Rapid changes in fish community structure and habitat distribution following the precipitation of lake phosphorus with aluminium

1. Fish community structure and habitat distribution of the abundant species roach, perch and ruffe were studied in Lake Nordborg (Denmark) before (August 2006) and after (August 2007) aluminium treatment to reduce internal phosphorus loading. 2. Rapid changes in fish community structure, abundance and habitat distribution occurred following a decline in in‐lake phosphorus concentrations from 280 to 37 μg P L^?1 and an increase in Secchi depth transparency from 1.1 to 1.9 m (August). The proportion of perch in overnight gill net catches increased, whilst roach decreased, and the average weight of all key species increased. 3. The habitat distribution of perch and roach changed from a high proportion in the upper pelagic and littoral zones in 2006, towards enhanced proportions in the deeper pelagic and profundal zone in 2007. The abundance of large‐bodied zooplankton increased and the abundance of benthic invertebrates decreased in the same period, suggesting that the habitat shift was not induced by food limitation. 4. Ruffe shifted from the littoral and upper profundal zones towards the deep profundal zone, likely reflecting an increased predation risk in the littoral zone and better oxygen conditions in the deep profundal. 5. Our results indicate that enhanced risk of predation in the upper pelagic and the littoral zones and perhaps improved oxygen concentrations in the deeper profundal zone at decreasing turbidity are responsible for the observed habitat shift. The results indicate that fish respond rapidly to changes in nutrient state, both in terms of community structure and habitat use.     

Molecular and morphometric variation in two sibling species of the genus Praomys (Rodentia: Muridae): implications for biogeography

The rodent genus Praomys is widely distributed in the African tropics. The species are cryptic, rendering the species taxonomy unclear. There are differences of opinion concerning the specific status of Praomys misonnei and Praomys tullbergi, and their geographical distribution. We sequenced the cytochrome b and/or the 16S gene of 221 specimens from 12 countries in order to evaluate the genetic variability within these two species, and to precisely determine their geographical distribution. Morphological and morphometrical analyses on the sequenced specimens were also performed to find criteria useful for the identification of museum specimens. Our results confirm that P. misonnei and P. tullbergi are two valid species that can be separated by molecular data. However, no single discrete morphological character or simple metric measurement can be used to discriminate them. The percentage of misclassified individuals in multivariate discriminant analysis is relatively high (10%). The two species have allopatric distributions: P. tullbergi occurs in West Africa, from eastern Guinea to western Ghana, and P. misonnei is widely distributed from eastern Ghana to western Kenya. Within P. misonnei we identified three or four major geographical clades: a West Central African clade, an East African clade, a Nigerian clade, and a possible West African clade. Within P. misonnei, high geographical morphometrical variability was also identified. The role of both rivers and Pleistocene forest refugia in promoting speciation within the genus Praomys is discussed. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 160 , 397–419.     

Biogeography meets conservation: the genetic structure of the endangered lycaenid butterfly Lycaena helle (Denis & Schiffermüller, 1775)

Cold‐adapted species are thought to have had their largest distribution ranges in central Europe during the glacial periods. Postglacial warming caused severe range shifts of such taxa into higher latitudes and altitudes. We selected the boreomontane butterfly Lycaena helle (Denis & Schiffermüller, 1775) as an example to demonstrate the genetic effects of range changes, and to document the recent status of highly fragmented remnant populations. We analysed five polymorphic microsatellite loci in 1059 individuals sampled at 50 different localities scattered over the European distribution area of the species. Genetic differentiation was strong among the mountain ranges of western Europe, but we did not detect similarly distinct genetic groups following a geographical pattern in the more eastern areas. The Fennoscandian populations form a separate genetic group, and provide evidence for a colonization from southern Finland via northern Scandinavia to south‐central Sweden. Species distribution modelling suggests a large extension of the spatial distribution during the last glacial maximum, but highlights strong retractions to a few mountain areas under current conditions. These findings, combined with our genetic data, suggest a more or less continuous distribution of L. helle throughout central Europe at the end of the last ice age. As a consequence of postglacial warming, the species retreated northwards to Fennoscandia and escaped increasing temperatures through altitudinal shifts. Therefore, the species is today restricted to population remnants located at the mountain tops of western Europe, genetically isolated from each other, and evolved into genetically unique entities. Rising temperatures and advancing habitat destruction threaten this wealth of biodiversity. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 155–168.     

