Negative Effect Of Density Research Articles

Reducing resin content and board density without adversely affecting the mechanical properties of particleboard through controlling particle size

Density and resin content are two factors that have a significant effect on the production cost of wood composite. However, particle size affects resin content and density, which suggests that the interaction of these three factors can be manipulated to reduce the board density and resin content of particleboard without adversely influencing its mechanical properties. Some mathematical functional forms based on resin content, board density and slenderness ratio were regressed and an appropriate form was chosen. According to analysis of the results using SHAZAM 9 software, the exponential function best fit the experimental data. Finally, “indifference curves” of mechanical properties were illustrated and analyzed. The results indicated that negative effects of density or resin content reduction on mechanical properties could be compensated for by controlling particles’ slenderness ratio. Interestingly, increases in slenderness ratio compensated for the negative effects of decreases in resin content or board density on module of rupture (MOR) and module of elasticity (MOE). Moreover, this “compensation ratio” intensified as resin content or density decreased and/or as the MOR or MOE increased. On the other hand, reduction in slenderness ratio indicated a complementary effect on reducing internal bond (IB) strength, a result of decreases in resin content or density. Moreover, this “complementary ratio” was intensified as resin content or density decreased and/or as IB strength increased.

Effects of infaunal bivalve density and flow speed on clearance rates and near-bed hydrodynamics

The influence of bed density (from 0 to 1000 ind. m − 2 ) and flow speed (2, 5, and 15 cm s − 1 , i.e. “low”, “medium” and “high”, respectively) on clearance rates (CR) of an infaunal suspension-feeding bivalve ( Austrovenus stutchburyi) and boundary layer dynamics were investigated in annular flumes. Near-bed flow speeds decreased and bed shear stresses increased with bivalve density due to the bed roughness generated by the shallow burrowers. At low densities (< 500 ind. m − 2 ) there was no detectable effect of feeding currents on bed shear stress, but at high densities (1000 ind. m − 2 ) and at the low flow speed bed shear stress was almost 80% higher when Austrovenus were feeding (0.0016 N m − 2 ), compared to when they were not feeding (0.0009 N m − 2 ). These results suggest that bed roughness generated by Austrovenus and their feeding currents are capable of influencing food supply to the bed. Individual CR were significantly ( p < 0.01) greater at the high flow speed (0.88 L h − 1 ind. − 1 ), compared to the medium and low flow speeds (0.34 to 0.54 L h − 1 ind. − 1 ). With increasing bed density, individual CR was significantly ( p < 0.001) reduced; at low densities CR ranged from 0.6 to 1.4 L h − 1 ind. − 1 , but at high densities they were 0.1 to 0.8 L h − 1 ind. − 1 . Bed CR (L h − 1 m − 2 ) did not scale proportionally with density, initially increasing up to 500 ind. m − 2 but remaining relatively constant thereafter. This was in part due to the negative effect of density on individual CR but also because the proportion of bivalves feeding decreased with increasing density. Our results demonstrate that recording the number of bivalves feeding is necessary to interpret the effect of density on bed CR. Moreover, if the effects of both bivalve density and flow speed are not considered, then scaling up individual CR obtained using animals at low densities will over estimate population filtration capacity. As high (but equivalent to in situ) densities reduced both the number of animals feeding and individual CR other factors may offset this negative interaction, such as protection from wave disturbance or enhanced resuspension of benthic microalgae.

Do sex-specific densities affect local survival of free-ranging great tits?

