SEARCH · PubMed Health

Results for “population dynamics”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 883 records · Page 49Linked to original sources

PubMed1996

Effects of initial litter contamination level with Eimeria acervulina on population dynamics and production characteristics in broilers.

The present experiment was done to obtain experimental evidence supporting the existence of an optimal initial contamination level of Eimeria acervulina with respect to broiler productivity, as suggested by simulation model outcomes. Three levels of initial (on Day 3) contamination of the litter were applied (low, intermediate and high). The peak of oocyst excretion during the flock cycle (grow-out) (Days 0-36) depended on the initial contamination level. Oocysts peaked at Day 15, 22 and 33 for the high, intermediate and low contamination level, respectively. Antibody titres and plasma carotenoid contents were not significantly affected by contamination levels. Average body weight at the end of the flock cycle (Day 36) and average daily body weight gain were significantly higher at the intermediate contamination level compared with the low and high contamination levels. Average body weight at Day 36 was 1681 g, 1712 g and 1674 g for the low, intermediate and high contamination level, respectively. Average daily weight gain was 45.7 g, 46.5 g and 45.5 g for the low, intermediate and high contamination level, respectively. Thus, the data from this experiment support the existence of an optimum initial contamination level for E. acervulina with respect to performance results.

Animals↗

PubMed2006

Culex population dynamics and West Nile virus transmission in east-central Illinois.

Temporal changes in the abundance Culex restuans and Culex pipiens were monitored in east-central Illinois for over a decade using infusion-baited oviposition traps. The 2 species typically exhibited a seasonal shift in relative abundance with a mean crossover date (when the proportion of egg rafts from both species is equal) of August 10 or 11, depending on leap year, with a 95% confidence interval of +/- 10.7 days. The date of crossover was linearly related to the date of last spring frost and occurred on average about 123 days after the last spring frost. Despite the predictability of crossover, the weekly pattern in the proportion of Cx. pipiens before and after crossover varied considerably, even between years with similar crossover dates. After West Nile virus became established in our area, we found that transmission based on Culex from gravid traps did not increase until Cx. pipiens abundance increased in oviposition traps. Infection rates peaked within the half-month period after crossover. The peak in Cx. pipiens abundance in oviposition traps during this 3-year period was between the 2nd half of August and the end of September. A higher magnitude of transmission in 2002 coincided with warmer temperatures during July and August and an extended period in which the 2 Culex species were in relatively equal abundance.

Animals↗

PubMed2004

Prospective studies of Bartonella of rodents. Part I. Demographic and temporal patterns in population dynamics.

The temporal dynamics of Bartonella infections in a rodent community were described by repeatedly capturing and sampling individual animals. Among six rodent species, from which bartonellae were isolated, cotton rats (Sigmodon hispidus) accounted for > 98% of the bacteremic animals. All cotton rats captured four or more times were Bartonella-culture positive at least once. The lowest monthly prevalence of Bartonella in cotton rats was in June (49%) and the highest was in October (95%). Prevalence of Bartonella infection increased to > 90% among juvenile and subadult rats before declining to < 40% among the largest-oldest individuals. Bacteremia levels ranged between 40 and 4.0 x 10(6) colony forming units (CFU) per 1 mL of blood. Male cotton rats had significantly higher CFUs than females (p = 0.006). The median of Bartonella bacteremia decreased monotonically by age group among cotton rats. Although Bartonella infections were highly prevalent among cotton rats, only 8.5% of rats had reactive antibodies at titers of > or = 1:32 and none had antibodies titers of > 1:256.

Age Factors↗

PubMed2005

Population dynamics of banded thrips (Aeolothrips intermedius Bagnall, Thysanoptera, Aeolothripidae) and its potential prey Thysanoptera species on white clover.

