Mean Population Density Research Articles

Fecal pellet production and sediment reworking potential of the polychaeteHeteromastus Filiformisshow a tide dependent periodicity

Abstract The sediment reworking potential of Heteromastus filiformis (a capitellid polychaete) was determined in a laboratory mesocosm by collecting and counting fecal pellets deposited on the sediment surface at 6-hour intervals over several simulated tidal cycles. Pellet production rates showed a marked 6-hour periodicity. Production was highest during the flooding and decreased during the ebbing tide. In the absence of a simulated tidal cycle, there was no periodicity in pellet production. With an annual mean population density of 1200 individuals/m2 in theJadebusen Bay, Wadden Sea, the quantity of sediment reworked by H. filiformis is about 175 ml/m2/day or 64 l/m2/year, which is approximately a deep-sediment layer of 6 em, transported to the surface annually. Pellet production by Heteromastus contributes substantially to the recycling of detritus and nutrients in the Wadden Sea, especially in areas with high population densities.

The ecology of three communities of small mammals at different altitudes in Malawi, Central Africa

This study compares the results of three studies and assesses the effects of seasonal changes in the environment on populations of small mammals at three altitudes in Malawi (Zomba Plateau [1900 m], Liwonde National Park [550 m] and Lengwe National Park [100 m]). Zomba Plateau had a higher annual rainfall (mean 2244 mm), longer wet season, shorter dry season, cooler temperatures and smaller water deficit than either Liwonde NP or Lengwe NP (which had similar climates). Maximum grass biomass (and fluctuation index) was 814 g/m2 (1.7) on Zomba Plateau, 1066 g/m2 (2.7) at Liwonde, and 854 g/m2 (30.5) at Lengwe. Sixteen species of rodents were recorded, 7–9 at each study area; the species on Zomba Plateau did not occur at the lower altitudes, and the lower altitude species did not occur on Zomba Plateau. Percentage Similarity and Coefficients of Community showed that there was considerable similarity between Liwonde and Lengwe, but no similarity between either of them and Zomba Plateau. Mean population densities of small rodents (range, fluctuation index) were 23/ha (15–35, 2.3) on Zomba Plateau, 12.6 (2.7–19.1, 7.1) at Liwonde, and 14.5 (0.9–30.9, 33.9) at Lengwe. Stability of the environment tends to confer stability in demographic characteristics. Reproduction was mainly confined to the wet season (December to April) at all altitudes. Comparison of the proportion of new individuals each month, and the duration of residence by individuals, suggests that turnover of the population was slowest on Zomba Plateau and fastest at Lengwe. There was no evidence for reduced litter size, reduced opportunity for reproduction, or increased age to maturity at the highest altitude compared with the lower altitudes as has been recorded in temperate environments.

Assessing Effects of Unreplicated Perturbations: No Simple Solutions

We address the task of determining the effects, on mean population density or other parameters, of an unreplicated perturbation, such as arises in environmental assessments and some ecosystem—level experiments. Our context is the Before—After—Control—Impact—Pairs design (BACIP): on several dates Before and After the perturbation, samples are collected simultaneously at both the Impact site and a nearby "Control." One approach is to test whether the mean of the Impact—Control difference has changed from Before to After the perturbation. If a conventional test is used, checks of its assumptions are an important and messy part of the analysis, since BACIP data do not necessarily satisfy them. It has been suggested that these checks are not needed for randomization tests, because they are insensitive to some of these assumptions and can be adjusted to allow for others. A major aim of this paper is to refute this suggestion: there is no panacea for the difficult and messy technical problems in the analysis of data from assessments or unreplicated experiments. We compare the randomization t test with the standard t test and the modified (Welch—Satterthwaite—Aspin) t test, which allows for unequal variances. We conclude that the randomization t test is less likely to yield valid inferences than is the Welch t test, because it requires identical distributions for small sample sizes and either equal variances or equal sample sizes for larger ones. The formal requirement of Normality is not crucial to the Welch t test. Both parametric and randomization tests require that time and location effects be additive and the Impact—Control differences on different dates be independent. These assumptions should be tested; if they are seriously wrong, alternative analyses are needed. This will often require a long time series of data. Finally, for assessing the importance of a perturbation, the P value of a hypothesis test is rarely as useful as an estimate of the size of the effect. Especially if effect size varies with time and conditions, flexible estimation methods with approximate answers are preferable to formally exact P values.

