Density-dependent Growth Research Articles

The Role of Density Dependence in Growth Patterns of Ceded Territory Walleye Populations of Northern Wisconsin: Effects of Changing Management Regimes

Abstract We assessed density-related changes in growth of walleye Sander vitreus in the ceded territory of northern Wisconsin from 1977 to 1999. We used asymptotic length (L ∞), growth rate near t 0 (ω), and body condition as measures of walleye growth to determine the relationship between growth and density. Among lakes, there was weak evidence of density-dependent growth: Adult density explained only 0–6% of the variability in the growth metrics. Within lakes, growth was density dependent, L ∞, ω, and body condition of walleyes changing with density for 69, 28, and 62% of the populations examined, respectively. Our results suggest that walleye growth was density dependent within individual lakes. However, growth was not coherently density dependent among lakes, which was possibly due to inherent differences in the productivity, surface area, forage base, landscape position, species composition, and management regime of lakes in the ceded territory. Densities of adult walleyes averaged 8.3 fish/ha and di...

Reevaluating evidence of density-dependent growth in northern fur seals (Callorhinus ursinus) based on measurements of archived skeletal specimens

Analysis of length-at-age measurements of archived skeletal material shows that somatic growth rates of male northern fur seals (Callorhinus ursinus) vary inversely with population density. Von Bertalanffy growth curves were estimated for two series of known-age mandibles collected 1911–1920 (n = 156) and 1940–1953 (n = 151), time periods representing the historic population minimum and maximum, respectively. Mandibles from the former time period are larger than mandibles from the latter time period, suggesting a density-dependent response in somatic growth. Although density-dependent growth in northern fur seals has been suggested before, previous studies have been hampered by the potentially confounding factors of fisheries interactions, variable environmental conditions, and harvest of adult female northern fur seals. The material analyzed here pre-dates the substantial development of the Bering Sea groundfish fishery and the period of heaviest culling of females. Likewise, the two time periods examined are characterized by broadly similar climatic and environmental conditions. Therefore, the results support the hypothesis that measurements of somatic growth rates provide an index of population levels relative to carrying capacity. Growth rate studies could therefore be used to evaluate the current population status of northern fur seals.

Relationship of size at return with environmental variation, hatchery production, and productivity of wild pink salmon in Prince William Sound, Alaska: does size matter?

Pink salmon (Oncorhynchus gorbuscha) returning to Prince William Sound (PWS), Alaska, have increased to historically high levels of abundance in recent years, but average body size at return has declined. We examined how body size at return of PWS pink salmon was related to 10 biophysical factors, including the scale of hatchery production. We also examined the effect of body size at return on productivity of wild pink salmon in PWS. For the 1975–1999 brood years, we found that an index of total abundance of pink salmon in the Gulf of Alaska and sea surface temperature during the year of return best explained the variation in pink salmon body size over time. Body size at return was significantly correlated with productivity of wild pink salmon. We used stepwise-regression to fit a generalized linear version of the Ricker spawner-recruit model to determine if body size would explain significant variation in wild-stock productivity in context with other environmental variation, including hatchery production. The results indicate that variability in wild-stock productivity is primarily driven by density-independent factors in the marine environment, but that body size of wild spawners also significantly affects productivity of wild PWS pink salmon. We conclude that the success of large-scale enhancement increasing the total run in PWS may have contributed to the decline in body size because of density-dependent growth in the Gulf of Alaska. We used a simulation model to estimate the impact of hatchery-induced changes in adult body size on wild-stock production in PWS. We estimated an annual wild-stock yield loss of 1.03 million pink salmon, less than 5% of the annual hatchery return of 24.2 million adult pink salmon for brood years 1990–1999.

