Using viable eggs to accurately determine the demographic and predation potential of Harmonia dimidiata (Coleoptera: Coccinellidae)

Life table parameters and predation rate of the coccinellid predator Harmonia dimidiata F. fed on Aphis gossypii Glover were determined at 25°C using the age‐stage, two‐sex life table. When the total number of eggs were included in our calculations, the intrinsic rate of increase (r), finite rate (λ), net reproductive rate (R₀) and mean generation time (T) for H. dimidiata were 0.1354/day, 1.1450/day, 280.8 offspring and 41.6 day, respectively. These values were significantly different, however, only when viable (=hatchable) H. dimidiata eggs were counted (0.0909/day, 1.0952/day, 67.6 offspring and 46.3 day, respectively). The values obtained using all eggs did not realistically reflect the effect of variable hatch rate and true population parameters of H. dimidiata. We therefore excluded unhatched eggs from our data and demonstrated mathematically that in future demographic studies, it should be a standard procedure to exclude all unhatched eggs when analysing hatch rates that vary with maternal age. A mathematical proof was derived in this study to substantiate this. To observe and quantify variations that occur in the predation rate due to the age and stage of the predator, the daily number of A. gossypii consumed by individual H. dimidiata was analysed using the age‐stage, two‐sex life table. The net predation rate of H. dimidiata on A. gossypii was 14 804 aphids. The transformation rate Q_p showed that the predator needs to consume an average of 219.1 aphids to produce one viable egg. The finite predation rate of H. dimidiata was 125.7 when only hatchable eggs were included in the analysis. Because the age‐stage, two‐sex life table takes both of the sexes and the variable predation rate occurring among stages into consideration, it becomes possible to use the population projection to quantify and time biological control procedures.     

Sooty Falcon Falco concolor reproduction and population dynamics on the islands in the Sea of Oman

Knowledge of demographic parameters affecting population dynamics is critical to the formulation of effective conservation strategies. Sooty Falcon Falco concolor is a little‐studied, Near‐threatened species; estimates of global population size and trend for this species are uncertain. They lay eggs during mid‐summer and sometimes nest in colonies. This unusual breeding ecology suggests that demographic parameters driving their population growth rate may differ from those of most other falcons. We studied Sooty Falcon reproduction at breeding aggregations on Fahal Island and the Daymaniyat islands in the Sea of Oman during 2007–2014, modelled population growth and identified important life history parameters using elasticity analysis. The mean (± se) clutch and brood size was 2.83 ± 0.06 and 2.11 ± 0.07, respectively. Overall, 11.7% of nests failed between the egg and nestling stages, and the failure rate differed significantly between Fahal and the Daymaniyats, and across years. The mean proportion of eggs that hatched annually was 0.66 ± 0.02, and broods were significantly smaller on the Daymaniyats than on Fahal. Falcons on Fahal Island had a higher rate of hatching, a higher rate of nests that produced at least one chick, and produced more chicks per nest than on the Daymaniyats. We suggest that Fahal's proximity to the mainland gives breeding Sooty Falcons access to a more plentiful and stable source of food, especially during the period between arrival from the wintering grounds and the onset of the autumn migration of prey birds, resulting in the better reproductive rates for falcons on Fahal Island, relative to those on the Daymaniyat Islands. The annual asymptotic population growth rate (λ) was 0.87 (95% confidence interval (CI) 0.75–0.99), suggesting a declining population, although Sooty Falcons enjoyed a slightly higher population growth rate on Fahal than on the Daymaniyats. Because our study population is on the edge of the breeding range and is isolated from other breeding areas, measures to improve reproductive success of Sooty Falcons breeding on the islands in the Sea of Oman could be important for conservation of Sooty Falcons in Oman.     

