bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial and temporal impacts of a diesel fuel spill on stream invertebrates
Authors: Lytle David A. , Peckarsky Barbara L.
Published: March 2003

1. We assessed the effects of a 26 500 L diesel fuel spill on the macroinvertebrate fauna of a small trout stream in central New York, U.S.A. To determine the spatial extent of the spill we sampled three locations (0.7, 5.0 and 11.8 km downstream of the spill), each containing a reference site (unaffected tributary) and an impact site (downstream of spill). Sampling was repeated four times over a 15‐month period to assess temporal recovery.

2. Immediately after the spill, invertebrate density at all three locations below the spill was significantly lower than reference density. Three months after the spill, density up to 5 km below the spill was still far lower (<100 individuals per sample) than reference density (800–1200 individuals per sample). A year after the spill, density was similar between reference and impact sites, suggesting that invertebrates had recovered numerically.

3. Taxonomic richness up to 5.0 km below the spill was less than half the reference taxonomic richness and this difference persisted for at least 3 months. Some significant differences between reference and impact sites were observed after 15 months, but these differences could not be attributed to the oil spill.

4. For at least 3 months following the spill, the site immediately downstream of the spill was dominated by Optioservus, a petrochemical‐tolerant riffle beetle. Twelve to 15 months after the spill, both the reference and impact sites near the spill were dominated numerically by the mayfly Ephemerella, but the degree of dominance was twice as large at the impact site.

5. We concluded that the diesel fuel spill significantly reduced the density of invertebrates (by 90%) and taxonomic richness (by 50%) at least 5.0 km downstream, but density recovered within a year. Throughout the study, however, the fauna immediately below the spill was species poor and significantly over‐represented by a single dominant taxon, suggesting that 15 months was not sufficient for full community recovery from the oil spill.
Biodiversity: towards a unifying theme for river ecology
Authors: Ward  , Tockner
Published: March 2003

1. A broadened concept of biodiversity, encompassing spatio‐temporal heterogeneity, functional processes and species diversity, could provide a unifying theme for river ecology.

2. The theoretical foundations of stream ecology often do not reflect fully the crucial roles of spatial complexity and fluvial dynamics in natural river ecosystems, which has hindered conceptual advances and the effectiveness of efforts at conservation and restoration.

3. Inclusion of surface waters (lotic and lentic), subsurface waters (hyporheic and phreatic), riparian systems (in both constrained and floodplain reaches), and the ecotones between them (e.g. springs) as interacting components contributing to total biodiversity, is crucial for developing a holistic framework of rivers as ecosystems.

4. Measures of species diversity, including alpha, beta and gamma diversity, are a result of disturbance history, resource partitioning, habitat fragmentation and successional phenomena across the riverine landscape. A hierarchical approach to diversity in natural and altered river‐floodplain ecosystems will enhance understanding of ecological phenomena operating at different scales along multidimensional environmental gradients.

5. Re‐establishing functional diversity (e.g. hydrologic and successional processes) across the active corridor could serve as the focus of river conservation initiatives. Once functional processes have been reconstituted, habitat heterogeneity will increase, followed by corresponding increases in species diversity of aquatic and riparian biota.
Taxonomic composition and biomass of heterotrophic flagellates in relation to lake trophy and season
Authors: Auer Brigitte , Arndt Hartmut
Published: March 2003

1. Taxonomic composition and abundance of heterotrophic flagellates (HF) were studied in 55 lakes with different trophy in northern Germany using a live‐counting technique.

2. Mean abundances and biomasses of HF ranged from 169 cells L−1and 22 μg L−1in mesotrophic lakes to 2439 cells mL–1and 475 μg L−1in hypertrophic lakes, respectively. Highest values were generally observed in spring, but mesotrophic lakes showed maximum values in early summer.

3. The taxonomic composition of HF was not significantly influenced by lake trophy and season. The major fraction of HF consisted of chrysomonads and Protista incertae sedis; other important groups were choanoflagellates and bicosoecids. The size distribution of HF changed with lake trophy and season, with a higher proportion of large HF (> 10 μm) in hypertrophic lakes and in spring, respectively.

4. Correlation analyses revealed a strong negative impact of cladocerans on total HF biomass and especially on large HF. Ciliates and large bacteria (> 10 μm) were strongly positively correlated with HF biomass; small bacteria (< 2 μm) showed a weak positive correlation.

5. Analyses at the level of species and genera revealed distinct distribution patterns of some taxa.Paraphysomonas,AulacomonasandQuadriciliaas large‐bodied HF showed highest abundance in hypertrophic lakes and in spring. Attached taxa (e.g.Monosiga,Salpingoeca amphoridium) were highly abundant in late summer and autumn, whereasSpumellaandKathablepharisoccurred frequently in most samples.
Adaptive significance of facultative paedomorphosis in Triturus alpestris (Amphibia, Caudata): resource partitioning in an alpine lake
Authors: Denoël Mathieu , Joly Pierre
Published: March 2003

1. Facultative paedomorphosis is a polymorphism that has important evolutionary implications in promoting morphological differentiation and variation in habitat use. It occurs in several urodele species throughout the world. Several hypotheses based on life‐history theory have been proposed to explain the wide range of habitats in which facultative paedomorphosis occurs, suggesting multifactorial causes.

