Showing papers in "Journal of Biogeography in 1997"

Functional groups and patterns of organization in North American ant communities: a comparison with Australia

Abstract: Ant distribution and behavioural dominance is examined at nine sites along an elevational gradient (1400–2600 m) in south eastern Arizona, in order to classify North American species according to a functional group scheme used extensively in Australia. The functional groups are then used as a basis for determining patterns of community structure along the environmental gradient, and for comparing community structure between Australia and North America. Quantitative information on species com- position was obtained from pitfall traps, and patterns of ant abundance at tuna baits were used to determine relative behavioural dominance among taxa. A total of eighty-three species from twenty-eight genera was recorded along the elevational gradient, with site species richness ranging from four (high elevation Douglas fir forest) to thirty-three (mid elevation oak–juniper woodland). There was a strong correlation between ant abundance and richness, which was not an artefact of sampling intensity. The most common ants were species of Forelius, Monomorium, Crematogaster and Pheidole at the three desert sites, species of Formica, Pheidole and Crematogaster at the three woodland sites, and species of Prenolepis and Formica at one forest site. No species were abundant at two other forest sites. The most common species in traps also tended to be the most common species at baits. In terms of behavioural dominance, highly competitive ants included species of Solenopsis, Forelius, Monomorium and Liometopum. Species of Pheidole and Crematogaster tended to be moderately competitive, whereas species of Dory- myrmex, Myrmica, Camponotus and Formica (fusca gp) had low competitive ability. On the basis of these results and on published records of other taxa, North American ants were assigned to functional groups as follows (major taxa only given here): Dominant Dolichoderinae—Forelius, Liome- topum; Subordinate Camponotini—Camponotus; Hot Climate Specialists—Pogonomyrmex, Myrmecocystus; Cold Climate Specialists—Formica (rufa, exsecta and microgyna groups), Leptothorax, Stenamma, Lasius, Prenolepis; Cryptic Species—Smithistruma, Solenopsis (subgenus Diplorhop- trum), Acanthomyops; Opportunists—Formica (fusca group), Myrmica, Paratrechina, Dorymyrmex; Generalized Myr- micinae—Pheidole, Crematogaster, Monomorium; Specialist Predators—no major taxa. Functional group composition varied systematically along the elevation gradient: Dominant Dolichoderinae, Generalized MyrAmicinae and Hot Climate Specialists were predominant at desert sites; Generalized Myrmicinae and Opportunists were predominant at woodland sites; and Opportunists and Cold Climate Specialists were predominant at forest sites. These patterns are consistent with published studies from elsewhere in North America. Almost all North American taxa can be matched with what appear to be ecologically equivalent taxa in Australia, and biogeographic patterns of functional group composition are broadly similar across the two continents. The major differences are that Australian ant communities are far richer in species, and are almost always dominated by dolichoderines, particularly species of Iridomyrmex. Generalized myrmicines are subdominant to dolichoderines in Australia, but are the behaviourally dominant ants throughout the warmer parts of North America. In cool-temperate North America, species of Formica (especially rufa and exsecta groups) are behaviourally dominant, as they are throughout the Palearctic. Some major features of the North American fauna can be linked to its poor representation of Dominant Dolichoderinae, including (1) the relatively low degree of physiological, morphological and behavioural specialization of Hot Climate Specialists; (2) behavioural dominance by formicines in cool-temperate habitats; and (3) the susceptibility to invasion by behaviourally dominant species such as the imported fire ant Solenopsis invicta and the Argentine ant Linepithema humile.

Spatial and temporal variations in boreal forest fire frequency in northern Alberta

Abstract: Spatial and temporal variations in fire frequency in the boreal forest of Wood Buffalo National Park (WBNP) were assessed using forest stand age, fire scar and historical data. I test the hypotheses that (1) fire frequency is higher in jack pine forests and aspen forests than in black spruce forests and white spruce forests, (2) these variations in fire frequency can be related to the mean waterbreak distance (MWD) around a site and (3) fire frequency has changed over the past 300 years. The fire cycles (the time required to burn an area equal in size to the entire study area) in jack pine forests (39 years) and in aspen forests (39 years) were significantly shorter than those in black spruce forests (78 years) and in white spruce forests (96 years). The length of the fire cycle varies inversely with the MWD around a site, and the MWD was significantly higher in jack pine and aspen forests than in black or white spruce forests. It is suggested that covariations between soil type and the MWD influence, respectively, variations in forest dominant and fire frequency. A change in fire frequency at 1860 was apparent in the fire history for all of WBNP, the black spruce dominated stands, and the near and medium MWD classes. The fire cycle estimates for these classes were all significantly shorter during the period 1750 to 1859 (fire cycles=25-49 years) than they were in the period 1860 to 1989 (fire cycles = 59-89 years). The possible roles of changes in climate and aboriginal burning practices in causing the temporal change in fire frequency are discussed.

Determinants of avian species richness at different spatial scales

Abstract: Studies of factors influencing avian biodiversity yield very different results depending on the spatial scale at which species richness is calculated. Ecological studies at small spatial scales (plot size 0.0025-0.4 kM2) emphasize the importance of habitat diversity, whereas biogeographical studies at large spatial scales (quadrat size 400-50,000 km2) emphasize variables related to available energy such as temperature. In order to bridge the gap between those two approaches the bird atlas data set of Lake Constance was used to study factors determining avian species diversity at the intermediate spatial scales of landscapes (quadrat size 4-36 kM2). At these spatial scales bird species richness was influenced by habitat diversity and not by variables related to available energy probably because, at the landscape scale, variation in available energy is small. Changing quadrat size between 4 and 36km2, but keeping the geographical extension of the study constant resulted in profound changes in the degree to which the amount of different habitat types was correlated with species richness. This suggests that high species diversity is achieved by different management regimes depending on the spatial scale at which species richness is calculated. However, generally, avian species diversity seems to be determined by spatial heterogeneity at the corresponding spatial scale. Thus, protecting the diversity of landscapes and ecosystems appears to ensure also high levels of species diversity.

