bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spatial and temporal variation in demography of a house sparrow metapopulation
Authors: Saether Bernt‐Erik , Ringsby Thor Harald , Bakke Øyvind , Solberg Erling Johan 
Published: March 2003

1. In order to compare spatial and temporal variation in the demography of a metapopulation of house sparrows living on four islands off the coast of Northern Norway, we computed the asymptotic population growth rate (λ) for three transitions between years, using a projection matrix model. 2. The mean growth rate of the metapopulation was positive (λ = 1·05). 3. Large variation was found in space and time in the asymptotic growth rate. Even though the standard deviations of the estimates were large, λ was significantly greater than 1 on one island in 2 out of 3 years. In contrast, λ significantly less than 1 occurred on an island on five occasions. 4. Decomposition of the magnitude of the spatial and temporal components of λ showed that one year (1995) had a particularly negative impact on λ. In contrast, one island had a great positive effect. 5. These differences in λ were most closely related to variation in the juvenile survival rate and in the fecundity rate, which, in turn, was closely related to variation both in space and time in the proportion of the eggs that produced a fledgling. 6. As expected from the large spatio‐temporal variation in λ, the sensitivities and the elasticities of λ to variation in the different elements in the projection‐matrix also differed both in space and time. When λ was small, it was most influenced by variation in adult survival rate. In contrast, for large λ, it was most sensitive to variation in the recruitment rate. 7. We suggest that conditions during the breeding season determine whether a population acts as a source or sink in this temperate small passerine metapopulation, and that the ratio of juveniles to adults can be used to characterize populations as sources or sinks. 8. These results demonstrate large variation in space and time in the demography of a small passerine metapopulation. These differences result from a combination of regional effects on the whole metapopulation, and factors that occur at one particular island in a single year.
Juvenile migration in brown trout: a consequence of energetic state
Authors: Forseth Torbjørn , Nesje Tor F. , Jonsson Bror , Hårsaker Karstein 
Published: March 2003

1. We explored the mechanisms determining age and size at juvenile migration in brown trout Salmo trutta L. A 133Cs tracer methodology was used to estimate food consumption of juvenile brown trout in a Norwegian stream, and the energy budgets of early migrants and stream residents were compared. 2. Fast‐growing brown trout migrated to the lake earlier and at a smaller body size than slower‐growing individuals. The 2+ migrants were significantly larger than those that remained 1 or more years longer in the stream. The 3+ migrants were significantly larger than the 2+ migrants. Some fast‐growing males matured in the stream, whereas all females left the stream before maturing sexually. 3. The food consumption and the energy budgets for 2+ migrants were more than four times higher than those of the resident 2+ fish. Total energy allocated to growth was also higher among migrants, and the total metabolic costs were five times higher among migrants than among resident fish. 4. The proportional energy allocation to growth among the 2+ migrants was much lower (about half) than that of those remaining longer in the stream. The reduction in the proportion of energy available for growth from age 1+ to 2+ was larger among migrants (88%) than among resident fish (68%). Reduction in the proportion of energy available for growth is a probable explanation for why migrations are initiated at age 2. 5. Our study supports the hypothesis that fast‐growing individuals shift their niche earlier and at a smaller body size than slower‐growing individuals because they maintain higher metabolic rates and are energetically constrained at a younger age by limited food resources than slow growers.
Threat from deforestation to montane and lowland birds and mammals in insular South‐east Asia
Authors: Brooks Thomas M. , Pimm Stuart L. , Kapos Valerie , Ravilious Corinna 
Published: March 2003

Summary1. A reduction in forest area should result in a reduction of its number of species and, moreover, do so in a characteristic way according to the familiar species‐area relationship.Brooks, Pimm & Collar (1997)applied this formula to the losses in forest area in the Philippines and Indonesia. Independently derived totals of the number of endemic bird species that are threatened with extinction broadly agree with these predicted losses. In some cases, however, predicted losses overestimate or underestimate the actual numbers of threatened species.2. Within an island, the proportionate deforestation to date might be most extensive where there are many endemic species, or where there are few. To test this possibility, we obtained recent forest cover data for the region. We separated lowland (< 1000 m a.s.l.) from montane (> 1000 m a.s.l.) forest cover by overlaying topographic maps. From these data, we predict separately the numbers of montane and lowland endemic bird species likely to become extinct as a result of deforestation. We then compared these totals with the numbers considered threatened in the latestRed List.3. Our predictions based on deforestation closely match the numbers of threatened endemic birds in the lowlands, but underestimate them in montane regions.4. Our predictions based on deforestation underestimate the number of threatened montane mammal species even more seriously.5. Lowland faunas of insular South‐east Asia are under extreme threat because of massive deforestation. The region's montane faunas appear seriously threatened even by low levels of deforestation.
What causes generation cycles in populations of stored‐product moths?
Authors: Briggs C. J. , Sait S. M. , Begon M. , Thompson D. J. , Godfray H. C. J. 
Published: March 2003

