bluuebunny/crossref_metadata_2025 huggingface dataset:
Reproductive traits, habitat use and templet theory: a synthesis of world‐wide data on aquatic insects
Authors: STATZNER BERNHARD , HOPPENHAUS KERSTIN , ARENS MARIE‐FRANCOISE , RICHOUX PHILIPPE
Published: November 2003

1. Using world‐wide data on the reproductive biology of 131 species (in eight orders) of aquatic insects, we used multivariate analyses to examine: (i) relationships among reproductive traits determining life cycle, fecundity, morphology, behaviour and physiology; (ii) relationships among traits determining spatial and temporal habitat characteristics at different scales; and (iii) the relationship between reproductive and habitat‐use traits. This provided a test of predictions of the habitat templet concept on trends of species traits along gradients of habitat heterogeneity.

2. The major trends observed in the relationships among reproductive traits were that larger females had larger eggs, which were more vulnerable to perturbations such as droughts and often laid in cocoons. In addition, they laid the eggs in larger numbers of smaller clutches than smaller females. Other traits (e.g. egg number or incubation time) did not show clear trends.

3. Females that deposited eggs at sites of low local temporal heterogeneity (within plants) used, at the same time, gross habitats of high temporal heterogeneity (temporary waters). In contrast, traits in habitat use hardly differed on well‐known gradients of temporal heterogeneity along running waters (from source to estuary). The number of habitat units used by ovipositing females generally increased with the spatial scale considered, most species oviposited in a single small habitat unit but in several gross habitats.

4. A significant (P < 0.01) relationship between traits in reproduction and habitat use demonstrated that habitat acted as a templet for reproductive strategies. This relationship was dominated by larger females having larger, unattached eggs which were more vulnerable to droughts and were oviposited in temporally more stable small‐scale habitats (within wood or macrophytes, or within cocoons spun by the female) but more unstable large‐scale habitats (primarily temporary waters). Thus, only on the small habitat scale did some of our observations correspond to the predictions of the habitat templet concept (e.g. larger size or higher vulnerability in more stable habitats). However, many species had traits in reproduction that did not show trends as predicted by the concept.

5. This and other recent studies of the relationships between traits of freshwater organisms and the heterogeneity of their habitats have shown that habitat acts as a templet for species life history traits. However, many of the details observed in these studies did not correspond to predictions of the templet concept because of trade‐offs among the traits and scale problems in the description of habitat heterogeneity. Therefore, future studies should focus on groups of organisms which are as similar as possible in the trade‐offs among their species traits and on the potential relationships of habitat heterogeneity across multiple scales.
Longitudinal patterns of organic matter transport and turnover along a New Zealand grassland river
Authors: YOUNG ROGER , HURYN ALEXANDER
Published: November 2003

1. We determined the longitudinal pattern of organic matter concentration, quality, size composition and spiralling length along a 310‐km grassland river system (Taieri River, New Zealand).

2. Organic seston concentration (0.24–4.05 mg ash‐free dry mass (AFDM) l–1) and dissolved organic carbon (DOC) concentration (2.3–5.7 mg C l–1) showed no obvious longitudinal patterns. In contrast, there was a significant downstream increase in inorganic seston concentration (0.13–13.73 mg ash l–1), presumably because of a downstream increase in the proportion of the catchment developed for agriculture.

3. Although there was a trend toward increasing particle size in the first 25 km of the river continuum, organic seston was primarily composed of ultrafine particles (0.6–30 μm) at all study sites. The ratio of coarse (> 250 μm) to ultrafine organic seston decreased logarithmically down the continuum. Organic content generally decreased with particle size. Ultrafine particles, however, had significantly higher organic fractions than fine (60–100 μm) and very fine (30–60 μm) particles.

4. Daily organic carbon turnover length ranged from 10 to 98 km and increased downstream. This is consistent with other studies along river continua and suggests that organic carbon turnover length is largely controlled by the relationship between channel dimensions and discharge, rather than the presence of specific retention devices.

5. Concentrations and nutritional quality of organic seston and concentrations of DOC were highest in an unconstrained floodplain reach in the upper river. These data suggest that new material enters the river channel in this reach, potentially providing an important energy source for the river community downstream. The effect of this reach on the longitudinal pattern of organic matter concentration and quality emphasizes how changes in channel form can alter river ecosystem structure and function.
Predation on meiobenthic assemblages: resource use of a tanypod guild (Chironomidae, Diptera) in a gravel stream
Authors: SCHMID P.E. , SCHMID‐ARAYA J.M.
Published: November 2003

1. Three predatory chironomid species constituted numerically 8.8% (± 95% CL 2.2) of the macro‐ and meiobenthic community at the sediment surface and in the hyporheic zone of Oberer Seebach, a gravel stream in Lower Austria. Larvae of Thienemannimyia geijskesi (Goetghebuer) and Nilotanypus dubius (Meigen) occurred in higher densities in sediment depths between 10 and 40 cm, whereas Conchapelopia pallidula (Meigen) achieved higher densities at the sediment surface. The three species completed one generation in a year.

