bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial and seasonal variation in nutrient excretion by benthic invertebrates in a eutrophic reservoir
Authors: DEVINE JENNIFER A. , VANNI MICHAEL J.
Published: March 2003

1. Nitrogen (N) and phosphorus (P) fluxes via excretion by benthic invertebrates were quantified in a eutrophic reservoir (Acton Lake, Ohio, U.S.A.). We quantified variation in nutrient fluxes seasonally (June until November 1997), spatially (three sites) and among taxa (chironomids, tubificid oligochaetes and Chaoborus).

2. The three taxa differed in spatial distribution and contribution to nutrient fluxes. Tubificids were the most abundant taxon at two oxic sites (1.5 and 4 m depth), and were exceedingly rare at an anoxic, hypolimnetic site (8 m). Chironomids were abundant only at the shallowest oxic site. Chaoborus was the only abundant taxon at the anoxic site. Total benthic invertebrate biomass was greatest at the shallowest site and lowest at the anoxic, hypolimnetic site.

3. Mass‐specific excretion rate [μmol NH4–N or soluble reactive P (SRP) excreted mg dry mass–1 h–1] varied among experiments and was influenced by temperature. Differences among taxa were not significant. Thus, nutrient flux through benthic invertebrates was affected more by total invertebrate biomass and temperature than by species composition.

4. Fluxes of N and P via benthic invertebrate excretion (μmol NH4–N or SRP m–2 day–1) were greatest at the oxic sites, where fluxes were dominated by the excretion of tubificids and chironomids. The N and P fluxes at the anoxic site were much lower, and were dominated by excretion by Chaoborus. The ratio of N and P excreted by the benthic invertebrate assemblage varied seasonally and was lowest at the anoxic site.

5. Comparison with other measured inputs shows that excretion by benthic invertebrates could be an important source of nutrients, especially of P. However, the relative importance of nutrient excretion by the benthos varies greatly spatially and temporally.
Decomposition of litter from submersed macrophytes: the indirect effects of high [CO2]
Authors: TITUS JOHN E. , PAGANO ANGELA M.
Published: March 2003

1. We grew the submersed freshwater macrophyte Vallisneria americana under controlled conditions at low and high [CO2] to produce litter with high and low tissue nitrogen concentration ([N]), respectively. We then followed mass and nitrogen dynamics in situ in this litter to test the indirect effect of [CO2] on its subsequent decomposition and colonisation by macroinvertebrates.

2. Litter from plants grown in high CO2 initially lost mass and N at a significantly lower rate but, by day 30, both litter types had lost about 90% of mass and N. Litter [N] did not appear to govern decay rate.

3. There was no effect of CO2 on the pattern of macroinvertebrate colonisation.

4. The potential exists for high [CO2] to increase rates of C and N cycling and, thereby, to increase internal N loading in macrophyte‐dominated shallow water ecosystems.
Effects of channelisation on stream habitat in relation to a spate and flow refugia for macroinvertebrates in northern Japan
Authors: NEGISHI J. N. , INOUE M. , NUNOKAWA M.
Published: March 2003

1. The effects of channelisation on macroinvertebrates were examined in relation to a spate and flow refugia. Habitat components that can function as flow refugia were identified in a small, low‐gradient stream in northern Hokkaido, Japan.

2. Macroinvertebrates and their habitat characteristics (depth, current velocity and substratum) were sampled and measured in natural and channelised sections on three occasions: before, during and immediately after a spate. For macroinvertebrate sampling and habitat measurements, five (riffle, glide, pool, backwater and inundated habitats) and three (channelised‐mid, channelised‐edge and inundated habitats) habitat types were classified in the natural and channelised section, respectively.

3. The rate of velocity increase with discharge was compared among habitat types to determine which habitat types were less affected by increased discharge. The rate was the highest in riffles followed by glides and channelised‐mids. Backwaters maintained low current velocity even at high flow. In addition, current velocity in both natural and channelised inundated habitats was low relative to other habitat types during the spate.

4. Through the spate, total density of macroinvertebrates in channelised‐mids and taxon richness in both channelised‐mids and edges decreased. In the natural section, however, such a significant decrease was not found except for taxon richness in pools. This indicated that the spate had a greater impact on assemblages in the channelised section. Riffle assemblages exhibited a rapid recovery immediately after the spate, suggesting the existence of flow refugia in the natural section. Among the habitat types we examined, backwaters and inundated habitats appeared to have acted as flow refugia, because these habitats accumulated macroinvertebrates during the spate.

5. The lower persistence of the macroinvertebrate assemblage in the channelised section was attributable to the lower availability of flow refugia such as backwaters and inundated habitats. Our results emphasised the importance of considering flow fluctuations and refugia in assessing the effects of channelisation. In addition, the lateral heterogeneity of stream channels should be considered in stream restoration and management.
Herbivory and growth in terrestrial and aquatic populations of amphibious stream plants
Authors: SAND‐JENSEN KAJ , JACOBSEN DEAN
Published: March 2003

1. Many amphibious plant species grow in the transition between terrestrial and submerged vegetation in small lowland streams. We determined biomass development, leaf turnover rate and invertebrate herbivory during summer in terrestrial and aquatic populations of three amphibious species to evaluate advantages and disadvantages of aerial and submerged life.

