bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sustainable exploitation of social species: a test and comparison of models
Authors: Stephens Philip A. , Frey‐Roos Fredy , Arnold Walter , Sutherland William J. 
Published: March 2003

SummaryOverexploitation is a major threat to the persistence of many species. A wide variety of approaches to setting ‘sustainable’ quotas for exploitation exist but there are major discrepancies between theory and practice, and only limited integration between different branches of exploitation literature. Here, we bring together and compare the efficacy of a range of different approaches to estimating sustainability.A simulated population of a social mammal was used to provide data for, and compare the recommendations of, 10 widely used estimators for setting levels of sustainable exploitation. Estimators tested included four methods for setting sustainable levels of constant‐effort harvesting, two approaches to assessing the sustainability of constant‐yield harvesting, and four systems for setting thresholds below which harvesting should cease.The method used to fit catch per unit effort data to a stock dynamic model had an important influence on the variance of recommendations. Recommendations were also affected by the length of data set available and the frequency of changes in exploitation effort. Observation‐error estimators were more consistent and more conservative than equilibrium, effort‐averaging and process‐error approaches. Harvesting at the point of maximum productivity was found to be unstable in a noisy system, suggesting the need for considerable caution when using any of these estimators.Constant‐yield indices, developed for use in the bush meat trade, overestimated the point at which exploitation was likely to become highly unsustainable. Sociality was an important factor underlying this finding and the assessment of sustainability in constant‐yield systems should give consideration to the effects of different social systems.Overall, threshold‐harvesting systems provided the highest mean yields in relation to extinction risk. However, the introduction of error into these systems, particularly in the form of less frequent censuses, greatly increased both variance in yields and risk of extinction.
Habitat diversity in forest plantations reduces infestations of the pine stem borerDioryctria sylvestrella
Authors: Jactel H. , Goulard M. , Menassieu P. , Goujon G. 
Published: March 2003

SummaryThe risk of pest damage in forest monocultures is a growing concern as the area of plantation forest expands world‐wide and sustainable management is becoming a general goal. Numerous studies have demonstrated that pest insects are less abundant in more diverse agroecosystems, but limited experimental evidence exists for a similar relationship in forestry. Because plantation forests are usually mosaics of single‐species stands, the aim of this study was to test the effect of forest diversity at a landscape level on pest insect infestations.Within a stand of maritime pine, trees attacked by the stem borerDioryctria sylvestrellashowed no spatial aggregation and clusters of 66 trees proved to be an optimal sampling unit for determining overall percentage infestation.The spatial distribution of stem borer infestation levels was examined in three maritime pine stands bordered by mixed‐species stands of broad‐leaved trees, and overall infestation levels compared between four such maritime pine stands and four other maritime pine stands of the same structure but far from any broad‐leaved stands.The percentage of trees infested was significantly lower in the pine stands bordered by broad‐leaved stands than in the pine stands surrounded by other pine stands, and in the former, stem borer infestation showed a significant logistic increase with distance from the stand edge. This could be due to effects of resource concentration or natural enemy attack, both of which are discussed.These results suggest that the conservation or restoration of non‐productive mixed‐species stands adjacent to intensively managed plantations is a useful preventive method for pest management in forest monocultures.
Great tits can reduce caterpillar damage in apple orchards
Authors: Mols Christel M. M. , Visser Marcel E. 
Published: March 2003