2. A total of ninety‐seven prey species and instars were identified by gut analyses, of which forty‐one benthic rotifer species constituted 69.5% of individuals and twenty‐three chironomid species and their instars, 22.9%. The three tanypod species showed shifts from mainly rotifer species in early instars to chironomids and diverse other meio‐ and macrofaunal taxa in later instars. Rather than shifting towards larger prey sizes, growing predators expanded their upper size thresholds and continued to include smaller prey species in their diet. The extent to which tanypod instars fed on similar prey size classes declined with increasing larval size. Predation by tanypods amounted to 2.2% (± 95% CL 0.1) of the combined prey densities and prey consumption averaged 1.32 (bootstrap 95% CL 1.26–1.39) individuals per predator individual.

3. Preferences for microhabitat flow differed between predator species and in the prey assemblage. Prey densities and densities of T. geijskesi and C. pallidula were highest in pool areas, whereas N. dubius achieved high densities in riffle sites.

4. Tanypod larvae fed non‐selectively among prey types. To test the significance of observed size(instar)‐specific spatial and dietary overlap values amongst tanypod species, simulations were generated from random models for pairs of intra‐ and interspecific associations of individuals and groups of prey and predator species. Groups and individuals of tanypod instars fed near randomly on groups of prey types and a high proportion (P > 0.60) of prey individuals are quasi‐randomly chosen by tanypods in those patches. Tanypod instar‐pairs did not show a sustained trophic resource partitioning in time, thus reducing the degree of competitive interactions for food in this predator guild. Spatially segregated and non‐segregated tanypod instars formed random aggregations independent of each other at different flow microhabitats.

5. Species‐rich prey assemblages such as benthic rotifers and larval chironomids increased the probability of non‐selective feeding upon a wide spectrum of prey species by tanypods. Prey choice was governed by prey availability and tanypod individuals fed on many species at rather even proportions independent of each other.
Development and application of a nutrient‐diffusing bioassay for large rivers
Authors: SCRIMGEOUR GARRY , CHAMBERS PATRICIA
Published: November 2003

1. Laboratory and field experiments were performed to develop and then apply a nutrient‐diffusing substratum (NDS) design suitable for use in large, fast‐flowing rivers.

2. Initial laboratory experiments quantified diffusion of PO4 and NO3 from new and previously used clay pots, which were soaked in deionized distilled water. Mean release rates initially exceeded 2.4 and 725 μmol l–1 day–1 P and 0.22 and 18 μmol l–1 day–1 N from new and used pots, respectively, but declined rapidly with increasing time spent in deionized distilled water and were below detectable levels after about 18 and 29 days, respectively.

3. A phosphorus (P) dose–response experiment in a P‐limited reach of the Athabasca River, Alberta, Canada showed that epilithic biomass and macroinvertebrate density on NDS increased with increasing concentrations of KH2PO4 up to about 0.5 m. Beyond this threshold, biomasses and densities were unaffected by initial KH2PO4 concentration. Coefficients of variation of epilithic biomass estimates declined with increasing KH2PO4 whereas invertebrate density appeared to be unaffected by KH2PO4 levels.

4. Release rates of both P and N from NDS filled with 0.5 m KH2PO4 or 0.5 m NaNO3 declined at a log‐negative rate from about 5000 μmol N‐NO3 l–1 day–1 and 3500 μmol

P‐PO4 l–1 day–1 on day 2, to 200 μmol l–1 day–1 for both N and P on day 32.

5. After development, we used the diffusing substrata to identify spatial patterns in nutrient limitation at seven sites along a 120 km reach in the Athabasca River, that receives two known point‐source nutrient inputs. NDS consisting of N, P, N + P and unenriched controls were attached to the river bottom for 22–23 days and then retrieved and sampled for epilithic chlorophyll a. Physicochemical parameters and epilithic biomasses on upper stone surfaces were also quantified when NDS were deployed and retrieved from each site.

6. Sites located immediately downstream of the two point source inputs had higher water column concentrations of PO4 and epilithic biomasses than the site immediately upstream; epilithic biomass was positively related to PO4 in the late autumn (r2= 0.58) but not in early autumn. Sites located immediately below nutrient inputs were not nutrient‐limited, whereas upstream reference sites were P‐limited.
Importance of consumptive and non‐consumptive prey mortality in a coupled predator–prey system
Authors: MCKEE MALCOLM , WRONA FREDERICK , SCRIMGEOUR GARRY , CULP JOSEPH
Published: November 2003

1. Laboratory experiments were completed to identify the mechanisms by which the predatory flatworm, Dugesia tigrina, imposes mortality on its Aedes aegypti and Daphnia magna prey. Feeding trials were completed in glass microcosms which contained one of three – nine densities of small or large individuals of each prey species.

2. Mortality by Dugesia on small and large Aedes followed a type II functional response, whereas the mortality of Daphnia resembled a type III functional response. Prey mortality imposed by Dugesia consisted of consumptive and non‐consumptive elements. Non‐consumptive mortality occurred when prey individuals trapped in mucus trails subsequently died but were not ingested.

3. Additional experiments were conducted to quantify consumptive (capture followed by ingestion) and non‐consumptive mortality (death not followed by ingestion).

