The population biology of the Orange Tip butterfly Anthocharis cardamines in Britain

ABSTRACT.

• 1 The population biology of Anthocharis cardamines (L.) is described and shown to vary with locality. Southern and Western populations emerge earlier than Northern ones, but Western and Northern populations occupy similar, wetter habitats and are associated primarily with Cardamine pratensis (L.). Southern populations are recorded mostly from Alliaria petiolata (Bieb.).
• 2 Studies on egg and larval survival indicate that host plant-induced death and parasitization by a tachinid are important mortality factors. However, a key-factor analysis on one population indicates that the major determinant of population size may be the number of eggs laid by ovipositing females, itself dependent upon weather during the oviposition period. Populations in different localities do show similar trends in abundance, corroborating the effect of weather.
• 3 Human effects on distribution and abundance are discussed, and some conservation strategies suggested.

     

Population dynamics of Arashiyama west Japanese macaques

Demographic data have been collected on the Arashiyama Japanese macaque population from 1954 until the present, through the fissioning of the original group into two parts in 1966, and through the translocation of one of the two groups to Texas in 1972. Population dynamics are reported for the Arashiyama West group in Texas during 1972 to 1979 and then compared to data from Japan. After a short period of adjustment for the translocated group, during which time natality rates were relatively low and mortality rates were relatively high, many aspects of population structure, birth rates, and survivorship showed trends similar to those observed in Japan. This suggests that both long-term homeostatic processes and shorter-term responses to environmental fluctuations are significant to the study of nonhuman primate demography.     

Large-scale manipulation of mayfly recruitment affects population size

Recruitment establishes the initial size of populations and may influence subsequent population dynamics. Although strong inference can be made from empirical relationships between recruitment and population sizes, a definitive test of recruitment limitation requires manipulating recruitment at relevant spatial and temporal scales. We manipulated oviposition of the mayfly Baetis bicaudatus in multiple streams and measured the abundance of late-stage larvae at the end of the cohort. Based on fundamental knowledge of mayfly behavior, we increased, eliminated, or left unmodified preferred mayfly oviposition sites in 45-m reaches of streams (N = 4) of one high-altitude drainage basin in western Colorado, USA. We compared egg densities before (2001) and after the manipulation (2002) using paired t tests and compared larval densities before and after the manipulation among treatments using repeated measures analysis of variance. This manipulation altered not only egg densities, but also larval abundances 1 year later. Compared to the previous year, we experimentally increased egg densities at the addition sites by approximately fourfold, reduced egg densities to zero in the subtraction sites, and maintained egg densities in the control sites. After the manipulation, larval densities increased significantly by a factor of approximately 2.0 in the addition sites and decreased by a factor of approximately 2.5 in the subtraction sites. This outcome demonstrates that dramatic changes in recruitment can limit larval population size at the scale of a stream reach, potentially masking previously observed post-recruitment processes explaining the patterns of variation in abundance of a stream insect. Furthermore, our results emphasize the importance of preferred oviposition habitats to population sizes of organisms.     

Preference–performance linkage in the neotropical spittlebug Deois flavopicta, and its relation to the Phylogenetic Constraints Hypothesis

1. Predictions from the Phylogenetic Constraints Hypothesis were tested for the first time in a tropical system using the pasture pest Deois flavopicta Stal, which oviposits into the ground and not into plant tissues. The prediction that there is no oviposition preference–larval performance linkage was supported. The absence of such a link provides an evolutionary basis for eruptive population dynamics. 2. The effects of host species and host plant quality on the preference of ovipositing females of D. flavopicta and performance of their offspring on the selected host plants were tested at the population level. 3. Female oviposition behaviour was affected by the presence of the host plant. Females of D. flavopicta showed a strong preference to oviposit close to host plants. The number of eggs was higher in pots containing Brachiaria ruziziensis (121.88 ± 13.70) than in pots containing only the wet oviposition substrate (5.2 ± 1.98) or dry oviposition substrate (0.067 ± 0.067). Ovipositing females did not, however, discriminate between plants of Brachiaria decumbens and Axonopus marginatus and did not show a strong oviposition preference in relation to differences in plant quality (protein and fibre content). They did show oviposition preference for plants under the high watering regime. The mean number of eggs collected from pots with non water‐stressed plants was 60% higher than the mean number of eggs collected on pots with water‐stressed plants. 4. Although females did not show ovipositional preference, spittlebug larval performance, measured as percentage survival and duration of nymphal period, was better on plants of high protein and low fibre content. These results indicate that there is not a linkage between female oviposition preference and subsequent nymphal performance in relation to differences in protein and fibre content in the host plants. There was, however, a limited linkage between oviposition preference and nymphal performance in relation to plant water content. Females showed preference for moist sites that have high survival of newly hatched nymphs. 5. Evidence indicates that for D. flavopicta, the influences of natality and female oviposition behaviour in response to plant quality are not the major factors driving population outbreaks, which is in accordance with the Phylogenetic Constraints Hypothesis.     

