Size-class Frequency Distribution Research Articles

Long‐Term Impacts of Selective Logging in a Tropical Rainforest in the East Region of Cameroon

ABSTRACTAlthough selective logging has become the primary cause of degradation in many African countries, little is known about its long‐term effects. This study investigated the long‐term effects of selective logging on forest tree species diversity and dynamics in the East Region of Cameroon. Six permanent monitoring plots of 1 ha each in unlogged and logged forests were established in 2005 and a recensus in 2011. Each 1 ha plot was divided into 25, 20 × 20 m quadrats. Each 20 × 20 m quadrat was further divided into 16, 5 × 5 m subquadrats, where the diameter at breast height (DBH) of all trees ≥ 2 cm was measured. There was a decrease in plant species density and richness in all forest types. Sloetiopsis usambarensis was the most important species in the unlogged forests and forests logged 21 years ago. The most important family was Putrangivaceae, Euphorbiaceae and Violaceae in the unlogged forests and forests logged 11 and 21 years ago, respectively. The frequency distribution of stem size classes indicated a reversed J‐shape of tropical forests. The above ground biomass (AGB) recovered more than 50% in all forests, and the unlogged forest had the highest AGB (961.8 Mg/ha). Larger stems indicated a forest at a stage of recovery from disturbance. Silvicultural management should be considered.

Facies created by the yellow coral Dendrophyllia cornigera (Lamarck, 1816): Origin, substrate preferences and habitat complexity

The yellow coral Dendrophyllia cornigera (Lamarck, 1816) is a NE Atlantic-Mediterranean scleractinian. It is considered a typical hard bottom species, generally reported on outcropping rocks from mesophotic to upper bathyal depths. Several evidences suggest that this species is able to tolerate a broad range of temperatures, which allows it to colonize numerous environments in a wide depth range.In the present study, we first provided a detailed ecological characterization of the D. cornigera dense aggregation thriving on the Mantice Shoal (NW Ligurian Sea, Mediterranean Sea). Information on substrate type and inclination, average extension and density, colonies size-class frequency distribution and associated fauna are reported. Then, we presented an extensive review of the available information on the ecology of this species, including 142 new ROV records from the Italian coast (40–1820 m). Results indicated that D. cornigera occurs on a wide range of substrates, including soft bottoms and hardgrounds (outcropping rocks, coralligenous rock and dead cold-water coral frameworks), with significant differences in colony density and size among different substrates.Dendrophyllia cornigera creates three main facies, each characterized by a specific combination of substrate, inclination, depth, and associated fauna. Scattered living colonies, as well as large thanatocoenoses, display a wide geographical and bathymetric distribution. Differently, the facies represented by dense meadows on horizontal soft-bottoms results rare, being reported only from the Mantice Shoal and the Amendolara Bank (Ionian Sea). The radiocarbon age of the thanatocoenoses varies between 400 (Corsica Channel) and 13000 (Vercelli Seamount) years before present.This study highlights the wide adaptability of D. cornigera in terms of environmental settings, changing the current view on the ecology of this species and providing essential insights for the implementation of international deep-sea habitat classification schemes and conservation measures.

Ecological aspects of Rhinoclemmys punctularia punctularia (Testudines: Geoemydidae) in two localities in northern Brazil

ABSTRACT Rhinoclemmys punctularia punctularia is the only turtle of the family Geoemydidae with part of its range in Brazil. The species is semi-aquatic and widely distributed across the Amazon basin but is still poorly studied. We evaluated aspects of the population structure, habitat use, seasonal activity, and diet of the species during one year, from the beginning of the rainy season to the end of the dry season, in two headwater localities in the Tocantins and Tapajós river basins, in the state of Pará, Brazil. We captured 45 individuals, 14 in the Tocantins basin and 31 in the Tapajós basin. The size-class frequency distributions of captured individuals did not differ between the two samples. The turtles were most frequently captured in first-order streams, followed by lentic (third-order dammed streams) and second-order streams. The capture rate did not vary significantly between sampling periods (start and peak of the rainy season; start and end of the dry season). The trapping effort to capture a single individual was much higher in the Tapajós basin (1,215 trap-hours) than in the Tocantins basin (136 trap-hours). Overall, the low capture rates confirm the secretive nature of the species in Amazonia and its apparent rarity. The individuals analyzed in this study consumed mainly plants.

