bluuebunny/crossref_metadata_2025 huggingface dataset:
Sustainable exploitation of social species: a test and comparison of models
Authors: Stephens Philip A. , Frey‐Roos Fredy , Arnold Walter , Sutherland William J.
Published: March 2003

Overexploitation is a major threat to the persistence of many species. A wide variety of approaches to setting ‘sustainable’ quotas for exploitation exist but there are major discrepancies between theory and practice, and only limited integration between different branches of exploitation literature. Here, we bring together and compare the efficacy of a range of different approaches to estimating sustainability.

A simulated population of a social mammal was used to provide data for, and compare the recommendations of, 10 widely used estimators for setting levels of sustainable exploitation. Estimators tested included four methods for setting sustainable levels of constant‐effort harvesting, two approaches to assessing the sustainability of constant‐yield harvesting, and four systems for setting thresholds below which harvesting should cease.

The method used to fit catch per unit effort data to a stock dynamic model had an important influence on the variance of recommendations. Recommendations were also affected by the length of data set available and the frequency of changes in exploitation effort. Observation‐error estimators were more consistent and more conservative than equilibrium, effort‐averaging and process‐error approaches. Harvesting at the point of maximum productivity was found to be unstable in a noisy system, suggesting the need for considerable caution when using any of these estimators.

Constant‐yield indices, developed for use in the bush meat trade, overestimated the point at which exploitation was likely to become highly unsustainable. Sociality was an important factor underlying this finding and the assessment of sustainability in constant‐yield systems should give consideration to the effects of different social systems.

Overall, threshold‐harvesting systems provided the highest mean yields in relation to extinction risk. However, the introduction of error into these systems, particularly in the form of less frequent censuses, greatly increased both variance in yields and risk of extinction.
Habitat diversity in forest plantations reduces infestations of the pine stem borerDioryctria sylvestrella
Authors: Jactel H. , Goulard M. , Menassieu P. , Goujon G.
Published: March 2003

The risk of pest damage in forest monocultures is a growing concern as the area of plantation forest expands world‐wide and sustainable management is becoming a general goal. Numerous studies have demonstrated that pest insects are less abundant in more diverse agroecosystems, but limited experimental evidence exists for a similar relationship in forestry. Because plantation forests are usually mosaics of single‐species stands, the aim of this study was to test the effect of forest diversity at a landscape level on pest insect infestations.

Within a stand of maritime pine, trees attacked by the stem borerDioryctria sylvestrellashowed no spatial aggregation and clusters of 66 trees proved to be an optimal sampling unit for determining overall percentage infestation.

The spatial distribution of stem borer infestation levels was examined in three maritime pine stands bordered by mixed‐species stands of broad‐leaved trees, and overall infestation levels compared between four such maritime pine stands and four other maritime pine stands of the same structure but far from any broad‐leaved stands.

The percentage of trees infested was significantly lower in the pine stands bordered by broad‐leaved stands than in the pine stands surrounded by other pine stands, and in the former, stem borer infestation showed a significant logistic increase with distance from the stand edge. This could be due to effects of resource concentration or natural enemy attack, both of which are discussed.

These results suggest that the conservation or restoration of non‐productive mixed‐species stands adjacent to intensively managed plantations is a useful preventive method for pest management in forest monocultures.
Great tits can reduce caterpillar damage in apple orchards
Authors: Mols Christel M. M. , Visser Marcel E.
Published: March 2003

The potential contribution of vertebrate predators to biological control in orchards has been largely overlooked to date. A few studies have shown that birds reduce numbers of pests, but data are scarce on the effects on the pattern or timing of damage. Consequently, the practical value of birds as biocontrol agents remains unclear.

This study considered whether great tits Parus major can reduce caterpillar numbers and fruit damage by caterpillars, and increase biological yield, in an experimental orchard of apple trees with high caterpillar numbers. The outcome would depend on the coincidence of the period during which great tits forage and the period during which caterpillars cause damage. In the first experiment nets were put over trees at different times of the growing season, thus creating different periods during which great tits had access to the trees. In the second experiment caterpillars were removed from trees at different times in the growing season. In both experiments, the resultant caterpillar damage to apples was assessed in the autumn.

The longer the period of foraging by great tits, from the start of egg incubation until fledging of young, the less the overall pest damage to fruit. Damage caused by caterpillars was greater the later they were removed, from the young apple stage onwards.

