bluuebunny/crossref_metadata_2025 huggingface dataset:
Male mating success and risk of predation in a wolf spider: a balance between sexual and natural selection?
Authors: Kotiaho Janne , Alatalo Rauno V. , Mappes Johanna , Parri Silja , Rivero Ana
Published: March 2003

1.  Traits that benefit males through sexual selection are simultaneously expected to impair males by provoking costs through natural selection. If we consider the two male fitness components, mating success and viability, then we may expect that the increase in male mating success resulting from a larger trait size will be counterbalanced by an increase in viability costs.

2.  We studied the benefits and costs of male mate searching and sexual signalling activity in the wolf spider Hygrolycosa rubrofasciata. In the field, males search females actively and court them by drumming dry leaves with their abdomen. Females have been shown to prefer males with high drumming rate. Male moving and especially drumming is energetically highly demanding and drumming results in significant mortality costs.

3.  Our objective in this study was to determine whether male mate‐searching activity or drumming activity affect male mating success and the risk of males being predated.

4.  It was evident that both higher mate‐searching activity and higher drumming activity benefited males by increasing their mating success. Higher mate‐searching activity clearly impaired males by causing direct increase in predation risk. There was also a slight tendency that more actively drumming males had higher risk of predation and from all of the predated males 13.3% were caught directly after they had drummed. Furthermore, male drumming activity decreased drastically in the presence of the predator.

5.  We conclude that in H. rubrofasciata both increased mate‐searching activity and drumming activity benefit males through sexual selection, but at the same time natural selection provokes direct balancing costs on the same traits.
Transmission of Plodia interpunctella granulosis virus does not conform to the mass action model
Authors: KNELL ROBERT. J. , BEGON MICHAEL , THOMPSON DAVID J.
Published: March 2003

1.  Transmission of insect pathogens is traditionally described by a term which states that transmission is proportional to the densities of the susceptible hosts and the infectious units, multiplied by a constant, the transmission coefficient. Theoretical studies suggest that deviations from this can be important in host–pathogen population dynamics, but little is known of how commonly pathogen transmission conforms to the conventional model.

2.  We describe a test of the traditional assumption for the Indian meal moth, Plodia interpunctella (Lepidoptera: Pyralidae) (Hübner) and its granulosis virus using a modification of the previous methods, which allows for unpredictable declines in the amount of infectious material present.

3.  The estimated transmission coefficient increased with the density of susceptible hosts and showed a marked decline with density of infectious cadavers. This suggests that the usual assumption does not adequately describe transmission in this system.

4.  The reasons for this deviation from the usual assumption are likely to be a combination of behavioural and physiological changes at high host density, and differential susceptibility to the pathogen leading to an effect analogous to pseudo‐interference in parasitoids.
Individualistic species responses invalidate simple physiological models of community dynamics under global environmental change
Authors: DAVIS ANDREW J. , LAWTON JOHN H. , SHORROCKS BRYAN , JENKINSON LINDA S.
Published: March 2003

1.  Most predictions of species distribution and abundance changes in response to global warming relate the individual requirements of a single isolated species to climate variables through some form of climate mapping. This method fails to account for the effects of species dispersal and species interactions, both of which may strongly affect distribution and abundance.

2.  We therefore examined the effects of dispersal and species interactions on the distribution and abundance of three Drosophila species in a laboratory system that mimicked a latitudinal cline of 15 °C. We then investigated how species distribution and abundance in this system responded to simulated global warming.

3.  Dispersal allowed populations to persist at non‐optimum temperatures, overriding physiologically imposed range limits.

4.  Temperature determined the outcome of competition. In pairwise interactions, Drosophila subobscura eliminated D. melanogaster or D. simulans at low temperatures but was itself eliminated at high temperatures.

5.  Competitive interactions changed abundance and range sizes thus shifting the position of species optima. These changes depended on both the number and the identity of the competing species.

6.  Enemy–victim interactions altered range and abundance. Adding the parasitoid Leptopilina boulardi affected the host assemblage directly at high temperatures where the parasitoid was present, and indirectly (mediated by dispersal) at low temperatures where it was scarce or absent. Host species coexisted for longer at low temperatures in clines when parasitoids were present than when they were absent.

7.  Simulated global warming produced complex, counter‐intuitive effects on distribution and abundance, including the reversal of species’ relative abundance at some temperatures.