4. Consumptive mortality followed a type II functional response for small and large individuals of both prey species, whereas non‐consumptive mortality increased with prey density, although the relationships differed with prey species and size. The non‐consumptive mortality of large Daphnia increased at an accelerating rate with prey density and exceeded consumptive mortality at intermediate prey abundances. In contrast, non‐consumptive mortality of small Aedes and small Daphnia was lower than consumptive mortality and either increased with prey density at a decelerating (small Aedes) or accelerating (small Daphnia) rate.

5. These results suggest that the importance of consumptive and non‐consumptive mortality to total prey mortality needs to be considered when modelling predator–prey dynamics.
Predation by underyearling perch (Perca fluviatilis) on a Daphnia galeata population in a short‐term enclosure experiment
Authors: HÜLSMANN STEPHAN , MEHNER THOMAS
Published: November 2003

1. The predation impact of underyearling perch (20 mm total length) on the dynamics of Daphnia galeata was studied in three 6.5‐m3 enclosures during a 17‐day experiment in June 1995. These data were compared with zooplankton succession in three fish‐free control enclosures and in the pelagic zone of Bautzen reservoir, Germany.

2. Due to individual growth during the experiment, fish biomass in the enclosures increased from 210 mg wet body mass (w.b.m.) m–3 to 830 mg w.b.m. m–3, equivalent to an increase from 20 kg ha–1 to 75 kg ha–1.

3. In the enclosures with fish, biomass of daphnids decreased steadily to values below 1 mg wet weight (w.w.) l–1 within 17 days, whereas in the fish‐free controls and in Bautzen reservoir the Daphnia biomass fluctuated around 8 mg w.w. l–1. Other zooplankton species exhibited little or no change. Approximately 60 kg ha–1 was calculated as the critical underyearling perch biomass which may induce a drastic decline of the Daphnia galeata population in Bautzen reservoir. Comparison with values from other lakes is difficult due to differences in water depths and Daphnia biomasses.

4. Mean individual biomass of daphnids, egg ratio and proportion of adult daphnids were significantly lower in the enclosures with fish compared with the control enclosures at the end of the experiment. This may be explained partly by preferential predation of the large, egg‐carrying daphnids by fish. However, no difference was found in clutch size and size at first reproduction, possibly due to the short duration of the experiment.

5. It must be assumed that the ‘summer depression’ of daphnids observed in many waters is not the exclusive effect of direct reduction of daphnids by fish predation. Even the high biomass of underyearling perch stocked in the enclosures did not completely account for Daphnia mortality. Instead, the selective loss of large size classes, combined with low food resources and reduced reproduction rates, may induce the marked declines in daphnids.
Environmentally induced spatio‐temporal variations in the fecundity of brown trout Salmo trutta L.: trade‐offs between egg size and number
Authors: LOBON‐CERVIA JAVIER , UTRILLA CARMEN , RINCÓN PEDRO , AMEZCUA FELIPE
Published: November 2003

1. Resident brown trout Salmo trutta in the Esva River basin (north Spain) live in a patchy environment with tracts of riparian forest or meadow along stream banks. This study assessed whether the reproductive traits of brown trout from four contrasting sites reflected site‐specific factors.

2. Length at maturity (10.5–11 cm of 1 + individuals) was the same in the four sites examined but slowest growers in slow‐growing sub‐populations delayed maturity for 1 year relative to fast‐growing fish. The analysis of monthly variations in egg size and number suggest that two ‘decisions’ in two consecutive years are required to complete spawning. The first concerns the number of eggs, determined when trout are still 0 +, and the second concerns egg size.

3. At three sites, egg size and number did not differ significantly between years but highly significant interannual variations were apparent at another site. Fish length was the major determinant of egg size and number at all sites but for any given length, brown trout at sites where the fish exhibited higher growth rates spawned more, but smaller, eggs than those at slow‐growing sites. This spatial pattern was identical to the temporal pattern exhibited by trout at another site. The combination of temporal (year‐to‐year) and spatial (between rivers) variations in egg size and number showed a significant negative correlation, supporting the operation of a trade‐off between these two traits.

4. The trade‐off between egg size and number seems to be determined by site‐specific factors, with slow‐growing trout at sites which are fully covered by canopy spawning fewer, but larger, eggs than fast‐growers in unshaded sites.
Planktonic green algae in western Lake Erie: the importance of temporal scale in the interpretation of change
Authors: NICHOLLS KEN
Published: November 2003

1. Total densities of planktonic Chlorophyceae collected in weekly sampling of the Kingsville (Ontario) municipal water intake in western Lake Erie were evaluated for potential effects of the recent zebra mussel (Dreissena polymorpha) invasion and for the longer term effects of the Lake Erie phosphorus loading control programme.

2. At a relatively small temporal scale of about 10 years, an apparent zebra mussel‐related impact was clearly revealed in 1988 as an inflection point on the cumulative sum chlorophyte density curve. However, at a temporal scale of nearly three decades, this inflection point was not distinct. There was a steady decline in total Chlorophyceae throughout the 1970s which accelerated during the early 1980s; this corresponds to declining western Lake Erie phosphorus loading rates and phosphorus concentrations reported by others over the same period. In the absence of zebra mussels, average annual chlorophyte density decreased by 94% between the early 1970s and the mid‐1980s.

