Medium Size Classes Research Articles

Distribution and Catch Characteristics of Portunus Pelagicus in North Madura Waters

Portunus pelagicus is one of fishery commodity with high economic value and great demand in domestic and foreign markets. P. pelagicus is commonly found in Madura Sea waters. This study aimed to know the catch characteristics of P. pelagicus in North Madura. The locations of this study are Masaran, Sampang Regency, and Pasean, Pamekasan Regency. In this study, census sampling was done using the census method, which involved gathering samples of all the P. pelagicus that fishermen caught on each trip. The catch method in North Madura is using folding traps. In Masaran, the location of the sampling is <2 mils near the coast, and the location of Pasean is around 2-4 miles from the coast. Based on in situ data the water quality in Masaran, Sampang, and Pasean of Pamekasan Regency had various conditions that were able to influence the existence of P. pelagicus. The total weight amount catches in Masaran, Sampang reach 13297 grams (99 individuals), and Pasean, Pamekasan reach 13967 grams (63 individuals). The sex ratio in Masaran, Sampang is 1:3 greater than in Pasean, Pamekasan that is 1:1. Carapace width was divided into small (<10 cm), medium (>10), and large (>12 cm) size classes. In Masaran, P. pelagicus is dominated by large and medium, the amount of large is 56 individuals of crabs, the medium is 32 individuals and 12 individuals are small and do not follow the rule of legal catch. Meanwhile, in Pasean 35 individuals are size large, 22 individuals are medium and 6 individuals are small. These results can be used as the basis for the management of P. pelagicus in North Madura.

Assessment of toxic trace elements (Cd, Pb, As, and Co) in small, medium, and large individuals of Mytilus galloprovincialis and Perna perna mussel species along the Algerian coast.

This research paper focused on the monitoring of marine sites using mussels, which are highly valuable organisms in assessing environmental health. However, a significant challenge arises when determining the appropriate size of mussels for monitoring purposes. The objective of this study was to examine the levels of Cd, Pb, As, and Co in three different size classes of two mussel species, Mytilus galloprovincialis and Perna perna, collected from three sites along the Algerian coast, each exhibiting varying degrees of pollution.At each of the study sites, a total of thirty individuals from small, medium, and large size classes of mussels were collected during four different time periods. The mussels were then dissected, and the concentrations of Cd, Pb, As, and Co were measured in the entire flesh of the mussels using ICP-MS.Across the various study sites, the concentrations of cadmium, lead, arsenic, and cobalt ranged from 0.06 to 1.32mg/kg, 0.09 to 12.56mg/kg, 4.23 to 18.31mg/kg, and 0.11 to 1.85mg/kg, respectively. Interestingly, the distribution of these metals in the three different size classes of mussels followed a consistent pattern at all the study sites. Large mussels exhibited higher concentrations, while small and medium-sized mussels displayed lower levels. These findings highlight substantial spatial and temporal variations in metal concentrations within the studied sites.

Size-dependent functional response of the round goby Neogobius melanostomus; implications for more accurate impact potential calculation

Abundance and per-capita foraging efficiency are essential factors for predicting and quantifying an invasive predator impact on prey, i.e., the impact potential (IP). However, population structure is not included in the calculation, and IP accuracy might be improved by incorporating predator body size. The population structure of the round goby Neogobius melanostomus, a highly invasive predator, was surveyed in the Elbe River. We determined the functional response (FR, per capita foraging) of the three most abundant size classes of N. melanostomus on the water louse Asellus aquaticus. We then calculated the IP for each size class and for the entire population with (the actual impact potential – IPA) and without (the impact potential for limit size rage – IPLSR) population body size structure (based on FR of the medium size class). All three size classes of the predator showed type II FR with respect to A. aquaticus. The estimated FR parameters, attack rate and handling time, as well as the maximum feeding rate, were size dependent. Despite the lowest per capita foraging efficiency, small individuals displayed the highest IP among the tested size classes because of their high abundance. Conversely, medium and large individuals, although showing highest per capita foraging efficiency, displayed lower IP. Hence, IPA showed more precise IP calculations compared to IPLSR. Overestimation of the potential impact as a consequence of omitting predator population size structure was negligible at the investigated locality. The IP of the N. melanostomus population five years post-invasion can be accurately calculated based on the FR of medium-sized fish.