8.  Because dispersal and species interactions strongly influenced both range and abundance (sometimes in unexpected ways) current species distributions are no guide to what they might be under global climate change. Furthermore, since both these factors are missing from climate envelope models of range and abundance change, their predictions are, at best, incomplete.
Effects of parental quality and effort on the reproduction of common terns
Authors: Wendeln Helmut , Becker Peter H.
Published: March 2003

1. Age‐related patterns of reproduction in birds are often interpreted in terms of changing reproductive value with age: as residual reproductive value decreases with age birds have to increase their effort at younger age. In contrast, the ‘state‐based’ approach to life history postulates that not age per se determines reproductive decisions, but the ‘state’, reflecting condition or quality that may differ considerably between individuals of the same age. In this respect, we investigated the stability of body conditon, as well as individual quality differences in common terns Sterna hirundo and outline the role of parental quality and parental effort in reproductive performance. For lifetime identification we marked terns with passive transponders. Quality and effort were derived from body condition, which we monitored during the whole breeding season and every year for a period of up to 5 years.

2. Parameters of body condition and reproduction varied significantly between individuals, whereas intra‐individual variation over years was very low. Hence, body condition is very stable and differs considerable between birds.

3. Among the factors number of chicks, year and parental body condition, the latter was the only significant factor influencing chick growth rates. Furthermore, high growth rates of chicks were correlated with good female condition, and breeding success was positively correlated with body condition of both parents during incubation and chick‐rearing.

4. Parental effort increased significantly with increasing breeding success. The amount of expended effort depended on condition during incubation: mass loss was correlated with incubation mass, but not with mass during chick‐rearing.

5. Age was not an important factor in terms of condition or quality and also in terms of reproduction. The age independent condition reflects bird quality, enabling high quality birds to invest high parental effort resulting in high reproductive success over years, yet without negative consequences on future reproduction.

6. We conclude that in the common tern condition is a stable and age‐independent individual feature with substantial effects on reproduction. Hence, our data strongly support the ‘state‐based’ approach to life history. The high constancy in condition within and great differences between birds may also result in differences in lifetime reproductive success and fitness.
Host resources govern the specificity of swiftlet lice: size matters
Authors: Tompkins Daniel. M. , Clayton Dale. H.
Published: March 2003

1.An important component of parasite diversity is the specificity for particular host taxa shown by many parasites. Specificity is often assumed to imply adaptive specialization by the parasite to its host, such that parasites are incapable of surviving and reproducing on ‘foreign’ hosts.

2.Specificity, however, need not be due to adaptation to particular hosts. Some parasites may be specific simply because they are incapable of dispersing among host taxa. For example, ‘permanent’ parasites like chewing lice spend their entire lifecycle on the body of the host and require direct contact between hosts for dispersal.

3.The role of adaptive constraints in parasite host‐specificity has seldom been tested in natural populations. We conducted such a test by comparing the relative fitness of host‐specific lice experimentally transferred among closely related species of cave swiftlets in northern Borneo.

4.The survival of lice in most of these transfers was significantly reduced in proportion to the mean difference in feather barb size between the donor and recipient species of hosts. Thus, adaptation to a particular resource on the body of the host does appear to govern the specificity of swiftlet lice.

5.In transfers where lice survived, microhabitat shifting on the body of the host was observed, whereby the mean barb diameter of the feathers on which the lice occurred was held ‘constant’.
Estimating handling times for herbivore diets: a statistical method using the gamma distribution
Authors: Kohlmann Stephan. G. , Matis James. H. , Risenhoover Kenneth. L.
Published: March 2003

1. We present a statistical model for the prediction of handling times for different diet items of herbivores foraging in heterogeneous environments, based on the distribution of time intervals between bites.

2. We propose the gamma distribution as a convenient and appropriate model for foraging data and illustrate its use with field observations of foraging Nubian ibex (Capra ibex nubiana Linnaeus 1758) in the Negev Desert of Israel.

3. Specifically, we demonstrate how to estimate handling times from skewed frequency data of intervals between bites within patches.

4. We compared two mathematically equivalent gamma models and found a pronounced difference in the numerical results in fitting empirical data.

5. Estimated handling times varied with bite size, but not with plant category or sex of the foraging animal.

6. Fitting a gamma model to foraging data allows the efficient estimation of minimum handling constraints, mean handling times and within‐patch cropping rates, which should be useful for models of the herbivore foraging process.
The comparative expression of life‐history traits and its relationship to the numerical dynamics of four populations of the least killifish
Authors: Leips Jeff , Travis Joseph
Published: March 2003

1.We examined the numerical dynamics in four natural populations of the least killifish [Heterandria formosaAgassiz (1855)]; to ascertain how those dynamics affected the expression of key life‐history traits and, in turn, whether life‐history variation among populations might be responsible for different dynamic properties. Populations were chosen from two types of communities, spring‐fed rivers and lakes, to examine the relative influence of community characteristics on these relationships.

2.Populations in lakes had lower densities, more female‐biased sex ratios and a smaller proportion of immature individuals than populations in rivers. Predator faunas differed between habitats and the ratio of predator toH. formosadensity was higher in lakes than in rivers.