Competition within sexes is expected when resources are sex specific, whereas competition between sexes can occur when similar resources are exploited. Local population density and sex ratio will determine the amount of sex-specific interactions and thus the potential degree of sex-specific competition. In contrast, high densities and the density of same-sex individuals may also positively influence survival, for example, by facilitating the exploitation of resources. The population density and sex ratio may therefore differently affect survival of males and females and thus also affect the expected fitness gains of producing a certain offspring sex. In this paper, we investigate experimentally whether and how sex-specific local densities affected sex-specific annual local survival of juvenile and adult great tits. We manipulated the density and sex ratio of fledgling great tits in 12 forest plots during 3 consecutive breeding seasons and monitored local survival until the next breeding season. We found no negative effects of the number of same- or opposite-sex competitors on juvenile local survival. Instead, local survival of juveniles of both sexes increased with the density of same-sex fledglings. Adult local survival was negatively affected by an experimental increase in density of nestlings, yet associated positively with the natural breeding pair density in a plot. Juvenile local survival related negatively to breeding pair density. Our results reveal experimental evidence for both negative effects of density on adult local survival and positive sex-specific effects on juvenile local survival, which shape sex-specific fitness prospects and might thus also alter optimal sex allocation decisions.

Density-dependent pre-dispersal seed predation and fruit set in a tropical tree

Negative density-dependent demographic processes operating at post-dispersal seed, seedling, and juvenile stages are the dominant explanation for the coexistence of high numbers of tree species in tropical forests. At adult stages, the effect of pollinators and pre-dispersal fruit predators are often dependent on the density or abundance of flowers and fruit in the canopy, but each have opposite effects on individual realized reproduction. We studied the effect of density on total and mature fruit set and pre-dispersal predation rates within individual tree canopies in a common canopy tree species, Jacaranda copaia in a 50-ha forest census plot in central Panama. We sampled all reproductive sized trees in the plot (n = 188) across three years and estimated fruit set and predation rates. Population-wide pre-dispersal seed predation averaged between 6-37% across years. Using linear mixed effects models, we found that increased density and fecundity of conspecific neighbours increased focal tree fruit set, but also the rate of pre-dispersal predation. An interaction between individual and neighbourhood fruit production predicted lower predation rates at high individual and neighbourhood fecundities, which suggests predator satiation at high fruit abundance levels. However, the rate at which fruit set increased with conspecific neighbour fruit production was greater than the rate at which fruit were lost to predation, resulting in an overall positive effect of neighbour density on mature fruit production in focal trees. Our results run counter to the expectation of a uniformly negative effect of density across all life stages in tropical trees and suggest further exploration of the role of spatial clumping, pollen dispersal limitation, and predation at pre-dispersal adult stages in maintenance of species diversity in plant communities.

Effect of Stocking Density on the Growth, Survival, and Behavior of Postpuerulus Western Rock Lobster, Panulirus cygnus (George) (Decapoda: Palinuridae)

Abstract The effect of four stocking densities (30, 60, 100, and 150 lobsters/m2) on the growth and survival of Panulirus cygnus postpueruli was determined over a 112‐d grow‐out trial. Agonistic behavior at each experimental density was recorded using infrared filming. Survival and growth decreased with increasing density, although this trend was only significant between the lowest (30/m2) and the highest densities (150/m2) (P &lt; 0.05) at the conclusion of the grow‐out trial. Density had no significant effect on apparent feed intake but significantly affected food conversion ratios (FCR) across all four densities, with FCR being best at 30/m2 and worst at 150/m2. The number and frequency of agonistic encounters per tank differed significantly with density, with agonistic encounters being highest at 150/m2 and lowest at 30/m2. Agonistic encounters coincided with the crepuscular foraging pattern of postpueruli. The reduction in survival and growth of postpueruli at the highest density (150/m2) can be attributed to the significant increase in the number of agonistic encounters. This study supports that P. cygnus postpueruli should be stocked at densities less than 100/m2 in order to minimize the negative effect of density on growth and survival.