Study of extinguishing a model fire of class "B" with bulk materials

The costs of components of the fire extinguishing system based on light loose materials for extinguishing a medium-sized class "B" model fire were experimentally determined. According to the results of preliminary studies on extinguishing a model fire of class "B" of small sizes, as components of such a system, granular foam glass with a granule size of 10–15 mm, expanded perlite with a granule size of 1,2±0,2 mm or vermiculite with a plate size of 1×2 mm and sprayed water. Styrofoam in such a system ensures its buoyancy and cooling of the surface layer of the burning liquid. The fine powder of expanded perlite improves the insulating properties of the fire extinguishing system. The water supplied to the upper layer of loose materials, in addition to increasing the insulating and cooling properties of the system, ensured the long-term absence of re-ignition. To increase the economic parameters of the fire extinguishing system, its composition was optimized according to the effect-cost parameter. It was established that the lowest economic costs for extinguishing gasoline are provided by the sequential supply of three components: crushed foam glass, dispersed expanded perlite and sprayed water with such specific surface costs – 6,7 kg/m2, 1,6 kg/m2 and 2,0 kg/m2 in accordance. For the optimized composition, a study was carried out on extinguishing a standard model fire 2"B", the results of which are close to the results obtained on model fires of small and medium sizes. It is shown that the proposed fire extinguishing system based on light loose materials has advantages in terms of economic and environmental parameters compared to existing and previously proposed means of extinguishing flammable liquids. Means of feeding light loose materials are proposed. The areas of work in the implementation of a fire extinguishing system based on light loose materials in the practice of fire extinguishing have been noted.

Impacts of harvesting intensity on carbon allocation to species, size classes and pools in mangrove forests, and the relationships with stand structural attributes

Mangroves are vital ecosystems that help mitigate climate change and natural hazards, despite representing only 0.5% of the world's coastlines. Recent studies have provided empirical evidence of the ongoing over-exploitation of mangrove forests in West Africa. Understanding the impact of such harvesting on mangroves’ carbon potential is essential to inform decision-making for management and carbon economy policies. This study investigated the impacts of harvesting intensity on (i) carbon allocation to species, size class, soil depth and pool (standing live trees, standing dead trees, litter and soil); and (ii) carbon stock in the different carbon pools, and its relationships with stand structural attributes, using the case study of Benin coastal line. Data were collected in 600 plots of 0.015 ha across 20 mangrove sites in high and low-harvesting-intensity areas. Sixty litter quadrats were also established to sample litter, while 160 soil samples were collected for soil carbon content analysis.Regardless of the harvesting intensity, two mangrove species, Rhizophora racemosa and Avicennia germinans, contributed more than 98% of the tree carbon. Small (1–10 cm) and medium (10–20 cm) size classes dominated tree carbon in high and low harvesting sites, respectively. Soil carbon up to 1 m depth had the greatest share (55%-70%) of the total carbon stock, followed by standing live trees (26%-40%) and litter, and was not influenced by harvesting intensity. Harvesting intensity influenced the carbon stocks in standing live and dead trees, with greater values in low and high harvesting sites. The total carbon stock was ∼ 1.46-fold higher in low harvesting sites (308.54 ± 32.74 MgC.ha−1) than in high harvesting sites (211.40 ± 14.91 MgC.ha−1). Mixed effect models showed that stand density and proportion of R. racemosa related positively with tree carbon stock, especially on low harvesting sites. Multiple factorial analyses revealed that carbon stocks in dead trees, litter and soil are high in low harvesting areas where stand densities are also high. However, in high harvesting sites, carbon stock in litter was positively related to relative density of A. germinans. This study expands our understanding of the carbon stock potential in a West African mangrove subject to different levels of disturbance and its contribution to mitigating greenhouse gas emissions. The implications for management were further discussed.