Succession from Pasture to Forest in a Mesic Southern Forest in Michigan, USA

After the southern part of an old-growth, mesic southern forest dominated by Fagus grandifolia and Acer saccharum in southwestern Michigan, USA, had been clearcut, it was converted to a pasture. In 1919 grazing ceased on the pasture, and it and the old-growth forest to the north were protected as a natural area, later named Warren Woods State Park. At that time the pasture began to develop into a second-growth forest from root and stump sprouts and seeds. In 2014, 2018, and 2019, the tree species composition of the old-growth and second-growth forest was studied to answer the following questions: (1) How, when, and from where did the current species of the second-growth forest arrive? (2) Is there any evidence that the second-growth forest is trending toward the composition of the old-growth forest? (3) If so, what changes are predicted to occur? Data show that the second-growth forest has become a hardwood forest dominated by A. rubrum, Liriodendron tulipifera, Prunus serotina, and Quercus rubra with a subcanopy of A. saccharum and F. grandifolia. Finally, size class frequency distributions of F. grandifolia and A. saccharum, but not of the current canopy dominants, indicate that the second-growth forest may be trending toward the composition and structure of the old-growth forest that preceded it. As it does, tree species richness and diversity will decrease as basal area increases.

Ecology of endangered Prunus korshinskyi Hand.-Mazz. in Jabal Al-Lauz, Saudi Arabia: Plant associations, size structure, and nutritional screening.

The wild Prunus korshinskyi has a restricted distribution in small scattered areas of Jabal Al-Lauz (2580 m above sea level), a mountain in northwestern Saudi Arabia. Major objective of current study is to provide information about P. korshinskyi by analyzing its ecology in terms of floristic diversity, plant associations, environmental features, and its size structure and nutritional value. For this purpose, 12 stands of 20 m2 were selected along the Jabal Al-Lauz mountain ridge. Three plant associations and their environmental variables were identified and characterized after application of a two-way indicator species analysis (TWINSPAN), detrended correspondence analysis (DCA). And canonical correspondence analysis (CCA) as follows: VGI: P. korshinskyi-Astracantha echinus, VGII: Artemisia siberi-P. korshinskyi, and VGIII: Retama raetam-Artemisia sieberi. The edaphic factor affecting the distribution of the associations were pH, potassium and manganese content. The size class frequency distribution of P. korshinskyi shows a J-shape in spring and fall for the whole population; there was no regeneration via seed. Nutritional evaluation showed the fruits had a higher content of total carbohydrate, fats, crude protein, phosphorus, and potassium, and lower content of ash, Fe, Ca, Mn, Mg, and Zn than that in stems and leaves. This ecological knowledge gained through this study would be beneficial for managing and conserving of P. korshinskyi in a Jabal Al-Lauz area with its distinct and unique vegetation.

Characterizing Wood Turtle (Glyptemys insculpta) Populations at the Northwestern Periphery of the Species' Range in Canada

We report morphometric and demographic characteristics of 2 distinct populations of Glyptemys insculpta (Wood Turtle), at the northwestern periphery of the range in Canada, where they are designated as a species at risk. Our surveys of the 2 study watersheds (2012–2015) were assisted by a trained canine unit which was demonstrably more efficient than human crews in detecting Wood Turtles. We observed that both populations were large—214 and 114 uniquely marked individuals documented over time. We found no significant differences (P ≥ 0.05) in age structure, sex ratios, sexual size-dimorphism, body condition, number of observed mating attempts, or frequency and type of injuries between populations. We observed female-biased sex ratios in both populations (1:1.47 and 1:1.84, respectively) that were not attributable to sampling bias. Our data generally support the postulate of an inverse relationship between Wood Turtle body size and number of frost-free days or latitude. The general health of the 2 study populations was evidenced by the numerous large and reproductively mature individuals of both sexes, relatively high percentage of juveniles observed (average = 26%), and size-class frequency distributions that indicated sustained juvenile recruitment over several years in both watersheds. Our data suggest that high-quality forested watershed habitats, even at the northwestern extreme of the species range in Canada, can and do support large, healthy populations of Wood Turtles.