2. In harsh habitats, such as mountain lakes, paedomorphosis might promote niche partitioning between morphs. This hypothesis was tested by comparing micro‐habitat use and diet of two coexisting morphs in an alpine lake.

3. Paedomorphs occupied all microhabitats in the lake while metamorphs occurred only along the shoreline or at the water surface. Paedomorphic newts were frequent in deep water, where they foraged mainly on plankton. Plankton was poorly exploited by metamorphic newts, which fed mainly on terrestrial insects. Difference between morphs in microhabitat use, and consequently in the diet, were consistent in both sexes and in juveniles.

4. In adults, the mass and energy value of stomach contents did not differ between morphs, suggesting a similar food availability in the habitats occupied.

5. This study indicates habitat partitioning between morphs involving dietary differences. Specific benefits and costs of each ontogenetic pathway may allow their coexistence in this deep and fishless lake. Paedomorphosis benefits individual newts by making new food resources available and presumably reducing competition at the shore of the lake. However, the proximate causes of such an ontogenetic switch remain unclear.
The influence of glacial runoff on stream macroinvertebrate communities in the Taillon catchment, French Pyrénées
Authors: Snook Deborah L. , Milner Alexander M.
Published: March 2003

1. Benthic communities were sampled from five sites within a glacial catchment in the Cirque du Gavaranie, French Pyrénées, over two consecutive years (i) to investigate whether longitudinal patterns in zoobenthic communities exist downstream of a glacial margin and (ii) to identify the principal environmental variables influencing such patterns.

2. There was a distinct zonation of communities with increasing distance from the glacial margin. Ordination of the zoobenthic distribution indicated sites were separated by the relative contributions of taxa rather than their presence or absence. A shift in community composition and diversity separated a kryal type community dominated by Diamesa spp., Prosimulium spp., Eriopterini and Empididae at ≥2200 m a.s.l., from a more rhithral community of Orthocladiinae, Ephemeroptera, Plecoptera and Trichoptera at 1900 m a.s.l.

3. Chironomidae showed a defined gradient in distribution from Pseudokiefferiella parva and Diamesa latitarsis groups close to the glacier, through D. zernyi and D. cinerella groups, Orthocladius, Parametriocnemus and Micropsectra further downstream with Rheocricotopus, Corynoneura and Nilotanypus furthest from the glacial margin. Diamesa cinerella/zernyi group was the most euryzonal taxon.

4. Gradients in channel and hydraulic stability, groundwater input and mean water temperature were identified as the principal environmental variables associated with the downstream distribution gradient of zoobenthos. Diamesa, Empididae, Eriopterini and Nematoda were most tolerant of channel and hydraulically unstable and cold water habitats. Simuliidae (Prosimulium), Crenobia alpina, Rhyacophila, Chaetopterygini, Drusus rectus, Capnioneura, Orthocladius and Parametriocnemus were associated with intermediate conditions. Corynoneura, Tanypodinae, Perlidae, Chloroperlidae, Agapetus fuscipes and Coleoptera were least tolerant of channel and hydraulic instability and low water temperature.
Chironomid (Diptera: Chironomidae) communities in six European glacier‐fed streams
Authors: Lods‐Crozet B. , Lencioni V. , Ólafsson J. S. , Snook D. L. , Velle G. , Brittain J. E. , Castella E. , Rossaro B.
Published: March 2003

1. A study on glacial stream ecosystems was carried out in six regions across Europe, from Svalbard to the French Pyrenees. The main aim was to test the validity of the conceptual model of Milner & Petts (1994) with regard to the zonation of chironomids of glacier‐fed rivers along altitudinal and latitudinal gradient.

2. Channel stability varied considerably, both on the latitudinal and altitudinal scale, being lowest in the northern regions (Svalbard, Iceland and Norway) and the Swiss Alps. Water temperature at the upstream sites was always <2 °C.

3. There was a prominent difference in taxonomic richness between the Alpine and the northern European regions, with a higher number of taxa in the south. In all regions, the chironomid community was characterized by the genus Diamesa and the subfamily Orthocladiinae. Of a total of 63 taxa recorded, two (Diamesa bertrami and Orthocladius frigidus) were common in all the regions except Svalbard.

4. On the basis of cluster analysis, seven distinct groups of sites were evident amongst glacial‐fed systems of the five regions (Pyrenees excluded). This classification separated the glacier‐fed streams on geographical, latitudinal and downstream gradients.

5. Canonical Correspondence Analysis (CCA) of environmental variables was carried out using 41 taxa at 105 sites. Slope, water depth, distance from source, water temperature and the Pfankuch channel stability index were found to be the major explanatory environmental variables. The analysis separated Diamesinae and typical upstream orthoclads from the other chironomids by low temperature and high channel instability.

6. In all six regions, Diamesa was present closest to the glacier. Within 200 m of the glacier snout, other genera of Diamesinae were found together with Orthocladiinae. Pioneer taxa like Diamesa species coexisted with later colonizers like Eukiefferiella minor/fittkaui in relatively unstable channels.