The effect of great tits on caterpillar damage to apples was small (percentage damage was reduced from 13·8% to 11·2%) but significant (P < 0·05), and the yield of fruit increased significantly (from 4·7 to 7·8 kg apples per tree, P < 0·05). The only cost to the producer was that of erecting nest boxes (c. 2 ha−1) to encourage great tits to breed in the orchard. Depending on the great tits’ numeric response to insect densities, their relative impact may be greater at lower densities more typical of commercial orchards and, if so, the presence of breeding great tits may allow economic thresholds for other controls to be reduced. Furthermore, the contribution of natural predators to biological control of insect pests may be especially useful in orchards and in the future when a further reduction of pesticide use may be enforced.
Amplification of RNA by NASBA allows direct detection of viable cells of Ralstonia solanacearum in potato
Authors: Bentsink L. , Leone G.O.M. , Van Beckhoven J.R.C.M. , Van Schijndel H.B. , Van Gemen B. , Van Der Wolf J.M.
Published: March 2003

Aims: The objective of this study was to develop a Nucleic Acid Sequence Based Amplification (NASBA) assay, targeting 16S rRNA sequences, for direct detection of viable cells of Ralstonia solanacearum, the causal organism of bacterial wilt. The presence of intact 16S rRNA is considered to be a useful indicator for viability, as a rapid degradation of this target molecule is found upon cell death. Methods and Results: It was demonstrated by RNase treatment of extracted nucleic acids from R. solanacearum cell suspensions that NASBA exclusively detected RNA and not DNA. The ability of NASBA to assess viability was demonstrated in two sets of experiments. In the first experiment, viable and chlorine-killed cells of R. solanacearum were added to a potato tuber extract and tested in NASBA and PCR. In NASBA, only extracts spiked with viable cells resulted in a specific signal after Northern blot analysis, whereas in PCR, targeting 16S rDNA sequences, both extracts with viable and killed cells resulted in specific signals. In the second experiment, the survival of R. solanacearum on metal strips was studied using NASBA, PCR-amplification and dilution plating on the semiselective medium SMSA. A positive correlation was found between NASBA and dilution plating detecting culturable cells, whereas PCR-amplification resulted in positive reactions also long after cells were dead. The detection level of NASBA for R. solanacearum added to potato tuber extracts was determined at 104 cfu per ml of extract, equivalent to 100 cfu per reaction. With purified RNA a detection level of 104 rRNA molecules was found. This corresponds with less than one bacterial cell, assuming that a metabolically active cell contains ca 105 copies of rRNA. Preliminary experiments demonstrated the potential of NASBA to detect R. solanacearum in naturally infected potato tuber extracts. Conclusions: NASBA specifically amplifies RNA from viable cells of R. solanacearum even present in complex substrates at a level of 100 cfu per reaction. Significance and Impact of the Study: The novel NASBA assay will be particularly valuable for detection of R. solanacearum in ecological studies in which specifically viable cells should be determined.
Environmental change over two decades since dredging and excavation of the lower Boro River, Okavango Delta, Botswana
Authors: Ellery W. , McCarthy T.
Published: March 2003

The Okavango Delta, southern Africa's largest wetland, is situated on the fringe of the semi‐arid Kalahari Desert. It is a large alluvial fan, occupying a graben structure which is an extension of the East African Rift system. Of the 16 km3 of water which enters the Delta each year, 96% is lost to the atmosphere by evapotranspiration, 2% to groundwater and only 2% leaves as surface flow. In order to increase surface outflow to meet human needs, the distal Boro channel–floodplain system was dredged, excavated and bunded between 1971 and 1974. The immediate impact of these measures was the destruction of in‐channel flora. After 20 years, the aquatic flora has recovered in the excavated channel. However, little recovery has occurred along the channel reach which was dredged. Moreover, there has been significant encroachment of terrestrial species onto the floodplain in the region of the dredged channel. In addition, dredging created a nick point which has been migrating upstream by headward erosion since dredging ceased. The average rate of advance of the nick point has been about 500 m per year. Incision associated with nick point migration has produced a channel which is indistinguishable in form from the dredged channel and, like the dredged channel, is almost completely devoid of in‐channel aquatic flora. The adverse environmental impact of dredging has therefore continued to propagate in an upstream direction, although the height of the nick point has decreased, suggesting a natural attenuation process. This is likely to result in eventual elimination of the nick point.
Species richness patterns of amphibians in southwestern Ontario ponds
Authors: Hecnar Stephen J. , M'Closkey Robert T.
Published: March 2003

Abstract. In southwestern Ontario amphibian species richness (α‐diversity) was investigated at 180 ponds from 1992 to 1994. Patterns of species richness were compared among regions and the relationship between species richness and local habitat and regional landscape variables was investigated. Patterns of incidence differed among regions, with species that use woodlands being rare in one of the regions. Repeated measures analysis of variance indicated that species richness differed significantly among regions but not among sub‐regions nested within regions. Species richness did not change significantly over time and there was no region by year effect. Species richness was highly correlated with local variables related to fish predation and to regional variables related to forest cover. Multiple regression indicated that a combination of local and regional variables best accounted for the variance in species richness, but the amount of regional woodlands was the single most important variable. The pattern of species richness can be explained by historical deforestation as the primary process.
Litterfall dynamics in a mixed conifer‐angiosperm forest in northern New Zealand
Authors: Enright N. J.
Published: March 2003

