Middle Size Classes Research Articles

Diversity, stand and population structure of riparian woody species in two contrasting land use types in the distal Okavango Delta, Northwestern Botswana

AbstractLand use change threatens the integrity of riparian woodland vegetation. The aim of this study was to investigate the diversity and population structure of riparian plant species in protected and communal areas. A total of 71 transects were sampled from each of the protected and communal areas. Total species richness recorded was 36 and 38 in communal and protected areas, respectively. Species diversity was significantly (p < 0.05) higher in the protected than communal areas. Vachellia tortilis (communal areas) and Croton megalobotrys (both areas) showed a reverse J shaped pattern with more individuals in the lower diameter size classes than in the large ones. Dichrostachys cinerea (both areas), Ziziphus mucronata (communal areas), Combretum imberbe (protected areas), C. hereroense (protected areas), Berchemia discolor (protected areas) and Vachellia erioloba (communal areas) showed a reverse-J distribution pattern, but with missing size classes. Philenoptera violacea (protected areas) was characterized by a bell-shaped distribution with more individuals in the middle size classes than in the lower and upper ones while Combretum hereroense, C. imberbe and B. discolor were characterized by irregular population structure in communal areas. Croton megalobotrys, D. cinerea, C. imberbe, C. hereroense, Z. mucronata, B. discolor and S. erubescens had higher Important Value Indices (IVIs) in protected than communal areas. Comparatively, Vachellia tortilis, P. violacea and V. erioloba had higher IVIs in communal than protected areas. We recommended that species with J-shaped population structure and those with only one size class be protected to enable them to attain healthy population structures.

Selektivitas Pancing Terhadap Hasil Tangkapan Ikan Selar (Selar crumenopthalmus) di Perairan Selat Seram

Gear selectivity is an important part of controlling the size of fish that are suitable for catching so that fish resources are maintained. The size of the hook is one of the factors that affect the selectivity of the fishing line. The purpose of this study is to analyze the selectivity of fishing lines on the results of catching Selar crumenopthalmus. Fish sampling was carried out by following a series of fishing operations by fishermen using hook sizes no. 17 and 18. The Holt method was used to analyze and calculate the selectivity of hook size operated by fishermen on the total length of the fish line. Size distribution of the total length of hook no. 17 in the middle-class size 16.5 cm – 22.5 cm and hook no. 18 in the middle-size class 16.5 cm – 20.5 cm. The distribution of length sizes on both hooks tends to be normally distributed and the proportion of large lengths is higher on hook no. 17. The 50% and optimal (100%) chance of being caught for hook size no. 17 is 18.3 and 20.1 cm, respectively. while the size of hook no. 18 is 167 cm and 18 cm. It is recommended to use hook size for trevally resources in the Seram Strait waters is hook no. 17.

Phototactic Response and Morphometric Characteristic of Climbing Perch Anabas testudineus (Bloch, 1792) Under Culture System

Abstract Phototaxis in climbing perch (Anabas testudineus) was investigated by subjecting fish to LED light traps (blue, green, yellow, orange, red, white) and control (total 13 traps). The trap was constructed of polyamide (PA) nylon monofilament (31.75 mm mesh size), fastened around two wire ring frames (∅ 490 mm) with a net height of 270 mm. A lamp was placed on the bottom of the trap. 96 individuals, consisting of 34 males and 62 females, were analysed. Both continuous and blinking light traps were considerably higher in the number of catch compared to the control. The body size of catch ranged from 76-135 mm TL and 8.00-55.00 g W. The mean YPUEs (yield per unit effort) for male and female were 4.00 ± 2.25 and 7.00 ± 4.50 g trap−1 trial-1, respectively. The CPUEs (catch per unit effort) for continuous, blinking light traps and the control ranged from 0.43 to 0.93, 0.21 to 0.86, and 0.21 fish trap−1night−1, respectively. The mean condition factor (K) values of 2.10 ± 0.40 for males and 2.13 ± 0.34 for females indicate fish with better condition. Positive group responses of fish were more pronounced in the middle size classes between 90 and 109 mm TL. Negative allometric growth pattern (b) (1.7271-1.8828) was observed, indicating that the culture system should be refined. A. testudineus showed positive phototaxis to the “colors of light”. In addition, efforts to collect climbing perch from the wild for breeding and commercial purposes may benefit from this study.

