bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimating asymptotic body size and testing geographic variation in Agama impalearis
Authors: Brown Richard P. , Znari Mohammed , Hassan El , Mouden El , Harris Peter
Published: July 2006

Methods for estimating ‘typical’ asymptotic‐ body size in populations of the North African agamid Agma impalearis using individuals of undetermined age were investigated, and the pattern of geographic variation in this characteristic described and tested against simple models based on putative causes. Resampling of a large single‐site data set indicated that use of the sample mean led to substantial underestimation of asymptotic size while use of the largest animal per sample led to overestimation, on average. The 80th percentile provided the most accurate estimate of asymptotic size and, compared with the largest individual per sample, had low variance, showed low dependence on sample size and was amenable to bootstrap estimation of confidence intervals. A clear pattern of geographic variation in asymptotic size was evident across Morocco: animals were smallest in the north and east and largest in the southwest. This pattern was discordant with previously‐described patterns of variation in scalation and size‐free body dimensions and, unlike these characteristics, could not be explained by a model based on secondary contact of previously vicariant populations. Among‐site differentiation was strongly associated with a model based on a proxy of current potential gene flow between sites, supporting an alternative in situ differentiation hypothesis based on the combined effects of isolation‐by‐distance and the dispersal barrier provided by the higher parts of the Atlas mountain range. Possible reasons for the discordance between the pattern of variation in body size and other morphological characteristics are discussed
Bird communities of natural and modified habitats in Panama
Authors: Petit Lisa J. , Petit Daniel R. , Christian Daniel G. , Powell Hugh D. W.
Published: July 2006

Only a small proportion of land can realistically be protected as nature reserves and thus conservation efforts also must focus on the ecological value of agroecosystems and developed areas surrounding nature reserves. In this study, avian communities were surveyed in 11 habitat types in central Panama, across a gradient from extensive forest to intensive agricultural land uses, to examine patterns of species richness and abundance and community composition. Wooded habitats, including extensive and fragmented forests, shade coffee plantations, and residential areas supported the most species and individuals. Nearctic‐Neotropical migratory species were most numerous in lowland forest fragments, shade coffee, and residential areas. IntroducedPinus caribbeaand sugar cane plantations supported the fewest species compared to all other habitats. Cattle pastures left fallow for less than two years supported more than twice as many total species as actively grazed pastures, such that species richness in fallow pastures was similar to that found in wooded habitats. Community similarities were relatively low among all habitat types (none exceeding the observed 65% similarity between extensive and fragmented lowland forests), but communities in shade coffee and residential areas were 43% and 54′% similar to lowland forest fragments, respectively. Fallow pastures and residential areas shared 60% of their species. Bird communities in shade coffee and residential areas were characterized by higher proportions of frugivorous and nectarivorous species than in native forests. These same guilds also were better represented in fallow than in grazed pastures. Raptors and piscivorous species were most prevalent in cattle pastures and rice fields. These results, though based upon only species richness and abundance, demonstrate that many human‐altered habitats have potential ecological value for birds, and conservation efforts in tropical areas should focus greater attention on enhancement of agricultural and developed lands as wildlife habitat. To understand the true conservation value of these modified lands will require examination not only of numbers but also of the types of species supported by these habitats, their reproductive output and survival rates.
Sexual reproductive ecology of Carex bigelowii an arctic‐alpine sedge
Authors: Stenström Anna
Published: July 2006

Carex bigelowii an arctic‐alpine sedge that shows an extensive clonal growth, and in many years also has a high degree of flowering. To see which factors are most important in determining the sexual reproductive success, the effects of self‐ and cross‐pollination, pollen donor distance, amount of pollen, temperature, and time of flowering were studied. The study was conducted at Latnjajaure Field Station, northern Sweden and Thingvellir National Park, Iceland during three field seasons. Experimentally increased air temperature raised the fruit set and the fruit weight, in two of the three seasons. Pollen donor distance did not influence either fruit set or fruit weight, and there was no difference in fruit weight between selfing and cross‐pollination. An increased amount of pollen raised the fruit set. but did not affect fruit weight. The time of flowering was also important; there was a negative relationship between flowering time and fruit set and fruit weight, i.e. late flowering ramets had a lower fruit set and fruit weight. The results suggest that Carex bigelowii is an outcrossed species where the reproductive success is mainly determined by the weather, and that there are differences between the two study sites.
The structure of a high latitude plant‐flower visitor system: the dominance of flies
Authors: Elberling Heidi , Olesen Jens M.
Published: July 2006

The species richness of insect flower visitors to all angiosperms at a subarctic‐alpine site in northern Sweden was described and the plant‐flower visitor matrix was analysed and compared to other high latitude systems and with systems from lower latitudes. In the habitat, 23 plant species had a total of 242 interactions with 388 flower‐visiting insects, belonging to 118 taxa. Connectance of the plant‐flower visitor matrix was 8.9. Comparing our findings with other studies, we get that the proportion of dipteran species of the total pollinator fauna increases with latitude but that the proportions of species of Diptera, Hymenoptera and Lepidoptera do not vary significantly among high latitude systems. Muscidae and Empididae were more abundant and generalised than other dipteran families visiting flowers in the arctic, their proportions of the total Diptera fauna increase with latitude and they are the most widespread families of flower‐visiting insects in the arctic. Several Muscidae species are typical to alpine habitats in the arctic‐subarctic zone. These species have special pollen feeding behaviour and an elongated proboscis, which improves access to closed flowers.