Litterfall in a mixed conifer‐angiosperm temperate forest in northern New Zealand was traced for 5 years to determine the patterns of litter production and turnover for conifer and angiosperm components of the forest. Basal area and above‐ground biomass was shared approximately equally between conifer (mostlyAgathis australis;New Zealand kauri) and angiosperm species (plus tree ferns). The five‐year mean annual litterfall, excluding macro‐litter, was 7.76± 0.39(SEM) t ha−1and ranged from 6.77±0.70 t ha−1in 1983–4 to 8.79±1.00 t ha−1in 1987–8. Mean monthly litterfall showed a strong seasonal pattern with low rates in winter and early spring, increasing to a peak in early autumn. There were major differences in the nature and timing of litterfall between the conifer and angiosperm fractions. Angiosperm leaf litter reached a maximum in early summer, while conifer litterfall showed highest rates for leaves, twigs and cone scales in late summer‐autumn. Conifer reproductive structures (strobili and cone scales) contributed from 13 to 21% of total litterfall, a value high relative to other temperate forests. However, conifer leaf turnover was low relative to that for the angiosperms.

Size of the microlitter store was 16.16±1.97 t ha−1prior to conifer cone fall, and 18.70±2.02 t ha−1following it, and conifer litter made up 76–78% of the total litter store. The estimated mean annual decomposition constant, k, was 0.39 overall, 0.33 for conifer leaf litter and 0.71 for angiosperm leaf litter, values which agree well with previously published rates for decomposition in this forest stand. Differences in the costs of biomass production and rates of turnover, as measured by litterfall and decomposition, may help to explain the functional coexistence of conifers and angiosperms in mixed forests.
Biogeography of the marine birds of a confined sea, the Mediterranean
Authors: Zotier Richard , Bretagnolle Vincent , Thibault Jean‐Claude
Published: March 2003

AimThe Mediterranean sea is a winter productive oligotrophic basin where Atlantic water replaces water lost through evaporation, this influx being a major source of productivity and fertility. The long coastlines and the large number of islands cause high oceanographic heterogeneity. Moreover, during its geological history, it has dried out several times. So we describe the consequences of these particular features on species richness, distribution, and breeding ecology of marine birds.

LocationThe Mediterranean sea (including the Black Sea and the Sea of Azov) communicates with the Atlantic Ocean only through a 14 km wide channel (Straits of Gibraltar), and since 1869, with the Red Sea through the Suez Canal.

MethodsThe Mediterranean was subdivided into different areas, according to physical oceanographic entities and productivity, linked to numbers and distribution of both breeding and wintering marine birds (defined as species strongly dependent on marine resources, breeding only on islands and/or the coastline).

ResultsThe total marine bird biomass, and species diversity, are lower in the Mediterranean than in the near Atlantic. The eastern Mediterranean, with lowest primary productivity, contains fewer marine bird taxa than the more productive western part. Taxa which mainly occur in the western and southern parts of the Mediterranean migrate through the Straits of Gibraltar to winter in the southern Atlantic, while those inhabiting the northern and eastern parts are sedentary, as a result of differences in species composition. Northern coastal basin communities (i.e. the Tyrrhenian and the Balearic Seas), are composed of less pelagic, and earlier breeding species, that rear chicks during the productive season. These latter taxa are actually the most typical Mediterranean taxa, in terms of endemism.

Main conclusionsThe Mediterranean marine bird community is not tropical, but rather, shows the highest affinity with the Atlantic temperate community. Its level of endemism is however high and comparable to other confined basins such as the Red Sea.
Mammalian biogeography of the Alexander Archipelago of Alaska: a north temperate nested fauna
Authors: Conroy Chris J. , Demboski John R. , Cook Joseph A.
Published: March 2003

AimA large number of studies have analysed the distribution of mammals within archipelagos, yet few have focused on islands that were heavily glaciated and subsequently colonized following deglaciation.

LocationWe explored the relative effects of island area and isolation on faunal composition based on twenty‐three mammalian taxa of twenty‐four islands of the Alexander Archipelago, Southeast Alaska.

MethodsWe used regression of log‐transformed variables and several indices of nestedness.

ResultsThese faunas showed significant nested structure using tests of nestedness and regression models. Unlike most landbridge and mainland archipelagos studied previously, isolation appears to be the primary factor determining patterns of species richness.

Main conclusionsColonization ability of particular taxa, rather than extinction, has determined this nested structure. We suggest that other higher latitude archipelagos may show similar historical patterns.
Reconstruction of early nineteenth‐century vegetation and fire regimes in the Missouri Ozarks
Authors: Batek Michael J. , Rebertus Alan J. , Schroeder Walter A. , Haithcoat Timothy L. , Compas Eric , Guyette Richard P.
Published: March 2003

Aim The purpose of this study was to reconstruct early nineteenth‐century vegetation and fire regimes to examine the role of fire, topography, and substrate interactions in shaping landscape and regional vegetation patterns.