3.Females in lake populations were 35−40% larger than river females. Female size was positively correlated with the number of broods carried by a female at any given time and the number of offspring in a particular brood. These correlations and the larger body size of females in lake populations indicate that the reproductive output per female was higher in lake than river populations.

4.Female size was negatively correlated with population density in two of the four populations. After adjusting for the variation in female size, brood size and brood numbers were negatively correlated with population density in only the highest density population.

5.Average offspring size was negatively correlated with brood size in all of the populations, indicating a general trade‐off between offspring size and number. The average offspring size in the highest density population was as much as 45% larger than that of all other populations, an effect independent of any phenotypic plasticity in offspring size with respect to female body size or density.

6.The effects of density on female body size are the major avenue for negative feedback of population density on the subsequent dynamics through life‐history expression. Whether such an effect is stabilizing or destabilizing cannot yet be determined. If the variation in offspring size among populations is adaptive, it may be a prominent example of density‐dependent life‐history evolution.
An alternative approach to the measurement of seasonal trends in bird breeding success: a case study of the bullfinch Pyrrhula pyrrhula
Authors: Newton I.
Published: March 2003

1. On the basis of juvenile:adult ratios among netted birds and studies of moult, inferences are drawn about seasonal and annual variation in the breeding output of a bullfinch population studied near Oxford, in southern England.

2. In most years during 1962–66, the juvenile:adult ratio among netted birds increased from July or August to October, and then declined. The ratio in October, taken as a measure of annual productivity, varied between 2·8 and 5·5 in different years.

3. In the Oxford area, egg‐laying among bullfinches occurred between mid‐April and late August, so that the last young of the year left the nest in late September/early October. However, not all pairs continued breeding this late in the year. Individual bullfinches started to moult when they finished breeding. The proportion of adults which started moult after 20 August (implying successful breeding from eggs laid after mid‐July) varied between 7 and 68% in different years (or between 19 and 63% using a different method of estimation). Juveniles from these late nests, identified as those starting moult after 31 August, formed 24–61% of the total juvenile population in different years, the rest having been produced from clutches begun before mid‐July.

4. In the 2 years when the greatest proportions of adults started to moult after 20 August and the greatest proportion of juveniles started after 31 August, the juvenile:adult ratios in October were highest. By implication, the two‐fold variations in overall productivity between years were associated primarily with variations in the amount of late breeding.

5. This study, based on moults and age‐ratios among netted birds, provided information on seasonal productivity that was practically impossible to obtain in this species by conventional nest finding. An implication was that an interaction between the seasonal pattern of breeding in particular years and a seasonal trend in predation on nest contents, had major effects on overall annual productivity.
Density‐dependent growth in brown trout: effects of introducing wild and hatchery fish
Authors: Bohlin T. , Sundström L. F. , Johnsson J. I. , Höjesjö J. , Pettersson J.
Published: March 2003

Although it is not clear to what extent density dependence acts on the survival, emigration or growth of organisms, experiments testing alternative explanations are rare. A field experiment on 1‐year‐old brown trout (Salmo truttaL.) was undertaken to address the following questions: are the mortality, movement and growth of wild stream‐living trout affected by population density? If so, are the density‐dependent effects of released hatchery trout different from the effects of wild fish?

In each of two small streams, two replicate treatment blocks were used, each with four treatments assigned to stream sections 50–70 m in length: (1) control, no fish was introduced and population density was kept at its original level. (2) Trout biomass was doubled by introducing additional wild fish. (3) Trout biomass was doubled by introducing additional hatchery fish. (4) Hatchery trout were introduced, but biomass was kept at its original level by the removal of some resident wild fish.

We found no treatment effects on the recapture rates of resident trout, which suggests that survival was not strongly affected by competition. They were also remarkably stationary, regardless of treatment. However, trout growth rate was reduced to the same extent in both treatments with increased density, suggesting that growth was negatively density‐dependent, and that the density‐dependent effects of hatchery trout and introduced wild fish were similar.

Wild resident fish grew faster than introduced wild trout, which in turn grew faster than hatchery trout. Hatchery fish and introduced wild fish moved more than wild resident fish.

The results show that population density affected growth in trout parr. We conclude that competition is not limited to the underyearlings, as has previously been suggested, and that density‐dependent growth is the main density‐dependent response in yearling trout. Furthermore, this effect was the same for wild and hatchery‐reared competitors, suggesting that stocking of hatchery fish may affect natural populations negatively through density dependence.
Consumer–resource interactions and cyclic population dynamics of Tanytarsus gracilentus (Diptera: Chironomidae)
Authors: Einarsson Árni , Gardarsson Arnthor , Gíslason Gísli Már , Ives Anthony R.
Published: March 2003

Tanytarsus gracilentus population dynamics in Lake Myvatn show a tendency to cycle, with three oscillations occurring between 1977 and 1999 having periods of roughly 7 years. The population abundance fluctuated over four orders of magnitude.