Summary

The potential contribution of vertebrate predators to biological control in orchards has been largely overlooked to date. A few studies have shown that birds reduce numbers of pests, but data are scarce on the effects on the pattern or timing of damage. Consequently, the practical value of birds as biocontrol agents remains unclear.
This study considered whether great tits Parus major can reduce caterpillar numbers and fruit damage by caterpillars, and increase biological yield, in an experimental orchard of apple trees with high caterpillar numbers. The outcome would depend on the coincidence of the period during which great tits forage and the period during which caterpillars cause damage. In the first experiment nets were put over trees at different times of the growing season, thus creating different periods during which great tits had access to the trees. In the second experiment caterpillars were removed from trees at different times in the growing season. In both experiments, the resultant caterpillar damage to apples was assessed in the autumn.
The longer the period of foraging by great tits, from the start of egg incubation until fledging of young, the less the overall pest damage to fruit. Damage caused by caterpillars was greater the later they were removed, from the young apple stage onwards.
The effect of great tits on caterpillar damage to apples was small (percentage damage was reduced from 13·8% to 11·2%) but significant (P < 0·05), and the yield of fruit increased significantly (from 4·7 to 7·8 kg apples per tree, P < 0·05). The only cost to the producer was that of erecting nest boxes (c. 2 ha−1) to encourage great tits to breed in the orchard. Depending on the great tits’ numeric response to insect densities, their relative impact may be greater at lower densities more typical of commercial orchards and, if so, the presence of breeding great tits may allow economic thresholds for other controls to be reduced. Furthermore, the contribution of natural predators to biological control of insect pests may be especially useful in orchards and in the future when a further reduction of pesticide use may be enforced.
Litterfall dynamics in a mixed conifer‐angiosperm forest in northern New Zealand
Authors: Enright N. J. 
Published: March 2003

SummaryLitterfall in a mixed conifer‐angiosperm temperate forest in northern New Zealand was traced for 5 years to determine the patterns of litter production and turnover for conifer and angiosperm components of the forest. Basal area and above‐ground biomass was shared approximately equally between conifer (mostlyAgathis australis;New Zealand kauri) and angiosperm species (plus tree ferns). The five‐year mean annual litterfall, excluding macro‐litter, was 7.76± 0.39(SEM) t ha−1and ranged from 6.77±0.70 t ha−1in 1983–4 to 8.79±1.00 t ha−1in 1987–8. Mean monthly litterfall showed a strong seasonal pattern with low rates in winter and early spring, increasing to a peak in early autumn. There were major differences in the nature and timing of litterfall between the conifer and angiosperm fractions. Angiosperm leaf litter reached a maximum in early summer, while conifer litterfall showed highest rates for leaves, twigs and cone scales in late summer‐autumn. Conifer reproductive structures (strobili and cone scales) contributed from 13 to 21% of total litterfall, a value high relative to other temperate forests. However, conifer leaf turnover was low relative to that for the angiosperms.Size of the microlitter store was 16.16±1.97 t ha−1prior to conifer cone fall, and 18.70±2.02 t ha−1following it, and conifer litter made up 76–78% of the total litter store. The estimated mean annual decomposition constant, k, was 0.39 overall, 0.33 for conifer leaf litter and 0.71 for angiosperm leaf litter, values which agree well with previously published rates for decomposition in this forest stand. Differences in the costs of biomass production and rates of turnover, as measured by litterfall and decomposition, may help to explain the functional coexistence of conifers and angiosperms in mixed forests.
Biogeography of the marine birds of a confined sea, the Mediterranean
Authors: Zotier Richard , Bretagnolle Vincent , Thibault Jean‐Claude 
Published: March 2003