Summary 1. Populations of stored‐products moths such as the Indian meal moth (Plodia interpunctella) frequently show generation cycles, fluctuations with a period of approximately one generation. 2. Three age‐structured models of stored‐product moth dynamics were investigated to see which best accounted for the observed period and pattern of Plodia dynamics. 3. A model of
Gurney, Nisbet & Lawton (1983) was modified to match Plodia biology. The model assumes uniform competition amongst larvae. It predicted generation cycles, but of too long a period and with the wrong larval cohort structure. 4. The introduction of asymmetric competition (young larvae more sensitive to resource depletion but exerting weaker competitive effects) could produce generation cycles but for parameters appropriate to Plodia predicted cycles with a period of half a generation. 5. Introducing egg cannibalism to the asymmetric competition model led to the prediction of generation cycles of the right period and cohort structure for Plodia parameters.
Chronic fishing disturbance has changed shelf sea benthic community structure
Authors: Kaiser M. J. , Ramsay K. , Richardson C. A. , Spence F. E. , Brand A. R. 
Published: March 2003

Summary 1. Bottom fishing using towed nets and dredges is one of the most widespread sources of physical disturbance to the continental shelf seas throughout the world. Previous studies suggest that degradation and ecosystem changes have occurred in intensively fished areas. Nevertheless, to date it has been difficult to attribute habitat and benthic community changes to fishing effort at a spatial scale that is truly representative of commercial fishing activities. 2. In this study we present convincing evidence that chronic bottom‐fishing disturbance has caused significant and widespread changes in the structure of two distinct soft‐sediment benthic assemblages and habitats. 3. Our study compared the benthic fauna found in areas that have been exposed to either high or low levels of bottom‐fishing disturbance over the past 10 years. We were able to validate the fishing effort data in some areas using scars in the shells of a long‐lived bivalve mollusc (Glycymeris glycymeris) which result from fishing disturbance. Shell scars occurred most frequently in bivalves collected from the area of highest fishing effort. 4. Multivariate analyses and the response of abundance/biomass curves indicated that chronic fishing has caused a shift from communities dominated by relatively sessile, emergent, high biomass species to communities dominated by infaunal, smaller‐bodied fauna. Removal of emergent fauna has thus degraded the topographic complexity of seabed habitats in areas of high fishing effort. The communities within these areas currently may be in an alternative stable state.
Bird diversity and environmental gradients in Britain: a test of the species–energy hypothesis
Authors: Lennon J. J. , Greenwood J. J. D. , Turner J. R. G. 
Published: March 2003

1. We tested the species diversity–energy hypothesis using the British bird fauna. This predicts that temperature patterns should match diversity patterns. We also tested the hypothesis that the mechanism operates directly through effects of temperature on thermoregulatory loads; this further predicts that seasonal changes in temperature cause matching changes in patterns of diversity, and that species’ body mass is influential.2. We defined four assemblages using migration status (residents or visitors) and season (summer or winter distribution). Records of species’ presence/absence in a total of 2362, 10 × 10‐km, quadrats covering most of Britain were used, together with a wide selection of habitat, topographic and seasonal climatic data.3. We fitted a logistic regression model to each species’ distribution using the environmental data. We then combined these individual species models mathematically to form a diversity model. Analysis of this composite model revealed that summer temperature was the factor most strongly associated with diversity.4. Although the species–energy hypothesis was supported, the direct mechanism, predicting an important role for body mass and matching seasonal patterns of change between diversity and temperature, was not supported.5. However, summer temperature is the best overall explanation for bird diversity patterns in Britain. It is a better predictor of winter diversity than winter temperature. Winter diversity is predicted more precisely from environmental factors than summer diversity.6. Climate change is likely to influence the diversity of different areas to different extents; for resident species, low diversity areas may respond more strongly as climate change progresses. For winter visitors, higher diversity areas may respond more strongly, while summer visitors are approximately neutral.
Species richness of insects and mites on trees: expanding Southwood
Authors: Brändle Martin , Brandl Roland 
Published: March 2003

