Population Growth Capacity Research Articles

Combined effects of temperature, photoperiod, and salinity on reproduction of the brine shrimp Artemia sinica (Crustacea: Anostraca).

Artemia sinica is a brine shrimp species distributed in hypersaline salt lakes in northern China and Siberia and a successful invasive species in some coastal salterns. Although it is a commercially harvested and cultured species, knowledge of its reproductive characteristics is limited, and existing studies are often contradictory. The combined effects of temperature, salinity, and photoperiod on reproduction characteristics are experimentally studied to better understand its reproductive features. There were 36 combinations of three environmental factors (3×3×4), each with three or four levels, namely temperature (16, 25, 30°C), photoperiod (6 L:18 D, 12 L:12D, 18 L:6D), and salinity (50, 100, 150, 200 PSU). In each treatment, 48 to 80 pairs of A. sinica from Yuncheng Salt Lake (Shanxi, China) were cultured. Females were observed daily for reproductive mode and the number of offspring produced. Temperature, photoperiod, salinity, and their interactions significantly affected the lifespan and reproduction of A. sinica. The reproductive period was the longest and accounted for the largest proportion of life span at moderate temperature (25°C). Total offspring, offspring per brood, and offspring per day increased as salinity decreased, and the number of broods per female was highest at 25°C. Temperature, photoperiod, and salinity significantly influenced reproductive modes, and interactions among these factors were identified. Artemia sinica primarily reproduces oviparously under low temperature and short daylight conditions, and ovoviviparously under high temperature and long daylight conditions, with the maximum oviparity ratio recorded in treatments of 16°C, 6L:18D, and 50 or 100 PSU. The maximum ovoviviparity ratio was recorded under 30°C, 12L:12D, and 100 PSU. Unlike that documented for other Artemia species or populations, the brood size of A. sinica kept increasing throughout the reproductive period. It did not decline even in the last two broods. For the same brood number, the sizes of oviparous and ovoviviparous broods were similar. The length of the oviparous interval was often greater than that of the ovoviviparous interval, suggesting that oviparous offspring might require additional energy and time to construct the multi-layered eggshell. Compared to other species and populations, the A.sinica from Yuncheng Salt Lake has a relatively shorter pre-reproductive development time, a preference for ovoviviparity, and relatively higher fecundity and population growth capacity, making it a suitable culture species for obtaining fresh biomass.

CARRYING CAPACITY OF SETTLEMENTS IN MEDAN PERJUANGAN SUB-DISTRICT

Research in Medan Perjuangan Sub-District is being conducted in order to assess the settlements' current capacity for population growth. Medan Perjuangan sub-district has the greatest population density in Medan, with 25,533 persons per square kilometer. In 2021, the District of Medan Perjuangan will have a total population of 104,432 people, occupying an area calculated by ArcGIS to be 462.47 hectares. As the population in Medan Perjuangan Sub-District grows, so will the demand for housing. While the land is fixed, it will encourage the development of new land uses. For data gathering, the study relied on field observations and documentation. The data is analyzed using a quantitative and geographical approach. There has been a shift in land use in Medan Perjuangan Sub-District, with 5.76 hectares of undeveloped land now serving as a function of communities and sites of activity, according to the results of satellite image interpretation. As a result, there has been an increase in settlements and centers of activity to 451.74 hectares, or 97.67 percent. The Medan Perjuangan Sub-District has a class C land capability with medium development ability and class D with moderate development ability, according to the results of the calculation of the land capability unit. According to settlement capacity calculations, the Medan Perjuangan Sub-District cannot satisfy the needs of settlements with DDP 1 anymore. Those involved in the planning of future development in the Medan Perjuangan Sub-District will find this study to be an important resource.

Climate and habitat configuration limit range expansion and patterns of dispersal in a non-native lizard.