Larval performance in relation to oviposition site preference in olive kernel moth (Prays oleae Bern., Yponomeutidae,Praydina)

1 The tri‐voltine moth Prays oleae Bern. spends its larval stages on the native olive tree (Olea europaea L. var. sylvestris Brot. and five cultivars, Oleaceae) mining the leaves, the flowers and the fruits in each generation; it seldom switches to other native or introduced confamilial plant species. 2 In this study the pattern of oviposition of the olive moth was examined in olive fields and natural vegetation, in relation to in situ recruitment as an outcome of processes such as density dependence or risk spreading. 3 Larval body size (width of epicranial sclerites) was also examined and compared between host substrates, years and morphological, physiological, ecological and nutritional attributes of the host. 4 The factors influencing the oviposition pattern of the olive moth such as the carbon/nitrogen ratio, number of flowers, branch length and previous leaf damage were ranked differently in different cultivars. 5 ‘Hot spots’, i.e. olive trees or parts of trees receiving a high egg load, were found to be the result of in situ recruitment. 6 Physiological mortality among first instar larvae was significantly negatively correlated with the number of oviposited upon leaves; suggesting that the adult selects for oviposition the best available substrate. 7 As adult moths selected leaves with minimal probability of abscission for oviposition, leaf abscission was not a major mortality factor, although first instar larvae reduced leaf longevity. 8 Host quality did not affect all larval stages in the same way. 9 The more nutritionally poor the substrate, the longer the duration of the larval stage feeding on it. The phenological timing of the insect life stages very closely tracks the phenological phases of its host plant, primarily focusing on the most nutritious host stage in terms of larval performance.     

Stochastic dynamic population model for northern corn rootworm (Coleoptera: Chrysomelidae).

A stochastic dynamic population model for the complete life cycle of northern corn rootworm, Diabrotica barberi Smith & Lawrence, is described. Adult population dynamics from emergence to oviposition are based on a published single-season model for which temperature-dependent development and age-dependent advancement determine adult population dynamics and oviposition. Randomly generated daily temperatures make this model component stochastic. Stochastic hatch is 50+/-8%. A stochastic nonlinear density-dependent larval survival model is estimated using field data from artificial infestation experiments. A regional model of corn phenology is estimated to incorporate the effect of dispersal on adult mortality. Random daily weather is generated using parameters for Brookings, SD. Model performance is evaluated with deterministic simulations, which show that the population converges to zero unless adult mortality is reduced by the availability of corn pollen from the regional model of corn phenology. Stochastic model performance is evaluated with stochastic daily weather, egg hatch, and larval survival in various combinations. Sensitivity analysis is conducted to evaluate model responsiveness to each parameter. Model results are generally consistent with published data.     

Oxycephalomyia, gen. nov., and life history strategy of O. styraci comb. nov. (Diptera: Cecidomyiidae) on Styrax japonicus (Styracaceae)

A new genus Oxycephalomyia is described to contain the gall midge that was previously known as Asteralobia styraci (Shinji). Oxycephalomyia styraci, comb. nov., produces leaf vein galls on Styrax japonicus (Styracaceae). The adult of O. styraci is redescribed, and its full‐grown larva and pupa are described for the first time. The annual life cycle of the gall midge in northern Kyushu was clarified; the first instars overwinter in the galls on the host plant. However, the galls of O. styraci mature much later in the season than those of other gall midges with a similar life history pattern, and the durations of second and third larval instars are remarkably short. Such a life history pattern is considered to have an adaptive significance in avoiding larval parasitism, particularly by early attackers. The number of host axillary buds as oviposition sites decreased in bearing years and increased in off years, but there was no sign of oviposition site shortage even in bearing years, probably due to the low population density of the gall midge. An unidentified lepidopteran that feeds on galled and ungalled host buds and a Torymus sp. that attacks pupae of O. styraci were recognized as mortality factors of the gall midge.     

