A Reference Value for the Interior-to-Edge Ratio of Isolated Habitats

Isolated habitats, the consequence of the fragmentation process, are the object of external disturbance. This divides the patch area into two zones: interior and edge. The interior-to-edge ratio quantifies the potential disturbance impact. A method is presented to calculate a reference value for the interior-to-edge ratio, based upon the minimum edge for a given interior. The method is based on pixel geometry features and mathematical morphology. A corrected interior-to-edge ratio is defined using the reference value. The method is illustrated for woodlot fragments in the Belgian Kempen region.     

The Fractal Dimension as a Measure of the Quality of Habitats

Habitat fragmentation produces isolated patches characterized by increased edge effects from an originally continuous habitat. The shapes of these patches often show a high degree of irregularity: their shapes deviate significantly from regular geometrical shapes such as rectangular and elliptical ones. In fractal theory, the geometry of patches created by a common landscape transformation process should be statistically similar, i.e. their fractal dimensions and their form factors should be equal. In this paper, we analyze 49 woodlot fragments ( Pinus sylvestris L. ) in the Belgian Kempen region to study the direct relationship between a transformation process and the concomitant patch geometry. Although the fractal dimension of the woodlots is scattered (i.e. they are not statistically similar), the perimeter-area relation of the fragments is characterized by a single, 'dimension-like' exponent. This exponent suggests a certain shape homogeneity among the patches, which is confirmed by the absence of hierarchical levels associated with sharp increases of the fractal dimension at scale transitions. The interaction of different natural (soil factor, vegetation type) and anthropogenic (afforestation, urbanization) processes during patch development is assumed to have generated this feature. Comparison of the area and perimeter fractal dimension with an ecological index for habitat quality, the interior-to-edge ratio, shows that the fractal dimension is suitable for predicting interior habitat presence, which is more likely for patches with smooth perimeters and compact areas. The ratio of the area to the perimeter fractal dimension confirms this observation, with high values for high interior-to-edge ratios, characteristic for regularly shaped patches.     

Dense habitats selecting for small body size: a comparative study on bovids

As a crucial adaptation impacting on most aspects of a species' biology, body size is likely to be under multiple selective pressures. This study aims to determine whether the physical structure of dense habitats selects directly for small size in order to reduce resistance to movement from the vegetation and facilitate concealment (Manoeuvrability hypothesis). This is unclear because other selective forces could indirectly cause habitat to covary with body size. Focusing on bovids, I tested the explanatory power of the Manoeuvrability hypothesis in an interspecific comparative analysis controlling for phylogenetic relatedness. Bovids in dense habitats were indeed found to be reduced in size. Confirming the Food choice hypothesis, grazers, who predominantly feed on abundant food in open habitats, were found to be larger than browsers in a multivariate analysis. However, after controlling for diet there remained a residual variation in body size which correlated negatively with habitat density. No support was found for Bergmann's hypothesis as the explanation for this remaining correlation since body size did not correlate with latitude of the species' range. Likewise, sexual selection on male body size in open habitats due to increased polygyny was an unlikely cause since body size did not correlate with sexual body size dimorphism in multivariate analysis. Rather, the finding that tail length was disproportionately shorter in closed habitats points to dense habitat structure selecting directly for compact body conformation and small size, as predicted by the Manoeuvrability hypothesis.     

Reproductive strategies and body shape in the European pond turtle (Emys orbicularis) from contrasting habitats in Italy

Comparisons within and among populations offer important insights into variation in life-history traits and possible adaptive patterns to environmental conditions. We present the results of observed differences in body size, body shape and patterns of reproduction in four separate populations of the European pond turtle Emys orbicularis in central and southern Italy – coastal ( n =3) and mountainous ( n =1) sites and pond ( n =2) and canal ( n= 2) habitats – to determine whether phenotypic plasticity affects reproductive output. Although we did not find any significant latitudinal variation in body size, we observed significant differences in body shape between canal (rounded body shape) and pond (elongated body shape) systems and smaller size with rounded shape in the mountainous population. Reproductive output is similar among populations (median=5 eggs per clutch), whereas reproductive investment (relative clutch mass to maternal body mass) is higher in the mountain population (one clutch per year) than in coastal populations (two clutches per year), suggesting differential trade-offs between geographic locality, elevation and habitat type. Turtle shell shape and geographic location together affect reproductive output in E. orbicularis in Italy.     