7. The longitudinal succession of chironomid assemblages across altitudinal and latitudinal gradients in glacial streams followed the same pattern, with similar genera and groups of species. The general aspects of the conceptual model of Milner & Petts (1994) were supported. However, Diamesa species have wider temperature limits than predicted and other Diamesinae as well as Orthocladiinae colonize metakryal habitats.
Whitemere, a lake that defies some conventions about nutrients
Authors: Kilinc Sabri , Moss Brian
Published: March 2003

1. Whitemere, a kettle‐hole lake in north‐west England (zm,14 m, area 22.5 ha) has extremely high maximal concentrations (around 1 mg L−1) of total phosphorus (TP) and soluble reactive phosphorus (SRP), and comparatively low maximal concentrations of dissolved inorganic nitrogen (<0.5 mg N L−1). Bioassays indicate that its phytoplankton is nitrogen limited, and it has surface blue‐green algal blooms in summer. Palaeoecological investigations have shown that high populations of cyanophytes occurred more than 6000 years ago, even before human settlement of the catchment.

2. The reasons for this combination of features are not immediately clear. This paper attempts to distinguish between two hypotheses: that the high phosphorus concentrations arise from input of phosphate‐rich groundwater; and that the high phosphorus concentrations arise from concentration and recycling mechanisms within the lake.

3. The lake is entirely fed by ground water, direct rainfall and surface sheet flow. The concentrations of phosphorus in the ground water are much lower than in the lake water. The lake is stratified and has high phosphorus concentrations in the anaerobic hypolimnion in summer as a result of substantial release from the sediment. Vertical turbulence in the relatively weakly stratified water column may transfer substantial amounts to the epilimnion.There is also substantial phosphorus release from the sediments under the aerobic epilimnion.

4. There is little outflow of water and phosphorus. Most of the phosphorus is returned to the sediment under winter isothermal conditions, to be released again the following summer. The lake has probably maintained these mechanisms for millennia. Recent eutrophication is likely to have been driven by nitrogen inputs from greater intensification of agriculture in the catchment.
Chlorella‐bearing ciliates dominate in an oligotrophic North Patagonian lake (Lake Pirehueico, Chile): abundance, biomass and symbiotic photosynthesis
Authors: Woelfl Stefan , Geller Walter
Published: March 2003

1. Large mixotrophic ciliates (Stentor araucanus, S. amethystinus and Ophrydium naumanni) were a characteristic component of a temperate, oligotrophic lake in North Patagonia. During a 1‐year study, the abundance, biomass and primary production of these large Chlorella‐bearing ciliates were compared with those of the total plankton community.

2. Mixotrophic ciliates peaked in spring and from late summer to autumn, accounting for 1.6–43% (annual average: 16.3%) and 67–99% (annual average: 92%) of total ciliate abundance and biomass, respectively. Their contribution to total zooplankton biomass, including flagellates, rotifers, ciliates and crustaceans, was 14–76%, or 47% as an annual average. Endosymbiotic algae accounted for up to 25% of total autotrophic biomass (annual mean: 3.9%).

3. Maximum cell‐specific photosynthetic rates of S. araucanus and S. amethystinus at light saturation varied between 80 and 4400 pg C ciliate–1 h–1 with high values during autumn and winter, and low values during summer. The depth‐integrated rates of photosynthesis (0–40 m) of algal endosymbionts contributed 1–25% to total photosynthesis (annual mean: 6.5%).

4. A comparison of calculated ingestion rates with photosynthetic rates of Stentor indicates that photosynthate produced by endosymbionts generally exceeded heterotrophic food supply of Stentor during autumn and winter, but was much lower during summer, when food supply was high.

5. The mixotrophic ciliates represent an important ‘link’ between nanoplankton and higher trophic levels within the plankton community because of their high heterotrophic biomass and considerable contribution to total photosynthesis.
Seasonal patterns in macroinvertebrate drift and seston transport in streams of an alpine glacial flood plain
Authors: ROBINSON C. T. , TOCKNER K. , BURGHERR P.
Published: March 2003

1. We measured drift of macroinvertebrates and organic matter in five different channel types (upper and lower main channel, intermittent side‐channel, side‐slope tributary, and a groundwater channel) draining a glacial flood plain in the Swiss Alps. Samples were collected seasonally over 3 years (May 1997 to November 1999) to encompass major periods of floodplain expansion and contraction.

2. Total wetted channel length ranged from ≤ 5 km during maximum floodplain contraction to ≥ 24 km under system expansion. Principal components analysis (PCA) of key physical and chemical measures collected over an annual cycle showed that the main and side channel sites differed spatially and seasonally from the tributary and groundwater sites, reflecting the glacial influence on the former.

3. Two‐way ANOVA indicated a significant Site × Date interaction for all measured variables. Transported organic matter, caused by blooms of Hydrurus foetidus, was typically five to 10 times higher in the lower main channel and side‐channel than the other channel types, and was least variable among dates in the groundwater and tributary channels.

4. The number of drifting macroinvertebrates was usually highest in the groundwater channel, although highly variable among years. Other channel types had highest drift rates in November and lowest rates in May, reflecting seasonal changes in the life cycles of particular taxa, such as Baetis alpinus and the Simuliidae. The lower main channel exhibited the greatest, and the groundwater the lowest, seasonality in drift compared with the other channels.