Population density, growth and diet of eels, Anguilla anguilla L., in two rivers in eastern England

. The population density, growth and diets of eels, Anguilla anguilla L., from four sites on two rivers in eastern England were studied over 2 years. Eel population density varied greatly between sites and seasons, few eels being caught during the winter. Mean population densities ranged from 50 to 518 eels/ha and mean biomass from 35 to 210kg/ha. Older eels were more numerous at upstream sites. Growth rates in the two rivers were generally similar, but eels 9–13 years old at upstream sites were significantly larger in terms of length and weight than their downstream counterparts. Of 868 eels examined, only 425 stomachs contained food, the percentage of empty stomachs being negatively correlated with temperature. Asellus aquaticus was the predominant food item at all sites in all seasons and in the three size classes of eels studied. Megaloptera and Trichoptera were also important. Fish, largely bottom-dwelling species, were found mainly in the largest size-class of eels and in the winter, when few large eels were feeding. Niche breadth expands with increasing size of cel.

Spatial Dispersion Patterns and Sequential Sampling Plans for Squash Bugs (Heteroptera: Coreidae) in Summer Squash

Squash bugs, Anasa tristis (De Geer), were intensively sampled in summer squash plots from three locations in Oklahoma in the spring and summer of 1987 and 1988. Data collected from whole-plant samples for adults, egg masses, and nymphs were fitted to the Poisson, negative binomial, and positive binomial frequency distributions, as well as Taylor’s power function and Iwao’s patchiness regression. None of the three theoretical distributions fit the squash bug populations on all sample occasions. Taylor’s power law provided a better fit to the count data than did Iwao’s patchiness regression. All life stages exhibited aggregated patterns of spatial dispersion; small nymphs exhibited the largest degree of aggregation, followed by large nymphs, adults, and egg masses. Sequential sampling plans for squash bugs were developed using estimated variance-mean relationships derived from Taylor’s power function. Because small nymphs were highly aggregated, greater numbers of plant samples were required to estimate population means of nymphs with specified levels of precision than were needed for adults or egg masses. Validation with Monte Carlo simulations indicated that these procedures may not always estimate mean population density at specified levels of precision.

Induction of Systemic Resistance of Cucumber toColletotrichum orbiculareby Select Strains of Plant Growth-Promoting Rhizobacteria

Ninety-four strains of plant growth-promoting rhizobacteria (PGPR) were screened for induction of systemic resistance using a model system of cucumber and anthracnose, caused by Colletotrichum orbiculare. Compared with a nonbacterized, challenged control, treatment of cucumber seeds with six PGPR strains resulted in a significant reduction in lesion size after challenge-inoculation with C. orbiculare. Four of the six PGPR strains that induced resistance in cucumber produced HCN in vitro. Antagonism in vitro toward Pythium ultimum, Rhizoctonia solani, and C. orbiculare on three media generally was absent with five PGPR strains and weak with one strain. Rifampicin-resistant mutants of the PGPR strains colonized roots at mean population densities of log 6.5 to 8.3 cfu g(-1) of root at 7 days after planting and log 4.1 to 6.1 cfu g(-1) at 21 days after planting. None of the strains was recovered from surface-disinfested petioles on the day of challenge with C. orbiculare. Roots from plants bacterized with PGPR strains showed less necrosis than the nonbacterized, challenged control. The results support the conclusion that some PGPR strains applied to seed can induce systemic resistance to C. orbiculare