Comparative Microhabitat Use of Ecologically Similar Benthic Fishes

Although benthic insectivorous fishes such as darters and sculpins represent a significant component of riffle communities, few studies have compared the habitat use of these non-related but ecologically similar fishes. The objectives of this study were to examine the habitat use of Etheostoma olmstedi (tessellated darter) compared to Cottus bairdi (mottled sculpin) in Nescopeck Creek and Cottus cognatus (slimy sculpin) in Jack's Creek, Pennsylvania through underwater observation. Etheostoma olmstedi occupied habitats with significantly deeper waters than those available, whereas adult and young of the year Cottus occupied habitats with significantly faster water velocities than those available. Canonical discriminant analysis revealed microhabitat partitioning between E. olmstedi and each Cottus species. Cottus bairdi and C. cognatus occupied significantly shallower habitats with faster water velocities than E. olmstedi. Sculpin species were observed most frequently under substrate whereas E. olmstedi occurred most frequently on the top surface of the substrate. Hurlbert's standardized niche breadth values indicated that C. bairdi and C. cognatus were habitat specialists with regard to water velocity measures, but exhibited generalistic patterns of depth and substrate size use. Etheostoma olmstedi was a habitat specialist with respect to depth, but exhibited generalistic patterns of resource use for substrate size. Differential habitat use by these benthic fishes is consistent with the hypothesis that resource partitioning facilitates species coexistence among stream fishes.     

基于几何形态学的北二星蝽种内形态差异分析(半翅目： 蝽科)(英文)

【目的】北二星蝽Eysarcoris aeneus是一种广泛分布于古北区的重要农业害虫,可危害多种经济作物。其刺肩型和钝肩型前胸背板后侧角长度存在差异,暗示其种内变异的存在。【方法】基于几何形态学的多元回归分析(multivariate regression)、主成分分析(principal component analysis, PCA)、典型变量分析(canonical variate analysis, CVA)和判别函数分析(discriminant function analysis, DFA),对采集于中国19个地区的142头标本(98头北二星蝽标本和44头作为外群的广二星蝽E.ventralis标本)的前翅、后翅、头和小盾片4个性状进行分析比较,研究北二星蝽钝肩型和刺肩型之间的形态变异。【结果】对于所研究的4个性状来说,北二星蝽钝肩型和刺肩型标本间均未检测到异速生长的存在。主成分分析中,钝肩型和刺肩型的标本均有重叠,典型变量分析则显示它们之间存在显著差异(马氏距离和普氏距离的P值均小于0.01)。判别函数分析显示,依据这4个性状两型样本间的正确判别率在67%~89%之间。【结论】结果表明,前翅、后翅、头和小盾片都可以作为北二星蝽钝肩型和刺肩型之间形态变异的评价指标,小盾片特征具有最高水平的鉴别价值;对于所研究的这4个性状来说,北二星蝽钝肩型和刺肩型之间都表现出显著的形状差异,而它们的质心距离差异不显著,说明相对于体型大小差异分析,形状差异分析能更灵敏地揭示谱系间的变异。本研究表明几何形态学可以有效地描述北二星蝽的种内形态变异,为蝽类昆虫种内变异的研究奠定了基础。     

Influence of physical environmental characteristics and anthropogenic factors on the position and structure of a contact zone between two chromosomal races of the house mouse on the island of Madeira (North Atlantic, Portugal)