Invasive species are one of the main causes of biodiversity loss worldwide. As introduced, populations increase in abundance and geographical range, so does the potential for negative impacts on native communities. As such, there is a need to better understand the processes driving range expansion as species become established in recipient landscapes. Through an investigation into capacity for population growth and range expansion of introduced populations of a non‐native lizard (Podarcis muralis), we aimed to demonstrate how multi‐scale factors influence spatial spread, population growth, and invasion potential in introduced species. We collated location records of P. muralis presence in England, UK through data collected from field surveys and a citizen science campaign. We used these data as input for presence‐background models to predict areas of climate suitability at a national‐scale (5 km resolution), and fine‐scale habitat suitability at the local scale (2 m resolution). We then integrated local models into an individual‐based modeling platform to simulate population dynamics and forecast range expansion for 10 populations in heterogeneous landscapes. National‐scale models indicated climate suitability has restricted the species to the southern parts of the UK, primarily by a latitudinal cline in overwintering conditions. Patterns of population growth and range expansion were related to differences in local landscape configuration and heterogeneity. Growth curves suggest populations could be in the early stages of exponential growth. However, annual rates of range expansion are predicted to be low (5–16 m). We conclude that extensive nationwide range expansion through secondary introduction is likely to be restricted by currently unsuitable climate beyond southern regions of the UK. However, exponential growth of local populations in habitats providing transport pathways is likely to increase opportunities for regional expansion. The broad habitat niche of P. muralis, coupled with configuration of habitat patches in the landscape, allows populations to increase locally with minimal dispersal.

Using life stage‐structured matrix models to determine natural enemy:pest release ratios for augmentative biological control

AbstractAugmentative biological control (ABC) is crucial for the integrated pest management (IPM) of greenhouse pests. The proper calculation of natural enemy:pest release ratio (NEPRR) stands out among the various challenges of ABC. Often, most NEPRR calculations only take into account the predation/parasitism efficiency of natural enemies, while disregarding pest population growth capacity, population structure and/or economic thresholds. In a model system consisting of Trichogramma pretiosum Riley parasitizing eggs of Tuta absoluta (Meyrick) on greenhouse tomatoes, we investigated whether a stage‐structured Lefkovitch matrix could be used to determine suitable NEPRRs. The results suggested that these matrix models can potentially provide more precise and realistic predictions of NEPRRs since they account for differential pest population growth over time as a response to natural enemy action. The matrix models could also allow us to choose an adaptable NEPRR based on parameters such as the period the grower wishes to keep the pest population below economic threshold.

How There Got to Be So Many of Us: The Evolutionary Story of Population Growth and a Life History of Cooperation

One of the defining features of human evolution is our demographic success. As of August 2019, the world’s population exceeds 7.7 billion. The human capacity for population growth has profound effe...

Implications of high rates of sexual recruitment in driving rapid reef recovery in Mo\u2019orea, French Polynesia

Coral abundance continues to decline on tropical reefs around the world, and this trend suggests that coral reefs may not persist beyond the current century. In contrast, this study describes the near-complete mortality of corals on the outer reef (10 m and 17 m depth) of the north shore of Mo’orea, French Polynesia, from 2005 to 2010, followed by unprecedented recovery from 2011 to 2017. Intense corallivory and a cyclone drove coral cover from 33–48% to <3% by 2010, but over the following seven years, recovery occurred through rapid population growth (up to 12% cover y−1) to 25–74% cover by 2017. The thirteen-year, U-shape trajectory of coral cover over time created by the loss and replacement of millions of corals through sexual reproduction underscores the potential for beneficial genetic responses to environmental conditions for at least one genus, Pocillopora. The high ecological resilience of this coral community appears to have been enhanced by variation among genera in the susceptibility to declining cover, and the capacity for population growth (i.e., response diversity). These results suggest that the outer coral communities of Mo’orea may be poised for genetic changes that could affect their capacity to persistence.

Rate of consumption, biological parameters, and population growth capacity of Orius laevigatus fed on Spodoptera exigua

Orius laevigatus (Fieber) (Hemiptera: Anthocoridae) is already successfully used to control Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) in protected crops. In the present work, the predatory capacity of O. laevigatus on the eggs and larvae of Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae) as well as the population growth capacity of O. laevigatus fed on eggs of the noctuid were determined. Fourth and 5th instar nymphs had a greater consumption of eggs than younger ones. Females consumed more eggs than males. Only 5th instar nymphs and adults preyed on the neonatal larvae of S. exigua. The intrinsic rate of natural increase did not differ between O. laevigatus fed with S. exigua eggs and those offered eggs of the substitute host Ephestia kuehniella (Zeller) (Lepidoptera: Pyralidae). Thus, O. laevigatus is a good candidate for the biological control of S. exigua, a cosmopolitan pest of many crops.

