bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of topography on rainforest tree community structure and diversity in American Samoa, and implications for frugivore and nectarivore populations
Authors: Webb Edward L. , Stanfield Brooks J. , Jensen Marya L. 
Published: March 2003

Summary Aim We investigated the spatial variation of rainforest tree community structure and composition to determine if forest structure and diversity varied as a function of topography; and in turn if this could influence patterns of habitat use by native forest birds and pteropodid bats. Location The study was undertaken on the island of Tutuila, American Samoa, located in the South Pacific Ocean. Methods All trees ≥10 cm diameter were censused in sixty 200 m2 plots in ridge, slope and valley forest across the island of Tutuila. ResultsForest structure varied significantly across topographical space. Ridge forest was shortest and had the highest stem densities, and valley forest was tallest with the fewest stems per unit area. Species richness was highest on ridges, and slope and valley forest were more similar in composition with each other than they were with ridge forest. Of the fifty‐two tree species encountered in the plots, nine showed a statistical affiliation to one of the three topographical positions. Main conclusionsWe explain patterns of forest structure and diversity in the context of chronic and catastrophic disturbances. Higher stem densities in ridge forest suggested a higher degree of disturbance on ridges, and this was supported by the fact that the height/diameter ratio of the forest was lowest on ridges, which indicated wind‐cropping. We hypothesize the potential effects of topographical variation and known phenological patterns on wildlife abundances. We predict that flowering episodes of ridge‐affiliated, bird‐visited species (particularly Syzygium inophylloides (A. Gray) C. Muell.; Myrtaceae) will concentrate honeyeater densities on ridges, and that fruiting of the tree Canarium vitiense A. Gray (Burseraceae) could localize populations of the Pacific pigeon (Ducula pacifica). Overall (i.e. net) bat foraging patterns are unlikely to be affected by either flowering or fruiting events. Most of the tree species on Tutuila are generalist in their demographic patterns, and the island is depauperate in wildlife fauna; the evolutionary and conservation implications are discussed. We conclude with the argument that conservation of vertebrate species is essential to maintain the current generalist demographic patterns of Samoan trees.
Latitudinal gradients in benthic community composition in Western Atlantic estuaries
Authors: Engle V. D. , Summers J. K. 
Published: March 2003

Summary AimThe community composition of benthic macroinvertebrates from 295 estuarine sites was examined in order to either confirm or challenge established boundaries of zoogeographical provinces. We also investigated the postulate that, while local distributions were determined by natural habitat characteristics such as salinity, sediment type and depth, distributions on a large geographical scale would be correlated with temperature. LocationThe Atlantic coast of the United States (on a latitudinal gradient from 42° to 25°N). MethodsUsing the descriptive techniques of cluster analysis and nonmetric multi‐dimensional scaling, we determined the similarities in benthic community composition between sites within 1° latitudinal bands and compared the biotic ordinations to natural habitat characteristics such as salinity, sediment type and depth. We then evaluated the overall community composition within each 1° latitudinal band and established whether or not similarities existed between adjacent 1° latitudinal bands. In this manner, we were able to confirm that a latitudinal gradient existed in estuarine benthic community composition along the western Atlantic coast. This latitudinal gradient was demarcated by biogeographical boundaries at (1) Biscayne Bay, Florida, (2) the southern end of the Indian River Lagoon, Florida, (3) St John's River, Florida, (4) Cape Island, South Carolina, (5) the mouth of the Cape Fear River, North Carolina and (6) Cape Cod, Massachusetts, with a subprovince boundary just north of Cape May at Wildwood, New Jersey. ResultsThe major divisions approximated widely recognized biogeographical boundaries. Average summer water temperatures correlated better than sediment type, depth, or salinity with the latitudinal groupings of sites determined by cluster analysis. ConclusionsBased on this relationship, we speculate on the potential impacts of current global climate change scenarios on the distribution of benthic macroinvertebrates along the western Atlantic coast.
Californian mixed‐conifer forests under unmanaged fire regimes in the Sierra San Pedro Mártir, Baja California, Mexico
Authors: Minnich R. A. , Barbour M. G. , Burk J. H. , Sosa‐Ramírez J. 
Published: March 2003