Detecting climate change induced range shifts: Where and how should we be looking?

Abstract: Global climate warming is expected to cause systematic shifts in the distribution of species and consequently increase extinction risk. Conservation managers must be able to detect, measure and accurately predict range shifts in order to mitigate impacts on biodiversity. However, important responses to climate change may go unnoticed or be dismissed if we fail to collect sufficient baseline data and apply the most sensitive analytical tests. Here we use randomizations of a contemporary data set on rainforest birds of north‐eastern Australia to quantify the sensitivity of three measures for assessing range shifts along altitudinal gradients. We find that smaller range shifts are detectable by analysing change in the mean altitude of presence records rather than upper or lower range boundaries. For a moderate survey effort of 96 surveys, measurements of change in the mean altitude of 34 species have the capacity to provide strong inference for a mean altitudinal range shift as small as 40 m across the species assemblage. We also show that range shifts measured at range boundaries can be potentially misleading when differences in sampling effort between contemporary and historical data sets are not taken into account.     

Colonization front of the understorey palm Astrocaryum sciophilum in a pristine rain forest of French Guiana

Aims Astrocaryum sciophilum (Miq.) Pulle (Arecaceae) is an understorey palm, endemic to north‐eastern South America with a patchy distribution. We tested the hypothesis that the spatial distribution of this palm species is not in equilibrium but is slowly colonizing the forest understorey. Location Inventories and seed dispersal studies were conducted in the undisturbed tropical forest close to the Nouragues research station, French Guiana. Additional data were collected in the entire territory of French Guiana. Methods We studied the demography of A. sciophilum on a 20‐ha plot located at the edge of its distribution. The age of the palms was estimated by postulating an exponentially decreasing abundance by age class. Direct seed dispersal experiments were also conducted, to estimate dispersal parameters. The seeds of A. sciophilum were dispersed only by rodents. This information was used to parameterize a forest growth simulator, to study the spatial spread of this species. Results Within the sampling plot, the density of A. sciophilum dropped sharply from about 500 individuals per hectare to zero. The maturation age was estimated to be 170 ± 70 years, and over 55 years with 95% confidence. Seed‐dispersal experiments yielded an average seed dispersal distance of 11 m and a maximum estimated dispersal distance of 125 m across a generational span of 55 years to maturity. Therefore, the maximal estimated colonization speed is 2.3 m/y. Conclusions Empirical results and numerical simulations suggest that the boundary of the A. sciophilum population is a colonization front, and that the range of this species is slowly expanding. The implications of this result in respect of palaeoenvironmental changes in this region are discussed.     

Bone Load Estimation for the Proximal Femur Using Single Energy Quantitative CT Data

A density-based load estimation method was applied to determine femoral load patterns. Two-dimensional finite element models were constructed using single energy quantitative computed tomography (QCT) data from two femora. Basic load cases included parabolic pressure joint loads and constant tractions on the greater trochanter. An optimization procedure adjusted magnitudes of the basic load cases, such that the applied mechanical stimulus approached the ideal stimulus throughout each model. Dominant estimated load directions were generally consistent with published experimental data for gait. Other estimated loads suggested that loads at extreme joint orientations may be important to maintenance of bone structure. Remodeling simulations with the estimated loads produced density distributions qualitatively similar to the QCT data sets. Average nodal density errors between QCT data and predictions were 0.24 g/cm(3) and 0.28 g/cm(3). The results indicate that density-based load estimation could improve understanding of loading patterns on bones.     

Ionic Diffusion Through the Nitella Cell Wall in the Presence of Calcium

Diffusion potentials (concentration and bi- or multi-ionic potentials)in KC1, NaCl, or LiCl solutions have been measured across anisolated cell wall of Nitella, with or without the same concentrationof CaCl² on either side of the cell wall. The absolute valueof the potentials decreases as the external Ca²⁺concentrationincreases and it may happen that an inversion of the sign ofthe concentration potentials results when the external Ca²⁺solution reaches 1 mM. Dosages of K⁺ and Ca²⁺ in the cell wallhave shown that Ca²⁺ easily displaces the monovalent ion fromthe exchange sites and tends to neutralize the cationic exchanger.However, in most cases, the measured potentials are still morenegative than the theoretical potentials which would be setup by a neutral-site membrane in the same conditions. Theseresults suggest that Ca²⁺ largely reduces the discriminationproperties of the cell wall between cations and anions.     

