bluuebunny/crossref_metadata_2025 huggingface dataset:
The accuracy of GPS for wildlife telemetry and habitat mapping
Authors: Hulbert Ian A.R. , French John
Published: March 2003

Decision support tools used for vegetation management require accurate information on the spatial array of different plant communities and a herbivore’s grazing location. We tested the accuracy and precision of locations derived using the satellite navigation global positioning system (GPS).

Before May 2000, the accuracy and precision of GPS‐derived locations were degraded by a process known as selective availability (SA); after May 2000, SA was disabled. In this study we investigated how to handle and improve the quality of data generated both when SA was enabled and when SA was disabled using relative GPS (rGPS). rGPS entails the post‐processed correction of the roving GPS module with simultaneously acquired positional errors recorded at a known stationary reference location.

With SA enabled, GPS data were obtained at a fixed known location to obtain baseline information, and from a roving module that essentially mimicked surveying techniques or the movement of a free‐ranging animal. The mean accuracy of GPS with SA enabled was 21 m for the fixed module and 25 m for the roving module. Use of rGPS and further manipulation of the data improved the mean accuracy of the data to 7 m for the fixed module and 10 m for the roving module. With SA disabled, data were similarly recorded from the fixed known location and resulted in a mean location accuracy of 5 m. The use of rGPS resulted in a significant improvement of this value to 3·6 m and precision measured by the 95% quantile was < 10 m. For mapping and wildlife tracking, such quality in terms of location accuracy and precision is unprecedented and demonstrates that rGPS may still be useful in many applications.

GPS enables the world‐wide collection of accurate and precise location information at 1‐second intervals. Furthermore, by programming the GPS receiver to overdetermine location by using information from all visible satellites, many of the limitations that arise in habitats or environments with a limited view of the sky may be overcome.

With SA now disabled, the potential use of GPS will increase. With further miniaturization, surveying of remote featureless landscapes or the tracking of crepuscular or far‐ranging animals will become more accurate and more quantifiable than ever before.
Habitat loss, fragmentation and predator impact: spatial implications for prey conservation
Authors: Schneider Michael F.
Published: March 2003

Because predators threaten the survival of endangered prey in many places, predator management is a widespread conservation tool. At the same time, the effects of predators on their prey are greatly influenced by landscape structure. Therefore, the management of landscapes could be an alternative to predator regulation.

A spatially explicit presence/absence model (a stochastic one‐layer cellular automaton) was used to investigate two different predator–prey systems that were subject to changes in the number and size of habitat patches in a model landscape.

The first scenario included grey‐sided voles Clethrionomysrufocanus, Norwegian lemmings Lemmus lemmus and small mustelids (stoats Mustelaerminea and weasels M. nivalis) interacting in a tundra landscape. In the second scenario, the effect of habitat perforation by human settlements with subsidized predators (house cats Felis silvestris catus) on the dynamics of lemmings (as surrogate for endangered prey) was studied.

Both the total area of lemming habitat and the degree of fragmentation were important determinants of the population size and persistence of lemmings. A qualitative change in the effect of fragmentation was observed when the area of lemming habitat decreased from 70% (positive effect) to 50% (negative effect). When lemming habitat covered 50% or less of the landscape, fragmentation had a negative effect on lemming population size and viability, even though habitat area did not decrease.

The spatial configuration of settlements as predator sources was important. A few evenly spaced predator sources had less negative effect on lemming populations than the same proportion of predator habitat that was randomly distributed, which in turn had less effect than many evenly spaced patches.

Including predator management in the model did not decrease the predators’ negative impact on the population size and persistence of the endangered prey when settlements occurred in many small patches.