Timber yield of commercial tree species in the eastern Brazilian Amazon based on 33 years of inventory data

Abstract Selective logging in neotropical forests has directly affected the dynamics of tree species, compromising species conservation and timber yield. Sustainable use of logged forests requires new tree recruitment and diameter growth in remaining trees to compensate for trees removed between cutting cycles. This long-term study investigated timber yields in four species groups with differing values (lower, intermediate, high, and mixed) in logged and unlogged forests in the plateau region of the Tapajós River in the eastern Brazilian Amazon. Analysis was based on two size classes: medium and large commercial-sized trees. In both forest types (logged and unlogged), we found relevant tree recruitment and changes in size classes for all value groups. Most of the recruited trees observed during the 33 years of monitoring remained in the medium size class, but they also occurred in the large size class in logged forests. Over the same period, a significant loss of timber yield was seen, resulting from high mortality among the remaining trees in both size classes due to natural processes and the aftereffects of logging. Timber yield was also seen to be influenced by species richness within the group of commercial species, and recruitment and tree diameter growth capacity to counterbalance losses from mortality of the remaining trees after logging had become restricted. Forest timber yield was mainly regulated by light-demanding species, and shade-tolerant species contributed little to timber yield during the first cut. Continuous monitoring of the remaining trees and measures to reduce tree mortality during cutting cycles can encourage growth and reduce losses in stocked trees. Additionally, the national rules for forest management in the Brazilian Amazon need to be improved to achieve long-term management sustainability.

Distribution and Growth Patterns of Crab (P. pelagicus) Based on Environmental Characteristics in Candi Waters, Pamekasan Regency, East Java Province

Blue swimming crab (BSC) is a fishery commodity with high economic value and great demand in domestic and foreign markets. P. pelagicus swimming crabs are commonly found in Indonesian sea waters, one of the largest contributors to the country's foreign exchange after shrimp and tuna. The high demand for blue crab resources will trigger an increase in fishing efforts. If this is done continuously, it is feared that it could endanger the population structure. Moreover, disrupting the sustainability of blue swimming crab resources in the waters, this study examines the morphometric distribution and growth pattern of P. pelagicus crabs based on environmental characteristics in Candi waters, Pamekasaan Regency. Census sampling was carried out using the census method; the census method was carried out by taking all crab samples caught by fishermen. The results obtained found 33 individual crabs, which were divided into three classes, namely small (&lt;10 cm), medium (&gt;10 cm), and large (&gt;12 cm) size classes. Male crabs dominated the research locations with wider straps than female crabs. The analysis results show that the width-weight relationship's b values are 1.47 (males) and 2.00 (females). In addition, male and female crabs have a positive allometric growth pattern. Blue swimming crabs are often found in habitats with a substrate of dusty mud, high salinity and organic matter.

Kebiasaan Makanan Ikan Tembang (Sardinella fimbriata) di Perairan Selat Sunda

Fringescale sardinella is a small pelagic fish in the Sunda Strait which has important ecological value. Studying fish food habits is basically to determine the quality and quantity of fish food and the ecological relationship in the tropic level. The aims of this research were to examine the food habits of fringescale sardinella in the Sunda Strait which includes the composition of the type of food, the area of ​​the niche and the overlap of the food niches. Sampling Sampling was conducted from the catch of fishermen who landed at Labuan Coastal Fishing Port, Banten. Fish samples taken during the study consisted of 620 males and 321 females. The results showed that the highest IP value was in the Thalassiothrix frauenfeldii organism, both in male (55%) and female (54%), so that Halassiothrix frauenfeldii which is a class of Bacillariophyceae was the main food for fringescale sardinella, the largest area of ​​food niches is in male was in the medium size class of 9,0028, while the largest area of ​​food niches in female was in the small size class of 8,9609, the largest overlap value of male and female food niches is in the small fish size group (101-129 mm ) with the medium fish size group (130-158 mm) were 0,9062 and 0,8105 respectively.