AbstractAim This study appraises historical fire regimes for Californian mixed‐conifer forests of the Sierra San Pedro Mártir (SSPM). The SSPM represents the last remaining mixed‐conifer forest along the Pacific coast still subject to uncontrolled, periodic ground fire.Location The SSPM is a north–south trending fault bound range, centred on 31°N latitude, 100 km SE of Ensenada, Baja California.Methods We surveyed forests for composition, population structure, and historical dynamics both spatially and temporally over the past 65 years using repeat aerial photographs and ground sampling. Fire perimeter history was reconstructed based on time‐series aerial photographs dating from 1942 to 1991 and interpretable back to 1925. A total of 256 1‐ha sites randomly selected from aerial photographs were examined along a chronosequence for density and cover of canopy trees, density of snags and downed logs, and cover of non‐conifer trees and shrubs. Twenty‐four stands were sampled on‐the‐ground by a point‐centred quarter method which yielded data on tree density, basal area, frequency, importance value, and shrub and herb cover.Results Forests experience moderately intense understory fires that range in size to 6400 ha, as well as numerous smaller, low intensity burns with low cumulative spatial extent. SSPM forests average 25–45% cover and 65–145 trees per ha. Sapling densities were two to three times that of overstory trees. Size‐age distributions of trees ≥ 4 cm dbh indicate multi‐age stands with steady‐state dynamics. Stands are similar to Californian mixed conifer forests prior to the imposition of fire suppression policy. Livestock grazing does not appear to be suppressing conifer regeneration.Main conclusions Our spatially‐based reconstruction shows the open forest structure in SSPM to be a product of infrequent, intense surface fires with fire rotation periods of 52 years, rather than frequent, low intensity fires at intervals of 4–20 years proposed from California fire‐scar dendrochronology (FSD) studies. Ground fires in SSPM were intense enough to kill pole‐size trees and a significant number of overstory trees. We attribute long fire intervals to the gradual build‐up of subcontinuous shrub cover, conifer recruitment and litter accumulation. Differences from photo interpretation and FSD estimates are due to assumptions made with respect to site‐based (point) sampling of fire, and nonfractal fire intensities along fire size frequency distributions. Fire return intervals determined by FSD give undue importance to local burns which collectively use up little fuel, cover little area, and have little demographic impact on forests.
Trajectories to extinction: spatial dynamics of the contraction of geographical ranges
Authors: Channell Rob , Lomolino Mark V. 
Published: March 2003

AbstractAim We examined the range contraction of 309 declining species of animals and plants to determine if the contraction dynamics better matched predictions based on the demographic characteristics of historical populations (demographic hypothesis) or based on the contagion‐like spread of extinction forces (contagion hypothesis).Location Species included in the analysis came from all biogeographic regions.Methods We obtained range maps for 309 species from literature or through personal correspondence with authorities. Hypotheses were contrasted by examining the sequence of changes in the proportion (C) of the remnant range that fell within the central region of the historical range. Monte Carlo simulations and polynomial regressions were employed to examine changes inCduring the process of range contraction.Results The results of the Monte Carlo simulations indicated that more species had observed range contractions consistent with the contagion hypothesis than expected by chance (z‐score = 2.922,P = 0.002). The Monte Carlo analysis also indicated that the number of species whose observed range contractions were consistent with the demographic hypothesis was no greater than expected by chance (z‐score = 0.337,P = 0.367). The results of the polynomial regression analysis for the two most common taxonomic groups (mammals and birds) and for all geographical regions (Australia, Africa, Eurasia, and North America) we examined also supported the contagion hypothesis.Main conclusions Most of the examined range contractions are consistent with the contagion hypothesis and that the most likely contagion is human related disturbance. These results have important implications for the conservation of endangered species.
The biogeographical distribution of microfungi associated with three palm species from tropical and temperate habitats
Authors: Taylor J. E. , Hyde K. D. , Jones E. B. G. 
Published: March 2003

