bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of freshwater shrimp assemblages on benthic communities along an altitudinal gradient of a tropical island stream
Authors: MARCH JAMES G. , PRINGLE CATHERINE M. , TOWNSEND MATT J. , WILSON AMANDA I.
Published: March 2003

1. In tropical island stream ecosystems freshwater shrimps are often the dominant macroconsumers and can play an important role in determining benthic community composition. However, most studies of the ecological role of shrimps are limited to high‐altitude shrimp‐dominated sites where other biota (fishes and snails) are absent or significantly less abundant than at lower altitudes.

2. We examined how effects of different shrimp assemblages on benthic communities changed along an altitudinal gradient in a tropical island stream in Puerto Rico. We used electroshocking and observations to quantify abundance and taxonomic composition of shrimp assemblages at three sites (300, 90 and 10 m a. s. l) along the Río Espíritu Santo. We also experimentally manipulated access of shrimps to the benthic environment simultaneously at each site using electric fences over a 35‐day period.

3. At the high‐altitude site, exclusion of shrimps (predominantlyAtyaspp. andXiphocariselongata) resulted in significantly greater accrual of organic and inorganic material, chlorophyllaand algal biovolume. In the absence of shrimps, the algal community was dominated by filamentous green algae (Chlorophyta:OedogoniumandRhizoclonium). Excluding shrimps did not affect total insect biomass but significantly increased sessile chironomids (Diptera: Chironomidae). We observed similar treatment effects at the mid‐altitude site where shrimps (primarilyMacrobrachiumspp. andX. elongata) occurred at lower densities. In contrast, at the low‐altitude site there were no treatment differences in organic and inorganic material, chlorophylla, algal biovolume, algal assemblage composition and insects.

4. The lack of treatment differences at the low‐altitude site was probably because of very high densities of grazing snails (ThiaragraniferaandNeritinaspp.) which reduced organic and inorganic resources and obscured potential shrimp effects.

5. This study demonstrates that freshwater shrimps can play an important role in determining benthic community composition; however, their effects vary and appear to depend on the presence of other biota. This study suggests that loss of shrimps as a result of anthropogenic disturbances will have different effects on the stream community depending upon location along the altitude gradient.
The drift distances and time spent in the drift by freshwater shrimps, Gammarus pulex, in a small stony stream, and their implications for the interpretation of downstream dispersal
Authors: ELLIOTT J. M.
Published: March 2003

1. The objectives were (i) to determine experimentally and to model the relationship between mean water velocity and both the mean distance travelled, and the mean time spent, in the drift by freshwater shrimps, Gammarus pulex; (ii) to develop a drift distance–water velocity model from the experimental study, and validate it with field data; (iii) to examine the relationship between drift rate, water velocity and benthic density with the latter expressed as a mean value for the whole stream and a mean value corrected for the distance travelled in the drift.

2. In field experiments at 10 water velocities (0.032–0.962 m s−1), the significant relationship between the mean drift distance and mean water velocity was described both by a power function (power, 0.96) and a linear relationship. The mean drift time was fairly constant at 8.3 s (95% CL ± 0.4). A simple model estimated the drift distance and time spent in the drift by different percentages of the drifting invertebrates. This model predicted correctly the positive relationship between drift rate and water velocity for field data over a year.

3. The relationship between drift rate per hour and the independent variables, water velocity and benthic density, was well described by a multiple‐regression model. Adding temperature and date did not improve model fit. Variations in water velocity and benthic density explained 96% of the variation in nocturnal drift rate (65% to velocity, 31% to benthic density), but only 40% of the variation in diurnal drift rate (29% to velocity, 11% to benthic density). Correcting benthic density for the drift distances did not improve model fit.

4. The significance of this study is that it developed models to predict drift distances and time, values being similar to those obtained in another, larger stream. It also illustrated the importance of spatial scale in the interpretation of drift by showing that when drift distances were taken into account, the impact of drift on the population was higher (4–10% lost day−1) than when drift distances were ignored (usually < 3% lost day−1), especially at a local level.
Temporal patterns of diatom ingestion by larval net‐winged midges (Diptera: Blephariceridae: Blepharicera)
Authors: Alverson Andrew J. , Courtney Gregory W.
Published: March 2003

SUMMARY 1. Monthly patterns of diatom ingestion by Blepharicera magna and B. similans (Diptera: Blephariceridae) larvae were examined to determine whether dietary attributes fluctuate within the final‐instar stadium. The two species are isolated temporally: B. magna diets were examined from October to December, and B. similans diets were examined from June to August. Each month, the diatom assemblage of larval diets was assessed and compared with that of the forage base. In addition, total diatom ingestion was estimated.

2. Larval gut samples were ordinated on the basis of relative abundance of common diatom taxa, and month–month comparisons of larval diets were made, which revealed that (i) B. magna dietary assemblages did not vary significantly from October to December; (ii) diatom species composition of B. magna diets generally resembled that of the forage base; and (iii) B. similans dietary assemblages varied significantly from June to August, with few changes attributable to seasonality of ambient diatom flora.