Population structure of two freshwater amphipods (Crustacea: Peracarida: Hyalellidae) from southern Brazil

Abstract Two recently described amphipods species from southern Brazil, Hyalella georginae Streck and Castiglioni, 2017 and Hyalella gauchensis Streck and Castiglioni, 2017, had their population structures characterized by sex, females’ ovigerous condition, cephalothorax length (mm), size-class frequency distribution, sex-ratio, reproductive period, and recruitment. The specimens were collected with a dip net from a stream source (H. georginae) and from a water reservoir (H. gauchensis) in the Palmeira das Missoes municipality, state of Rio Grande do Sul, Brazil, from August 2012 to July 2013 (12 months). Both species showed a bimodal frequency distribution for total and seasonal size classes, with males larger than females. Overall, the sex ratio favored females when analyzed monthly and seasonally. Ovigerous females were recorded throughout the year, with higher frequency in spring (H. georginae) and summer (H. gauchensis), characterizing a seasonal reproduction. Both species showed continuous recruitment, with greater intensity in the spring. The population structure of these two Hyalella species had similar features, showing continuous recruitment and seasonal reproduction related to their life-history strategies, which promote adaptations to their habitat.

Population dynamics of Rimapenaeus constrictus (Stimpson, 1874) (Penaeoidea) on the southeastern Brazilian coast: implications for shrimp fishing management from a 5-year study on a bycatch species.

This is the first study to evaluate in broad spatiotemporal scales the growth parameters and population structure of Rimapenaeus constrictus, a barely damaged species composing the bycatch from shrimp fishing in the Western Atlantic. The abundance and size-class frequency distribution, growth, longevity and sex ratio were evaluated from monthly samples obtained in the northern littoral of São Paulo state from Jan/1998 to Jun/2003. We measured 5,812 individuals in which the sex ratio was skewed toward females; this was more evident in size classes greater than 10 mm in CL (carapace length) (binomial test, p<0.05). We selected 16 growth cohorts of females, and 8 of males, the majority consisting of younger individual cohorts excluded from the fisheries closure period. Growth estimates resulted in a CL∞ of 17.42 mm, a growth coefficient of 0.008 and a longevity of 579 days (1.60 year) for females, as well as a CL∞ of 16.3 mm, a growth coefficient of 0.01 and a longevity of 425 days (1.17 year) for males. Our results provide information of incontestable relevance to our knowledge of fishing management. We therefore strongly recommend that the fisheries closure period be changed to protect this species' recruitment period and consequently its adult individuals.

Desert Massasauga Rattlesnakes (Sistrurus catenatus edwardsii) in Southeastern Colorado: Life History, Reproduction, and Communal Hibernation

Abstract We studied Desert Massasauga Rattlesnakes (Sistrurus catenatus edwardsii) in southeastern Colorado in 1998 and 2005–2007. Mark–recapture data for 770 snakes indicated a population size of >3,500 snakes in an area of approximately 4,800 ha. Field growth rates and size class frequency distributions showed that average snake age was 3 yr; 4 yr old snakes were frequently encountered, but less than 4% were 5 yr or older, suggesting low survivorship beyond this age. Conversely, initial growth was rapid; snakes grew an average of 0.57 mm/day in their first full year. Desert Massasaugas mated in fall and spring, producing 2–7 (mean 3.3) young in late August to early September, and reproduction appeared to be biennial. Desert Massasaugas showed maternal attendance for at least 5 days postparturition, and neonate dispersal corresponded with the first shed. Radioed Desert Massasaugas (N = 15) used rodent burrows as hibernacula, and within 50 m of Desert Massasauga hibernacula, eight snake, five anuran, and ...

Population dynamics of a freshwater amphipod from South America (Crustacea, Amphipoda, Hyalellidae)

This study aimed to characterize the population dynamics of Hyalella bonariensis Bond-Buckup, Araujo & Santos, 2008 from headwater spring in a rural area of state of Rio Grande do Sul, Brazil. Four samples were collected in August (winter) and October (spring) of 2012 and January (summer) and April (autumn) of 2013. Ovigerous females and precopula pairs were separated from other individual in the field. A total of 5,266 specimens were sampled, being 1,878 males, 2,073 females (including 240 ovigerous females) and 1,315 juveniles. The frequency distribution of size classes (measured as cephalothorax length, CL) was polymodal and bimodal in males and females, respectively. Males reach larger size than females. Sexual maturity of males and females was estimated at 0.40 and 0.38 mm for CL, respectively. Total sex ratio favored females, and these were more frequent in intermediate size classes, while males were more frequent in larger size classes. Ovigerous females and couples were found in four seasons, but both were more abundant in winter. Juveniles were also found in all seasons, being more frequent in winter and spring. These results showed that this H. bonariensis population has similar dynamics to other species of Hyalella Smith, 1874 from Brazil, but present variations when compared to other freshwater amphipods.