2. Terrestrial populations had higher area shoot density, biomass and leaf production than aquatic populations, while leaf turnover rate and longevity were the same. Terrestrial populations experienced lower percentage grazing loss of leaf production (average 1.2–5.1%) than aquatic populations (2.9–17.3%), while the same plant dry mass was consumed per unit ground area.

3. Grazing loss increased linearly with leaf age apart from the youngest leaf stages. Grazing loss during the lifetime of leaves was therefore 2.4–3.1 times higher than mean apparent loss to standing leaves of all ages. The results imply that variation in density of grazers relative to plant production can account for differences in grazing impact between terrestrial and aquatic populations, and that fast leaf turnover keeps apparent grazing damage down.

4. We conclude that the ability of amphibious plants to grow submerged permits them to expand their niche and escape intense competition on land, but the stream does not provide a refugium against grazing and constrains plant production compared with the terrestrial habitat.
The life history of Salicaceae living in the active zone of floodplains
Authors: KARRENBERG S. , EDWARDS P. J. , KOLLMANN J.
Published: March 2003

1. Exposed riverine sediments are difficult substrata for seedling establishment because of extremes in the microclimate, poor soil conditions and frequent habitat turnover. Various species of willows and poplars (Salicaceae) appear to be particularly successful in colonising such sediments and are often dominant in floodplain habitats throughout the northern temperate zone.

2. In many Salicaceae regeneration seems to be adapted to regular disturbance by flooding. Efficient seed dispersal is achieved by the production of abundant seed in spring and early summer, which are dispersed by air and water. Seeds are short‐lived and germinate immediately on moist surfaces. Seedling establishment is only possible if these surfaces stay moist and undisturbed for a sufficient period of time.

3. Larger plants of Salicaceae have exceptional mechanical properties, such as high bending stability, which enable them to withstand moderate floods. If uprooted, washed away or fragmented by more powerful floods these plants re‐sprout vigorously.

4. While these life characteristics can be interpreted as adaptations to the floodplain environment, they may also cause a high genetic variability in populations of Salicaceae and predispose Salicaceae to hybridization. Thus, a feed back between adaptive life history characteristics and the evolutionary process is proposed.
Riparian vegetation diversity along regulated rivers: contribution of novel and relict habitats
Authors: JOHNSON W. CARTER
Published: March 2003

1. The creation and maintenance of spatial and temporal heterogeneity by rivers flowing through floodplain landscapes has been disrupted worldwide by dams and water diversions. Large reservoirs (novel ecosystems) now separate and isolate remnant floodplains (relict ecosystems). From above, these appear as a string of beads, with beads of different sizes and string connections of varying lengths.

2. Numerous studies have documented or forecast sharp declines in riparian biodiversity in relict ecosystems downstream from dams. Concurrently, novel ecosystems containing species and communities of the former predam ecosystems have arisen along all regulated rivers. These result from the creation of new environments caused by upper reservoir sedimentation, tributary sedimentation and the formation of reservoir shorelines.

3. The contribution of novel habitats to the overall biodiversity of regulated rivers has been poorly studied. Novel ecosystems may become relatively more important in supporting riverine biodiversity if relict ecosystems are not restored to predam levels. The Missouri River of the north‐central U.S.A. is used to illustrate existing conditions on a large, regulated river system with a mixture of relict and novel ecosystems.
Fluvial landscape ecology: addressing uniqueness within the river discontinuum
Authors: POOLE GEOFFREY C.
Published: March 2003

1. As rivers and streams are patchy and strongly hierarchical systems, a hierarchical patch dynamics perspective can be used as a framework for visualising interactions between structure and function in fluvial landscapes. The perspective is useful for addressing fundamental attributes of lotic ecosystems, such as heterogeneity, hierarchy, directionality and process feedback occurring across spatial scales and for illustrating spatio‐temporal linkages between disparate concepts in lotic system ecology such as the River Continuum Concept, the Serial Discontinuity Concept, the Flood Pulse Concept and the Hyporheic Corridor Concept.

2. At coarse spatial scales, the hierarchical patch dynamics perspective describes each river network as a unique, patchy discontinuum from headwaters to mouth. The discontinuum is comprised of a longitudinal series of alternating stream segments with different geomorphological structures. Each confluence in the steam network further punctuates the discontinuum because the sudden change in stream characteristics can create a `gap' in the expected pattern of downstream transitions. The discontinuum view recognises general trends in habitat characteristics along the longitudinal profile, but creates a framework for studying and understanding the ecological importance of each stream's individual pattern of habitat transitions along longitudinal, lateral or vertical vectors at any scale.

3. Object‐oriented modelling and programming techniques provide a means for developing robust, quantitative simulation models that describe the dynamic structure of patch hierarchies. Such models can simulate how the structure and function of lotic ecosystems are influenced by the landscape context of the system (the ecological conditions within which the system is set) and the metastructure (structural characteristics and juxtaposition) of finer‐scale patches comprising the system.