3. Total diatom ingestion by B. magna was relatively stable from October to December. For B. similans, total diatom ingestion was greatest in July, when larvae were midstage of instar IV. The latter result was accompanied by increased ingestion of grazer‐resistant diatom taxa (e.g. Achnanthes deflexa var. alpestris, Achnanthidium minutissimum, and Cocconeis placentula var. lineata), which can be more digestible than grazer‐susceptible taxa (e.g. chain‐forming Fragilaria and rosette‐forming Synedra species). This result suggests demand for a large quantity of nutritionally rich food at midstage of instar IV, which could represent a period of critical growth for B. similans.
Fish induced macrophyte loss in shallow lakes: top–down and bottom–up processes in mesocosm experiments
Authors: Williams Adrian E. , Moss Brian , Eaton John
Published: March 2003

SUMMARY 1. Macrophyte loss from Sites of Special Scientific Interest in England has become widespread over the last 20 years. One reason for this may be changing trends in angling, a multimillion pound industry that has an enormous impact on aquatic ecosystems. Stocking with cyprinid fish is a common angling management practice but the particular fish species and distribution of their biomass may be crucial to the ecosystem.

2. Carp (Cyprinus carpio), roach (Rutilus rutilus), bream (Abramis brama) and tench (Tinca tinca) at biomasses ranging from 0 to 800 kg ha−1 and at various sizes were placed into experimental mesocosms in Little Mere, a shallow, fertile lake in Cheshire, U.K. The effects these treatments had on the aquatic ecosystem were studied over two summers. Specifically the effects of the treatments on macrophyte growth, benthic and macrophytic macro‐invertebrate populations, water chemistry, epiphyton production and plankton survival were investigated.

3. Carp had a greater detrimental effect on the macrophytes than bream, tench and in particular roach. A biomass of fish > 200 kg ha−1 adversely affected the extent of macrophyte growth.

4. The decline in macrophyte growth was most likely as a result of increased epiphyton growth that probably reduced the amount of light and carbon dioxide available to the plant. There were no observed direct fish impacts on macrophytes.

5. The chemical data suggested that inorganic nitrogen levels were low and it is possible that release of nitrogen, from fish excreta, followed by immediate uptake, could have been a major factor stimulating epiphyton growth and subsequently macrophyte loss. Phosphorus concentrations increased even in the controls and substantial amounts were available. Phosphorus stimulation can therefore be discounted. Macrophyte‐associated macro‐invertebrates were positively correlated with epiphyton load but had no impact on the extent of epiphytic growth. Shading from disturbed sediment or phytoplankton was also unimportant.
Effects of a filter‐feeding fish [silver carp, Hypophthalmichthys molitrix (Val.)] on phyto‐ and zooplankton in a mesotrophic reservoir: results from an enclosure experiment
Authors: Radke Robert J. , Kahl Uwe
Published: March 2003

SUMMARY 1. Silver carp, Hypophthalmichthys molitrix (Val.), feeds on both phyto‐ and zooplankton and has been used in lake biomanipulation studies to suppress algal biomass. Because reports on the effects of silver carp on lake food webs have been contradictory, we conducted an enclosure experiment to test how a moderate biomass of the fish (10 g wet weight m−3) affects phytoplankton and crustacean zooplankton in a mesotrophic temperate reservoir.

2. Phytoplankton biomass <30 μm and particulate organic carbon (POC) <30 μm were significantly higher in enclosures with silver carp than in enclosures without fish, whereas Secchi depth was lower. Total copepod biomass declined strongly in both treatments during the experiment, but it was significantly higher in fish‐free enclosures. Daphnid biomass was also consistently higher in enclosures without fish, although this effect was not significant. However, the presence of fish led to a fast and significant decrease in the size at maturity of Daphnia galeata Sars. Thus, the moderate biomass of silver carp had a stronger negative effect on cladoceran zooplankton than on phytoplankton.

3. Based on these results and those of previous studies, we conclude that silver carp should be used for biomanipulation only if the primary aim is to reduce nuisance blooms of large phytoplankton species (e.g. cyanobacteria) that cannot be effectively controlled by large herbivorous zooplankton. Therefore, stocking of silver carp appears to be most appropriate in tropical lakes that are highly productive and naturally lack large cladoceran zooplankton.
Differences in composition of macroinvertebrate communities with invasive and native Gammarus spp. (Crustacea: Amphipoda)
Authors: Kelly D. W. , Dick J. T. A. , Montgomery W. I. , Macneil C.
Published: March 2003

SUMMARY 1. Assessing the effects on communities of invasive species is often confounded by environmental factors. In Irish rivers, the introduced amphipod Gammarus pulex replaces the native G. duebeni celticus in lowland stretches. The two amphipods are associated with different macroinvertebrate communities, which may in part be the result of natural longitudinal physicochemical change. However, this hinders assessment of any direct community impacts of the invasive as compared with the native species. Here, we report on a fortuitous circumstance that allowed us to uncouple the community effects of Gammarus species from environmental differences.

2. The lowland stretch of the River Lissan is dissected by a weir, which has slowed the upstream invasion by G. pulex. We took physicochemical measurements and macroinvertebrate samples from three contiguous 150 m reaches of this stretch with G. pulex only, mixed Gammarus and G. d. celticus only communities.