3. The dramatic long‐term decline of planktonic chlorophytes in western Lake Erie reveals the success of the phosphorus control programme, places the recent impact of the zebra mussels in its proper perspective and underscores the need for and value of long‐term limnological data for management of the Laurentian Great Lakes.
Feeding ecology of the freshwater detritivore Ptychoptera paludosa (Diptera, Nematocera)
Authors: WOLF BEATE , ZWICK PETER , MARXSEN JÜRGEN
Published: November 2003

1. We examined selected aspects of the nutritional ecology of larval Ptychoptera paludosa and their role in nutrient cycling in the Breitenbach, a first‐order stream in Hesse, Germany.

2. Food preference experiments demonstrated significant preference for sediments with a high organic matter content and live bacteria.

3. pH was circumneutral in all sections of the gut.

4. Enzymatic activity (β‐glucosidase and amino‐peptidase) in different parts of the gut was measured using 4‐methylumbelliferyl‐β‐D‐glucopyranoside (MUF‐Glc) and leucine‐4‐methylcoumarinyl‐7‐amide (Leu‐MCA). β‐glucosidase activity was highest in the hindgut.

5. The mean larval gut passage time was between 7 and 8 h.

6. The egestion rate of last instar larvae was about 0.35 mg dry weight (DW) faeces per larva h–1 and about 1.25 mg ash‐free dry weight (AFDW) faeces per mg larval AFDW day–1.

7. Larval faeces contained at least 4–18 times more organic matter than the average in the sediments in which they were feeding, that is, larvae fed selectively, extracting organic matter from sediments.

8. P. paludosa larvae are important in the dynamics of detritus in slow‐flowing reaches of the Breitenbach. They gather organic material from the sediment to a depth of 3 cm, and release it as faeces onto the sediment surface. A total of 770 g DW faeces m–2 yr–1, comprising about 16% organic matter, was produced by the Ptychoptera population.
Comparison of diatoms, fossil pigments and historical records as measures of lake eutrophication
Authors: HALL ROLAND , LEAVITT PETER , SMOL JOHN , ZIRNHELT NORMAN
Published: November 2003

1. Analysis of fossil diatoms and pigments was used to examine the effects of land‐management practises on the trophic status of Williams Lake, a eutrophic lake in central British Columbia, Canada. Published weighted‐average (WA) models were used to infer changes in total phosphorus concentration (TP) during the past 200 years.

2. Diatom‐inferred TP (DI‐TP) was compared to 20 years of direct chemical TP measurements to determine the accuracy of diatom‐TP models in inferring mean summer TP in Williams Lake. Plant pigments were measured using high performance liquid chromatography (HPLC) to quantify historical changes in gross algal community composition and abundance and to evaluate further diatom‐TP inferences.

3. Palaeolimnological analyses showed that Williams Lake has been productive throughout the last 200 years. Diatoms characteristic of alkaline, eutrophic conditions were continuously present c. 1765–1990 AD. Carotenoids from filamentous cyanobacteria (myxoxanthophyll, aphanizophyll) were regularly present in Williams Lake sediments, although cryptophytes (alloxanthin), diatoms (diatoxanthin), chlorophytes (lutein‐zeaxanthin, b‐phorbins), and siliceous algae (diatoms, chrysophytes) or dinoflagellates (fucoxanthin) were also important components of past algal communities. Terrestrial disturbance (railway and road constructions, cattle ranching) increased lake production, but resulted in relatively little permanent environmental change.

4. Comparison of DI‐TP with measured TP (1972–91) showed that inferences from simple WA models were similar to average summer TP (39.1 vs. 35.2 μg TP l–1). Inferences resulting from data manipulations that down‐weighted eutrophic lakes (outlier elimination, bootstrapping) or diatom species (square‐root transformation, tolerance‐weighting) were weakly and negatively correlated with measured TP, introduced bias into inference models, or underestimated measured TP. These patterns suggest that, when using diatom‐TP models developed from sparsely populated regions, accurate palaeoecological inferences for TP in eutrophic lakes should avoid data manipulations which down‐weight the most productive sites and taxa.

5. Comparison of DI‐TP and fossil‐inferred algal abundance during the past 200 years suggested that changes in nutrient inputs accounted for relatively little variation in past algal abundance. Although past changes in total algal biomass (as β‐carotene) and DI‐TP were broadly similar, the two variables were not significantly correlated (α = 0.05). In contrast, changes in DI‐TP were significantly correlated with mean concentrations of diatom‐specific carotenoids (diatoxanthin), although the explanatory power was low (r2 = 0.16). These patterns suggest that the DI‐TP model reflects more closely environmental conditions in Williams Lake during periods of diatom growth, and not necessarily those when total algal biomass is greatest.
Shredder–collector interactions in temporary streams of western Oregon
Authors: DIETERICH MARTIN , ANDERSON N.H. , ANDERSON TRACEY
Published: November 2003

1. Field data and results from laboratory rearing are combined to describe shredder–collector interactions in western Oregon temporary streams.

2. The composition of functional feeding groups in the temporary streams conforms to that predicted for permanent headwaters by the River Continuum Concept (RCC).