Compared to other published pollination system studies, the connectance of low latitude systems ranges between 3.4 and 28.1, whereas high latitude and high altitude systems vary between 8.6 and 19 (‐60).
Determinants of helminth aggregation in natural host populations: individual differences or spatial heterogeneity?
Authors: Haukisalmi Voitto , Henttonen Heikki
Published: July 2006

We assessed the importance of spatial heterogeneity for the aggregation of helminth populations in the bank vole Clethrionomys glareolus (Arvicolinae) using a previously published method which allows to analyse parasite aggregation at two host population levels, i.e., within and between spatial samples of the host population.

In the main empirical material from Finnish Lapland (Pallasjärvi), all five helminth species were significantly aggregated within study sites, but only three rare species showed significant aggregation among sites. In all helminth species, the total aggregation was primarily (79‐98%) determined by aggregation within sites, i.e., between host individuals. Despite the larger spatial scale and more heterogeneous landscape, the comparative material from South Finland (Luhanka) supported the generally high proportion of the total aggregation due to within‐site heterogeneity.

Despite the clear interspecific differences in patchiness of helminth populations, the proportion of the total aggregation due to among‐site heterogeneity did not vary significantly among helminth species. The results indicate a link between aggregation at two population levels; species that showed strong within‐site aggregation were also characterised by pronounced spatial heterogeneity and significant among‐site aggregation.
Developmental strategies of Koenigia islandica, a high‐arctic annual plant
Authors: Heide Ola M. , Gauslaa Yngvar
Published: July 2006

Seed germination, growth and flowering of the arctic‐alpine annual Koenigia islandica were studied in controlled environment. Intact (unabraded) seeds germinated poorely at temperatures up to 18°C, with an optimum at 24°C (89% in 10 d). Scarified seeds germinated rapidly, and reached 100% germination in 3 d at 21°C, but no >40% germination occurred at 9 and 12°C, The seeds had no light requirement for germination, nor did fluctuating temperatures improve germination

Dry matter production was optimal at 12°C in both short day (SD) and long day (LD) conditions, but was markedly higher in LD than in SD at identical fluences at all temperatures except 21°C where the plants showed symptoms of severe heat stress. The temperature compensation point for net productivity was estimated to 24°C, and negative carbon balance at higher temperatures might be an important physiological mechanism limiting the distribution of K. islandica in Scandinavia.

Flowering was extremely rapid and independent of daylength, even in a high‐arctic population from 79°N, In full summer daylight anthesis was reached 24 d after germination and seeds ripened after 36 d at 15°C, Days to anthesis varied little across the temperature range from 6 to 21°C, giving a linear decrease in the heat‐sum requirement for the attainment of flowering with decreasing temperature.

It is concluded that conservative seed germination strategy, tininess and rapid development, low temperature optima for growth and reproduction, and daylength indifference of flowering are important adaptations for success of an annual plant in high‐arctic and high‐alpine environments, Daylength neutrality has facilitated the wide‐latitudinal distribution of K. islandica. including the penetration of the species to the southern hemisphere.
Detecting decline in a formerly widespread species: how common is the common blue butterfly Polyommatus icarus?
Authors: León‐Cortés Jorge L. , Cowley Matthew J. R. , Thomas Chris D.
Published: July 2006

Grid square distribution maps have been used widely to measure rates of decline and target conservation resources. However, common species that may have many populations per grid square can decline substantially from within squares without being lost from entire squares. In order to quantify this process, fine scale population and habitat data have been collected for the common blue butterfly Polyommatus icarus in a 35 km2 area of fragmented landscape in north Wales. Present day habitat associations, determined from over 2000 transect walks, combined with data on historical and present day habitat distributions reveal that the species has declined by about 74% since 1901. Similar data concerning the species major host plant Lotus corniculatus indicate a decline of 46%. Based on 1 km2 grid maps, neither species have been assessed as declining at all. These results suggest that apparently ‘common’ species may have declined just as much as many of Britain's rare species: using present methods of assessment these declines are undetected.
Effects of salinity on rates of infestation of waterbirds by haematozoa
Authors: Figuerola Jordi
Published: July 2006

A recent hypothesis suggested that migration patterns in waders and other birds could be shaped by the distribution of parasites and diseases. This hypothesis assumes a reduced exposure to parasites in species living in saline habitats. To test this assumption. the number of species of haematozoa and rates of infection reported for bird species living in fresh and salt‐water habitats were compared. Speceses living in more saline habitats had fewer haenatozoic parastte species than freswater birds., Relative frequency of infection was also lover in saltwater species. Neither phylogeny not the number of individuals examined for blood parasies in each species explained these diferencfes. Thus there is indece evidence hat birds living in saline habitats have a reduced risk of being parasitized by haematozoa. Probably due to a reduced abundance of the inverebtare vectors.
Body size and migration rate in moths
Authors: Nieminen Marko , Rita Hannu , Uuvana Paavo
Published: July 2006