多食性瓢虫捕食5种蚜虫的统计学比较:实验室研究(英文)

通过食蚜瓢虫Propylea dissecta(Mulsant)的捕食统计学参数的比较,尝试回答瓢虫是如何克服食物基础季节性的变动问题。在实验室中饲养五世代的瓢虫从五种蚜虫(Rhopalosiphum maidis(Fitch),Aphis craccivora Kock,Aphis gossypii Glover,Uroleucon compositae(Theobald)和Lipaphis erysimi(Kalt))为食物来源获得营养。相对适合的猎物次序是A.gossypii,A.craccivora,R.maidis,U.compositae和L.erysimi。新生幼虫的死亡率最高,其次是卵。统计表明,净生殖率、内懔增长率和有限增长率为(407.18,0.2274天-1,1.2553天-1)最高的在A.gossypii和最低的(176.02,0.1533天-1,1.1657天-1)在L.erysimi,一个世代时间最短的26.43天是捕食A.gossypii;而最长的33.73天为捕食L.erysimi。本研究为P.dissecta捕食A.gossypii高发生提供一种解释,因为它经历了高内懔增长率和统计参数最佳值。     

COMPARATIVE DEMOGRAPHICS OF A GENERALIST PREDATORY LADYBIRD ON FIVE APHID PREY: A LABORATORY STUDY

Abstract  Prey driven demographic parameters of an aphidophagous ladybird, Propylea dissecta (Mulsant) were studied in attempt to answer how ladybird overcomes the problem of seasonally fluctuating food base. The ladybird reared for five generations in laboratory derived differential nutrition from five food sources ( i.e . aphid species, Rhopalosiphum maidis (Fitch), Aphis craccivora Koch, Aphis gossypii Glover, Uroleucon compositae (Theobald) and Lipaphis erysimi (Kalt.)). The order of relative prey suitability was A. gossypii, A. craccivora, R. maidis, U. compositae and L. erysimi . Neonates suffered maximum mortality followed by eggs. Estimates of net reproductive rate, intrinsic rate of increase and finite rate of increase were highest (407. 18, 0.2274 day^-1, 1.2553 day^-1) on A. gossypii and lowest (176.02, 0.1533 day^-1, 1.1657 day^-1) on L. erysirni . Generation time was shortest (26.43 days) on A. gossypii and longest (33.73 days) on L. erysirni . The present study thus, provides an explanation to the high incidence of P. dissecta on A. gossypii , as it experienced high intrinsic rate of increase and optimal values for related demographic parameters.     

Demographic study of two population outbreaks of Elasmoderus wagenknechti (Liebermann) (Orthoptera: Tristiridae) in the transitional desert of Chile

Under certain environmental conditions, several species of grasshoppers inhabiting rangeland areas (e.g., inter-valleys) of the Chilean transitional desert can irrupt demographically. One of them is Elasmoderus wagenknechti (Liebermann), an endemic species. We studied two outbreaks occurred in 1996 and 1999. The objectives of the research were to (i) estimate some demographic parameters associated with the aforementioned events, and (ii) compare between them the population parameters. The parameters we studied were density (ind/m(2)), sexual proportion, female fertility (i.e., eggs/female), and the relationship eggs/female versus female size. Density (ind/m(2)) ranged from 0.2 to 0.4 in 1996 and from 0.5 to 0.6 in 1999. ANOVA-tests registered differences in density among study sites and between years. In some of the study sites, females were more abundant than males (e.g., Lomas del Sauce). Females fertility ranged from 27 to 39 eggs per female, with significant differences among sites in 1996 but not in 1999. For females of 30-50 mm body size, a linear relationship was detected between egg number/female and body size. It is concluded that the E. wagenknechti outbreaks are site-specific in the study area and that the demographic parameters examined show a high variability among sites and between events.     

Population dynamics in a Danish metapopulation of spadefoot toads Pelobates fuscus