Density-dependent growth performance of Indian major carps in rainwater reservoirs

Summary The study was carried out to evaluate growth performance of Indian major carps at different stocking densities in rainwater reservoirs. In this experiment, the absolute growth performance of Catla catla, Labeo rohita and Cirrhinus mrigala at stocking densities of 5000, 8000 and 11 000 fingerlings per hectare was 377.7, 215.4 and 241.9; 370.2, 186.7 and 219.1; and 306.7, 163.4 and 180.6 g, respectively. The recorded biomass yield at 5000, 8000 and 11 000 fingerlings per hectare was 1035, 1572 and 1573 kg ha−1 per 180 days of culture. The effect of stocking density on production performance (performance index, PI) was highly significant (P < 0.05) at the higher stocking density of 11 000 ha−1, while there was no significant variation between PI at stocking densities of 5000 and 8000 ha−1. This indicates optimum production performance at 8000 ha−1, where yield is significantly higher (P < 0.05) than yield at 5000 ha−1 and almost equal to the yield at 11 000 ha−1. An increase in stocking density from 8000 to 11 000 ha−1, however, showed a sharp decline in average mean body weight of each species, even with supplemental feeding. With an increase in stocking density, the biomass yield increased to an optimum (1572 kg ha−1), with no substantial increase thereafter. Reductions in growth, which occurred at high density, did not appear to be due to poor water quality as the water quality did not differ significantly among various treatments. Thus, the reduced survival and growth at high density appears to be a behavioural interaction or physiological response to density itself.

A growth and yield model for naturally-regenerated mixed shortleaf pine forests in the southern United States of America

SUMMARY A site- and density-dependent matrix growth model for naturally-regenerated stands of mixed shortleaf pines (Pinus echinata Mill.) and hardwoods was developed. The data came from 1,047 re-measured plots in seven states in the southern United States. Growth, mortality and recruitment equations gave the parameters to predict the number of shortleaf pine, soft hardwood, and hard hardwood trees per unit area in each of 13 diameter classes. Equations to calculate the volume of trees growing in different stand conditions are also presented. The model predictions were tested on observations on 209 random plots not used in model estimation. Long-term simulations of the model suggested that, with natural succession and without major disturbance, hardwood trees would gradually replace the currently dominant softwood trees.

Verifying Residuals from Catch Curves to Detect Recruitment Variation in Largemouth Bass and Crappies

Residuals associated with catch-curve regressions can represent variable recruitment in fish populations, but the use of this method to quantify recruitment variation has not been verified. I computed age-0 and age-1 catch rates of crappies Pomoxis spp. collected with trap nets set in the fall in three Alabama reservoirs and the age-1 catch rate of largemouth bass Micropterus salmoides captured with electrofishing during spring over a 13-year period in a single Georgia reservoir. These indices of juvenile abundance were correlated (r = 0.52–0.81, P < 0.01) to residuals generated from catch-curve regressions for electrofishing data collected when these same year-classes recruited to the fishery at age 3 and older. At higher age-0 crappie and age-1 largemouth bass catch rates, these relations became curvilinear, and improved fit was computed with data transformation and nonlinear fits to the data. An asymptotic relation was observed between age-0 and age-1 catch rates for the same crappie year-classes, and an inverse relation was evident between mean length at age 1 and juvenile crappie catch rates. This result suggested that density-dependent growth suppression and mortality occurred, as age-0 fish did not proportionally recruit to the age-3+ fishery. However, the age-1 crappie (about 18 months old) catch rate was linearly related (r2 = 0.48–0.55; P < 0.01) to residuals when data were compared separately for each reservoir, which suggested that full recruitment to the population occurred at this age. For largemouth bass, mean length at age 1 was positively related to age-1 catch rate, and recruitment of strong year-classes to the fishery appeared proportionally greater than for abundant age-0 crappies. Residuals generated from catch-curve regressions can serve as a useful quantitative index of juvenile crappie and largemouth bass abundance that can be used in subsequent analyses to explain recruitment variation. However, in some instances, initial strong year-class abundance may not be fully expressed in the fishery later in life.

P53 mediates density-dependent growth arrest

While the stress-response-associated importance of the p53 tumor suppressor is well established, recent studies have also linked p53 with several basic parameters in the normal behavior of cells. Here, we present evidence that basal p53 expression in WI38 human embryonic lung fibroblasts restricts growth rate and mediates density-dependent inhibition of growth and the associated G1 phase arrest of the cell cycle by affecting the density-dependent regulation of p16/INK4a. Additionally, we show that prolonged culturing of hTert-immortalized WI38 cells leads to a loss of density-dependent growth inhibition that correlates with p27/KIP deregulation as well as the previously shown INK4a locus silencing, and to an onset of contact-induced, p53-dependent cell death.