Climatic influences on fire regimes along a rain forest‐to‐xeric woodland gradient in northern Patagonia, Argentina

Abstract: Influences of annual climatic variation on fire occurrence were examined along a rainfall gradient from temperate rainforest to xeric woodlands in northern Patagonia, Argentina. Fire chronologies were derived from fire scars on trees and related to tree-ring proxy records of climate over the period 1820-1974. Similarly, fire records of four Patagonian national parks for the period 1940-1988 were compared to instrumental weather data. Finally, the influences of broad-scale synoptic weather patterns on fire occurrence in northern Patagonia were explored. Fire in Nothofagus rainforests is highly dependent on drought during the spring and summer of the same year in which fires occur and is less strongly favoured by drought during the spring of the previous year. The occurrence of fire in dry vegetation types near the steppe ecotone is less dependent on drought because even during years of normal weather fuels are thoroughly desiccated during the dry summer. In xeric Austrocedrus woodlands, fire occurrence and spread are promoted by droughts during the fire season and also appear to be favoured by above-average moisture conditions during the preceding 1 to 2 growing seasons which enhances fuel production. Thus, in the xeric woodlands fire is not simply dependent on drought but is favoured by greater climatic variability over time scales of several years. Fire activity in northern Patagonia is greatly influenced by the intensity and latitudinal position of the subtropical high pressure cell of the southeast Pacific. Greater fire activity is associated with a more intense and more southerly located high pressure cell which blocks the influx of Pacific moisture into the continent. Although long-term changes in fire occurrence along the rainforest-to-xeric woodland gradient have been greatly influenced by human activities, annual variation in fire frequency and extent is also strongly influenced by annual climatic variation.

Ecological and biogeographical effects of forest disturbance on tropical butterflies of Sumba, Indonesia

Abstract: Butterfly assemblages within lowland monsoon forest were compared at four sites on Sumba, Indonesia that differed in terms of protection and exhibited associated differences in levels of human disturbance. A numerical method employing principal components analysis was devised for describing forest structure at each site. The first principal component (PRINI) grouped attributes tending towards dense forest with closely-spaced trees, a closed canopy and a poorly developed field layer, with trees that tended to be large with the point of inversion in the upper half of the trunk. The highest values for PRINI were recorded within protected forest, and PRINI values were considered to be a useful index of forest disturbance at each site. Species diversity of butterflies was highest in unprotected secondary forest, but was not affected by lower levels of disturbance. Those species occurring at highest density in secondary forest generally had wide geographical distributions, whereas those species occurring at highest density in undisturbed primary forest had restricted ranges of distribution, in most cases with a separate subspecies on Sumba. Overall, an index of biogeographical distinctiveness decreased with increasing disturbance, and this supports the hypothesis that the most characteristic species of undisturbed climax forest have the smallest geographical ranges of distribution. Species abundance data for butterflies fitted a log-normal distribution at all but the most disturbed site. These results indicate that the pattern of proportional abundance of tropical butterfly species may be used as an 'instantaneous' indicator of forest disturbance, and that changes in the structure of tropical forests in S.E. Asia resulting from human disturbance, even within partially-protected forest, may result in the presence of butterfly assemblages of higher species diversity but of lower biogeographical distinctiveness, and therefore of lower value in terms of the conservation of global biodiversity.

Is there an influence of historical events on contemporary fish species richness in rivers? Comparisons between Western Europe and North America

Abstract: Freshwater fish species richness on 132 West European and North American rivers is analysed using eleven variables related to contemporary ecology (nine) and history (two). This is done in order to examine the relative and joint effects of both historical and ongoing processes on the contemporary richness of these two regional fish faunas. Relationships are quantified by simple and stepwise multiple regression procedures. Species-area curves are presented for the fish faunas within both continents. We show that ecological factors statistically explain most of the variation in freshwater fish species richness for both continents. Effects of historical factors are shown to be statistically significant, but add only a little to the variance already explained by ecological factors. Our analyses further indicate that rivers (which flow directly into the ocean) support fewer species of fish than do similarly sized tributaries. The immigration-extinction hypothesis appears to provide a plausible explanation for this observed pattern. The fact that in our final model, a continental effect is still highly significant, leads us not to exclude the possibility of some other historical influences in generating different overall species richness levels on the two continents.

Factors affecting the regeneration and distribution of riparian woodlands along a northern prairie river: the Red Deer River, Alberta, Canada