3. A distinct functional feeding group phenology was found, with shredders emerging first and collectors emerging last in the season. Scrapers were intermediate.

4. Presence of shredders enhanced collector growth in laboratory experiments (P < 0.01;n = 12). The species reared in the study trials accounted for 67% of the shredder biomass and 76% of the collector biomass in the natural systems.

5. Field data and laboratory rearing trials both support the hypothesis of a close shredder–collector interaction in the processing of allochthonous material in the summer‐dry headwaters studied.
A yellow–green algal symbiont in the freshwater sponge, Corvomeyenia everetti: convergent evolution of symbiotic associations
Authors: FROST THOMAS , GRAHAM LINDA , ELIAS JOAN , HAASE MARK , KRETCHMER DONALD , KRANZFELDER JAMES
Published: November 2003

1. A previously undescribed symbiotic relationship is reported between the freshwater sponge Corvomeyenia everetti, which occurs throughout eastern North America, and a yellow‐green alga.

2. Ultrastructural and pigment analyses place the algal endosymbiont within the class Eustigmatophyceae in the division Heterokontophyta.

3. The relationship of the alga with C. everetti appears to be specific and it contributes significantly to the energy budget of the host.

4. Although the growth form of C. everetti is very similar to other freshwater sponges that usually have green‐algal symbionts, its phylogeny has been proposed to be quite distinct, suggesting convergent evolution by both algae and sponges in the development of symbiotic associations in fresh water.
The influence of catchment land use on stream integrity across multiple spatial scales
Authors: ALLAN DAVID , ERICKSON DONNA , FAY JOHN
Published: November 2003

1. Despite wide recognition of the need for catchment‐scale management to ensure the integrity of river ecosystems, the science and policy basis for joint management of land and water remains poorly understood. An interdisciplinary case study of a river basin in south‐eastern Michigan is presented.

2. The River Raisin drains an area of 2776 km2, of which some 70% is agricultural land. The upper basin consists of till and outwash, and both topography and land use/cover are diverse. The lower basin consists of fine textured lake deposits, is of low relief, and land use is primarily agricultural.

3. The River Raisin basin historically was a region of oak‐savannah and wetlands. It was deforested, drained and converted to farmland during the mid‐nineteenth century. Human population reached a plateau at about 1880, and then underwent a second period of growth after 1950, mainly in small urban areas. More recently, the amount of agricultural land has declined and forested land has increased, in accord with a general decline in farming activity.

4. It could be suggested that the influence of land use on stream integrity is scale‐dependent. Instream habitat structure and organic matter inputs are determined primarily by local conditions such as vegetative cover at a site, whereas nutrient supply, sediment delivery, hydrology and channel characteristics are influenced by regional conditions, including landscape features and land use/cover at some distance upstream and lateral to stream sites.

5. Sediment concentrations measured during low flows were higher in areas of greater agriculture. In a comparison of two subcatchments, sediment yields were up to ten times greater in the more agricultural location, in response to similar storm events. A distributed parameter model linked to a geographical information system predicted that an increase in forested land cover would result in dramatic declines in runoff and sediment and nutrient yields.

6. Habitat quality and biotic integrity varied widely among individual stream sites in accord with patterns in land use/cover. Extent of agricultural land at the subcatchment scale was the best single predictor of local stream conditions. Local riparian vegetation was uncorrelated with overall land use and was a weak secondary predictor of habitat quality and biotic integrity.

7. Investigation of the regulatory agencies involved in land and water management in the basin revealed a complex web of overlapping political jurisdictions. Most land‐use decision‐making occurs at the local level of township, city or village. Unfortunately, local decision‐making bodies typically lack the information and jurisdictional authority to influence up‐ and downstream events.
Sensitivity of Daphnia to toxic cyanobacteria: effects of genotype and temperature
Authors: HIETALA JAANA , LAURÉN‐MÄÄTTÄ CAMILLA , WALLS MARI
Published: November 2003

1. We studied the effects of both acute and chronic exposure of Daphnia pulex to toxic Microcystis aeruginosa. We focused on the effects of Daphnia genotype and temperature (19 and 24 °C).

2. The study revealed variation among ten Daphnia pulex clones in survivorship under acute Microcystis exposure, measured as EC50. An increase in temperature caused a clear decrease in EC50, although the ranking of clones according to sensitivity remained the same at both temperatures.

3. In the chronic exposure of two of the clones, toxic Microcystis reduced survival and reproduction. The two clones differed in their responses, indicating different means of coping with toxic cyanobacteria. Toxic cyanobacteria reduced slightly more at 24 °C than 19 °C.

4. The clonal difference in sensitivity to toxic cyanobacteria at acute exposure was reversed at chronic exposure. This indicates that the results from short‐term toxicity cannot be used to predict life history responses under sublethal exposure.
The photosynthetic response of eight species of Acer to simulated light regimes from the centre and edges of gaps
Authors: LEI T. T. , LECHOWICZ M. J.
Published: November 2003

1. Seedlings of eight Acer species grown under two light treatments simulating forest gap edge (photosynthetic photon flux density, PPFD=30μmolm–2s–1; R:FR=0·6) and gap centre (PPFD=400μmolm–2s–1; R:FR=1·1) were studied to explore the effect of growth irradiance on transient‐ and steady‐state photosynthesis.