Location Our study area was the Current River watershed of the Ozark Highlands in south‐central Missouri, USA.

Methods We combined analysis of early nineteenth‐century Public Land Survey (PLS) notes and dendrochronology‐based fire histories to reconstruct vegetation and disturbance regimes of pine‐oak (Pinus‐Quercus) woodlands.

Three methods were used to display and analyse PLS data within a Geographic Information System (GIS): (1) simple point distributions for each tree species; (2) section line descriptions of each tree species and other coded features (e.g. ‘prairie’); and (3) spatial interpolation of the point‐tree data.

Vegetation patterns were then related to geological parent material, topography, and mean fire‐return intervals from 23 sites using correlation and Canonical Correspondence Analysis (CCA).

Results The most striking patterns in the early 1800 s were extensive stands of shortleaf pine (Pinus echinata Mill.) and oak‐dominated ‘barrens’ (savanna) in the frequently burned areas south‐west of the Current River, and more mesophytic, fire‐sensitive species (red oaks (Quercus rubra L., Q. coccinea Muenchh.), maples (Acer rubrum L., Acer saccharum Marsh), eastern red cedar (Juniperus virginiana L.) in a fire shadow north‐east of the river. Several kilometre‐wide ecotones of pine‐mixed hardwood encompassed the major pineries and barrens.

Fire‐return intervals and relative dominance of several tree species were strongly correlated at both fine (3–64 km2) and coarse (> 100 km2) spatial scales. At fine scales, relative dominance of shortleaf pine increased with increasing fire frequency during 1701–1820. Relative dominance of black oak (Q. velutina Lam.), and to a lesser extent post oak (Q. stellata Wang.), decreased with increasing fire frequency. Shortleaf pine and these xerophytic oak species occurred on similar bedrock types but were strongly differentiated by fire regimes.

Main conclusions Fires exerted strong constraints on vegetation composition and patterns. Historical patterns of Native American occupancy in the region are consistent with the reconstructed vegetation and fire histories and suggest that anthropogenic fire regimes played an overriding role in the development of Ozark vegetation in the 1800s.
Fire and succession in the ultramafic maquis of New Caledonia
Authors: McCoy S. , Jaffré T. , Rigault F. , Ash J. E.
Published: March 2003

Aim This study investigates the role of fire and post fire succession in determining the structure and composition of vegetation on ultramafic iron crust soils.

Location The study was conducted in the Plaines des Lacs region of southern New Caledonia.

Methods A survey was made of eighty‐eight sites, recording floristic composition, trunk size‐class distributions, regeneration after fire, growth ring counts of Dacrydium araucarioides (Podocarpaceae) and historical information on past fires. Floristic data was ordinated using multidimensional scaling and an index of succession based on structural and historical information. A transition matrix model was developed to predict the effect of fire frequency on vegetation composition.

Results The vegetation is undergoing postfire succession from maquis to forest, after about 75 years, and eventually to rainforest. Gymnostoma deplancheanum has a key role as an early colonist that produces shade, the bulk of the litter, and forms nitrogen fixing nodules with Frankia sp. However, the open canopy of Gymnostoma and slow litter decay creates flammable conditions. Though many species resprout from rootstocks, only thirty‐nine persist through fires while 114 others colonize at later successional stages, as the litter layer and shade increase. Some early successional species are later excluded but these can persist locally in swamps and on rocky hill tops. Forest and rainforest are less flammable and the matrix model suggests that ignition frequency has a critical role in determining the abundance of maquis or forest.

Main conclusions The vegetation mosaic represents a post fire succession from open maquis to forest. Palynological and charcoal records from late Pleistocene sediments suggest that fire has been a major factor determining the development of maquis vegetation since before the arrival of humans. Recently, frequent fires have converted much of the vegetation to maquis, posing a threat to some forest species and largely eliminating rainforest from iron crust soils.
Mammalian species richness and morphological complexity along an elevational gradient in the arid south‐west
Authors: Shepherd Ursula L. , Kelt Douglas A.
Published: March 2003

AimWe examined the relationship between species richness and morphological complexity of terrestrial mammal communities along an elevational gradient.

LocationThe gradient is in the Sonoran Desert in Southern California and extends from a sand dune habitat near sea level to coniferous forest ending at >2600 m.

MethodsMorphological diversity, characterized by both size and shape of coexisting mammal species, was estimated within and between sites from projections of variables on principal components axes. Similarities among species were calculated as Euclidean distances. To tease apart size and shape, we constructed two principal component analyses: one based on log‐transformed original measurements, the other on log‐transformed proportional shape variables. To test whether species number accounted for the morphological diversity at each site we designed two null models. The models generated were random communities generated from the forty‐two‐species pool. Indices of morphological diversity for real communities were compared with the results of 500 simulations of each null model.