Migration rate is often thought to be affected by species distribution, abundance, body size, and niche width, but empirical results are controversial and fragmentary. In this study we examined these relationships in a large assemblage of noctuid moths. Migration rate was measured using two approaches, directly with a mark‐recapture study in a network of small islands, and indirectly on the basis of the occurrence of moths outside their breeding habitat. The effects of the factors assumed to affect migration rate were adjusted for taxonomy using a simple yet novel approach based on logistic regression. Both with and without adjusting for taxonomy, the results indicate that abundance and body size influence migration rate, that the effects of abundance and body size have a negative interaction, and that the effects of ecological specialization on migration rate are evident (monophagous species migrate less than oligophagous or polyphagous species). The incidence of island or habitat patch occupancy was not affected by body size, most likely because body size has several contrasting consequences on the processes that determine island occupancy. Migration rate appears to be an evolutionarily labile character, which can readily transform in different phylogenetical lineages of moths.
Woody plant colonization in an experimentally fragmented landscape
Authors: Yao Jin , Holt Robert D. , Rich Paul M. , Marshall Wendy S.
Published: July 2006

The pattern of distribution and abundance of woody plants colonizing old fields is influenced by landscape spatial features, in particular, by the distance from the old field to propagule sources and the size of the habitat patches undergoing succession. Colonization is also influenced by species life history traits, such as dispersal mode, growth form, and fecundity. As part of a long‐term project studying effects of habitat fragmentation on secondary succession at the prairie‐forest ecotone, we have examined the colonization patterns of early‐successional woody plants in an experimentally fragmented old field, with emphasis on the three woody species [Cornus drummondii C. A. Mey (rough‐leaved dogwood), Ulmus rubra Muhl. (slippery elm), and Juniperus virginiana L. (red cedar)], which currently dominate the woody community on the site. The shapes of the colonization curve (proportion of colonized quadrats vs time) differed between C. drummondii and U. rubra. The rate of colonization by C. drummondii showed a pattern of acceleration after its initial colonization, consistent with rapid in situ recruitment from clonal growth and early seed production. By contrast, colonization by U. rubra fits a roughly linear pattern, consistent with recruitment only from external propagule sources. For both C. drummondii and U. rubra, density is currently greater in large patches than in small patches. No patch size difference was found for J. virginiana. The stern density of both C. drummondii and U. rubra exponentially decreased with distance to external propagule sources. The negative exponential pattern of U. rubra (wind‐dispersed) with distance is sharper than that of C drummondii (bird‐dispersed). Moreover, the amount of spatial variation in density explained by distance to source is greater on small patches. Our results highlight the importance of life history traits of colonizing species and spatial aspects of habitat during succession.
Socioecologies
Authors: Haila Yrjö
Published: July 2006

I chart ways in which ecology could improve its performance in assessing the humanity‐nature relationship. The life of humans, similar lo all biological organisms, depends on utilization of their environment which is changed as a result. To evaluate the consequences, a broad range of issues needs to be addressed ranging from the historical dynamics of cultural development to specific idiosynchratic features of particular environmental issues. One should avoid nature‐culture dualism both in theoretical thinking and practical research. A typical form of such dualism in ecologically informed environmentalism is an assumption that productivity of socio‐economic systems vs natural systems is a zero‐sum game: this assumption is unfounded. Ecology should take the ecological conditions of human existence seriously and make judgements on the relationship of people with their natural environment in various historical situations in a contextually sensitive way. I end by listing several types of positive contribution that ecology could give to societal discussion on the human environmental predicament; the most Important challenge is to point out new possibilities even in situations which seem hopeless.
The influence of fragment size and edge on nest predation in urban bushland
Authors: Matthews Alison , Dickman Christopher R. , Major Richard E.
Published: July 2006

To test the effects of habitat fragmentation and edge on the rate of nest predation in an urban ecosystem, 20 artificial nests each containing 2 plasticine eggs were distributed in each of 24 bushland sites in Sydney, Australia. the eastern yellow robin Eopsaltria australis was adopted as a target species, and variables of nests, eggs and nesting behaviour were manipulated in experiments. Sites ranged in size from 3.8 ha to 14717 ha and were divided into three size classes: 1) 0–10 ha. 2) 11–100 ha and 3) ≥101 ha. Nests were positioned either around the edge of the fragment (within 50 m from the fragment boundary) or within the centre of the fragment (< 50 m from the fragment boundary). The predation rate was calculated as the percentage of nests that had one or both eggs damaged or removed after 15 d of exposure. Nest predation rates were high (average 70.6%) but were not affected by patch size or distance from fragment edges. Predators were identified by marks of the beak or teeth left in the plasticine eggs. Nest predators identified were birds, black rats, brown antechinus and ringtail possum, with the majority of predation being by birds (61.7%), Our findings differ from those of most previous studies of nest predation, and perhaps reflect the ubiquity of generalist predators and the degree of habitat modification throughout remnants of bushland in the urban environment.
Distribution patterns of Cladocera in subarctic Fennoscandian lakes and their potential in environmental reconstruction
Authors: Korhola Atte
Published: July 2006