Aim This study aimed to investigate if and how environmental characteristics (physical factors of the natural environment and the human impact on the landscape) influence the position and structure of a contact zone between two chromosomal races of the house mouse (Mus musculus domesticus Rutty 1712) from the island of Madeira. Location The western part of Madeira, a volcanic island in the North Atlantic. Methods Mice were sampled along a south/north‐western transect following the main road, in human‐modified outdoor habitats. Karyotypes of mice were determined using the yeast‐stimulated bone marrow cell method. Trapping sites were characterized in terms of their physical (altitude, temperature, precipitation and soil type) and habitat (human landscape use and occupancy) features. Demographic parameters of mouse populations, based on trapping‐with‐removal techniques, were also analysed (relative abundance, sex‐ratio, juvenile ratio and female fertility ratio), as well as body size (weight and length). Results Four chromosomal zones were identified on the basis of the frequency of two diagnostic rearrangements (Rb(6.7) in race E. Calheta and Rb(7.15) in race A. Cruz). E. Calheta was present in the two southern‐most zones, followed by the contact zone characterized by the presence of two inter‐racial hybrids and the co‐occurrence of mice belonging to the two races. The northern‐most part of the transect was occupied by A. Cruz. Environmental features differed leading us to split the transect into two parts. The southern part is characterized by lower altitude and precipitation, milder temperature, better soil quality supporting vegetable crops and vineyards, and more abundant and evenly distributed human habitats. This southern part is occupied by E. Calheta mice. The north‐western part presents characteristics opposite to those described above with cereals as the main cultivated crop, and it includes the contact zone as well as the zone inhabited by A. Cruz mice. The demographic parameters evaluated in this study did not differ significantly between chromosomal zones. Main conclusions This ecological survey highlights differences in climatic and edaphic features that have moulded the agricultural activities of humans, contributing to a differentiation of their spatial development, and hence the structure of potential habitats for mice. Results are interpreted within the source–sink framework of population dynamics, following which E. Calheta may function as a source and the areas where A. Cruz and the contact zone are located may function as a sink. Our study suggests that the position and chromosomal composition of the contact zone is influenced by the human component underlying broader environmental features. Similar characteristics were most likely present during the historical settlement of Madeira. They may have favoured the independent divergence of the two races and influenced the dynamics of the contact zone.     

Risk factors in habitats of the tick Ixodes ricinus influencing human exposure to Ehrlichia phagocytophila bacteria

Ixodes ricinus L. (Acari: Ixodida) were sampled during 1996-99 in southern Scotland, on vegetation using cloth drags, on humans by removal from clothing and on roe deer (Capreolus capreolus L.) by searching legs of culled deer. Developmental microclimate was recorded by automatic recorders and questing microclimate by portable instruments during tick collections. Ticks and deer were examined for infection with Ehrlichia phagocytophila bacteria (Rickettsiales) using microscopy and polymerase chain reaction. This pathogen causes tick-borne fever of sheep in Europe and human granulocytic ehrlichiosis in North America, but in Europe human clinical ehrlichiosis due to E. phagocytophila has not been recorded despite serological evidence of exposure. Among three types of habitat, coniferous woodland was most infested with questing ticks (560 ticks/km of drag; mean numbers collected on long trousers: 24.3 larvae, 13.5 nymphs and 0.8 adult ticks/km walked), deciduous woodland had slightly lower infestation (426 ticks/km drag) and upland sheep pasture had much lower infestation (220 ticks/km drag). Of the three main vegetation types, bracken was least infested (360 ticks/km drag), ericas most (430 ticks/km drag) and grassland had intermediate infestation density (413 ticks/km drag). Questing and developmental microclimates were poor predictors of exposure within these habitats, except lower infestation of pastures was attributed to greater illumination there. Collectors who walked a total of 300 km through all habitats (taking 360 h in all seasons), wearing cotton trousers hanging outside rubber boots, were bitten by only four nymphs and 11 larvae of I. ricinus (but no adult ticks). There was a negative correlation between densities of deer and ticks collected, although presence of deer remains a major indicator of exposure. The proportion of infected ticks was fairly uniform at four sites studied. Overall prevalence of E. phagocytophila in I. ricinus was 3.3% in nymphs (40/1203) but only approximately 1.5% in adults of both sexes (although males do not bite). It was estimated that nymphs of I. ricinus gave 4.4% probability of one infected bite/person/year (for occupational exposure during this research) due to presence in all seasons and habitats, their human biting rate of 0.011 nymphs/h or 0.013 nymphs/km and widespread infection with E. phagocytophila. The frequency distribution of intensity of infection in ticks was approximately normal (mean 98 morulae/nymph infected), thus there is a high risk of receiving a high dose from any one infected tick bite.     