ResultsSpecies richness varied along the gradient, peaking in the mid‐elevation agave‐ocotillo habitat. Morphological diversity of shapes and sizes correlated strongly with species richness. Locomotor, tooth, and skull traits were all important in distinguishing among species.

Main conclusionsTwo important patterns emerged: (1) diversity of both sizes and of shapes of species within communities correlated positively with species number, and both sets of variables behaved similarly across this gradient; (2) the most species rich sites were not composed of specialists on these best places, but rather, a community of species derived from overlapping faunal groups.
Late Quaternary biomes of Canada and the eastern United States
Authors: Williams John W. , Webb Thompson , Richard Pierre H. , Newby Paige
Published: March 2003

Pollen data have been used to construct biome maps for today, 6000 14C yr bpand 18,000 14C yr bpfor Canada and the eastern United States.

The inferred modern biome distributions agree well with independent reconstructions of North American vegetation prior to European settlement. Some discrepancies between the pollen data and the modern potential vegetation are caused by post‐settlement clearing of the landscape and the consequent increase of herbaceous types in the recent pollen record.

Biome distributions at 6000 14C yr bpreflected the warmer and drier conditions then prevalent in the continental interior, but the overall position of biomes was similar to that of today. The boreal treeline in North America was not significantly north of its present position, in contrast to the 100–200 km shift reported for Siberia. At the last glacial maximum (18,000 14C yr bp), steppe and tundra were prevalent in the Midwest and north‐western Canada, and coniferous forests and woodlands grew in eastern North America. The open vegetation at 18,000 14C yr bpwas probably due to drier conditions and/or lower concentrations of atmospheric CO2.

The composition and physical structure of biomes is not constant over time. Mid‐Holocene biomes were similar in structure to those of today, but shifts in the relative importance of individual plant functional types are large enough that the physical properties of biomes, such as albedo, canopy conductance and surface roughness, are likely to have varied even during the Holocene. Last glacial maximum biomes were structurally different from their modern counterparts. The biome maps therefore may obscure significant vegetational changes in space and time during the late Quaternary.

The difference between the highest and next highest affinity scores for each sample measures how strongly affinity scores discriminate among biomes. For many biomes, the difference is not large, and affinity score ties are not uncommon, highlighting the importance of tie‐break procedures when using the biomization method.
Why are very large herbivores absent from Australia? A new theory of micronutrients
Authors: Milewski A. V. , Diamond R. E.
Published: March 2003

Aim

We propose a Megacatalyst Theory, based on the pivotal role of the micronutrients iodine (I), cobalt (Co) and selenium (Se), in answer to the body size anomaly of herbivores on different continents, and the previously unexplained absence of megaherbivores in certain environments.

Location

It is anomalous that megaherbivores are absent from Australia while present in even dry and nutrient‐poor parts of southern Africa, and that they have been exterminated from the Americas, but not south‐east Asia.

Methods

We hypothesize that I, Co and Se are micronutrients in quantity, but megacatalysts in effect, determining maximum body size and pace of life, hence whether energy is used by animals or fire. The Megacatalyst Theory suggests that the greater the reproductive rate and brain size relative to body size, the greater the probable demand for I, Co and Se.

Results

Balanced supply of I, Co and Se, within narrow tolerances, is elusive because of disparate cycles: I gravitates towards the sea, whereas Co and Se are concentrated in ultramafics and organic shales, respectively. Sufficiency of these micronutrients, at less than toxic concentrations, is vital for rapid metabolism and growth, particularly of the nervous system. Iodine controls thermogenesis, Co controls the gut fermentation supplying herbivores, and Se controls biochemical damage where both processes occur rapidly. The supply of Co allows vegetation to be metabolized instead of combusted, by promoting digestion of fibre by gut microbes. Herbivores demand I, Co and Se in greater concentrations than palatable plants necessarily contain, as an increasing proportion of energy is fermented from fibre with increasing body size. Economy of scale is limited by loss of I in urine (partly compensated by thyroid size), Co in faeces (partly compensated by gut compartments), and Se both ways.

Main conclusions

The larger the herbivore species, the more it may depend on supplementation in order to survive predation by humans. As body mass increases, Co becomes deficient before I, because it is essential for rumination, and cannot be absorbed by the skin. Moderate uplift of a fairly flat landscape sustainably supplies I from mineralized springs, and Co from rocks (and Se from both), avoiding the excess of I in the sea and the excess of Co on high mountains. Iodine and Se leached to groundwater under dry climates are inaccessible to herbivores on a continent as flat as Australia, where even kangaroos have limited fecundity and intelligence compared to southern African ruminants of similar body mass. Where springs and associated earth‐licks were available in the late Pleistocene, megaherbivores could evolve to survive the era of domestication.
Plant dispersal in boreal rivers and its relation to the diversity of riparian flora
Authors: Andersson Elisabet , Nilsson Christer , Johansson Mats E.
Published: March 2003

Aim

The paper has four major objectives: (1) to determine whether diaspore mimics accurately represent dispersal dynamics of real diaspores in a free‐flowing river; (2) to estimate distance travelled and reasons for stranding of floating diaspores along a free‐flowing river; (3) to test if species composition and seedling recruitment vary with the ability of the riverbank to trap waterborne drift; and (4) to compare diaspore dispersal in a free‐flowing river with that in a regulated river where current velocity has been reduced.