SummaryAimThe Mediterranean sea is a winter productive oligotrophic basin where Atlantic water replaces water lost through evaporation, this influx being a major source of productivity and fertility. The long coastlines and the large number of islands cause high oceanographic heterogeneity. Moreover, during its geological history, it has dried out several times. So we describe the consequences of these particular features on species richness, distribution, and breeding ecology of marine birds.LocationThe Mediterranean sea (including the Black Sea and the Sea of Azov) communicates with the Atlantic Ocean only through a 14 km wide channel (Straits of Gibraltar), and since 1869, with the Red Sea through the Suez Canal.MethodsThe Mediterranean was subdivided into different areas, according to physical oceanographic entities and productivity, linked to numbers and distribution of both breeding and wintering marine birds (defined as species strongly dependent on marine resources, breeding only on islands and/or the coastline).ResultsThe total marine bird biomass, and species diversity, are lower in the Mediterranean than in the near Atlantic. The eastern Mediterranean, with lowest primary productivity, contains fewer marine bird taxa than the more productive western part. Taxa which mainly occur in the western and southern parts of the Mediterranean migrate through the Straits of Gibraltar to winter in the southern Atlantic, while those inhabiting the northern and eastern parts are sedentary, as a result of differences in species composition. Northern coastal basin communities (i.e. the Tyrrhenian and the Balearic Seas), are composed of less pelagic, and earlier breeding species, that rear chicks during the productive season. These latter taxa are actually the most typical Mediterranean taxa, in terms of endemism.Main conclusionsThe Mediterranean marine bird community is not tropical, but rather, shows the highest affinity with the Atlantic temperate community. Its level of endemism is however high and comparable to other confined basins such as the Red Sea.
Mammalian biogeography of the Alexander Archipelago of Alaska: a north temperate nested fauna
Authors: Conroy Chris J. , Demboski John R. , Cook Joseph A. 
Published: March 2003

SummaryAimA large number of studies have analysed the distribution of mammals within archipelagos, yet few have focused on islands that were heavily glaciated and subsequently colonized following deglaciation.LocationWe explored the relative effects of island area and isolation on faunal composition based on twenty‐three mammalian taxa of twenty‐four islands of the Alexander Archipelago, Southeast Alaska.MethodsWe used regression of log‐transformed variables and several indices of nestedness.ResultsThese faunas showed significant nested structure using tests of nestedness and regression models. Unlike most landbridge and mainland archipelagos studied previously, isolation appears to be the primary factor determining patterns of species richness.Main conclusionsColonization ability of particular taxa, rather than extinction, has determined this nested structure. We suggest that other higher latitude archipelagos may show similar historical patterns.
Reconstruction of early nineteenth‐century vegetation and fire regimes in the Missouri Ozarks
Authors: Batek Michael J. , Rebertus Alan J. , Schroeder Walter A. , Haithcoat Timothy L. , Compas Eric , Guyette Richard P. 
Published: March 2003

Summary Aim The purpose of this study was to reconstruct early nineteenth‐century vegetation and fire regimes to examine the role of fire, topography, and substrate interactions in shaping landscape and regional vegetation patterns. Location Our study area was the Current River watershed of the Ozark Highlands in south‐central Missouri, USA. Methods We combined analysis of early nineteenth‐century Public Land Survey (PLS) notes and dendrochronology‐based fire histories to reconstruct vegetation and disturbance regimes of pine‐oak (Pinus‐Quercus) woodlands.Three methods were used to display and analyse PLS data within a Geographic Information System (GIS): (1) simple point distributions for each tree species; (2) section line descriptions of each tree species and other coded features (e.g. ‘prairie’); and (3) spatial interpolation of the point‐tree data.Vegetation patterns were then related to geological parent material, topography, and mean fire‐return intervals from 23 sites using correlation and Canonical Correspondence Analysis (CCA). Results The most striking patterns in the early 1800 s were extensive stands of shortleaf pine (Pinus echinata Mill.) and oak‐dominated ‘barrens’ (savanna) in the frequently burned areas south‐west of the Current River, and more mesophytic, fire‐sensitive species (red oaks (Quercus rubra L., Q. coccinea Muenchh.), maples (Acer rubrum L., Acer saccharum Marsh), eastern red cedar (Juniperus virginiana L.) in a fire shadow north‐east of the river. Several kilometre‐wide ecotones of pine‐mixed hardwood encompassed the major pineries and barrens.Fire‐return intervals and relative dominance of several tree species were strongly correlated at both fine (3–64 km2) and coarse (> 100 km2) spatial scales. At fine scales, relative dominance of shortleaf pine increased with increasing fire frequency during 1701–1820. Relative dominance of black oak (Q. velutina Lam.), and to a lesser extent post oak (Q. stellata Wang.), decreased with increasing fire frequency. Shortleaf pine and these xerophytic oak species occurred on similar bedrock types but were strongly differentiated by fire regimes. Main conclusions Fires exerted strong constraints on vegetation composition and patterns. Historical patterns of Native American occupancy in the region are consistent with the reconstructed vegetation and fire histories and suggest that anthropogenic fire regimes played an overriding role in the development of Ozark vegetation in the 1800s.
Fire and succession in the ultramafic maquis of New Caledonia
Authors: McCoy S. , Jaffré T. , Rigault F. , Ash J. E. 
Published: March 2003