The over-expression of a chrysanthemum WRKY transcription factor enhances aphid resistance

Members of the large WRKY transcription factor family are responsible for the regulation of plant growth, development and the stress response. Here, five WRKY members were isolated from chrysanthemum. They each contained a single WRKY domain and a C2H2 zinc finger motif, so were classified into group II. Transient expression experiments demonstrated that all five were expressed in the nucleus, although CmWRKY42 was also expressed in the cytoplasm. When expressed heterologously in yeast, the products of CmWRKY22 and CmWRKY48 exhibited transactivation activity, while those of CmWRKY21, CmWRKY40 and CmWRKY42 did not. The transcription of the five CmWRKY genes was profiled when the plants were challenged with a variety of abiotic and biotic stress agents, as well as being treated with various phytohormones. CmWRKY21 proved to be markedly induced by salinity stress, and suppressed by high temperature exposure; CmWRKY22 was induced by high temperature exposure; CmWRKY40 was highly induced by salinity stress, and treatment with either abscisic acid (ABA) or methyl jasmonate (MeJA); CmWRKY42 was up-regulated by salinity stress, low temperature, ABA and MeJA treatment and aphid infestation; CmWRKY48 was induced by drought stress, ABA and MeJA treatment and aphid infestation. The function of CmWRKY48 was further investigated by over-expressing it transgenically. The constitutive expression of this transcription factor inhibited the aphids' population growth capacity, suggesting that it may represent an important component of the plant's defense machinery against aphids.

Temperature-Dependent Fecundity and Life Table of the Fennel Aphid Hyadaphis foeniculi (Passerini) (Hemiptera: Aphididae).

Hyadaphis foeniculi (Passerini) (Hemiptera: Aphididae) is a cosmopolitan species and the main pest of fennel in northeastern Brazil. Understanding the relationship between temperature variations and the population growth rates of H. foeniculi is essential to predict the population dynamics of this aphid in the fennel crop. The aim of this study was to measure the effect of constant temperature on the adult prereproductive period and the life table fertility parameters (infinitesimal increase ratio (rm), gross reproduction rate (GRR), net reproduction rate (R0), finite increase ratio (λ), generation time (GT), the time required for the population to double in the number of individuals (DT), and the reproduction value (RVx)) of the fennel pest H. foeniculi. The values of lx (survival of nymphs at age x) increased as the temperature rose from 15 to 28°C and fell at 30°C, whereas mx (number of nymphs produced by each nymph of age x) increased from 15 to 25°C and fell at 28 and 30°C. The net reproduction rates (R0) of populations of H. foeniculi increased with temperature and ranged from 1.9 at 15°C to 12.23 at 28°C for each generation. The highest population increase occurred with the apterous aphids at 28°C. The rate of population increase per unit time (rm) (day) ranged from 0.0033 (15°C) to 0.1995 (28°C). The highest values of rm were recorded at temperatures of 28°C and 30°C. The rm values were a good fit to the models tested, with R2 > 0.91 and R2 adj > 0.88. The models tested (Davidson, Sharpe and DeMichele modified by Schoolfield et al., Logan et al., Lamb, and Briere et al.) were very good fits for the rm values observed, with R2 > 0.91 and R2 adj > 0.88. The only exception was the Davidson model. Of the parameters studied, the reproductive capacity was higher in the apterous aphids, with the unique exception of daily fecundity at 28°C, which was higher in the alate aphids of H. foeniculi. Parameters relating to the age-specific fertility table for H. foeniculi were heavily influenced by temperature, with the highest biotic potential and population growth capacity found at 34°C. Therefore, the results obtained in this study could be of practical significance for predicting outbreaks of fennel aphids and improving the management of this aphid in fennel crops.