Location

The field work was conducted in two 7th‐order boreal rivers in northern Sweden, the free‐flowing Vindel River and the regulated Ume River.

Methods

We performed a series of dispersal experiments. We tested the usefulness wooden cubes of diaspore mimics for performing dispersal experiments by releasing cubes and achenes ofHelianthus annuusand compare their dispersal patterns in the free‐flowing Vindel River. We used the cubes to identify 50‐m long sections along the river with different trapping capacity, i.e. the number of stranded diaspore mimics within a 50‐m section. We then related the number of stranded diaspore mimics to the vascular plant flora, the proportions of species with long or short floating times (i.e. more than or less than 2 days, respectively), the number of seedlings, and to environmental variables within the sections. We also released wooden cubes in a run‐of‐river impoundment to determine the dispersal capacity of diaspores in a regulated river.

Results

The cubes were useful as diaspore mimics. They dispersed similarly to achenes ofH. annuus. The stranding pattern of diaspore mimics was significantly associated with water current. Species richness of vascular plants per 50‐m section increased with the number of stranded mimics. Seedling recruitment, and the proportions of species with short‐floating and long‐floating diaspores, did not vary with the number of stranded mimics. The ability of a river to transport diaspores downstream was strongly reduced by impoundment.

Main conclusions

We conclude that patterns of species richness of riparian vegetation is in part determined by the ability of the riverbank to trap waterborne diaspores, but differences in floating ability among species did not affect the species composition along free‐flowing rivers.
Does the phylogeny of pelomedusoid turtles reflect vicariance due to continental drift?
Authors: Noonan Brice P.
Published: March 2003

Aim

The turtle hyperfamily Pelomedusoides has been long regarded as one of the best reptilian examples of the shared biological history of Africa and South America, and of vicariance due to continental drift. The currently accepted phylogeny of the Pelomedusoides is based on morphological and serological evidence. This study uses molecular data to examine the relationships within the Pelomedusoides and tests the hypothesis that the speciation within this group was caused by the separation of the Gondwanan continents.

Methods

Phylogenetic analysis of 921 bp of 12S and 16S mitochondrial rRNA obtained from GenBank.

Results

Our analysis resulted in a well‐supported phylogenetic hypothesis for the extant Pelomedusoides that does not agree with previous hypotheses based on morphology and serology. The new hypothesis of pelomedusoid relationships is (Pelusios + Pelomedusa) (Peltocephalus[Erymnochelys + Podocnemis]). The molecular evidence supports the monophyly of the Podocnemidae and Pelomedusidae of de Broin (1988). However, the relationships within the Podocnemidae differ in that the Madagascan Erymnochelys is the sister taxon of the neotropical Podocnemis.

Main conclusion

This result is in conflict with the hypothesis of pelomedusoid speciation being a result of the continental drift of South America and Africa/Madagascar, with the separation of those three continents resulting in three separate evolutionary groups. Based on an extensive fossil record, the Pelomedusoides are known to have been a wide‐ranging group. This latest phylogenetic hypothesis, combined with that of Meylan (1996) for the Pelomedusoides, suggests that current pelomedusoid distributions and relationships could be the result of large‐scale extinctions with extant taxa being relicts of this widespread group.
Effects of postsettlement human activities on forest composition in the north‐eastern United States: a comparative approach
Authors: Bürgi Matthias , Russell Emily W. B. , Motzkin Glenn
Published: March 2003

Aim

This study compares human impacts and forest ecosystem response across geographical regions. Such a comparison allows us to evaluate the relationship between regional changes in forest composition and regional patterns of human activity.

Location

Four study areas in the north‐eastern USA were investigated, two of which were dominated by oak‐pine forests at the time of European settlement (Central Massachusetts, MA; Pike County, PA), and two of which were dominated by beech and hemlock (South Berkshire, MA; Wayne County, PA).

Methods

Trees recorded in early land survey records were compiled and compared with data on modern forest composition obtained from recent forest inventories. To assess the similarity of the four regions with regard to species composition, Euclidean Distances (ED) were calculated between the colonial and modern forest composition for each of the four regions. Information about the history of human impacts in the four study regions was used to interpret the changes in forest composition.

Results

General changes in forest composition through the historical period include a decline in beech, hemlock and chestnut, and an increase in maple and birch. Changes in pine and oak were minor by comparison. Supraregional human impacts are generally linked with supraregional trends in species composition, whereas regional patterns of land use caused regional patterns of change in species composition.