Decrease in density of the apple snail Pomacea canaliculata (Lamarck) (Gastropoda: Ampullariidae) in paddy fields after crop rotation with soybean, and its population growth during the crop season

We compared the densities of the apple snail, Pomacea canaliculata, between fields that had been planted with soybean or rice in the previous summer. The densities of overwintered snails soon after irrigation at the beginning of rice planting were all very low in the fields after soybean. These values were much lower than the control threshold for the apple snail in direct seeding. Therefore, crop rotation with soybean seems to be a good economic measure to control the apple snail in direct seeding. The snail populations increased very rapidly in both types of fields, in particular, after soybean. Within two and a half summer months, the snail densities in the fields after soybean reached almost the same level as those in the fields after rice. This rapid population recovery in fields after soybean seems to be caused by density-dependent growth and reproduction in this species.

Within-host dynamics of a microsporidium with horizontal and vertical transmission: Octosporea bayeri in Daphnia magna.

The fresh-water crustacean Daphnia magna may acquire an infection with the microsporidium Octosporea bayeri either by ingesting spores from the water (horizontally), or directly from its mother (vertically). Due to differences in the time and mechanisms of transmission, horizontal and vertical infections may lead to differences in the growth of the parasite within the host. This may influence parasite virulence, transmission to new hosts, and, consequently, epidemiology and evolution. Here we describe the within-host dynamics of 3 spore-types of O. bayeri from infections that were acquired either horizontally or vertically. In all treatments the number of spores increased exponentially until spore density reached a plateau, suggesting density-dependent within-host growth. The spore types seen differ in their growth dynamics, suggesting different roles in the parasite life-cycle. Horizontally-infected hosts harboured significantly fewer spores than vertically-infected hosts. Further, host survival was affected by infection route, with mortality being higher in horizontal infections than in vertical infections. Our results suggest that different routes of infection have an immediate effect on within-host parasite growth and thus on parasite fitness and epidemiology.

Interference competition for space in nursery habitats: density-dependent effects on growth and dispersal in juvenile shore crabs Carcinus maenas

In marine organisms with dispersing larval stages, current ecological theory suggests that recruitment of benthic juveniles may be limited by juvenile habitats and regulated by early post- settlement processes. However, few studies have attempted to identify the density-dependent mech- anisms responsible for these demographic bottlenecks. I conducted a series of experiments to assess if interference competition for space, within nursery habitats, could result in density-dependent juve- nile growth and dispersal from refuge habitats, and regulate local populations of juvenile shore crabs Carcinus maenas in shallow nursery areas in Sweden. In laboratory mesocosms, increased natural densities of similarly sized crabs resulted in decreased growth and increased per capita emigration from mussel habitats, even though food was provided in excess, suggesting that competition for space and mutual interference mediated the density-dependent growth and dispersal. This was supported in a field experiment where a density-dependent relation was found between the abundance of juve- nile crabs in nursery areas and their migration rates to experimental mussel patches. The results sug- gest that interference competition for space and density-dependent emigration from refuge habitats, coupled with habitat-specific mortality, is an important regulating mechanism for juvenile shore crab populations, in particular for older juvenile cohorts that have escaped inter-cohort cannibalism through a size refuge. Density-dependent effects on growth were found only at unusually high nat- ural densities and may, therefore, be less important as a regulating mechanism. However, negative effects on feeding rates and growth at high conspecific densities may represent an important selec- tive force in juvenile migration behavior. Density-dependent dispersal was found at juvenile densi- ties that are regularly found in nursery areas, suggesting that nursery habitats become saturated with juveniles during the recruitment season and represent a limiting resource for local populations, con- sistent with field observations of shore crab populations in the study area.