Demography of Amboseli baboons, 1963–1983

Repeated censuses of a population of yellow baboons (Papio cynocephalus) in Amboseli National Park, Kenya, revealed a decrease from over 2,500 animals in 1963–1964 to 123 individuals in 1979, or from a density of about 73 to 1.8 baboons per km² over a 15-year period. Median group size decreased from 43 in 1964 to 27 in 1979. The largest and smallest groups declined the most; groups near the median have maintained fairly stable size and age distributions. The population seemed to have stabilized by 1983 at approximately 150 animals in six groups (median group size 28; density 2.2/km²). Although baboon population and group size appeared to be stable during 1963–1964, the age distribution and demographic parameters (age-specific mortality and natality for one social group) during that year indicate that the population decline had already started. The rate of population decline was greatest in the 1964–1969 period and remained appreciable during the next 5 years. The decline of the baboon population was paralleled by that of other Amboseli savannah woodland mammalian species and took place during a period of very high mortality of fever trees (Acacia xanthophloea) and extensive invasion of the area by halophytes, a transition brought on by rising ground water and consequent elevation of the soil salinity zone. In this and several other primate populations, mortality of infants and juveniles appears to be the demographic variable most sensitive to environmental change.     

The dynamics of laboratory populations ofCallosobruchus chinensis andC. Maculatus (Coleoptera: Bruchidae) in patchy environments

Experiments are described showing the long-term dynamics of two species of bruchid beetles (Callosobruchus chinensis and C. maculatus) in arenas in which the resource of 50 black-eyed beans is divided between 5, 10 or 50 ‘patches’. Both species of adult beetles exhibit clumped distributions between patches. Within a patch there is a tendency for a density dependent reduction in (1) eggs laid per female, (2) the proportion of eggs hatching per bean (C. chinensis only) and (3) larval survival which is strongly overcompensating (particularly in C. maculatus). A discrete generation model is used as a framework to draw these results together and show how the different factors affecting natality and mortality can influence the population dynamics. Finally, the importance of the resource renewal interval in influencing the period of the population cycles is discussed.     

Life budgets for a population of Tipula sacra (Diptera; Tipulidae)

Abstract.

• 1 A population of Tipula sacra was studied intensively from 1969 to 1974 in a series of abandoned beaver ponds. Beavers recolonized the ponds from 1974 to 1976 and again in 1978.
• 2 The basic life-cycle is of 2 years duration, but cohort-splitting occurs in the autumn as a result of some larvae growing faster and completing the life-cycle in 1 year.
• 3 Some periods are more favourable for growth than others and the size of the fast-growing cohort varies from year to year. This insight allows some anomalies in the estimates of population size to be explained and life budgets have been produced for three year-classes.
• 4 The short-fall in realization of egg potential is massive, apparently due to heavy female mortality by predation and the prevention of oviposition by inclement weather.
• 5 Mortality rate is relatively low and constant from stage II larvae until pupation, but increases to adult emergence. There is a correlation between larval density and mortality rate.
• 6 Certain aspects of the life-history (e.g. high fecundity, variability in growth rate) appear to fit the species to life in a temporally unstable habitat.

     

Biology ofhyphantria cunea drury (lepidoptera : Arctiidae) in Japan. IX. population dynamics