Abstract: Flooding patterns and variations in the composition and successional trends of riparian vegetation in the upper and lower Red Deer River in southern Alberta, Canada, were studied in order to establish which flood regimes were most important in the regeneration and maintenance of riparian vegetation communities, with a particular focus on riparian poplars. The dominant riparian tree in the upper river is Populus balsamifera with some Picea glauca and in the lower river Populus deltoides (the plains cottonwood). Dendrochronological studies of the poplars along the river show that major periods of regeneration correspond with major flood events during the record period. Extensive cottonwood regeneration occurred in the period 1900-20, corresponding with a series of floods, some as high as the 1 in 100-year event. In addition, just prior to and during this period there was a significant reduction in use of the floodplain by bison, clearance of forests and a higher incidence of fires in upper reaches of the river and a series of high rainfall years. A series of floods greater than the 1 in 10-year flood occurred in the 1950s and stimulated the most extensive regeneration of poplars experienced since the 1920s. Parts of the lower Red Deer floodplain are now at elevations well above the 1 in 100- year flood event. It is suggested that fringe replenishment of riparian poplars is currently the dominant form of regeneration and that the large stands of mature poplars found on the floodplain, initiated during the end of the last century and first decades of this century, are unlikely to be replaced unless large floods (>1 in 50-year events) occur again. Construction of the Dickson Dam above the city of Red Deer in 1983 has led to attenuation of floods and a reduced likelihood that extensive flooding and poplar regeneration will occur again. A number of recommendations are made regarding flow management to both retain the fringe regeneration of poplars currently occurring and to stimulate more widespread regeneration of poplars on the floodplain.

Seasonal dynamics of Mediterranean pasture seed banks along environmental gradients

Abstract: The size and dynamics of seed banks were studied in grazed and ungrazed Mediterranean pastures at different altitudes and topography positions. The soil samples were collected in autumn and spring and the seed banks composition was determined by greenhouse germination over a 9-month period. The percentage of bare ground and the presence of new seedlings were recorded monthly from October to July in the field. A fall in seed density and species richness in the banks and a tendency for seeds to remain in the banks were linked to a rise in altitude. Germination in lower pastures mainly occurred in October in the numerous gaps left by the summer drought. At higher altitudes, the scarcity of gaps and the harsh climate led to an autumn–spring segregation of germination. On a local scale, the low slope positions and the ungrazed plots had a larger number of persistent seed bank species and a lower percentage of bare ground where seeds could germinate than their respective plots in the upper positions and grazed plots. A higher seed density in ungrazed than grazed plots was only detected in the three highest plots. No seed bank species richness trend was detected. In populations of the same species in different types of environments, the seasonal variation of seed numbers was environment-dependent for the majority of the species. In general, perennial grassland and its related low gaps availability appear to favour persistent seed banks. Se estudian las diferencias en el tamano y dinamica de los bancos de semillas de pastizales Mediterraneos sometidos o no a consumo por herbivoros en diferentes altitudes y posiciones topograficas. Se determino el tamano y composicion de los bancos de semillas mediante la toma de muestras de suelo en otono y primavera y conteo de las germinaciones en invernadero por un periodo de 9 meses. Ademas se registro mensualmente en el campo el porcentaje de suelo desnudo y de germinaciones en el periodo de Octubre a Julio. El aumento de altitud esta asociado a una disminucion de la densidad de semillas y de la riqueza de especies de los bancos y a la tendencia de las semillas a persistir en los bancos. En los pastizales mas bajos la germinacion ocurre fundamentalmente en Octubre, en los numerosos huecos dejados por la sequia estival. A mayores altitudes se observa una segregacion de la germinacion entre los periodos de otono y primavera que esta relacionada probablemente con la baja disponibilidad de huecos y con la dureza climatica invernal. A escala local, las zonas bajas de las laderas y las privadas del consumo por herbivoros presentan un mayor nuAƒÂƒmero de especies con banco persistente y un menor porcentaje de suelo desnudo que sus respectivas zonas altas de ladera y zonas pastoreadas. A esta escala no se observa ninguna tendencia respecto a la riqueza de especies en los bancos de semillas y solo se detecta una mayor densidad de semillas en las zonas clausuradas frente a las pastoreadas en las tres posiciones mas altas del gradiente altitudinal. La variacion estacional en el nuAƒÂƒmero de semillas de poblaciones de diferentes ambientes resulto ser dependiente de estos para la mayoria de las especies. En general se observa que el aumento de herbaceas perennes, relacionado con la baja disponibilidad de huecos, parece favorecer la existencia de bancos persistentes.

Vegetation dynamics in central Africa since 18,000 yr BP: pollen records from the interlacustrine highlands of Burundi, Rwanda and western Uganda

Abstract: A standardized analysis of palaeoecological data, in the form of six pollen sequences and forty- four radiocarbon ages, has permitted a region-wide reconstruction of Late Quaternary vegetation dynamics for the interlacustrine highlands of central Africa. A landscape widely dominated by ericaceous scrub and grasslands, but also supporting sparse patches of open-canopied montane forest, possibly in those areas with a topography most favourable to the growth of trees, is indicated for the last glacial maximum of 18,000 yr bp. Major expansions in the extent of upper altitudinal forms of montane forest occurred from around 12,500 yr bp, while lower moist montane forest—the expected climax for much of the region today—did not become prominent until 11,000 yr bp to 10,000 yr bp. From the palaeoecological evidence at least, it appears that the major east Central forest refuge, proposed by some workers on the basis of current species’ distribution patterns, did not extend to the eastern flanks of the Albertine Rift. A late glacial–early Holocene transition is only fully chronicled in two of the sites. However, it appears that the expansion of lower montane forest had a time-transgressive pattern across the region, and was not simply from low to high altitude. The composition of forests during the early Holocene appears to have been different to that in the later stages of the present interglacial, as taxa presently associated with wetter and/or more open forest types were much more common. Pollen data also indicate that higher altitude parts of the interlacustrine highlands were more attractive to the earliest (possibly Bantu-speaking) farmers and metal-workers. There is evidence of wide-spread forest clearance around the beginning of the present millennium, possibly as a result of substantial changes in socio-economic conditions, and patterns of settlement, associated with the onset of the Late Iron Age.