3. We found no biologically significant differences in physicochemistry among the three reaches. Overall invertebrate densities did not differ among reaches. However, G. pulex numerically dominated its reach, whilst G. d. celticus abundance was relatively low in its reach. The G. pulex reach had significantly higher overall biomass because of high invader abundance. In addition, both diversity and species richness of macroinvertebrate communities were lower in the G. pulex than the G. d. celticus reach, with the mixed Gammarus reach intermediate.

4. Ordination indicated distinctly different associations of invertebrate community samples and taxa that were best explained by the distributions of the Gammarus species. Again, the mixed Gammarus species samples were intermediate.

5. This study indicates that the invasive G. pulex has a greater impact on macroinvertebrate community composition than the native G. d. celticus, probably through biotic interactions such as predation.
Stream macroinvertebrate response to catchment urbanisation (Georgia, U.S.A.)
Authors: Roy A. H. , Rosemond A. D. , Paul M. J. , Leigh D. S. , Wallace J. B.
Published: March 2003

SUMMARY 1. The effects of catchment urbanisation on water quality were examined for 30 streams (stratified into 15, 50 and 100 km2 ± 25% catchments) in the Etowah River basin, Georgia, U.S.A. We examined relationships between land cover (implying cover and use) in these catchments (e.g. urban, forest and agriculture) and macroinvertebrate assemblage attributes using several previously published indices to summarise macroinvertebrate response. Based on a priori predictions as to mechanisms of biotic impairment under changing land cover, additional measurements were made to assess geomorphology, hydrology and chemistry in each stream.

2. We found strong relationships between catchment land cover and stream biota. Taxon richness and other biotic indices that reflected good water quality were negatively related to urban land cover and positively related to forest land cover. Urban land cover alone explained 29–38% of the variation in some macroinvertebrate indices. Reduced water quality was detectable at c. >15% urban land cover.

3. Urban land cover correlated with a number of geomorphic variables such as stream bed sediment size (–) and total suspended solids (+) as well as a number of water chemistry variables including nitrogen and phosphorus concentrations (+), specific conductance (+) and turbidity (+). Biotic indices were better predicted by these reach scale variables than single, catchment scale land cover variables. Multiple regression models explained 69% of variation in total taxon richness and 78% of the variation in the Invertebrate Community Index (ICI) using phi variability, specific conductance and depth, and riffle phi, specific conductance and phi variability, respectively.

4. Indirect ordination analysis was used to describe assemblage and functional group changes among sites and corroborate which environmental variables were most important in driving differences in macroinvertebrate assemblages. The first axis in a non‐metric multidimensional scaling ordination was highly related to environmental variables (slope, specific conductance, phi variability; adj. R2=0.83) that were also important in our multiple regression models.

5. Catchment urbanisation resulted in less diverse and more tolerant stream macroinvertebrate assemblages via increased sediment transport, reduced stream bed sediment size and increased solutes. The biotic indices that were most sensitive to environmental variation were taxon richness, EPT richness and the ICI. Our results were largely consistent over the range in basin size we tested.
Herbivory on a chemically defended plant as a predation deterrent in Hyalella azteca
Authors: Rowell Kirsten , Blinn Dean W.
Published: March 2003

SUMMARY 1. We investigated whether a population of the freshwater amphipod, Hyalella azteca, which consumed plants with defensive secondary compounds, reduced predation as reported for terrestrial and marine systems.

2. Field observations in Montezuma Well, U.S.A., indicated a strong association between the emergent macrophyte, Berula erecta and H. azteca. We hypothesised that this geographically isolated population of sedentary amphipods was able to consume roots of the chemically defended B. erecta as a deterrent against predation. Berula erecta is in the family Apiaceae, which commonly produce coumarins that deter herbivory in terrestrial systems.

3. Hyalella azteca consumed roots of B. erecta at a significantly greater rate than alternative macrophyte substrata in Montezuma Well. Additionally, H. azteca moulted at a significantly higher rate when consuming B. erecta compared with a diet of periphyton.

4. Two insect predators (Telebasis salva and Belostoma bakeri) with different feeding strategies were used to assess the effects of a B. erecta diet on predation rates in the laboratory and in Montezuma Well. Hyalella azteca was preyed on at a significantly lower rate by both predators when given a strict diet of B. erecta roots compared with a diet of periphyton.

5. This is the first experimental evidence that predation on a freshwater herbivore, H. azteca, was reduced when it consumed a chemically defended plant.
All creatures great and small: patterns in the stream benthos across a wide range of metazoan body size
Authors: Stead Tracey K. , Schmid‐Araya Jenny M. , Hildrew Alan G.
Published: March 2003

SUMMARY1. The whole metazoan community (i.e. including the meiofauna) of an acidic, fishless stream in south‐east England was surveyed over 14 months between March 1999 and April 2000. Invertebrate density, biomass and taxonomic richness were assessed on each sampling occasion in relation to physico‐chemical variables.

2. The meiofauna were more numerous and diverse than the macrofauna, while their total biomass occasionally equalled that of the macrofauna.