A partial autocorrelation function (PACF) accounting for measurement error revealed a strong positive lag‐1 autocorrelation and a moderate negative lag‐2 partial autocorrelation. This suggests that the dynamics can be explained by a simple second‐order autoregressive process.

We tested the alternative hypotheses that the cyclic dynamics of T. gracilentus
were driven by consumer–resource interactions in which
T. gracilentus
is the consumer, or predator–prey interactions in which
T. gracilentus is the prey. We analysed autoregressive models including both consumer–resource interactions and predator–prey interactions.

Wing length of T. gracilentus
was used as a surrogate for resource abundance and/or quality, because body size is known to fluctuate with resource abundance and quality in dipterans. Furthermore, the wing lengths of
Micropsectra lindrothi
, a species ecologically similar to
T. gracilentus
, fluctuated synchronously with
T. gracilentus wing lengths, thereby indicating that the shared resources of these two species were indeed cycling. Wing lengths of other chironomid species were not synchronized.

The predators of T. gracilentus
included midges in the genera
Procladius
and
Macropelopia
, and the fish
Gasterosteus aculeatus (three‐spined stickleback).

The autoregressive models supported the hypothesis that T. gracilentus dynamics were driven by consumer–resource interactions, and rejected the hypothesis that the dynamics were driven by predator–prey interactions.

The models also revealed the consequences of consumer–resource interactions for the magnitude of fluctuations in T. gracilentus
abundance. Consumer–resource interactions amplified the exogenous variability affecting
T. gracilentus per capita population growth rates (e.g. temperature, rainfall, etc.), leading to variability in abundance more than two orders of magnitude greater than the exogenous variability.
The importance of biotic interactions in abundance–occupancy relationships
Authors: Holt Alison R. , Warren Philip H. , Gaston Kevin J.
Published: March 2003

Metapopulation dynamics have been postulated as a possible mechanism giving rise to positive interspecific relationships between local abundance and regional occupancy. These may operate through the carrying capacity or the rescue effect hypotheses. However, both are based on single species models that sum independent occurrences of species to form an assemblage, ignoring interspecific interactions.

Here we test experimentally whether interspecific interactions and dispersal influence the formation of the abundance–occupancy relationship in metapopulation systems in laboratory microcosms containing protists and bacteria.

The effect of species interactions was tested by comparison of the abundance–occupancy relationship in multiple habitat patch systems containing all species together, with the relationship formed by combining data from equivalent systems containing each protist species alone.

Abundance–occupancy relationships in interacting communities were better defined than those in non‐interacting communities. The inclusion of interspecific interactions was found to cause a reduction in the abundance and occupancy of the majority of species, as a consequence of which the position of species within the relationship changed drastically.
The role of males in the dynamics of ungulate populations
Authors: Mysterud Atle , Coulson Tim , Stenseth Nils Chr.
Published: March 2003

In this review, we focus on how males can affect the population dynamics of ungulates (i) by being a component of population density (and thereby affecting interpretation of log‐linear models), and (ii) by considering the mechanisms by which males can actively affect the demographic rates of females.

We argue that the choice of measure of density is important, and that the inclusion or exclusion of males into models can influence results. For example, we demonstrate that if the dynamics of a population can be described with a first‐order auto‐regressive process in a log‐linear framework, the asymmetry between the effects of females on the male dynamics and vice versa can introduce a second order process, much in the same way that the interaction between disease and host or predator and prey can. It would be useful for researchers with sufficient data to explore the affects of using different density measures.

In general, even in harvested populations with highly skewed sex ratios, males are usually able to fertilize all females, though detailed studies document a lower proportion of younger females breeding when sex ratios are heavily female biased. It is well documented that the presence of males can induce oestrus in females, and that male age may also be a factor. In populations with both a skewed sex ratio and a young male age structure, calving is delayed and less synchronous. We identify several mechanisms that may be responsible for this.

Delayed calving may lower summer survival and autumn masses, which may lead to higher winter mortality. If females are born light, they may require another year of growth before they start reproducing. Delayed calving can reduce future fertility of the mother. As the proportion of calves predated during the first few weeks of life is often very high, calving synchrony may also be an important strategy to lower predation rates.

We argue that the effects of males on population dynamics of ungulates are likely to be non‐trivial, and that their potential effects should not be ignored. The mechanisms we discuss may be important – though much more research is required before we can demonstrate they are.
The effect of an environmental change on mobile butterfly larvae and the nutritional quality of their hosts
Authors: Hellmann Jessica J.
Published: March 2003

Herbivores that forage on resources that change over time may be strongly affected by environmental factors that alter their temporal overlap with host plants. The magnitude of these effects may be mediated by the availability of alternative hosts and by behavioural adaptations for foraging on temporal food resources.