Dendrochronological reconstruction of the epicentre and early spread of emerald ash borer inNorthAmerica

AbstractAimEmerald ash borerAgrilus planipenniswas identified in 2002 as the cause of extensive ash (Fraxinusspp.) decline and mortality in Detroit, Michigan, and has since killed millions of ash trees in theUSand Canada. When discovered, it was not clear how long it had been present or at what location the invading colony started. We used dendrochronological methods to document the onset and progression of ash mortality and the spatio‐temporal dynamics of the invasion. Reconstructing the progression of ash mortality serves as a proxy to draw inferences about the colonization and spread of emerald ash borer in North America.LocationSoutheastern Michigan,USA.MethodsWe collected increment cores from dead, declining or non‐symptomatic ash trees on a systematic 4.8 × 4.8 or 2.4 × 2.4 km grid in 2004–2006. Geo‐referenced samples were cross‐dated to determine the earliest date emerald ash borer‐killed trees in each location. Interpolated dates of ash mortality were analysed to determine rates and patterns of emerald ash borer spread across the 1.5 million ha study area.ResultsWe identified a location in southeastern Michigan where ash trees were killed by emerald ash borer as early as 1997. Rates of ash mortality subsequently progressed at 3.84 km year−1from 1998 to 2001 and then increased to 12.97 km year−1from 2001 to 2003 as satellite colonies coalesced with the primary infestation. From 1998 to 2003, new satellites formed at a rate of 7.4 per year, with average jump distances of 24.5 km.Main conclusionsEmerald ash borer was likely established in southeastern Michigan by at least the early to mid‐1990s. Anthropogenic‐aided stratified dispersal and the coalescence of satellite colonies with the primary population resulted in biphasic range expansion, rapidly expanding the footprint of the invasion. Our reconstruction of the emerald ash borer invasion demonstrates this invaders’ remarkable capacity for population growth and spread.

Sensitivity to thermal extremes in AustralianDrosophilaimplies similar impacts of climate change on the distribution of widespread and tropical species

Climatic factors influence the distribution of ectotherms, raising the possibility that distributions of many species will shift rapidly under climate change and/or that species will become locally extinct. Recent studies have compared performance curves of species from different climate zones and suggested that tropical species may be more susceptible to climate change than those from temperate environments. However, in other comparisons involving responses to thermal extremes it has been suggested that mid-latitude populations are more susceptible. Using a group of 10 closely related Drosophila species with known tropical or widespread distribution, we undertake a detailed investigation of their growth performance curves and their tolerance to thermal extremes. Thermal sensitivity of life history traits (fecundity, developmental success, and developmental time) and adult heat resistance were similar in tropical and widespread species groups, while widespread species had higher adult cold tolerance under all acclimation regimes. Laboratory measurements of either population growth capacity or acute tolerance to heat and cold extremes were compared to daily air temperature under current (2002-2007) and future (2100) conditions to investigate if these traits could explain current distributions and, therefore, also forecast future effects of climate change. Life history traits examining the thermal sensitivity of population growth proved to be a poor predictor of current species distributions. In contrast, we validate that adult tolerance to thermal extremes provides a good correlate of current distributions. Thus, in their current distribution range, most of the examined species experience heat exposure close to, but rarely above, the functional heat resistance limit. Similarly, adult functional cold resistance proved a good predictor of species distribution in cooler climates. When using the species' functional tolerance limits under a global warming scenario, we find that both tropical and widespread Drosophila species will face a similar proportional reduction in distribution range under future warming.

Integrating physiological and biomechanical drivers of population growth over environmental gradients on coral reefs