2. The increase in maximum photosynthetic rate (Amax) from gap edge‐ to gap centre‐grown seedlings ranged between 20% in Acer saccharum and 138% in Acer ginnala. Amax differed significantly among species (2·3 to 12·3μmolm–2s–1) but assimilation rates under dim light (30μmolm–2s–1) were more similar (0·6 to 1·4μmolm–2s–1).

3. Significant differences among species in stomatal conductance indicate that species of high photosynthetic performance maintain higher dim light conductance and show a much greater excursion in stomatal opening under saturating light.

4. Lightfleck response based on actual photosynthetic rates was more rapid in gap centre‐ vs gap edge‐grown plants but the latter demonstrated more rapid rates of photosynthetic induction (PI).

5. We suggest that the estimation of photosynthetic induction state is prone to an inverse relationship with maximum photosynthetic rate (Amax) and so may not be directly related to efficiency in sunfleck response. Conversely, higher Amax can result in low PI but is also associated with higher transient rates of assimilation during a lightfleck and, therefore, be equally relevant as induction properties.

6. It appears that leaves with characters such as greater specific leaf mass and area‐based leaf N, even within the same irradiance treatment, may confer a carboxylation advantage to sunfleck utilization not reflected in PI. However, whether the total carbon return on such a leaf is better assessed by PI or transient photosynthetic rate remains to be determined.
Ecological correlates of the thermal quality of an ectotherm’s habitat: a comparison between two temperate lizard populations
Authors: DÍAZ J. A.
Published: November 2003

1. Although thermal factors are of paramount importance to the quality of the habitats occupied by small ectotherms (e.g. lizards), the hypothesis that the relative abundance of squamate populations is related to the thermal quality of their habitats remains untested. If differences in the availability of thermally suitable microhabitats was the primary determinant of the overall quality of a lizard’s habitat, population density in a habitat should be proportional to its thermal quality.

2. The influence of the thermal quality of a habitat on thermoregulatory behaviour, body temperatures, expected physiological performance and relative abundance was compared in two populations of the temperate lizard Psammodromus algirus separated by 700 m altitude in central Spain. Habitat thermal quality was estimated with an index of how closely the available operative temperatures in a habitat match the range of body temperatures that lizards attempt to maintain in a laboratory thermogradient (Hertz, Huey & Stevenson 1993).

3. Operative temperatures, measured using copper models, were higher at the lowland site, where a large proportion of readings fell within or above the preferred range, especially in the early morning. Thermal habitat quality was also higher at the low altitude site, with smaller absolute deviations from the preferred range throughout most of the morning hours. Moreover, lizard body temperatures, the accuracy of thermoregulation and the predicted running performance of lizards were somewhat higher at the lowland site, although differences were smaller than expected on the basis of operative temperatures. A log‐linear analysis showed that lizard selectivity for basking sites was more pronounced at the thermally inferior montane site. Thus, the observed differences in the thermal quality of habitats appeared to influence the behaviour of lizards.

4. Nevertheless, the relative abundance of lizards, as estimated by repeated transect counts, was higher at the montane site. This unexpected result suggests that thermal constraints may not be the most important factor determining lizard population densities on a regional scale. Alternatively, food availability and/or predation pressure might have a greater impact on the overall quality of a habitat for temperate lizards.
Predator–prey instability: individual‐level mechanisms for population‐level results
Authors: BEISNER B. E. , MCCAULEY E. , WRONA F. J.
Published: November 2003

1. In previous work we established that increasing temperature led to a destabilization of the population dynamics of the invertebrate carnivore Mesostoma ehrenbergii and its prey Daphnia pulex, which ultimately resulted in the local extinction of Daphnia at higher temperatures. Two mechanisms are proposed to explain the population‐level phenomena: (1) quantitative changes in carnivore vital rates with increasing temperature led to stronger functional and numerical response and (2) qualitative changes in the dynamic allocation of energy to reproduction by the predator with increasing temperature introduces inverse density dependence in the predator’s response.

2. The growth of individual M. ehrenbergii was monitored under various food conditions to determine the effect of two temperatures (18 and 24 °C) and five food levels on rates of growth, prey consumption and reproduction and on reproductive allocation patterns.

3. The first mechanism was supported by both higher consumption rates (stronger functional response) and faster growth rates with earlier age at maturity and shorter generation time (stronger numerical response).

4. Evidence for mechanism two was also provided by an alteration of the reproductive allocation pattern with temperature. Viviparous (subitaneous) eggs were more likely to be produced by this carnivore at low food levels at 24 °C, while at 18 °C, high food levels were required before individuals made this switch. This shift actually introduces inverse density dependence in the predator’s numerical response which is highly destabilizing.

5. Based on the results of this study, the differential effect of M. ehrenbergii on the dynamics and structure of its D. pulex prey populations can be attributed to changes in both physiological rates and reproductive allocation patterns with temperature.
Physical and chemical response of juvenile Acacia tortilis trees to browsing. Experimental evidence
Authors: GOWDA J. H.
Published: November 2003

1. Changes in nutritional value and accessibility of leaves following browsing are important in the dynamics of plant–herbivore interactions because they influence the fitness of the plant attacked and the future utilization of it by the herbivore.