Comparative study of sinus earthquake forces and ground motion on structure behavioral response using linear time history analysis method

This study aimed to calculate the design earthquake with a harmonic sine wave approach at a frequency of 1.5 Hz; 2.5 Hz; 3.5 Hz; 4;5 Hz, as well as Loma Prieta, Northridge, and Kobe ground motion. In addition, a structural response review was also carried out based on a comparison of the effects of the ground motion and sine wave earthquake forces. This study used an experimental method of modelling an apartment building with a scale of 1: 50. The case study was located in Mantrijeron, Yogyakarta, which has a seismic category in the medium-size class. The analysis phase began with material definition, element dimension estimation, modelling by analysis software, loading estimation, structural analysis, and comparison of structural responses based on the deviation. The results indicate that the building model could withstand dynamic loads from harmonic waves up to a frequency of 5.5 Hz for one minute of vibration. The most significant deviation is shown at a frequency of 4.5 Hz with an x-axis direction of 0.110 and a y-direction of 0.160. The structural response resulting from ground motion loading shows that the highest deviation occurred due to the influence of the Kobe earthquake, with a deviation of 0.063 in the x-axis direction and 0.054 in the y-axis direction. Based on these results, the effect of harmonic sine waves is greater than the ground motion loading on the response of the building structure, so it is used as an experimental loading through a vibrating table with the actual residual deviation results showing a value of 0.9 mm in the y-axis direction. The difference in structural response results could be caused by the supports and connections modelling in planning through analysis software which could not precisely represent the actual implementation of the building model.

Within-family variation in larval viability and growth is controlled by different genes: a case study with Crassostrea gigas

Variation in growth and survival of planktonic larvae has profound effects on marine population abundance. Environmental causes of differential larval growth and mortality are well studied, but genetic variation in these traits is less well understood. Here, we reveal genetic variation in survival and growth of full-sib larvae of the Pacific oyster Crassostrea gigas reared under identical conditions. We size-selected 1.42 million, 24 d old larvae to produce small, medium, and large size classes, constituting 93% of the population. Parental tissues and a total of 144 larvae sampled from each size class were individually genotyped with a panel of 45 mapped DNA markers. Consistent with previous work, 11 markers had genotypic frequencies that differed significantly from their Mendelian expectations and, upon mapping, are explained by 6 viability quantitative trait loci (vQTL). Notably, shell-length variance among size classes maps to 6 major growth QTL (gQTL), with just 2 collectively explaining 18% of the variance. We found little overlap between vQTL and gQTL, suggesting that variation in these larval traits is controlled by different genes. This study demonstrates the feasibility of genotyping single larvae for the identification of multiple QTL. Understanding genetic variation in larval biology is important for a comprehensive understanding of marine recruitment.

POST MORTEM VARIATION OF TOTAL VOLATILE BASE NITROGEN (TVB-N) AND TRIMETHYLAMINE NITROGEN (TMA-N) IN VETKI (Lates calcarifer)

Total Volatile Base Nitrogen (TVB-N) and Trimethylamine Nitrogen (TMA-N) contents of Vetki (Lates calcarifer) were investigated following Conway’s Microdiffusion technique at 4 hour interval in Fish Quality Control Laboratory, Fisheries and Marine Resource Technology Discipline, Khulna University. Observed TVB-N and TMA-N value did not vary significantly among different size classes. At fresh condition, TVB-N content was observed as 11.106±0.8 mg, 11.162±0.8 mg, and 11.162±0.8 mg in small, medium and large size classes of fish respectively and it increased to 59.087±0.8 mg, 68.417±1.5 mg and 75.967±2.7 mg for 100 g-1 respectively at complete spoilage stage (after 28 hrs). At fresh condition, TMA–N content was 6.7±0.016 mg, 11.069±1.79 mg and 11.172±1.01 mg for 100 g-1 in small, medium and large size classes of fish respectively and it increased to 48.893±3.01 mg, 52.492±.089 mg and 57.717±1.95 mg for 100 g-1 respectively at complete spoilage stage. TVB-N and TMA-N values started to increase gradually in all size groups with the passage of time but the rate of increase became faster after 20th hour and continued till the final stage was reached.