Coral reefs exhibit marked spatial and temporal variability, and coral reef organisms exhibit trade-offs in functional traits that influence demographic performance under different combinations of abiotic environmental conditions. In many systems, trait trade-offs are modelled using an energy and/or nutrient allocation framework. However, on coral reefs, differences in biomechanical vulnerability have major demographic implications, and indeed are believed to play an essential role in mediating species coexistence because highly competitive growth forms are vulnerable to physical dislodgment events that occur with high frequency (e.g. annual summer storms). Therefore, an integrated energy allocation and biomechanics framework is required to understand the effect of physical environmental gradients on species' demographic performance. However, on coral reefs, as in most ecosystems, the effects of environmental conditions on organisms are measured in different currencies (e.g. lipid accumulation, survival and number of gametes), and thus the relative contributions of these effects to overall capacity for population growth are not readily apparent. A comprehensive assessment of links between the environment and the organism, including those mediated by biomechanical processes, must convert environmental effects on individual-level performance (e.g. survival, growth and reproduction) into a common currency that is relevant to the capacity to contribute to population growth. We outline such an approach by considering the population-level performance of scleractinian reef corals over a hydrodynamic gradient, with a focus on the integrating the biomechanical determinants of size-dependent coral colony dislodgment as a function of flow, with the effects of flow on photosynthetic energy acquisition and respiration.

Grazing impact of the invasive clam Corbula amurensis on the microplankton assemblage of the northern San Francisco Estuary

Grazing by the overbite clam Corbula amurensis (formerly known as Potamocorbula) may be the cause of substantial declines in phytoplankton biomass and zooplankton in the San Fran- cisco Estuary (SFE) following its introduction in 1986. While grazing rates have been examined on bacteria, phytoplankton, and copepod nauplii, the consumption of protistan microzooplankton by C. amurensis has not previously been measured. In this study, laboratory feeding experiments revealed that C. amurensis cleared 0.5 l ind -1 h -1 of microzooplankton (ciliates) and 0.2 l ind -1 h -1 of chlorophyll (chl) a. Despite the higher clearance rate on microzooplankton, clams obtained more of their carbon from phytoplankton, which dominated the prey assemblage on most dates. When the measured clearance rates are extrapolated to field populations of clams, fractional loss rates (50 to 90% d -1 ) exceed the population growth capacity of microzooplankton. Although microzooplankton may not be a major component of the diet of these clams, C. amurensis may further alter food web dynamics through consumption of this important trophic intermediary, thus disrupting this link from bacteria and phytoplankton to higher trophic levels.

Infection with an insect virus affects olfactory behaviour and interactions with host plant and natural enemies in an aphid

AbstractAphid ecology and population dynamics are affected by a series of factors including behavioural responses to ecologically relevant chemical cues, capacity for population growth, and interactions with host plants and natural enemies. Using the aphid Rhopalosiphum padi (L.) (Homoptera: Aphididae), we showed that these factors were affected by infection with Rhopalosiphum padi virus (RhPV). Uninfected aphids were attracted to odour of uninfected aphids on the host plant, an aggregation mechanism. However, infected aphids were not attracted, and neither infected nor uninfected aphids were attracted to infected aphids on the plant. Infected aphids did not respond to methyl salicylate, a cue denoting host suitability. Infected aphids were more behaviourally sensitive to aphid alarm pheromone, and left the host plant more readily in response to it. RhPV reduced the lifespan and population growth rate of the aphid. The predacious ladybird, Coccinella septempunctata (L.) (Coleoptera: Coccinellidae), consumed more infected aphids than uninfected aphids in a 24‐h period, and the aphid parasitoid Aphidius ervi Haliday (Hymenoptera: Aphidiidae) attacked more infected than uninfected aphids. However, the proportion of mummies formed was lower with infected aphids. The results represent further evidence that associated organisms can affect the behaviour and ecology of their aphid hosts.

Prey suitability of western flower thrips, Frankliniella occidentalis, and onion thrips, Thrips tabaci, for the predatory mite Amblyseius swirskii

Western flower thrips, Frankliniella occidentalis, and onion thrips, Thrips tabaci, are both important polyphagous pests of vegetables and ornamentals in greenhouses. Difficulties in biological control of these pests have prompted a search for new natural enemies. Most recently, the predatory mite Amblyseius swirskii has been commercialised as biological control agent of whiteflies and thrips. However, little is known about the suitability of thrips as prey for A. swirskii. We therefore assessed prey acceptance and life history of A. swirskii when feeding on F. occidentalis and T. tabaci at 25±1°C. Amblyseius swirskii juveniles preyed upon first larval instars of both F. occidentalis and T. tabaci but suffered from high mortality (67 and 78%). Developmental time (egg to adult) of A. swirskii was 7.8 days with either prey species. Adult A. swirskii females readily accepted first larval instars of both thrips species, which were attacked in <20 min on a leaf and <10 min in an artificial cage. Oviposition rates (0.92 and 0.99 eggs/female/day) and offspring sex ratios (63 and 70% females) were similar with F. occidentalis and T. tabaci as prey. Less than one-third of juveniles reaching adulthood and oviposition rates below one egg/female per day resulted in relatively low intrinsic rates of increase (r m) (0.056 and 0.024 per day with F. occidentalis and T. tabaci, respectively). Altogether, our study suggests that the recently reported superiority of A. swirskii to the widely used Neoseiulus cucumeris in suppression of thrips is due to other traits than its population growth capacity with thrips as prey.