If an amphibian species has a high degree of site fidelity to its natal pond, subpopulations do not mix, and this may have implications: the subpopulations may get different because of genetic drift, and their status may be affected due to stochastic events. During a four-year period (1994–1997), demographic parameters of a Danish metapopulation consisting of ca 1000 adult Pelobates fuscus in five subpopulations were investigated with the aim of quantifying exchange of individuals in subpopulations and potential differences in demographic parameters, and to clarify population regulating mechanisms. This was done through the use of drift fences surrounding the five breeding ponds, individual marking (PIT-tagging) and weight recordings of the adult females. Metamorphs were recorded when leaving the pond. There was no significant differences between ponds in sex ratio, eggs laid per female, fraction of females breeding and survival of eggs to froglets and of adults. However, there was a significant difference in juvenile survival (52% in one pond and 31% in the others). Sex ratio was 1.70 males:1 female. Mean number of eggs laid per female in the pond was 1762. The number of eggs laid was age-specific, fecundity peaking at age five. Larval survival rate was density dependent: decreasing in an overcompensating fashion at high densities. Exchange rate between ponds was low; 1.09% of the marked and recaptured adult population was found to change pond during the study period. The low exchange rate was confirmed in a simple translocation experiment. This population shows features of a source-sink metapopulation where the identity of the source pond changes due to succession. It is presumably regulated either in the larval stage by density dependent mechanisms (in the subpopulations with many adults) or in the adult stage by density independent mechanisms (in the subpopulations with few adults).     

Jaatha: a fast composite-likelihood approach to estimate demographic parameters

While information about a species’ demography is interesting in its own right, it is an absolute necessity for certain types of population genetic analyses. The most widely used methods to infer a species’ demographic history do not take intralocus recombination or recent divergence into account, and some methods take several weeks to converge. Here, we present Jaatha, a new composite‐likelihood method that does incorporate recent divergence and is also applicable when intralocus recombination rates are high. This new method estimates four demographic parameters. The accuracy of Jaatha is comparable to that of other currently available methods, although it is superior under certain conditions, especially when divergence is very recent. As a proof of concept, we apply this new method to estimate demographic parameters for two closely related wild tomato species, Solanum chilense and S. peruvianum. Our results indicate that these species likely diverged 1.44·N generations ago, where N is the effective population size of S. chilense, and that some introgression between these species continued after the divergence process initiated. Furthermore, S. peruvianum likely experienced a population expansion following speciation.     

On Ewens'' equivalence theorem for ascertainment sampling schemes

The usual likelihood formulations for segregation analysis of a genetic trait ignore both the at-risk but unobservable families and the demographic structure of the surrounding population. Families are not ascertained if, by chance, they have no affected members or if the affected members are not ascertained. Ewens has shown that likelihoods which take into explicit account both unobservable families and demographic parameters lead to the same maximum likelihood estimates of segregation and ascertainment parameters as the usual likelihoods. This paper provides an alternative proof of Ewens' theorem based on the Poisson distribution and simple continuous optimization techniques.     

Comparing epidemic tuberculosis in demographically distinct heterogeneous populations

There is wide variation in endemic tuberculosis (TB) levels between countries and we seek to identify possible causes of these differences. In this study we present an epidemiological model of Mycobacterium tuberculosis infection to investigate the effects of host genetics and demographic factors on epidemic TB. We discuss the general framework for this approach and present analytical results to identify important parameters affecting steady-state prevalence and incidence rates of TB disease. We then use numerical simulations of our model to observe the effects of a genetically susceptible subpopulation on TB disease dynamics at the population level. Finally, we simulate infection within a genetically heterogeneous population in two demographic settings: India (a typical population with high TB prevalence) and the USA (a typical population with low TB prevalence). Results show that changes in transmission parameters, the fraction of the population genetically susceptible to infection, and demographic factors strongly affect TB prevalence and incidence rates.     

Demography of a population of Moina micrura kurz (Crustacea: Cladocera) in a temporary pond,peninsula of paraguaná, Venezuela

A population of M. micrura Kurz from a shallow, muddy and temporary pond, located in Peninsula of Paraguaná, western Venezuela, was studied from filling to drying phase. Population density, age structure, fecundity, and length of females, were determined. This population showed a low population density (< 50 ind/1), a low and density-dependent fecundity (mean eggs/adults = 1.3; mean clutch size = 2.1 eggs + embryos), and low juveniles to adults ratio (0.71). No significant correlation was detected between mean clutch size and mean body length of ovigerous females. Our results suggest effects of food limitations, and fish predation on demographic parameters of this population. Still, in unfavourable conditions, some demographics features associated to opportunistic species were evident.     