Fluctuations in population density of Hyphantria cunea in Japan are characterized by a gradation-like pattern. Analysis of the life table data taken from two stations during eight successive generations showed that (1) mortality during egg and early larval stages was density-independent, (2) mortality during later larval stages was inversely density-dependent, and (3) mortality during prepupal and pupal stages was density-independent. Thus the overall mortality process from egg to adults eclosion was inversely density-dependent. The inverse density-dependence in mortality process during later larval instars was mainly attributed to the ‘escape’ (VOÛTE, 1946) of H. cunea populations from the predation pressure of polyphagous predators such as birds and Politses wasps. This inverse density-dependence was considered to be a cause of gradation-like fluctuation. Field collection of egg-masses showed that the mean number of eggs per egg-mass, which was believed to be a good representation of mean fecundity, varied from 425 to 1050 during 4 years. Density-dependent reduction in the mean number of eggs per egg-mass was demonstrated, and this reduction was a factor regulating the population density. Assuming fixed sex ratio and survival rate of adults, a preliminary population model was constructed. The number of eggs laid in the survey station could be predicted well by the model based on the number of eggs laid in the previous generation, in 9 out of 13 cases. An attempt to apply a model of the same type to mimic the fluctuation of abundance (peak number of larval colonies per tree) on road-side trees suggested another density-dependent process, that is, insecticide application by man. Discussion was also presented on the causes responsible for the turn of population trend from decreasing to increasing in the 1st generation of 1968.     

Mortality dynamics and population regulation in Bemisia tabaci

Natural mortality is an important determinant of the population dynamics of a species, and an understanding of mortality forces should aid in the development of better management strategies for insect pests. An in situ, observational method was used to construct cohort‐based life tables for Bemisia tabaci (Gennadius) Biotype B (Homoptera: Aleyrodidae) over 14 generations on cotton in central Arizona, USA, from 1997 to 1999. In descending order, median marginal rates of mortality were highest for predation, dislodgment, unknown causes, egg inviability, and parasitism. The highest mortality occurred during the 4th nymphal stadium, and the median rate of immature survival over 14 generations was 6.6%. Predation during the 4th nymphal stadium was the primary key factor. Irreplaceable mortality was highest for predation and dislodgment, with the absence of these mortality factors leading to the greatest increases in estimated net reproduction. There was little evidence of direct or delayed density‐dependence for any mortality factor. Wind, rainfall, and predator densities were associated with dislodgment, and rates of predation were related to densities of Geocoris spp., Orius tristicolor (White), Chrysoperla carnea s.l. Stephens, and Lygus hesperus Knight. Simulations suggest that immigration and emigration play important roles in site‐specific dynamics by explaining departures from observed population trajectories based solely on endogenous reproduction and mortality. By a direct measurement of these mortality factors and indirect evidence of adult movement, we conclude that efficient pest management may be best accomplished by fostering greater mortality during the 4th stadium, largely through a conservation of predators and by managing immigrating adult populations at their sources.     

The population dynamics of Notothenia rossii from South Georgia (Antarctica)

Summary The population dynamics of nearshore juvenile Notothenia rossii were studied at South Georgia during 1978 and 1979. Mortality of the population was calculated from length-class abundance of fish sampled by trammel nets, and the population size estimated using a mark and recapture technique. Instantaneous natural mortality in the nearshore population was high (M=0.78) although other author's estimate for the mortality in the offshore population was only 0.35. Therefore it is likely that no single estimate of mortality will apply to fish of all ages. The population density of juvenile N. rossii was about 11 g m^-2 nearshore. The size of the offshore population was estimated by calculating survival from the nearshore age classes. The data suggest that the population around South Georgia has been reduced by overfishing to about one tenth of its previous unexploited level. Yield could have been increased by fishing less intensively, and the population maintained at or near its initial level if recruitment remained constant.     

Oviposition in an eruptive moth species, Yponomeuta evonymellus, is insensitive to the population density experienced during the larval period

We studied if the population density experienced during larval development affects the reproductive schedule of Yponomeuta evonymellus L. (Lepidoptera, Yponomeutidae), a moth species characterized by outbreak population dynamics. More specifically, we predicted that reproduction would be delayed to facilitate emigration from sites with suboptimally high densities of conspecifics. We manipulated larval densities in the laboratory, as well as in those pupae collected from the extremes of natural densities. As the response, we also recorded the timing and sizes of egg clutches laid. The results did not support our initial predictions: the timing of oviposition was not dependent on larval growth conditions. This apparent lack of adaptation might be related to the loss of ‘memory’ during metamorphosis in holometabolous insects. However, oviposition schedules were also only minimally sensitive to elevated adult density. An inability to respond to high larval densities may contribute to the outbreak dynamics in this species.     