It is concluded that predator management is not a viable strategy to combat the threat to the survival of endangered prey, but that careful planning of landscape pattern could compensate for negative predation effects. The location and size of patches of predator habitat should be optimized in order to minimize the negative effects of predators visiting adjacent areas of natural habitat.
The effects of disturbance on habitat use by black‐tailed godwits Limosa limosa
Authors: Gill Jennifer A. , Norris Ken , Sutherland William J.
Published: March 2003

Human disturbance of wildlife is widely considered to be a serious conservation problem. However, despite many qualitative studies, little attempt has been made to assess whether human presence limits the number of animals that sites can support. This can be quantified by incorporating measures both of human presence and of resource distribution into analyses of population distribution. The effects of disturbance can then be measured from any reduction in resource use at disturbed sites, which in turn indicates any reduction in the number of animals supported.

Shorebirds are often considered highly susceptible to disturbance because of their very obvious flight responses to humans and because they use areas that are generally subject to high levels of human recreational use.

This study addressed the effect of human presence on the distribution of black‐tailed godwits Limosa limosa islandica on coastal areas in eastern England. We identified the prey types selected by godwits and related their depletion to different levels and types of human disturbance at a range of spatial scales.

Three methods of analysis are described: simple regressions of the effect of human activity on the number of godwits supported; multiple regression analyses of the effect of human presence and prey density on godwit numbers; and analyses of the effect of human presence on prey density at the end of the season. The latter method assumes that godwits are responsible for the majority of resource depletion. None of the analyses showed any effect of human presence on the number of godwits supported by the food supply at any of the spatial scales examined.

Many species may appear to avoid human presence but this may not reduce the number of animals supported in an area. Assessing the influence of disturbance on the relationship between animal distribution and resource distribution provides a means of assessing whether numbers are constrained by disturbance.
Effects of fungal pathogens on seeds of native and exotic plants: a test using congeneric pairs
Authors: Blaney C.S. , Kotanen P.M.
Published: March 2003

It has previously been hypothesized that low rates of attack by natural enemies may contribute to the invasiveness of exotic plants.

We tested this hypothesis by investigating the influence of pathogens on survival during a critical life‐history stage: the seed bank. We used fungicide treatments to estimate the impacts of soil fungi on buried seeds of a taxonomically broad suite of congeneric natives and exotics, in both upland and wetland meadows.

Seeds of both natives and exotics were recovered at lower rates in wetlands than in uplands. Fungicide addition reduced this difference by improving recovery in wetlands, indicating that the lower recovery was largely attributable to a higher level of fungal mortality. This suggests that fungal pathogens may contribute to the exclusion of upland species from wetlands.

The effects of fungicide on the recovery of buried seeds did not differ between natives and exotics. Seeds of exotics were recovered at a higher rate than seeds of natives in uplands, but this effect was not attributable to fungal pathogens.

Fungal seed pathogens may offer poor prospects for the management of most exotic species. The lack of consistent differences in the responses of natives vs. exotics to fungicide suggests few aliens owe their success to low seed pathogen loads, while impacts of seed‐pathogenic biocontrol agents on non‐target species would be frequent.
Changes in survival rates and population dynamics of greater snow geese over a 30‐year period: implications for hunting regulations
Authors: Menu Stéphane , Gauthier Gilles , Reed Austin
Published: March 2003

In recent decades, the populations of several goose species have increased dramatically and are severely impacting on their habitat. We examined the relative contribution of reproduction and mortality to changes in the dynamics of the entire North American population of greater snow geeseAnser caerulescens atlanticusfrom 1970 to 1998.

The total population increased 10‐fold over this period, with two phases of rapid population growth in 1970–74 and 1984–98 separated by an intervening period of stagnation. The reproductive rate was estimated from age ratios in the autumn, survival from ring recoveries, and harvest rates from hunter surveys.

Variations in population growth could not be explained by changes in reproduction, which was similar across the three periods (overall mean 26 ± 3% young in the autumn flock) with no evidence of density‐dependence.

Adult survival did not differ between the two periods of rapid population growth (0·84 ± 0·04 during 1970–74 vs. 0·80 ± 0·04 during 1990–96), thus providing no evidence of density‐dependence effects either. The survival rates of young could only be estimated during 1990–96, when they varied greatly (mean 0·36 ± 0·12, annual range 0·11–0·48).