Demographic consequences of nestbox use for Red‐footed Falcons Falco vespertinus in Central Asia

Nestbox programmes are frequently implemented for the conservation of cavity‐nesting birds, but their effectiveness is rarely evaluated in comparison with birds not using nestboxes. In the European Palaearctic, Red‐footed Falcon Falco vespertinus populations are both of high conservation concern and are strongly associated with nestbox programmes in heavily managed landscapes. We used a 21‐year monitoring dataset collected on 753 nesting attempts by Red‐footed Falcons in unmanaged natural or semi‐natural habitats to provide basic information on this poorly known species; to evaluate long‐term demographic trends within this population; and to evaluate response of demographic parameters of Red‐footed Falcons to environmental factors including use of nestboxes. We observed significant differences among years in laying date, offspring loss and numbers of fledglings produced, but not in egg production. Of these four parameters, offspring loss and, to a lesser extent, number of fledglings exhibited directional trends over time. Variation in laying date and in numbers of eggs were not well explained by any one model of environmental factors, but instead by combinations of models, each with informative terms for nest type. Nevertheless, laying in nestboxes occurred 2.10 ± 0.70 days earlier than in natural nests. In contrast, variation in both offspring loss and numbers of fledglings produced were fairly well explained by a single model including terms for nest type, nest location and an interaction between the two parameters (65 and 81% model weights, respectively), with highest offspring loss in nestboxes on forest edges. Because, for other species, earlier laying dates are associated with more fit individuals, this interaction highlighted a possible ecological trap, whereby birds using nestboxes on forest edges lay eggs earlier but suffer greater offspring loss and produce lower numbers of fledglings than do those in other nesting settings. If nestboxes increase offspring loss for Red‐footed Falcons in heavily managed landscapes where populations are at greater risk, or for the many other species of rare or endangered birds supported by nestbox programmes, these processes could have important demographic and conservation consequences.     

Progeny quality of Gonatocerus ashmeadi (Hymenoptera: Mymaridae) reared on stored eggs of Homalodisca coagulata (Hemiptera: Cicadellidae)

This study assessed the effects of refrigerated storage on the suitability of eggs of the glassy-winged sharpshooter, Homalodisca coagulata (Say) (Hemiptera: Cicadellidae), as hosts for propagation of the parasitoid Gonatocerus ashmeadi Girault (Hymenoptera: Mymaridae). Development of the host eggs was terminated by chilling at 2 degrees C for 5 d before storage was initiated at 10 degresC for up to 70 d. Parasitism, adult emergence rate, developmental time, and sex ratio were used to gauge the suitability of the eggs as hosts after storage. In addition to these measures, demographic growth parameters also were used to assess the quality of the wasp progeny through the F2 generation. Host eggs stored 20 d remained fully acceptable to the wasps for attack. Although the parasitism rate decreased with storage time, > 80% adult parasitoid emergence was realized from eggs stored 30 d. After 70 d storage, adult emergence rate was decreased by 48%, fecundity decreased by 53%, female production by 19%, developmental time was extended 3 d, and female longevity was shortened 5 d. The emergence pattern of F1 but not F2 adults varied with storage time of the parental and grandparental hosts, respectively. For the F1 generation, emergence rate, development, and sex ratio did not vary with storage time when the F1 parents parasitized fresh host eggs. Demographic parameters for the F, population showed that net reproductive rate was > 20 although it decreased significantly after their parental host eggs were stored for > 30 d. The intrinsic and finite rates of increase, population doubling time, and mean generation time decreased only after storage for 60 d. Our results show that short-term cold storage could be used for maintaining wasp populations in a mass-rearing program and that the detrimental effects of chilling host eggs in storage for over 30 d do not extend to F2 generation.     

Derivatives of the stochastic growth rate

We consider stochastic matrix models for population driven by random environments which form a Markov chain. The top Lyapunov exponent a, which describes the long-term growth rate, depends smoothly on the demographic parameters (represented as matrix entries) and on the parameters that define the stochastic matrix of the driving Markov chain. The derivatives of a-the “stochastic elasticities”-with respect to changes in the demographic parameters were derived by Tuljapurkar (1990). These results are here extended to a formula for the derivatives with respect to changes in the Markov chain driving the environments. We supplement these formulas with rigorous bounds on computational estimation errors, and with rigorous derivations of both the new and old formulas.     

