岩松鼠和松鸦对辽东栎坚果的捕食和传播

Predation and dispersal of Quercus liaotungensis Koidz. acorns by Chinese Rock squirrel (Sciurotamias davidianus) and Eurasian jay (Garrulus glandarius) were examined in a Pinus tabulaeformis Carr. forest in Dongling Mountain. Both of them were important acorn dispersal agents. Chinese Rock squirrels frequently forage food in this forest. They consumed a small portion of acorns in situ, while they transported large quantities of acorns in their big cheek pouches. Eurasian jays have great capacity to transport acorns, although they were uncommon visitors to this forest. They carry acorns in their sublingual pouches to other forest. Of the 18 acorns scatterhoarded by a Chinese Rock squirrel, only 3 remained in two different caches 111 days after they were cached. These results indicate that vertebrates play an important role in acorn dispersal and seedling establishment of Quercus liaotungensis.     

Primary Colonization of Volcanic Rocks by Plants in Arid Baja California, Mexico

Abstract: In an arid region of Baja California Sur, Mexico, field observations, combined with chemical and physical analyses, mineral analysis and scanning electron microscopy of unweathered and weathered volcanic rocks, revealed the presence of rock-colonizing plants (most are tree-shaped cacti, possibly rock weathering), growing in volcanic rocks without benefit of soil. Many are at the seedling stage. At least four cactus species ( Pachycereus pringlei [S. Wats] Britt. and Ross, Stenocereus thurberi [Engelm.] Buxb. subsp. thurberi, Mamillaria fraileana [Britt. and Rose] Boed., Opuntia cholla F. A. C. Weber), and one tree (wild fig, Ficus palmeri [S. Wats]) were capable of cracking, growing in and colonizing cliffs and rocks formed from ancient lava flows and, consequently, forming soil for succession by other plant species. This study shows that plant colonization of volcanic rocks may assist soil formation, which eventually leads to accumulation of soil, water and nutrients in a desert terrestrial ecosystem that otherwise lacks these essential plant-growth variables.     

Abiotic factors,competition or predation: what determines the distribution of young crayfish in a watershed?

In the headwaters of the New River in western North Carolina, the dominant crayfish species changes with increasing stream size. One transition occurs between third- and fourth-order streams. Cambarus chasmodactylus is the dominant species in third-order tributaries. Orconectes cristavarius is the dominant species in the fourth-order South Fork of the New River. While adult C. chasmodactylus are present in the South Fork, the young-of-the-year (YOY) of this species are absent despite evidence of reproduction. In this study we evaluated the factors that may be responsible for the absence of C. chasmodactylus YOY from the South Fork. A field experiment was used to evaluate the role of abiotic factors and competition with YOY O. cristavarius. There was no significant effect of either of these factors on mortality or growth of C. chasmodactylus YOY. The growth rate of O. cristavarius was 3× faster than that of C. chasmodactylus in this experiment. Since neither abiotic factors nor competition appeared responsible for the exclusion of C. chasmodactylus YOY from the South Fork we evaluated the potential importance of selective predation by rock bass (Ambloplites rupestris), a fish species that is common in the South Fork but virtually absent in the tributaries. In a laboratory experiment, C. chasmodactylus YOY experienced significantly higher mortality than O. cristavarius YOY in the presence of rock bass. Field observations and a laboratory experiment suggest that the two crayfish species differ in their anti-predator behaviors. Cambarus chasmodactylus was less likely to swim when initially disturbed and swam shorter distances than O. cristavarius. The differences in escape behavior and growth rate may contribute to the differences in the vulnerability of the two species to rock bass predation. Our results suggest that intense predation pressure exerted by the rock bass may contribute to the virtual exclusion of C. chasmodactylus YOY from the fourth-order South Fork. Handling editor: J. Trexler     

« Pister » les images préhistoriques : un exemple saharien

The chronological assignation of Laghchiwat's engravings, a new major rock art site in the south of Morocco, has not been established yet. In that purpose, we are wondering in an unprecedented way about the entanglement in local and prehistoric graphic productions in general. The capacity of reusing a same line by incorporating it into different forms constitutes a codified virtuosity and a complex intellectual exercise. We try to connect this approach with another kind of concrete clue decoding, the tracking, and with the interpretative ability which is required among human societies of hunter-gatherers. By comparing final Paleolithic images (rather predatory societies), which often use the plural reading of the line, to those of the Neolithic (rather productives societies), favorising its monosemia, we seek to highlight the cognitive skills which preside over this or that choice and thus, by extension, perhaps to catch a sight of the oldest iconographical phase of both site and region.     