Summary Data on the species richness of phytophagous insects and mites associated with 25 tree genera occurring as natives in Germany were compiled and compared to data for British trees published byKennedy & Southwood (1984). For tree genera occurring in Germany and Britain patterns of species richness and composition of phytophage faunas were similar. Present abundance of trees, their distributional history during the Holocene, morphological traits and taxonomic isolation were used to explain the variance of species richness and proportion of specialists across tree genera occurring as natives in Germany. Tree genera were either used as independent data points or to calculate phylogenetically independent contrasts. For the latter approach, a phylogeny for the tree genera was generated from publishedrbcL gene sequences. In general, the conclusions from the two types of analyses were similar. The species richness of phytophages on German tree genera were positively related to present tree abundance, tree height and tree abundance derived from pollen samples. For phylogenetically independent contrasts the length of time a genus was present since the end of the last glaciation also became significant. The proportions of specialists showed a negative relationship with present abundance of trees, a positive relationship with taxonomic isolation as well as the length of time of genus was present since the end of the last glaciation. For phylogenetically independent contrasts only the latter two variables remained significant. Overall the results support the species–area and the coevolutionary hypotheses.
High predictability in introduction outcomes and the geographical range size of introduced Australian birds: a role for climate
Authors: Duncan Richard P. , Bomford Mary , Forsyth David M. , Conibear Louise 
Published: March 2003

Summary

We investigated factors hypothesized to influence introduction success and subsequent geographical range size in 52 species of bird that have been introduced to mainland Australia.
The 19 successful species had been introduced more times, at more sites and in greater overall numbers. Relative to failed species, successfully introduced species also had a greater area of climatically suitable habitat available in Australia, a larger overseas range size and were more likely to have been introduced successfully outside Australia. After controlling for phylogeny these relationships held, except that with overseas range size and, in addition, larger‐bodied species had a higher probability of introduction success. There was also a marked taxonomic bias: gamebirds had a much lower probability of success than other species. A model including five of these variables explained perfectly the patterns in introduction success across‐species.
Of the successful species, those with larger geographical ranges in Australia had a greater area of climatically suitable habitat, traits associated with a faster population growth rate (small body size, short incubation period and more broods per season) and a larger overseas range size. The relationships between range size in Australia, the extent of climatically suitable habitat and overseas range size held after controlling for phylogeny.
We discuss the probable causes underlying these relationships and why, in retrospect, the outcome of bird introductions to Australia are highly predictable.
Intraguild predation in larval parasitoids: implications for coexistence
Authors: Borer Elizabeth T. 
Published: March 2003

SummaryMany coexisting parasitoids interact via intraguild predation (IGP); however, in IGP theory without stage structure the intraguild predator and intraguild prey coexist via this mechanism over only a relatively narrow region of parameter space. A recent formulation of IGP theory with a stage of the intraguild prey species that is invulnerable to attack by the intraguild predator shows that coexistence between guild members can occur across a much broader range of resource productivity than is predicted by IGP theory without stage structure. These general theoretical predictions are used to explore the implications for coexistence ofAphytis melinus(DeBach) andEncarsia perniciosi(Tower), a pair of parasitoids that coexist on California red scale.Reanalysis of a published laboratory competition experiment between two parasitoid species suggests thatAphytis, an ectoparasitoid, survives at a lower rate when the reparasitized host contains a more developed juvenile endoparasitoid (Encarsia). This pattern is contrary to a common assumption that ectoparasitoids always consume endoparasitoids in a shared host, and may affect coexistence. The experiment covered only the first ∼30% of theEncarsiadevelopment period and did not describe the outcome forEncarsia, so the dynamic effects of this interaction in the context of IGP remain unclear. In addition,Encarsiais capable of parasitizing much younger hosts than isAphytis, which the experiment did not examine.The experiment was repeated, and extended to cover the full developmental duration ofEncarsia. An additional experiment was performed to explore whetherEncarsiacould pre‐emptAphytisby attacking younger hosts.Aphytisjuvenile survival was found to decrease as a function of the age of the juvenileEncarsiaonto which it was laid. WhenEncarsiaparasitized very young hosts, it was increasingly invulnerable to attack byAphytisand increasingly more likely to survive to emergence. However, until the formation of an invulnerable pseudomoult,Encarsiawas always killed in larger hosts, regardless of its age at the time ofAphytisattack.According to stage‐structured IGP theory, the decline inAphytissuccess combined with an invulnerableEncarsiastage may promote coexistence in this system.
Factors affecting the establishment of Cytisus scoparius in southern France: implications for managing both native and exotic populations
Authors: PAYNTER QUENTIN , FOWLER SIMON V. , MEMMOTT JANE , SHEPPARD ANDREW W. 
Published: March 2003