4. A simple object‐oriented, multiscale, discontinuum model of solute transformation and biological response along a stream channel illustrates how changing the branching pattern of a stream and the arrangement of its component patches along the downstream profile will result in substantial changes in predicted patterns of solute concentration and biotic community structure.

5. The importance of context, structure, and metastructure in determining lotic ecosystem function serves to underscoreHynes' (1975) concept that `every stream is likely to be individual.' Advancing the discipline of fluvial landscape ecology provides an excellent opportunity to develop general concepts and tools that address the individual character of each stream network and integrate the concept of `uniqueness within the river discontinuum' into our ecological understanding of rivers and streams.
Littoral macroinvertebrate communities: spatial scale and ecological relationships
Authors: Johnson R. K. , Goedkoop W.
Published: March 2003

SUMMARY 1. Spatial correlations between ecological patterns and processes are thought to be scale‐dependent, yet surprisingly few studies have evaluated the correspondence between different levels of spatial scale and ecosystem structure and function.

2. We evaluated the strength of relationships between the benthic macroinvertebrate communities of stony littoral habitats and levels of ecological scale and geographical position, using partial constrained ordination. Our hypothesis was that correlation strength would be inversely related to ecological scale, i.e. habitat > ecosystem > riparian > catchment > ecoregion.

3. The effect of habitat was greater than that of other levels of spatial scale: 23% of the variance in taxonomic composition and 11% of that in functional composition was explained by habitat variables alone. However, greater spatial scales were also important. For example, the combined influence of riparian, catchment and ecoregion classification accounted for 24% (taxonomic) and 11% (functional) of the explained variance.

4. Relationships between organisms and scale variables were, however, non‐linear and a substantial amount of the functional variance was hidden in joint effects. These findings were not unexpected, and presumably indicate a close interdependence between local and regional‐scale variables.
Effects of fathead minnows and restoration on prairie wetland ecosystems
Authors: Zimmer Kyle D. , Hanson Mark A. , Butler Malcolm G.
Published: March 2003

SUMMARY 1. Research has shown that fish influence the structure and processes of aquatic ecosystems, but replicated studies at the ecosystem level are rare as are those involving wetlands. Some wetlands of the Prairie Pothole Region (PPR) of North America support fish communities dominated by fathead minnows (Pimephales promelas) while others are fishless, providing an opportunity to assess the influence of these fish on wetland ecosystems. Additionally, many wetlands have previously been drained and subsequently restored, but the success of these efforts is poorly known and restoration may be impeded by the presence of fish.

2. We assessed the effects of fathead minnows and drainage by studying 20 semipermanent, prairie wetlands in Minnesota from 1996 to 1999. We used a 2 × 2 factorial design to examine the effects of presence and absence of minnows and drainage history (restored/never drained) on the abundance of aquatic invertebrates and amphibians, as well as on the concentrations of chlorophyll a, total phosphorus, total nitrogen and turbidity in the water column.

3. Results showed that fathead minnows are an important determinant of many biotic and abiotic characteristics of wetlands in the eastern PPR. Wetlands with fathead minnows had fewer aquatic insects, large‐ and small‐bodied cladocerans, calanoid copepods, ostracods and larval tiger salamanders, as well as a higher abundance of corixids and greater turbidity and chlorophyll a. A higher concentration of phosphorus in restored basins was the only consistent effect of past management.

4. Fathead minnows usually dominate fish communities in eastern PPR wetlands where fish are present, and can have several strong ecosystem effects. While abiotic variables are important determinants of ecosystem structure in prairie wetlands, they can be strongly influenced by biotic factors.
Activity and food choice of piscivorous perch (Perca fluviatilis) in a eutrophic shallow lake: a radio‐telemetry study
Authors: Jacobsen Lene , Berg Søren , Broberg Mads , Jepsen Niels , Skov Christian
Published: March 2003

SUMMARY 1. Radio transmitters were implanted in large perch (27–37 cm) in a shallow lake in Denmark. Between 6 and 13 perch were tracked every 3 h for 24‐h periods twice (summer) or once a month (winter) from August 1997 to July 1998. Activity levels were recorded as minimum distance moved per hour.

2. No significant differences in activity levels of individual fish were observed.

3. Highest activities were observed at daytime with peaks at dawn and dusk or midday. This diel pattern was most pronounced from October to April, whereas diel variations were less in the summer months, with no peaks occurring in midsummer. The general lack of activity at night supports the idea that perch is a visually oriented forager.

4. There was no significant relationship between daytime activity during the year and temperature or day length, but nighttime activity was correlated with temperature. In contrast with previous findings, activity levels varied little seasonally, except for high activity levels that occurred concomitantly with high temperatures in August. Instead, we found a significant relationship between the total distances moved per day and temperature, indicating that perch moved at the same average speed in the wintertime, but did so for shorter periods than in summer because of shorter day lengths.