Genotype-by-environment interactions leads to variable selection on life-history strategy in Common Evening Primrose (Oenothera biennis)

Monocarpic plant species, where reproduction is fatal, frequently exhibit variation in the length of their prereproductive period prior to flowering. If this life-history variation in flowering strategy has a genetic basis, genotype-by-environment interactions (G x E) may maintain phenotypic diversity in flowering strategy. The native monocarpic plant Common Evening Primrose (Oenothera biennis L., Onagraceae) exhibits phenotypic variation for annual vs. biennial flowering strategies. I tested whether there was a genetic basis to variation in flowering strategy in O. biennis, and whether environmental variation causes G x E that imposes variable selection on flowering strategy. In a field experiment, I randomized more than 900 plants from 14 clonal families (genotypes) into five distinct habitats that represented a natural productivity gradient. G x E strongly affected the lifetime fruit production of O. biennis, with the rank-order in relative fitness of genotypes changing substantially between habitats. I detected genetic variation in annual vs. biennial strategies in most habitats, as well as a G x E effect on flowering strategy. This variation in flowering strategy was correlated with genetic variation in relative fitness, and phenotypic and genotypic selection analyses revealed that environmental variation resulted in variable directional selection on annual vs. biennial strategies. Specifically, a biennial strategy was favoured in moderately productive environments, whereas an annual strategy was favoured in low-productivity environments. These results highlight the importance of variable selection for the maintenance of genetic variation in the life-history strategy of a monocarpic plant.     

Communities of Social Bees (Apidae: Meliponini) in Trap-Nests: the Spatial Dynamics of Reproduction in an Area of Atlantic Forest

As most stingless bee species depend on preexisting cavities, principally tree hollows, nesting site availability may represent an important restriction in the structuring of their forest communities. The present study examined the spatial dynamics of stingless bee communities in an area of Atlantic Forest by evaluating their swarming to trap-nests. The field work was performed in the Michelin Ecological Reserve (MER) on the southeastern coast of the state of Bahia, Brazil. Seven hundred and twenty trap-nests were distributed within two forest habitats in advanced and initial stages of regeneration. The trap-nests were monitored between September 2009 and March 2011. Twenty-five trap-nests were occupied by five bee species, resulting in a capture ratio of 0.035 swarms/trap (approximately 0.14 swarms/ha), corresponding to 10 swarms/year (0.056 swarms/ha/year). According to previous study at MER, the most abundant species in natural nests were also the most common in trap-nests in the two forest habitats examined, with the exception of Melipona scutellaris Latreille. Swarms of higher numbers of species were captured in initial regeneration stage forests than in advanced regeneration stage areas, and differences in species compositions were significant between both habitats (p?=?0.03); these apparent differences were not consistent, however, when considering richness (p?=?0.14) and total abundance (p?=?0.08). The present study suggests the existence of a minimum cavity size threshold of approximately 1 L for most local species of stingless bees and sustains the hypothesis of a mass effect of Tetragonisca angustula Latreille populations from surrounding disturbed habitats on the MER forest community in terms of propagule (swarm) pressure. Examining swarm densities with trap-nests can be a promising technique for comparative analyses of the carrying capacities of forest habitats for stingless bee colonies, as long as size thresholds of cavities for nesting are taken into consideration.     