Age and growth of redfish (Sebastes marinus, S. mentella, and S. fasciatus) on the Flemish Cap (Northwest Atlantic)

Abstract Age determination of redfish is difficult. In this paper, the ages of Sebastes mentella on the Flemish Cap are validated by following year classes from 1991 to 2000. The criteria used for S. mentella are consistent and coherent. The growth of different year classes is described and compared, and density-dependence is demonstrated to influence the growth rate of the strong 1990 year class, growth of that year class being the slowest of those followed. The slow rate of growth prevented that year class from maturing at the anticipated age. Growth is also compared between sexes, of S. mentella, S. marinus, and S. fasciatus, revealing that females grow faster than males. Finally, growth rate is compared among species. S. marinus grows fastest and S. mentella slowest, although the influence of density-dependent growth in S. mentella needs to be taken into consideration.

Responses to Gizzard Shad Recovery following Selective Treatment in Walker County Lake, Alabama, 1996‐1999

Gizzard shad Dorosoma cepedianum is an important prey fish that is capable of influencing both the upper and lower trophic levels in aquatic systems. Contrary to our predictions, during the 4 years after a selective reduction of gizzard shad in Walker County State Fishing Lake (WCL), Alabama, the sport fish population structure did not decline as gizzard shad abundance rebounded. Adult gizzard shad catch rates in electrofishing transects (g/h) increased annually, and we saw a concomitant reduction of the WCL zooplankton community over the 4-year period. Limnetic larval gizzard shad density was highest in the second postreduction year and declined during the third and fourth years. In years when larval gizzard shad appeared in limnetic larval fish samples before larval white crappies Pomoxis annularis, larval white crappie densities were low. Conversely, the density of limnetic larval sunfishes Lepomis spp. was unrelated to that of larval gizzard shad, probably because of the protracted reproduction periods of the sunfishes. The combination of the density-dependent growth of juvenile gizzard shad and continual production of age-0 sunfishes provided abundant prey for largemouth bass Micropterus salmoides. Consequently, both the electrofishing catch rates and relative weights of largemouth bass remained high throughout the 4-year postreduction period, contrary to the a priori expectations that prompted the reduction. Although gizzard shad biomass increased markedly during the recovery period, a decline in the sport fishery was not apparent within the 4-year period of this study. Our findings suggest that the interval between treatments to reduce the gizzard shad population in WCL may be increased to more than 3 years, potentially saving time and personnel costs and providing an opportunity for positive public relations with respect to fish management in such a system.

Modeling the density–area relationship in a dynamic landscape: an examination for the beetle Tetraopes tetraophthalmus and a generalized model

The relationship between local population density and habitat area is an important factor in spatial population ecology. I examined how density dependence in the growth of local insect populations and their host plant patches, combined with patch birth and death, and insect dispersal affect the density–area relationship. I constructed a simulation model to examine the relationship for an insect herbivore, Tetraopes tetraophthalmus, inhabiting patches of its host plant, Asclepias syriaca. Given the observed growth of insect populations, patch growth, dispersal of insects, and change in the number of patches within the landscape, the model predicts that T. tetraophthalmus density should decrease with increasing A. syriaca patch size. The model also predicts moderate amounts of temporal variation in the relationship. A more general insect herbivore-host plant model was also developed to extend the results. The general model shows that density dependence in patch and insect population growth rates have large effects on the density–area relationship. The density–area relationship was strongly affected by density dependence in insect growth. Increasing density dependence in insect growth caused insect density to decrease with increasing patch size. Temporal variation in the relationship was most strongly affected by density dependence in patch growth. Variation in the density–area relationship increased as density dependence in patch growth increased. The results of this study show that density–area relationships can be variable and are not necessarily a species-specific trait. Application of density–area relationships, especially in dynamic landscapes, need to be aware of and account for factors that affect the size and number of patches as well as growth and dispersal of the target populations.

Density-dependent mortality is mediated by foraging activity for prey fish in whole-lake experiments.