コナヒョウヒダニとヤケヒョウヒダニの個体群動態に関する比較研究

Surveys were undertaken to reveal the population dynamics of house dust mites, Dermatophagoides spp., in floor dusts collected from living rooms and bedrooms of 10 homes in and around Nagoya City, at about 3 month intervals from September 1983 to June 1985. All homes were more or less infested with both species of D. farinae (D. f.) and D. pteronyssinus (D. p.). Mean population density of D. f. exhibited seasonal fluctuation with the highest number in September or June and the lowest in March in most of these homes, irrespective of room types and floor materials. The population structure of D. f. changed by season; relative increase of nymphs in winter populations was characteristic, suggesting the appearance of some desiccation-tolerant nymphs. On the contrary, seasonal fluctuation of D. p. populations varied from home to home according to the types of rooms and floor materials. Relatively large numbers of D. p. were found in December or March in some homes. No marked difference was seen in the population structure of D. p. between summer and winter populations. It was noted that the population density and structure of D. p. were almost constant in bedrooms with tatami floors. D. p. had a tendency to dominate in homes with fewer rooms to the family size. From these results, it was concluded that the population dynamics of D. f. and D. p. differed to some degree, although they have similar ecological niche. The difference seemed to be due mainly to the appearance of diapause nymphs in winter populations of D. f., but not in D. p. populations.

Evaluation ofChaoborus predation on natural populations of herbivorous zooplankton in a eutrophic lake

The effect of Chaoborus predation on natural zooplankton communities was tested in enclosure experiments during June, July and August in the eutrophic Frederiksborg Slotsso, Denmark. Natural densities of Chaoborus larvae in enclosures reduced the abundance of copepod nauplii and Chydorus sphaericus with up to 60% and 80%, respectively, compared with controls. In contrast, Chaoborus was not able to suppress populations of Eudiaptomus graciloides and Daphnia cucullata. Predation was strongest during June and decreased thereafter as Chaoborus pupae emerged. Laboratory experiments showed that a considerable part (20–30% of the population day −1) of Chaoborus larvae emerged as pupae at 18–20 °C in July and August. Chaoborus larvae occurred in the lake as migratory individuals from May to September with mean population densities of about 100 larvae m−2. Results from the enclosure experiments suggest that the populations of herbivorous zooplankton in Frederiksborg Slotsso during June, July and August are not controlled by natural populations of Chaoborus larvae.

Ravenstein on Global Carrying Capacity

Earnest George Ravenstein (1834-1913) delivered a lecture (entitled Lands of the Globe Still Available for European settlement) in Leeds to the Geographical and Economic Section of the British Association in September 1890 attempting to quantify global population carrying capacity. His main theme also touched on estimating total world population its rate of increase and the size of cultivable area. He projected a mid-20th century population of 2.3 billion which was close to the 2.5 billion reached around 1950. In his view the final limits to population growth would be posed around 2072 by the food supply and the worlds carrying capacity arriving at the figure of 5994 million. He proved to be wrong on assuming regional self-sufficiency in food persisting differentials in consumption and improvement in cultivation per unit of land. In 1890 world population was estimated to have a total 1467600000 people broken down to 380200000 in Europe 850000000 in Asia 127000000 in Africa 4730000 in Australasia 89250000 in North America and 36420000 in South America. Less than 40% of total arable area was under cultivation in Europe with 156 inhabitants/sq. mile. Population density was 175/sq. mile in India 295 in China and 264 in Japan. In the fertile regions mean population density was 207/sq. mile thus their maximum carrying capacity would amount to 5851 million people. The steppes could support 10 people/sq. mile and deserts only 1 person/sq. mile thus yielding the potential maximum of 5994 million people.

Distribution and population density of the bushcricket Decticus verrucivorus in a damp-meadow biotope.

A population of Decticus verrucivorus (Orthoptera: Tettigoniidae) was studied in the field over two successive years. The majority of insects accumulate only in certain parts of a diverse habitat. In this area the mean population density of adult Decticus verrucivorus was 3.1/100 m2. Analysis of nearest neighbour distances shows that males have a clumped distribution in the undisturbed habitat. It is concluded that larval distribution reflects the distribution of oviposition sites but that the distribution of adult males, though also depending on the distribution of natural resources and the climatic conditions, is produced mainly by the acoustic interactions with other males. The distribution of adult females does not appear to be determined by the acoustic behaviour of the males. The role of environmental factors such as the availability of food, humidity and temperature, and of the acoustic communication within this species, is discussed with respect to the problem of the high site fidelity of Decticus verrucivorus.