5. Diet of the tagged perch shifted from fish dominance between August and January to invertebrates from February to June. There was no correlation between the diet shift and activity levels, indicating that feeding on invertebrate requires similar activity levels as predation on fish.

6. The results of this telemetry study throughout a year suggest that perch are more active during the winter than previously inferred from gill‐net catches. This observation underscores the importance of perch as a predator of 0+ planktivorous fish in lakes and has potential implications for pelagic food web structure and lake management by biomanipulation.
Subsurface hydrology and degree of burial affect mass loss and invertebrate colonisation of leaves in a woodland stream
Authors: Tillman Danielle C. , Moerke Ashley H. , Ziehl Carrie L. , Lamberti Gary A.
Published: March 2003

SUMMARY 1. In deciduous forest streams, fallen leaves form a large component of the total organic matter budget, and many leaves become buried within stream sediments. We examined the processing of buried leaves as compared with those at the surface, and the influence of subsurface hydrology on processing rates.

2. Leaf packs were secured on the streambed surface or buried 10 cm deep in upwelling and downwelling reaches of a second‐order stream in Michigan, U.S.A. Mass loss and invertebrate colonisation were measured from October to February.

3. Leaves buried in upwelling reaches lost mass more slowly (exponential decay coefficient, k=−0.0097) than did leaves from the other treatments (buried downwelling: −0.017; surface upwelling: −0.022; surface downwelling: −0.021).

4. Initially, more invertebrates colonised surface leaf packs than buried packs. During the remainder of the study, however, hydrology had a greater effect on invertebrate abundance than did burial, as more invertebrates were found in packs in downwelling reaches than in upwelling reaches.

5. Local subsurface hydrology and degree of burial, factors rarely considered in studies of detritus processing, can significantly influence mass loss and invertebrate colonisation of fallen leaves in streams. Furthermore, because of slower processing, subsurface zones may function as organic matter reservoirs that gradually ‘spiral’ carbon to downstream subsurface and surface habitats.
Allochthonous and autochthonous particulate organic matter in floodplains of the River Danube: the importance of hydrological connectivity
Authors: Hein Thomas , Baranyi Christian , Herndl Gerhard J. , Wanek Wolfgang , Schiemer Fritz
Published: March 2003

SUMMARY 1. The elemental composition, the proportion of living organic carbon and the carbon stable isotope signatures of particulate organic matter (POM) were determined in a large river floodplain system in order to elucidate the major carbon sources in relation to the hydrological conditions over a 13‐month period.

2. Two floodplain segments and the main channel of the River Danube downstream of Vienna (Austria), were compared on the basis of discharge and water age estimations. The more dynamic floodplain was connected to the main channel for 46% of the study period and drained up to 12% of total discharge at high water.

3. The mean C : N ratio and δ13C signature of the POM increased from the floodplain site that was more isolated from the river (6.6; −33‰) to the main channel (8.4; −25‰). At the dynamic floodplain site, the C : N ratio and the δ13C signature of the POM increased with hydrological connectivity (expressed as water age).

4. Only during flood events (4% frequency of occurrence), a considerable input of riverine POM was observed. This input was indicated by a C : N ratio of the POM pool of more than 10, the amount of detrital carbon (>80% of the total POM pool) and a δ13C signature of POM of more than −25‰ in the dynamic floodplain.

5. Plankton derived carbon, indicated by C : N ratios less than eight and δ13C values lower than −25‰, dominated the particulate organic carbon (POC) pool at both floodplain sites, emphasising the importance of local (autochthonous) production. Phytoplankton was the major plankton compartment at the dynamic site, with highest biomasses at medium water ages.

6. At the dynamic floodplain site, the Danube Restoration Project has enhanced the duration of upstream surface connection with the main channel from 4 to 46% frequency of occurrence. Therefore, the export of living POC to the main channel is now established during phases of maximum phytoplankton production and doubled the estimated total export of non‐refractory POM compared with prerestoration conditions.
Lignotuber reserves support regrowth following clipping of two Mediterranean shrubs
Authors: Canadell J. , López‐Soria L.
Published: March 2003

1.We investigated whether reserves stored in the lignotubers of two Mediterranean shrubs,Arbutus unedoandErica arborea, were significantly mobilized to support the demands of regrowth and respiration after clipping the tops at different frequencies.

2.After a single clipping,Arbutusshowed a 29% decrease of phosphorus concentration by the end of the first growing season. Two years after recovery from clipping, the starch levels remained lower than those of unclipped plants. Similarly,Ericashowed depletion of starch, but no nutrient reserves were depleted significantly.

3.Regrowth after multiple clippings mobilized a large fraction of the starch and nutrients stored in the lignotuber. Mean starch concentrations were depleted by 87–93% after multiple clippings and concentrations of nitrogen, phosphorus, potassium and magnesium were depleted by 10–45%, 27–41%, 19–39% and 23–31%, respectively.

4.An average‐sized lignotuber produced 288 resprouts forArbutusand 1990 resprouts forEricaduring a 27 month period of multiple clippings, at the end of which the first plants died.