Regeneration of planted conifers across climatic moisture gradients on the Canadian prairies: implications for distribution and climate change

Abstract: The influence of dry climates on white spruce (Picea glauca (Moench) Voss)) regeneration was examined by conducting surveys of seedlings and small trees that had regenerated naturally at 100 farm shelterbelts and plantations in southern Saskatchewan, Canada. The sites surveyed were located along a climate moisture gradient extending from the relatively moist boreal forest, across the aspen parkland, to the semi-arid prairie grasslands. Natural regeneration was greatest at sites in the boreal forest and northern aspen parkland, decreased in the southern aspen parkland, and was negligible in the grassland zone. Furthermore, the few seedlings found in the drier zones were usually in poor condition. Similar results were obtained for the introduced Colorado spruce (Picea pungens Engelm.) and Scots pine (Pinus sylvestris L.). It is concluded that the present climate of the southern parkland and grassland is too dry to permit natural regeneration of white spruce and other conifers. If increases in atmospheric CO2 levels lead to a drier future climate in the southern boreal forest of western Canada, the ability of conifers to regenerate naturally may be significantly reduced.

Distribution of Proteus (Amphibia : Urodela, Proteidae) and its possible explanation

Abstract: Approximately 250 localities of the nominal species Proteus anguinus Laurenti 1768 have been evaluated and listed. The species is limited to the Dinaric Karst; it ranges from the Isonzo-Soĉa River in southeastern Venezia Giulia, Italy, through the southern half of Slovenia, southern Croatia, and parts of Bosnia and Hercegovina, to the Trebisnica River in eastern Hercegovina. In some regions, populations have been extinguished or endangered by pollution or human-induced hydrographical changes. The distribution of Proteus is compared with those of some cave Crustacea: Troglocaris (Crustacea: Decapoda), Monolistra, and Titanethes (Crustacea: Isopoda). The similarity of distribution patterns within this ecologically diverse assemblage supports their paleogeographic rather than ecological foundation. The paleogeographical and paleoclimatological data, in combination with the physiological requirements of Proteus, strongly suggest that these animals invaded the caves, at least in the NW parts of their ranges, only after the last glaciations, within the last 10,000 years. It is suggested that the high heterozygosity of populations can best be explained by fusion of some locally restricted immigration waves. The close morpho- logical similarity of nearly all populations of Proteus is probably due to the convergent evolution of previously differentiated populations (or even species) after their withdrawal underground. Nastetih je približno 250 nahajalisĉ moĉerila ali ĉloveske ribice (Proteus anguinus Laurenti 1768), vse so v Dinarskem krasu med Soĉo-Isonzo v severovzhodni Julijski Beneĉiji (Venezia Giulia) in Trebinjem v Hercegovini. Areal zajema majhen kosĉek sverovzhodne Italije, južno Slovenijo, južno Hrvasko, dele Bosne in Hercegovine. Ponekod so bile populacije uniĉene ali vsaj moĉno ogrožene zaradi onesnaženja ali umetnih hidrografskih sprememb. Razsirjenost moĉerila primerjam z nekaterimi jamskimi raki: jamsko kozico (Troglocaris Dormitzer; Crustacea: Decapoda), jamskimi ježki (Monolistra Gerstaecker) in jamskimi mokricami (Titanethes Schioedte; Crustacea: Isopoda). Podobni vzorci razsirjenosti znotraj te ekolosko raznolike skupine kažejo, da so pogojeni paleogeografsko in ne ekolosko. Paleogeografski in paleoklimatoloski podatki, skupaj z moĉerilovimi fizioloskimi zahtevami, kažejo, da so se te živali vselile v podzemlje, vsaj v severozahodnih delih svojih arealov, sele po zadnjih poledenitvah, torej v zadnjih 10.000 letih. Domnevam, da visoko heterozigotnost populacij zlahka razložimo z zlivanjem veĉ vselitvenih valov. Velika morfoloska podobnost med skoraj vsemi moĉerilovimi populacijami je najbrž posledica konvergentne evolucije zaradi prilagajanja na podzemlje; te so bile poprej lahko že morfolosko razliĉne, morda pa so celo diferencirane v veĉ vrst.

A comparative ecological study of Norwegian mountain plants in relation to possible future climatic change