Evaluation of different tags on survival, growth and stress response in the flatfish Senegalese sole

Internal electronic tagging is a major issue in flatfish species due to the small size of abdominal cavity. In this study, three tag types, referred to as Nonatec, nano and mini, were evaluated in three weight classes of Senegalese sole: small (0.3 g), middle (0.8 g) and large (2.0 g). Tags were injected from the blind side and fish were carefully handled to minimize sharp movements. Tag losses were 8% in the small size class, between 5.2 and 15.1% in the middle size class and 2–4% in the large size class. The mortality rates ranged between 2.0 and 15.0% with the lowest values in the large size class. No negative effects of tags on growth (tagged vs non-tagged fish using a middle size class) were found after 57 days of culture. Four additional trials using mini tags in a large size class at industrial scale validated our experimental results. With respect to morphology, no differences in the area, ellipticity and circularity were found except for a slight higher aspect ratio index in mini- and nano-tagged soles when compared with untagged fish. A longitudinal analysis of growth using the tag type, sex and tag position (anterior, medium or posterior) as fixed factors revealed a significant and strong effect of sex, with females appearing significantly heavier (13.6%) than males. In addition, the significant interactions between tag position and tag type with the time indicated a delayed growth of Nonatec-tagged fish and specimens with tags in the posterior section of abdomen. Expression analysis of stress-related genes revealed an activation of HPI axis and cellular stress defenses at 2 days just after tagging (dat) not evident at 11 dat. All these data indicate that soles can be successfully tagged at very small sizes both at experimental and industrial scales if tag type is properly selected and fish correctly handled. Moreover, sex and tag position are significant factors affecting growth that need to be controlled in longitudinal studies and selective breeding programs.

Phosphorus content as a function of soil aggregate size and paddy cultivation in highly weathered soils.

Red soils are the major land resource in subtropical and tropical areas and are characterized by low phosphorus (P) availability. To assess the availability of P for plants and the potential stability of P in soil, two pairs of subtropical red soil samples from a paddy field and an adjacent uncultivated upland were collected from Hunan Province, China. Analysis of total P and Olsen P and sequential extraction was used to determine the inorganic and organic P fractions in different aggregate size classes. Our results showed that the soil under paddy cultivation had lower proportions of small aggregates and higher proportions of large aggregates than those from the uncultivated upland soil. The portion of >2-mm-sized aggregates increased by 31 and 20% at Taoyuan and Guiyang, respectively. The total P and Olsen P contents were 50-150 and 50-300% higher, respectively, in the paddy soil than those in the upland soil. Higher inorganic and organic P fractions tended to be enriched in both the smallest and largest aggregate size classes compared to the middle size class (0.02-0.2mm). Furthermore, the proportion of P fractions was higher in smaller aggregate sizes (<2mm) than in the higher aggregate sizes (>2mm). In conclusion, soils under paddy cultivation displayed improved soil aggregate structure, altered distribution patterns of P fractions in different aggregate size classes, and to some extent had enhanced labile P pools.

Differentiating size-dependent responses of juvenile pink salmon ( Oncorhynchus gorbuscha) to sea lice ( Lepeophtheirus salmonis) infections

Salmon infected with an ectoparasitic marine copepod, the salmon louse Lepeophtheirus salmonis, incur a wide variety of consequences depending upon host sensitivity. Juvenile pink salmon ( Oncorhynchus gorbuscha) migrate from natal freshwater systems to the ocean at a young age relative to other Pacific salmon, and require rapid development of appropriate defenses against marine pathogens. We analyzed the early transcriptomic responses of naïve juvenile pink salmon of sizes 0.3 g (no scales), 0.7 g (mid-scale development) and 2.4 g (scales fully developed) six days after a low-level laboratory exposure to L. salmonis copepodids. All infected size groups exhibited unique transcriptional profiles. Inflammation and inhibition of cell proliferation was identified in the smallest size class (0.3 g), while increased glucose absorption and retention was identified in the middle size class (0.7 g). Tissue-remodeling genes were also up-regulated in both the 0.3 g and 0.7 g size groups. Profiles of the 2.4 g size class indicated cell-mediated immunity and possibly parasite-induced growth augmentation. Understanding a size-based threshold of resistance to L. salmonis is important for fisheries management. This work characterizes molecular responses reflecting the gradual development of innate immunity to L. salmonis between the susceptible (0.3 g) and refractory (2.4 g) pink salmon size classes.