5. The Chironomidae displayed the highest drift rates in most seasons, especially in summer when other taxa were relatively low in the drift. The number of taxa in the drift also varied among channel types and season, ranging from less than two in early spring to four to six in other seasons.

6. The observed differences in drift rate and transported organic matter among channel types and seasons have important implications for ecosystem dynamics, through its effect, for instance, on dispersal among channel types or on organic matter exchange.
Exotic riparian vegetation lowers fungal diversity but not leaf decomposition in Portuguese streams
Authors: BÄRLOCHER FELIX , GRAÇA MANUEL A. S.
Published: March 2003

1. We characterised the fungal communities of eight streams in Portugal, four bordered by native deciduous forest and four bordered by pure stands of Eucalyptus globulus.

2. Aquatic hyphomycete species richness and evenness, but not numbers of water‐borne conidia, of aquatic hyphomycetes were significantly lower in eucalypt bordered streams.

3. Multivariate analyses subdivided the fungal communities into two distinct groups corresponding to riparian vegetation.

4. Despite these differences in the dominant decomposer community, decay rates of eucalypt leaves (accounting for ≥98% of naturally occurring leaves in eucalypt bordered streams, absent in native forest) and chestnut leaves (occurring naturally in native forests) did not differ between the two groups of streams.
A simple method for approximating the supportive capacities and metabolic constraints in lakes and reservoirs
Authors: REYNOLDS C. S. , MABERLY S. C.
Published: March 2003

1. A method for calculating and comparing the stoichiometric yields of phytoplankton standing crop (as chlorophyll a) is presented.

2. Some worked examples show how the model distinguishes lakes in which the supportive capacity is constrained mainly by the available phosphorus or by the nitrogen supply or by the light availability. Sites are identified where control moves among the constraining factors.

3.  An instance of lake management is given where the diagnosis, remedy and the remediation have conformed closely to the model predictions.
Macro‐zooplankter responses to simulated climate warming in experimental freshwater microcosms
Authors: MCKEE D. , ATKINSON D. , COLLINGS S. , EATON J. , HARVEY I. , HEYES T. , HATTON K. , WILSON D. , MOSS B.
Published: March 2003

1. We report data collected from 48 replicated microcosm communities created to mimic plant‐dominated shallow lake and pond environments. Over a 2‐year period, the microcosms were subjected to warming treatments (continuous 3 °C above ambient and 3 °C above ambient during summer only), a nutrient addition treatment and the presence or absence of fish. We tracked macro‐zooplankter dynamics, censusing cladoceran populations at the species level, copepods at the order level and ostracods as a class.

2. Responses to warming were subtle. Cladoceran diversity and overall abundance were not significantly affected by warming, although measures of community evenness increased. Warming effects on patterns of population trajectories tended to be strongly seasonal and most apparent during periods of pronounced increase. Populations of the prevalent cladocerans, Chydorus sphaericus and Simocephalus vetulus, displayed idiosyncratic patterns, with evidence in the case of S. vetulus for a negative relationship between warming and body‐size at maturity. Copepod populations were reduced in size by warming, but those of ostracods increased.

3. The effects of the nutrient addition and fish treatments were strong and consistent, interacting little with warming effects in statistical models. Zooplankter abundance tended to be the highest in the fish‐free microcosms receiving additional nutrient inputs and lowest when fish were present and no nutrients were added. Both treatments reduced cladoceran diversity and community evenness.

4. We suggest that warming, independently, is unlikely to supplant the effects of changing nutrient loading and fish predation as the major driver of zooplankter dynamics in shallow lakes and ponds. Moreover, in the situations where warming was of significant influence in our experiment, the distinction between summer‐only warming and year‐around warming was blurred. This suggests that warming effects were most pervasive during the summer, at the upper end of the temperature spectrum.
Image analysis of Daphnia populations: non‐destructive determination of demography and biomass in cultures
Authors: Færøvig Per J. , Andersen Tom , Hessen Dag O.
Published: March 2003

SUMMARY 1. An image analysis technique was developed for the semiautomatic determination of abundance, size distribution and biomass in Daphnia cultures. This allowed detailed observations of growth, demography and biomass accumulation in live populations, avoiding artifacts caused by subsampling and sampling losses.

2. The image analysis method gave fast, non‐destructive and reliable individual counts, even in cultures with high density and a large fraction of juveniles.

3. In Daphnia, animal width changes with nutritional status and growth within instar, while length changes only at the moult. Thus, estimation of individual biomass using an ellipsoidal model based on animal width gave improved biomass calculations compared to manual counting, sizing, and length : weight regressions.

4. The power of the image analysis technique for assessing population growth and size structure was demonstrated in two 40‐day experiments, with Daphnia magna feeding on the green algae Selenastrum capricornutum in a two‐stage chemostat system.
Effects of waterfowl and fish on submerged vegetation and macroinvertebrates
Authors: Marklund Ola , Sandsten Håkan , Hansson Lars‐Anders , Blindow Irmgard
Published: March 2003

SUMMARY 1. With the aim to assess the combined and separate effects of waterfowl and fish on submerged vegetation and macroinvertebrates, we performed a replicated selective exclosure study in a shallow, eutrophic lake in southern Sweden. Our results are presented together with a literature review of the effects of fish and waterfowl on macroinvertebrates and submerged vegetation.

