bluuebunny/crossref_metadata_2025 huggingface dataset:
Modelling the effect of cultivation on seed movement with application to the prediction of weed seedling emergence
Authors: Grundy A.C. , Mead A. , Burston S.
Published: March 2003

1. Effective weed control is essential in field vegetables. However, the range of available herbicides has been continually reduced for commercial and toxicological reasons over the last decade. In order to predict the optimum weeding period and to apply alternative control strategies successfully, a realistic estimate is needed of the size, timing and duration of a flush of weed emergence in a crop. The soil weed seed bank is the primary source of future weed populations, and therefore provides a unique resource for predictive management purposes.

2. Models have previously been developed to predict the emergence of weed species from different burial depths and to simulate the vertical movement of weed seeds following seed bed preparation.

3. In this investigation a vertical movement model was extended to include the effects of four cultivation implements on the horizontal displacement of weed seeds. These implements were a rotavator, a spring tine, a spader and a power harrow.

4. The rotavator caused a backward movement of seeds; neither the spring tine nor spader had a significant effect on the horizontal displacement of seeds; whilst the power harrow had the greatest capacity to move seeds forward > 0·5 m in the soil.

5. This investigation combined depth of burial and vertical movement models to simulate the likely outcome of different sequences of spring tine, spader, rotavator and power harrow on subsequent weed seedling emergence. For example, sequences including multiple passes of a spader increased the numbers of emerged seedlings, whilst for those where the rotavator dominated the sequence, a marked reduction in seedling numbers was predicted. The findings of a series of simulations are viewed in the light of existing methods of weed control based on soil cultivation, for example the stale seed bed technique.

6. The combined model provides the basis for a decision support system to aid the control of weeds. Additionally, it provides a research tool to improve understanding of the dynamics of the weed seed bank and the implications of seed bed preparations for future populations. The combined model has helped to identify areas of weed seed ecology requiring further study, essential for the development of true dynamic models.
Demography and the decline of the grey partridgePerdix perdixin France
Authors: Bro E. , Sarrazin F. , Clobert J. , Reitz F.
Published: March 2003

1. Bird populations can be efficiently managed only if the demographic mechanisms that cause change are correctly understood. Here we illustrate the demographic variables causing decline among grey partridgePerdix perdixpopulations in France by comparing populations that show contrasting trends. The analysis combined a field survey at 10 contrasting sites during 3 years, modelling and statistical analyses; survival rates and reproductive success were estimated through the largest‐ever radio‐tracking study of hens, while density was estimated through counts.

2. Population viability analyses showed that, in France, north‐western populations of grey partridge were healthy whereas south‐eastern populations were declining.

3. Elasticity analyses accounting for environmental stochasticity indicated that the survival rate during shooting, over winter and at the time of the first nesting attempt were the most important demographic influences on population growth rate. The hatching rate, covey size at hatching of first clutches and chick survival rate were secondary. The contribution of replacement clutches to population change was low.

4. Multiple regression showed that hen survival during the first nesting attempt explained 33% of the variability in the population growth rate across populations. The shooting pressure increased with the health of the population.

5. Improving survival rate during winter and the first nesting attempt was not sufficient for recovery in a declining population. It was also necessary to increase simultaneously the hatching rate of first clutches and chick survival rate to produce a stable population that could sustain shooting.

6. Low hen survival rates, in particular during the breeding period, explain the recent decline of grey partridge populations in some regions of France. However, the recovery of populations will need a simultaneous improvement of several demographic parameters.
Responses of ants to selective logging of a central Amazonian forest
Authors: Vasconcelos H.L. , Vilhena J.M.S. , Caliri G.J.A.
Published: March 2003

1. Relatively little information exists on the effects of logging on rain forest organisms, particularly in the Neotropics where logging operations have increased dramatically in recent years. In this study we determined experimentally the effects of selective logging of a central Amazonian forest on ground‐living ants.

2. The experimental design consisted of three 4‐ha replicated plots representing control unlogged forest, forest logged 10 years prior to the start of the study (1987), and forest logged 4 years prior to the start of the study (1993). The logging operation removed 50% of the basal area of trees of commercial value, or about eight trees per hectare. This resulted in a significant decrease in canopy cover, and an increase in understorey vegetation density in logged plots relative to controls.

3. Collection and identification of ants from a total of 360 1‐m2 samples of leaf‐litter revealed 143 ant species, of which 97 were found in the control plots, 97 in the plots logged in 1987, and 106 in those logged in 1993. Species richness, evenness and mean abundance (ants m−2) per plot did not vary among treatments. Most of the species found in the control plots were also present in the logged plots. However, population density of many species changed as a result of logging, an effect that persisted for at least 10 years after logging. Species commonly found in sites that were directly disturbed by logging (gaps and tracks) were rare in the undisturbed forest, as revealed by an additional collection of ants.