Summary Aim This study investigates the role of fire and post fire succession in determining the structure and composition of vegetation on ultramafic iron crust soils. Location The study was conducted in the Plaines des Lacs region of southern New Caledonia. Methods A survey was made of eighty‐eight sites, recording floristic composition, trunk size‐class distributions, regeneration after fire, growth ring counts of Dacrydium araucarioides (Podocarpaceae) and historical information on past fires. Floristic data was ordinated using multidimensional scaling and an index of succession based on structural and historical information. A transition matrix model was developed to predict the effect of fire frequency on vegetation composition. Results The vegetation is undergoing postfire succession from maquis to forest, after about 75 years, and eventually to rainforest. Gymnostoma deplancheanum has a key role as an early colonist that produces shade, the bulk of the litter, and forms nitrogen fixing nodules with Frankia sp. However, the open canopy of Gymnostoma and slow litter decay creates flammable conditions. Though many species resprout from rootstocks, only thirty‐nine persist through fires while 114 others colonize at later successional stages, as the litter layer and shade increase. Some early successional species are later excluded but these can persist locally in swamps and on rocky hill tops. Forest and rainforest are less flammable and the matrix model suggests that ignition frequency has a critical role in determining the abundance of maquis or forest. Main conclusions The vegetation mosaic represents a post fire succession from open maquis to forest. Palynological and charcoal records from late Pleistocene sediments suggest that fire has been a major factor determining the development of maquis vegetation since before the arrival of humans. Recently, frequent fires have converted much of the vegetation to maquis, posing a threat to some forest species and largely eliminating rainforest from iron crust soils.
Mammalian species richness and morphological complexity along an elevational gradient in the arid south‐west
Authors: Shepherd Ursula L. , Kelt Douglas A. 
Published: March 2003

Summary AimWe examined the relationship between species richness and morphological complexity of terrestrial mammal communities along an elevational gradient. LocationThe gradient is in the Sonoran Desert in Southern California and extends from a sand dune habitat near sea level to coniferous forest ending at >2600 m. MethodsMorphological diversity, characterized by both size and shape of coexisting mammal species, was estimated within and between sites from projections of variables on principal components axes. Similarities among species were calculated as Euclidean distances. To tease apart size and shape, we constructed two principal component analyses: one based on log‐transformed original measurements, the other on log‐transformed proportional shape variables. To test whether species number accounted for the morphological diversity at each site we designed two null models. The models generated were random communities generated from the forty‐two‐species pool. Indices of morphological diversity for real communities were compared with the results of 500 simulations of each null model. ResultsSpecies richness varied along the gradient, peaking in the mid‐elevation agave‐ocotillo habitat. Morphological diversity of shapes and sizes correlated strongly with species richness. Locomotor, tooth, and skull traits were all important in distinguishing among species. Main conclusionsTwo important patterns emerged: (1) diversity of both sizes and of shapes of species within communities correlated positively with species number, and both sets of variables behaved similarly across this gradient; (2) the most species rich sites were not composed of specialists on these best places, but rather, a community of species derived from overlapping faunal groups.
Late Quaternary biomes of Canada and the eastern United States
Authors: Williams John W. , Webb Thompson , Richard Pierre H. , Newby Paige 
Published: March 2003