2. Based on our experiment and on published data, we conclude that waterfowl normally will reduce submerged vegetation only at high waterfowl densities, at very low vegetation densities, or in the colonisation phase of the vegetation.

3. Further, we conclude that in shallow temperate eutrophic lakes, a naturally occurring mixed fish assemblage rarely reduces submerged vegetation. Unless the vegetation is very sparse, the risk of severe reduction of submerged vegetation as a result of waterfowl or fish grazing, should thereby be low.

4. Even relatively low densities of fish seem to reduce macroinvertebrate biomass, while a mixed waterfowl assemblage rarely has a significant effect on macroinvertebrate biomass.
On the cost of vertical migration: are feeding conditions really worse at greater depths?
Authors: Winder M. , Boersma M. , Spaak P.
Published: March 2003

SUMMARY 1. The ultimate explanation for diel vertical migration (DVM) of zooplankton is the avoidance of visual predation in surface waters. Studies on migrating zooplankton have shown that remaining in the cold and food‐poor hypolimnion during the day, however, has demographic costs. Higher temperatures and greater food concentrations in the surface waters are thought to be the main reasons why Daphnia species move upwards at night.

2. In this study, we investigated the growth condition of daphniids raised on seston taken from different depths from a lake with and without a deep‐water chlorophyll maximum.

3. Juvenile growth rates of Daphnia galeata x hyalina from the lake without a deep‐water chlorophyll maximum were similar for all treatments. After temperature correction, however, growth rates were significantly higher on seston taken from the surface layers.

4. In contrast, in the lake with the deep‐water chlorophyll maximum, D. galeata growth rates were higher in deeper strata, even after temperature correction. Although this lake had a weak temperature gradient, D. galeata left the food‐rich strata at night and migrated into the surface food‐poor environment. Invertebrate predation and oxygen depletion are probably not the reasons for the nocturnal upward migration into the surface strata. Therefore, we assume that D. galeata migrates upwards to take advantage of higher temperatures. Using several temperature–egg‐development models, we could not, however, fully explain this behaviour.
Optimal diet choice for large herbivores: an extended contingency model
Authors: Farnsworth K. D. , Illius A. W.
Published: March 2003

1. A more general contingency model of optimal diet choice is developed, allowing for simultaneous searching and handling, which extends the theory to include grazing and browsing by large herbivores.

2. Foraging resolves into three modes: purely encounter‐limited, purely handling‐limited and mixed‐process, in which either a handling‐limited prey type is added to an encounter‐limited diet, or the diet becomes handling‐limited as it expands.

3. The purely encounter‐limited diet is, in general, broader than that predicted by the conventional contingency model.

4. As the degree of simultaneity of searching and handling increases, the optimal diet expands to the point where it is handling‐limited, at which point all inferior prey types are rejected.

5. Inclusion of a less profitable prey species is not necessarily independent of its encounter rate and the zero‐one rule does not necessarily hold: some of the less profitable prey may be included in the optimal diet. This gives an optimal foraging explanation for herbivores’ mixed diets.

6. Rules are shown for calculating the boundary between encounter‐limited and handling‐limited diets and for predicting the proportion of inferior prey to be included in a two‐species diet.

7. The digestive rate model is modified to include simultaneous searching and handling, showing that the more they overlap, the more the predicted diet‐breadth is likely to be reduced.
An experimental device for studying seed responses to naturally fluctuating temperature of surface soil under a constant water table
Authors: Araki S. , Shiozawa S. , Washitani I.
Published: March 2003

1. A simple experimental device was designed, in which seeds can be exposed to natural fluctuation of surface soil temperature under a constant soil moisture condition maintained by an automatic water supply system based on the principle of a Mariotte siphon.

2. Except for the period during summer drought, surface soil temperature at a depth of 5 cm and its fluctuation within the device were largely similar to the temperature of the surface soil subjected to natural fluctuation of moisture.

3. The seeds of Persicaria lapathifolia placed at the depth of 0·5 cm in the soil within the device germinated during the natural germination season of the species, while the seeds placed at the depth of 5 cm or beneath the 10 cm‐thick layer of litter failed to germinate.

4. The ungerminated seeds retrieved in August did not germinate at the favourable alternating temperature in the laboratory test unless exposed to previous moist chilling, suggesting the induction of secondary dormancy. Therefore, higher summer temperatures but not summer drought or moisture fluctuation seem to have been responsible for the dormancy induction, because the dormancy was induced in the fully hydrated seeds.
Oocyte maturation and ovariole number in lines of Drosophila melanogaster selected for postponed senescence
Authors: Carlson K. A. , Nusbaum T. J. , Rose M. R. , Harshman L. G.
Published: March 2003

1. Postponed senescence lines of Drosophila melanogaster have previously been generated by selection for delayed female reproduction.

2. This study addresses the question of whether the selection regime has differentiated lines with respect to oocyte maturation or ovariole number.

3. Oocyte stage and ovariole number were characterized in replicate postponed senescence lines (O) and in replicate control lines (B).