4. These results suggest that the persistence of ant assemblages typical of undisturbed forest is likely to depend on the amount of structural damage incurred by logging. Thus management techniques that minimize logging impacts on forest structure are likely to help maintain the conservation value of logged forests for ground‐dwelling ants. It is particularly important to minimize the extent of logging roads and tracks created by heavy machinery because these areas appear more prone to invasion by non‐forest species.
Consequences of large‐scale processes for the conservation of bird populations
Authors: Baillie Stephen R. , Sutherland William J. , Freeman Stephen N. , Gregory Richard D. , Paradis Emmanuel
Published: March 2003

1. Detailed studies of population ecology are usually carried out in relatively restricted areas in which emigration and immigration play a role. We used a modelling approach to explore the population consequences of such dispersal and applied ideas from our simulations to the conservation of wild birds.

2. Our spatial model incorporates empirically derived variation in breeding output between habitats, density dependence and dispersal. The outputs indicate that dispersal can have considerable consequences for population abundance and distribution. The abundance of a species within a patch can be markedly affected by the surrounding habitat matrix.

3. Dispersal between habitats may result in lower population densities at the edge of good quality habitat blocks and could partially explain why some species are restricted to large habitat fragments.

4. Habitat deterioration may not only lead to population declines within that habitat but also in adjacent habitats of good quality. This may confound studies attempting to diagnose population declines.

5. Although mobile species have the advantages of colonizing sites within metapopulations, dispersal into poorer quality territories may markedly reduce total populations.

6. There are two main approaches to conservation: one is to concentrate on establishing and maintaining protected areas, while the other involves conservation of the wider countryside. If dispersal is an important process then protecting only isolated areas may be insufficient to maintain the populations within them.
Vegetation structure and prey abundance requirements of the Iberian lynx: implications for the design of reserves and corridors
Authors: Palomares F.
Published: March 2003

Habitat alteration and fragmentation are two of the greatest threats to biodiversity. The conservation of most species in highly encroached areas requires reserves that are connected by suitable habitat corridors to increase the effectiveness of the area under protection. However, the quality required for such corridors is still debated. This study investigated the habitat characteristics (vegetation structure and prey abundance) of sites used by resident and dispersing Iberian lynx in south‐western Spain.

 Vegetation structure and an index of rabbit abundance (the staple prey of lynx) were measured at sites used by radio‐collared lynx in 1996 and 1997. Data from 128 plots used by resident lynx and 310 plots used by dispersing individuals were compared with data from 162 randomly located plots in sites considered to be unused by lynx.

3. Resident sites had a lower percentage of tree cover, shorter tree height, higher percentage of tall shrub cover, higher percentage of overall understorey and higher number of rabbit pellets than both dispersal and unused sites. The height of the short shrub layer was taller and the rabbit abundance index was higher in dispersing sites than in unused sites.

 Gender did not affect habitat selection by lynx. During dispersal, lynx frequently (50% of cases) used vegetation patches narrower than 300 m. In these cases, sites used by lynx had higher understorey cover and taller shrub height than adjacent unused sites. The percentage of short shrub cover used by lynx increased with the length of time taken to disperse; this was the only variable that changed over time.

 Range size of resident individuals declined significantly with the index of rabbit abundance but increased with the percentage of short shrub cover. Both variables were good predictors of range size.

 The study shows that corridors connecting reserves do not have to be prime habitats; they can even support moderate habitat degradation due to human activity. This result has implications both for the conservation of existing corridors, and for the restoration of the many corridors between reserves that have been lost.
The benefits of extensive agriculture to birds: the case of the little bustard
Authors: Wolff Axel , Paul Jean‐Philippe , Martin Jean‐Louis , Bretagnolle Vincent
Published: March 2003

The little bustard Tetrax tetrax is among many birds thought to be declining because of agricultural intensification in western Europe. In contrast with the situation elsewhere, bustard numbers have greatly increased during the last 50 years in the Crau, southern France, as agriculture has been developing. We wished to ascertain which features of agricultural development might have supported this population increase.

Using data on habitat‐specific densities obtained by surveys of the Crau in 1998 and 1999, we assessed how breeding male little bustards used habitats representing various levels of agricultural intensification. We also documented historical changes in bustard numbers and agricultural trends in the Crau, comparing them with present patterns of habitat use, to determine how changes in farmed landscapes may have driven population trends.

Male bustards used natural steppe and extensive agricultural habitats (fallow, grazed crops, legume crops), whereas more intensive agricultural habitats (hay‐meadows, grain crops) were little used. Mean densities on extensive agricultural habitats were always high, but densities on steppe varied with landscape composition: densities were low where steppe was dominant in the landscape, but high where steppe and extensive agriculture were mixed.

Available literature showed that little bustards settled in the Crau around 1950, after 40% of the original steppe had been converted into arable land. We estimate a current population of 473–539 breeding males. Only 17% of the original steppe remains, but extensive agricultural habitats still represent 30% of arable land.

Both historical data and present habitat use suggest that little bustard population trends in the Crau are driven by the development of extensive agriculture. Extensive agricultural habitats may provide little bustards with resources unavailable or scarce in natural steppe. Severe declines in little bustard numbers observed elsewhere could be reversed within a few decades by restoring extensive agricultural habitats. The potential impact of current European agricultural policies is discussed, with special reference to agri‐environmental measures and set‐aside policy.