Summary

The ecology of the woody shrub Cytisus scoparius was studied for 4 years in its native range in southern France to investigate how it can become an invasive weed.
The proportion of the seed bank that germinated each year was highest in disturbed plots and was correlated with the March rainfall. The seed bank declined at a rate of c. 50% per year when fresh seed rain was excluded.
The fate of 2863 seedlings was followed for a variety of treatments.
Seedling survival depended on disturbance: none survived their first summer in undisturbed plots; more than 40% survived their first summer and c. 14% survived to flowering age in plots that were initially cultivated.
Seedlings flowered first in their fourth year, although only c. 10% set seed.
Neither inter‐ nor intraspecific competition was found to affect significantly seedling survival on cultivated plots. However, some seedlings grown in the absence of interspecific competitors flowered and set seed in their third year.
Applications of insecticide, molluscicide or fungicide did not affect significantly seedling survival, growth or minimum age of reproduction on cultivated plots.
It is concluded that management strategies should minimize disturbance to competing vegetation, which can inhibit germination and smother emerging seedlings. In many circumstances strategies that target the seed bank, such as burning, are not expected to work.
Herbivores and pathogens may prevent stand re‐establishment indirectly, by reducing the size, vigour and density of broom plants so that competing vegetation can persist and smother emergent seedlings following the death of the parent stand.
Host‐plant affinities of two biotypes of Dactylopius opuntiae (Homoptera: Dactylopiidae): enhanced prospects for biological control of Opuntia stricta (Cactaceae) in South Africa
Authors: Volchansky C. R. , Hoffmann J. H. , Zimmermann H. G. 
Published: March 2003

1. Until recently, neither the phycitid moth Cactoblastis cactorum nor the cochineal insect Dactylopius opuntiae have been satisfactory biological control agents of Opuntia stricta in South Africa. 2. In marked contrast, both of these agents have kept O. stricta under biological control for many decades in Australia. 3. In an attempt to improve the situation in South Africa, a stock of D. opuntiae was obtained from O. stricta in Australia during 1996. 4. Host‐specificity tests confirmed that the newly imported D. opuntiae from Australia is a different biotype to the one already established in South Africa. 5. The Australian (‘stricta’) biotype thrives on O. stricta but is unable to develop satisfactorily on O. ficus‐indica, while the converse is true for the South African (‘ficus’) biotype, which thrives on O. ficus‐indica but fares poorly on O. stricta. 6. The integrity of the host‐plant specificity of the two biotypes of D. opuntiae has important implications for biological control of Cactaceae in South Africa, and has greatly enhanced prospects that O. stricta can be brought under biological control successfully.
Variation in the effectiveness of symbiotic associations between native rhizobia and temperate Australian Acacia: within‐species interactions
Authors: Burdon J. J. , Gibson A. H. , Searle Suzette D. , Woods M. J. , Brockwell J. 
Published: March 2003

1. The ability of different rhizobial isolates collected from any one site to establish effective nitrogen‐fixing associations with host‐plants from that site showed significant variation in 22 host Acacia species and nearly all of 67 populations. The average Acacia host–Rhizobium strain combination was only about 70% effective. Many combinations were far poorer; in a few cases the worst combination resulted in plants less than one‐tenth the size of the best combinations. 2. The ability of rhizobial isolates to form effective symbiotic interactions showed marked host population and rhizobial‐isolate effects in a study of eight, four and nine populations of A. dealbata, A. implexa and A. mearnsii. A more complete trial involved three populations of each of A. dealbata, A. implexa, A. irrorata, A. mearnsii and A. melanoxylon. These were inoculated with a range of rhizobial isolates previously shown to be highly, moderately or weakly successful in forming an effective association. Evidence of marked host population and rhizobial origin effects was found but there was very little evidence of isolate–host population interaction effects. 3. The general lack of host population–rhizobial origin interaction effects suggests that rhizobial strains selected as highly effective for an Acacia species growing in a particular population will generally perform well symbiotically with that species in other populations. This will make their practical application as inoculants in revegetation and forestry situations much easier. 4. Significant host‐based variability in the ability to form effective symbiotic interactions was detected in comparisons of half‐sib families of A. dealbata, A. mearnsii and A. melanoxylon. In the case of A. dealbata, the interaction between half‐sib family lines and rhizobial isolates was complex, with ‘locally’ derived isolates performing better than ‘foreign’ ones. There were also significant interaction effects. In A. mearnsii, on the other hand, the only significant differences were detected between the response of different half‐sib families to the same rhizobial isolate. The occurrence of host‐based variability indicates that in Acacia breeding programmes attention should be given to the possibility of inadvertent selection affecting these relationships.