Main conclusions

These results suggest that human activities do not necessarily lead to more similar species composition between regions, especially if these activities show clear spatial patterns at about the same resolution that species composition is evaluated. Comparing species‐specific changes in forest composition with species‐specific human activities on the same spatial scale is crucial in order to evaluate human impacts on ecosystems and to make more robust generalizations about the temporal dynamics of landscapes.
Molluscan successions from two Holocene tufas near Northampton, English Midlands
Authors: Meyrick R.A. , Preece R.C.
Published: March 2003

Aim

To investigate the molluscan successions from two Holocene tufa sequences in the English Midlands to establish whether similar patterns of colonization occur and to document how they relate to other successions reported from southern Britain and elsewhere.

Location

Courteenhall and Weston Favell near Northampton, English East Midlands.

Methods

Close serial sampling and quantitative analyses have allowed detailed faunal successions to be reconstructed for each site. Radiocarbon dating ofCepaeashells by AMS has provided a chronology for each site.

Results

Remarkable similarities were found to exist between the two sites. The record from Courteenhall extended back to the end of the Devensian late‐glacial and continued until about 6000 yr BP. The sequence from Weston Favell was shorter, commencing at the beginning of the Holocene and ending about 7500 yr BP. Both successions show a progressive replacement of open country assemblages by those of woodland. At Courteenhall arctic‐alpine species, such asColumella columella(Martens) andVertigo genesii(Gredler), were present in these early open‐ground communities. Both sites supported extremely rich (> 30 species) land snail assemblages during the mid Holocene. This richness cannot be matched at any single site in Britain today. These mid Holocene assemblages include species such asSpermodea lamellata(Jeffreys),Leiostyla anglica(Wood) andVertigo alpestrisAlder that are rare or absent today in southern Britain.Discus ruderatus(Férussac), which has a modern boreo–montane range, occurred at Courteenhall between about 9700 and 8750 yr BPbut was also present in two consecutive samples just below a level dated at about 7000 yr BP, its latest known occurrence in Britain. These assemblages have no modern analogue because the ranges of several species (e.g.Discus ruderatusandLeiostyla anglica) never overlap today.

General conclusions

During the Holocene land snails appear to have colonized southern Britain in a relatively ordered sequence. The history of some species is unpredictable and they may occur at different sites at different times. For others, the general pattern shows greater consistency, enabling the recognition of a series of mollusc zones applicable over large areas of southern Britain. These Northamptonshire sites also contribute to the debate surrounding the notion of a ‘late Holocene tufa decline’. Tufa formation began unusually early (c. 10,280 yr BP) at Courteenhall but it had ceased to form at both sites by 6000 year (maybe by 7500 yr BPat Weston Favell). There is no evidence for late Holocene tufa formation at either site, a pattern consistent with many other British sites. Rates of tufa growth from 2.7 to 7.0 cm 100 years–1, calculated from the radiocarbon dates from Courteenhall, are comparable with accumulation rates established from other Holocene tufas.
A contribution to the discussion of biota dispersal with drift ice and driftwood in the North Atlantic
Authors: Johansen S. , Hytteborn H.
Published: March 2003

Aim

The present work aims to review the early proposed hypothesis of biota dispersal by driftwood and drift ice.

Location

The North Atlantic region.

Methods

New knowledge gained about drift ice patterns and sources and transport routes of ice‐rafted debris and dendrochronologically dated driftwood is used to investigate chance dispersal of diaspores. In addition, the extremely disjunct distribution patterns of some vascular plants in Scandinavia and East Greenland are examined in the light of this new data.

Results

Both drift ice and driftwood are thought to be important in the chance dispersal of diaspores from Siberia and North‐west Russia to parts of the North Atlantic region, in the Late Weichselian or early Holocene. It is proposed that the extremely disjunct distribution of some vascular plants in northern Scandinavia and East Greenland (e.g. Draba sibirica, Oxytropis deflexa ssp. norvegica, Potentilla stipularis and Trisetum subalpestre) are examples of this type of long‐distance dispersal.

Main conclusions

The concentration of extremely disjunct distributed vascular plant species in parts of northern Norway and East Greenland is suggested to relate to the Late Weichselian ice free conditions and the topography and exposure of the coastline in these areas, allowing accumulation of ice‐rafted debris and driftwood. A systematic survey of debris samples obtained from drift ice and driftwood trees is needed to evaluate the significance of these vectors for dispersal of biota to the North Atlantic region.
Genetic diversity in New Zealand Galaxias vulgaris sensu lato (Teleostei: Osmeriformes: Galaxiidae): a test of a biogeographic hypothesis
Authors: Wallis Graham P. , Judge Karen F. , Bland Julie , Waters Jonathan M. , Berra Tim M.
Published: March 2003

Aim

To test whether a geologically recent region with low endemism shows low genetic diversity in a freshwater fish species complex, in contrast to an adjacent area with high diversity. The low endemism is generally postulated to be the combined effect of Pleistocene glaciations and the unstable nature of the recent gravel outwash from young mountains to the west. This rock aggradation has formed a plain, crossed by several braided rivers. The faunas of these rivers have the potential to interchange through flooding or course changes.