This work provides an example of an avian species that benefits from cultivated landscapes, providing that they are extensive rather than intensive. We propose a simple conceptual model to illustrate how little bustards, and possibly grassland birds in general, might respond where natural habitats are modified along orthogonal axes representing cultivation and agricultural intensification.
Dispersal and survival of juvenile feral ferrets Mustela furo in New Zealand
Authors: Byrom Andrea E.
Published: March 2003

Introduced feral ferrets Mustela furo are a significant pest of both conservation and economic importance in New Zealand. Ferrets prey on indigenous wildlife and they also carry bovine tuberculosis (TB), a disease which may threaten New Zealand's international beef, dairy and venison markets.

Very little is known about the role of dispersal and survival of juvenile ferrets in the recovery of ferret populations after control operations, and how these parameters might affect ferret impacts on native wildlife and their role in the spread of TB.

Fifty‐two juvenile ferrets were radio‐collared at emergence from their natal dens on six study sites during 2 years, 1997–98 and 1998–99. On three sites, most introduced mammalian predators (including ferrets) had been removed by kill‐trapping from October to January to protect critical bird nesting areas. Three sites were left as non‐removal sites. Dispersal and survival of juvenile ferrets was therefore measured at low and normal ferret densities.

Survival of juvenile ferrets showed a strong density‐dependent response to predator removal. In year 1, survival of juvenile ferrets from emergence to the end of the dispersal period (about 4 months) was 86% (95% confidence limits 63–100%) on removal sites, whereas survival on non‐removal sites was 19% (0–38%). In year 2, survival was 100% on removal sites compared with 71% (45–97%) on non‐removal sites. Dispersal of juvenile ferrets was not related to population density at source.

A frequency distribution of dispersal distances of juvenile ferrets showed a typical negative‐exponential pattern. The median dispersal distance of juvenile ferrets was 5·0 km (range 0·5–45·0 km). There was no apparent sex bias in survival, dispersal distances or timing of dispersal in either season.

Density‐dependent survival of juvenile ferrets should be a key parameter of interest in determining frequency and seasonal timing of ferret control. Ferret control to conserve native wildlife and minimize TB spread should be carried out in late autumn after dispersal, to provide a longer lag time before juveniles reinvade an area.

This study fills a critical gap in the understanding of introduced mustelids in island systems such as New Zealand. It has direct implications for management of this important introduced predator, and it augments literature on dispersal and survival of mammalian carnivores.
Modelling disease spread in a novel host: rabies in the European badger Meles meles
Authors: Smith G. C. , Wilkinson D.
Published: March 2003

Although the red fox Vulpes vulpes is the main reservoir of rabies in Europe, badger Meles meles populations are known to be drastically affected. Models of badger population dynamics are combined with a fox/rabies model to examine the possibility of rabies spread in high‐density badger populations, such as those found in the United Kingdom (UK).

Although some data exist on rabies epizootiology in the badger, there are no data on badger‐to‐badger contact rates (either healthy or diseased animals). As a starting point consensus expert opinion was used to devise contact probabilities, and the model was found to be insensitive to reasonable variation in these rates for the density of badgers at which these estimates were made.

Density‐dependent (but not density‐independent) contact probabilities simulated short chains of infections that may occur in continental Europe at low badger densities, and simulated true epizootics at higher densities.

Another possible reason for these short chains of infections in continental Europe is a very high level of fragmentation between social groups.

Given the high level of territorial contiguity and possible contact rates found in some parts of the UK, the model suggests that rabies is capable of spreading within the UK badger population, and a provisional map showing the likelihood of an epizootic is presented.
Nicotine‐like effects of cotinine on protein kinase C activity and noradrenaline release in bovine adrenal chromaffin cells
Authors: Vainio P. J. , Viluksela M. , Tuominen R. K.
Published: March 2003

1 We studied the effect of cotinine, a slowly eliminated metabolite of nicotine, on protein kinase C (PKC) distribution and noradrenaline release in primary cultured bovine adrenal chromaffin cells. Changes in PKC activity were detected by [3H]‐phorbol‐12,13‐dibutyrate binding, histone phosphorylation assay and by Western blot.

2 Cotinine (10–32 mm) increased phorbol binding to chromaffin cells in response to 10 min but not to 24 h exposure. The increased binding was reversed by a nicotinic antagonist hexamethonium (10 μm).

3 Cotinine (10 mm, 30 min) also increased membrane‐associated PKC activity and membrane‐associated PKC α and ε immunoreactivity.

4 Cotinine (0.1–32 mm for 10 s to 20 min) dose‐ and time‐dependently increased the release of preloaded [3H]‐noradrenaline from the cultured cells. The release increased with increasing duration of the contact period. In treatments lasting 1 min or longer, a peak effect was followed by a reduced response at higher concentrations.

5 We confirm the earlier findings that cotinine is biologically active, and conclude that its effects are at least partly mediated via nicotinic cholinergic receptors and through PKC.
Effect of early stage of experimental diabetes on vascular functions in isolated perfused kidneys
Authors: García V. M. C. , Ochoa J. E. , Elías M. M.
Published: March 2003

1 The present study investigates the renal vascular responsiveness to vasoactive agents in diabetic rats which present an early stage of renal failure.