Multivariate statistical techniques were used to examine the relationships between surface‐sediment cladoceran assemblages and 28 physical and chemical variables in 53 small subarctic lakes from northern Fennoscandia. The lakes were distributed along a steep eco‐climatic gradient, spanning boreal corniferous forest to treeless tundra. In general, the sites were small, oligotrophic, and bathymetrically simple, with little or no disturbance in their catchments. From the initial 53 localities, only 36 contained a sufficient number of cladoceran remains for reasonable quantification. From these, a total of 29 cladoceran taxa representing 19 genera were identified, comprising predominantly littoral chydorid species. A constrained redundancy analysis (RDA) and associated Monte Carlo permutation tests indicated that maximum lake depth, sediment organic content, epilimnetic summer temperature, lake perimeter, and lake catchment area made statistically significant (p le; 0.05) contributions to explaining the variance in the cladoceran taxon data. These five variables together accounted for 67.7% of the explained variance, and made a unique contribution of 26.8% to the total variance: all physical determinants independently captured 33.2% of the total variance. The significance of the most powerful explanatory variables is discussed in the paper in detail, and autecological information regarding the most common cladoceran taxa is given.

To assess the potential of cladoceran assemblages in environmental reconstruction, quantitative inference models for mean July water and air temperatures were developed for the cladoceran assemblage using partial least squares (PLS) regression. The final prediction model yielded a root mean squared error of prediction (RMSEP). as assessed by jackknifing, of 1.19°C for Cladocera‐water temperature data‐set, whereas the cladoceran assemblages showed only very weak relationships to mean July air temperature. The overall results emphasize the role of physical factors in regulating species abundance and distributions in these environmentally sensitive ecotonal lakes.
Temporal dynamics of grouse populations at the southern edge of their distribution
Authors: Cattadori Isabella M. , Hudson Peter J.
Published: July 2006

Studies of grouse conducted at northern latitudes have shown that tetraonids frequently exhibit cyclic fluctuations in abundance but little is known about the dynamics of grouse species at the southerly edge of their range. Hunting statistics from four species of grouse based on 30 yr of data collected from 210 hunting areas were examined from the Dolomitic Alps in the province of Trentino. These data were summed to represent 18 time series from discrete mountain groups. Analyses identified cycles of ca 5 yr in the minority of rock ptarmiganLagopus mutusand hazel grouseBonasa bonasiapopulations. These cycles only showed significant negative autocorrelation at half the cycle period and were classified as phase‐forgetting quasi‐cycles. Cycles were not found in time series of black grouseTetrao terixor capereaillieTetrao urogallus.Correcting time series for hunting effort or hunting restrictions tended to increase the proportion of populations that exhibited cycles but no difference in the strength of second order density dependence, A linear first order density‐dependent autoregressive model described the dynamics of most of the populations with the exception of a proportion of rock ptarmigan and black grouse populations where a non linear first order model provided the best tit. We compare the findings with studies conducted in Finland and suggest possible reasons for the reduced tendency to cycle in the populations of southern Europe.
Dynamics of plant and arthropod diversity during old field succession
Authors: Siemann Evan , Haarstad John , Tilman David
Published: July 2006

The successional dynamics of arthropod diversity in 18 abandoned agricultural fields (age 15‐54 yr) at Cedar Creek. MN. USA were determined using sweep net sampling (44833 individuals of 618 species). Total arthropod species richness and equitability (J), but not abundance, increased significantly with field successional age. Herbivore and parasite species richness, but not detritivore and predator species richness, also increased significantly with field age. All of these arthropod variables were significantly positively correlated with plant species richness in the fields. When plant species richness was included as a covariate in regressions, there were no longer any significant effects of field age. These results supported the hypothesis that increases in arthropod diversity with field age are influenced by increases in plant diversity. The additional significant positive dependence of herbivore species richness on predator species richness suggests that predator‐prey interactions may also influence the successional dynamics of arthropod diversity. Nine of the ten most common arthropod species decreased in abundance with field age, two of them significantly. The abundances of these two generalist forb‐feeding species, Melanoplus femurrubrum (Orthoptera: Acrididae) and Scaphytopius acutus (Homoptera: Cicadellidae). each depended significantly on amount of forbs. The average body size of arthropod species (total and herbivores) decreased significantly with field age. An efficiency vs specialization hypothesis predicts such a decrease. Because plants in later secondary succession are generally less palatable, a diversity of smaller, potentially more specialized herbivores may have an advantage over larger and more efficient herbivores in later succession.
Differential microdistributions and interspecific interactions in coexisting Gammarus and Crangonyx amphipods
Authors: MacNeil Calum , Elwood Robert W. , Dick Jaimie T. A.
Published: July 2006