2. Hand pruning of Acacia tortilis, a spinescent tree common in savanna ecosystems of eastern Africa, resulted in higher biomass of spines and new shoots in pruned trees than in unpruned controls.

3. Pruned trees allocated a higher proportion of shoot biomass to spines than unpruned ones, whereas the proportion of leaf biomass in new shoots was slightly reduced. Because increases in spine biomass and density following pruning are coupled with an increase in shoot production, it is concluded that higher production of spines is an inducible response of Acacia tortilis to pruning.

4. No significant changes in the concentration of total phenolics, condensed tannins or leaf nitrogen were induced by pruning.

5. Irrespective of treatment, high foliar concentrations of nitrogen were correlated with an increase in twig production for a given leaf biomass and a reduction in the concentration of secondary substances in leaves. This relation may lead to a conflict between foraging efficiency and nutrition for browsers of A. tortilis.
Intrathalline and size‐dependent patterns of activity in Lasallia pustulata and their possible consequences for competitive interactions
Authors: HESTMARK G. , SCHROETER B. , KAPPEN L.
Published: November 2003

1. In dense populations of the saxicolous lichen Lasallia pustulata the margins of adjacent thalli overlap each other in intraspecific competition for space and light.

2.
In situ non‐destructive monitoring of hydration‐dependent potential photosynthetic activity by modulated fluorescence systems in different parts of the thallus shows that the activity is structured by a centre‐to‐margin gradient, with the centre of the thallus remaining active for substantially longer periods than the margins when the thalli dry up after being activated by wetting. The pattern reflects the water status of different parts of the thallus; the margins which are thin and exposed dry up first.

3. The activity pattern within individual lichen thalli suggests that marginal overlapping between neighbours may have a less detrimental effect on the shadowed individuals than expected from a pure consideration of the amount of area shadowed. Because the centre of the lichen thallus is active for longer periods, shadowing of this region may possibly be more harmful per area unit than an overlap at the less active margins.

4. Larger thalli are active for substantially longer periods than small ones. Even the margins of larger thalli tend to be active for a longer period than the centre of small thalli.
The ecological function of extrafloral nectaries: herbivore deterrence by visiting ants and reproductive output in Caryocar brasiliense (Caryocaraceae)
Authors: OLIVEIRA P. S.
Published: November 2003

1. Shrubs of Caryocar brasiliense are intensively visited by many ant species in the cerrado vegetation of south‐east Brazil. Ants collect nectar from the extrafloral nectaries (EFNs) located on the buds at the apex of the plant.

2. The proportion of C. brasiliense shrubs occupied by ants greatly surpassed that of neighbouring plants without EFNs and this resulted in many more termites being attacked and removed on this plant than on plants lacking EFNs. Ant attacks on Caryocar were more frequent near the EFNs.

3. Ant‐exclusion experiments with Caryocar shrubs revealed that ants significantly reduce the infestation levels by the butterfly Eunica bechina, the sucking bud Edessa rufomarginata, the bud‐destroying fly Prodiplosis floricola and by a stem‐galling wasp. Ants had no effect on the infestation by a leaf‐galling wasp.

4. Control (ants present) and treatment (ants excluded) plants produced equal numbers of buds but flower and initial fruit production was significantly greater for ant‐visited plants. Higher abortion rates of initial fruits by control plants resulted in similar final fruit and seed sets for plants in either experimental category.

5. The extremely low fertility of cerrado soils is suggested as a possible factor constraining the ability of Caryocar shrubs to provide the resources necessary for growth and development of their heavy fleshy fruits. Higher production of initial fruits by ant‐visited shrubs would be neutralized by competition among developing fruits and subsequent abortion.

6. Possible ant‐derived benefits to C. brasiliense include: protection of vegetative tissues during plant growth, larger floral display and increased attractiveness to bat pollinators, increased male contribution to fitness through pollen donation and selective abortion of genetically inferior progeny as the maternal investment is adjusted to match available resources.
Variation in leaf longevity of Pistacia lentiscus and its relationship to sex and drought stress inferred from leaf δ13C
Authors: JONASSON S. , MEDRANO H. , Flexas J.
Published: November 2003

1. Leaf formation, loss, retention, longevity and biomass on male branches of the evergreen mediterranean shrub Pistacia lentiscus, L. correlated strongly with water‐use efficiency inferred from leaf δ13C across a gradient of precipitation on the island of Mallorca, Spain.

2. The correlations suggest that the leaf phenology is under control of drought‐induced constraints on the carbon balance.

3. In fruiting female branches, the correlations between the inferred water‐use efficiency and number of formed and retained leaves, leaf biomass and leaf longevity were non‐significant. Leaf formation was strongly reduced by fruiting and the females compensated the reduced photosynthetic capacity by retaining older leaves for a longer time than male plants.