2 Adult male Wistar rats were administered alloxan (150 mg kg–1, s.c.). Seven days later the right kidneys were isolated and perfused. Renal perfusion pressure was measured continuously. Concentration‐response curves were plotted for noradrenaline (NA), sodium nitroprusside (SNP) and carbachol.

3 In basal conditions, kidneys from diabetic rats presented a decreased vascular resistance compared with those from control rats.

4 The vasoconstrictor response to NA showed decreased EC50 values in preparations from diabetic rats compared with control ones (EC50 nmols, control: 2.03 ± 0.44, n = 8; diabetic: 0.84 ± 0.18, n = 6, P < 0.05). This enhanced sensitivity to NA could be in line with the decreased glomerular filtration rate and cortical renal plasma flow previously described in vivo in our laboratory (
Garcia et al. 1998
) . Vasoconstrictor responses to phenylephrine were not however, different between diabetic and control rat kidneys. This suggests that the increased sensitivity to NA was due to impaired neuronal uptake since phenylephrine is not a substrate for neuronal uptake.

5 After precontraction with phenylephrine, both endothelium‐dependent (carbachol) and endothelium independent (SNP) vasodilator agents caused similar response in the preparations taken from the two groups of animals. So, the enhanced sensitivity to NA is not associated with a deficient dilator responsiveness of the renal vasculature.

6 The vasodilator response to carbachol was the same in absence or presence of
l‐arginine in the perfusate, suggesting no alteration in its availability at this stage of diabetes.

7 Diabetic animals showed increased plasma level of fructosamine and glycosylated haemoglobin (Hb A1c), indicating the presence of early glycated products at this stage of diabetes, which could be involved in a possible structural alteration of the vessels.
Effects of propranolol and L‐NAME on β‐adrenoceptor‐mediated relaxation in rat carotid artery
Authors: MacDonald A. , McLean M. , MacAulay L. , Shaw A. M.
Published: March 2003

1 The properties of β‐adrenoceptors mediating vascular relaxation in rat isolated carotid artery were investigated. Ring segments of arteries were preconstricted with the thromboxane A2 receptor agonist U‐46619 and relaxation to β‐adrenoceptor agonists determined.

2 Isoprenaline produced a concentration‐dependent relaxation of U‐44619‐constricted arteries. The concentration‐response curve (CRC) to isoprenaline was shifted to the right by propranolol (1 μm) although the shift was less (105 fold; pA2, 8.02) than would be expected for an effect of isoprenaline at classical β‐adrenoceptors (300–1000 fold; pA2, 8.5–9). L‐NAME (100 μm) significantly reduced responses to isoprenaline, lowering the slope of the CRC and reducing the maximum response.

3 The selective β3‐adrenoceptor agonists, BRL 37344 and ZD2079, also produced concentration‐dependent relaxation of the arteries. L‐NAME (100 μm) shifted the BRL 37344 CRC to the right 15 fold with no reduction in the slope or maximum response. L‐NAME (100 μm) had no significant effect on the ZD2079 CRC.

4 In conclusion, relaxation to isoprenaline in rat carotid artery is inhibited by propranolol in a manner suggesting a mixed population of classical (β1‐/β2‐) and atypical (β3‐) adrenoceptors. The presence of β3‐adrenoceptors was confirmed by the relaxant effects of the selective β3‐adrenoceptor agonists BRL 37344 and ZD2079. L‐NAME attenuated responses to both isoprenaline and the β3‐adrenoceptor agonist BRL 37344, suggesting a role for endothelial release of nitric oxide in β‐adrenoceptor mediated relaxation. However, the relaxant effect of BRL 37344 was attenuated by L‐NAME to a lesser extent than that of isoprenaline. In addition, L‐NAME had no effect on relaxation induced by ZD2079. These results suggest that there may be a differential contribution of endothelium to classical β‐and β3‐adrenoceptor‐mediated effects, with endothelium contributing less to β3‐adrenoceptor‐mediated relaxation.
Adrenergic nerves compensate for a decline in calcium buffering during ageing
Authors: Pottorf W. J. , Duckles S. P. , Buchholz J. N.
Published: March 2003