Morphometric study of ultrastructural modifications in the maternal hepatocyte during normal gestation in the Wistar rat

Quantitative changes in hepatocyte ultrastructures during normal gestation were studied in Wistar rats with morphometric methods. On the 18th day of the gestation, variations in nuclearcytoplasmic ratio, size of R.E.R., mitochondria, lysosomes and microbodies were observed, with variations according to the localisation of hepatocyte inside the lobule. We report the most obvious effects as follows: An increase of R.E.R. in the central and perilobular zones. Mitochondria are larger and the rounded forms are more numerous inside the two lobular zones. The number of lysosomes and microbodies are only elevated in the perilobular cells. In conclusion, it is suggested that the hepatocyte organelles are significantly increased during gestation. This is probably due to the metabolic activation. These cellular modifications are only one aspect of the liver increase.     

Why are human newborns so big and fat?

Human newborns and infants have morphological and physiological traits protecting them against hypothermia. These traits are unusual for primates, with some of them rarely seen in other mammals evolving in an African environment. We can include the following: 1.) A non-allometric, bigger size of the newborn, resulting in the decrease of surface to body mass ratio (S/W). 2.) Greater amount of subcutaneous fat tissue (SFT) increasing insulation. 3.) Greater amount of brown fat tissue increasing nonshivering thermogenesis. 4.) Active thermoregulation when sleeping. 5.) Thermal balance moved in the direction of heat conservation in a few months' old babies. I here present a hypothesis that it was the risk of nocturnal hypothermia in open habitats of late Pliocene that was the selective pressure promoting evolutionary emergence of these traits inHomo erectus. The inverse radiation at night in open habitats causes strong gradient of temperatures. In effect the temperatures near the ground (even in the tropics) can be low enough to endanger newborns and infants with hypothermia. If earlyHomo was naked, slept on the ground and if mortality of their babies caused by hypothermia was high, then selection pressures could have promoted those traits protecting infants against the risk of hypothermia. Since the most important traits (1. & 2.) in respect of heat conservation, depend on mother size, it is postulated that they appeared when female body size increased dramatically i.e. duringHomo erectus stage of human phylogeny.     

跨太平洋生物入侵研究展望

跨太平洋生物入侵是当代最受关注、最具影响的生物学现象之一 ,这一过程导致并促进了新东亚 -北美间断分布格局 (与许多众所周知的古间断分布相对应 )的形成。为了更好地了解这一现象以及相关的生物类群 ,我们探讨了以下几个问题 :1)哪些类型的物种参与或可能会参与跨太平洋生物入侵 ,2 )这些入侵种在入侵之后会发生什么变化以及会导致什么样的后果 ,3)为了有效地监控生物入侵 ,我们应该从哪些方面着手研究入侵种及其原生和非原生生境。为了解决这些问题 ,我们应该对原产地和入侵地的这些物种进行比较研究 ,这些研究包括 :1)遗传学 ,2 )生活史 /形态学 (如 :个体大小、种子大小等 ) ,3)生态学 (如 :生活型 /生长型、传粉媒介和竞争对手等 ) ,4 )在原产地和入侵地的地理分布 (如 :分布区的大小、形状以及纬度等 ) ,5 )物理影响因子 (如土壤、水分和气候等 )。这些研究的目的在于 :1)确定外来种在其原生生境中影响其分布的限制因子 ,2 )了解入侵种能够在入侵地成功的原因 ,3)预测可能进一步发生的生物入侵 ,4 )为有效地监控和管理生物入侵提供资料。     

Biogeography of the Primates of Guyana: Effects of Habitat Use and Diet on Geographic Distribution