5.Plant mortality after multiple clipping was 10% forArbutusand 30% forErica, and was primarily attributed to exhaustion of carbon reserves because starch concentrations decreased by 96% in dead plants.
Chemical contents of Macaranga food bodies: adaptations to their role in ant attraction and nutrition
Authors: Heil M. , Fiala B. , Kaiser W. , Linsenmair K. E.
Published: March 2003

1.
Macaranga (Euphorbiaceae) is a paleotropical tree genus comprising myrmecophytic and non‐myrmecophytic species. All species are presumed to possess food bodies (FBs) to maintain or attract ants as anti‐herbivore defence.

2. The hypothesis was tested that Macaranga species differing in their mode of association with ants would produce FBs differing in their chemical composition. We investigated contents of carbohydrates, proteins and lipids in FBs of four myrmecophytic and one non‐myrmecophytic Macaranga as well as one Parthenocissus (Vitaceae) species.

3. On a dry weight basis, FBs of myrmecophytes contained relatively higher amounts of proteins compared to carbohydrates than those of non‐myrmecophytes. Soluble carbohydrates showed species‐specific patterns and were found in especially high amounts in both non‐myrmecophytes. Furthermore, Parthenocissus FBs contained higher amounts of soluble compared to polymerous substances not only in carbohydrates but also in proteins.

4. FBs seem to be specifically adapted to their respective role in ant attraction and nutrition, with myrmecophytes providing ants with high amounts of lipids and proteins and non‐myrmecophytes mainly offering carbohydrates in the form of common soluble sugars.
Average daily metabolic rate of rodents: habitat and dietary comparisons
Authors: Degen A. A. , Kam M. , Khokhlova I. S. , Krasnov B. R. , Barraclough T. G.
Published: March 2003

1.Average daily metabolic rate (ADMR) is the metabolizable energy intake required by a caged animal to maintain constant body energy content. Linear regression of standardized, phylogenetically independent contrasts was used to describe the allometric relationship between ADMR and body mass in rodents. It was predicted that desert species would have a lower ADMR than non‐desert species and that granivores would have a lower ADMR than those of herbivores and omnivores. The efficiency of utilization of energy for maintenance was also determined in these species. Here, it was predicted that the efficiency in granivores would be higher than in both herbivores and omnivores and in desert species would be higher than in non‐desert species.

2.The regression of the phylogenetic contrasts of ADMR on body mass (mb) for 53 independent data points based on 63 species of rodents was highly significant (P< 0·0001) with an allometric slope of 0·53. Independent comparisons of both basal metabolic rate (BMR) and ADMR showed significantly lower rates in desert than in non‐desert species. There was a trend for granivores to have a lower ADMR per g0.53than either omnivores or herbivores, but this trend is not significant in independent comparisons between the categories. Thus, the predictions in regard to desert and non‐desert habitats were confirmed, and there is a non‐significant trend in the predicted direction with respect to diet. Herbivores and omnivores showed no significant difference in either BMR or ADMR.

3.In independent comparisons between categories, there was no evidence for trends in the efficiency of utilization of energy for maintenance (BMR:ADMR ratio orkm) with either habitat or diet categories. Thus, these results are not in agreement with our predictions. Taking simple means,kmequals 0·47±0·21, 0·37±0·12 and 0·56±0·11 for granivores, omnivores and herbivores, respectively, and 0·37±0·12 and 0·55±0·16 for desert and non‐desert mammals, respectively.

4.It is recommended that conditions for ADMR measurements be standardized, as is common for basal metabolic rate measurements. This would allow more reliable comparisons among species measured in different laboratories and also provide more accurate estimates of efficiency of utilization of energy.
The effect of plant size on the expression of cleistogamy in Mimulus nasutus
Authors: Diaz A. , Macnair M. R.
Published: March 2003

1. Most dimorphic angiosperm species produce chasmogamous flowers adapted for allogamy and cleistogamous flowers adapted for autogamy. Plant size is an important internal environmental factor and several studies have suggested an adaptive strategy whereby cleistogamous flowering ensures a basic seed output while larger plants can spare resources to make additional investment in the more expensive but presumably more fit outcrossed seed produced by chasmogamous flowering. This study tests the effect of plant size on the percentage of chasmogamy in a species, Mimulus nasutus, where both the cleistogamous and chasmogamous flowers are autogamous and so seed from chasmogamous flowers has no genetic advantage.

2. We measured change in expression of cleistogamy/chasmogamy in glasshouse‐grown plants of different sizes and architecture. Size was manipulated by varying the length of time for which the plants were grown under short days. Architecture was manipulated by removing stems.

3. We found that increased size led to an increase in the percentage of chasmogamy in M. nasutus. This is unexpected given the lack of genetic advantage of outcrossing and suggests that this effect can occur as a direct result of increased resource availability without the necessity of selection for progeny fitness.

4. An increase in plant size was also found to lead to an increase in resource sinks (developing flowers and seed capsules on other parts of the plant). As increased plant size can therefore produce both increased total resources and increased number of resource sinks, the net resources available to a developing flower will be a balance of these two effects. Resource re‐allocation is shown to occur between flowers on a stem, between stems and between flowers and seed set. In each case, this results in a net decrease in resources to new flowers and so results in there being only sufficient resources for cleistogamous flowering.