1 The ubiquitous involvement of intracellular calcium ([Ca2+]i) in multiple neuronal pathways has led investigators to suggest that dysfunction of calcium homeostasis may be the primary mediator of age‐related neuronal degeneration. Recently, it was shown that sympathetic neurones from superior cervical ganglion (SCG) of aged rats demonstrate decreased sarco‐/endoplasmic reticulum Ca2+‐ATPase (SERCA) function and that aged neurones are more dependent upon mitochondria to control K+‐evoked [Ca2+]i transients.  2 Therefore, in the present study we investigated age‐related changes in ATP‐dependent calcium pumps of plasma membrane Ca2+‐ATPase (PMCA) and SERCA in acutely dissociated SCG cells from Fischer‐344 rats aged 6 and 20 months. To distinguish between PMCA and SERCA pump activity, we applied the Ca2+‐ATPase blocker vanadate and measured rates of recovery of K+‐evoked [Ca2+]i transients by fura‐2 microfluorometry.  3 Young SCG cells showed a biphasic response to vanadate over the vanadate concentration range (0.01–100 μm); however, old SCG cells showed only a single response over the same concentration range. Additionally, old SCG cells showed a greater sensitivity to Ca2+‐ATPase blockade by vanadate.  4 The contribution of mitochondrial calcium uptake to regulate [Ca2+]i was also investigated. To measure the impact of mitochondrial calcium uptake, PMCAs and SERCAs were blocked with vanadate (100 μm) and extracellular sodium was replaced with tetraethylammonium (TEA) to block Na+/Ca2+‐exchange. Treated SCG cells showed a decline of 50% in rate of recovery of [Ca2+]i in both 6‐ and 20‐month‐old cells; however, this effect did not vary with age.  5 These data suggest that there is an age‐related decline in function of SERCAs, with an increased reliance on PMCAs to control high K+‐evoked [Ca2+]i transients. In addition, there appears to be no age‐related change in the capacity of the mitochondria to restore [Ca2+]i transients to basal levels.
Metabolic dependency of ionophore A23187‐induced contraction of ileal longitudinal smooth muscle
Authors: Nasu T. , Nishikawa M.
Published: March 2003

1 Tonic contraction in response to K+ is well known to be highly dependent on aerobic metabolism in ileal muscle. The ionophore A23187 (10−5 m) induced an initial contraction and successive rhythmic contraction in ileal muscle, but did not induce tonic contraction. This study, therefore, was performed to investigate the metabolic dependency during contraction induced by A23187.  2 Under hypoxic conditions, A23187 (10−5 m) induced an initial contraction accompanied by an increase in lactate release. However, it induced only small rhythmic contractions and decreases in ATP, phosphocreatinine (PCr) and glycogen contents.  3 In glucose‐free medium, A23187 (10−5 m) induced an initial contraction and concomitant significant decrease in the ATP and glycogen contents. However, it did not induce successive rhythmic contractions. In ‘glycogen‐depleted muscle’ stimulated repeatedly with 60 m
m K+ in glucose‐free medium, 60 m
m K+ induced a phasic contraction without tonic contraction. A23187 induced no contraction under these conditions.  4 These results suggested that the initial contraction induced by A23187 was dependent on endogenous glycogen, while successive rhythmic contractions were dependent on aerobic metabolism after supply of external glucose to the ileal muscle.
Wall tension and contraction of the aorta in 6‐month‐old spontaneously hypertensive rats
Authors: Nunes J. P. L. , Guimarães Serafim
Published: March 2003

1 The present study aimed at comparing the influence of passive tension on the effect exerted by noradrenaline on the thoracic aorta of 6‐month‐old Wistar and spontaneously hypertensive rats (SHR).

2 Concentration–response curves to noradrenaline were obtained in aorta rings, at two levels of passive tension: 3 and 0.5 g.

3 The maximal responses (in percentage of the maximal response to noradrenaline obtained in the beginning of the experiment at a tension of 2 g) were significantly larger (P < 0.05) at 3 g than at 0.5 g in both kinds of rats: 171 versus 69%, respectively, for SHR; 139 versus 76%, respectively, for Wistar rats.

4 When expressed as mg of active tension per mg of tissue, the maximal contraction at both 3 and 0.5 g was smaller in SHR than in Wistar rats (at 3 g: 64.6 ± 6.7, n=6 versus 122.3 ± 19.1, n=8, respectively, P < 0.05; at 0.5 g: 24.0 ± 1.0, n=6 versus 49.0 ± 5.9, n=8, respectively, P < 0.05).

5 Maximal responses to noradrenaline were markedly decreased by cytochalasin B (50 μM) (to 15.2 ± 6.0%, n=6, at 3 g and 2.8 ± 1.9%, n=6, at 0.5 g in SHR; to 11.8 ± 2.3%, n=4, at 3 g and 4.3 ± 1.3%, n=4, at 0.5 g in Wistar rats). Cytochalasin B at a lower concentration (4 μM) produced a less marked decrease in responses to noradrenaline in both strains of rats. The presence of cardiovascular structural changes in SHR was confirmed by the fact that the heart weight (mg):body weight (g) was higher in SHR (3.37 ± 0.06, n=10) than in Wistar rats (2.40 ± 0.12, n=11) (P < 0.05).

6 It is concluded that in 6‐month‐old SHR the contractile capacity of the aortic tissue is reduced. However, the differential sensitivity of aortic smooth muscle at the two different levels of tension remains present. This difference may depend on filament interaction. Contractions to noradrenaline in the rat aorta are highly dependent on actin polymerization.
Testing vicariance: melanopsid snails and Neogene tectonics in the Western Mediterranean
Authors: Altaba Cristian R.
Published: March 2003