Reproductive Declines in an Endangered Seabird: Cause for Concern or Signs of Conservation Success?

Collection and analysis of demographic data play a critical role in monitoring and management of endangered taxa. I analyzed long-term clutch size and fledgling productivity data for California least tern (Sternula antillarum browni), a federally endangered subspecies that has recently become a candidate for down-listing. While the breeding population grew from approximately 1,253 to 7,241 pairs (578%) during the study period (1988–2009) both clutch size and fledgling productivity declined. Clutch size decreased by approximately 0.27 eggs (14%) from 1990–2004 then showed a moderate increase of 0.11 eggs from 2004–2009. Estimates of fledgling productivity showed a similar pattern of decline and moderate increase even after controlling for clutch size. Sea surface temperature anomalies, an index of El Niño-Southern Oscillation activity, did not influence clutch size but were associated with fledgling productivity through a non-linear relationship. Both clutch size and fledgling productivity increased with latitude, potentially indicating a gradient of life-history trade-offs. Random site effects explained little of the overall variation in clutch size (3%) or fledgling productivity (<1%) suggesting that site characteristics beyond those associated with latitude had little bearing on either measure of reproduction. Despite intensive monitoring and management, causes of variation in key demographic parameters remain poorly understood. Long-term declines in clutch size and fledgling productivity may reflect: 1) reduced food availability, 2) increased density-dependent competition, and/or 3) age-dependent reproduction coupled with a shifting population age-structure. Until the mechanisms shaping demographic parameters and population change are better understood, the success of past management and the probability of ongoing recovery will remain difficult to characterize.     

Quantifying telemetry collar bias when age is unknown: A simulation study with a long-lived ungulate

Radiotelemetry collars are frequently used to estimate demographic parameters of animals, such as annual survival and parturition rates. If animals are collared for multiple years and statistical adjustments are not made, these estimates can be biased by an unrepresentative age structure and individual variability of collared animals. To quantify the effects of different factors on the magnitude of these potential biases, we created a computer simulation of the female portion of a barren-ground caribou (Rangifer tarandus granti) herd and then randomly assigned collars to individuals within the simulated population. Under our default model, based on the Western Arctic Herd monitoring program, caribou were collared randomly from all females aged 2 years and over, and they remained collared for a mean of 7 years. Our simulations revealed that survival rates were underestimated by approximately 3.4% and parturition rates were overestimated by approximately 3.3%. The magnitude of these biases increased when individuals remained collared for longer periods. Increased individual variability in the population resulted in only small increases in survival and parturition rates. Because the magnitude of the bias increased steadily during the first years of the study, we found a substantial risk of incorrectly identifying a significant decline in survival in the first 7 years after marking. Including the number of years individual animals have been collared as a covariate in analyses can reduce the biases in demographic parameters and should be considered for inclusion in analyses when animal age is unknown. Actual survival rate estimates from telemetry data for the Western Arctic Herd were generally consistent with the results of these simulations. These potential biases should be considered when interpreting demographic parameters from multi-year collaring studies. © 2012 The Wildlife Society.     

The role of breeding system in community dynamics: Growth and mortality in forests of different successional stages

Plant sexual systems appear to play an important role in community assembly: Dioecious species are found to tend to have a higher propensity to colonize communities in early successional stages. Here, we test two demographic hypotheses to explain this pattern in temperate forests. First, we test demographic differences between hermaphrodite and dioecious species in stressful younger successional stages: Previous theory predicts that hermaphrodite seed production is more harmed in stressful environments than that of dioecious populations leading to an advantage for females of dioecious species. Second, in primary forest, we hypothesized that dioecious species would show demographic advantage over monomorphic ones. We used data from two temperate forest plots in Northeast China surveyed over 10 years to compare the rates of growth and mortality of tree species with contrasting breeding systems in both secondary and primary forests. We assessed the effect of breeding system on the growth‐mortality trade‐off, while controlling for other traits usually considered as correlates of growth and mortality rates. We show that in the secondary forest, dioecious species showed weak advantage in demographic rates compared with monomorphic species; dioecious species showed considerably both lower relative growth and mortality rates compared to the hermaphrodites in the primary forest over 10 years, consistent with a priori predictions. Hermaphrodites showed strong growth‐mortality trade‐offs across forest stages, even when possibly confounding factors had been accounted for. These results suggest that sexual system influences community succession and assembly by acting on the rates of growth and mortality, and the trade‐off between them. As vegetation develops, the demographic differences between breeding systems are much larger. Our results demonstrate the association between breeding system, succession, and community assembly and that this relationship is succession‐stage dependent. Our findings support the suggestion that the demographic advantage of dioecious species facilitates the coexistence of sexual systems in primary forest.     