Abstract: Mountain plants constitute an important part of the Norwegian flora. They are also believed to be the plant group in Norway most threatened by the expected climatic warming due to an enhanced greenhouse effect in the near future. In this study the distributions of 107 mountain Norwegian vascular plants were modelled in relation to present-day climate using Gaussian logit regression. Most species are found to have a surprisingly broad amplitude to mean July and January temperatures, suggesting that a 2°C increase in summer temperature and 4°C increase in winter temperature (as expected with a 2×CO2 increase) may not have a dramatic direct effect on most of the species investigated. A comparative study between estimated July and January temperature optima and tolerances and other ecological attributes such as habitat characteristics, dispersal mechanisms, range sizes and other climatic optima and tolerances was done using multivariate analysis. The results suggest that species most vulnerable to climatic warming, namely the species with narrow July and January temperature tolerances, are characterized by small range sizes and small population sizes, i.e. they are nationally rare species. Furthermore, these vulnerable species are found in all habitats along the major moisture gradient in alpine vegetation. A classification of the species into Rabinowitz's seven forms of rarity confirms that the species most vulnerable to climatic warming are characterized by being habitat specialists with a small geographic range size. Bergpflanzen machen einen bedeutenden Teil der Norwegischen Flora aus. Man nimmt auch an, dass sie die Planzengruppe darstellen, die in der naheren zukunft am meisten durch die erwartete Verstarkung des Triebhauseffekts gefahrdet ist. In der vorliegenden Studie wird mit Hilfe der Gausschen logistischen Regression ein Modell der Verteilungen von 107 norwegischen Gefaspflanzen in Verhaltnis zum gegenwartigen Klima erstellt. Die meisten Arten haben eine erstaunlich grose Bandbreite betreffend die durchschnittlige Julitemperatur. Dies last den Schlus zu, daseine Erhohung der Sommertemperatur um 2 Grad Celsius (wie sie von einer Verdeppelung des CO2-Gehalts erwartet wird) moglicherweise keinen direkten dramatischen Effekt auf die meisten der untersuchten Arten haben wird. Eine vergleichende Studie zwischen geschatzen Julitemperatur-Optima und Toleranzen und anderen okologischen Eigenschaften wie Habitatcharakteristika, Verbreitungsmechanismen, Ausbreitungsflachen, und anderen klimatischen Optima und Toleranzen wurde auf der Basis von Multivarianzanalysen durchgefuhrt. Die Ergebnisse legen den Schlus nahe, dass die Arten, die gegenuber klimatischer Erwarmung am empfindlichsten sind, namlich die Arten mit schmalen Januar- und Juli-Temperatur-Toleranzen, charakterisiert sind durch geringe Ausbreitungsflachen und kleine Populationen, mit anderen Worten die seltenen Arten. Daruber hinaus sind diese empflindlichen Arten in allen Habitaten entlang des Feuchtigkeitsgradienten in alpiner Vegetation anzutreffen. Eine Klassifikation der Arten nach Rabinowitz’ sieben Stufen der seltenheit bestatigt, das die Arten mit der grosten Empfindlichkeit gegenuber klimatischer Erwarmung Standortspezialisten mit geringer geographischer Verbreitung sind.

Larger seeds in tropical floras: consistent patterns independent of growth form and dispersal mode

Abstract: Many species of tropical moist forests have large seeds compared to those found in temperate floras. This could be attributed to a prevalence of woody growth forms, or adaptation to dispersal by vertebrates, or the dense shade of a closed canopy, rather than to an intrinsic tropical v. temperate difference. We compared tropical v. temperate seed mass data at two geographic scales; firstly within Australia between tropical, subtropical and temperate open woodlands, then between six tropical and temperate datasets from five continents. Within Australia we found that seed mass increased with decreasing latitude in ten out of eleven growth form-dispersal mode combinations: only wind-dispersed graminoids showed no significant effect. While the pattern of generally larger seeds in the tropical flora was associated with tropical families tending to have larger seeds than temperate families, we also found that tropical species had larger seeds than temperate cofamilials. As a preliminary test of the generality of these findings we included a further four tropical and temperate data sets in a second analysis. Average tropical seed masses were larger than temperate seed masses in all testable growth form- dispersal mode combinations, and statistically larger in five out of seven cases: unassisted, vertebrate- and wind- dispersed woody species, and unassisted and vertebrate- dispersed forbs. No difference was found for wind-dispersed forbs or for graminoids lacking dispersal structures. That an effect was found in these combinations rules out explanations based solely on characteristics of tropical v. temperate dispersers, although this may be a contributing factor. Instead we suggest that some aspect of tropical systems, for example higher metabolic costs of seedling production, has selected for a general increase in seed mass among tropical taxa.

Fire in the tropical gallery forests of Belize

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Plant colonization: are wind dispersed seeds really dispersed by birds at larger spatial and temporal scales?

Abstract: It is suggested that many plant species often thought of as wind dispersed may in fact be largely dispersed by animals, mostly birds, at larger spatial and temporal scales. This possibility is illustrated by using data on Holocene tree migrations in Europe. It is suggested that exploratory movements, often by young birds, may play an important role in such dispersal rather than the classic return migrations of birds. In the case of European trees there could have been active selection for rapid migrations occurring even in the glacial refugia sites in the mountains of southern Europe. Plant migration rates, and hence the ability to deal with climatic change, may have been lower before the evolution of a diverse avifanua. It is suggested that for many 'wind dispersed' seeds the wind dispersal mechanism is adapted to local dispersal (over distances of a few canopy diameters) and larger scale dispersion is due to birds.

Distribution of C3 and C4 grasses along an altitudinal gradient in Central Argentina

Abstract: The distribution pattern of C3 and C4 grasses was studied in eight sites located between 350 m and 2100 m along an altitudinal gradient in Central Argentina. Of 139 taxa fifty-nine are C3 and eighty C4. Species of the C3 tribes (Stipeae, Poeae, Meliceae, Aveneae, Bromeae and Triticeae) and C3 Paniceae species increase in number at higher elevations; only one C3 species was found below 650 m. C4 Aristideae, Pappophoreae, Eragrostideae, Cynodonteae, Andropogoneae and Paniceae increase at lower altitudes. The floristic crossover point is at about 1500 m; the ground cover cross-over point is at about 1000 m. Analysis of the relationships between % C4 species along the gradient and nine climatic and environmental variables showed the highest correlation with July mean temperature, but all temperature variables show highly significant correlations with % C4. Correlation with annual rainfall is lower but also significant. These results are consistent with previous research showing the relative importance of C4 grasses as temperature increases. C3 species make a high contribution to relative grass coverage below the C3/C4 floristic crossover point but are rare below 1000 m.