Whereas the effects of density-dependent growth and survival on population dynamics are well-known, mechanisms that give rise to density dependence in animal populations are not well understood. We tested the hypothesis that the trade-off between growth and mortality rates is mediated by foraging activity and habitat use. Thus, if depletion of food by prey is density-dependent, and leads to greater foraging activity and risky habitat use, then visibility and encounter rates with predators must also increase. We tested this hypothesis by experimentally manipulating the density of young rainbow trout (Oncorhynchus mykiss) at risk of cannibalism, in a replicated single-factor experiment using eight small lakes, during an entire growing season. We found no evidence for density-dependent depletion of daphnid food in the nearshore refuge where most age-0 trout resided. Nonetheless, the proportion of time spent moving by individual age-0 trout, the proportion of individuals continuously active, and use of deeper habitats was greater in high density populations than in low density populations. Differences in food abundance among lakes had no effect on measures of activity or habitat use. Mortality of age-0 trout over the growing season was higher in high density populations, and in lakes with lower daphnid food abundance. Therefore, population-level mortality of age-0 trout is linked to greater activity and use of risky habitats by individuals at high densities. We suspect that food resources were depleted at small spatial and temporal scales not detected by our plankton sampling in the high density treatment, because food-dependent activity and habitat use by age-0 trout occurs in our lakes when food abundance is experimentally manipulated (Biro, Post & Parkinson, in press).

Density-dependent growth and metamorphosis in the larval bronze frog Rana temporalis is influenced by genetic relatedness of the cohort.

Effects of density and kinship on growth and metamorphosis in tadpoles of Rana temporalis were studied in a 2 4 factorial experiment. Fifteen egg masses were collected from streams in the Western Ghat region of south India. The tadpoles were raised as siblings or in groups of non-siblings at increasing density levels, viz. 15, 30, 60 and 120/5 l water. With an increase in density level from 15 to 120 tadpoles/5 l water, duration of the larval stage increased and fewer individuals metamorphosed irrespective of whether they belonged to sibling or non-sibling groups by day 100 when the experiments were terminated. The size of individuals at metamorphosis declined significantly with increase in the density of rearing. However, at higher densities (60 and 120 tadpoles/5 l water) sibling group tadpoles performed better compared to mixed groups and took significantly less time to metamorphose. Also, more individuals of sibling groups metamorphosed compared to non-sibling groups at a given density. Mixed rearing retarded growth rates, prolonged larval duration resulting in a wider spectrum of size classes, and lowered the number of individuals recruited to terrestrial life. The study shows that interference competition occurred more strongly in cohorts of mixed relatedness than in sibling groups.

Density Dependence in Growth and Size Structure of NorthernPike Populations

The density of northern pike Esox lucius was estimated using mark–recapture techniques and compared with measures of growth and population size structure among 12 north-central Minnesota lakes. The relationships between density and either proportional stock density (PSD, a length-frequency index) or mean back-calculated length were negative and nonlinear. Regression of loge density and PSD explained 63% of the variation in PSD, and regressions of loge density and mean back-calculated length by sex for ages 2–5 explained 47% to 67% of the variation in growth rates among lakes. The relationships remained consistent when data from 17 northern Wisconsin lakes were pooled with those from the 12 Minnesota lakes (although the R2 was reduced). The fastest growth rates and highest PSDs were observed at northern pike densities of less than 12–14 fish/ha. Inclusion of variables related to the productivity of the lakes only marginally improved the predictive capabilities of the relationship between loge density and growth in the Minnesota lakes. Lake productivity was more important, however, when data from Wisconsin and Minnesota lakes were pooled. In the pooled data, mean back-calculated length at age was negatively related to Secchi disk visibility and positively related to total alkalinity. Our results highlight the importance of density dependence in growth and population size structure for populations of northern pike within their native range.