Terrestrial population models for ecological risk assessment: A state‐of‐the‐art review

AbstractFew attempts have been made to formulate models for predicting impacts of xenobiotic chemicals on wildlife populations. However, considerable effort has been invested in wildlife optimal exploitation models. Because death from intoxication has a similar effect on population dynamics as death by harvesting, these management models are applicable to ecological risk assessment. An underlying Leslie‐matrix bookkeeping formulation is widely applicable to vertebrate wildlife populations. Unfortunately, however, the various submodels that track birth, death, and dispersal rates as functions of the physical, chemical, and biotic environment are by their nature almost inevitably highly species‐ and locale‐specific. Short‐term prediction of one‐time chemical applications requires only information on mortality before and after contamination. In such cases a simple matrix formulation may be adequate for risk assessment. But generally, risk must be projected over periods of a generation or more. This precludes generic protocols for risk assessment and also the ready and inexpensive predictions of a chemical's influence on a given population. When designing and applying models for ecological risk assessment at the population level, the endpoints (output) of concern must be carefully and rigorously defined. The most easily accessible and appropriate endpoints are (1) pseudoextinction (the frequency or probability of a population falling below a prespecified density), and (2) temporal mean population density. Spatial and temporal extent of predicted changes must be clearly specified a priori to avoid apparent contradictions and confusion.

The effect of sudden changes in temperature, light and salinity on the population density and export of zooxanthellae from the reef corals Stylophora pistillata Esper and Seriatopora hystrix Dana

Bleaching (loss of pigmentation by corals) is a widespread phenomenon in coral-reef ecosystems. Despite this, the underlying causes of some forms of bleaching are poorly understood. This study explores the conditions that induce bleaching in two species of reef coral-zooxanthellae associations from Lizard Island, Great Barrier Reef, Australia. Naturally bleached Stylophora pistillata Esper and Seriatopora hystrix Dana, collected from the edge of Lizard Island lagoon, had the same amount of Chl a · zooxanthellae −1, yet had reduced population densities of zooxanthellae when compared to normal-looking colonies. In this case, the lack of pigment in the bleached corals was explained by low numbers of zooxanthellae and not by pale zooxanthellae. This is contrary to results obtained by some other workers and suggests that closer inspection of the underlying reasons for the pale color of bleached corals is warranted. In laboratory experiments, sudden exposures to full sunlight induced the bleaching of S. pistillata previously grown at 25% sunlight. The pale color of colonies exposed to full sunlight was explained by the low pigment content of the zooxanthellae rather than by low population densities of zooxanthellae. In addition, the specific expulsion rate of zooxanthellae from S. Pistillata and S. hystrix was not influenced by sudden increases in solar irradiance. Sudden exposures to reduced salinities (30%.) did not affect S. Pistillata or S. hystrix in this study. Both species bleached rapidly, however, when exposed to water temperatures of > 30 °C. Bleached corals in this case had reduced population densities of zooxanthellae despite normal zooxanthella pigment contents. The specific expulsion rate of zooxanthellae from both species of coral was very sensitive to temperature. 7-h exposures to 30 and 32 °C resulted in specific expulsion rates of > 1000 times that of controls. Specific expulsion rates remained high, even when corals were returned to control temperatures (27 °C). After high temperature stress, S. Pistillata and S. hystrix had high and sustained colony respiratory rates ( r c ), reduced colony photosynthetic rates ( p c net max ) and reduced P c g max : r c ratios. The O 2 metabolism of the S. pistillata and S. hystrix symbioses remained abnormal for up to 4 days after a 7-h exposure to 32 °C. Evidence suggestive of recovery was apparent 19 days later. By this time, the mean population density of zooxanthellae and p c g max : r c ratios of exposed fragments had returned to normal.