Temporal Variation of Population Structure of the Invasive &lt;i&gt;Isognomon bicolor&lt;/i&gt; (Mollusca, Bivalvia), &lt;i&gt;Brachidontes solisianus&lt;/i&gt; (Mollusca, Bivalvia) and &lt;i&gt;Ulva&lt;/i&gt; spp. (Chlorophyta, Ulvales) Biomass, Pernambuco - Brazil

Specifically in Piedade reef, where we performed the present study, Isognomon bicolor invasive bivalve showed greater abundance in the mid intertidal band before dominated by the bivalve Brachidontes solisianus and the barnacle Tetraclita stalactifera. However, the abundance and size structure of Isognomon bicolor and Brachidontes solisianus are variable in the local collection related to desiccation and the presence of Ulva spp.. In this context, this study aims to evaluate the population structure of Isognomon bicolor and Brachidontes solisianus from density and shell length data. For that, were randomly collected 3 quadrats of 20 X 20 cm in February and May 2012, dry and rainy seasons respectively. The animals were scraped, and placed in labeled plastic bags, and frozen for later sorting. After sorting the length of the bivalve shells were measured with the aid of caliper, the seaweed Ulva spp. was also screened, dried and weighed. The Chi-Square test was used to assess the difference between the frequency distribution of the different size classes. The bivalves were divided into 10 size classes. The chi-square test detected a significant difference between the population structure of bivalves. Isognomon bicolor had lower density in May 2012 during the drought, while more individuals Brachidontes solisianus were found in May. However the largest proportion of individuals was always between 13-16 mm in both months of collection for Isognomon bicolor and 3 mm for Brachidontes solisianus presenting both bivalve unimodal distribution these sizes could be more resistant to desiccation and predation stress. The Mann-Whitney test showed a lower density for Ulva spp. in May 2012.

Multiple-pathway succession in coastal Tsuga heterophylla, Thuja plicata, and Abies amabilis forests on northeastern Vancouver Island, British Columbia

Sustainable forest practices are often designed to mimic natural disturbance and successional processes, yet succession is poorly understood in many ecosystems. On northeastern Vancouver Island, the “disturbance hypothesis” is a widely assumed succession model asserting that shade-tolerant western redcedar (Thuja plicata Donn ex D. Don) and the ericaceous shrub salal (Gaultheria shallon Pursh) invade and colonize highly productive western hemlock (Tsuga heterophylla (Raf.) Sarg.) – Pacific silver fir (Abies amabilis Douglas ex J. Forbes) stands (HA) on zonal sites in the absence of stand-replacing wind disturbance. This leads to the development of low-productivity, low-density, uneven-aged, open-crowned redcedar–hemlock–salal stands (CH). In conflict with this model, old, apparently stable HA stands lacking redcedar can be found on such sites as well. We sought evidence for the predicted transition to CH stands by examining stand composition, crown closure, tree size class frequency distributions, salal cover, and redcedar establishment on young HA (∼90 years old), old HA (&gt;160 years), and CH (&gt;160 years) stands. When adjacent to a redcedar stand, young HA stands had fewer redcedar seedlings but more redcedar adult trees than old HA stands. However, redcedar abundance did not differ between young and old HA stands at distances further than 10 m from adjacent redcedar stands. This could indicate that redcedar recruits into HA stands at stand establishment and that redcedar seedling establishment is low under the thick canopy of young HA stands. The chronosequence data also suggest that both old HA and CH stands are self-replacing stand types in these forests, contrary to the disturbance hypothesis. We develop a new, multipathway model for this ecosystem that is based on the chronosequence data and life-history traits of the focal tree species and suggest that disturbance plays a role opposite to the equilibrium model.