AbstractThe microfungi of three palm species were investigated in their natural habitats and in habitats where the palms were cultivated outside their natural ranges.The palms that were selected differed in their habitats and ecology. Archontophoenix alexandrae is endemic to tropical rainforests in Australia, Cocos nucifera is pan‐tropical and Trachycarpus fortunei occurs in warm‐temperate China.Different assemblages of fungi were found in association with palms in temperate regions as compared to those in tropical regions. These differences were more related to climatic influences than to the hosts sampled, as few fungi were host‐species specific.The status of the hosts at the site, i.e. indigenous or introduced, and the degree of disturbance of the habitats within which the palms grew were also influential.When sampled in its natural habitat, Archontophoenix alexandrae had a distinct palmicolous mycota typical of other palms in tropical rainforests. Outside of the palm’s natural habitat, a widely different mycota were recorded that comprised tropical species of a more plurivorous nature.A similar plurivorous assemblage characterized the fungi associated with Cocos nucifera, probably due to the palm’s long history of cultivation.Similarly, plurivorous, but temperate or widespread fungi were associated with Trachycarpus fortunei, both within and outside of its natural habitat. This palm is also highly cultivated.A reduction in palm fungi associated with palms in disturbed habitats has implications for conservation of these fungi. However, it is acknowledged that the data for fungal diversity and distribution is incomplete and fragmentary.
Relationship between avian range limits and plant transition zones in Maine
Authors: Boone Randall B. , Krohn William B. 
Published: March 2003

AbstractAimTo determine if vegetation complexity associated with transition zones may be a contributing factor affecting bird species distributions in Maine, USA, and in increased numbers of bird species at about 45° north latitude in northeastern North America.LocationMaine, USA; North America north of Mexico.MethodsWe delineated the ranges within Maine (86,156 km2) of 186 bird species and 240 woody plants using literature and expert review. Maps showing species richness and numbers of range limits, at 324 km2resolution, were developed for woody plants and groups of breeding birds: forest specialists, forest generalists, and those that used barren and urban habitats, early successional areas, and wetlands or open water. Two plant transition zones for Maine were identified previously, with the north–south transition zone mapped across eastern North America. Patterns in bird distribution maps were compared to woody plant maps and to transition zones.ResultsWhen the distributions of forest specialists were compared to the north–south vegetation transition zone in Maine, they were spatially coincident, but were not for other groups. Forest specialists had more species with range limits in the state (61%) than generalists (13%) or any other group. At a continental‐scale, the vegetation transition zone within eastern North America agreed fairly well with the areas of highest bird richness.Main conclusionsA bird transition zone occurs in Maine and across eastern North America, akin to and overlapping the vegetation transition zone. Seasonality is likely the primary source of the inverse gradient in bird richness in the eastern USA, as reported by others. However, vegetation structure and habitat selection at very broad spatial scales appear to contribute to the reversed gradient. North of the vegetation transition zone, forest structure is simpler and coniferous forests more dominant, and this may contribute to reduced bird species richness. However, the northern (> 49°) typical gradient in bird species richness has been related to many hypotheses, and several are likely involved in the genesis of the gradient.
Distribution patterns of the small mammals (Insectivora and Rodentia) in a transitional zone between the Eurosiberian and the Mediterranean regions
Authors: Sans‐Fuentes Maria A. , Ventura Jacint 
Published: March 2003