This study examines the temporal interaction of a butterfly species and its two host plants to determine how larvae utilize their host resources and are affected by conditions of accelerated host senescence. By changing host use over time, this butterfly may track temporal declines in host quality and buffer the impacts of environmental variation and change. At the same time, it is hypothesized that host declines and changes in the host environment affect larval survivorship and hence butterfly population size.

With three sets of field and greenhouse experiments, the following were examined: (i) larval host plant use and the dependence of larval diet on oviposition, (ii) nutritional differences between hosts, and (iii) the impact of conditions that accelerate host plant death (i.e. temperature) on larval survivorship and growth.

Larvae were observed to forage widely, vary their diet through time, and use hosts independently of their natal plant. Larvae tracked changes in host quality by steadily increasing their use of the longer‐lasting, but nutritionally variable, host plant. Temperature conditions that accelerated host death actually conferred a survivorship advantage when larvae were able to utilize this host.

These results suggest that larval diet choice and movement may be an adaptive strategy for foraging on declining food resources. It also suggests that the net effect of environmental extremes on larvae is strongly mediated by host plant use. Differences in larval survivorship when one or both hosts are available suggest that the long‐lasting host is essential to butterfly population persistence. By comparing this mobile taxa to species with fewer host‐switching opportunities, we better understand the diversity of foraging strategies of food‐limited insects and the effects of environmental change.
Habitat switching by Bewick's swans: maximization of average long‐term energy gain?
Authors: Nolet B. A. , Bevan R. M. , Klaassen M. , Langevoord O. , Van Der Heijden Y. G. J. T.
Published: March 2003

In a system where depletion drives a habitat shift, the hypothesis was tested that animals switch habitat as soon as the average daily net energy intake (or gain) drops below that attainable in the alternative habitat.

The study was performed in the Lauwersmeer area. Upon arrival during the autumn migration, Bewick's swans first feed on below‐ground tubers of fennel pondweed on the lake, but subsequently switched to feeding on harvest remains in sugar beet fields.

The daily energy intake was estimated by multiplying the average time spent foraging per day with the instantaneous energy intake rate while foraging. In the case of pondweed feeding, the latter was estimated from the functional response and the depletion of tuber biomass. In the case of beet feeding, it was estimated from dropping production rate. Gross energy intake was converted to metabolizable energy intake using the assimilation as determined in digestion trials. The daily energy expenditure was estimated by the time–energy budget method. Energetic costs were determined using heart rate.

The daily gain of pondweed feeding at the median date of the habitat switch (i.e. when 50% of the swans had switched) was compared with that of beet feeding. The daily gain of beet feeding was calculated for two strategies depending on the night activity on the lake: additional pondweed feeding (mixed feeding) or sleeping (pure beet feeding).

The majority of the swans switched when the daily gain they could achieve by staying on the pondweed bed fell just below the average daily gain of pure beet feeders. However, mixed feeders would attain an average daily gain considerably above that of pondweed feeders. A sensitivity analysis showed that this result was robust.

We therefore reject the hypothesis that the habitat switch by swans can be explained by simple long‐term energy rate maximization. State‐dependency, predation risk, and protein requirements are put forward as explanations for the delay in habitat switch.
A demographic comparison of two southern elephant seal populations
Authors: Mcmahon Clive R. , Burton Harry R. , Bester Marthán N.
Published: March 2003

To estimate concurrent age‐specific survival for southern elephant seals at Macquarie and Marion islands, seals were marked from 1993 to 1997 in the first 3 weeks of life and resighted (recaptured) on return to their natal islands (1994–2001). These recaptures formed the basis for the survival analysis in the mark–recapture program mark. Weaning masses were collected at each location.

Recapture probabilities were (= 376·480, P < 0·0001) higher at Marion Island than at Macquarie Island. There are two possible reasons: (1) the population at Marion Island is smaller and less dense than at Macquarie Island and (2) seals hauled out along a smaller section of the coast at Marion Island than at Macquarie Island, which: (1) facilitates the detection and individual identification of seals and (2) increases access to hauled out seals.

Age‐specific survival estimates (corrected for preweaning mortality and tag loss) differed ( = 22·264, P < 0·05) at the two islands and were consistently higher at Macquarie Island. The survival estimates for male and female seals were different at Macquarie Island (= 34·657, P < 0·0001) and Marion Island (= 20·373, P = 0·002). Female survival estimates were higher than male survival estimates. The combined survival estimates for juvenile seals (1–3 years) differed between islands but survival of older seals (4–6 years) did not. The inclusion of gender in the survival models did not improve model performance and hence male and female estimates were considered jointly.