Breeding games and dimorphism in male salmon

In certain species of salmon, male phenotypes occur in two distinct morphs: the large ‘hooknose’ or the small ‘jack’. Hooknoses fight each other for access to females, while jacks occupy refuges near spawning beds to sneak fertilizations. Jacks also fight each other over opportunities for sneaking without immediate gains. To explore whether the jack behavioural strategy is equally adaptive to that of the hooknose, we built a game-theoretic model similar to the classic hawk–dove game, with and without conditions of density dependence. Our model demonstrates that fitness of the jack strategy increases with the frequency of the hooknose strategy, because jacks can steal the benefits otherwise accrued by hooknoses. The coexistence of strategies is much more easily achieved in this game than in the hawk–dove game. When negative density effects on benefits are introduced to the model, coexistence conditions are further relaxed. Hence, the jack and hooknose strategies can be viewed as equally adaptive, resulting in a stable mixed evolutionarily stable strategy (ESS).

Climate and intraspecific competition control the growth and life history of juvenile sockeye salmon (Oncorhynchus nerka) in Iliamna Lake, Alaska

Recent climate changes have had marked effects on the ice-free season and thermal conditions in many high-latitude lakes, but their ecological effects combine with density-dependent processes to affect fish growth and life history. To better understand the relative roles of climate and intraspecific density, we applied Gaussian state–space models to long-term data (1962–2006) on growth of juvenile sockeye salmon ( Oncorhynchus nerka ) in Iliamna Lake, Alaska, USA. Both temperature and density influenced fry size at the end of their first growing season, but the positive effect of temperature exceeded the negative effects of density. Fry growth was affected by the magnitude of their own cohort more strongly than by the previous brood (i.e., yearlings). In contrast, density was more important than temperature in Lake Aleknagik, also in Bristol Bay, over the same period of record, probably because Iliamna Lake is cooler and has generally lower densities of juvenile sockeye salmon than Lake Aleknagik. In both lakes, the size of the fish at the end of the first growing season affects smolt size and age at seaward migration, hence survival at sea and age at maturity, so the relative effects of climate and density depend on the ecological context.

Non‐additive effects of density‐dependent and density‐independent factors on brown trout vital rates

Interactions between density‐dependent and density‐independent processes can lead to variation in both growth and survival rates. Detecting such effects, however, will often require sampling on an individual level and at the appropriate spatial and temporal scale. This study documents substantial variation in survival and growth of stream‐dwelling brown trout Salmo trutta from a small Norwegian stream. The data is based on seasonal capture–recaptures of individually marked trout on fixed stations during eight years. The fish were small‐sized, rarely reaching sizes larger than 20 cm and ages older than seven years. Density varied between 0.2–0.8 fish m−2. Variation in survival and recapture probabilities was analysed using program MARK. Apparent survival (the probability of being alive and present within the study area) generally decreased with increasing trout density and increasing drought level (measured as lowest observed water flow) during both winter and summer. Further, there was a significant interaction effect between density and water flow, indicating that density‐dependent effects on survival predominated when environmental conditions were benign (no drought), while density‐independent processes were most important under harsh environmental conditions (drought). Observed length‐at‐age during autumn indicated a more or less linear growth trajectory throughout life, and no effect of density, water flow or temperature was found. However, using the individual‐based capture–recapture data to estimated specific growth rate, significant positive effects of water flow and temperature and a negative effect of density were identified. Thus, the capture–recapture data suggest a strong potential for population regulation at the rather low densities found in this stream, and regulation may occur both through effects on survival and growth.

Evidence for a negative fitness−density relationship between parent density and offspring quality for two Xenopsylla spp. parasitic on desert mammals