4. It is suggested that leaf longevity in females is under strong control of resource allocation to fruit formation which is ‘overlaid’ on the drought‐induced carbon stress, which led to the observed longer leaf longevity in females than in males.
Sexually dimorphic eggs, nestling growth and sibling competition in American Kestrels Falco sparverius
Authors: ANDERSON D. J. , REEVE J. , BIRD D. M.
Published: November 2003

1. American Kestrel (Falco sparverius) nestlings are sexually dimorphic, with daughters larger than sons. The larger daughters have an advantage during sibling competition for food in excess of their higher per capita food requirements, and we predicted that parents would reduce this competitive disparity by differentially enhancing the growth of sons, specifically by laying them in larger eggs.

2. In a captive breeding population, eggs producing sons were significantly larger than eggs producing daughters; laying order effects were controlled.

3. The influence of sibling egg size ratios on post‐natal size relationships persisted through the nesting period, providing parents with a tool to manipulate size‐related phenomena in their offspring.
Thermal influences on foraging ability: body size, posture and cooling rate of an ambush predator, the python Morelia spilota
Authors: AYERS D. Y. , SHINE R.
Published: November 2003

1. The interface between thermal biology and foraging mode has attracted little scientific attention, but may be crucially important to the biology of ectothermic predators. Slip & Shine (1988c) suggested that the ability of large heavy‐bodied snakes to ambush nocturnally active mammals relied on the snakes’ control of cooling rates through their thermal inertia (via body size and postural adjustments) and microhabitat selection.

2. We tested assumptions underlying this hypothesis, using Diamond Pythons (Morelia s. spilota) from southeastern New South Wales. Our laboratory studies confirmed that larger body sizes and coiled postures significantly retarded cooling rates, and that body temperature affected the snakes’ ability to detect potential prey items.

3. The magnitude of these effects on cooling rates was great enough to extend the time period substantially over which an adult Diamond Python, lying in ambush in a suitable microhabitat, would be able to detect and capture nocturnally active prey. For example, the times taken for pythons to reach thermal equilibration under our experimental conditions (cooling from 33 to 12°C) were <1h for hatchling pythons regardless of posture, 1 h for outstretched juveniles, 2 h for coiled juveniles and outstretched adults, and almost 8 h for coiled adults.

4. The high rates of cooling of juvenile pythons, even when they are tightly coiled, may force them to rely upon diurnally active prey rather than crepuscular or nocturnal species.
Feeding behaviour of Red Deer (Cervus elaphus) offered Sitka Spruce saplings (Picea sitchensis) grown under different light and nutrient regimes
Authors: HARTLEY S. E. , IASON G. R. , DUNCAN A. J. , HITCHCOCK D.
Published: November 2003

1. In addition to exhibiting preferences for particular plant species, vertebrate herbivores select particular individuals of these species whilst leaving others undamaged. This pattern of diet selection may reflect differences in the chemical composition (and hence nutritional quality) between individual plants, and/or variability in the physical constraints on intake rate, such as plant structure.

2. An experiment was conducted to test the effects of environmental manipulations on the morphology and chemical composition of Sitka Spruce saplings, and to evaluate the consequences for herbivory by Red Deer. Fertilizing the trees increased tree height, branch span and leader length, twig width and needle width, and decreased the concentrations of total phenolics, condensed tannins, fibre and lignin but monoterpene content was not altered. Shading also reduced phenolic and tannin concentrations.

3. When the fertilized and shaded trees were offered to deer in feeding trials, the probability of a tree being visited by a deer and the biomass removed were influenced by tree morphological variables, as were the bite rate and intake rate of the deer. More biomass was removed from larger trees.

4. Once the effects of tree morphology had been taken into account, there was no effect of the fertilizer and shade treatments on deer browsing behaviour that could be attributed to changes in chemical composition of the trees. The relationship between intake rate and bite size at each tree varied between individual deer, but the functional response relationship between intake rate and bite size was not influenced by the treatments applied to the trees.

5. Tree morphology may have a larger influence on deer feeding behaviour than tree chemical composition.
Seedling growth of four fire‐following Mediterranean plant species deprived of single mineral nutrients
Authors: HANLEY M. E. , FENNER M.
Published: November 2003

1.
Anthyllis vulneraria, Cistus creticus, Hippocrepis unisiliquosa and Pinus brutia are frequent post‐fire colonizers whose seedlings are subjected to the mineral conditions imposed by ash in the early stages of growth. We test the hypothesis that the effective internal supply of mineral elements in the seeds of these species may complement the external availability of specific nutrients.

2. Newly germinated seedlings were grown in nutrient solutions, each deficient in one of the following elements: nitrogen, phosphorus or potassium. Control treatments consisted of full nutrients and distilled water. Seedling growth was monitored over 12weeks. The final dry masses of the seedlings were taken as a measure of the availability of each element from the seeds’ own stored reserves.

3. For the two legume species nitrogen was the most limiting element followed by phosphorus. Potassium deficiency had no effect on the final legume dry biomass. For Cistus, the order was nitrogen followed by potassium, while phosphorus deprivation had no effect on growth during the 12weeks of the experiment. Deprivation of single minerals had no significant effect on seedling growth of Pinus over the same period. The two legumes and Cistus when denied nitrogen had relatively greater relative root ratios than control plants.

4. The relative seedling requirements of each species for early external supplies of the various nutrients for establishment in the field are discussed with reference to the adaptation of the four species to post‐fire regeneration.