3. The meiofaunal and macrofaunal assemblages appeared to respond to different environmental factors. The meiofauna showed genuine species turnover through the year, while the macrofauna varied less in taxonomic composition though there were substantial variations in density.

4. These data suggest that the meiofauna and macrofauna exist at different temporal and spatial scales and perceive their environment with a different ‘grain’.
Photosynthesis of the cyanobacterial soil‐crust lichen Collema tenax from arid lands in southern Utah, USA: role of water content on light and temperature responses of CO2 exchange
Authors: Lange O. L. , Belnap J. , Reichenberger H.
Published: March 2003

1. The gelatinous cyanobacterial Collema tenax is a dominant lichen of biotic soil crusts in the western United States. In laboratory experiments, we studied CO2 exchange of this species as dependent on water content (WC), light and temperature. Results are compared with performance of green‐algal lichens of the same site investigated earlier.

2. As compared with published data, photosynthetic capacity of C. tenax is higher than that of other cyanobacterial and green‐algal soil‐crust species studied. At all temperatures and photon flux densities of ecological relevance, net photosynthesis (NP) shows a strong depression at high degrees of hydration; maximal apparent quantum‐use efficiency of CO2 fixation is also reduced. Water requirements (moisture compensation point, WC for maximal NP) are higher than that of the green‐algal lichens. Collema tenax exhibits extreme ‘sun plant’ features and is adapted to high thallus temperatures.

3. Erratic rain showers are the main source of moisture for soil crusts on the Colorado Plateau, quickly saturating the lichens with liquid water. High water‐holding capacity of C. tenax ensures extended phases of favourable hydration at conditions of high light and temperature after the rain for substantial photosynthetic production. Under such conditions the cyanobacterial lichen appears superior over its green‐algal competitors, which seem better adapted to habitats with high air humidity, dew or fog as prevailing source of moisture.
Pattern of defoliation and its effect on photosynthesis and growth of Goldenrod
Authors: Meyer G. A.
Published: March 2003

1. Leaf area was removed from Solidago altissima in either a dispersed pattern (half of every leaf removed) or a concentrated pattern (every other leaf removed) and effects on leaf gas exchange, vegetative growth and flowering were examined relative to undefoliated controls. Gas exchange was measured for leaves remaining after defoliation and for regrowth leaves that developed post‐damage (at 7, 16 and 26 days post‐defoliation).

2. Area‐based photosynthetic rates of leaves remaining after defoliation were not affected by either dispersed or concentrated damage, but damage of both types enhanced area‐based photosynthesis of regrowth leaves at 16 days post‐defoliation and to a lesser extent at 26 days post‐defoliation.

3. Dispersed damage, but not concentrated damage, stimulated mass‐based photosynthesis of undamaged leaves remaining after defoliation. Undamaged leaves remaining after defoliation and regrowth leaves on damaged plants had higher specific leaf area (leaf area/leaf mass) than comparable leaves on control plants. Mass‐based photosynthesis was more strongly elevated by defoliation than area‐based photosynthesis because of this increase in specific leaf area.

4. Plants with dispersed damage recovered more quickly from defoliation; they had higher relative growth rates in the first week post‐defoliation than plants with concentrated damage. Both types of defoliation caused similar reductions in flower production.

5. These results add to accumulating evidence that dispersed damage is generally less detrimental to plants than concentrated damage and suggest that physiological changes in leaves may be part of the reason.
Carbon transfer between plants and its control in networks of arbuscular mycorrhizas
Authors: Fitter A. H. , Graves J. D. , Watkins N. K. , Robinson D. , Scrimgeour C.
Published: March 2003

1. Two studies using the stable‐isotope 13C have shown that large amounts of carbon can move between plants linked by arbuscular mycorrhizal fungi. Quantities comparable to the carbon cost of the symbiosis for an individual plant may be transferred.

2. We measured C transfer between linked plants of the grass Cynodon dactylon (C4, δ13C ≈– 14‰) and the herb Plantago lanceolata (C3, δ13C ~ – 28‰). To test the hypothesis that the carbon transferred between plants remained in fungal structures at all times, plants were grown for two harvests; at the first harvest they were clipped to ground level, so that shoot re‐growth required the transport of carbon from the roots. We also tested the influence of the direction of growth of the fungus, to determine whether C was transported out of or into a newly colonized root, and of growing plants in elevated CO2, to increase the availability of carbon compounds in the roots.

3. Large amounts of C were transferred between linked plants, more so into Plantago than into Cynodon roots. Transfer occurred whether root systems were separated by a 20 μm mesh, that excluded roots but not hyphae, or a 0·45 μm mesh, intended to act as a barrier to hyphae as well. We believe that the high root densities achieved in the experiment allowed hyphae to cross the finer mesh between the two dense root mats.

4. Clipping the plants did not result in any movement of C from roots to shoots, thus confirming the prediction that all C transferred remains in fungal structures.

5. The direction of growth of the fungus did not affect the direction of transfer, nor did the CO2 concentration in which the plants were grown.

6. The amount of C transferred was a positive correlate of the frequency of vesicles in the roots but a negative correlate of the frequency of hyphae. If C were moving into developing colonization units, thus effectively giving the plant a ‘free’ symbiosis, the correlation with internal hyphae should be positive. The positive correlation with vesicles suggests that C is moving into fungal storage structures.