Population Characteristics and Ecological Role of Northern Pike in Shallow Natural Lakes in Nebraska

Abstract Northern pike Esox lucius were sampled in Nebraska's Sandhill lakes during 1998 and 1999 to determine population characteristics and their influence on the fish community in these shallow, warm lakes at the southwestern edge of this species' natural range. Density-dependent growth, size structure, and condition were not evident in the northern pike populations sampled. Relative abundance of largemouth bass Micropterus salmoides was positively related to size structure of yellow perch Perca flavescens and bluegills Lepomis macrochirus when northen pike were absent. When northern pike and largemouth bass populations were sympatric, these relationships were less evident. Population size structure of yellow perch was lower in lakes with northern pike, but decreased size structure was not evident for bluegills. Northern pike growth decreased with July bottom water temperature, which ranged from 20°C to 25°C. Recruitment patterns of northern pike in the Sandhill lakes appeared to be lake-specific, stro...

Effects of Recreational Fishing on the Population Dynamics of Lake-Dwelling Brook Trout

Data collected over 7 consecutive years were used to examine the population dynamics of the exploited brook trout Salvelinus fontinalis of Meach Lake in central Ontario. Numbers of age-1 and older trout averaged 975 among years. The largest trout were 490 mm long and weighed 1,807 g. Few trout lived beyond age 4. Annual mortality rates varied among age-classes and between sexes; average total instantaneous mortality was 0.95 and average total and fishing mortalities were 78% and 44%, respectively. Exploitation was greatest for age-2 and age-3 brook trout of both sexes. Catchability was uncorrelated with abundance. There was evidence of density-dependent growth at age-2 or age-3 but no indication of density-dependent mortality. A “hockey stick” model appeared to best describe the stock–recruitment relationship. Abundance of potential competitors was not correlated with brook trout size, although abundance of white suckers Catostomus commersoni was correlated with numbers of age-2 male brook trout. We conclude that total mortality rates are naturally very high and existing levels of harvests in this lake may not be increasing total mortality. To ensure the sustainability of brook trout fisheries, lake-dwelling populations should be managed to maintain total mortality rates below those observed in this study.

Putative role for EPC‐1/PEDF in the G0 growth arrest of human diploid fibroblasts

EPC-1/PEDF expression is closely associated with reversible growth arrest in normal human diploid fibroblast-like (HDF) cells and is diminished with proliferative senescence in vitro. EPC-1 expression in HDF cells is induced under conditions of density-dependent contact inhibition and growth factor deprivation. Antiserum generated against EPC-1 recognizes a secreted protein of approximately 50 kDa from medium conditioned by early passage HDF cells, but not from senescent cells. The addition of EPC-1 antiserum to early population doubling level (PDL) cultures near the plateau phase of growth significantly increases the number of cells entering DNA synthesis. Affinity purified EPC-1 antibodies alone enhance the ability of near plateau-phase early PDL WI-38 cells to synthesize DNA by as much as threefold. Further, the addition of recombinant EPC-1 (rEPC-1) to logarithmically growing cells resulted in a marked decrease in the ability of these cells to enter DNA synthesis. We also demonstrate the loss of EPC-1 expression in WI-38 and IMR-90 HDF cell lines with both senescence and simian virus 40 (SV40) transformation. The loss of EPC-1 expression with SV40 transformation occurs at the level of steady-state mRNA and protein accumulation with genomic EPC-1 sequences grossly intact. Taken together, these results suggest that EPC-1 may play a role in the entry of early passage fibroblasts into a G(0) state or the maintenance of such a state once reached.

Degradation of N-acylhomoserine lactones, the bacterial quorum-sensing molecules, by acylase

Porcine kidney acylase I was shown to be able to deacylate N-acylhomoserine lactones, a family of chemicals employed by Gram-negative bacteria as quorum-sensing molecules for cell population density-dependent growth (such as biofilm formation). The enzyme transformed both N-butyryl-and N-octanoyl- l-homoserine lactones into l-homoserine. An optimal pH of 10 at 23 °C and an optimal temperature of 76 °C at pH 9 were found for the enzyme in hydrolyzing N-butyryl-homoserine lactone. At pH 9 and 23 °C, the enzymatic catalysis had a K m of 81±3 mM and a k cat of 127±2 nmol min −1 per mg. The enzyme was also shown to be able to reduce the biofilm growth in an aquarium water sample. Potential physiological significance and medicinal/industrial applications of the N-acylhomoserine lactone-degrading activity of acylase are discussed.