Aspek Biologi Ikan Kepar (Belontia hasselti Valenciennes, 1831)

This study aims to determine the biological aspects of twill fish in the swamp waters of PTPN Ajamu III. The method used is exploratory and the determination of the sampling point is done by purposive sampling. Fish samples were caught using fishing rods. All fish caught were measured for total length and weight. The results showed that for the small size class interval (9-11.9 cm) 11 males and 14 females were obtained; medium size class (12-14.9 cm) for 5 individual male fish and 19 individual female fish; and the large size class (15-17.9 cm) found only females with a total of 2 individuals. The relationship between length and weight of twill is negative allometric because of the value of the constant b &gt; 3. The sex ratio of fish for males and females obtained is 1: 2. In conclusion, the population of twill fish is categorized as still maintained.&#x0D; Keywords: Biological Aspect, Belontia hasselti, Swamp Waters

The influence of body size and phylogeny on trabecular microstructure in the proximal femur and humerus of rodents and primates

Life history theory states that organisms maximize their fitness via energetic trade‐offs between various biological functions. It has been well‐established that life history strategy is related to intraspecific variation in body size and that body size predicts some bone microstructural properties, but the relationship between life history strategy and skeletal variation has not been sufficiently examined across multiple mammalian clades. Generally, small‐bodied mammals have “fast” life histories and faster growth rates than large‐bodied mammals, meaning small mammals deposit bone tissue at a faster rate, which may affect skeletal morphology. Therefore, the goal of this study was to conduct a preliminary analysis of trabecular bone structure in the rodent and primate humerus and femur to evaluate the influence of life history traits, particularly body size, on bone properties in a phylogenetically diverse sample. Using a sample of 67 size‐matched adult rodent and primate individuals from 8 extant rodent genera (N=26) and 10 extant primate genera (N=41) ranging in body size from 0.04kg to 70kg, we analyzed trabecular bone structure in the proximal femoral and humeral head. Regression analyses were used to assess associations between trabecular bone properties and body size and one‐way ANOVAs were used to compare bone properties between rodents and primates across three size‐matched classes.Regression results are consistent with previous primate and mammal studies. Bone volume fraction (BV/TV) scales with weak positive allometry in both groups and both elements except for the rodent humerus, which scales isometrically. Degree of anisotropy (DA) varies across all groups and shows no consistent relationship with body size. Trabecular thickness (Tb.Th) and trabecular separation (Tb.Sp) increase with body size, while connectivity density (Conn.D) and bone surface density (BS/BV) decrease with body size across both clades and elements. In both groups and both bones, Tb.Th, Tb.Sp, and Conn.D scale with strong negative allometry while BS/BV scales with strong positive allometry. ANOVAs reveal that Tb.Th and Tb.Sp are higher in the primate femur than in the rodent femur for medium and large size classes, while Conn. D is higher in the rodent femur for medium and large size classes. Other bone properties do not show consistent patterns of differences between primates and rodents. Overall, while overlapping confidence intervals for all slopes suggest body size scales similarly with these bone properties across clades, ANOVA results suggest that medium and large bodied rodents have thinner, more numerous trabeculae in the femur compared to similarly‐sized primates. Further investigation is necessary to elucidate the biological significance of this result and the underlying mechanisms driving the observed phenomenon.

Impact of correcting sub-daily climate model biases for hydrological studies

Abstract. The study of climate change impact on water resources has accelerated worldwide over the past 2 decades. An important component of such studies is the bias-correction step, which accounts for spatiotemporal biases present in climate model outputs over a reference period, and which allows for realistic streamflow simulations using future climate scenarios. Most of the literature on bias correction focuses on daily scale climate model temporal resolution. However, a large amount of regional and global climate simulations are becoming increasingly available at the sub-daily time step, and even extend to the hourly scale, with convection-permitting models exploring sub-hourly time resolution. Recent studies have shown that the diurnal cycle of variables simulated by climate models is also biased, which raises issues respecting the necessity (or not) of correcting such biases prior to generating streamflows at the sub-daily timescale. This paper investigates the impact of bias-correcting the diurnal cycle of climate model outputs on the computation of streamflow over 133 small to large North American catchments. A standard hydrological modeling chain was set up using the temperature and precipitation outputs from a high spatial (0.11∘) and temporal (1 h) regional climate model large ensemble (ClimEx-LE). Two bias-corrected time series were generated using a multivariate quantile mapping method, with and without correction of the diurnal cycles of temperature and precipitation. The impact of this correction was evaluated on three small (&lt; 500 km2), medium (between 500 and 1000 km2), and large (&gt; 1000 km2) surface area catchment size classes. Results show relatively small (3 % to 5 %) but systematic decreases in the relative error of most simulated flow quantiles when bias-correcting the diurnal cycle of precipitation and temperature. There was a clear relationship with catchment size, with improvements being most noticeable for the small catchments. The diurnal cycle correction allowed for hydrological simulations to accurately represent the diurnal cycle of summer streamflow in small catchments. Bias-correcting the diurnal cycle of precipitation and temperature is therefore recommended when conducting impact studies at the sub-daily timescale on small catchments.