Aboriginal fire regimes in Queensland, Australia: Analysis of the explorers' record

Abstract: The record of eighteenth and nineteenth century explorers' references to Aboriginal fire in Queensland was stratified according to fourteen vegetation types and season of fire. It was demonstrated that references to 'current' fire (i.e. flames or smoke) may not represent traditional Aboriginal activity and that many fires were lit to frighten or harm, to protect themselves from, or to signal to kinfolk the presence of the European intruders. Because of this interpretational difficulty the records to 'current' fire were treated separately from 'past' fire (i.e. burnt ground). The data were analysed as the number of observations per 100 km spent in each vegetation type for any one season to compensate for bias created by differing amounts of travel. The record suggests highest frequency of burning in grassland around the Gulf of Carpentaria, relatively high fire frequency of most coastal and subcoastal vegetation types and relatively infrequent burning of inland Queensland. The analysis indicates a propensity for winter and autumn fire relative to spring and summer fire in all vegetation types combined and in most individual vegetation types.

Ecological and biogeographical studies on the tropical rain forest of south Yunnan, SW China with a special reference to its relation with rain forests of tropical Asia

Abstract: Ecological and biogeographic analyses of the tropical rain forest in south Yunnan were made using data from seventeen sample plots and floristic inventories of about 1000 species of seed plants. The rain forest is shown to be a type of true tropical rain forest because it has almost the same profile, physiognomic characteristics, species richness per unit area, numbers of individuals in each tree species and diameter classes of trees as classic lowland tropical rain forests. As the area is at the northern margin of monsoonal tropics, the rain forest differs from equatorial lowland rain forests in having some deciduous trees in the canopy layer, fewer megaphanaerophytes and epiphytes but more species of lianas as well as more species of microphylls. In its floristic composition, about 80% of total families, 94% of total genera and more than 90% of total species are tropical, of which about 38% of genera and 74% of species are tropical Asian. Furthermore, the rain forest has not only almost the same families and genera, but also the same families rank in the top ten both in species richness and in dominance of stems, as lowland forests in southeast Asia. It is indisputable that the flora of the rain forest is part of the tropical Asian flora. However, most of the tropical families and genera have their northern limits in south Yunnan and most have their centre of species diversity in Malesia. More strictly tropical families and genera have relatively lower species richness and importance compared with lowland rain forests in tropical southeast Asia. Thus, the flora also shows characteristics of being at the margin of the tropics. Based mainly on physiognomy and floristic composition the tropical rain forest of Yunnan is classified into two types, i.e. seasonal rain forest and wet seasonal rain forest, the latter is further divided into two subtypes, i.e. mixed rain forest and dipterocarp rain forest. From analysis of geographic elements it is also shown that the tropical rain forest of Yunnan occurs at a geographical nexus with its flora coming mainly from four sources, i.e. Malesia, south Himalayas, Indochina and China.

The ecology and distribution of lichens in tropical deciduous and evergreen forests of northern Thailand

Abstract: During three years of research on epiphytic lichen communities as indicators of environmental change in northern Thailand plots were set up in a range of forest types between 400 and 1600 m in 1991/2 and revisited in 1993. Other areas were visited in 1993 and collections made in a wider range of geographical, altitudinal and vegetation conditions in Thailand. From this data factors influencing the distribution of lichens in a monsoon climate are outlined and characteristic components of the lichen flora given at family, generic and where possible specific level. Dominant taxa of the montane forests include hygrophilous macrolichens of the ‘Lobarion’ that are also a characteristic component of old growth fagaceous forests in Europe, whereas the evergreen forests are dominated by moisture-dependent crustose taxa with a trentepohlioid photobiont, and the deciduous dipterocarp forests by often brightly coloured xerophytic lichens with a trebouxioid photobiont. Taxa are proposed as indicators of forest type including those that are indicators of old-growth forests and of disturbance. Quantitative recording of selected taxa at genus and species level is suggested to estimate rates of change in monsoon forests in southeast Asia.

Four centuries of forest clearance and regeneration in the hinterland of a large city

Abstract: In the last 350 years, forests of eastern North America have experienced widespread clearance and regrowth with local variation in timing and extent determined by patterns of human land use. This paper describes the history of forest in the hinterland of a large city (Wilmington, Delaware) surrounded by fertile soils and having access to a navigable estuary. Forests were cleared between 1650 and 1780 to accommodate shifting cultivation of cereal crops and to provide fuelwood for nearby cities. Proximity to urban markets supported a vigorous agricultural economy through the 19th century and delayed widespread forest regeneration. Reforestation began on a large scale following the local decline of agriculture 1920-1940. In the late 20th century, forest competes for land with suburban housing. Although a similar sequence has occurred throughout eastern North America, the study area is unique in that a -larger proportion of original forest was cleared and reforestation began much later than in other regions. Today, the history of land use is evident in the high proportion of young, successional forest and the verv small area of long-established forest.

An evolutionary framework for the polar regions

Abstract: Our knowledge of the nature, generation and maintenance of largescale biodiversity patterns is still far from complete. This is particularly so in the Southern Hemisphere and in the marine realm, where recent taxonomic investigations of Mollusca and other invertebrate groups has cast doubt upon the existence of a simple cline in species richness between the tropics and the pole. Comparatively high regional diversity values for the shelled gastropods and other epifaunal taxa implies a considerable evolutionary legacy; this is supported, at least in part, by available evidence from the fossil record. Certain families within the living gastropod fauna maintain their prominence when traced back 40 m.y., and perhaps even longer; in addition, several Southern Ocean gastropod and bivalve genera can now be traced back to at least the late Eocene. Use of a variety of refugia may have enabled many taxa to survive repeated glacial advances. As we begin to revise our concept of the nature of latitudinal diversity gradients, so we also need to examine regional variations in evolutionary rates. Clearly this is a complex issue, but recourse to a pilot study based on the molluscan fossil record suggests that there may be no significant difference between the rates of radiation of tropical and cold-temperate/polar taxa. The most diverse clades, which are all tropical, are simply the oldest. What data are available from the fossil record indicate that there is no appreciable latitudinal variation in rates of extinction either. Time, but not necessarily environmental stability, would appear to be crucial to the development of pockets of high taxonomic diversity. Recent improvement in our understanding of the biology of many polar marine invertebrates suggests that life in cold water is not an insuperable evolutionary problem. Of equal importance to any intrinsic properties of organisms which may have governed the differentiation of large-scale biodiversity patterns is the role of extrinsic processes. Foremost among these has almost certainly been repeated range shifts in response to Cenozoic climatic cycles.