Biología poblacional del cangrejo de manglar &lt;i&gt;Ucides cordatus&lt;/i&gt; (Decapoda: Ucididae) en un estuario tropical semiárido

The mangrove crab Ucides cordatus is an important resource of estuarine regions along the Brazilian coast. U. cordatus is distributed from Florida, U.S.A., to the coast of Santa Catarina, Brazil. The species plays an important role in processing leaf litter in the mangroves, which optimizes the processes of energy transfer and nutrient cycling, and is considered a keystone species in the ecosystem. Population declines have been reported in different parts of the Brazilian coast. In the present study we evaluated aspects of the population structure, sex ratio and size at morphological sexual maturity. We analyzed 977 specimens collected monthly over 24 months (2010-2012), in a mangrove of the Jaguaribe River, in the municipality of Aracati on the East coast of Ceará state, Northeastern Brazil. The study area has a mild semiarid tropical climate, with mean temperatures between 26 and 28 degrees C. The area is located within the eco-region of the semiarid Northeast coast, where mangroves occur in small areas and estuaries are affected by mesomareal regimes. The population structure was evaluated by the frequency distribution of size classes in each month, and the overall sex ratio was analyzed using the chi-square test. Size at morphological sexual maturity was estimated based on the allometry of the cheliped of the males and the abdomen width of the females, using the program REGRANS. The size-frequency distribution was unimodal in both sexes. The overall sex ratio (M:F) (1:0.6) was significantly different from 1:1. Analysis of the sex ratio by size class showed that the proportion of males increased significantly from size class 55-60 mm upward, and this pattern persisted in the larger size classes. In the smaller size classes the sex ratio did not differ from 1:1. The size at morphological sexual maturity was estimated at a carapace width (CW) of 52 mm and 45 mm for males and females, respectively. Analysis of the population parameters indicated that the population of U. cordatus in the Jaguaribe River mangrove is stable. However, constant monitoring of the population is required to detect any changes in the population attributes that may affect this stability.

Seasonal bathymetric migrations of deep-sea fishes and decapod crustaceans in the NW Mediterranean Sea

Seasonal variations in the photophase length seem to drive migrations of marine animals, a phenomenon still largely unknown in deep-sea fishes and decapod crustaceans. Here, we report depth-oriented migrations of species living in the continental slope of the NW Mediterranean after repeated trawl sampling between 900 and 1500m depths in four seasons. To understand the variations in the catchability of animals as a function of water depth, we analysed the relationship between population depth shifts and environmental factors by performing a multiparametric habitat monitoring at sea surface (PAR), in the water column (temperature and salinity), and on the seabed (organic matter flux and total mass flux). Significant connections are studied by NMDS and GAM analyses. Bathymetric changes in most targeted species are identified from winter, when distribution was the deepest, to spring and summer, and finally autumn, when the shallowest distribution was observed prior to a sudden bathymetric retreat. The analysis of size-class frequency distributions (Kolmogorov–Smirnov test) discards an effect of the juvenile recruitment on these bathymetric changes. Which environmental factor imparts seasonality to these depth-oriented migrations has not yet been clarified. A strong connection is found with water temperature and salinity, associated to flow of the Levantine Intermediate Water (LIW) and the Western Mediterranean Deep Water (WMDW). The studied depth range was affected by seasonal fluctuations of both water masses and the interphase amongst them. LIW showed a stronger seasonal pattern, getting warmer, saltier in autumn and fresher in winter. The migration of most species towards shallower depths in spring, summer and autumn, and the sudden migration to deeper grounds in winter could therefore be related to changes in LIW temperature and salinity.

Reproductive traits and population structure of &lt;i&gt;Astyanax aeneus&lt;/i&gt; (Characiformes: Characidae) from a subtropical river in Mexico

Champotón River is an unknown area within the Mesoamerican hotspot in Southestern México. Reproductive traits and population structure of Astyanax aeneus were analyzed along an environmental gradient of the upper, middle and lower sections of the river, where diverse environmental factors were recorded. For this, nets were cast for 1 h at each site and A. aeneus were collected from all sections with sweep nets (5 and 10 m long by 5 m deep, 0.03m mesh size) and a casting net (0.05m mesh size). At each study site and campaign, a total of 80 specimens (in average) were collected and were fixed in 10% formaldehyde for further analysis. Population structure by size was analyzed for each study site, based on the relative frequencies by standard length classes. The length-weight relationship was determined, and the identification of gonadal developmental stages, reproductive period, size at first sexual maturity, relative fecundity, sex ratio and somatic indexes (gonadosomatic, hepatosomatic and Fulton's condition factor) were also assessed. Seven size classes were found in the upper and middle sections, and nine downstream, with seasonal and spatial pattern in size-class frequency distribution. Size at first maturity was 45.7mm for females and 40.8mm for males. The maximum relative fecundity was recorded at the downstream site and was positively correlated with body weight and standard length. Sex ratio (1.8:1 males: females) differed significantly from expected values (1:1). Gonadosomatic index scores indicated that the reproductive period of this species in the Champot6n River was from April to July, during the warm and wet season. Hepatosomatic index was negatively correlated with the Gonadosomatic index, evidencing transfer of energy from the liver towards gamete production. This strategy enabled A. aeneus to maintain robustness during the study period with tiny changes in condition factor. A. aeneus in the Champotón River, as opposed to South American river congeneric species of similar size, shows early sexual maturity, a short reproductive period with high gonadosomatic index values, and high fecundity, a trade-off for the short reproductive period. Spatio-temporal segregation was evident: breeders congregate downstream, while juveniles prefer the upper reaches. This pattern allows A. aenus to be successful in a river with high frequency of hurricanes.

