had no effect on haematocrit levels but blood haemoglobin levels were reduced. In both experiments hypochloraemia occurred in response to confinement. However, values returned to pre-confinement levels 22 h after confinement. These results show that rearing isogenic carp strains, under identical conditions, results in a reproducable response to an acute stressor and that these carp respond in a similar manner to other teleost species.     

An ecological digest of the small hive beetle (Aethina tumida), a symbiont in honey bee colonies (Apis mellifera)

The small hive beetle (Aethina tumida Murray) is an endemic scavenger in colonies of western honey bee subspecies (Apis mellifera L.) inhabiting sub-Saharan Africa where it only occasionally damages host colonies. Such damage is usually restricted to weakened/diseased colonies or is associated with after absconding events (all bees, including the queen, leave the hive) due to behavioral resistance mechanisms of its host. In sharp contrast, the beetle has proven deleterious to honey bee colonies in introduced ranges of the United States and Australia. With this review we synthesize the existing data in a manner that allows us to discuss the beetle’s natural history from an ecological perspective. A thorough exploration of beetle ecology allows us to 1) illuminate the unique symbiotic relationship it and its host share and understand how this relationship is fostered, 2) place this relationship in context with those of other arthropods inhabiting social insect colonies, 3) understand its natural reliance on honey bee colonies, 4) predict its spread outside its native range, and 5) predict its effects on non-African honey bees and non-target species. Here we present an amalgamation of information that will contribute to a more thorough and appropriate understanding of not only small hive beetles as symbionts, but of social insect symbionts in general. Received 4 April 2005; revised 15 October 2005; accepted 18 October 2005.     

Urban domestic gardens (VIII) : environmental correlates of invertebrate abundance

Domestic gardens associated with residential zones form a major component of vegetated land in towns and cities. Such gardens may play a vital role in maintaining biodiversity in urban areas, but variation in the abundance of organisms in gardens has been little explored. We report the results from a case study of 61 domestic gardens in the city of Sheffield, UK. Across 22 invertebrate groups, the median number of individuals recorded per garden was 49, 178, and 1012 in litter collections, pitfall and Malaise trap samples, respectively. Abundance was analysed by stepwise multiple regression and hierarchical tree analysis in relation to garden and landscape variables. The amount of variation explained in regression models ranged from 4 to 56%, for data based on pitfall and litter samples, and from 16 to 92% for data from Malaise traps. In total, 31 out of 36 explanatory variables entered into stepwise regression models, and 29 of them did so more than once. Although there was strong evidence only for approximately half of such relationships, in these cases the two methods of analysis corroborated one another. General correlates of invertebrate abundance were lacking, and likely reasons for inconsistencies in the relationships are discussed in the context of sampling and species biology. Correlates of the greatest significance occurred at both landscape (e.g. altitude) and garden scales (e.g. area of canopy vegetation). These factors were associated with species richness as well as abundance.