We tested the hypothesis of negative fitness-density relationships and predicted that an increase in the density of parent fleas would result in lower survival rates and longer development time of pre-imagoes as well as shorter time to death from starvation of newly emerged imagoes. These predictions were experimentally tested on Xenopsylla conformis Wagner and Xenopsylla ramesis Rothschild feeding on two rodent species, Meriones crassus Sundevall or Dipodillus dasyurus Wagner. Survival of larvae and pupae, but not eggs, was negatively affected by parent density. An increase in parent density led to a decrease in the number of imagoes of the next generation. Eggs of both species developed faster when the parents were at low densities on either host. The same was true for larval X. ramesis, but not larval X. conformis. The negative effects of parent density on the duration of pupal development were evident in X. conformis, parents of which fed on both hosts, and X. ramesis from parents fed on M. crassus, whereas X. ramesis from parents fed on D. dasyurus developed faster at low densities. A negative effect of density on the development of offspring from egg to imago in X. conformis was manifested mainly when parent fleas fed on D. dasyurus, whereas the negative effect of density on offspring development in X. ramesis was manifested mainly when parent fleas fed on M. crassus. Although there was no general effect of parent density on the resistance of imago offspring to starvation, male X. ramesis from parents fed at the highest density survived starvation for significantly shorter times compared with those from parents fed at lower densities. Manifestation of the negative effect of parent density on offspring quality appears to vary with flea species and may be affected by host species.

Production dynamics of the giant lions-paw scallop Nodipecten subnodosus cultivated off-bottom

The dynamics of production of the giant lions-paw scallop Nodipecten subnodosus were studied at a coastal location within the ‘El Vizcaíno’ Biosphere Reserve, Mexico. Production parameters were estimated testing three culture densities. The basis to control cultivation density was 40, 60, and 80% of the area occupied by scallops in nestier-type plastic trays. After 689 days, length was 11.9±0.7, 10.9±0.5, and 9.8±0.5 cm; total weight was 407±13, 310±19.7, and 232±8.5 g; adductor muscle was 44±0.4, 38±2.8, and 26±0.6 g; and survival was 72.7±2.9, 63.5±1.1 and 67.9±1.6% for increasing cultivation density, respectively. Nonlinear regression modeling was used to study the dynamics of production. Invariance tests carried out on parameter estimates of a growth curve indicated a significant negative effect of culture density on growth during the trial (P<0.001). The invariance test on parameters of a mortality curve also produced a significant result (P<0.001), although there was not a systematic negative effect of density on survival. Periodic variations in growth rate were associated with spawning and water temperature. The quadratic equation indicated that a significant relationship existed between gain of muscle weight per day and water temperature (P<0.001). The maximum weight gains occurred in periods when temperature was around 18 °C. An increase in mortality was attributed to the possible synergistic effect of spawning and high water temperature. Maximum muscle yields per tray occurred at the end of the growth trial and were 394, 597, and 674 g for increasing density. The results indicate a complex process of production dynamics that is influenced by density, the reproductive condition of the scallops, and water temperature.

Is the pollen‐limited mistletoe Peraxilla tetrapetala (Loranthaceae) also seed limited?

Abstract Seed production in the endemic New Zealand mistletoe Peraxilla tetrapetala (Loranthaceae) has been shown to be consistently pollen limited, but to date there has been no test of whether the species is also seed limited. If it is not seed limited, then pollen limitation may have no effect on population size. We tested for seed limitation by sowing seeds onto host trees at high and low densities at two sites, and following survival for up to 69 months. Our rationale was that unless there is strong density‐dependent seedling mortality sufficient to negate increases in seed supply, the species would be seed limited. We simultaneously measured pollen limitation at both sites using pollen augmentation. Peraxilla tetrapetala was strongly pollen limited at both sites over 7 years at Ohau (mean Pollen Limitation Index 0.62), and 12 years at Craigieburn (mean PLI 0.44), before and during the seed‐limitation study. There was no significant overall negative effect of density on survival in sown P. tetrapetala seeds over 42–69 months. There was a significant positive effect: seeds were more likely to adhere to branches when sown at high densities. This initial advantage to high‐density seeds was gradually eroded by slightly (but non‐significantly) lower survival rates of adhered seeds at high density. By the end of the study there was no significant difference in overall survival in high and low density plantings. This means that P. tetrapetala was apparently both pollen limited and seed limited at both our sites. Hence, reduced densities of native bird pollinators caused by introduced mammalian carnivores are likely to reduce the density of adult mistletoes in the next generation. However, the generality of this result may be affected by the fact that mistletoes do not have a dense ‘seedling shadow’ under the parent mistletoe.