5. We discuss the difficulties of using species with varying growth forms to test the hypothesis that expression of allogamous chasmogamy increases with plant size because of the genetic advantage of outcrossing.
Life‐history responses of British grasshoppers (Orthoptera: Acrididae) to temperature change
Authors: Willott S. J. , Hassall M.
Published: March 2003

1.Ectotherms may be thermal generalists, or high‐ or low‐temperature thermal specialists. The thermal strategy of four species of grasshoppers occurring in Britain is determined, where unpredictable variation in the generally cool climate should preclude the low‐temperature thermal specialist strategy. It is predicted that temperature sensitivity will determine geographical distribution, with generalist species widespread, and thermally specialized species restricted to warmer habitats.

2.The developmental and reproductive responses to different rearing temperatures of the grasshoppers are examined in a laboratory experiment. Life‐history traits are integrated into a fitness model to determine the sensitivity of each species to temperature change.

3.Growth and development rates increased with temperature for each species. The frequency with which an additional instar was inserted during nymphal development increased with temperature inChorthippus brunneus. Adult mass and size increased with temperature.

4.Egg pod production rate increased with temperature. InOmocestus viridulus, Myrmeleotettix maculatusandStenobothrus lineatus, temperature had no effect on egg mass, eggs per pod or number of pods per female. Number of pods per female increased with temperature inC. brunneus.

5.Fitness ofS. lineatusdecreased by 88% for a 5 °C fall in temperature compared with 58% and 56% forC. brunneusandM. maculatus, respectively.Omocestus viridulusis least sensitive to temperature change with only a 27% reduction in fitness at the lower rearing temperature.

6.It is concluded that all the species are high‐temperature thermal specialists, and variation in their sensitivity to temperature is a good predictor of their distribution. The most generalist species,O. viridulus, is the most widespread, while the more specialist speciesS. lineatusandM. maculatusare restricted to warmer habitats.Chorthippus brunneusis also a high‐temperature specialist, but is more widespread as a consequence of developmental and reproductive plasticity and efficient behavioural thermoregulation.
Distribution of leaf photosynthetic properties in tree canopies: comparison of species with different shade tolerance
Authors: Kull O. , Niinemets Ü.
Published: March 2003

1.
Parameters of the photosynthesis vs CO2 response curve, nitrogen and chlorophyll contents were studied in Populus tremula, Tilia cordata and Corylus avellana leaves along a natural light gradient in the canopy.

2. In all species, leaf nitrogen content per unit area (Ns) declined with decreasing fractional transmission of photon flux density (Ksum), measured by a hemispheric photographic technique. However, the shape of the relationship between Ns and Ksum depended on species. Ns was almost linearly related to Ksum in the most light‐demanding species P. tremula but this relationship was curved in two other species. Populus tremula possessed the largest values of Ns at given Ksum, while C. avellana, the most shade‐tolerant species, had the lowest values of Ns.

3. Both the initial slope, characterizing the maximum carboxylation efficiency, and the plateau value, providing an estimate of the photosynthetic electron transport capacity, of the photosynthesis vs CO2 response curves, were linearly related to Ns and only minor differences were observed among the studied species. Leaf chlorophyll content per area was also related to Ns but the ratio of Chl/N increased substantially at low Ksum in the lower canopy. It was concluded that the partitioning of nitrogen between light harvesting, electron transport and carboxylation components of the photosynthetic apparatus may change with depth in the canopy as a result of a relative increase in the light‐harvesting complexes in relation to the rest of the photosynthetic apparatus.

4. The interspecific differences in species’ photosynthetic potentials are mainly associated with different nitrogen distribution patterns along the canopy and in minor part with differences in nitrogen partitioning among photosynthetic machinery.
Air pollution fades the plumage of the Great Tit
Authors: Eeva T. , Lehikoinen E. , RÖnkÄ M.
Published: March 2003

1. Great Tits (Parus major) derive the carotenoid pigments for their yellow plumage via the prey items in their diet. Air pollution is known to affect the abundance of many forest insects, e.g. green caterpillars, which are an important source of food and pigments for tits. This study investigates whether air pollutants indirectly affected the intensity of the yellow colour in P. major plumage via the reduced access to carotenoid sources.

2. The intensity of the yellow colour in the plumage of P. major nestlings was scored and the relative abundance of green herbivorous larvae in territories around a polluting copper smelter in SW Finland was simultaneously measured.

3. Both the intensity of yellow colour in nestling plumage and caterpillar abundance increased with increasing distance from the pollution source. The colour intensity correlated significantly with the density of green herbivorous larvae in a territory.

4.
Parus major nestlings were significantly heavier at distant sites than close to the pollution source which suggests that the future survival probability of pale nestlings may be lowered.