In freshwaters in Northern Ireland, several amphipods occur, with the native Gammarus dubeni celticus and introduced Gammarus pulex and Crangonyx pseudogracilis often being found together in the same river and lake systems. We examined what may happen when the three amphipod species co‐occur within the same patch of lake or pooled area of a river. We conducted a laboratory simulation of a lake/river habitat, and this showed that G. d. celticus and G. pulex exhibited very similar distribution patterns to one another, when presented with the same complex habitat template. Such microdistribution patterns contrasted markedly with the microhabitat usage by C. pseudogracilis. Cannibalism was low for all species in both single and mixed species treatments. Intraguild predation (IGP) was also very low on both G. pulex and G. d. celticus when all three species co‐occurred. However, C. pseudogracilis suffered heavy IGP from both Gammarus species, with 33% of the tank population of C. pseudogracilis being eliminated in the presence of Gammarus within only 12 h. Such IGP may account for C. pseudogracilis occurring more frequently and in greater abundance in patches of natural lotic and lentic systems where predatory Gammarus are either absent or scarce.
Artificial nest predation rates in tropical and temperate forests: a review of the effects of edge and nest site
Authors: Söderström Bo
Published: July 2006

Nest predation rates are believed to be higher in tropical than in temperate forests. This notion is central in explaining different life history traits of tropical and temperate birds, but it is not known whether this assertion is true for all nest sites, such as ground and shrub nests, and at different distances from forest edge. I reviewed 22 studies using artificial nest experiments which concurrently contrasted predation rates of ground and shrub nests in temperate and tropical forests and found, contrary to the current dogma, no overall difference in predation rates between regions. However, there was a significant interaction between region and nest site. Ground nest predation rates were significantly higher in the tropical region, while predation rates on shrub nests were similar between regions. Within the tropical region, ground nests had significantly higher predation rates than shrub nests. Elevated nest predation rates at forest edges were found in both temperate and tropical forests. The results may have great implications for expected patterns of avian life histories and for the effects of forest fragmentation in temperate and tropical regions. First, if nest predation affects avian life histories, my results predict ground‐nesting species in tropical forests to have shorter nestling periods, more broods and smaller clutch sizes than shrub‐nesting species. Second, vulnerability of ground‐ and shrub‐nesting guilds is suggested to differ between regions due to differences in forest vegetation structure, and the composition of predator faunas and their specific responses to forest fragmentation. Data to test these hypotheses are limited, but agree with the results of this review.
Seasonal growth and diet of juvenile chinook salmon (Oncorhynchus tshawytscha) in demonstration channels and the main channel of the Waitaki River, New Zealand, 1982–1983
Authors: Power G.
Published: July 2006

Abstract– Juvenile chinook salmon in the Waitaki River, New Zealand and demonstration channels, living at about 16°C, increased in length by 0.32 mm day−1 between 4 November and 4 March. They gained weight quickly, accumulated large visceral fat deposits and had high conditions factors. At 1600 h, stomachs averaged half full. The number of prey tended to decline as the fish grew and consumed larger items. Initially the diet was based mainly on chironomid larvae, but by December it included a diversity of prey in more equal proportions. These included Deleatidium in the Waitaki; amphipods in the demonstration channels; various trichopterans, hemipterans, elmid beetles, zooplankton. terrestrial dipterans and a variety of other prey. There were significant differences between sites in numbers of prey consumed and these probably reflected differences in the benthos. Diets in the Waitaki differ from those in the Rakaia River and the food of juvenile salmon appears closely linked to the availability of a diverse range of possible prey.
Influence of geomagnetism on the activity and orientation of the eel, Anguilla anguilla (L.), as evident from laboratory experiments
Authors: Tesch F. ‐W. , Wendt T. , Karlsson L.
Published: July 2006

Abstract– Studies were performed with both a mechanical and a photosensory arrangement of the experimental tanks. Silver (migratory) eels were more active than yellow (stationary) eels. Comparison of pooled data on yellow eels tested under natural geomagnetic field conditions with those on eel tested under unnatural ones prcded no evidence of difference in activity. Silver and yellow eels showed stronger activity during the 6 days around new moon compared with the phase around full moon as well as a peak before new moon and a smaller peak before full moon. Under each kind of unnatural field condition, the activity relationships reversed or were cancelled. The directional choice of eels under natural conditions (controls) pointed to magnetic NW and mostly also in the opposite direction. When the magnetic north was changed by 90°, the tested yellow eels followed this change to about the same degree. The additional change of both the inclination (from 68° or 45° or 30°) and total intensity (by a reduction to 31% of the natural field) resulted in a change of the preferences of about 90° relative to magnetic north. Reversal of magnetic north by 180°, which is identical to a change of the inclination from 68° to 112°, also resulted in a change of the preferences by about 90°. Three experiments using compensation of both the horizontal and the vertical geomagnetic field led to circular directional preferences at random in two cases and in one case to about NW of the residual field magnetic north. The navigational abilities of the eel, on the basis of its magnetic sensitivity, are discussed.
Tests for migratory history of the New Zealand common smelt (Retropinna retropinna (Richardson)) using otolith isotopic composition
Authors: Northcote T. G. , Hendy C. H. , Nelson C. S. , Boubee J. A. T.
Published: July 2006