To determine, by means of quantitative analyses, the distribution patterns of the insectivores and rodents in Catalonia using physiographical regions as Operative Geographical Units (OGUs).Catalonia (north‐eastern Iberian Peninsula).Based on the presence/absence of twenty‐five small mammals in thirteen physiographical regions, which were used as OGUs, the following aspects were studied: (a) identification of biotic boundaries; (b) determination of chorological association of species; (c) climatic characterization of the biotic regions and the chorotypes. Groups of biotic regions and species were established, and their statistical significance was tested. The possible effect of several climatic factors on these groupings was studied using discriminant analyses.A significant biotic boundary was found to separate the central and eastern Pyrenees from the remaining physiographical regions. The climatic variables that defined this boundary were related to the severity and the availability of environmental energy. Four chorotypes were identified. One chorotype was constituted by Pyrenean or Pre‐Pyrenean species, an association determined by their mid‐European requirements; another chorotype was formed by Eurosiberian species, but showed a variable degree of tolerance to Mediterranean conditions; a third chorotype included species with a wide distribution that are Mediterranean, anthropic, generalist or have very specific habitats; and finally the fourth chorotype was constituted by a strictly Mediterranean species. The climatic factors that accounted for the distribution of these chorotypes were the mean July temperature and the mean annual precipitation.We conclude that the axial zone of the Pyrenees, except the coastal portion, determines two biotic regions in Catalonia. As for the classification of species, using quantitative techniques for the first time, we offer a new biogeographicalal configuration for the small mammals in this temperate‐Mediterranean transition.
Geographical patterning of species richness among granivorous birds in Australia
Authors: Franklin Donald C. , Woinarski John C. Z. , Noske Richard A. 
Published: March 2003

AbstractAimTo examine and compare patterns of species richness and prominence across the Australian continent for taxonomic and ecological subsets of the granivorous bird fauna.LocationThe Australian continental mainland and island of Tasmania.MethodsBird species records from the Atlas of Australian Birds (Blakers et al., 1984) were arranged in degree cells and analysed as raw tallies of species richness, and as averaged proportions of the recorded land bird assemblage.ResultsThere were striking differences in the geographical distribution of absolute and relative abundance of foraging and taxonomic classes of granivorous birds. Granivorous birds that forage in trees are confined to the parrots and cockatoos (Psittaciformes), are most speciose in areas dominated by evergreen forests or woodlands and are equally species‐poor in the arid‐zone and the monsoonal tropics. In contrast, obligate terrestrial foragers are morphologically diverse and occur in all the families considered (Phasianidae, Turnicidae, Pedionomidae, Columbidae, Cacatuidae, Psittacidae, Passeridae). They are most speciose over a broad area of eastern, south‐eastern and north‐western Australia. Among obligate terrestrial foragers there is a marked latitudinal sequence of replacement of granivore taxa: finches (Passeridae) are most prominent in the monsoonal savannas, pigeons (Columbidae) are most prominent in the semiarid tropics, and parrots (Cacatuidae and Psittacidae) in the winter‐rainfall arid and semiarid zones.Main conclusionsThese striking patterns may be related to differences in the size, bill shape and heat tolerance of the taxa, and to the history of evolution and/or colonization of the taxonomic group within Australia.
Ecological biogeography of North American mammals: species density and ecological structure in relation to environmental gradients
Authors: Badgley Catherine , Fox David L. 
Published: March 2003