Cultivated milkweed hosts high diversity of surface-active and soil-dwelling arthropods in a New England case study

New land uses can drive complex changes to local biodiversity. In the Northeastern U.S., cultivated milkweed has arisen as a new crop with potentially promising outcomes for monarch butterflies, but has unknown effects on surface-active and soil-dwelling arthropods. We assessed differences in arthropod communities among nearby sites containing milkweed and three common regional land uses: conventional corn, conventional hay, and forest, representing a spectrum of high to low land use intensity. In each land use, we sampled surface-active and soil-dwelling arthropods, and we classified organisms at the taxonomic order level for all collected arthropods and at the taxonomic genus level for surface-active beetles. To address differences in functional traits between sites, we measured organisms’ body sizes and calculated average body mass, total biomass, and abundance of arthropods in small, medium, and large size classes. In almost all analyses, taxonomic diversity values were significantly higher in the milkweed site than in corn and similar between the milkweed and hay sites. Milkweed had significantly higher diversity of surface-active arthropods than forest (for both orders and beetle genera), but did not have higher diversity of soil-dwelling arthropods, indicating possible different mechanisms driving aboveground versus belowground trends. Community composition differed significantly among land uses (demonstrated in NMDS ordination plots), with milkweed most similar to hay. Body size analyses demonstrated high total biomass and generally higher abundance of larger individuals in milkweed than in other land uses, with the exception of corn, which was dominated by large carabid beetles. We discuss the implications of our findings to land use properties and ecological function. Our case study indicates promising benefits of milkweed cultivation for soil biodiversity and soil health, with more research needed to validate and build from our results.

Ontogenetic diet shifts of rough scad Trachurus lathami in the North Patagonian shelf (south-west Atlantic Ocean).

Rough scad Trachurus lathami is a key pelagic fish in the Argentinean continental shelf (ACS, south-west Atlantic Ocean), with recent increases in abundance. It is a main prey of fishes and marine mammals, and shares the environment with commercially relevant pelagic species (Engraulis anchoita and Scomber colias), playing an important role linking lower and upper trophic levels in the ecosystem. This study aims to determine the ontogenetic changes in the diet composition, feeding strategy, trophic niche breadth and trophic level of T. lathami in the North Patagonian Shelf (43°-45°30'S). The stomach contents of adult fish (n=238) were analysed. The results suggest a clear ontogenetic shift in the diet at a size of ~190 mm. Smaller individuals (160-190 mm) were specialized on misidaceans, and showed the highest trophic level, while larger T. lathami (221-230 mm) consumed decapods (Peisos petrunkevitchi) and teleosts (eggs and larvae). Trophic niche breadth was higher at the medium-sized class (191-220 mm), which mainly preyed on copepods (Calanoides carinatus) and chaetognaths (Sagitta spp.), evidencing a more diverse diet and a rather generalist strategy. Updated information on the trophic ecology of T. lathami evidences its extremely plastic feeding behaviour, being able to adapt its trophic niche to the most readily available food items from the mesopelagic community.