Abstract– Stable oxygen and carbon isotopic analyses were made for water at 24 sites, mainly from the Waikato watershed (North Island, New Zealand), and for carbonate from fish sagittal otolith material at each of the sites, mainly from the common smelt (Retropinna retropinna (Richardson)), to test their potential use in identification of resident and anadromous/migratory stocks suggested in an earlier pilot study. Results provide strong evidence that 18O is precipitated in otoliths close to isotopic equilibrium with rearing waters. The smelt rearing and residency waters examined have characteristic oxygen and carbon isotopic ‘signatures’, and the 18O composition of the smelt otoliths mirrors this within about 1%0, making it possible to use the technique for determining resident and/or migrant history of the fish. The 13C otolith composition, though usually tracking that of probable rearing and/or residency waters, has a larger and more variable offset, possibly of metabolic origin, making its use less reliable as a habitat signature.
Study of a sand smelt (Atherina boyeri Risso 1810) population reproducing in fresh water
Authors: Rosecchi E. , Crivelli A. J.
Published: July 2006

A population of sand smelts, Atherina boyeri, lives in the Camargue wetland, southeast France. This study deals with the part of the population that migrates towards the Fumemorte drainage canal, flowing into the brackish lagoon, the Etang du Vaccarès. Between autumn and early spring, some sand smelts migrate from the canal into seasonally flooded freshwater marshes, where they breed, and then leave between March and July, just before the marshes dry out. The sand smelts remaining in the canal use the vegetation‐choked smaller branches of the canal for breeding. In summer, most of the sand smelts leave freshwater habitats for the Vaccarès. Male and female sand smelts reach a maximum age of 4 years (5 winters), have the same weight and show a peak in condition in spring. Breeding occurs from March to July. Sand smelts are multiple spawners and batch fecundity increases with the female size. The mean egg diameter is independent of the female length but decreases towards the end of the spawning season. Sand smelts feed mainly on zooplankton and secondarily on benthic invertebrates. Temporary marshes are richer in submerged macrophytes needed for spawning and have lower densities of fish than the canal. In these marshes, sand smelts feed on the large forms of zooplankton that develop because of the low fish abundance. The life‐history traits of this population of A. boyeri living in fresh water in Camargue indicate that this environment is not unfavourable for this species. This study showed that this species can undertake local migrations to colonize various habitats. The adaptability of A. boyeri favours its survival in very unstable Mediterranean environments.
Ontogenetic diet shifts of age‐0 smallmouth bass (Micropterus dolomieu Lacepède) in the New River, West Virginia, USA
Authors: Easton R. S. , Orth D. J.
Published: July 2006

Larval and juvenile smallmouth bass (Micropterus dolomieu Lacepède; 8.5–85.0 mm total length (TL)) were collected from 2 sites in the New River, West Virginia, in the late spring and early summer to document diet shifts during early ontogeny. The first foods of smallmouth bass (TL = 9 mm) were primarily Chironomidae and microcrustaceans (primarily Copepoda). Other aquatic insects, primarily Ephemeroptera, became more abundant in the stomachs as TL increased. A shift in the proportions and types of prey consumed began at approximately 15 mm TL and was primarily attributed to fin development and increased mouth size. Foraging success, measured by number of prey per stomach, stomach fullness, and average prey volume was lower for first‐feeding smallmouth bass than for later life stages. Mouth width appeared to restrict the size of prey consumed by larval smallmouth bass, but the maximum prey width never approached the mouth width for fish longer than 35 mm TL.
Vertical distributions of two herbivorous cichlid fishes of the genus Tropheus in LakeTanganyika, Africa
Authors: Kohda M. , Yanagisawa Y.
Published: July 2006

The vertical distributions of two herbivorous cichlid fishes,Tropheus mooriiandTropheus duboisi, were studied on the rocky slope at Luhanga and Bemba, 12 km apart, in Lake Tanganyika, Zaire, Africa. At Luhanga, whereT duboisiwere not present,T. mooriiranged from the shoreline to a site 30 m deep. At Bemba,T mooriioccupied areas less than 18 m andT duboisiareas between 5 and 30 m. In the overlapping zone, 5–18 m depth, each fish held an intra‐ and interspecific feeding territory, involving size‐dependent dominance relationship between neighbors irrespective of species. We indicate that the vertical distributions of these species are restricted by competitive interactions.
Application of a cluster‐bootstrapping method for identifying the dietary patterns of fish populations
Authors: Baltanás A. , Rincón P. A.
Published: July 2006