The Effects of Herbivory by a Mega- and Mesoherbivore on Tree Recruitment in Sand Forest, South Africa

Herbivory by megaherbivores on woody vegetation in general is well documented; however studies focusing on the individual browsing effects of both mega- and mesoherbivore species on recruitment are scarce. We determined these effects for elephant Loxodonta africana and nyala Tragelaphus angasii in the critically endangered Sand Forest, which is restricted to east southern Africa, and is conserved mainly in small reserves with high herbivore densities. Replicated experimental treatments (400 m2) in a single forest patch were used to exclude elephant, or both elephant and nyala. In each treatment, all woody individuals were identified to species and number of stems, diameter and height were recorded. Results of changes after two years are presented. Individual tree and stem densities had increased in absence of nyala and elephant. Seedling recruitment (based on height and diameter) was inhibited by nyala, and by elephant and nyala in combination, thereby preventing recruitment into the sapling stage. Neither nyala or elephant significantly reduced sapling densities. Excluding both elephant and nyala in combination enhanced recruitment of woody species, as seedling densities increased, indicating that forest regeneration is impacted by both mega- and mesoherbivores. The Sand Forest tree community approached an inverse J-shaped curve, with the highest abundance in the smaller size classes. However, the larger characteristic tree species in particular, such as Newtonia hildebrandtii, were missing cohorts in the middle size classes. When setting management goals to conserve habitats of key importance, conservation management plans need to consider the total herbivore assemblage present and the resulting browsing effects on vegetation. Especially in Africa, where the broadest suite of megaherbivores still persists, and which is currently dealing with the ‘elephant problem’, the individual effects of different herbivore species on recruitment and dynamics of forests and woodlands are important issues which need conclusive answers.

Feeding ecology of invasive Perccottus glenii (Perciformes, Odontobutidae) in Slovakia

Stomach contents of 331 specimens of &lt;I&gt;Perccottus glenii (Perciformes: Odontobutidae&lt;/I&gt;) were analysed. Chironomids and ephemeropterans dominated the diet of all size classes of fish; however, the frequency of crustaceans was also high. Micro-crustaceans (ostracods, copepods and cladocerans) dominated in lower size classes (20–39 mm); macro-crustaceans &lt;I&gt;(Isopoda, Amphipoda&lt;/I&gt;) dominated in higher size classes (up to 79 mm). The proportion of crustaceans decreased from the size class 80–89 mm. With the increasing size of fish the frequency of molluscs (&lt;I&gt;Gastropoda&lt;/I&gt;) increased, the maximum was in size class 70–79 mm. Cannibalism occurred from 60 mm, and it was significant from 80 mm. The highly mobile invertebrates (&lt;I&gt;Coleoptera, Heteroptera&lt;/I&gt;) were found in the largest size classes. In middle size classes (40–59 mm), the widest spectrum of prey units was documented; the food variability of small (90 mm) individuals was poor. Differences in the diet composition of small individuals were negligible; the diet of the largest ones differed significantly. According to diet, two feeding size class groups were recognised: the first

In Vitro Growth of Mouse Oocytes: Oocyte Size at the Beginning of Culture Influences the Appropriate Length of Culture Period

It has been established that mouse oocytes grow under appropriate culture conditions. To be able to utilize a broad range of growing oocytes, a way of estimating the optimal culture period is required. In the present study, a detailed analysis was conducted of the relationship between the initial oocyte size and necessary length of culture period to achieve full growth. Oocyte-granulosa cell complexes were obtained from juvenile mice, and classified into three groups according to oocyte size: 50.0–54.5, 55.0–9.5, and 60.0–64.5 μm. The complexes were cultured for various periods up to 12 days. Mean oocyte size increased in a linear fashion, eventually reaching the full size for mouse oocytes. Meiotic competence was acquired during the last 4 days of culture, when oocytes approached full size in all size classes. During this period, the rate of oocytes incompetent to resume meiosis decreased sharply, while that of oocytes having competence to progress to metaphase II increased. This relationship was particularly clear cut in the large- and middle-size classes. Thus, appropriate length of culture period is mostly determined by the oocyte size at the start of culture. Considerable attention should be paid to the oocyte size as well as to the duration of culture period.