Determination of the Length of the Vegetative and Pre-floral Stages in the Day-Neutral Plant Helianthus annuus by Chilling Pulses

Helianthus annuus seedlings grown in an 18 h day at 28 ?C wereexposed to one 6 d chilling pulse of 12 ?C, at spaced timesduring the first 21 d from sowing. At 2 d intervals, the terminalbuds of 5 plants were dissected to determine leaf number andto score the vegetative or flowering state of the shoot apex.It was found that, while the rate of leaf initiation was reducedequally by each chilling pulse, pulses commencing on days 9or 12 reduced the total leaf number from 30 to 26, while pulsesapplied earlier had little effect. This variation is interpretedin terms of the time available for leaf production. The apicesof control plants commenced the visible transition to flowering16 d after sowing. Chilling pulses applied from days 3 or 6delayed this transition by about 5 d, whereas later pulses causedonly a 1•5 d delay. In a second experiment, where the chillingwas reduced to 2 d duration, it was again found that chillingdelayed flowering during the first 8 d and was progressivelyless effective when applied later. From this variation in temperaturesensitivity it is proposed that chilling sunflower plants immediatelyafter sowing delays flowering by extending the vegetative phaseof growth and so delaying the attainment of a ‘ripenessto flower’ state that appears to coincide with the expansionof the first pair of leaves. From day 8 onwards processes leadingto flowering that are relatively temperature insensitive apparentlybecome dominant in the apex and result in visible signs of flowering8 d later, although during this transitional stage leaf primordiacontinue to be initiated on the flanks of the apex.     

Functional Anatomy of the Association Between Motor Units and Muscle Receptors

Muscle spindles and tendon organs occur in most somatic musclesof the mammal and are particularly concentrated in muscles subservingfine movements, including postural muscles and small musclesof the distal extremities. In those mixed muscles in which thedifferent fiber and motor unit types are "compartmentalized,"the spindles, and perhaps tendon organs also, are virtuallylimited to those compartments predominated by "oxidative" musclefibers. These morphological observations based on a broad arrayof muscles in many species, complement electrophysiologicalstudies which have emphasized that (1) the "oxidative" motorunits have low reflex thresholds and (2) segmental proprioceptivereflexes may be primarily concerned with the control of finelygraded contractions. Consideration of the functional anatomyof the association between motor units and muscle receptorssuggests the need for detailed structural-functional analysesof those muscles with specializations in architecture, fiber-typecomposition and distribution, and in the number and distributionof their muscle spindles and tendon organs. An electrophysiologicalanalysis of the relationship between the spinal cord and suchmuscles might also reveal certain strategies and mechanismsunderlying segmental motor control which are either absent orobscured in the analysis of that select number of "homogenously-mixed"muscles conventionally used in the study of the mammalian segmentalmotor control system.     

Action of Mono- and Difluorodinitrobenzene on Induced Electrical Modifications by External pH Changes in Nitella

The action of mono- (FNB) or difluorodinitrobenzene (DFNB) onion permeability is mainly attributed to its interactionwithamino groups of the membrane by dinitrophenylation. Nitella cells were dimtrophenylated at pH 7.3 and the membranepotential and electrical resistance were then measured in acidicor basic solutions. No matter what the pH value was, FNB andDFNB induced a depolarization of the membrane potential andcaused a diminution of resistance. However these effects ofFNB and DFNB were more drastic at alkaline pH and in the presenceof a weak concentration of potassium. Neither the addition of0.1 mM calcium nor the substitution of chlorides by nitratesmodified the DFNB effect. These results are compatible withthe assumption that the DFNB binding to the membrane leads toan augmentation of the negative charges of the membrane bringingabout an increased cation conductance and a modification ofthe affinity of a K⁺/H⁺exchange pump. The transient responseof the membrane potential at the time of dinitrophenylationwas used to roughly estimate the total density of amino groupsof the membrane of Nitella.