Variable age structure and apparent density dependence in survival of adult ungulates.

Large herbivores have strongly age-structured populations. Because recruitment often decreases as population density increases, in unexploited populations the proportion of older adults may increase with density. Because survival senescence is typical of ungulates, ignoring density-dependent changes in age structure could lead to apparent density-dependence in adult survival. To test for density dependence in adult survival, we used data from three populations that underwent considerable changes in density. Bighorn sheep (Ovis canadensis) on Ram Mountain, Alberta, ranged from 94 to 232, mountain goats (Oreamnos americanus) on Caw Ridge, Alberta, varied from 81 to 147, and estimates of roe deer (Capreolus capreolus) older than 1year at Chizé, France, ranged from 157 to 569. We used recent developments of capture-mark-recapture modelling to assess the response of adult survival to changes in density when age structure was and was not taken into account. Survival rates were 10-15% higher during the prime-age stage than during the senescent stage for all sex-species combinations. When adults were pooled into a single age class there was an apparent negative effect of density on female survival in bighorns and roe deer, and negative trends for female mountain goats, male roe deer and male bighorn sheep. When age class was taken into account, there were no significant effects of density on adult survival. Except for male mountain goats, the strength of density dependence was lower when age was taken into account. In ungulate populations, age structure is an important determinant of adult survival. Most reports of density dependence in adult survival may have been confounded by changes in age structure.

Density‐dependent regulation in an invasive seaweed: responses at plant and modular levels

Summary The effects of density on the vital rates, growth form and population size structure of the invasive seaweed Sargassum muticum (Yendo) Fensholt were evaluated experimentally. The initial difference in plant number between the highest and the lowest density (200 and 6400 plants m−2) was considerably reduced by the end of the experiment. Surprisingly, this was mostly due to numbers increasing at lower densities, probably because microscopic forms were not removed during the experimental thinning. The allometric length–dry mass relationship fitted a simple linear model on log‐log scale for both the highest and the lowest densities, but had different slopes. At higher densities plants became taller and thinner as a consequence of variations in the production and growth of modules. Mean size (dry mass) and the development of size hierarchies of plants were affected by both the addition of further (microscopic) recruits and asymmetrical competition among plants. Plant length distributions were also influenced by changes in the growth form of plants. The length hierarchies of main branches also suggested the presence of asymmetrical competition at this modular level. Density influenced both mean size and morphology of the plants and thus induced changes in reproduction. The negative effect of density on individual plant size reduced the percentage of fertile plants and possibly their annual reproductive allocation, but these effects may be attenuated by morphological responses. The responses of S. muticum to crowding are closely linked to its ability to colonize bare space. The massive reproductive output and very limited dispersal range account for local and dense recruitment patterns. Our results suggest that the responses of S. muticum to crowding allow the establishment of dense populations with high persistence and resistance to colonization by other species.

Phase variation in the Kanzawa spider mite, Tetranychus kanzawai Kishida (Acari: Tetranychidae).

We examined the phase variation in Tetranychus kanzawai Kishida with regard to density effects and dispersal capacity. The fecundity of females was reduced when they had lived together with senior female adults during the juvenile period was reduced. This negative density effect was not attributed to direct interference by the senior female adults, but to local alternation of the food resource caused by their feeding damage. Moreover, offspring that had developed with the female adults had a higher dispersal capacity than those that developed without female adults. This physiological and behavioral plasticity in response to local density can be considered as a kind of phase variation.