Spring densities and calling activities of Rock Ptarmigan ( Lagopus muta helvetica ) in the Austrian Alps

According to the European Bird Directive (Council Directive 79/409/EEC of 2 April 1979 on the conservation of wild birds), particular efforts must be made to preserve the Rock Ptarmigan (Lagopus muta helvetica) and its habitats. Protection and management of this species require basic knowledge of the current status of each of its populations. Within the Austrian distribution range of Rock Ptarmigan, only two study sites from the inner parts of the Alps have been investigated and no data on the most eastern pre-alpine populations are available. In the present study, we conducted simultaneous counts of calling Rock Ptarmigan cocks and recorded calling activities. We calculated spring densities for alpine and pre-alpine study areas and compared them. Spring densities for different habitat types in one study area were observed and compared. Spring densities and calling activities differed between study sites, even within the most eastern border of distribution. Generally, spring densities seem to be higher in alpine habitats than in pre-alpine study sites. In one alpine study area, the highest spring densities were found for habitat patches with a heterogeneous mixture of rocky surface and dwarf pine.     

The rapid effects of a whole-lake reduction of coarse woody debris on fish and benthic macroinvertebrates

1. Ecosystems can enhance the biodiversity of adjacent ecosystems through subsidies of prey, nutrients and also habitat. For example, trees can fall into aquatic ecosystems and act as a subsidy that increases aquatic habitat heterogeneity. This habitat subsidy is vulnerable in lakes where anthropogenic development of shorelines coincides with a thinning of riparian forests and the removal of these dead trees (termed coarse woody debris: CWD). How the disruption of this subsidy affects lake ecosystems is not well understood.
2. We performed a whole ecosystem experiment on Little Rock Lake, a small (18 ha), undeveloped, and unfished lake in Vilas County, WI, U.S.A., that is divided into two similar-sized basins by a double poly-vinyl chloride curtain that prevents both fish and water exchange between basins. In 2002, we removed about 70% of the littoral CWD in the treatment basin, while the reference basin was left unaltered. We tested for changes in both fish and benthic macroinvertebrate community composition in the two years following the CWD reduction.
3. Yellow perch ( Perca flavescens ) was the most abundant fish species in the lake prior to our experiment, but declined to very low densities in the treatment basin after manipulation. We found no evidence of an effect on macroinvertebrates – the treatment basin's macroinvertebrate community composition, diversity and density did not change relative to the reference basin.
4. Our results indicate that different trophic groups may have differential responses to the loss of a habitat subsidy, even if anthropogenic effects on that subsidy are severe. In the case of Little Rock Lake, fish community responses were evident on a short-time scale, whereas the macroinvertebrate community did not rapidly change following CWD reduction.     

New combinatorial clustering methods

Sixteen clustering methods are compatible with the general recurrence equation of combinatorial SAHN (sequential, agglomerative, hierarchical and nonoverlapping) classificatory strategies. These are subdivided into two classes: the d-SAHN methods seek for minimal between-cluster distances the h-SAHN strategies for maximal within-cluster homogeneity. The parameters and some basic features of all combinatorial methods are listed to allow comparisons between these two families of clustering procedures. Interest is centred on the h-SAHN techniques; the derivation of updating parameters is presented and the monotonicity properties are examined. Three new strategies are described, a weighted and an unweighted variant of the minimization of the increase of average distance within clusters and a homogeneity-optimizing flexible method. The performance of d- and h-SAHN techniques is compared using field data from the rock grassland communities of the Sashegy Nature Reserve, Budapest, Hungary.Abbreviations CP = Closest pair - RNN = Reciprocal nearest neighbor - SAHN = Sequential, agglomerative, hierarchical and nonoverlapping     

Phosphate supplying power of rock phosphates in an oxisol

Summary The P-supplying power of triple superphosphate, three apatitic rock phospates and a calcined aluminum rock phosphate were tested by measuring the quantities of fertilizer P recovered in soybean and in four chemical extractants, after 3-day and 75-day periods of contact between soil and fertilizer.The triple superphosphate supplied the highest amounts of P, but it lost efficiency during the longer incubation period. The rock phosphates maintained their original efficiencies, probably as a result of a balance between P released from the fertilizer and P converted into non-labile forms.The following coefficients of correlation between P uptake by soybean from an acid oxisol and P extracted by chemical extractants, after the two incubation periods, were found: 0.902^** for 0.01M CaCl₂; 0.823^** for anion-exchange resin; 0.720^** for 0.03N NH₄F+0.025N HCl; –0.037 (n.s.) for 0.025N H₂SO₄+0.050N HCl.The acid NH₄F solubilized residual calcined aluminum phosphate particles, and double acid extracted P from residual apatite particles, thus accounting for their poorer performances in predicting availability of fertilizer P.The relative efficiencies of the rock phosphates could largely be predicted after an incubation period of only three days. This finding attests to the presence in these rock phosphates of an easily soluble fraction of P which is not indicative of the degree of reactiveness of the phosphate as a whole.on leave at the Agricultural University during 1977.