4. Oocyte maturation is delayed in O females.

5. The delay in oocyte maturation in O lines corresponds to reduced early age fecundity.

6. Selection may have resulted in an increased number of ovarioles in O females.
Impact of an ecological factor on the costs of resource acquisition: fighting and metabolic physiology of crabs
Authors: Sneddon L. U. , Huntingford F. A. , Taylor A. C.
Published: March 2003

1. Current game theory models and recent experimental evidence suggests that the strategy an animal adopts in agonistic encounters is determined by individual state. Therefore manipulation of an individual’s state should elicit different behavioural responses. In this paper, mechanisms are examined that underlie state‐dependent strategies using Shore Crabs, Carcinus maenas, and how, by altering the environment, behaviour and physiology are affected.

2. Fights were staged between pairs of male crabs under normoxic and severely hypoxic (<15 torr) conditions to determine if the metabolic costs of fighting and resource acquisition are affected by water PO2. After fighting, blood and tissue samples from each crab were taken and analysed for metabolites associated with anaerobiosis (L‐lactate, glucose and glycogen).

3. The spectrum of behavioural acts performed during contests was unaffected by hypoxic conditions. However, fight duration was significantly shorter in the hypoxic treatment.

4. The phenomenon of being of a larger relative size and winning had a greater influence in the contests staged under hypoxia with 93% of the victors being of a larger size compared to 78% in normoxic conditions. Fight duration and intensity had no relationship with relative size in either treatments.

5. The accumulation of L‐lactate was significantly greater in the blood and tissues of crabs after fighting under hypoxia than in normoxic conditions. In addition, there was greater glycolytic activity in the tissues of these crabs, shown by elevated concentrations of glucose in the blood and increased breakdown of glycogen.

6. This study demonstrates that the internal state of the crabs altered the length of time they were willing to engage in fighting and that fighting was energetically more expensive under hypoxic conditions.
Resistance to thermal stress in desert Drosophila
Authors: Stratman R. , Markow T. A.
Published: March 2003

1. Four species of Drosophila are endemic to the Sonoran Desert of North America where daily and seasonal high temperatures exceed those experienced by other species in this genus. The close association between these species and their cactus hosts means that they reside only in the desert and raises the question as to whether they are better able to survive heat stress than are non‐desert species of Drosophila. The tolerance of adult flies of the four desert species D. mojavensis, D. nigrospiracula, D. pachea and D. mettleri and the cosmopolitan D. simulans to acute heat stress was tested.

2. There was considerable variability among the desert endemic species with respect to survival following heat exposure. Two species, D. mojavensis and D. pachea, were more resistant at 44 °C and 46 °C than the others, with D. mettleri exhibiting similar heat stress resistance to D. simulans.

3. While there was no consistent influence of gender on heat resistance, younger flies (1‐day‐old) showed significantly greater survival than did older flies (7‐ or 14‐days old).
An energetic evaluation of a predator–prey (leech–amphipod) couple in Montezuma Well, Arizona, USA
Authors: McLoughlin N. J. , Blinn D. W. , Davies R. W.
Published: March 2003

1. The highly stable conditions in Montezuma Well, Arizona, have contributed to a very close predator–prey relationship between the endemic leech, Erpobdella montezuma, and its endemic amphipod prey, Hyalella montezuma, which forms nearly 90% of the leech diet.

2. Using a simple bioenergetic model, it was determined why a benthic opportunistic foraging strategy, typical of most other erpobdellids, is inferior to the specialized foraging behaviour utilized by E. montezuma and why reproduction by the leech is restricted during certain times of the year.

3. Our model demonstrated that to attain a biomass in excess of 2000 mg (maximum field size) during periods of low amphipod densities in the winter E. montezuma must feed on alternative prey types and have a foraging activity < 4 h per day.

4. Leech reproduction 4–6 months prior to the onset of winter food shortages of prey increases juvenile and adult survivorship with highest reproductive success for E. montezuma occurring in June–July.

5. Rather than being an obligate forager on H. montezuma, E. montezuma exploits a periodically abundant amphipod during most of the year in addition to alternate prey types during the winter thereby achieving an overall higher rate of energy gain than could be achievable by other closely related species of erpobdellids utilizing an opportunistic foraging approach.
Does substrate quality influence take‐off decisions in Common Starlings?
Authors: Bonser R. H. C. , Norman A. P. , Rayner J. M. V.
Published: March 2003

1. An instrumented perch was used to measure the reaction forces during take‐off of starlings from perches of three thicknesses. There was no significant decrease in reaction force with decreasing perch thickness; however, over the range of perch sizes there was a 10‐fold decrease in safety factor and a 400‐fold increase in the energy of deflection of the thinnest perch.

2. The implications of these results are that birds do not change their take‐off strategy when faced with perches of variable thickness and that, as a result, leaps from thin perches are very much less efficient than those from thicker perches. Birds appear not to adjust their leaping behaviour to minimize the risk of substrate failure during take‐offs.
Sexual dimorphism of head size in Gallotia galloti: testing the niche divergence hypothesis by functional analyses
Authors: Herrel A. , Spithoven L. , Van Damme R. , DE Vree F.
Published: March 2003

1. Two often cited hypotheses explaining sexual head size dimorphism in lizards are: sexual selection acting on structures important in intrasexual competition, and reduction of intersexual competition through food niche separation.