Does the rare Banksia goodii have inferior vegetative, reproductive or ecological attributes compared with its widespread co-occurring relative B. gardneri?

Abstract: Banksia goodii (rare) and B. gardneri var. gardneri (widespread) are closely related rhizomatous evergreen subshrubs of south western Australian scrub-heath and woodland. B. goodii is restricted to sixteen populations, most of which are remnants on roadsides due to landscape fragmentation from agricultural activities. Bioclimatic profiles indicate that B. gardneri spans a wider range of climates than B. goodii. However, their post-fire survival and resprouting vigour, rates of seedling growth and soil penetration and susceptibility to seedling predators are similar. Both have the potential for geographic range extension, especially B. goodi. Seedlings of both species survived for at least 3 years at sites with 2 (but not 3) months shorter and 1 month longer growing seasons than experienced by natural B. goodii populations. Seedling establishment did not occur in the absence of fire and was low (1.3% of released intact seeds for B. goodii) even following en masse release of seeds after fire. Sowing of intact seeds, especially in cleared areas and with protection from herbivores, increased this to 35%. Fire survival among adults of both species was 100% following two fires. B. goodii, which roots along its rhizomes, produces ramets, while B. gardneri, with a lignotuber instead, does not. Seed production, pre-dispersal granivory and canopy seed storage are low but similar for both species, although B. gardneri has a superior level of germination. The biology of B. gardneri thus provides few insights as to why B. goodii is rare. There were no differences in topo-edaphic attributes, community structure, shading or litter cover between localized sites where either species occurred alone or together. Differences in present or prehistoric fire regimes, clearing (habitat fragmentation), susceptibility to generalist fungal pathogens, or impacts of alien invasives, cannot explain the distribution of B. goodii relative to B. gardneri. The rarity of B. goodii may be a result of its recent origin, habitat specialization (dense woodland), and the impacts of habitat fragmentation within its current range, rather than inferior vegetative, reproductive and/or ecological attributes.

On identifying common distribution patterns and their causal factors: a probabilistic method applied to pteridophytes in the Iberian Peninsula

Abstract: The aim of this quantitative biogeographical analysis is to identify the existence of specific groups of pteridophytes with significantly similar distribution patterns (chorotypes) in the Iberian Peninsula, as well as to infer the environmental factors that may explain such groupings. We have applied a classification method to the pteridophyte species and have then tested the significance of the resulting groups. This allows the distinction of groups of species that occur together more frequently than expected at random from those which are just a product of the cluster analysis. The majority of the 113 pteridophyte species in the Iberian Peninsula are not distributed independently from each other, but eighteen chorotypes exist that are common to various species and three chorotypes that consist of one species each. Five species are distributed independently of the other species, and so their distribution areas overlap and segregate from the others at random. With the aim of finding a relation between the chorotypes identified and the processes that determine them, we investigated the possible incidence of certain environmental factors on the chorotype distributions by means of logistic regression. Factors that appear most frequently as possible causes of the distribution of the chorotypes are the water availability, climatic stress, availability of environmental energy, and disturbances caused by floods.

The nature of three ancient woodland soils in southern England

Abstract: Despite a wealth of published research on the nature of woodland soils, little is known about the nature of soils on sites that have supported woodland for many hundreds of years, namely ancient woodland. The properties and variability of soils in three ancient woods; one in the New Forest, Hampshire and two in Berkshire, were compared with those under recent woods. The acidity of ancient and recent woodland soils was high and remarkably similar. Only where cultivation of soils had preceded woodland establishment was soil acidity lower. The quantity of carbon in the soils studied was inversely related to soil acidity and the ancient woods had accumulated larger quantities of carbon than their recent counterparts. The quantities of Ca 2+ , Mg 2+ and K + were larger in the ancient woods except where prior cultivation had taken place. Total and organic phosphate contents of the ancient woodland soils were also consistently larger. The nature and pattern of soil variability in ancient woodland soils was quite distinct from that found in recent woods. Overall; the variability of soil acidity, carbon content and organic phosphate was larger in the ancient woodland soils but the pattern of variability differed between the soil properties. No clear association existed between the pattern of soil acidity and individual trees. At the surface of some of the woodland soils, however, carbon distribution appeared to be associated with individual trees. At depth in the ancient woodland soils, the association with the existing vegetation cover was not so clear. It is probable that the ancient woodland soils retained relict features of previous vegetation cover. Organic phosphate distribution was very strongly associated with the present vegetation cover. The pattern of distribution of organic phosphate appeared to be stronger than that of soil acidity and carbon content.