AbstractPollen data have been used to construct biome maps for today, 6000 14C yr bpand 18,000 14C yr bpfor Canada and the eastern United States.The inferred modern biome distributions agree well with independent reconstructions of North American vegetation prior to European settlement. Some discrepancies between the pollen data and the modern potential vegetation are caused by post‐settlement clearing of the landscape and the consequent increase of herbaceous types in the recent pollen record.Biome distributions at 6000 14C yr bpreflected the warmer and drier conditions then prevalent in the continental interior, but the overall position of biomes was similar to that of today. The boreal treeline in North America was not significantly north of its present position, in contrast to the 100–200 km shift reported for Siberia. At the last glacial maximum (18,000 14C yr bp), steppe and tundra were prevalent in the Midwest and north‐western Canada, and coniferous forests and woodlands grew in eastern North America. The open vegetation at 18,000 14C yr bpwas probably due to drier conditions and/or lower concentrations of atmospheric CO2.The composition and physical structure of biomes is not constant over time. Mid‐Holocene biomes were similar in structure to those of today, but shifts in the relative importance of individual plant functional types are large enough that the physical properties of biomes, such as albedo, canopy conductance and surface roughness, are likely to have varied even during the Holocene. Last glacial maximum biomes were structurally different from their modern counterparts. The biome maps therefore may obscure significant vegetational changes in space and time during the late Quaternary.The difference between the highest and next highest affinity scores for each sample measures how strongly affinity scores discriminate among biomes. For many biomes, the difference is not large, and affinity score ties are not uncommon, highlighting the importance of tie‐break procedures when using the biomization method.
Why are very large herbivores absent from Australia? A new theory of micronutrients
Authors: Milewski A. V. , Diamond R. E. 
Published: March 2003

AbstractAimWe propose a Megacatalyst Theory, based on the pivotal role of the micronutrients iodine (I), cobalt (Co) and selenium (Se), in answer to the body size anomaly of herbivores on different continents, and the previously unexplained absence of megaherbivores in certain environments.LocationIt is anomalous that megaherbivores are absent from Australia while present in even dry and nutrient‐poor parts of southern Africa, and that they have been exterminated from the Americas, but not south‐east Asia.MethodsWe hypothesize that I, Co and Se are micronutrients in quantity, but megacatalysts in effect, determining maximum body size and pace of life, hence whether energy is used by animals or fire. The Megacatalyst Theory suggests that the greater the reproductive rate and brain size relative to body size, the greater the probable demand for I, Co and Se.ResultsBalanced supply of I, Co and Se, within narrow tolerances, is elusive because of disparate cycles: I gravitates towards the sea, whereas Co and Se are concentrated in ultramafics and organic shales, respectively. Sufficiency of these micronutrients, at less than toxic concentrations, is vital for rapid metabolism and growth, particularly of the nervous system. Iodine controls thermogenesis, Co controls the gut fermentation supplying herbivores, and Se controls biochemical damage where both processes occur rapidly. The supply of Co allows vegetation to be metabolized instead of combusted, by promoting digestion of fibre by gut microbes. Herbivores demand I, Co and Se in greater concentrations than palatable plants necessarily contain, as an increasing proportion of energy is fermented from fibre with increasing body size. Economy of scale is limited by loss of I in urine (partly compensated by thyroid size), Co in faeces (partly compensated by gut compartments), and Se both ways.Main conclusionsThe larger the herbivore species, the more it may depend on supplementation in order to survive predation by humans. As body mass increases, Co becomes deficient before I, because it is essential for rumination, and cannot be absorbed by the skin. Moderate uplift of a fairly flat landscape sustainably supplies I from mineralized springs, and Co from rocks (and Se from both), avoiding the excess of I in the sea and the excess of Co on high mountains. Iodine and Se leached to groundwater under dry climates are inaccessible to herbivores on a continent as flat as Australia, where even kangaroos have limited fecundity and intelligence compared to southern African ruminants of similar body mass. Where springs and associated earth‐licks were available in the late Pleistocene, megaherbivores could evolve to survive the era of domestication.