Butterfly oviposition preference is not related to larval performance on a polyploid herb

The preference–performance hypothesis predicts that female insects maximize their fitness by utilizing host plants which are associated with high larval performance. Still, studies with several insect species have failed to find a positive correlation between oviposition preference and larval performance. In the present study, we experimentally investigated the relationship between oviposition preferences and larval performance in the butterfly Anthocharis cardamines. Preferences were assessed using both cage experiments and field data on the proportion of host plant individuals utilized in natural populations. Larval performance was experimentally investigated using larvae descending from 419 oviposition events by 21 females on plants from 51 populations of two ploidy types of the perennial herb Cardamine pratensis. Neither ploidy type nor population identity influenced egg survival or larval development, but increased plant inflorescence size resulted in a larger final larval size. There was no correlation between female oviposition preference and egg survival or larval development under controlled conditions. Moreover, variation in larval performance among populations under controlled conditions was not correlated with the proportion of host plants utilized in the field. Lastly, first instar larvae added to plants rejected for oviposition by butterfly females during the preference experiment performed equally well as larvae growing on plants chosen for oviposition. The lack of a correlation between larval performance and oviposition preference for A. cardamines under both experimental and natural settings suggests that female host choice does not maximize the fitness of the individual offspring.     

The influence of leaf age on the oviposition preference of Chrysophtharta bimaculata (Olivier) and the establishment of neonates

1 The degree of discrimination shown by a herbivore when selecting oviposition sites has been suggested as a key factor to understanding herbivore population dynamics. Chrysophtharta bimaculata (Coleoptera: Chrysomelidae) is a primary pest of Tasmanian eucalypt forests and can cause severe defoliation. Previous work suggests that females show discrimination when selecting oviposition sites. Our aim was to test the degree of oviposition discrimination exhibited by C. bimaculata with regards to leaf toughness, a character that is critical to neonate survival. 2 We conducted an experiment examining the leaf toughness critical for neonate survival and found that significant larval mortality occurs above a toughness of 46.9 g. We also determined that the maximum toughness of leaves upon which larvae established in the field was 48.2 g, supporting the laboratory result. 3 Field surveys showed that although the majority of eggs were laid on leaves suitable for larval establishment, many eggs were laid on unsuitable, tougher leaves. However, all eggs were normally placed within 20 cm of suitable leaves and glasshouse trials demonstrated the neonates could move this distance without mortality occurring. 4 We conclude that egg batch distribution and larval performance of C. bimaculata will influence the population dynamics of C. bimaculata in two ways. Firstly, the availability of expanding/newly expanding leaves of eucalypt hosts will determine larval carrying capacity. Secondly, at a more localized level, the deposition of large numbers of egg batches on both suitable and unsuitable leaves followed by successful neonate migration increases the risk of resource depletion and poor larval development.     

Predator effects on prey population dynamics in open systems

Animal population dynamics in open systems are affected not only by agents of mortality and the influence of species interactions on behavior and life histories, but also by dispersal and recruitment. We used an extensive data set to compare natural loss rates of two mayfly species that co-occur in high-elevation streams varying in predation risk, and experience different abiotic conditions during larval development. Our goals were to generate hypotheses relating predation to variation in prey population dynamics and to evaluate alternative mechanisms to explain such variation. While neither loss rates nor abundance of the species that develops during snowmelt (Baetis bicaudatus) varied systematically with fish, loss rates of the species that develops during baseflow (Baetis B) were higher in streams containing brook trout than streams without fish; and surprisingly, larvae of this species were most abundant in trout streams. This counter-intuitive pattern could not be explained by a trophic cascade, because densities of intermediate predators (stoneflies) did not differ between fish and fishless streams and predation by trout on stoneflies was negligible. A statistical model estimated that higher recruitment and accelerated development enables Baetis B to maintain larger populations in trout streams despite higher mortality from predation. Experimental estimates suggested that predation by trout potentially accounts for natural losses of Baetis B, but not Baetis bicaudatus. Predation by stoneflies on Baetis is negligible in fish streams, but could make an important contribution to observed losses of both species in fishless streams. Non-predatory sources of loss were higher for B. bicaudatus in trout streams, and for Baetis B in fishless streams. We conclude that predation alone cannot explain variation in population dynamics of either species; and the relative importance of predation is species- and environment-specific compared to non-predatory losses, such as other agents of mortality and non-consumptive effects of predators. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Temperature-dependent reproduction of the spruce bark beetle Ips typographus,and analysis of the potential population growth