Successful establishment of range-shifting, warm-water Labridae in temperate South Western Australia

Climate change is rapidly altering the distributions of species and the composition of communities that have evolved over evolutionary time scales. Quantifying changes in species distributions and abundance in response to warming is critical to understanding how these changes modify structure, function and services provided by recipient communities. Changes in size structure of warm- and cool-affiliated species is an important indicator for climate-driven species redistributions over time, and has received relatively little attention. We quantified changes in length and biomass distributions of 25 species of Labridae fishes from 112 sites spanning 2000 km across a warm-cool temperate transition zone in south Western Australia. Length and biomass data were collected in 2005-2006 and 2014-2015 using diver operated stereo-video. In the decade between sampling events, south Western Australia experienced an extreme marine heatwave followed by repeated summers of anomalously warm ocean temperatures. Biomass of tropical and subtropical species increased 10-fold and 3-fold, respectively, between 2006 and 2015, whereas temperate species biomass remained relatively stable. In 2014-2015, the abundance and biomass of tropical species (e.g. Scarus ghobban) increased in the warmest regions and established multiple size classes poleward of their recorded 2005-2006 distributions, suggesting successful overwintering and recruitment where viable populations were not recorded in 2005-2006. Large, slow-growing temperate species such as Achoerodus gouldii and Bodianus frenchii decreased in small and medium size classes in warm regions. Our findings report a substantial change in the size structure and composition of labrid assemblages over a decade of climatic variability.

Intraspecific competition in size-structured populations: ontogenetic shift in the importance of interference competition in a key marine herbivore

Individuals rarely have equal competitive abilities, with body size being one of the most important attributes affecting the mechanism (i.e. exploitative and interference) and consequences of competition. Competitive interactions within size-structured populations are complex and can have major implications for population dynamics, community structure and evolutionary processes. Destructive grazing of kelp beds by the green urchin Strongylocentrotus droebachiensis creates barrens where high-quality food is scarce and intraspecific competition may have an important role in structuring populations. In this study, we experimentally identified the mechanisms underlying size-asymmetric competition between small, medium, and large size classes of the green urchin. A field-based mesocosm experiment showed that small and medium sea urchins grew less and produced smaller gonads when competing for food with large conspecifics. Surprisingly, when food was provided ad libitum but large urchins were present, small individuals’ growth and foraging behavior were reduced, providing strong evidence for interference competition between small and large sea urchins. Interactions between medium and large sea urchins were, however, more influenced by exploitative competition, suggesting that sea urchins shift ontogenetically from a situation of intense interference competition to one dominated by exploitative competition. The size structure of the population can thus determine the relative importance of interference and exploitative competition. In turn, the importance of interference competition may influence size structure by inhibiting the growth of smaller urchins, a pattern consistent with the prediction of theoretical models. The consideration of size-asymmetric competitive interactions can lead to a better understanding of population size structure and dynamics.

The Effectiveness of Concept Maps for Students’ Learning and Retention

The active learning literature has greatly expanded over the past few years. This article investigates the utility of employing concept map activities in a medium-sized class, and whether or not it improves students’ learning and retention of material. We find that concept mapping activities significantly enhance students’ mastery and recollection of class material. The size of the effect is considerably greater in our treatment group, relative to our control group. We discuss the advantages of this specific active learning technique, and offer suggestions for its incorporation into different institutional settings.

Profitability and Sustainable Use of Traps for Amazon Shrimp (Macrobrachium amazonicum) From the Amazon River

The objective of this study was to evaluate the profitability, productivity and selectivity of traps used for the capture of freshwater prawn using different spacings between the laths. This study was developed in the estuary of the Amazon River near Santana island, Amapá, Brazil. Collections were conducted using traps called “matapi”, which are cylindrical shrimp traps made with wooden slats or laths, with funnel-shaped entrances at both sides, and the spacings between the laths ranged between 1 to 10 mm in 1 mm increments. Each trap was covered with a net called a “sobrematapi”, or trap cover. The length of carapace in centimeters and the weight in grams were measured for all specimens. The shrimp were categorized into small, medium, and large size classes. Selectivity curves were used to determine selectivity for the different lath spacings. Traps with lath spacing below 7mm should be considered as being predatory because they allow for the capture of small individuals, with more than 50% of these being captured using spacings from 1 to 5mm. Despite the fact that spacings between 8 and 10mm captured lower quantities of shrimp, this enabled the capture of larger specimens with a similar total biomass yield, and this spacing is considered to be the most ecologically and economically viable. In order to minimize the capture of young shrimp without drastically affecting economic yield, it is suggested that shrimp trap lath spacings be above 6mm.