Species that exploit a wide range of resources or habitats (generalists) tend to be widely distributed, whereas species that exploit a narrow range of resources or habitats (specialists) often have a limited distribution. The distribution patterns are thought to result from specialists using relatively smaller habitats than those exploited by generalists. I used data from 1,725 km of primate surveys that I conducted in Guyana to test these hypotheses. Habitat breadth is the total number of different habitat types occupied by each species. I used the total number of different food categories exploited by each species to measure dietary breadth. Geographic range size is correlated with habitat breadth but not with dietary breadth or body size for the 8 primate species in Guyana. Habitat generalists—red howlers and wedge-capped capuchins—range into all habitats. Habitat specialists—spider monkeys, brown bearded sakis, and golden-handed tamarins—range only into large habitats. Habitat generalists tend to be dietary type specialists in Guyana. I suggest that only habitat generalists can subsist on the low-quality foods in small habitats in Guyana. Conversely, habitat specialists tend to be dietary type generalists in Guyana. They must feed on a variety of food types in large habitats. However, using the number of food categories exploited as a measure of dietary breadth may be only a weak aspect of multidimensional niche. Researchers testing biogeographic hypotheses associated with dietary breadth should consider including multivariate indicators of both the types of food categories eaten and the number of plant species exploited.     

Environmental and vegetation variables have a greater influence than habitat fragmentation in structuring lizard communities in remnant urban bushland

Abstract The expansion of urban areas and adjacent farming land into natural landscapes modifies habitats and produces small isolated pockets of native vegetation. This fragmentation of the natural habitat subdivides animal communities, reduces population sizes and increases vulnerability to extinction. In this paper we investigate whether fragmentation decreases lizard species richness, composition, overall abundance and abundance at the species level. Urban remnants consisting of five small (< 10 ha) and four large (> 10 ha) fragments of natural bushland were paired with continuous bushland areas located near Hobart, Tasmania, Australia. These remnants were surveyed six times, using pitfall traps, from November 2001 to March 2002. Lizard species richness and abundance were not significantly influenced by habitat fragmentation or fragment size. Egernia whitii was the only lizard species significantly influenced by fragment size, and was only present in large fragments and continuous bush. Vegetation type and structure as well as environmental variables (geology and aspect) influenced the structure of reptile communities. Lizard species that were able to use a number of different habitat types were found to persist at most sites, irrespective of fragment size. Edge environment did not significantly influence lizard species richness or abundance in remnant areas. Lizard species richness was significantly lower in sites that had a high ratio of exotic to native plant species. Therefore, if remnants continue to be invaded by exotic plants, lizard species that require native plant communities will become increasingly vulnerable to local extinction. Our results suggest that lizard species requiring specialized habitats, such as E. whitii, may persist in large urban remnants rather than small urban remnants because large reserves are more likely to encompass rare habitats, such as rocky outcrops. Habitat heterogeneity, rather than size, may be the key to their persistence.     

Spatial variations in Eulemur fulvus rufus and Lepilemur mustelinus densities in Madagascar

I present data on variations in Eulemur fulvus rufus and Lepilemur mustelinus densities as well as tree characteristics (height, diameter and stem frequency) between edge and interior forest habitats in southeastern Madagascar. Line transect surveys were conducted from June 2003 to November 2005 in edge and interior forest habitats in the Vohibola III Classified Forest. Although E. f. rufus densities were significantly lower in edge habitats than in interior habitats, density estimates for L. mustelinus did not differ significantly between habitats. Trees in edge habitats were significantly shorter, had smaller diameters and had lower stem frequencies (for those >25 cm in diameter) than trees in interior habitats. Spatial characteristics of food abundance and quality may explain lemur density patterns in Vohibola III. Low E. f. rufus densities may reduce seed dispersal in edge habitats, which has important consequences for the long-term viability of forest ecosystems in Madagascar.     