The mean wean masses of male and female seals combined from 1993 to 1998 were not different between islands (T6837 = 1·169, P = 0·242). At Macquarie Island the mean annual wean mass was 118·8 kg (SD = 27·2, n= 6504) while at Marion Island it was 120·6 kg (SD = 24·7, n= 335).

The mean age at first breeding was different (P < 0·001) at the two island populations. At Macquarie Island the mean age of first breeding was 4·68 years, and at Marion Island it was 3·95 years. More (= 67·39, P < 0·0001) 3‐year‐old females breed at Marion Island (28·7%) than at Macquarie Island (1·2%) and the proportion of seals that had bred at least once by age 7 was greater at Marion Island than at Macquarie Island.

We conclude that the observed decreases in elephant seal numbers between the 1950s and 1990s in the Pacific and Indian Ocean sectors were driven principally by resource limitation in the Southern Ocean. A conglomerate of factors including local predation by killer whales and intraspecific resource competition is postulated as a cause for the inter‐island (regional) differences in population trends. It appears that more resources are available per capita to the Marion Island population than are available to the Macquarie Island population.
An insect (Argyresthia retinella, Lep., Yponomeutidae) outbreak in northern birch forests, released by climatic changes?
Authors: Tenow O. , Nilssen A. C. , Holmgren B. , Elverum F.
Published: March 2003

1. In the early 1990s, birch Betula pubescens L. forests in north‐western Norway were damaged by the bud‐ and shoot‐mining larvae of Argyresthia retinella not previously known for outbreaks. In 1993–96, the outbreak was mapped and changes in attack intensity and foliage structure were quantified by sampling birch twigs along transects from coast to inland. Results were considered in relation to a variable climate.

2. The outbreak extended 400 km along the coast, mainly within the lowest 100–150 m a.s.l. It started in the late 1980s and the attack intensity culminated in 1993–94. Repeatedly, 30–50% of the leaf‐carrying shoots were damaged or killed. Trees compensated by sprouting clusters of shoots from undamaged shoots and, hence, increased foliage clumping. Eventually, twigs and branches died.

3. The overwintering post‐diapause egg, the larva and the adult stages were considered the most sensitive to changes in temperature climate. The air temperature, averaged for a combination of these stages, was calculated for each year, as well as deviations from the long‐term (1868–1996) average.

4. The 5‐year running average of deviations approached or exceeded + 1 °C three times: in the 1930s, around 1960 and around 1990. The third peak coincided with the outbreak of the 1990s. There are no reports of an A. retinella outbreak in either the 1930s or 1960s. However, in one photographic documentation from 1940, clumped foliage structure of birch suggests an outbreak in the 1930s.

5. Severe A. retinella attacks appear to be a fairly new phenomenon, possibly connected to recent high temperature deviations. If so, with the present air temperature climate, outbreaks may occur at intervals of ≈20–25 years. With a trend of decreasing air temperature, outbreaks may be less frequent. At higher temperatures, natural or from anthropogenic global warming, the outcome is more uncertain although more frequent outbreaks may occur initially.

6. It is recommended that foresters learn to identify damage made by A. retinella and include observations on this insect in their reporting. Monitoring A. retinella damage in the North and elsewhere, should contribute to the understanding of the outbreak ecology of this insect.
The horizontal movement of seeds in arable soil by different soil cultivation methods
Authors: Marshall E. J. P. , Brain P.
Published: March 2003

1. To assess the impact of soil cultivation on the horizontal movement of seeds in arable soil, plastic beads and barley or triticale seeds were used as seed models. Different coloured beads were introduced in the field immediately before each of five cultivations: ploughing, two tine cultivations, harrowing and seed drilling. Beads were recovered from 20‐cm soil cores divided into four 5‐cm deep soil horizons.

2. After a typical cultivation sequence of five operations, beads were found up to 15 m from their source, although most beads were found within 2 m. Most beads were recovered from the surface 5 cm of the soil profile, except for those introduced onto the surface or at 20 cm depth before ploughing, which were concentrated below 10 cm.

3. Regression analysis was used to determine the pattern of bead movement by seed drilling. A novel analysis using Fast Fourier Transforms established the probability distribution functions of the remaining cultivation operations for horizontal movement. Using the final seed distributions, the effects of each cultivation were sequentially deconvoluted and the probability distribution functions smoothed. The proportions of beads moved were also calculated.

4. Ploughing and seed drilling moved seed the least distance compared with other cultivations. The mean distances moved were 0·36 m and 0·26 m, respectively. Tine cultivations moved beads 0·71 m and 1·21 m, while harrowing moved seed a mean distance of 1·58 m. Cultivation sequences based on ploughing are likely to limit seed movement in soil.