7. We propose a mycocentric view of the phenomenon of interplant C transfer, in which the fungal colonies within roots are seen as parts of an extended mycelium between which the fungus moves resources depending on the dynamics of its own growth. We do not believe that the transfer has an impact on plant C budgets or fitness, but that it may be a major element in the understanding of fungal C budgets.
Photosynthesis and respiration rates depend on leaf and root morphology and nitrogen concentration in nine boreal tree species differing in relative growth rate
Authors: Reich P. B. , Walters M. B. , Tjoelker M. G. , Vanderklein D. , Buschena C.
Published: March 2003

1. To test several hypotheses about acclimation and adaptation of photosynthesis and respiration to differing light conditions, we investigated the interspecific relationships between leaf and root metabolism, chemistry and morphology in high and low light conditions for young seedlings of nine boreal tree species that differ in relative growth rate (RGR).

2. Light‐saturated net photosynthesis (Asat), whole‐plant nitrogen (N) uptake rates, leaf and root respiration and morphology, and RGR all varied in parallel among the nine species when grown in both 5% and 25% of full sunlight. RGR, Asat, leaf and root respiration (Rd), and N uptake rate per unit root mass or length differed significantly among species, ranking (from high to low): Populus, Betula and Larix spp. (all deciduous) and then to five evergreen conifers (Pinus, Picea and Thuja spp.), which were generally comparable in these measures.

3.
A
sat, leaf and root Rd and N uptake rates were all correlated (r≈ 0·8 to 0·9) with species traits, such as seed mass, leaf life span and shade‐tolerance rankings. Mass‐based Asat was greater in conifer seedlings raised in low than high light. In contrast, area‐based Asat was higher for plants grown in high than low light, especially in the deciduous species. Once adjusted for differences in plant mass, leaf or root respiration rates did not differ for plants grown in low vs high light.

4. Interspecific variation in RGR was positively correlated (r≈ 0·9) with rates of photosynthesis, respiration and N uptake. Leaf photosynthesis and respiration rates were correlated to specific leaf area and leaf N concentrations (r≈ 0·9). Root respiration rates, N uptake rates, specific root length (root length per root dry mass) and root N concentrations were all highly correlated with each other (r≈ 0·8 to 0·9). These data suggest a close coupling of tissue‐level metabolism, chemistry and structure with whole‐plant performance and species ecophysiological and life‐history traits.
The responses of Briza media and Koeleria macrantha to drought and re‐watering
Authors: Milnes K. J. , Davies W. J. , Rodwell J. S. , Francis B. J.
Published: March 2003

1. To test whether differences in response to drought can help to explain the differing distributions of Briza media and Koeleria macrantha, changes in their leaf growth and water relations during soil drying were measured. After droughting, plants were re‐watered and recovery recorded.

2. Leaf growth of the two species showed a similar sensitivity to drought with respect to duration of soil drying and soil moisture content.

3. In both species tiller base relative water content (RWC) was maintained at similar levels to controls until soil moisture content had fallen to less than 9%. This may aid survival in habitats subject to periodic droughting by preventing damage to the meristems.

4.
Briza media did not respond to re‐watering. However, plants of K. macrantha re‐grew after periods of over 20 days of drought, when tiller base RWCs had fallen as low as 13%. This ability to resurrect may explain the occurrence of K. macrantha in xeric calcicolous grasslands subject to episodes of severe droughting, from which B. media is absent.
Effects of elevated temperature and carbon dioxide on the nutritional quality of leaves of oak (Quercus robur L.) as food for the Winter Moth (Operophtera brumata L.)
Authors: Buse A. , Good J. E. G. , Dury S. , Perrins C. M.
Published: March 2003

1. Pedunculate Oak trees were grown in ambient and elevated temperatures and CO2. Leaves were fed to Winter Moth caterpillars reared either in constant conditions or with the trees (caged or on‐tree).

2. Caterpillars in constant conditions ate the same mass and produced the same mass of faeces whether fed elevated or ambient temperature leaves. However, less was assimilated from elevated leaves, resulting in lighter pupae and fewer, lighter eggs.

3. Caterpillars in constant conditions ate more and produced more faeces when fed elevated CO2 leaves than when fed ambient CO2 leaves, but the mass assimilated and pupal mass were unchanged.

4. Caged caterpillars reared with the trees from which they were fed had constant pupal mass in all treatments, but pupated earlier at elevated temperature. Pupal mass was also unaffected when caterpillars fed on the trees.

5. Nitrogen was reduced in both elevated temperature and elevated CO2 leaves. Increased fibre in the former prevented increased consumption and resulted in reduced pupal mass and fecundity. Reduced fibre in the latter allowed increased consumption, resulting in pupae of normal mass.