Observational challenges of A-type stars

In the last few years, new instruments mounted at modern large telescopes, as well as satellite instruments, have given to us the possibility of obtaining observations of much higher quality than in the past. Yet, the large majority of observations of A-type stars are performed with small to middle size class telescopes. In this paper I discuss the scientific case for the use of large size class telescopes for the A-star research.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Forest canopy and community dynamics in a temperate old‐growth evergreen broad‐leaved forest, south‐western Japan: a 7‐year study of a 4‐ha plot

Summary Forest canopy gap and community dynamics were studied in a 4‐ha permanent plot of an old‐growth evergreen broad‐leaved forest dominated by Castanopsis cuspidata var. sieboldii and Distylium racemosum in the Tatera Forest Reserve, Tsushima Islands, south‐western Japan. The forest was affected by a powerful typhoon in 1987 and was monitored from 1990 to 1997. In 1990, all woody stems ≥ 5 cm diameter at breast height (d.b.h.) in the plot were identified, mapped and marked, and the state of 1600 5 m × 5 m contiguous quadrats used to locate canopy gaps. Gaps occupied 17.1% of the plot, which contained 4494 tree and shrub stems (total basal area 63.48 m2 ha−1). Gaps were re‐censused in 1997 and both marked and newly recruited (≥ 5 cm d.b.h.) stems were recorded in 1992 and 1997. Over 7 years the rates of canopy gap formation and closure were 0.72% year−1 and 1.61% year−1, respectively, mortality and recruitment rates were 0.97% year−1 and 0.99% year−1, and the rates of loss and gain in basal area were 0.95% year−1 and 0.83% year−1. The mortality of stems was size‐dependent, with those in middle size classes having the lowest rates. Mortality of stems was lower in canopy and higher in the understorey, while the proportion of stems killed by disturbances increased with height. Stems that died during the 7 years were predominantly located in newly created gaps, whereas stems were recruited into both established and new gaps. Deciduous broad‐leaved species were largely restricted to gaps that remained open throughout the study. Both composition and structure of the forest changed in response to disturbance‐related effects on canopy dynamics.

VARIATIONS IN OLD-GROWTH STRUCTURE AND DEFINITIONS: FOREST DYNAMICS ON WACHUSETT MOUNTAIN, MASSACHUSETTS

One of the largest old-growth forests in southern New England was recently discovered on the exposed upper slopes of Wachusett Mountain, Massachusetts, a heavily used recreational area located 150 yr. Historical data suggest that most of the area's forests were composed of a mixture of Quercus rubra and northern hardwood species. Species abundances and recruitment dynamics in the four stands exhibit highly variable spatial and temporal patterns across sites that differ in aspect and exposure. Three uneven-aged hardwood stands contain Quercus rubra in the largest size classes, various amounts of Fagus grandifolia, Acer, and Betula species in the middle size classes, and dense thickets of several shrub species in the small size classes. Several of a set of randomly aged individuals of Q. rubra, B. Ienta, and B. alleghaniensis are at or very near the maximum longevity known for these species. A Tsuga canadensis stand contains unimodal size and age distributions, with trees <60- cm dbh and 100-300 yr old. Quercus rubra recruitment occurred on all sites from the 1 600s through the early 1 800s, when it dropped precipitously on most sites and was replaced by either Tsuga or Acer and Betula species. These recruitment changes were apparently driven by changes in disturbance regime over the. last two centuries, from fire in the early record to hurricanes (1815 and 1938), and more recently, frequent wind, ice, and snow damage but no fire. Asynchronous tree-ring releases and suppression and relatively low amounts of coarse woody debris corroborate this interpretation. Chronic canopy damage produced short-statured and unusually gnarled trees, which gave the forest unusual resis- tance to severe winds from hurricanes, discouraged logging, and prevented the recognition of the forest's old-growth status despite its heavy recreational use.

The effects of interactions with reef residents on the settlement

Recruitment limitation models of coral reef fishes assume that interactions between demersal individuals and settling larvae are of little consequence to local population dynamics, as are interactions among reef residents. To test this premise, I examined the effects of interactions on the settlement and persistence of the ocean surgeonfish, Acanthurus bahianus. I also looked at behavioural exchanges among ocean surgeonfish of different sizes and between ocean surgeonfish and other reef residents to determine whether the nature of these exchanges changes ontogenetically. Settlement of ocean surgeonfish to Tague Bay Reef, St. Croix, U.S.V.I. was increased in the presence of conspecifics and decreased in the presence of a common Caribbean damselfish, the beaugregory Stegastes leucostictus. Additionally, post-settlement persistence was negatively related to the level of aggression received from beaugregories. Interactions among ocean surgeonfish and between ocean surgeonfish and damselfish were size-dependent; the largest and smallest size classes had higher levels of association with conspecifics than did the middle size classes, and larger size classes received more aggression from damselfish than did the smaller size classes. These results suggest that behavioural interactions may significantly affect the distribution, abundance and early post-settlement persistence of ocean surgeonfish settlers, and that the nature of these interactions changes over the lifetime of individuals.