In 2002, the occurrence of banded thrips (Aeolothrips intermedius Bagnall) and some other Thysanoptera species on white clover (Trifolium repens L.) was monitored at two locations in the continental part of Slovenia. White clover presents in many countries important intercrop in integrated vegetable production. Light blue sticky boards were placed on grasslands (one parcel on each location) with high percentage of white clover. Sticky boards were changed in about 10-days intervals from the end of April till the beginning of October. Number of caught individuals on the boards was counted. They were classified in three different groups: 1. Aeolothrips intermedius, 2. representatives of Haplothrips, Odontothrips and Frankliniella genera, 3. representatives of Thrips genus. We stated that, compared with the other Thysanoptera species in the open, predatory thrips occurs in lower number. Predatory species Aeolothrips intermedius was the most numerous during the flowering of white clover. It was established that other Thysanoptera species (the most of them are facultative phytophagous species) were more numerous also in the periods of less favourable weather conditions and during the non-flowering growing stages of white clover. Based on the results of present research we concluded that A. intermedius has a potential to control onion thrips (Thrips tabaci Lindeman), especially in July and August, when in the open both species occur in high numbers.

Animals↗

PubMed1995

Echinostoma macrorchis: life history, population dynamics of intramolluscan stages, and the first and second intermediate hosts.

Eggs of Echinostoma macrorchis were laid at the 1-cell stage and took 9 days (26-27 C) or 6 days (30 C) to hatch. The following accounts are based on studies undertaken at 24-26 C. Maximum survival of miracidia was 7 hr. Miracidia reached the ventricle of Gyraulus chinensis 15-20 hr after penetration and transformed into sporocysts. The earliest degeneration of sporocysts occurred 20 days postinfection (DPI), but some survived for 120 days. Mature mother rediac were first seen inside the sporocyst at 7 DPI, then were released to the ventricular cavity and migrated to other anatomical locations of the host. Among the germ balls present in a sporocyst, 1-3 developed concurrently to the mother redia stage. Young daughter rediae first appeared at 15 DPI and mature ones at 19 DPI. Snails of larger size produced more daughter rediae and cercariae than smaller ones. Initial shedding of cercariae from infected snails occurred between 25 and 48 DPI, with a mean of 34 DPI. The cercariae were phototactic and each snail shed a daily average of 34 cercariae. Gyraulus chinensis was proven to be the only snail capable of serving as the first intermediate host. Tadpoles of Rana latouchi and Bufo bufo, 9 species of gastropods, the bivalve Corbicula fluminea, and 1 unidentified planarian species served as experimental second intermediate hosts.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2002

Population dynamics of euglossinae bees (Hymenoptera, Apidae) in an early second-growth forest of Cajual Island, in the state of Maranhão, Brazil.

A study was conducted in an early second-growth forest aiming at knowing the richness, relative abundance, seasonal distribution, and hourly frequency of euglossine bees, and their association with scent baits. Male bees were attracted to cineole, vanillin, methyl salicylate, and eugenol. The baits were hooked 1.5 m high and 6 m from one another. The specimens were collected from December 1997 to November 1998, once a month, from 7:00 to 17:00 h. A total of 339 male euglossine bees were caught, accounting for 19 species and four genera. The most common species was E. cordata, making up 69.9% of the individuals, followed by E. truncata (2.3%), E. violaceifrons, and E. smaragdina (2.1%). The most attractive scent was cineole, which baited 87% of the specimens and 73.7% of the species. Vanillin, the second most visited bait, eured 7.6% of the specimens and 26.3% of the species. E. surinamensis was only collected with this bait. Methyl salicylate and eugenol baited combined 2.6% of the specimens. However, by species numbers Methyl salicylate attracted 21% whereas eugenol was attractive for 15.8% of them. In general, the species were more abundantly found in the rainy season (January-June). The hourly activity data showed that the euglossine bees were attracted to the baits all day long, but at a higher frequency in the morning period, peaking between 8:00 and 10:00 h.

Animals↗

PubMed1994

Population dynamics of anophelines in a malathion treated village in the intermediate zone of Sri Lanka.