Scanning electron microscopy of Penicillium conidia

The morphology of conidia in 211 species and 12 varieties belonging to the genus Penicillium Link ex Gray have been studied and compared.According to surface ornamentation, conidia have been classified into six groups: A, smooth-walled (7% of the species); B, delicately roughened (13%); C, warty (28%); D, echinate (10%); E, striate with low irregular ridges (36%); and F, striate with scarce high ridges or bars (6%). Whereas the first two groups are closely related in both shape and average size, a gradual reduction was observed in size and in the length/width (l/w) ratio in the remaining groups. Echinate conidia were globose, having the largest average size. Only four species produced conidia not surpassing 2 m in diameter. Maximum length observed was 8 m, and most elongated conidia had a l/w ratio of 3.5. Forty per cent of the species studied had globose conidia.Conidia of the monoverticillate species were generally smaller, more globose and frequently with ridges. In the Asymmetrica, the conidia were generally larger, and showed ridges in comparatively few species. Conidia of the Symmetrica, which were frequently striate with ridges, presented the most elongated forms. The largest average size was found in the conidia of the Polyverticillata which were generally warty. Finally, we have considered the variations in surface ornamentation of conidia during the evolution of the genus Penicillium and drawn attention to their possible relationship with certain habitats and ways of conidial dispersion.     

Variations of flower size and reproductive traits in self-incompatible <Emphasis Type="Italic">Trollius ranunculoides</Emphasis> (Ranunculaceae) among local habitats at Alpine Meadow

For plants that rely on animals for pollination, the ability to attract the animals to their flowers can be a crucial component of fitness. A large number of studies have documented pollinators to be important selective agents driving the evolution of flower size and correlated traits on a large scale. In this paper, we studied variations of reproductive traits in self-incompatible Trollius ranunculoides (Ranunculaceae) among local habitats at Alpine Meadow. The results showed significant variations of floral size, seed mass per fruit and sex allocation (male/female mass ratio) between different habitats, where floral size and seed mass was not explained fully by variation of plant size among habitats. It suggested that other factors unrelated to plant size might also influence floral variation. However, in our manipulated experiment, it showed no effects of manipulated floral size not only on visit rate of effective pollinators (bees and flies) but also on female success (seed set, seed mass per fruit), irrespective of flower density. Consequently, we could not conclude that the variation of floral size in T. ranunculoides was due to phenotypic plasticity, or natural selection. But if selection occurred, it should not be mediated by pollinators. It was likely that variation of sex allocation between habitats lead to changes of flower or corolla size, because plant invested much less to male function (female-biased sex allocation and larger single seed mass) in shade habitat (bottom of bush) than other exposed habitats, to gain higher fitness. In addition, high-floral density in T. ranunculoides had a negative effect on service of main pollinator (bees) and female success. This situation would influence the strength of selection on floral size.     

重庆中梁山不同石漠化生境中石生南亚毛灰藓斑块的空间分布格局

基于重庆市中梁山喀斯特(Karst)地区3种不同石漠化生境(潜在石漠化、轻度石漠化和中度石漠化)中0.75 hm2样地的数据,以石生南亚毛灰藓(Homomallium simlaense)的3种斑块(小斑块、中斑块和大斑块)为研究对象,运用点格局O-ring的单变量和双变量统计方法对斑块空间格局以及斑块间的关联性进行生态学特性与形成过程分析,取得以下结果。(1)南亚毛灰藓总斑块数量关系为轻度石漠化潜在石漠化中度石漠化;在3种石漠化生境中,各种类型的斑块均呈现出小斑块中斑块大斑块的数量变化。(2)小斑块和中斑块在小尺度上主要为聚集分布,其它尺度上为随机分布;大斑块在整个尺度上都呈随机分布。(3)中斑块与小斑块在3种生境中均在小尺度上有显著的关联性;大斑块与中斑块仅在潜在石漠化生境中的小尺度上有关联性,其它斑块间在不同生境与尺度上均无关联性。(4)环境因子中坡度和石缝数对斑块的分布起很大作用,但是相对湿度是影响分布的主要因子。(5)在相对湿度和郁闭度胁迫方面,小斑块和中斑块随环境胁迫增大而趋于聚集分布。研究结果表明,苔藓斑块大小及其分布式样在石漠化地区裸露岩石的生态恢复中具有重要指示意义。