2. In this study some implicit assumptions of the latter hypothesis were tested, namely that an increase in gape distance and bite force should accompany the observed increase in head size. These assumptions are tested by recording bite forces, in vivo, for lizards of the species Gallotia galloti. In this species, male lizards have significantly larger heads than female conspecifics of similar snout–vent length.

3. Additionally, the average force needed to crush several potential prey species was determined experimentally and compared with the bite force data. This comparison clearly illustrates that animals of both sexes can bite much harder than required for most insect food items, which does not support the niche divergence hypothesis. The apparent ‘excess’ bite force in both sexes might be related to the partially herbivorous diet of the animals.

4. To unravel the origin of differences between sexes in bite capacity, the crushing phase of biting was modelled. The results of this model show different strategies in allocation of muscle tissue between both sexes. The origin of this difference is discussed and a possible evolutionary pathway of the development of the sexual dimorphism in the species is provided.
Towards a predictive description of forest canopies from litter properties
Authors: ROBERTS J. , HOPKINS R. , MORECROFT M.
Published: March 2003

1.Specific leaf area (SLA), carbon isotope ratio (δ13C) and leaf nitrogen content (N) were measured in litter in 1993 and in the litter layer and canopy in 1996 in a pedunculate Oak (Quercus robur) wood at Wytham, Oxford.

2.The frequency distribution of SLA of leaves falling through the late summer and autumn of 1993 changed with a greater contribution of leaves of high SLA earlier in the period. For the same SLA leaves falling earlier in the season had less negative δ13C and higher N content than leaves falling later.

3.The frequency distribution of SLA of litter leaves was similar in both years but litter leaves had lower N and less negative δ13C in 1996.

4.In the canopy, there was a highly significant negative relationship between height in the canopy and SLA in green and senescent leaves. The relationship between SLA and both δ13C ratio and leaf N was different between green, senescent and litter leaves.

5.The frequency distribution of foliage in the canopy estimated from the frequency of SLA in the litter and the vertical pattern of SLA in the canopy was similar to the distribution measured by the ‘drop‐line’ method.
Simplifying the phytohaemagglutinin skin‐testing technique in studies of avian immunocompetence
Authors: Smits J. E. , Bortolotti G. R. , Tella J. L.
Published: March 2003

1. Researchers involved in ecology and toxicology, as well as many other aspects of avian biology, use phytohaemagglutinin (PHA) skin testing as a means of evaluating the immune status of individuals.

2. Immune function, one measure of individual quality, can be used as a sensitive, non‐lethal variable that may be negatively affected in animals exposed to degraded, contaminated or otherwise disturbed ecological zones.

3. Typically this test has been applied by challenging one wing web with the immunostimulant PHA, while the other ‘control’ wing is injected with phosphate buffered saline (PBS). Injection sites on the wing web are measured before and 24 h after injection with PHA or PBS. The immune response is considered to be the difference between the two wings.

4. Results from PHA skin tests conducted on 608 birds in seven studies representing passerines, waterfowl, upland game birds and raptors are examined.

5. Numerous advantages to eliminating the PBS injection as the experimental control are: (i) decrease by half, the time required for testing; (ii) decrease handling‐related stress on the birds (proportional to handling time); (iii) reduce the probability of errors at injection time; (iv) spare the other wing for different tests or uses (e.g. tuberculin DTH testing); and (v) decrease the coefficient of variation that is due to measurement inaccuracies.

6. The only disadvantage identified is that hypersensitive individuals (outliers) could be missed, which in this case represents 2 of 608 individuals.
Interacting components of interspecific relative growth rate: constancy and change under differing conditions of light and nutrient supply
Authors: Meziane D. , Shipley B.
Published: March 2003

1. One thousand three hundred and twenty plants from 22 species of herbaceous angiosperms, typical of open sunny habitats, were grown from seed for 35 days under controlled conditions in four experimental environments: high (1100 μmol m–2 s–1 PAR) and low (200 μmol m–2 s–1 PAR) light, combined with high (full‐strength) and low (1/6 dilution) levels of hydroponic nutrient solution. Plants of each species were harvested at 15, 20, 25, 30 and 35 days post‐germination.

2. Relative growth rate (RGR), net assimilation rate (NAR), specific leaf area (SLA) and leaf mass ratio (LWR) were estimated for each species in each treatment combination.

3. Both light and nutrient levels affected RGR and each of the growth components. Average NAR increased, while SLA and LWR decreased, with increasing light. Increasing nutrient levels increased all three growth components. Light and nutrient levels interacted in their effects on NAR and SLA, but not in their effects on LWR.

4. Those species having the highest RGR in the most productive environment were most severely depressed in the less productive environments. This same pattern also occurred with NAR and SLA, but not with LWR.

5. The rank order of species with respect to SLA and LWR remained similar across the treatment environments; with respect to NAR the rank order remained similar in only four of the six treatment contrasts; with respect to RGR the rank order remained similar in only two of the six treatment contrasts and the rank order actually reversed in one treatment contrast.

6. RGR did not display strong bivariate correlations with any of the growth components in any of the treatment groups. It had positive, moderately strong correlations with NAR but only in the low‐nutrient treatments. It had positive, moderately strong correlations with LWR only in the high‐nutrient treatments. After controlling for the other growth components, each showed strong positive relationships with RGR. Furthermore, the effects of the treatments disappeared after controlling for the components, showing that the treatment effects were completely mediated through their effects on these underlying components.