Density effects in sputtering at normal and oblique ion bombardment

The author's earlier work on computer simulation of density effects in sputtering is extended to higher energies and oblique incidence of bombarding ions. Sputtering of amorphous Ge with an artificially varied density by 0.05–100 keV Ar ions is considered in great detail and the influence of density on the yield, angular and energy distributions of sputtered atoms is analysed. It is shown that at normal incidence the sputtering yield increases with density as N p , where p=0.56, 0.43, 0.28 and 0.24 at E 0=0.1, 1, 10 and 100 keV, respectively. At grazing incidence the sputtering yield is a decreasing function of N due to surface scattering of bombarding ions (the negative density effect). This finding lent impetus to a successful search for the density effects in sputtering of different elemental targets at grazing bombardment. Overall, the effects of density on the main sputtering characteristics turn out to be significant, which contrasts with the predictions of a number of analytical theories of sputtering.

Effect of patch size and plant density of Paterson"s curse (Echium plantagineum) on the oviposition of a specialist weevil, Mogulones larvatus.

This study examines the oviposition response of a specialist weevil (Mogulones larvatus) to patches of its host, the noxious weed Paterson"s curse/salvation Jane (Echium plantagineum). We simultaneously examined the effect of patch size and plant density (and their interaction), on the recorded oviposition patterns. Our results show that oviposition first occurred on the largest patches with the highest number of plants. However, there was no significant effect of patch size or number of plants per patch at the end of the experiment. At this time the level of attack per plant was negatively correlated with plant density. This negative effect of density on the level of oviposition was not mediated by a reduction in plant size at higher densities. The pattern observed may indicate a risk-spreading strategy by females.

Seedling Dynamics over Thirty-Two Years in a Tropical Rain Forest Tree

We examined patterns of seedling recruitment and their underlying mechanisms in a population of Chrysophyllum sp. nov. (Sapotaceae), a shade-tolerant canopy species in mature tropical rainforest in Queensland, Australia. We considered spatial scales ranging from 1 m2 to 1 ha, and temporal scales ranging from 1 to 32 yr. Over the 32-yr study period there were six episodes of very high seedling recruitment (masts) at intervals ranging from 4 to 10 yr. Less than 2% of new recruits were found in the nine censuses in other years. We found no significant correlations between the numbers of seedlings per census and either seasonal or annual rainfall, number of dry months per year, or El Niño Southern Oscillation (ENSO) events but found two correlations with mean seasonal air temperatures in the years preceding flowering. There were long-term changes in abundance in both time and space. In 1965 there were 163 seedling-sized plants in two dense patches, whereas in 1996, there were 4000 in 15 patches. Once a new patch became established, seedlings recruited there in each succeeding mast episode. Adult trees varied in their production of seedlings. Only 25% of the trees in the sample analyzed participated in all mast years; others had few seedlings for up to 28 yr before beginning to produce many seedlings. Seedlings were shade tolerant. They grew extremely slowly in the shaded understory, mean height only doubling in 27 yr. They were also quite long-lived; 6% of seedlings recruited in 1969 were still alive 27 yr later. There was little effect of natural enemies on seeds or seedlings. We found weak positive and negative effects of density on seed germination, seedling mortality, and growth. Mortality rates of Chrysophyllum seedlings did not show any trends with time, nor with distance from conspecific adults. These results suggest that abundance of older stages is determined by recruitment as well as subsequent growth and mortality. Mortality rates of seedlings of species other than Chrysophyllum decreased with distance from adult Chrysophyllum trees. Under present conditions, the Chrysophyllum population may be increasing in relation to that of other species, perhaps leading to a reduction in tree diversity in this tropical rainforest.