Dietary data usually exhibit considerable statistical awkwardness and the analytical techniques commonly used in the study of fish diet suffer from various problems (especially at the intraspecific and intrapopulation levels) resulting from difficulties in group definition and pooling of data. Considering that, we advocate the use of a combination of cluster analysis and bootstrapping to identify statistically significant groups of individual predators. Both basic and extended versions of the procedure (yielding slightly different results) are outlined. We also suggest the use of detrended correspondence analysis (DCA) for further interpretation of significant clusters. When applied to dietary data from a brown trout population, the method successfully finds different feeding patterns, even though possible sources (geographical and temporal) of dietary variation were very limited. Dietary patterns appear to be related to the seasonal dynamics of the prey community coupled with seasonal shifts in microhabitat use by the predator; and, in a finer time‐scale, to diel macroinvertebrate drift periodicity or interindividual, size‐related differences in preyhandling capabilities.
Long‐term territory maintenance by female Tropheus duboisi (Cichlidae) involving foraging during the mouth‐brooding period
Authors: Yanaglsawa Y.
Published: July 2006

Abstract– The herbivorous cichlid fish Tropheus duboisi in Lake Tanganyika held feeding territories that were defended against individuals of the same but not the opposite sex. The male home ranges were 3 times as large as female home ranges, each overlapping with the ranges of 2–5 females. After spawning in the male's territory, each female foraged actively within her own territory while brooding the young in the buccal cavity. Both males and females rarely shifted their territories during the 6‐month observation period. The social organization of this fish was compared with that of a congener, Tropheus moorii.
Regular, cyclic oscillations in cohort strength in an allopatric population of brown trout. Salmo trutta L.
Authors: Borgstem R. , Heggenes J. , Nothcote T. G.
Published: July 2006

Abstract– Dominant year‐classes of brown trout occurred at regular time‐intervals in the alpine Lake Skavatn, Norway. In samples obtained by beach scining, electrofishing and gill‐netting during 1989–1992, yearclasses 1979, 1982, 1985, 1988 and 1991 were much more abundant than their neighbouring year‐classes. Correspondingly, in a sample of gillnetted fish from 1979, the year‐classes 1973 and 1976 were dominant. Spawning areas in the outlet are virtually absent, and lotic rearing areas for juveniles very restricted. Young‐of‐the‐year immigrated to the lake during the autumn, and juveniles inhabited the restricted littoral cobble areas until they reached a length of about 10–12 cm and an age of 3+. Competitive exclusion by dominant year‐classes may cause the regular, cyclic oscillations in cohort strength. An abundant year‐class of juveniles occupying the restricted suitable lacustrine rearing areas may exclude younger fish by inter‐cohort interference. The smaller fish are forced to unsheltered marginal rearing areas where they presumably suffer increased mortality. A new strong year‐class can arise every 3 years when the dominant fish leave the rearing areas.
Fish populations in tropical floodplain pools: a re‐evalution of Holden's data on the River Sokoto
Authors: Chapman L. J. , Chapman C. A.
Published: July 2006

Abstract– In this study we asked whether the fish populations of residual pools in a seasonally fluctuating African river varied between years. We used a series of data on the fish of the permanent floodplain pools of the River Sokoto, Nigeria compiled by M. J. Holden (1963) to address this objective. Holden provided estimates for the size and biomass of fish populations in 12 permanent dry season pools over a period of 2 to 3 years. On average, only 22% of the species present in a pool were absent from that pool in the following sampling period. Despite low interannual variability in the species composition of the pools, rank correlation analysis indlcated significant variation in the relative numbers and biomass of the 10 most numerically abundant species in most pools. Altering the spatial scale of analysis to include all possible combinations of 2 and 6 pools did not affect the results. Indices of similarity also indicated relatively high annual variability in the relative abundance of species in the pool communities. We suggest that habitat selection may contribute to the continued occurrence of fish species in pools from year to year, and such factors as changes in the overall abundance of fish species in the system and haphazard trapping during flood decline may contribute to annual variation in their relative abundance.
Migratory behaviour of brown trout,Salmo truttaL: importance of genetic and environmental influences
Authors: Näslund I.
Published: July 2006

Lake Storvindeln in northern Sweden supports a population of fast‐growing lake‐run brown trout. Spawning and early rearing take place in the River Vindelälven, while most growth occurs in the lake (piscivory). A smaller tributary to the lake, Låktabäcken Creek, holds a resident, early maturing, short‐lived brown trout population, although no migratory barriers have existed since 1947. To establish a lake‐run trout population, fry from the migratory R. Vindelälven stock were introduced into the creek during 1985–1991. Introduced trout descended to the lake prior to maturing. As a result of the introduction, large adult trout returned from L. Storvindeln to the creek to spawn in 1991 and 1992; i. e., the introduced trout were able to complete a migratory life cycle. Genetic factors appeared to have a primary influence on the predisposition to migrate in this case, and it is suggested that migratory populations rarely develop from strictly resident ones.
Comparative growth and diet of tench Tinca tinca (L.) larvae and juveniles from river floodplain biotopes in France and England
Authors: Copp G. H. , Mann R. H. K.
Published: July 2006