1. The spruce bark beetle Ips typographus (L.) is one of the most important forest pests in Central Europe, but despite this the effects of temperature on life history and population growth are largely unknown. This study examines the effects of temperature on reproduction and intrinsic demographic statistics. 2. Laboratory experiments on oviposition were carried out at six temperatures in the range 12–33 °C, using the so-called sandwich rearing technique for bark beetles. 3. A linear relationship between oviposition rates and temperatures in the range 15–25 °C was used to estimate the lower temperature threshold for oviposition as 11.4 °C. With a nonlinear model fitted to the data across the whole range of experimental temperatures, the lower and upper limiting temperatures and optimum temperature were found to be 7.9, 33.7, and 28.9 °C, respectively. A model for daily oviposition rate was fitted, which describes the pattern of oviposition over the entire oviposition period. 4. The analysis of life tables, combining developmental rates, reproduction, mortality, and sex ratio, suggests maximum population growth (r_m) at near 30 °C. 5. After generating a first brood, spruce bark beetles often re-emerge from the tree and produce other sister broods. The effects of temperature and number of sister broods on demography were evaluated using age-specific life-table analyses. It is hypothesized that sister broods play an important role in regions where I. typographus is monovoltine, but have only moderate significance where this species has more than one generation per season.     

Use of prey and non-prey food by the ladybird beetle Eriopis connexa (Coleoptera: Coccinellidae) under laboratory-rearing conditions

Prey for predators can fluctuate in abundance and in quality over time requiring predator strategies to cope with food shortage. Coccinellinae are often associated with sap-sucking pests that exhibit high population unpredictability such as aphids and psyllids. Eriopis connexa (Germar) (Coleoptera: Coccinellidae) is a predator with potential for biological control, especially a well-studied population which is resistant to pyrethroids used to control insect defoliators. Both larvae and adult E. connexa were provided ad libitum prey and non-prey foods (pollen and honey water solution) at increasing intervals from 1 to 10 days. Neonate larvae of E. connexa required eating prey daily to develop into adults. However, non-prey food such as honey water solution did prolong larval and adult survival but neither fulfilled larval development nor adult reproduction. Honey water solution promoted 100% adult survival up to 25 days in the adult stage without prey with oviposition returning after daily feeding on prey. Females subjected to increased feeding intervals over four days reduced oviposition and lived longer, but 10-day feeding intervals correlated with risk to adult survival. These results indicate the importance of non-food sources in E. connexa maintenance and the ability of larvae and adult females to compensate for prey scarcity.     

The effect of a predatory leech,Nephelopsis obscura,on mortality,growth, and production of chironomid larvae in a small pond

Summary The effect of a predatory leech, Nephelopsis obscura, on survivorship, growth, and production of chronomid larvae was studied by enclosure experiments carried out in a small pond. The prey population was composed almost entirely of the tubiculous, microphagous chironomid larvae, Chironomus riparius and Glyptotendipes paripes. Nephelopsis significantly reduced chironomid survivorship within the enclosures, and accounted for most of the measured mortality of fourth instar larvae. The cropping by Nephelopsis was not significantly biased toward either prey species. In long-term experiments (66 d) chironomid biomass in enclosures without leeches reached much higher levels than in enclosures containing Nephelopsis. This increase in biomass was due to growth of surviving larvae, rather than recruitment, since emergence and oviposition were not going on during the course of the experiments. The enhanced survivorship of larvae within leech-free enclosures was eventually accompanied by reduced growth and specific production (daily production/biomass) for C. riparius, which made up about 90% of the larval population. Growth and specific production of G. paripes (10% of larval population) was not affected. Short-term experiments (25 d) involving manipulation of densities and species ratio (9:1 CR:GP and 1:9 CR:GP) of larvae revealed that growth of the majority species was strongly influenced by larval density, whereas growth of the minority species was not. The same pattern was observed both in the presence and in the absence of Nephelopsis and was a result of differences in resource utilization between the two species. In the shortterm experiments, growth rates estimated for larvae exposed to leeches were significantly less than those for larvae in leech-free enclosures. This could be due either to size-biased consumption of larvae by Nephelopsis, or possibly a disturbance factor leading to reduced larval food intake and/or increased metabolic costs.