First detection of the pest fruit fly, Bactrocera tau (Diptera: Tephritidae), in the field in Japan: Evidence of multiple invasions of Ishigaki Island and failure of colonization

In 1998, several males of Bactrocera tau, a common pest fruit fly in Asia, were captured on Ishigaki Island, Okinawa, by a trap set for monitoring the melon fly (B. cucurbitae) invasion. In 2003, one male was trapped again. We collected vast amounts of host fruit of B. tau on Ishigaki, but could not confirm infestation by this species. These results indicated that B. tau had invaded Ishigaki at least twice but failed to colonize. B. tau may have come from Taiwan, considering its geographic proximity to Ishigaki and the abundance of the species in Taiwan. The invasions could not be fully explained by natural factors alone; it was possible that human-induced means were also involved. We believe that this species can colonize Okinawa, since the host plants are abundant year-round, a potential competitor, B. cucurbitae, is not currently present, and Okinawa is located south of the northern limit of B. tau. Since B. tau has a host range and population growth capacity similar to B. cucurbitae, the species could cause severe damage to crops in Okinawa, much like that caused by B. cucurbitae in the past. We must remain alert for possible re-invasion by B. tau.

Life-history of predatory mites Neoseiulus californicus and Phytoseiulus persimilis (Acari: Phytoseiidae) on four spider mite species as prey, with special reference to Tetranychus evansi (Acari: Tetranychidae)

The commercially available strains of Phytoseiulus persimilis Athias-Henriot, the biological control agent of Tetranychus urticae Koch, perform poorly in the Western Mediterranean, probably because they are not well adapted to local climatic conditions. For that reason, efforts are being focused on the development of a biological control programme using native phytoseiid mites. Four species of red spider mites can be found in vegetable crops in eastern Spain: T. urticae , Tetranychus turkestani Ugarov and Nikolski, Tetranychus ludeni Zacher and the recently introduced Tetranychus evansi Baker and Pritchard. To evaluate their potential role as biological control agents, the present study evaluates the life-history of local populations of Neoseiulus californicus (McGregor) and P. persimilis when fed on T. urticae , T. turkestani , T. evansi , and T. ludeni in the laboratory. Results indicate that N. californicus and P. persimilis are able to feed and complete their development on the four tested red spider mite species. The predators may exhibit a particularly high capacity for population increase when fed on T. urticae , T. turkestani , and T. ludeni , thus may be able to provide effective control of these species in the field. When fed T . evansi , however, predator performance was poor; significant increase in development and preoviposition times, and a reduction in oviposition period and fecundity were recorded. The resultant low capacity for population growth suggests poor ability of the two tested predators to suppress T. evansi populations on commercial crops. It is unlikely therefore that P. persimilis and N. californicus , now being widely used to control T. urticae in greenhouse crops in Central Europe, will be able to halt any spread of T. evansi to greenhouse crops in temperate areas.