Adult harvest rates were much higher during the period of no population growth (0·11 ± 0·01%) than before (0·04 ± 0·01%) or after (0·06 ± 0·01%). The increased harvest starting in 1975 was due to the re‐opening of the US hunting season. Thus, reduced survival due to increased hunting mortality apparently caused the stagnation of growth between 1975 and 1983.

We conclude that hunting mortality has had the most impact on recent population dynamics in the greater snow goose and, in the absence of density‐dependent effects, hunting could be used to limit the growth of this population.
Comparative foraging and nutrition of horses and cattle in European wetlands
Authors: Menard Catherine , Duncan Patrick , Fleurance Geraldine , Georges Jean‐Yves , Lila Marc
Published: March 2003

Equids are generalist herbivores that co‐exist with bovids of similar body size in many ecosystems. There are two major hypotheses to explain their co‐existence, but few comparative data are available to test them. The first postulates that the very different functioning of their digestive tracts leads to fundamentally different patterns of use of grasses of different fibre contents. The second postulates resource partitioning through the use of different plant species. As domestic horses and cattle are used widely in Europe for the management of conservation areas, particularly in wetlands, a good knowledge of their foraging behaviour and comparative nutrition is necessary.

In this paper we describe resource‐use by horses and cattle in complementary studies in two French wetlands. Horses used marshes intensively during the warmer seasons; both species used grasslands intensively throughout the year; cattle used forbs and shrubs much more than horses. Niche breadth was similar and overlap was high (Kulczinski’s index 0·58–0·77). Horses spent much more time feeding on short grass than cattle. These results from the two sites indicate strong potential for competition.

Comparative daily food intake, measured in the field during this study for the first time, was 63% higher in horses (144 gDM kg W−0·75 day−1) than in cattle (88 gDM kg W−0·75 day−1). Digestibility of the cattle diets was a little higher, but daily intake of digestible dry matter (i.e. nutrient extraction) in all seasons was considerably higher in horses (78 gDM kg W−0·75 day−1) than in cattle (51 gDM kg W−0·75 day−1). When food is limiting, horses should outcompete cattle in habitats dominated by grasses because their functional response is steeper; under these circumstances cattle will require an ecological refuge for survival during winter, woodland or shrubland with abundant dicotyledons.

Horses are a good tool for plant management because they remove more vegetation per unit body weight than cattle, and use the most productive plant communities and plant species (especially graminoids) to a greater extent. They feed closer to the ground, and maintain a mosaic of patches of short and tall grass that contributes to structural diversity at this scale. Cattle use broadleaved plants to a greater extent than horses, and can reduce the rate of encroachment by certain woody species.
Nest‐site limitation and density dependence of reproductive output in the common goldeneyeBucephala clangula: implications for the management of cavity‐nesting birds
Authors: Pöysä H. , Pöysä S.
Published: March 2003

Hole‐nesting birds are frequently faced with a shortage of suitable nest sites in regions of intensive forest management. Nest boxes are sometimes provided to alleviate nest‐site limitation in cavity‐nesting waterfowl and are also recommended for several rare and endangered species. However, the impacts on effective breeding numbers and breeding success have rarely been considered, particularly in instances where density dependence might operate.

 We experimentally manipulated nest sites to assess limits on the population size of a secondary cavity‐nesting species, the common goldeneyeBucephala clangula, living on freshwater lakes. We also examined density dependence in their reproductive output.

 Breeding pairs were counted in experimental and control areas over a 12‐year period; for 4 years (1988–91) before nest box addition (1992–94 in the experimental area) and for 5 years (1995–99) afterwards. Broods were counted each year between 1988 and 1999 to study reproductive output.

 Mean number of pairs per lake increased after the addition of nest boxes in the experimental area but not in the control area. However, neither the mean number of broods per lake nor the mean number of fledged birds per lake increased significantly in the experimental area.

 When the whole period of 1988–99 was considered and data pooled from all the lakes, the numbers of broods and fledged birds showed negative density dependence of reproductive output.