Effets de la densité sur la croissance du bivalve Macoma balthica (L.) en zone intertidale

Experimental and descriptive field studies were conducted on an intertidal population of the infaunal bivalve Macoma balthica (L.) in the St Lawrence estuary in order to investigate the effect of density on growth and recruitment. The study of spatial variations in density and shell growth on the tidal flat was based on a stratified random sampling using three tidal level zones as strata. Mean population density over the whole area was 1302 · m −2; densities were higher and more variable near mean water level. Shell-growth rate and mean shell length of each generation increased with immersion time. There was a strong density effect on shell growth which increased with tidal level. The population was food limited in the upper two-thirds of the flat. The effect of density on shell growth was confirmed by a completely randomized block design experiment in the upper intertidal level. There was also a density effect on total tissue dry weight and on gonad size, but there was no significant effect of adult density on recruitment.

TERRESTRIAL POPULATION MODELS FOR ECOLOGICAL RISK ASSESSMENT: A STATE-OF-THE-ART REVIEW

Few attempts have been made to formulate models for predicting impacts of xenobiotic chemicals on wildlife populations. However, considerable effort has been invested in wildlife optimal exploitation models. Because death from intoxication has a similar effect on population dynamics as death by harvesting, these management models are applicable to ecological risk assessment. An underlying Leslie-matrix bookkeeping formulation is widely applicable to vertebrate wildlife populations. Unfortunately, however, the various submodels that track birth, death, and dispersal rates as functions of the physical, chemical, and biotic environment are by their nature almost inevitably highly species- and locale-specific. Short-term prediction of one-time chemical applications requires only information on mortality before and after contamination. In such cases a simple matrix formulation may be adequate for risk assessment. But generally, risk must be projected over periods of a generation or more. This precludes generic protocols for risk assessment and also the ready and inexpensive predictions of a chemical's influence on a given population. When designing and applying models for ecological risk assessment at the population level, the endpoints (output) of concern must be carefully and rigorously defined. The most easily accessible and appropriate endpoints are (1) pseudoextinction (the frequency or probability of a population falling below a prespecified density), and (2) temporal mean population density. Spatial and temporal extent of predicted changes must be clearly specified a priori to avoid apparent contradictions and confusion.

Lectin-Detectable Effects of Localized Pneumonia on Airway Mucous Cell Populations: Role of Cyclooxygenase Metabolites

We examined the airway secretory apparatus of adult sheep with experimental pneumonia to look for morphologic and lectin-binding correlates of increased mucus production. The animals were inoculated in the right caudal lobar bronchus either with starch broth containing Pasteurella haemolytica (INF, n = 6), starch broth alone (SHAM, n = 6), or with P. haemolytica and subsequently treated (INF/T, n = 5) with 2 mg/kg indomethacin, subcutaneously three times daily for 6 days. In the INF and INF/T groups, a localized pneumonic infiltrate containing P. haemolytica organisms was present. The bronchi (18-23rd generation) adjacent to the pneumonic lesion had an increased gland volume fraction (6.3 +/- 3.7% in INF, 11.3 +/- 2.4% in INF/T, and 3.1 +/- 1.9% in SHAM, p less than 0.05 among the three). The mean population densities of BSA-reactive (identifying alpha-D-gal) cells were 41.9 +/- 2.7% in the INF, 40.1 +/- 5.6% in the INF/T, versus 14.3 +/- 1.5% in the SHAM group (p less than 0.05), while the corresponding values for PNA-reactive [identifying beta-D-gal(1----3)-D-galNAc] cells were 28.8 +/- 5.1%, 0%, and 0%, respectively. Nor morphologic abnormalities were seen in the trachea, but BSA staining was shifted to morphologically different mucous cells in the INF and INF/T. We conclude that in localized P. haemolytica pneumonia in sheep (1) there are morphologic changes of the airway secretory apparatus adjacent to the lesion, (2) the glycoconjugate profile of secretory cells adjacent to and remote from the lesion is altered, and (3) cyclooxygenase products influence the chemical composition of secretory cells.

Ichthyophthirius (Ciliophora): population studies suggest reproduction in host epithelium.