Abstract. Vicariance on a microplate dispersed by the formation of the Western Mediterranean is the probable origin of Melanopsis etrusca Villa in Brot, the only melanopsid (Gastopoda: Melanopsidae) living in the Italian Peninsula. It is distantly related to extant melanopsids in Iberia and Morocco, and is restricted to thermal springs in the Maremma of southern Tuscany. This area was an island throughout the Miocene, inferred to have become detached geographically from the Corso—Sardinian block. Alternative explanations conflict with geological, paleontological, ecological and systematic evidence. In the geologically young Italian Peninsula fossil freshwater melanopsids are known only from Lower Pleistocene sites located around the area occupied by living populations. Their similarity to extant specimens supports the hypothesis that they represent the same lineage, having expanded its range during a brief, favourable period. Introduction of M. etrusca by humans, birds or wind is most improbable given its distinctness, similarity to local fossils, and inability for passive dispersal. Long‐distance dispersal along brackish lagoons during the late Messinian conflicts with the inferred inability of melanopsids living there to colonize freshwater habitats. Indeed, there are ecological, phylogenetic and geological reasons against invoking the Messinian salinity crisis in order to explain the distribution of most taxa. Other freshwater taxa show distribution patterns similar to that of living and fossil melanopsids. However, congruent area cladograms or generalized tracks may not constitute reliable evaluators of biogeographical hypotheses. The detection of vicariance, as that of any other cause, requires robust reconstructions of the past. By pointing at areas of endemism that deserve urgent action, biogeography can provide a contribution to conservation.
Stand structure of the emergent conifer Agathis ovata in forest and maquis, Province Sud, New Caledonia
Authors: Enright N. J. , Goldblum D.
Published: March 2003

Abstract. The size structure of the endemic New Caledonian conifer Agathis ovata is reported for sample stands in forest and maquis from three areas on ultramafic substrates in the south of the main island (Grand Terre). In closed forest Agathis ovata is typically represented by a low density of emergent adult trees with only limited evidence of seedling recruitment. In maquis, Agathis ovata is represented by individuals of all sizes, with seedlings and saplings abundant in most sample stands. Preliminary evidence from tree‐ring studies indicates that rings may be annual. Estimated diameter growth rate is about 2 mm y−1 for trees ≥ 10 cm d.b.h., and ring counts suggest tree ages of up to 400 years in maquis and 500 years in forest.

Agathis ovata, and three other members of the Araucariaceae found in New Caledonia (Araucaria laubenfelsii, A. montana and A. rulei), are the only tree species which regularly occur scattered in maquis in this way, creating an unusual structural assemblage. No angiosperm tree species show this behaviour. The circumstances under which the Agathis ovata– maquis stands arise and are maintained are the subject of further investigation. Preliminary evidence for tree ages indicates that these stands predate European arrival in New Caledonia and so are not the result of recent increases in the frequency and intensity of human disturbances. The presence of fire scars on many individuals, and location of most stands on slopes and spurs with outcropping laterite (cuirasse), suggests that this assemblage may owe its existence to the interplay of fire regime, topography and rockiness, and a resistance to fire in Agathis ovata which increases with plant size and age.
Disturbance and climatic influences on age structure of ponderosa pine at the pine/grassland ecotone, Colorado Front Range
Authors: Mast Joy Nystrom , Veblen Thomas T. , Linhart Yan B.
Published: March 2003

Abstract. In the Colorado Front Range, disturbances and climatic variation influence stand structure of ponderosa pine (Pinus ponderosa) along the lower timberline ecotone. Over the past 100 years there has been a shift to a greater density and extent of ponderosa pine at the forest‐grassland boundaries. Ponderosa pine regeneration at lower timberline appears to be influenced by fires in the 1860s and decreased grazing pressure in the 1970s–1980s. Climatic variation may also have influenced age structure, even though analyses of age structure at a 10‐year class scale prevented the detection of climatic influences occurring at a finer scale. These changes in disturbance regimes, possibly together with moister springs/early summers, created favourable conditions for the increase in density and extent of ponderosa pine at lower timberline ecotone.
Biodiversity on oceanic islands:a palaeoecological assessment
Authors: Sadler Jon P.
Published: March 2003

Islands are bounded ecosystems and serve as excellent laboratories for assessing changes in Biodiversity. Some oceanic islands, such as Madagascar, Bermuda and notably the islands in the Pacific (e.g. Hawaii), are home to unique forms of endemic plants and animals that have evolved in isolation over millions of years. The palaeoecological record indicates that such islands are characterized by waves of extinctions concomitant with colonization by humans. By way of contrast, the biota of the islands of the north Atlantic (Greenland, Iceland and Faroe) do not follow the expected pattern and the few extinctions recorded are very localized. This is not a result of the scale of human impact, which is as great as on other islands, but relates to the virtual lack of endemics. The dearth of endemic forms and the disharmonic nature of these island communities indicates a youthful biota and the operation of severe filters and sweepstakes during colonisation over the last 10,000 years. This paper draws upon an extensive invertebrate fossil record to contrast and examine these spatial and temporal patterns in island Biodiversity.
Do local abundances of British birds change with proximity to range edge?
Authors: Blackburn Tim M. , Gaston Kevin. J. , Quinn Rachel M. , Gregory Richard D.
Published: March 2003

Aim Species generally vary in the density they attain at different sites, prompting the question of whether this variation is systematic across their range. We investigate this question using data on the abundance and distribution of thirty‐two species of passerine birds across Britain derived from censuses organized by the British Trust for Ornithology.