6. Despite the clear effect of nutrient quality, experiments rearing caterpillars and trees together suggest that anticipated climatic change will have no nutritional effect on Winter Moth development.
Effects of tail loss on the movement patterns of the lizard, Psammodromus algirus
Authors: Martin J. , Avery R. A.
Published: March 2003

1. Many lizards use caudal autotomy as a defensive strategy. However, subsequent costs related to the alteration of locomotor abilities might decrease the fitness of individuals. In this paper, the movement patterns of spontaneously moving Psammodromus algirus lizards and their escape performance running at high speed were compared before and after tail loss. A control tailed group was also studied to assess the repeatability of locomotor patterns between trials.

2. Tail loss had a significant effect on spontaneous movement patterns. Tailless individuals moved at significantly slower speeds during bursts of locomotion, and distances moved within bursts were significantly reduced. The overall time spent pausing increased, and, as a result, overall speeds decreased to an even greater extent than burst speeds. However, mean durations of individual locomotor bursts and mean pause durations did not change significantly after tail loss.

3. Loss of the tail decreased mean stride length, although the positive relation between stride length and speed was retained.

4. Escape performance was also greatly affected; loss of the tail resulted in substantially reduced attained, maximal and overall escape speeds. These changes resulted in shorter escape distances (the time of the first pause after the initiation of the escape response) because the mean duration of escape responses did not change.

5. The relevance of these alterations for the ecology of this species, and how individuals may compensate for the costs of tail loss, favouring autotomy as an escape strategy, are discussed.
Leaf photosynthetic light response: a mechanistic model for scaling photosynthesis to leaves and canopies
Authors: Kull O. , Kruijt B.
Published: March 2003

1. The response of photosynthesis to radiation is an often‐studied but poorly understood process, represented empirically in most photosynthesis models. However, in scaling photosynthesis from leaf to canopy, predictions of canopy photosynthesis are very sensitive to parameters describing the response of leaves to Photosynthetic Photon Flux Density (PPFD).

2. In this study, a mechanistic, yet still simple, approach is presented that models the degree of light saturation in leaves explicitly, assuming a heterogeneous environment of PPFD and chlorophyll.

3. Possible mechanisms determining the ratio of chlorophyll to nitrogen are considered, including a direct dependence on PPFD, a mechanism involving the red/far‐red ratio of light in the canopy, and an approach based upon maximizing photosynthesis.

4. Comparison of model predictions with two data sets of light, nitrogen and chlorophyll from canopies of Populus and Corylus suggests that the red/far‐red mechanism is the most realistic. The data also show that the trees studied do not always optimize their nitrogen partitioning to maximize photosynthetic yield.

5. We then apply the model to the data sets, to predict the shape of light response curves of leaves within canopies and assess the applicability of simple scaling schemes, in which full acclimation of photosynthesis to PPFD justifies the use of big‐leaf models. We conclude that, at least for the data used, basic assumptions of such schemes do not hold.
Leaf structure (specific leaf area) modulates photosynthesis–nitrogen relations: evidence from within and across species and functional groups
Authors: Reich P. B. , Ellsworth D. S. , Walters M. B.
Published: March 2003

1. Net photosynthetic capacity (Amax, defined as light‐saturated net photosynthesis under near optimal ambient environmental conditions) of mature leaves often depends on the level of leaf nitrogen (N), but an assortment of relationships between these variables has been observed in studies of diverse plant species. Variation in leaf structure has been identified as an important factor associated with differences between the area‐ and mass‐based expressions of the Amax–N relationship. In this paper we test the hypothesis that leaf structure, quantified using a measure of leaf area displayed per unit dry mass invested [specific leaf area (SLA)], is more than just a conversion factor, but itself can influence Amax–N relationships. We test this using several kinds of comparisons, based on field data for 107 species from sites representing six biomes and on literature data for 162 species from an equally diverse set of biomes.

2. Species and genera with thicker and/or denser leaves (lower SLA) consistently have flatter slopes of the Amax–N (mass‐based) relationship than those with higher SLA. These and all other contrasts usually applied as well using area‐based expressions, although such relationships were less consistent and weaker overall. A steeper slope indicates greater incremental change in Amax per unit variation in N.

3. Functional groups (e.g. needle‐leafed evergreen trees, broad‐leafed trees or shrubs, forbs) show the same patterns: groups with lower SLA have lower Amax–N slopes. Functional groups differ in mean leaf traits as well as in Amax–N relationships. Forbs have the highest SLA and mass‐based N and Amax, followed by deciduous species (whether needle‐leafed or broad‐leafed, shrub or tree), with lowest values in evergreen species (again regardless of leaf type or functional group).

4. Interspecific variation in mass‐based Amax is highly significantly related to the combination of leaf N and SLA (r2 = 0·86). At any value of leaf N, Amax increases with increasing SLA and at any value of SLA, Amax increases with increasing leaf N. Because this relationship, between Amax and the combination of N and SLA, is similar in two independent data sets, and as well, across broad taxonomic and geographic gradients, we hypothesize that it is universal in nature. Therefore, for broad interspecific contrasts among dicotyledons in any biome, we can reasonably well predict Amax based on the combination of SLA and leaf N. These findings have important implications for convergent evolution of leaf adaptation and great potential utility in models of global vegetation functioning.
The influence of year‐to‐year variations in winter weather on the dynamics of Daphnia and Eudiaptomus in Esthwaite Water, Cumbria
Authors: George D. G. , Hewitt D. P.
Published: March 2003

1. Micro‐crustacea of the genus Daphnia and Eudiaptomus have evolved different physiological mechanisms for coping with life in a rapidly changing environment. In this paper, we analyse some of the physical and biological factors influencing the winter abundance of the two species in a small lake (Esthwaite Water in Cumbria).