Location

Southern and central South Island, New Zealand (NZ). We define the boundary of these two biogeographical regions as the Waitaki River, the most southerly braided river. To the north lies the Canterbury Plain, formed from coalesced alluvial fans; to the south is the Otago peneplain and associated mountain ranges.

Methods

Previous work has revealed considerable genetic structuring in the stream‐resident fish Galaxias vulgaris Stokell sensu lato, including a species complex in the southern region of South Island, NZ. Using isozyme electrophoresis, we have now examined genetic variation among a total of 58 samples of non‐migratory river galaxias from 24 river systems in South Island: 16 in the central region and eight to the south.

Results

Whereas samples from the central region do exhibit significant genetic structuring (Wright’s FST=0.331), they are more genetically homogeneous (mean Nei’s D= 0.032) than populations to the south of the Waitaki River (FST=0.826, mean D=0.374).

Main conclusions

The results concur with our expectations of differences between the central and southern regions. We suggest that the divergence in the south reflects geological stability, whereas relatively shallow divergences within the central region reflects the more recent formation of the Canterbury Plain and its unstable braided rivers. The genetic structuring of this group has been promoted by the absence of the marine juvenile phase that is found in five other members of the genus native to NZ. This diversity of the southern region mirrors its diverse flora and invertebrate fauna, and has conservation implications that parallel those resulting from our improved knowledge of the NZ herpetofauna through the application of genetic analysis.
Regional gradient analysis of freshwater biota: do similar biogeographic patterns exist among multiple taxonomic groups?
Authors: Heino Jani
Published: March 2003

Aim

To examine if different groups of freshwater organisms show concordant distribution patterns at large spatial scales.

Location

Northern Europe: Denmark, Sweden, Norway, Finland.

Methods

I analysed provincial distribution records of macrophytes, dragonflies, stoneflies, dytiscid beetles and teleost fishes in northern Europe. I conducted multivariate analyses, including two‐way indicator species analysis (TWINSPAN), canonical correspondence analysis (CCA) and Mantel test to reveal biogeographical patterns and the degree of concordance in the distribution patterns among taxa.

Results

TWINSPAN and Mantel tests indicated that broadly similar biogeographical patterns existed among the taxonomic groups. The results of CCA confirmed that variation in provincial species composition was generally related to climatic variation along latitudinal and altitudinal gradients. However, variation partitioning revealed that less than 50% of variation in the distribution patterns of each taxonomic group was accounted for by the climatic and geographical variables.

Main conclusions

The distribution patterns of most taxonomic groups were strongly concordant and related to provincial climate and geographical location. Such patterns suggest that large‐scale factors determine not only provincial species combinations, but also express severe constraints on the composition of local communities. Therefore, these factors should also be considered in studies on the structure and conservation of local freshwater systems.
Panbiogeography from tracks to ocean basins: evolving perspectives
Authors: Grehan John R.
Published: March 2003

Misconceptions arising from efforts to translate panbiogeography into terms used in other biogeographic and evolutionary theories are discussed with respect to Cox’s (1998, Journal of Biogeography, 25, 813–828) critique of panbiogeography. Croizat’s rejection of ‘Darwinian dispersal’ applies only to efforts to utilize this concept as a general explanation for biogeographic patterns. The conceptual difference between distribution and panbiogeographic dispersal maps is illustrated to show that Croizat did not synonymize distribution and dispersal. Croizat’s position on continental drift and plate tectonics does not support Cox’s (1998) claim that Croizat ‘for a long time’ refused to accept the theory of plate tectonics. The methodological relationship between panbiogeographic analysis and geology suggests an independence of methodology that prevents geological theory from falsifying panbiogeographic predictions. Panbiogeographic predictions for the eastern Pacific are shown to be in agreement with current historical geological models. Claims by Cox (1998) that the panbiogeographic method is variable and questionable are evaluated with respect to the biogeographic homology of primitive frogs, ratite birds, and southern beeches to demonstrate the consistent application of minimal distance, main massing, phylogenetic affinity and baseline criteria. Panbiogeographic classification concepts are contrasted with the Darwinian system (supported by Cox) utilizing a concept of unitary geographical area based on the language of Roman military rule. Inconsistent positions expressed in recent critiques of panbiogeography may indicate an underlying and implicit acceptance of the empirical and theoretical progress generated by panbiogeography within modern biogeography.

‘The formation of groups has an invigorating effect in all spheres of human striving, perhaps mostly due to the struggle between the convictions and aims represented by the different groups’ (Einstein, 1938. Collier’s, 26 November).