Development of areolae and growth of the peripheral prothallus in the crustose lichen Rhizocarpon geographicum: an image analysis study

Areolae of the crustose lichen Rhizocarpon geographicum (L.) DC., are present on the peripheral prothallus (marginal areolae) and also aggregate to form confluent masses in the centre of the thallus (central areolae). To determine the relationships between these areolae and whether growth of the peripheral prothallus is dependent on the marginal areolae, the density, morphology, and size frequency distributions of marginal areolae were measured in 23 thalli of R. geographicum in north Wales, UK using image analysis (Image J). Size and morphology of central areolae were also studied across the thallus. Marginal areolae were small, punctate, and occurred in clusters scattered over the peripheral prothallus while central areolae were larger and had a lobed structure. The size-class frequency distributions of the marginal and central areolae were fitted by power-law and log-normal models respectively. In 16 out of 23 thalli, central areolae close to the outer edge were larger and had a more complex lobed morphology than those towards the thallus centre. Neither mean width nor radial growth rate (RaGR) of the peripheral prothallus were correlated with density, diameter, or area fraction of marginal areolae. The data suggest central areolae may develop from marginal areolae as follows: (1) marginal areolae develop in clusters at the periphery and fuse to form central areolae, (2) central areolae grow exponentially, and (3) crowding of central areolae results in constriction and fragmentation. In addition, growth of the peripheral prothallus may be unrelated to the marginal areolae.

Annual production and its dynamics of four dominant mayflies in Hujiaxi Stream of Qingjiang River catchment,Yangtze River Basin

2006年4月至2007年3月对长江支流清江二级支流——胡家溪的大型底栖动物群落结构和生产量进行为期一周年的调查和研究.结果表明,主要蜉蝣优势种小裳蜉(Leptophlebia sp.)、扁蜉(Electrogena sp.)、四节蜉(Indobaetis sp.)的生活史为一年三代,细蜉(Caenis sp.)为一年两代;小裳蜉的年均密度和年均生物量分别为407 ind./m²、1.00 g/m²;扁蜉为150 ind./m²、0.37 g/m²,四节蜉为232 ind./m²、0.30 g/m²,细蜉为91 ind./m²、0.17 g/m².采用龄期频率法测算的周年生产量和P/B分别为:小裳蜉为441.42 g/m²(WW),14.3;扁蜉为434.88 g/m²(WW),7.6;四节蜉为747.21 g/m²(WW),15.0;细蜉为40.52 g/m²(WW),7.2.四种蜉蝣生产量的时间重叠比例相似系数较高,均大于0.55,这可能与四种蜉蝣的生境及食物资源较为相似有关.;During the period of April 2006 to March 2007,secondary production and its dynamics of the dominant species of mayfly community in a second order river (Hujiaxi Stream) of Qingjiang River,Yangtze River Basin were investigated.From the upper to the lower reach of the stream,we sampled at six sites of different habitats quantitatively.The life cycles of the four dominant mayflies, namely Leptophlebia sp.,Electrogena sp.,Indobaetis sp.,and Caenis sp.,were analyzed by the monthly size-class frequency distribution,the cohort and annual production were estimated by size frequency method,and the production dynamics were examined by the method sensu Benke and Wallace (1997).The results show that Leptophlebia sp.,Electrogena sp.,and Indobaetis sp.appear to develop three generations per year,while Caenis sp.completed two generation a year.Their average annual standing stocks were: for Leptophlebia sp.,407 ind./m²,1.00 g/m²;for Electrogena sp.,150 ind./m²,0.37 g/m²;for Indobaetis sp., 232 ind./m²,0.30 g/m²;and for Caenis sp.,91 ind./m²,0.17 g/m²,respectively.The annual production (g/m² (WW)) and the annual P/B ratio of four mayflies were: for Leptophlebia sp.,441.42 g/m² (WW),14.3;for Electrogena sp.,434.88 g/m² (WW),7.6;for Indobaetis sp.,747.21 g/m² (WW),15.0;and for Caenis sp.,40.52 g/m² (WW),7.2.Temporal overlap of secondary production dynamics of the four species,which measured with the proportional similarity index as 0.55,indicates that they utilize similar or same food resources along time dimension.