5. Young birds, after their first moult, were studied for the relationships between condition, size and plumage colour by the means of ptilochronology. The plumage colour intensity did not correlate with the size corrected width of the growth bars in fifth rectrix (condition at moult) but was correlated positively with the length of the rectrix (size).

6. The implications of colour change for survival and mate choice are discussed.
δ13C of wood in growth‐rings indicates cambial activity of drought‐stressed trees of Eucalyptus globulus
Authors: Macfarlane C. , Adams M. A.
Published: March 2003

1. Growth, density and δ13C of wood and leaf area were measured in two adjacent stands of 6 year‐old Eucalyptus globulus growing in the 600–700 mm year–1 rainfall region of south‐western Australia. Study sites were identical except for differences in the availability of water owing to physical properties of soil profiles and location of sites within the landscape.

2. Abundance of 13C (expressed as δ13C) in wood of trees growing on the drought‐prone site (– 24·8‰±1·4) was greater than in other trees (– 25·8‰±1·2, P<0·001) throughout the 6 years and, with further development, the δ13C signatures of wood may become useful indices of drought‐susceptibility in plantations within a few years of establishment. The seasonal pattern of δ13C of wood appeared to reflect seasonal variation in water availability and duration of cambial activity.

3. Basic density of wood of trees growing on the more drought‐prone site (496±14·0 kg m–3) was reduced compared to other trees (554±5·3 kg m–3, P<0·001). δ13C of wood across boundaries of growth‐rings suggested that drought stopped cambial activity resulting in less production of late wood and less dense wood.

4. The stand growing on the drought‐prone site had reduced growth, wood yield and leaf area but identical specific leaf area. Annual growth was correlated with the previous season’s rainfall. Together, these results suggested that within the same evaporative climate, drought reduces growth primarily by reducing leaf area and that there is a lag between onset of drought and reduced productivity.
The effect of variation in light and nitrogen on growth and defence in young Sitka Spruce
Authors: Wainhouse D. , Ashburner R. , Ward E. , Rose J.
Published: March 2003

1.Young plants of a northern (Alaska) and southern (Oregon) provenance of Sitka Spruce,Picea sitchensis, were subject to high and low light and high and low nitrogen treatments in a polyhouse experiment. The effect of treatments on growth, needle and resin duct size, water content and concentration of quantitative defences (resin and polyphenols), sugars and nitrogen in needles, stems and roots was determined.

2.Concentrations of resin, polyphenols and carbohydrates were higher in low nitrogen treatments as predicted by resource‐availability models of defence and the changes were similar in all parts of the trees including roots and in tissues formed prior to experimental treatments. Variation in the relative concentration of resin and polyphenols between tissues may indicate a defensive trade‐off. The size of needle resin ducts was positively correlated with tree growth but no evidence for ‘structural’ limitation of resin concentration in needles was found.

3.Changes in concentration of quantitative defences did not appear to be the result of a direct trade‐off with growth but reflected treatment‐induced variation in the root/shoot ratio. Production of quantitative secondary chemicals may therefore be part of an integrated response of the trees to environmental stress.

4.Bioassays withElatobium abietinum, Gilpinia hercyniaeand the fungusPhacidium coniferarumshowed that changes in needle size, the nutritional and water content of tissues and the balance between nutrients and secondary chemicals influenced performance of one or more of the organisms. Changes in the concentration of carbon‐based secondary chemicals alone were, therefore, of only limited value in predicting susceptibility of Spruce to insects and fungi.
Measurement of prestrain in trees: implications for the determination of safety factors
Authors: Bonser R. H. C. , Ennos A. R.
Published: March 2003

1. It has long been known that wood in trees is under internally generated tensile or compressive forces, known as ‘prestrains’. These prestrains are thought to limit compressive loading at points of high strain within the tree to counteract the mechanical anisotropy of wood. Prestrains can be relieved by making cuts in wood, allowing it to recover to an unstrained state.

2. Recently, electrical resistance strain gauges have been used to measure surface strains on the trunk, roots and branches of trees. We have found that, by making a shallow cut above and below gauges, the prestrain can be measured as an apparent residual negative strain. This negative strain, after prestrain relief, is indicative of a tensile prestrain having been present in the wood before cutting.

3. It is a simple procedure to determine prestrain magnitude at the site of gauge attachment. By knowing the prestrain state of wood at the measurement site of strain determination, a more reliable estimate of surface stress and safety factors in tree design can be made.
Intraspecific variation in habitat availability among ectothermic animals near their climatic limits and their centres of range
Authors: Thomas J. A. , Rose R. J. , Clarke R. T. , Thomas C. D. , Webb N. R.
Published: March 2003

1. In a modelling exercise, the quantity and distribution of habitat patches within a heathland biotope for four ectothermic heathland animals (silver‐studded blue butterfly [Plebejus argus], a red ant [Myrmica sabuleti], heath grasshopper [Chorthippus vagans] and sand lizard [Lacerta agilis]) were compared in space and time assuming two climates: that experienced at the northern edge of the species’ ranges and that 300–400 km further south, where mean summer temperatures are 2–3 °C warmer.