 Our results indicate that nest sites limit the population size of breeding common goldeneye, but show also that density‐dependent factors operate to limit reproductive output. The possibility that density dependence may negate management actions directed at increasing breeding numbers in cavity‐nesting waterfowl should be considered carefully before taking these actions. This also applies to nest box provisioning programmes aiming to manage populations of endangered species.
Biological control of cactus weeds: implications of hybridization between control agent biotypes
Authors: Hoffmann J. H. , Impson F. A. C. , Volchansky C. R.
Published: March 2003

Results of recent research on Dactylopius opuntiae, a biological control agent for cactus weeds (Opuntia spp.) in South Africa and elsewhere, challenge the maxim that genetic diversity of agents necessarily enhances the chances of success in biological weed control.

Two biotypes of D. opuntiae, each specific to a different Opuntia species, interbred freely, at least under insectary conditions. We therefore carried out cross‐breeding experiments to determine the viability and host‐preferences of progeny produced by these crosses.

Unlike their parents, F1 hybrids were not species‐specific, developing equally well on either of the parental hosts, Opuntia ficus‐indica and Opuntia stricta. The situation was more complex in F2 back‐crosses between hybrids and in crosses between parent strains and hybrids because male cochineal insects contributed only maternally inherited genes to their progeny, due to their unusual haploid‐diploid (lecanoid) mechanism of sex determination. Some F2 combinations produced cohorts of progeny that were either entirely true‐bred (i.e. host‐specific) or entirely hybrid (i.e. not host‐specific) genotypes, while other combinations produced groups of siblings with some individuals (theoretically half) that were true‐bred genotypes and the balance were hybrid genotypes.

The lack of host‐specificity of hybrids should enhance overall biological control of the target species directly, because hybrids attack both host‐plants, and indirectly, because hybrid nymphs have greater chances of finding a suitable host‐during passive dispersal. However, this advantage will be negated when F2 crosses produce host‐specific nymphs on host‐plants that are incompatible for their survival.

These findings show that only pure strains of D. opuntiae should be released in monocultures of the target weeds. More generally, they caution that the possible consequences of mixing genotypes of a biological control agent species should be investigated before different provenances are amalgamated to enhance genetic diversity.
Effects of experimental irrigation and drought on the composition and diversity of soil fauna in a coniferous stand
Authors: Lindberg Niklas , Engtsson Jan B. , Persson Tryggve
Published: March 2003

The effects of experimental long‐term summer drought and irrigation on soil fauna were studied in a Norway spruce stand in south‐western Sweden. The treatments, carried out over 8 and 10 years respectively, were chosen to simulate two scenarios of climate change, involving drier and wetter summers.

Different microarthropod communities developed in the different treatments. The abundances of enchytraeids, mesostigmatid mites and macroarthropod predators were all lowest in the drought plots. Drought decreased and irrigation increased the abundance and diversity of Oribatida. Drought decreased the abundance of Collembola.

The dominance structure of Oribatida and Collembola also changed, but less markedly. Drought affected community composition of both groups more than irrigation.

The study confirms that soil microarthropods can be useful environmental indicators, but their responses did not support the widely held view that deviations from a log‐normal dominance structure indicates a stressed community.

The results also indicate that a drier climate with summer drought will lead to the local extinction of some soil animal species in this region.
Effects of extremely low frequency magnetic fields on pain thresholds in mice: roles of melatonin and opioids
Authors: Jeong J. H. , Choi K. B. , Yi B. C. , Chun C. H. , Sung K.‐Y. , Sung J.‐Y. , Gimm Y.‐M. , Huh I. H. , Sohn U. D.
Published: March 2003

1 We studied the effects of extremely low frequency (ELF, 60 Hz) magnetic fields (MFs) on pain thresholds using the hot plate test. The implication of opioid and benzodiazepine system in the MFs‐induced alteration of pain thresholds was also studied.

2 There was an increase at night time and a decrease at daytime of pain thresholds in normal mice. Exposure of MFs (24 h, 20 gauss (G)) inhibited the increase of pain thresholds at night time and even produced hyperalgesia at daytime.