胜利河连续系统中蜉蝣优势种的生产量动态和营养基础

大型底栖动物在河流生态系统中发挥着重要作用, 2009 年3月至2010 年3月间对长江中游支流巴河流域的胜利河大型底栖动物群落进行1 周年的调查研究。结果表明, 主要蜉蝣优势种扁蜉一种、等蜉一种和红斑蜉的生活史为3代/a、3代/a和 2代/a。现存量呈现出1-3级河流增加、4级又较3级有所下降的趋势。采用体长频率法( 实则 size-frequency method) 测算的周年生产量分别为:扁蜉, 200.13 g·m^-2·a^-1, <em>P/B</em>为23.69; 等蜉, 82.06 g·m^-2·a^-1, <em>P/B</em>为18.12;红斑蜉, 12.30 g·m^-2·a^-1, <em>P/B</em>为8.78。3种蜉蝣生产量时间动态与现存量较一致,但彼此各不相同;扁蜉日均产量于2009年3月在二级河流中达到最大(363.56 mg·m^-2·d^-1),等蜉于2010年3月在三级河流中到达最大(282.76 mg·m^-2·d^-1),而红斑蜉于2009年3月在一级河流中到达最大(33.36 mg·m^-2·d^-1)。生产量的营养基础分析结果表明,3种蜉蝣前肠内含物中无形态碎屑均占最大比例(41.14%-74.37%),其对生产量的贡献率也最大(46.67%-77.15%),其它食物类型均相对较小,且总体上与作者在黑竹冲和叹气沟的研究结果存在一定差异,可能与这些溪流自身环境和地区分布有关。;The macrozoobenthos community plays an important role in material cycling and energy flow in riverine ecosystems. During the period of March 2009 to March 2010, an investigation was conducted on the life cycle, production dynamics and trophic relationships of the dominant mayfly species in first-order to fourth-order rivers-a continuum of Shenglihe Stream in the upper reaches of the Bahe River, a main branch of the Yangtze River. According to the diversity of micro-habitats, from the upper to the lower reaches of Shenglihe Stream, 12 types of habitats were chosen for quantitative sample collection. At each station, two samples were taken with a 250 μm, D-frame kick net or a Surber net, and the samples were sieved with a 250 μm net and sorted in a porcelain dish without magnification. The specimens were kept in 10% formalin for later processing. The life cycles of the three dominant mayflies, <em>Heptagenia</em> sp., <em>Isonychia</em> sp., <em>Ephemera rufomaculata</em> Zhou & Zheng, 2003, were analyzed by their monthly size-class frequency distribution and their cohort and annual production were estimated by the size-frequency method. The results showed that <em>Heptagenia</em> sp<em>.</em> and <em>Isonychia</em> sp. appeared to develop in 3 generations per year, while <em>E. rufomaculata</em> had 2 generations a year. Their standing stocks exhibited a rough trend of increase from the first- to third-order rivers, then a little decrease in the fourth-order river. The estimated mean annual production of <em>Heptagenia</em> sp. was 200.13 g·m^-2·a^-1 and the mean annual <em>P/B</em> was 23.69; those of <em>Isonychia</em> sp<em>.</em> were 82.06 g·m^-2·a^-1 and 18.12; while those of <em>E. rufomaculata</em> were 12.30 g·m^-2·a^-1 and 8.78, respectively. Production dynamics of the three mayflies were in rough agreement with those of their biomasses, but differed significantly from each other. The daily production rate of <em>Heptagenia</em> sp. reached its peak (363.56 mg·m^-2·d^-1 ) in the second-order river in March, 2009, that of <em>Isonychia</em> sp. had its maximum value of 282.76 mg/m²·d in the third-order river in March, 2010, while the maximal daily production rate (33.36 mg·m^-2·d^-1) of <em>E. rufomaculata</em> appeared in the first-order river in March, 2009. By analyzing their foregut contents, the proportions of six type of diet (amorphous detritus, animal materials, vascular plant detritus, filamentous algae and diatoms) for <em>Heptagenia</em> sp. were 74.37%, 4.19%, 17.11%, 4.29%, 0.04%, respectively, and the contribution rates to the secondary production were 77.15%, 11.27%, 6.57%, 4.95%, 0.04%; for <em>Isonychia</em> sp., the proportions of its diets were 65.64%, 6.17%, 23.04%, 0.54%, 4.53%, 0.09%, respectively, and their contribution rates were 68.16%, 16.61%, 8.86%, 1.03%, 5.23% and 0.10%; while for <em>E. rufomaculata</em>, the proportions were 41.14%, 5.96%, 38.04%, 1.34%, 11.21%, 2.31%, respectively, and their contribution rates were 46.67%, 17.52%, 15.98%, 2.81%, 14.13% and 2.91%. The above results were different to some extent from our previous reports in Hezhuchong Stream, a second-order river of Hangjiang River and in Tanqigou Stream, a second-order river in upper reach of Changjiang River. The probable reasons resulted from the different environments and distribution regions.