5. The Fourier deconvolution approach has potential for predicting future seed distributions and thus the spatial behaviour of weed patches within fields.
Lack of native species recovery following severe exotic disturbance in southern Californian shrublands
Authors: Stylinski Cathlyn D. , Allen Edith B.
Published: March 2003

1. Urban and agricultural activities are not part of natural disturbance regimes and may bear little resemblance to them. Such disturbances are common in densely populated semi‐arid shrub communities of the south‐western US, yet successional studies in these regions have been limited primarily to natural successional change and the impact of human‐induced changes on natural disturbance regimes. Although these communities are resilient to recurrent and large‐scale disturbance by fire, they are not necessarily well‐adapted to recover from exotic disturbances.

2. This study investigated the effects of severe exotic disturbance (construction, heavy‐vehicle activity, landfill operations, soil excavation and tillage) on shrub communities in southern California. These disturbances led to the conversion of indigenous shrublands to exotic annual communities with low native species richness.

3. Nearly 60% of the cover on disturbed sites consisted of exotic annual species, while undisturbed sites were primarily covered by native shrub species (68%). Annual species dominant on disturbed sites included Erodium botrys, Hypochaeris glabra, Bromus spp., Vulpia myuros and Avena spp.

4. The cover of native species remained low on disturbed sites even 71 years after initial exotic disturbance ceased. Native shrub seedlings were also very infrequent on disturbed sites, despite the presence of nearby seed sources. Only two native shrubs, Eriogonum fasciculatum and Baccharis sarothroides, colonized some disturbed sites in large numbers.

5. Although some disturbed sites had lower total soil nitrogen and percentage organic matter and higher pH than undisturbed sites, soil variables measured in this study were not sufficient to explain variations in species abundances on these sites.

6. Non‐native annual communities observed in this study did not recover to a predisturbed state within typical successional time (< 25 years), supporting the hypothesis that altered stable states can occur if a community is pushed beyond its threshold of resilience.
Alternative methods for predicting species distribution: an illustration with Himalayan river birds
Authors: Manel Stéphanie , Dias J.M. , Buckton S.T. , Ormerod S.J.
Published: March 2003

1. Current emphasis on species conservation requires the development of specific distribution models. Several modelling methods are available, but their performance has seldom been compared. We therefore used discriminant analysis, logistic regression and artificial neural networks with environmental data to predict the presence or absence of six river birds along 180 Himalayan streams. We applied each method to calibration sites and independent test sites. With logistic regression, we compared performance in predicting presence–absence using map‐derived predictors (river slope and altitude) as opposed to detailed data from a standardized river habitat survey (RHS).

2. Using the entire calibration data, overall success at predicting presence or absence was only slightly greater using artificial neural networks (89–100%) than either logistic regression (75–92%) or discriminant analysis (81–95%), and on this criterion all methods gave good performance.

3. When applied to independent test data, overall prediction success averaged 71–80%, with logistic regression marginally but significantly out‐performing the other methods. Encouragingly for researchers with limited data, model performance in jack‐knife tests faithfully represented performance in more rigorous validations where calibration (n = 119) and test sites (n = 61) were in separate geographical regions.

4. All three methods predicted true absences (83–92% success) better than true presences (31–44%). Results from logistic regression were the most variable across species, but positive prediction declined with increasing species rarity in each method.

5. Applications with logistic regression illustrated that significant habitat predictors varied between data sets within species. Hypotheses about causal effects by habitat structure on distribution were thus difficult to erect or test. Logistic regression also showed that detailed data from the river habitat survey substantially improved positive prediction by comparison with prediction using slope or altitude alone.

6. We conclude that discriminant analysis, logistic regression and artificial neural networks differ only marginally in performance when predicting species distributions. Model choice should therefore depend on the nature of the data, on the needs of any particular analysis, and on whether assumptions for each method are satisfied. All three methods share drawbacks due to systematic effects by species rarity on performance measures. They also share limitations due to the correlative nature of survey data often used for model development at the spatial scales required in macro‐ecology and conservation biology. Tests with independent data, using a wider range of performance measures than those used traditionally, will be important in examining models and testing hypotheses for such applications.
Sampling termite assemblages in tropical forests: testing a rapid biodiversity assessment protocol
Authors: Jones David T. , Eggleton Paul
Published: March 2003

1. Termites play a key role in decomposition processes in tropical ecosystems. Rapid assessment of local termite assemblages requires a standardized sampling protocol capable of producing an accurate picture of species composition. This paper evaluates the efficacy of a sampling protocol designed to assess termite species richness and functional diversity in tropical forests.