Evidence that Ichthyophthirius multifiliis trophonts may reproduce within the epithelium of the host was obtained from experimental infections of channel catfish. Mean number of parasites spontaneously leaving the fish increased from 0 on day 3 postexposure (PE) to 66.5 per fish on day 7 PE. Mean population density in fin, however, increased five-fold from day 3 to day 5 PE in the absence of opportunity for reinfection. At day 3 PE, 100% of parasite loci in fin and gill arches contained solitary trophonts. At day 4 PE, 10% of loci in fin contained clusters of two trophonts; at day 7 PE, 69% contained clusters of two or more trophonts. The first clusters of four trophonts in fin were observed day 5 PE and of eight trophonts, day 8 PE. Trophonts in clusters were flattened against one another.

Specificity of the spatial power-law exponent in ecology and agriculture

Accounting for the spatial distribution of individuals is an important issue in ecology and applied biology. The exponent, b, in the established empirical relationship1, s2 = amb, between s2, the spatial sample variance and m, the mean population density, conveys information about the spatial distribution of individuals of a particular species. When randomness occurs, variance and mean are equal. Usually b > 1 and, for given a, individuals randomly dispersed at some low density become more aggregated as density increases at a rate associated positively with the species' b value. The frequent recurrence of the same b value in field samples of a particular species has facilitated efficient sampling programmes2 for pests and wildlife. But Downing3 claimed that the index b does not differ between species, is inconsistent within species, and is statistically biased, depending substantially and systematically on sample attributes. We report here technical deficiencies in his analyses and examine more substantial data that support none of these claims.

Electron microscopic evidence for stimulation of melanosomal maturation by lysosomotropic agents and monensin in cultured B16 mouse melanoma cells.

Mouse melanoma cells, B16-C2M in monolayer culture were treated with either lysosomotropic agent, 10 mM NH4Cl, or 20 microM chloroquine, an ionophore, or 10 microns monensin for 3 h at 37 degrees C, and examined with regard to the site of melanin deposition and numbers of melanized (type 1) and unmelanized (type 2) melanosomes under a transmission electron microscope. The numbers of these two types of melanosomes were counted on electron micrographs of thin sections of 20 to 40 cells for each experimental group and expressed in terms of number per unit area of sectioned cytoplasm. Although most melanosomes were largely swollen in monensin-treated cells, melanin deposition was apparently confined in melanosomes in all experimental groups. The compound melanosomes were scarcely found. The mean population density (number per unit cytoplasmic area) of type 1 melanosomes was highest in the NH4Cl-treated cell group followed by monensin-treated, chloroquine-treated, and control cell groups. When the relative abundance of type 1 melanosomes was expressed as a fraction of total number of type 1 and 2 melanosomes (melanosomal maturation index, MMI), the differences were much more evident. Type 1 melanosomes were found in every cell (MMI not equal to 0) of the groups treated with NH4Cl and chloroquine only, which suggested the existence of a subpopulation of cells responsive to lysosomotropic agents but not to monensin in regard to melanosome maturation. All these findings indicate that the stimulation of melanogenesis proceeds mainly through maturation of preexisting melanosomes under these conditions.

The performance of a small catch-and-release fishery stocked with rainbow trout, Salmo gairdneri Richardson, and thoughts on stocking densities

Abstract. An assessment of the angling performance of a small put-and-take/or release fishery slocked with rainbow trout, Salmo gairdneri Richardson, at a density in the range 345–565 fish/hectare (140–230/acre) showed that the correlations of mean daily and weekly catch per unit effort with population of fish were low and of uncertain significance at the 5% level. A pilot comparison with other fisheries indicates that the annual mean catch per full day and the annual mean population density may be related by the equation Catch/full day = 0·74 Fish/hectare0·33 The roles of catch per unit effort and frequency distributions in the estimation of fish abundance are discussed.

Effect of interreplicate variance on zooplankton sampling design and data analysis1

The variance of replicate marine and freshwater zooplankton samples is related (r2 > 0.99) to the mean population density and the volume of the sample taken. A general variance relationship calculated from 1,189 sets of replicate samples taken throughout the world is presented. This function can predict the variance of both marine and freshwater samples taken with several types of sampling gear. Only 12% of individual taxa examined showed variance relationships that departed significantly from this general function. The variance function shows how the requisite number of samples decreases with increased population density, sampler volume, and lowered precision requirements. The X0.2power transformation is recommended on empirical grounds, although caution is advised in the use of all data transformations.