Community dynamics of Ogawa Forest Reserve, a species rich deciduous forest, central Japan

Forest community dynamics were studied for 4 years in a 6 ha permanent plot of species rich, old-growth, temperate deciduous forest in Ogawa Forest Reserve, central Japan. The gap formation rate, recruitment, mortality, gain and loss rate in basal area during 4 years were 42 m2 ha−1 yr−1, 1.74% yr−1, 1.19% yr−1, 1.12% yr−1 and 0.88% yr−1, respectively. The turnover time calculated from them ranged from 58 to 240 years. Both the mortality and mortality factors were size dependent; trees in middle size class had smallest mortality, and the proportion of the trees killed by disturbances increased with size. Gap creations were concentrated in a particular year, suggesting a large heterogeneity in time. Spatial distribution of recruited trees were biassed to the old gaps (older than 4 years), especially that of the species with Bell-shaped dbh distribution (shade intolerant) strongly associated with the gaps. Recruitment in tree stems and the loss of basal area, thus had the larger variability than mortality of stems and this forest, and the species with L-shaped dbh distribution seemed to going to increase the importance in the future if the present trend continues to be held. The turnover time of population is positively correlated with the maximum dbh size of the species, indicating the slow change of the population of large sized species.

Population ecology of the paddy field‐dwelling fish Channa gachua (Günther) (Perciformes, Channidae) in Sri Lanka

A population of Channa gachua in a small irrigation canal that supplies rice fields was studied by monthly sampling over 2 years. The population density was positively correlated with the rainfall and varied from 0.34 to 0.95 individuals m−2. The growth parameters of the von Bertalanffy growth equation determined on monthly size–frequency data were Lx= 179 mm total length and K=0.50. Overall male to female ratio was 0.82 and there were more females than males in the middle size classes. Spawning occurred throughout the year, but all evidence indicated enhanced breeding during major rainy periods of May to July and October to December. The length at first spawning was 102 mm, which is reached in about 20 months. Fecundity, which varied between 389 and 2130, was positively correlated with gonad weight, body weight and total length. Longevity and natural mortality were estimated as 6 years and l.27 yr−1, respectively. However, 99% of the population appeared to live for only 3 years. The mean biomass, average annual production and turnover ratio of the population were 7.35 g m−2, 12.06 g m−2 and 1.64, respectively.

Effect of Neighbouring Trees on Eucalypt Growth in a Semi-Arid Woodland in Australia

(1) The effects of neighbouring trees on the growth of Eucalyptus populnea in a native semi-arid woodland in Queensland, Australia, were investigated using three different measures of interference: (i) nearest-neighbour distance (NN); (ii) Weiner's neighbourhood interference (W); (iii) a competitive-interference measure (CI) which included the size of the influenced individual. (2) The relationship between relative girth increment and the interference measures was obscured by the range of tree sizes and it was necessary to treat the data in three separate size classes. (3) The performance of the three different measures of interference in acting as predictors of relative girth increment varied across the size classes. All three measures gave a usable result for the large size class (>60 cm gbh), both W and CI performed well for the small size class (0-30 cm gbh), but only CI gave a stable result for the middle size class (30-60 cm gbh). (4) Use of a vector in the model for plant influences allowed the generation of an influence surface, which was then used to derive CI values. This surface could also be used to calculate values for relative-recruitment potential at any point within the system. (5) The competitive-interference model used leaf area as a measure of plant size which is related to resource demand. This measure reflects important functional variables such as water uptake, litter input, root volume and shading, and can be applied to different growth forms. It should then be possible to generate influence surfaces which combine trees, shrubs and grasses and to investigate interactions between these different growth forms.

Interactions among factors affecting growth, development and survival in experimental populations of Bufo terrestris (Anura: Bufonidae).

We designed a series of field experiments to investigate the importance of interactions between biotic and abiotic factors on the survival and development of larval cohorts of Bufo terrestris. Five "blocks" in a large pond represented environments of varying physical harshness. In the more severe blocks, increased density inhibited growth rates, yet in the more benign blocks, increased density enhanced growth rate. Although different blocks produced very different levels of survival to metamorphosis and size at metamorphosis, there were no interactions with density. Increased density produced lengthened development times in the harsher blocks, but had no effect in the less stressful blocks. Hatchlings that were in the lowest of 3 initial size classes never caught up with their larger contemporaries and survived poorly. Hatchlings in the middle and largest size classes performed equivalently in all parameters of growth and development, but hatchlings from the middle size class were less likely to survive than their larger contemporaries. The effects of initial size did not interact with block. The inhibitory patterns displayed by density in conjunction with varying physical environments are similar to those found in comparable experiments with plants.