The growth and diet of larvae and 0 + juveniles of riverine tench Tinca tinca (L.) were compared in two stagnant floodplain biotopes from the upper River Rhône, France, and the River Great Ouse, England. The diet of tench was generally similar at the French and English sites, with Cladocera being the predominant prey of young larvae (English site only). Cladocera and Copepoda were the principal prey of older larvae and 0 + juveniles, though the latter took a variety of other, larger prey items. Ontogenetic changes in diet at both sites probably reflect prey availability. Protracted spawning at the French site contrasted a single spawning effort in the English backwater. Fluctuations in growth rate and condition were observed to coincide with shifts in diet, suggesting that tench developing in riverine biotopes may be vulnerable to competition at particular transitional intervals in their early ontogeny.
Abundance estimates of perch fry (Perca fluviatilis), complicated by grouped behaviour
Authors: Kubečka J. , Švátora M.
Published: July 2006

Schnabel's mark and recapture abundance estimates of perch fry in KliČava Reservoir (Czech Republic), differentially marked in autumn and in spring, partly failed due to the existence of groups of individuals which behaved differently. There were three groupings. 1) a group of fry caught by shore seining from autumn of the first year (O+) to summer of the second year of life (1+), the only group in the littoral during late autumn and early spring and the fry with the slowest growth rate; 2) a group of perch fry that consisted of males maturing at 1 year and that dominated the trap catches in reservoir; 3) a group of fry that avoided the littoral in late autumn and during March‐May 1983, which appeared in the littoral in May and June 1983, thus diluting the previously marked littoral fry. These 3 groupings of fry were relatively stable and separable throughout 1–2 years, apart for the mixing of groups 1 and 3 that took place in the littoral during the summer. The density of perch fry of 1982 year class in spring 1983 was estimated to be about 0.094 individuals per m2.
Substrate selection by Geotria australis ammocoetes in the laboratory
Authors: Kelso J. R. M.
Published: July 2006

Lamprey ammocoetes typically emerge from the substrate at night in their search for suitable habitat. When presented with a range in substrate depths, ammocoetes were found in deeper layers (>2.5 cm, range 1.0–7.7) of substrate and were usually in the deepest substrate. When offered a choice between 0.2 mm and any other coarser substrate, ammocoetes selected the coarser substrates in apparent contradiction with current knowledge. When offered a choice between intermediate (0.6, 0.85 mm) and coarse (1.5, 3.5 mm) substrates, ammocoetes were found in intermediate substrates. Geotria australis ammocoetes grew 0.10 mm day−1 and 0.00038 g day−1 when held in the laboratory and fed adlibitum. Survival was 90% over 154 days. Ammocoetes grew better in the laboratory on a diet of yeast and mixed plankters than in New Zealand streams and apparently selected substrate on the basis of underlying, not surficial, particle size and substrate depth.
A conceptual model for examining density dependence in the growth of stream trout
Authors: Newman R. M.
Published: July 2006

Determination of the occurrence and importance of densitydependent responses is central to understanding stream trout population dynamics. I propose a conceptual model of growth, based on a distribution of feeding site quality, that considers the effects of density on growth. The site quality model assumes that trout select the best feeding sites available and, as the number of trout increases, they will be forced to use less energetically profitable sites, resulting in decreased growth, but also an increase in variance of size or growth. Results from a 3‐year study of a brown trout (Salmo trutta) population show that growth to age 1 was significantly reduced for the 1981 year class, which was about 4 times more dense than other year classes. The reduction in growth was not due to a decrease in the growth of all trout but rather an increase in the number of slower growing fish. These results are consistent with my site quality distribution model and suggest that individual fish growth, the distribution of growth, and the variance of growth rates should be considered in addition to mean size and growth.
Coastal movement and growth of domesticated rainbow trout (Oncorhynchus mykiss (Walbaum)) in Norway
Authors: Jonsson N. , Jonsson B. , Hansen L. P. , Aass P.
Published: July 2006

Between 1979 and 1991, hatchery‐reared 1+ and 2+ rainbow trout were released in May and June in the Boknafjord at the mouth of the River Imsa, and from April to June in the Oslofjord, southern Norway. The fish were recaptured in the fjords of release, in rivers emptying there and from rivers and sea further along the Norwegian coast. Of the total recaptures, 35.6% ascended rivers in the year of release. Some fish released at the River Imsa returned to the area of release after spending 1 to 3 years at sea. Among those that were recaptured in rivers, 11.9% were recaptured in other rivers than the Imsa. The growth rate of the fish varied inversely with size at release. The growth rate was higher in the Oslofjord than in the Boknafjord, and in both areas the growth rate decreased with time after release. Rainbow trout that had escaped from local fish farms entered the River Imsa between March and December. Adults ascending in spring remained a shorter time in the river (37 days) than those ascending in autumn (200 days). Fish entering in autumn decreased more in weight during their river stay than those ascending in spring, and females more than males. Spawning took place in April‐May. The monthly mean river stay of juvenile entrants ranged from 2 weeks to 6 months. In total, 27.8% of the rainbow trout escaped from fish farms and captured in the Imsa strayed to other rivers for repeat spawning. There is no evidence for continuing survival of escaped Norwegian rainbow trout in the wild.