SEEDLING DYNAMICS OVER THIRTY-TWO YEARS IN A TROPICAL RAIN FOREST TREE

We examined patterns of seedling recruitment and their underlying mechanisms in a population of Chrysophyllum sp. nov. (Sapotaceae), a shade-tolerant canopy species in mature tropical rainforest in Queensland, Australia. We considered spatial scales ranging from 1 m2 to 1 ha, and temporal scales ranging from 1 to 32 yr. Over the 32-yr study period there were six episodes of very high seedling recruitment (masts) at intervals ranging from 4 to 10 yr. Less than 2% of new recruits were found in the nine censuses in other years. We found no significant correlations between the numbers of seedlings per census and either seasonal or annual rainfall, number of dry months per year, or El Nino Southern Oscillation (ENSO) events but found two correlations with mean seasonal air temperatures in the years preceding flowering. There were long-term changes in abundance in both time and space. In 1965 there were 163 seedling-sized plants in two dense patches, whereas in 1996, there were 4000 in 15 patches. Once a new patch became established, seedlings recruited there in each succeeding mast episode. Adult trees varied in their production of seedlings. Only 25% of the trees in the sample analyzed participated in all mast years; others had few seedlings for up to 28 yr before beginning to produce many seedlings. Seedlings were shade tolerant. They grew extremely slowly in the shaded understory, mean height only doubling in 27 yr. They were also quite long-lived; 6% of seedlings recruited in 1969 were still alive 27 yr later. There was little effect of natural enemies on seeds or seedlings. We found weak positive and negative effects of density on seed germination, seedling mortality, and growth. Mortality rates of Chrysophyllum seedlings did not show any trends with time, nor with distance from conspecific adults. These results suggest that abundance of older stages is determined by recruitment as well as subsequent growth and mortality. Mortality rates of seedlings of species other than Chrysophyllum decreased with distance from adult Chrysophyllum trees. Under present conditions, the Chrysophyllum population may be increasing in relation to that of other species, perhaps leading to a reduction in tree diversity in this tropical rainforest.

Effect of density on survival and growth of cyprinid fish fry

One of the bottlenecks in Israel's cold water ornamental fish industry is the large loss of fish during the post-larval stage. As a first step towards increasing survival rates, the optimal stocking density in earthen ponds for fry of each species should be determined. The results of five consecutive experiments with fry of goldfish (Carassius auratus), common carp and koi (respectively, edible and ornamental morphotypes of Cyprinus carpio) are presented here. The experiments were run in 18 cages of 1 m3 and 0.8 mm mesh size placed in a 0.02 ha earthen pond, stocked at 50,100 and 200 fry per cage. The variables analyzed were growth rate, harvesting weight, biomass and survival. Equations to estimate growth rates under different conditions are given. The three fish types present different growth rates and survival patterns in relation to stocking density and season, which lead to different management implications. Koi can be stocked up to 2 million fry per ha without showing negative density effects. Goldfish should be stocked at low density (500,000–1 million fry per ha) in spring and at higher rate (2 million fry per ha) in summer. Common carp stocking density should be adjusted to obtain the required fish size at harvest.

Density-dependent population dynamics in larvae of the dragonfly Pachydiplax longipennis: a field experiment.

Several features of dragonfly population biology suggest that population regulation occurs in the larval stage. This study was designed to determine if density-dependent interactions among larval odonates can affect survival, growth and emergence. First-instar larvae of the dragonfly Pachydiplax longipennis were raised in outdoor experimental ponds at initial densities of 38, 152, and 608 larvae · m-2, under two levels of food availability. Food availability was supplemented in half the pools by volumetric addition of zooplankton every other day. Pools in the low food treatment did not receive the zooplankton supplement.There was a strong negative effect of density on the mean growth rate of survivors, which included both emerging tenerals and individuals overwintering in the larval stage. A higher proportion emerged from low density than high density pools. Metamorphs from high density populations were smaller and emerged slightly later than those from low density, but the absolute number of metamorphs did not differ significantly among density treatments. Food supplementation significantly increased the proportion of overwintering larvae. There were no significant food-by-density interactions, indicating that food and density acted independently on larval population dynamics. Density-dependent mechanisms can clearly contribute to odonate population regulation, especially by controlling the number of larvae which emerge and the average age at reproduction. Population-level responses to density may be a result of interference among larvae.