AbstractAim To evaluate the relationship of climate and physiography to species density and ecological diversity of North American mammals.Location North America, including Mexico and Central America.Methods Species density, size structure and trophic structure of mammalian faunas and nine environmental variables were documented for quadrats covering the entire continent. Spatial autocorrelation of species density and the environmental variables illustrated differences in their spatial structure at the continental scale. We used principal component analysis to reduce the dimensionality of the climatic variables, linear multiple regression to determine which environmental variables best predict species density for the continent and several regions of the continent, and canonical ordination to evaluate how well the environmental variables predict ecological structure of mammalian faunas over North America.Results In the best regression model, five environmental variables, representing seasonal extremes of temperature, annual energy and moisture, and elevation, predicted 88% of the variation in species density for the whole continent. Among different regions of North America, the environmental variables that predicted species density vary.Changes in the size and trophic structure of mammalian faunas accompany changes in species density. Redundancy analysis demonstrated that environmental variables representing winter temperature, frostfree period, potential and actual evapotranspiration, and elevation account for 77% of the variation in ecological structure.Main conclusions The latitudinal gradient in mammalian species density is strong, but most of it is explained by variation in the environmental variables. Each ecological category peaks in species richness under particular environmental conditions. The changes of greatest magnitude involve the smallest size categories (< 10 g, 11–100 g), aerial insectivores and frugivores. Species in these categories, mostly bats, increase along a gradient of decreasing winter temperature and increasing annual moisture and frostfree period, trends correlated with latitude. At the opposite end of this gradient, species in the largest size category (101–1000 kg) increase in frequency. Species in size categories 3 (101–1000 g), 5 (11–100 kg) and 6 (101–1000 kg), herbivores, and granivores increase along a longitudinal gradient of increasing annual potential evapotranspiration and elevation.Much of the spatial pattern is consistent with ecological sorting of species ranges along environmental gradients, but differential rates of speciation and extinction also may have shaped the ecological diversity of extant North American mammals.
The ostrich in Egypt: past and present
Authors: Manlius Nicolas 
Published: March 2003

AimThis article tracks the evolution of the distribution of ostrich populations, Struthio camelus L., 1758, in Egypt from the Late Pleistocene up to present times with a view to establishing a series of distribution maps for the historical period. An attempt is then made to describe and interpret these maps.LocationThe country considered is Egypt.MethodsWe compiled all the information about the presence of the ostrich in Egypt collected from the study of fossil remains, archaeological materials and from the narrative of travellers since the fourteenth century. From the accounts of these travellers, three maps showing the location of this birds in this country are established: from the end of the fourteenth century to the end of the seventeenth century; from the beginning of the eighteenth to the end of the nineteenth century; and lastly, for the twentieth century.ResultsThe ostrich was abundant and broadly distributed in Egypt in the past. However, it has been constantly in decline. It disappeared from the north of the country and lived only in the southeast up to the end of the nineteenth century. The birds reappeared in the latter region at the beginning of the 1960s up to 1991 before disappearing from the country.Main conclusionsThe principal reasons for the decline of the ostrich in Egypt are the aridification caused by climatic changes and intensive hunting by humans. It is possible that this bird was not sighted in the country between the beginning of the twentieth century and the 1960s, not because it had disappeared, but most probably because it was sufficiently discrete to be noticed.
Determinants of inselberg floras in arid Nama Karoo landscapes
Authors: Burke Antje 
Published: March 2003

AimThis study investigated the relationship between inselberg floras in floristic and functional terms and their correlation with environmental variables at macro‐scale and landscape level.LocationFour inselberg landscapes in Namibia’s arid Nama Karoo in southern Africa were selected.MethodsPlant surveys were undertaken over a 3‐year period and species composition, growth form and dispersal spectra were used as measures for floristic and functional composition. Canonical correspondence analysis (CCA) was employed as the main tool to explain the perceived patterns.ResultsRegarding floristic affinities, inselberg floras formed distinct groups per study area and thus geographical position, with strong correlations between inselbergs within a particular study area. Neither growth form nor dispersal spectra closely resembled the pattern that emerged in the ordination of floristic composition. The influence of geographical position lessened when functional rather than floristic measures were introduced in the analysis.Main conclusions(1) On landscape and macro‐scale, floristic composition of inselberg floras was largely determined by geographical position, geology, elevation, habitat diversity, rock outcrop in the surrounding and surface area of inselbergs. (2) Environmental variables operating at landscape level had greater influence on functional composition than on floristic composition. (3) Stochastic variables were more important in shaping the flora of these arid Nama Karoo inselbergs than deterministic processes such as niche relations and competition.