Flightless insects: a test case for historical relationships of African mountains

Abstract: Flightless insects give a clearer view of former distribution of montane habitat in Africa compared with highly mobile animals as birds and butterflies because passive long distance transport and long distance dispersal can be discounted. Only a few species in the twenty-one genera under study are shared between neighbouring mountains which can be explained in all cases by a Pleistocene lowering of the montane habitat by 850m. Therefore a montane forest cover connecting the mountains at colder times as suggested by the pluvial theory can be refuted which is in correspondence with palynological findings suggesting a dry corridor between the mountains. No montane refuge for flightless insects can be identified, because the most species-rich mountain of a genus differs among the genera under study. Instead, each mountain served as a species refuge with a stable habitat. The requirement of a smaller habitat compared to vertebrates is indicated by endemic species on each single mountain suggesting pre-Pleistocene speciation which results even in endemic genera to one mountain. Different small patches of suitable habitat on one mountain could also explain the radiations found in some genera of flightless insects. In some genera species are lacking on Mt Kenya which indicates-with the findings of no endemic passerine bird on the mountain-a probably very dry condition during colder times. On Mt Cameroon no species of the flightless insect genera occurring on the Eastern mountains are found. This contrasts with the existing patterns of birds, grasses and butterflies.

Taxonomic diversity of the terrestrial bird and mammal fauna in temperate and boreal biomes of the northern hemisphere

Abstract: . Using comprehensive range information of northern Hemisphere birds and mammals, we assessed the taxonomic diversity of these two groups in four different regions: Europe, east Asia, and western and eastern North America. East Asia is the richest region in the number of bird and mammal species, genera, families and orders, except that mammal species richness is highest in western North America. Eastern North America is taxonomically the poorest region, but when only forest-associated taxa were considered in mammals taxonomic diversity is equally low in Europe and in eastern North America, and in birds, Europe is the least diverse region. Patterns in endemic taxa follow overall taxonomic diversity. The proportion of shared taxa between regions is higher among boreal species and genera than among all taxa. A comparison with tree species diversity underpins the role of east Asia as the most diverse of all northern biota. Largely congruent patterns at different taxonomic levels emphasizes the role of historical processes, such as differential extinction rate in response to paleoenvironmental fluctuations, in producing these patterns, but we stress the need for more research on the coevolution of species diversity and habitat diversity.

Land use and forest habitat distribution in the hinterland of(r)a large city

Abstract: The cumulative effect of many local forest disturbances can be estimated from an analysis of forest distribution at the scale of the entire landscape. To gauge the regional impact of forest clearance and regeneration, a history of forest cover was compiled for the twentieth century in the hinterland of a large city (Wilmington, Delaware, U.S.A.). Forest distribution and character were described by point sampling of historical aerial photographs. Environmental features were measured on visits to sample points in the field. Regional forest coverage has grown from c. 5% in 1890 to 22% in 1990. Most modern stands are <60 years old; only 2.5% of the modern landscape is in forest more than 100 years old. Since 1890, patterns of clearance and regeneration have caused a proportional shift in forest cover from uplands to lowlands and flood plains. Older stands are found on rock fields and steep slopes, indicating abandonment from agriculture according to the quality of local sites. Residential development has been concentrated in uplands, precluding regeneration of forest in that landscape position. In general, land use turnover reflects the character of the local site; there is no evidence of region-wide gradients of regeneration or clearance. Modern forest is concentrated along steep-sided stream valleys and away from roads. The great majority of forest lies within 50 m of a forest margin placing it in the microclimatic and vegetational edge zone. Although most forest is within 200 m of a residence, pedestrian traffic appears to have had only a minor impact in the biological community. By contrast, widespread species impoverish- ment is suggested by the overwhelming youthfulness of modern forest and the low degree of connectedness of forest within the landscape. Management for biological conservation should focus on protection of remnant primary forest, rather than relying on succession to restock secondary stands.

Importance of historical factors on species richness and composition of butterfly assemblages (Lepidoptera: Rhopalocera) in a northern Iberian mountain range

Abstract: . The butterfly assemblages of three vegetation types (pasture, heathland and rocky outcrop with Genista spp.) and two geographical orientations (a northern slope and a sheltered gorge) were studied along an altitudinal gradient in the Picos de Europa in northern Spain. In order to study the effects or historical climatic changes on current butterfly assemblages, it was examined if changes in richness and faunal composition of assemblages were joined with changes in their biogeographical composition. The three vegetation types showed characteristic butterfly assemblages, but no difference in species richness and biogeographical composition was found. Species richness in the sheltered gorge was higher than in the northern slope. Faunal composition also varied between orientations and there were more widespread and Mediterranean species in the sheltered gorge than in the northern slope. Species richness declined with increasing altitude, though a midaltitudinal peak was observed. There was a faunal segregation between high and low localities. Species richness of widespread and Mediterranean butterflies decreased as altitude increased, whereas the reverse was true for montane species. Moreover, biogeographical elements differed in their climatic tolerances measured as altitudinal ranges. Therefore, changes in richness and composition of butterfly assemblages between both slopes and along the altitudinal gradient were joined in part with variation in their biogeographical composition. These results suggest that current species richness and composition of butterfly assemblages in the Picos de Europa might be the consequence of differential colonization of refuges during the past climatic changes.

Fire in tropical dry forests: corticolous lichens as indicators of recent ecological changes in Thailand

Abstract: The distribution of lichens in lowland deciduous and evergreen forests in Thailand is used to interpret recent changes in the distribution of these forests. The role of fire in changing the forest structure, microclimate and species content is discussed. Characteristic corticolous lichen communities of dry deciduous and moist evergreen forests are described, as well as changes in the composition of the flora following fire events. Where frequent fires have altered the forest rates of change in forest type are suggested using lichen data from randomly selected trees in forest plots, and growth rates of sampled species in quadrats. The disjunct nature of the lichen floras in lowland deciduous and evergreen forests is discussed, their origin and use in interpreting changes in forest types in monsoon climates over long periods of time.