Methods Analysis is complicated by the issue of quantifying the distance of any particular census location from the edge of the range of a species when the study area encompasses only part of its entire distribution. No measure of this quantity is a priori the correct one, and so we use a variety of different measures which make differing assumptions about how abundances might be structured across species ranges.

Results None of the measures used reveal any consistent relationships between the density attained by species at census sites and the spatial positions of those sites. Only thirteen species show significant relationships with any of the measures, and no more than seven species with any single measure.

Main conclusion In summary, there is no convincing evidence that passerine bird densities are usually lower towards range edges in Britain. We discuss possible reasons for these findings.
Molecular genetic evidence for the post‐Pleistocene divergence of populations of the arctic‐alpine ground beetle Amara alpina (Paykull) (Coleoptera: Carabidae)
Authors: Reiss Rebecca A. , Ashworth Allan C. , Schwert Donald P.
Published: March 2003

Aim This study examines the hypothesis that the biogeographic history of a species is reflected in the distribution of molecular genetic diversity and the phylogenies of extant populations.

Location Populations of arctic‐alpine ground beetle Amara alpina were analysed from Beringia (Alaska and northernmost British Columbia), the Hudson Bay region, the northern Appalachian Mountains, and the central Rocky Mountains of North America.

Methods Mitochondrial restriction site variation of specimens from twenty‐two populations were assayed by using radioactively labelled mtDNA to probe Southern membranes containing restriction enzyme digested total DNA. Restriction sites were mapped and genetic distances were calculated by pairwise comparison of presence and absence of restriction sites. Genetic distances were used in a molecular analysis of variance and to construct a minimal spanning tree. Parsimony methods were used to investigate the phylogenetic relationships between the haplotypes. These results were compared to an existing model for postglacial dispersal based on fossil and modern occurrences of arctic‐alpine beetles.

Results Among the twenty‐two populations, fifteen haplotypes were detected. Genetic variation within each of the four regions corresponded to that expected from the palaeontologically based model. Beringian populations were the most genetically diverse. In contrast, no restriction site variation was observed in populations from the Hudson Bay region. Intermediate amounts of variation were observed in alpine populations of the Rocky and Appalachian Mountains. Maximum parsimony and cluster analysis provide evidence that at least two ancestral haplotypes existed in the Southern refugium from which the Rocky and the Appalachian Mountains populations were founded.

Main conclusions The genetic results are generally consistent with the palaeontologically based model. The diversity of Beringian populations is consistent with this region having been continuously inhabited by Amara alpina throughout the Pleistocene. The Hudson Bay region was not deglaciated until about 6000 years, and its populations have no restriction site variation. The molecular genetic data support the interpretation that the Hudson Bay region was colonized from Beringia based on the occurrence of the same haplotype in both regions.
Urban plant ecology patterns and processes: a case study of the flora of the City of Plymouth, Devon, U. K.
Authors: Kent M. , Stevens R. A. , Zhang L.
Published: March 2003

AimUsing a large database that has been created over the past 5 years with the RECORDER package, presence/absence data for 829 species of vascular plants in the 103 1‐km2 squares that cover the city of Plymouth (pop. 243,373) have been analysed by two‐way indicator species analysis (TWINSPAN) and canonical correspondence analysis (CCA) to establish the major species assemblages and to examine their spatial distribution across the city in relation to variation in land use.

LocationThe City of Plymouth.

MethodsNine groupings of squares emerged and their distribution was mapped across the city. Interpretation of those groups and their variation in relation to the land use ordination axes showed that TWINSPAN groups lying along the first axis of variation correlated floristic variation with the process of urban development and the historical evolution of urban structure. The second axis appeared to be related to particular remnant semi‐natural habitats within the city that could be regarded as ‘hot‐spots’ for survival of many plant species. Species were categorized into four types on the basis of their recency and mode of arrival in the city and by using the historical flora of Plymouth produced by T. R. Archer‐Briggs in 1880. Variations in the sources of species in relation to the TWINSPAN classification groups were then examined. A second ordination was also computed; this time with geological, altitudinal and distance variables. TWINSPAN groups were then superimposed on the ordinations using polygons to assist with biogeographical interpretation.

Results and conclusions The results of both the multivariate analyses and distribution of species by source are then discussed in the context of previous research into urban plant ecology, particularly in Central Europe. The problems of inferring process from pattern in this meso‐scale study are reviewed and suggestions are made for further research into urban ecology and biogeography in the city.
Seven forms of rarity in mammals
Authors: Yu Jinping , Dobson F. Stephen
Published: March 2003

Conservation biologists have identified threats to the survival of about a quarter of the mammalian species; to identify patterns of rarity and commonness of mammals, we studied a global sample of 1212 species (about 28% of the mammals) using the ‘7 forms of rarity’ model (in which species are roughly divided into above and below the median for local population density, species’ range area, and number of habitat types).

From a niche‐based hypothesis of abundance and distribution, we predicted that mammals would exhibit a bimodal pattern of rarity and commonness, with an overabundance of species in the relatively rarest and most common categories; and just such a significant bimodal pattern emerged, with over a quarter of the species classified as exceedingly rare and a further quarter very common, supporting the niche‐based hypothesis.