Importance of demography and dispersal for the resilience and restoration of a critically endangered tropical conifer Araucaria nemorosa

Aims In situ species survival involves persistence at current sites and/or colonization of new locations. Determining the likelihood of these events requires an understanding of population dynamics and dispersal. We address these issues in populations of a critically endangered tropical conifer Araucaria nemorosa and provide conservation recommendations. Location Port Boise, island of Grand Terre, New Caledonia, Pacific Ocean. Methods We characterize the demographic structure of six populations of A. nemorosa based upon size class frequencies and relative basal area compared to competing angiosperm trees. Using genotype data from 280 adult individuals at seven microsatellite loci, we indirectly estimate dispersal distances and project a maximal dispersal envelope around the extant populations. Results Our survey detected marked differences in demographic parameters including the proportion of basal area occupied by A. nemorosa versus angiosperm trees (ranging from 25% to 77%), the size class frequency distributions of A. nemorosa and seedling densities (ranging from 500 to 37300 seedlings ha−1) among some populations. Wright’s genetic neighbourhood ranged from 22 to 876 trees, and historic gene dispersal ranged from 10.8 to 82.4 m, indicating that most seed dispersal is <100 m. Main conclusions This study indicates that the risk of recruitment failure in remnant populations of Araucaria nemorosa is low in most of the stands but is high in the inland population Forêt Nord. In situ natural regeneration appears to be constrained in this population, most likely as a consequence of competitive exclusion. Our results also suggest that the majority of seed dispersal is too short to allow A. nemorosa to disperse to new more hospitable sites within an ecologically relevant time-scale. Our findings have implications not only for this emblematic tree species but also for a wide range of fragmented and degraded plant species populations with limited dispersal that are vulnerable to competitive exclusion.

Population dynamics ofSesarma rectum(Crustacea: Brachyura: Grapsidae) in the Ariquindá River mangrove, north-east of Brazil

This study was carried out in order to provide basic information on the population ecology of the crabSesarma rectumin the Ariquindá River mangrove, Tamandaré, State of Pernambuco, Brazil. The population was analysed with regard to the following aspects, in particular: the size-class frequency distribution of carapace width (CW), mean body size (CW) of males and females, morphological sexual maturity, sex-ratio, reproductive period, and recruitment. Samples were collected monthly from April 2008 through to March 2009; the crabs were collected manually, with a capture effort by one person for 30 minutes, during low tide. The specimens obtained were measured for CW, length of the propodus of males, and abdomen width of females; and the sex and ovigerous condition were noted. Altogether, we obtained 511 specimens (132 juvenile and 137 adult males, and 171 juvenile and 71 adult females, of which 32 were ovigerous). The median CW of males (16.15 mm) was significantly larger than that of females (13.82 mm) (P &lt; 0.05). The size at morphological sexual maturity was 15.73 mm in males and 16.71 mm in females. The sex-ratio for the total of specimens analysed was 1.11:1 (male:female) (P &gt; 0.05). The sex-ratio by size-class showed an anomalous pattern, with a greater abundance of males in the larger size-classes. The reproductive period was continuous and the highest frequency of ovigerous females was recorded in the spring and summer. The major pulse of recruitment occurred during autumn and winter, which is related to greater reproductive activity during the warmer months of the year.