3 The increase of pain thresholds induced by melatonin at daytime was inhibited by exposure to MFs (24 h, 20 G) or opioid antagonist naloxone. The MFs and naloxone synergically inhibited hypoalgesia produced by melatonin. The hyperalgesia at daytime after MFs exposure was potentiated by the benzodiazepine agonist, diazepam, and inhibited by the benzodiazepine antagonist, flumazenil. There was no significant difference in all rotarod performance we tested.

4 From these results, it is suggested that exposure to MFs inhibits the increase of pain thresholds at night time and produces hyperalgesia at daytime with the involvement of opioid and benzodiazepine systems.
Long‐term effects of daily grazing orbits on nutrient availability in Sahelian West Africa: 2. Effects of a phosphorus gradient on spatial patterns of annual grassland production
Authors: Turner Matthew D.
Published: March 2003

Abstract. This paper reports on an investigation of the effect of a livestock‐generated gradient in phosphorus‐availability on spatial patterns of annual rangeland production around pastoral watering points in the Sahelian region of West Africa. The study was conducted along a major transhumance corridor used for at least the past century by herds managed by agropastoralists of the Inland Niger Delta of Mali. Eighteen sites on sandy substrate were established at varying distances from: (1) a more persistent pan from which livestock disperse to graze primarily during the early dry season (D1); and (2) a line of ephemeral pans from which livestock disperse to graze during the rainy season (D2). Data on the species composition, standing herbaceous mass, and annual herbaceous cover were collected at these sites over the 2 years following a significant drought. These vegetative parameters show considerable interannual variation in their spatial pattern. As reported elsewhere (companion paper), chemical analyses of soil and plant samples collected at these sites show a significant negative correlation between phosphorus availability and D2. This is consistent with livestock‐mediated nutrient transfer from outlying zones toward rainy‐season pans. The effect of this phosphorus gradient on annual rangeland production was analysed using a regression modelling approach. Two vegetative production parameters, vegetated surface fraction (VSF) and herbaceous above‐ground standing mass of vegetated surface (VAGM), were regressed in a two‐and three‐step process on the following factors: (1) background soil and rainfall data; (2) forb fraction of herbaceous production (for VAGM only), followed by: (3) D1 and D2. These analyses find that while the phosphorus‐availability gradient had a significant effect on spatial patterns of herbaceous production during the year immediately following the drought, it had little effect in the subsequent year's production. This difference is explained by the increased importance of nitrogen in limiting herbaceous production during the second year, resulting from its different rainfall history.
Area‐relationships in the Neotropical lowlands: an hypothesis based on raw distributions of Passerine birds
Authors: Bates John M. , Hackett Shannon J. , Cracraft Joel
Published: March 2003

Abstract. Using raw geographic distributions for Neotropical species and subspecies of the perching birds (Order Passeriformes), we present an hypothesis of area‐relationships for twelve avian areas of endemism in the lowland Neotropics. With 1717 characters (distributions of species and subspecies) we find a single most parsimonious tree of area‐relationships. This topology does not match area‐relationships determined from phylogenetic studies of morphologic characters in some Neotropical birds. Analyses of data partitions representing major taxonomic subdivisions within Passerine birds provide many different hypotheses of area‐relationships. These results suggest that a single set of Neotropical area‐relationships is not likely. In the future, we suggest greater emphasis be placed on research to document patterns in the Neotropics, particularly phylogenetic patterns, than on speculation about what processes have been important for diversification.
Snails of the genusPachnodus(Mollusca; Gastropoda; Enidae): their origins and evolution
Authors: Gerlach Justin
Published: March 2003

AimThe phylogeny of the enid land‐snail genusPachnoduswas determined in order to provide information on biogeographical patterns within the granitic Seychelles islands.

LocationThe genusPachnodusis endemic to the granitic islands of Seychelles (Mahé, Silhouette, Praslin, La Digue and Fregate).

MethodsPhylogeny was determined using a cladistic analysis of nineteen shell and soft‐body anatomy characters. The outgroup used was the central‐east African genusCerastus.