2. The protocol entails a 100 m long transect consisting of 20 sections (each 5 × 2 m). One hour of human sampling effort per section is used to search for and collect termites from dead wood, soil, termite nests and other microhabitats up to a height of 2 m above ground. The protocol was tested in three forest sites where the local termite fauna was already comprehensively documented. Two transects were run at Danum Valley (Sabah, Borneo), one at Pasoh Forest Reserve (Peninsular Malaysia) and one at Mbalmayo Forest Reserve (Cameroon).

3. At the three sites the transect samples contained 31–36% of the known local termite species pool. The taxonomic and functional group composition of the transect samples did not differ significantly from that of the known local fauna. The two transects run at Danum Valley gave very similar patterns, suggesting that the protocol produces consistent within‐site results. After sampling 20 sections, pseudoturnover between the two Danum transects had declined to a relatively low level.

4. The transect method is effective because it utilizes collecting expertise within a protocol that standardizes sampling effort and area. The protocol provides a much more rapid and cost‐effective method for studying termite assemblage structure than sampling regimes designed to estimate population abundances. It was demonstrated that one supervised training transect was sufficient to ensure the protocol was conducted with the required level of sampling efficiency.

5. The protocol offers a rapid tool for investigating spatial and temporal patterns of termite assemblage structure in tropical forest sites. Existing data also suggest that termites warrant further investigation as ecological indicators. Termite assemblage composition shows a strong response to habitat disturbance and may be indicative of quantitative changes in the decomposition process. The termite transect has potential as a useful addition to any suite of organisms recommended for monitoring functional processes in tropical forests.
Modelling ecological half‐lives for radiocaesium in Norwegian brown trout populations
Authors: Hessen Dag O. , Skurdal Jostein , Hegge Ola , Andersen Tom
Published: March 2003

1. Models of ecological half‐life may be valuable and cost‐effective predictive tools for authorities setting restrictions on human consumption of freshwater fish after environmental releases of radioactivity. This work aimed to validate such a model for radioactive caesium (134Cs and 137Cs) in brown trout Salmo trutta populations. Data were drawn from lakes with a wide variability in abiotic and biotic factors and initial caesium load.

2. In Norway, the highest fallout (more than 150 kBq m–2 of 137Cs) from the Chernobyl accident occurred in Oppland county, in south central Norway. Radioactivity was measured in more than 1800 samples of brown trout in nearly 100 localities in this region during 1986–95.

3. The back‐calculated maximum initial radioactivity on 1 January 1987 showed a strong regional variability (range 443–13 370; average 3855 Bq kg–1). Large variation in initial radioactivity was also recorded on a local scale (within 50 km).

4. The ecological half‐life model for caesium in brown trout populations for 1987–94/95 gave a close fit to real data from all localities with sufficient time series. Predicted half‐lives ranged from 1·2 to 4·2 years (average 2·5) but 95% confidence limits were narrow (2·7 and 2·3 years).

5. The overall variability in radioactivity levels over time was almost entirely related to the initial load and, with few exceptions, 88% of the changes in radioactivity was explained by the simple regression model. Modest variability in ecological half‐life was not correlated with initial activity, and no clear effects of water quality or season could be detected. For most lakes, levels of radioactivity in brown trout appeared to be predictable, with high accuracy after a fallout event, without extensive information on population ecology and water quality. However, more detailed work may be required to assess patterns within individual lakes.
Local extinction of British farmland birds and the prediction of further loss
Authors: Gates Simon , Donald Paul F.
Published: March 2003

1. The populations of many UK farmland birds declined between 1970 and 1990, frequently accompanied by contractions in breeding ranges. Ornithological atlas data, land use data and environmental data at the scale of 10‐km squares were used to investigate the relationship between local extinctions and habitat suitability for six species, and to predict where future losses are most likely.

2. For each species we tested the hypothesis that local extinctions were concentrated in environments that were inherently less suitable. We also tested the hypothesis that spatial patterns of loss were not independent between species due to their concurrence in the same habitats.

3. Multivariate analyses (PCA) showed that areas where each species became extinct between 1970 and 1990 were more similar in land use type, climate and topography to areas where a species was never present than those where it was retained; local extinction was more likely in less suitable environments. Multiple logistic regression showed that for five of the six species the environmental gradient best predicting presence or absence in 1970 was also that best predicting loss between 1970 and 1990. For the six species studied, local extinctions were least likely in lowland arable areas.

4. For any pair of species, local extinctions were more frequent outside the area of overlap of the two species' ranges than inside. Within the area of overlap, species tended to be lost from the same squares. For each species, likelihood of local extinction declined with increasing number of the other five species present.

5. We used model parameters to map the probability of future local extinctions of the six species considered, allowing the identification of key areas for conservation management at a spatial scale appropriate to agri‐economic incentives.