7. There were also strong negative partial correlations between each of the growth components. These compensatory relationships buffered RGR from large changes in response to changing environments.
Diurnal and seasonal changes in cladode photosynthetic rate in relation to canopy age structure in the leguminous shrub Retama sphaerocarpa
Authors: Haase P. , Pugnaire F. I. , Clark S. C. , Incoll L. D.
Published: March 2003

1. Changes in canopy area and canopy age structure of the leguminous shrub Retama sphaerocarpa were estimated non‐destructively by monitoring growth and survivorship of cladodes on marked shoots.

2. Gas exchange of cladodes of different age classes was measured by infra‐red gas analysis during a period of 18 months. The effects of seasonal and year‐to‐year variation in the area and age structure of the canopy on daily carbon assimilation were assessed.

3. New canopy area produced by spring growth was highly variable between years and also affected the age structure of canopies because of differential survivorship of older cohorts of cladodes.

4. During the first year (1993), predawn water potential of cladodes and, therefore, their maximum diffusive conductance (0·35–0·45 mol m–2 s–1) and photosynthetic rate (20–26 μmol CO2 m–2 s–1), changed little with the season because the deep‐rooted shrubs had access to permanent water sources. Lack of rainfall in the winter of 1993/1994 constrained predawn water potential and rates of gas exchange in the following growing season when daily maxima of A declined continuously and fell to a minimum of 10 μmol CO2 m–2 s–1 in July 1994.

5. Nitrogen concentration and specific cladode area, but not nitrogen content, were significantly different between annual cohorts. Mainly as a result of secondary diameter increment of cladodes, specific cladode area and nitrogen concentration and therefore photosynthetic rate generally declined with increasing age of cladodes, but the differences in the photosynthetic rate between cohorts were insignificant during the cool season.

6. Variation in canopy area caused variation in daily carbon assimilation by 30–36% within years and by 37–52% between years. Seasonal and between‐year variation in the age structure of canopies, however, only accounted for changes in daily carbon assimilation of ± 2%. Canopy age structure thus appears to be an insignificant variable affecting carbon gain in R. sphaerocarpa.
Influence of tree growth rate, shoot size and foliar chemistry on the abundance and performance of a galling adelgid
Authors: Mckinnon M. L. , Quiring D. T. , Bauce E.
Published: March 2003

1. The abundance and performance of the Eastern Spruce Gall Adelgid, Adelges abietis, was evaluated on young, open‐grown trees of White Spruce, Picea glauca, whose growth rates had been increased through fertilization or decreased through root‐pruning.

2. In general, gall densities were highest on control trees and on mid‐crown branches. Reduced galling success on fertilized trees was largely due to higher overwintering mortality of first‐generation nymphs. Foliar magnesium, total tannin and total phenol contents were positively, and nitrogen and total monoterpene contents negatively, related to gall density and/or galling success.

3. Although short shoots were more abundant, shoot length was parabolically related to gall density. There was a non‐significant parabolic trend between shoot size and galling success and volume. The number and average size of A. abietis females emerging from galls were positively related to gall volume, and realized fecundity was positively correlated to female size. Consequently, fitness was approximately twice as high for nymphs colonizing intermediate‐sized than small or large shoots.

4. These results do not support the plant vigour or plant stress hypotheses. The results do, however, agree with predictions of the modified plant stress hypothesis for sucking insects. It is speculated that Adelges abietis lacks the necessary resources for successful gall formation on small shoots and is unable to produce a stimulus large enough to induce gall formation on large shoots.
Maintenance of the alcohol dehydrogenase polymorphism in Tiger Salamanders, II. Differences in biochemical function among allozymes
Authors: Carter P. A. , Mitton J. B. , Kocher T. D. , Coelho J. R.
Published: March 2003

1. Previous studies of Tiger Salamanders demonstrated that variation in alcohol dehydrogenase (Adh) contributed significantly to associations between multilocus heterozygosity and oxygen consumption traits, and that Adh variation was associated with levels of pond‐oxygen and metamorphic ability in extreme oxygen environments. Here Adh allozymes are characterized kinetically, and relationships between Adh and oxygen‐related physiological traits (ATP/Hb, 2,3‐DPG/Hb) are measured.

2. Kinetic differences were measured among Adh allozymes in the acetaldehyde‐to‐ethanol direction:kcat/Kmratios (the catalytic constant divided by the Michaelis–Menton constant) were significantly higher in Adh‐SF than the other two genotypes, and in Adh‐SS compared with Adh‐FF. No significant differences were measured in the ethanol to acetaldehyde direction.

3. Adh‐SS had a significantly higher ATP/Hb than Adh‐FF, with the Adh‐SF intermediate. In addition, a significant interaction between Hb and body mass was measured, such that Adh‐FF showed a negative relationship between Hb concentration and body mass while the other two genotypes showed a positive relationship.

4. These results are consistent with the hypothesis that variation at the Adh locus has adaptive and physiological significance, and that functional differences among Adh allozymes partly explain significant associations between multilocus genotype and organismal traits.