ResultsThe proposed phylogeny indicates that the genus divided into two distinct subgenera early in its history. Subsequent speciation occurred in parallel in the two subgenera, resulting in several islands supporting at least two distinct species representing the two subgenera.

Main conclusionsThe pattern of speciation is largely explicable by vicariance as a result of sea‐level rises, followed by habitat specialisation and further speciation. The pattern is in contrast to previously published scenarios for other taxa in the islands and indicates significant differences between evolutionary and habitat factors in the biogeography of the Seychelles fauna
Biodiversity and pollen analysis: modern pollen studies and the recent history of a floodplain woodland in S. W. Ireland
Authors: Brown A. G.
Published: March 2003

One of the problems with biodiversity for palynologists is that their samples come from an unbounded area and source area varies with both pollen/spore type and vegetation type. There have been two broad approaches to the problem of inferring diversity from pollen/spore samples; firstly the use of pollen type richness as a proxy for species richness, and secondly the ‘identification’ of past vegetation communities aided by ecological inference and historical or modern data concerning species affinities and typical diversity. The estimation of biodiversity from pollen analysis depends upon the pollen count, taxonomic precision, source strength for individual types and dispersal/transport of pollen from source areas to the site. A transect of surface pollen samples is used here to test the effect of a vegetation boundary on pollen/spore diversity and compare the pollen/spore diversity with the species richness of the woodland. Palynological richness (at a constant count sum) does, to some extent, reflect changing local vegetation along the transect. Type count curves also reflect the changes in vegetation type along the transect due to the partial influence of species richness on pollen/spore richness. This study suggests that depending upon the woodland composition, the woodland may not entirely drown‐out the pollen signal of the surrounding vegetation, and that a small woodland may be more representative (as a sampling site) of the valley floor diversity than a raised mire. The surface transect is also used in the interpretation of Medieval pollen levels from The Gearagh.
Mountain Park area: a plant refugium in the Canadian Rocky Mountains?
Authors: Strong W. L
Published: March 2003

AimThe purpose of this study was to evaluate evidence related to the occurrence of a hypothesized Wisconsinan glacial refugium along the eastern slopes of the Rocky Mountains in western Canada.

LocationThe study area was located ≈60 km south of Hinton, Alberta. The area of interest occurred within the vicinity of the abandoned early 1900s coal mining town known as Mountain Park (52°55 N, 117°16 W).

MethodsContemporary botanical, palynological, and geomorphic information for the Mountain Park and surrounding area was compiled. For comparative purposes, vascular and nonvascular floristic lists were developed from available literature for five national parks along the Canadian cordilleran. All species were classified according to their phytogeographical affiliations.

ResultsThe available data suggested that most of the Mountain Park area was glaciated during the Wisconsinan, except possibly at high elevations (> 2075–2255 m above sea level). Palynological evidence from the surrounding area indicated that coniferous forest developed in the area after 11,400 yearsBP. If vegetation did exist in the Mountain Park area before 11,400 yearsBP, it would probably have been tundra. The known Mountain Park area flora (554 species) contained only one vascular and six nonvascular species with an exclusively arctic‐alpine affiliation. A comparison of Mountain Park flora with five other locations indicated that vascular species were more strongly associated with areas further south. No significant statistical difference (Chi‐square Goodness of Fit,P< 0.05 level) was found among the nonvascular floras.

Main conclusionsLate Wisconsinan and postglacial migrations were considered to be stronger ecological possibilities for explaining the current vascular flora of the Mountain Park area thanin situsurvival. Some nonvascular species may have survived in high elevation nunatak areas during glaciation. These circumstances were probably similar to more interior Rocky Mountain locations which are known to have been glaciated during the Wisconsinan.
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

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

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

Aim 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

Aim 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

The 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

AimTo 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

Aim

To examine and compare patterns of species richness and prominence across the Australian continent for taxonomic and ecological subsets of the granivorous bird fauna.

Location

The Australian continental mainland and island of Tasmania.

Methods

Bird 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.

Results

There 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 conclusions

These 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.