2. The results demonstrate that much of the year‐to‐year variation in their relative abundance can be related to long‐term changes in the weather. The highest numbers of Daphnia were typically found in cold, calm winters when small flagellates were relatively abundant. In contrast, the highest numbers of Eudiaptomus were found in mild, windy winters when the phytoplankton community was dominated by colonial diatoms.

3. Year‐to‐year variations in the winter abundance of Eudiaptomus had no effect on their subsequent development but the numbers of overwintering Daphnia had a significant effect on the size of their first spring ‘cohort’. The most important factor influencing the overwintering performance of the two species was the water temperature.

4. Winter air temperatures over much of Europe are influenced by the atmospheric pressure variation known as the North Atlantic Oscillation (NAO). Winter water temperatures in Esthwaite Water were strongly correlated with this empirical index and there was a significant positive correlation between the NAO and the number of overwintering Eudiaptomus.
Thermal and fitness‐related consequences of nest location in Painted Turtles (Chrysemys picta)
Authors: Weisrock D. W. , Janzen F. J.
Published: March 2003

1. Laboratory experiments have documented substantial temperature effects on the physiological ecology of reptilian eggs, embryos and offspring. However, functional links between important habitat characteristics, nest microenvironments and fitness‐related traits of neonates in natural nests have rarely been studied.

2. A field study of 11 Painted Turtle (Chrysemys picta) nests was conducted to quantify the relationships between a habitat characteristic (i.e. vegetational cover around nests at oviposition) and (1) developmental temperature and its effect on offspring sex ratio and (2) hibernation temperature and its effect on offspring survivorship.

3. Vegetational cover was negatively correlated with nest temperatures in July, the period when offspring sex is determined. However, neither vegetational cover nor mean nest temperature predicted nest sex ratios, although correlations among these variables were consistent with causal relationships derived from laboratory studies.

4. Summer vegetational cover was also negatively correlated with measures of winter nest temperatures. Of the three nests exhibiting overwinter mortality, two were surrounded by thick vegetation and all experienced temperatures below – 8 °C. The remaining nests reached temperatures as low as – 6 °C without mortality, indicating that hatchlings in these nests exhibited remarkable supercooling ability.

5. The results suggest that habitat characteristics and nest microenvironments are functionally linked and have fitness consequences for both embryos and offspring, implying that nest‐site choice by female turtles could have considerable utility.
Interactive effects of elevated CO2, P availability and legume presence on calcareous grassland: results of a glasshouse experiment
Authors: STÖCKLIN J. , KÖRNER CH.
Published: March 2003

1. We investigated the interactive effects of elevated CO2, supply of phosphorus (P) and legume presence in model communities of calcareous grassland. Half of the communities contained six graminoids and eight non‐legume forb species. In the other half, four non‐legume forbs were replaced by legumes.

2.
Ecosystem responses. Above‐ground phytomass (>5 cm) hardly responded to elevated CO2 alone. However, when P and legumes were combined, the CO2 effect on above‐ground community phytomass in year two was a stimulation of 45% (P<0·001). Below‐ground community dry matter was stimulated by elevated CO2 alone by + 36% (P<0·01), but was only + 20% (P<0·05) when legumes were present and P was added. At the final (late season) harvest the mean effect of elevated CO2 on total above‐ and below‐ground phytomass was + 23% (P<0·001) and revealed no significant interactions among treatment combinations, because above‐ and below‐ground effects of CO2 enrichment had opposite directions.

3.
Functional group responses. When legumes were absent, graminoids increased their total above‐ and below‐ground phytomass in elevated CO2 by 60% (P<0·001) but there was no increase when legumes were present. The response of forbs to CO2 was not significant, irrespective of co‐treatment. Legumes, however, were significantly stimulated by P supply and their CO2 response was much larger when P was added (+ 55%, P<0·01 vs + 25%, NS).

4.
Species responses. CO2 effects on species ranged from highly positive (+ 143%) to moderately negative (– 43%).

5. Our results demonstrate that the effect of CO2 enrichment in such natural grassland communities will be low on above‐ground phytomass and largely below‐ground if no additional nutrients are provided. N2‐fixing legumes appear to be crucial for the community response to elevated CO2 but legume responsiveness is largely controlled by P availability.
Atmospheric and hydraulic limitations on transpiration in Brazilian cerrado woody species
Authors: MEINZER F. C. , GOLDSTEIN G. , FRANCO A. C. , BUSTAMANTE M. , IGLER E. , JACKSON P. , CALDAS L. , RUNDEL P. W.
Published: March 2003

1. Seasonal regulation of transpiration was studied in four evergreen woody species growing in a Brazilian cerrado (savanna) site with a 5 month dry season.

2. Both seasonal and interspecifc variation in leaf water potential (ΨL) were relatively small. Predawn ΨL was about 0·1–0·25 MPa more negative in the dry season than in the wet season.