Relationship between female body size and demographic parameters inBactrocera Malaysian A (Diptera: Tephritidae)

The effect of body size, as measured by the head width, of the female Bactrocera sp. Malaysian A (kept separately in sexual pairs) on the demographic parameters was investigated in the laboratory under ambient conditions of 28–30°C, 78–85% RH and natural photoperiod. Body size was shown to influence significantly all the demographic parameters. The expectation of life of females at eclosion from pupae was respectively for head widths of 1.6, 1.8, 1.9, 2.0 and 2.1 mm: 76.2, 73.4, 73.8, 102.4 and 115.2 days. The mean number of eggs laid per female in its life time was respectively: 86.4±48.7, 181.8±56.1, 229.7±72.6, 364.3±69.4 and 477.5±109.3 which was significantly different from one another (F=3.73,P<0.05) especially the two smaller sizes from the two larger sizes. The regression line for total eggs laid (Y) against head width (X) was Y=785.2X−1208.7 (R²=0.35,P<0.001). The net reproductive rate (R₀) was respectively 15.8, 34.0, 43.5, 66.9 and 88.8 eggs, while the intrinsic rate of increase (r) was respectivley 0.0435, 0.0538, 0.0670, 0.0665 and 0.0711. The results confirm that for mass rearing purposes, larger females which produce more offspring are to be preferred.     

The paradox between the long-term decrease of egg mass size of the calanoid copepod Eurytemora affinis and its long-term constant abundance in a highly turbid estuary (Gironde estuary, France)

Eurytemora affinis egg mass size—a commonly used demographicparameter—was surveyed in the Gironde estuary. Its decreasebetween 1978 and 2003 contrasted with the stability of populationdensity during this long-term period. Different hypotheses weretested to explain this paradox. (i) Upstream shift of the population:Even though the population of E. affinis shifted upstream dueto a greater penetration of marine water, no relationship betweenthe population shift and demographic parameters was observed:the egg mass size exhibited the same evolution upstream. (ii)Water warming: No early egg production and no change of femalesize that could metabolically limit the egg mass size was observed.(iii) Food limitation: The change in food quality observed didnot result in any change in total copepod abundance. (iv) Fasterrenewal of egg masses: The paradox cannot be explained by thisfactor and the number of adults observed nowadays is higherthan the number of eggs produced by females, whereas fecundityrates strongly increased. The paradox is probably explainedby the expulsion of viable subitaneous eggs. This may representa recent behaviour adaptation of the copepod to environmentalchanges.     

Changes in the reproductive biology of Biomphalara glabrata infected with different doses of Echinostoma paraensei miracidia

The egg-laying rate, number of egg masses, number of eggs/mass, number of eggs hatched/snail and egg viability of Biomphalaria glabrata exposed to different doses (5 and 50) of Echinostoma paraensei miracidia were analyzed as indicators of reproductive activity. Polystyrene plates were placed in aquariums containing the snails and every other day for four weeks after infection the plates were removed to count the number of egg masses and eggs laid. After this, the plates were numbered individually and placed in new aquariums free of snails and the egg masses were observed daily to determine the hatching rate. On average there was an increase in the parameters evaluated in the infected snails in relation to the controls (uninfected snails), except for egg viability, which was significantly lower in the groups infected with 50 miracidia. These findings indicate that when infected, this host snail is able to increase its reproductive activity, suggesting an ecological strategy to maintain the species.