Orders that include large mammals, including perissodactyls, primates, diprotodonts, and carnivores, exhibited significantly high proportions of relatively rare species; and tropical zoogeographic regions, especially Indomalaya, had relatively high proportions of species in the rarest category.

Significant biases in the available data on mammals included under‐sampling of small species like rodents and bats, and a relative paucity of data on zoogeographic regions outside of North America and Australia.

Mammalian species listed as of conservation concern by the IUCN occurred in all cells of the model, indicating that even relatively common species can be listed as threatened under some conditions; but we also found that sixty‐three species were relatively rare in all three criteria of the 7‐forms model but were not listed as threatened, indicating potential candidates for further study.

Mammals may be a group of animals where rarity or commonness is a natural aspect of species biology, both confirming and perhaps partly explaining the large proportion of mammals assigned threatened status.
Mammalian responses to Middle Holocene climatic change in the Great Basin of the western United States
Authors: Grayson Donald K.
Published: March 2003

In spite of decades of intense research directed toward understanding the climates and ecology of the Great Basin (western United States) during the past 10,000 years, the responses of mammals to the extreme aridity of the Middle Holocene (c. 8000–5000 years ago) in this region have been poorly understood. Using a well‐dated small mammal sequence from Homestead Cave, north‐central Utah, I show that the Middle Holocene small mammal faunas of this area underwent a decrease in species richness and evenness, driven largely by a series of local extinctions and near‐extinctions coupled with a dramatic increase in the abundance of taxa well‐adapted to xeric conditions. At the end of this period, some taxa that require relatively mesic habitats began to increase in abundance immediately, others did not rebound in abundance until several thousand years later, while still others have not returned at all. This suite of responses has been difficult to detect because climatic change at the beginning of the Middle Holocene was so much more substantial than that which occurred toward its end.
Latitudinal distribution of body size in north‐eastern Pacific marine bivalves
Authors: Roy Kaustuv , Martien Karen K.
Published: March 2003

Aim

To understand the latitudinal patterns in body size distributions of north‐eastern Pacific bivalves, as well as the factors influencing those patterns.

Locations

The north‐eastern Pacific continental shelf from 5 °S latitude to 70 °N latitude.

Methods

We used data on the body size and latitudinal ranges of 915 species of north‐eastern Pacific marine bivalves to test for the presence of interspecific latitudinal size trends. We tested for trends in both mean body size as well as variance in body size using randomization tests.

Results

Overall, there is no significant linear relationship between either mean size or variance in size and latitude. Rather, there is a mid‐latitude trough and peak in mean body size and variance in body size, respectively, with changes in the sign of the correlations occurring at provincial boundaries. A significant decreasing trend in mean size with latitude exists within the tropical Panamic province. In contrast, variance in body size shows a significant increasing trend with latitude within the tropics, and a significant decreasing trend with latitude in the cold temperate and Arctic provinces. For north‐eastern Pacific bivalves, latitudinal trends in mean body size and variance in body size show very little correlation with latitudinal trends in species richness. Close to an order of magnitude difference in species numbers between tropical and polar latitudes does not appear to significantly affect either mean size or variance in size. Changes in mean body size associated with biogeographic boundaries are significantly larger than changes elsewhere along the range.

Main conclusions

The spatial distribution of major environmental barriers along the north‐eastern Pacific margin plays a major role in structuring the latitudinal distribution of body size in marine bivalves along this coast.
Allozyme variation in Polyommatus coridon (Lepidoptera: Lycaenidae): identification of ice‐age refugia and reconstruction of post‐glacial expansion
Authors: Schmitt Thomas , Seitz Alfred
Published: March 2003

Aim

The effects of glacial disjunctions on intraspecific differentiations are in the focus of phylogeographical studies. Several studies investigate the consequences of post‐glacial expansions from glacial refugia on the composition within major genetic lineages.

Location and methods

We analysed the geographical pattern of allozyme variation of twenty loci of Polyommatus coridon (Poda, 1761) (Lepidoptera: Lycaenidae) from thirty‐six localities spread throughout large regions of its European range. A total of 1566 individuals were analysed.

Results

We obtained a significant genetic differentiation (FST 0.060 ± 0.007). Further analyses showed a division into two major genetic lineages with a mean genetic distance (Nei, 1978) of 0.041 (± 0.010 SD). Applying an AMOVA, more than three quarters of the variance between populations was between these lineages and less than one quarter within these lineages. Both genetic lineages showed a significant decline in the number of alleles from southern to northern populations. Furthermore, we found a contact zone of these two major genetic lineages in eastern Central Europe extending throughout north‐eastern Germany, then following the mountain regions along the Czech‐German border and passing through the eastern Alps in a north–south direction.

Main conclusions

We assume that this differentiation evolved during the last ice‐age as a result of isolation in the Adriato‐ and the Ponto‐Mediterranean region. The loss of genetic diversity from the south to the north within both lineages reflects the decline of diversity during the post‐glacial expansion.