3. The dependence of maximum whole‐plant sap flow rates on sapwood area was similar among all four species during both the wet and dry seasons. When total daily sap flow on a leaf area basis was normalized by the daily average air saturation deficit (ASD), only one of the four species showed significantly greater water use during the wet season.

4. Although seasonal differences in regulation of transpiration were not pronounced, strong stomatal limitation of both maximum daily transpiration rates and total daily transpiration was evident during both the wet and dry seasons. Sap flow typically increased sharply in the morning, briefly attained a maximum value by about 09.30–10.30 h, then decreased sharply, despite steadily increasing solar radiation and atmospheric evaporative demand.

5. The total leaf area‐specific apparent hydraulic conductance of the soil/leaf pathway (Gt) varied among plants and diurnally. The identical linear dependence of transpiration and stomatal conductance (gs) on Gt among the four study species suggested that stomatal adjustment to variation in Gt limited transpiration over the entire range of Gt observed.

6. When gs was normalized for daily variation in Gt, about 80% of the remaining variation in gs was associated with variation in ASD. The results suggested that transpiration in these species was not limited by soil water availability per se, but by high atmospheric evaporative demand and hydraulic constraints possibly arising from their deep rooting habit.
The influence of leaf thickness on the CO2 transfer conductance and leaf stable carbon isotope ratio for some evergreen tree species in Japanese warm‐temperate forests
Authors: Hanba Y. T. , Miyazawa S.‐I. , Terashima I.
Published: March 2003

1. The influence of leaf thickness on internal conductance for CO2 transfer from substomatal cavity to chloroplast stroma (gi) and carbon isotope ratio (δ13C) of leaf dry matter was investigated for some evergreen tree species from Japanese temperate forests. gi was estimated based on the combined measurements of gas exchange and concurrent carbon isotope discrimination.

2. Leaves with thicker mesophyll tended to have larger leaf dry mass per area (LMA), larger surface area of mesophyll cells exposed to intercellular air spaces per unit leaf area (Smes) and smaller volume ratio of intercellular spaces to the whole mesophyll (mesophyll porosity).

3.
g
i of these leaves was correlated positively to Smes but negatively to mesophyll porosity. The variation in gi among these species would be therefore primarily determined by variation of the conductance in liquid phase rather than that in gas phase.

4.δ13C was positively correlated to mesophyll thickness and leaf nitrogen content on an area basis. However, gi values did not correlate to δ13C. These results suggest that difference in δ13C among the species was not caused by the variation in gi, but mainly by the difference in long‐term photosynthetic capacity.

5. Comparison of our results with those of previous studies showed that the correlation between leaf thickness and gi differed depending on leaf functional types (evergreen, deciduous or annual). Differences in leaf properties among these functional types were discussed.
Effects of herbivory on internal ethylene production and sex expression in Cucurbita texana
Authors: Krupnick G. A. , Avila G. , Brown K. M. , Stephenson A. G.
Published: March 2003

1. Field‐grown Cucurbita texana was used in a study to determine if stress ethylene from damaged leaves promotes changes in sex expression.

2. Internal ethylene concentrations were experimentally enhanced by inserting an ethylene‐filled syringe into the hollow chamber of an internode seven nodes from the growing tip of a branch. Branches enhanced with ethylene produced significantly more pistillate buds than control branches and experienced greater bud abortion later in floral development.

3. The timing and magnitude of Diabrotica beetle leaf damage was simulated using a paper‐hole puncher (15% removed from all leaves). Simulated herbivory was applied to new growth every 3 days throughout the growing season.

4. Endogenous ethylene concentrations recovered from the internode adjacent to the growing tip were significantly greater in damaged plants than undamaged plants 1 day after damage to new growth during the second and third week of the experiment, and 2 days after damage during the fourth and fifth week. By the sixth week, no significant differences were evident.

5. Damaged plants produced fewer pistillate buds than undamaged plants, indicating that stress ethylene from simulated herbivory does not induce femaleness. A second messenger that suppresses pistillate bud production may be produced during damage.
Long‐range foraging by the honey‐bee, Apis mellifera L.
Authors: Beekman M. , Ratnieks F. L. W.
Published: March 2003

1. Waggle dances of honey‐bees (Apis mellifera L.) were decoded to determine where and how far the bees foraged during the blooming of heather (Calluna vulgaris L.) in August 1996 using a hive located in Sheffield, UK, east of the heather moors. The median distance foraged was 6·1 km, and the mean 5·5 km. Only 10% of the bees foraged within 0·5 km of the hive whereas 50% went more than 6 km, 25% more than 7·5 km and 10% more than 9·5 km from the hive.

2. These results are in sharp contrast with previous studies in which foraging distances were much closer to the hive. In May 1997 the mean foraging distance was 1 km, showing that long‐range dancing is not the rule in Sheffield.

3. The observed foraging distances described in this study may not be exceptional in a patchy environment where differences in patch size and patch quality are large. When travel distances to patches are large, distant patches can probably be utilized only by individuals that live in groups and recruit foragers to the patches found. Only then are the benefits of scouting for distant patches high enough to enable the exploitation of these patches.