Effects of Temperature on Population Growth and Reproduction of Two Strains of &lt;i&gt;Moina mongolica&lt;/i&gt; Daday (Cladocera: Moinidae)

本文报道两品系蒙古裸腹溞(Moina mongolica Daday)(晋南、内蒙)在5种温度梯度下(15℃、18℃、25℃、28℃、32℃)的种群内禀增长率(r_m)、总生殖量、寿命、产幼间隔期、生殖频率和产幼前发育期,以及在28℃条件下两品系生物学的研究结果.结果表明,温度对两品系蒙古裸腹潘的种群繁殖均具有显著的影响.在试验温度范围内,随着温度升高,两品系蒙古裸腹潘的产幼前发育期、产幼间隔期、寿命随之缩短;而内禀增长率、总生殖量、生殖频率随温度升高而先升后降.温度28℃是两品系蒙古裸腹溞种群增长的最适温度,28-32℃是其种群增长的最适温度范围.晋南品系10组个体重复试验的内禀增长率结果仍高于内蒙品系.经比较可知:在相同温度条件下,晋南品系在种群增长能力方面要明显强于内蒙品系,反映在前者的内禀增长率要大于后者.在相对较高或较低的温度条件下,内蒙品系则表现出更强的耐受能力.;The intrinsic rate of increases(r_m), fecundity, longevity, reproduction interval, brood numbers and pre-reproduction period of two strains of Moina mongolica (Jinnan and Neimeng) were studied under 15℃,18℃,25℃, 28℃ and 32℃.Relevant population characters of two strains of M.mongolica at 28℃ were also studied.The results indicated that temperature is very importance to the reproduction of two both strains.The pre-reproduction period, reproduction interval, longevity decreased with increasing temperature in this experiment, also r_m, fecundity and brood numbers increased with temperature from 18℃-28℃, while decreased with temperature > 28℃.The optimum temperature for population growth of two strains was 28℃ and the range of suitable temperature for population growth was 28 to 32℃.The intrinsic rate of increases of Jinnan strain was higher than those of Neimeng strain, even if the experimental temperature reached 28℃, From the comparison of the resultant data, we are of the opinion that the population growth capacity of Jinnan strain is higher than that of the Neimeng strain, whereas Neimeng strain has stronger thermal adaptability.

Dynamics of regional coexistence for more or less equal competitors

Summary Competition between two species in a metapopulation involves each inhibiting the other's ability firstly to colonize an already occupied area and then to persist in it. Models for regional competition of this kind have 3‐D dynamics, from which it has proved difficult to extract useful predictions except for special conditions. We introduce a 2‐D general model for species that are equally vigorous at inhibiting the ability of others to remain in an occupied patch as to arrive there. The model covers the full spectrum of competitive interactions, from weak to strong and symmetrical to asymmetrical. Its Lotka–Volterra dynamics extend the general theory of competitive coexistence by generating clear predictions for community structure, amenable to cross‐system comparisons and experimental manipulations. Previous 2‐D models of interactions between dominant and fugitive species are special cases of the 2‐D general model. Moderately asymmetrical competition has two outcomes distinctly different from dominant–fugitive interactions, at both the scale of metapopulation and population: (i) slow growing and weak competitors coexist with faster growing superior competitors, albeit at reduced densities; and (b) habitat removal always yields relative gains in abundance for species with higher growth capacity, but the gains are absolute only for species subjected to competitive impacts that exceed within‐species impacts. Extinctions of slow growing and weak competitors provide the most sensitive indication of habitat degradation, and their losses also have the least effect on community structure. The 2‐D general model further predicts that highly productive communities will tolerate differences between species in their capacity for population growth, whereas less productive communities will tolerate stronger competitive interactions between species. This prediction applies equally to a population of resource consumers as to a metapopulation of colonists. The model explicitly links local and regional population dynamics to r–K selection in community structure by predicting a prevalence of growth‐orientated species in resource‐poor habitats and competition‐orientated species in resource‐rich habitats.

The influence of host dynamics on the clonal composition of Escherichia coli populations.

Species, be they plant or animal, vary in their capacity for population growth or decline. Populations of the same species may also differ in their capacity for population change. A series of mathematical models were developed with the aim of determining if host population dynamics could influence the clonal composition of the Escherichia coli community in that host population. The biological assumptions underlying the models are described in some detail. Analytical and numerical approaches were used to investigate the behaviour of these models. The results demonstrate that host dynamics can have a profound influence on the E. coli clonal composition of the host population. This outcome is largely independent of the nature of the assumptions underlying the models. The ways in which the predictions of these models may be tested empirically are discussed, as are the implications of these models for understanding the nature of host-bacterial pathogen dynamics.