2. Habitats both at the northern edge of their ranges and 300–400 km further south for the four species were defined qualitatively from existing sources and then expressed quantitatively in terms of the attributes recorded in the Dorset Heathland Survey. The Survey was then used as a GIS to map the occurrence of the habitats of the four species under two climates and a decade apart.

3. The model predicts that an increase of 2–3 °C can result in a large increase in the area of habitat available to these north temperate species, that the length of time that individual patches of successional habitat may be occupied increases and that the distance between habitat patches within the biotope decreases.

4. The warmer conditions should result in a more stable metapopulation structure for P. argus, with fewer metapopulations existing in the landscape but each, on average, containing a greater number of larger and more stable constituent populations.

5. These predictions are of significance to ectothermic species which currently live at the northern limits of their ranges in the British Isles. The reverse effect is likely for species at the southern limits of their ranges. Conservationists who wish to maintain the status quo may be able to reduce some effects of these changes by appropriate habitat management.
Effects of environmental change, including drought, on water use by competing Calluna vulgaris (heather) and Pteridium aquilinum (bracken)
Authors: Gordon C. , Woodin S. J. , Mullins C. E. , Alexander I. J.
Published: March 2003

1. Competition for water between Calluna vulgaris (heather) and Pteridium aquilinum (bracken) was studied in conditions of increased temperature, drought and increased nitrogen supply. All these factors increased the intensity of competition for water, with the combination of drought and increased nitrogen having the greatest effect on water use.

2. Both species increased water‐use efficiency in response to increased nitrogen and drought. The effects of temperature were however, equivocal. Calluna had a greater water demand than Pteridium but acclimated to water stress more readily.

3.
Calluna was the superior competitor for water; its water‐use efficiency was reduced as a consequence of its roots depleting water from the Pteridium rooting zone. Pteridium, the poorer competitor, increased water‐use efficiency to cope with reduced water availability owing to competition.

4. There was a strong relationship between carbon isotope discrimination (Δ) and instantaneous water‐use efficiency for both species, but discrimination provided a more sensitive measure of seasonal water‐use efficiency. Reconstruction of the plant's history of water‐use efficiency by retrospective measurement of Δ proved a useful technique for Calluna leaves but was inappropriate for Pteridium rhizome.
Effects of long‐term exposure to elevated CO2 and increased nutrient supply on bracken (Pteridium aquilinum)
Authors: Caporn S. J. M. , Brooks A. L. , Press M. C. , Lee J. A.
Published: March 2003

1. Bracken (Pteridium aquilinum) is an important fern with a global distribution. Little is known of the response of this species to elevated CO2. We investigated the effects of high CO2 (570 compared with 370 μmol mol–1) with and without an increased nutrient supply (a combined N, P, K application) on the growth and physiology of bracken, growing in containers in controlled‐environment glasshouses, over two full growing seasons. Results of growth and physiology determinations are reported for the second season.

2. Elevated CO2 had little impact on the growth or allocation of dry mass in bracken. No significant changes were detected in dry mass of the total plant or any of the organs: rhizomes, roots and fronds. In contrast to the small effects of high CO2, the high nutrient treatment caused a three‐fold stimulation of total plant dry mass and an increase in the allocation of dry mass to above ground when compared with low nutrient controls.

3. Net photosynthetic rates in saturating light were increased by both high CO2 and nutrient treatments, particularly in spring months (May and June). Growth in elevated CO2 did not cause a down‐regulation in light‐saturated rates of photosynthesis. The increased carbon gain in the high CO2 treatments was accompanied, in the low‐nutrient plants, by higher concentrations of carbohydrates. However, in high‐nutrient plants the CO2 treatment did not cause an accumulation of carbohydrates. The absence of a growth response to elevated CO2 in bracken despite significant increases in photosynthesis requires further investigation.
Echolocation constraints of Daubenton’s Bat foraging over water
Authors: RYDELL J. , MILLER L. A. , JENSEN M. E.
Published: March 2003

1. Daubenton’s Bats (Myotis daubentonii) foraging over a stream concentrated their activity over calm surfaces, avoiding an adjacent area with small ripples (< 3 cm high). Aerial insects were most abundant over the ripples, so insect distribution could not explain why the bats avoided this area.

2. The bats flew low over water and always (N = 22) directed the head forwards, presumably emitting the echolocation beam parallel to the surface, thus minimizing clutter. At an angle of incidence of 30° there was significantly more clutter from the rippled water.

3. The ripples produced ultrasonic noises in the form of transient pulses at an average rate of 6·2 per second. In the present case, such pulses were common enough potentially to interfere with target detection by the bats. Transient noises and echo clutter from moving ripples may be the principal reason why bats generally avoid foraging low over turbulent water.

4. The target strength of a potential insect prey at the water surface and the source levels of the bats’ searching signals were measured to use in estimating the echo level at the bat when it detects the prey. The echo level at detection (+ 38 dB sound pressure level) was about the same as the clutter level extrapolated to the detection distance. This suggests that Daubenton’s Bat operates at very low signal‐to‐noise ratios when foraging for insects near the water surface.