As part of research programme on malaria transmission in Sri Lanka, a study was made of man-biting anophelines at Nikawehera, a village on the border of the intermediate and dry rainfall zones. Weekly mosquito collections by night human bait (NHB) were performed inside and outside four fixed stations from October 1992 till March 1993. Houses in the village were treated with malathion by the Anti-Malaria Campaign in October and at the end of January 1993. An. culicifacies and An. tesselatus were the most abundant species. An. culicifacies was probably the only species responsible for malaria transmission. An. culicifacies densities varied between stations and reflected differences in availability of breeding places. An. culicifacies aggressivity is closely related to the rainfall pattern, increasing after the first monsoon rains in November and reaching a peak in late December--early January. Vectorial capacity, however, decreased during the first weeks of the rainy season. The maximum vectorial capacity was found in January. The night biting cycle of An. culicifacies showed a peak between 20.00 and 23.00 h. Since the introduction of electricity in the village, people go to bed later. This might reduce the impact of impregnated bednets on malaria transmission. The results show that malathion spraying as performed now is not very effective. The timing of the spray rounds should be improved. In order to limit malaria transmission, we suggest to advance the malathion spraying campaign of January with one month.

Animals↗

PubMed2006

[Comparison of specific composition and mosquitoes population dynamics in two villages of the centre of Côte-d'Ivoire, with and without irrigated rice growing area].

Entomological surveys were undertaken between October 1994 and August 1995 and from April to August 1995 in the villages of Kafiné and Pékaha, respectively These villages are located in the centre of Côte-d'Ivoire in a humid savannah area in the prefecture of Niakaramandougou. Rice plots are located to about 500 meters from the first habitations of Kafiné. They also form an enclosure around the village causing a great culicidian nuisance. On the other hand in the village of Pékaha, situated at 8 km from the enclosure, one can find a non-developed low ground area with swamps according to the season which has caused the multiplication of anthropophilic Culicidae. Five genera of mosquito were caught in the two villages: Anopheles, Aedes, Culex, Mansonia and Uranotaenia. The genus Anopheles is by far the most predominant in Kafiné with 84.3% (n=17556). Mansonia, Culex and Aedes respectively constitute 12%, 3% and 0.01% of the total anthropophilic mosquitoes. In the contrary the genus Mansonia was the most predominant in Pékaha with 78.2% (n=6642). Anopheles, Aedes and Culex respectively represent 13.2%, 8.3% and 0.1% of the total number of mosquitoes caught during the surveys. If in the village of Kafiné, the culicidian nuisance is mainly due to anopheles mosquitoes (84.3%) and particularly to An. gambiae s.s. (70.6%), in the village of Pékaha, dwellers suffer more from Mansonia (78.2%) bites than those of Anopheles (13.2%).

Agriculture↗

PubMed1997

Population dynamics of the parasitic stages of Oesophagostomum dentatum in pigs in single and trickle infections.

A mathematical model was developed to describe the dynamics of the parasitic stages of Oesophagostomum dentatum in pigs. An immigration-death model with constant establishment, development and death rates was fitted to L3, L4 and adult worm burdens observed in a single-infection experiment. Female worm length was modelled by a function of worm age and total worm burden, while worm egg production (eggs per gram faeces per female worm) was modelled by a function of worm age and worm length. The model was then used to predict worm burdens observed in a trickle-infection experiment. The predicted worm burdens were much higher than those observed, suggesting that worm death rates were higher during the trickle infection. After increasing worm death rates to fit the observed worm burdens, female worm lengths and egg production in the trickle infection were predicted. At the medium- and high-dose rates, predicted worm lengths and, thus, egg production were lower than observed, while at the low-dose rate predicted egg production was too high. It appeared that in the trickle infections, total worm burden had less influence on observed female worm length and egg production than in the single infections. The results suggest that the demography of O. dentatum in pigs differs between single and trickle infections.

Animals↗

PubMed2005

A simple model of plankton population dynamics coupled with a LES of the surface mixed layer.

The concentration of phytoplankton in the sea is affected by biological processes, such as growth/mortality rates, predatory zooplankton concentrations and nutrient levels. Phytoplankton concentrations are also influenced by physical processes, in particular the mixing properties of the local fluid environment. On planktonic scales (approximately 10-1000 microm) one can assume the local turbulent flow is isotropic, with no distinction between horizontal and vertical mixing. However, agglomerations of phytoplankton into patches are observed on larger scales of up to hundreds of metres, whose formation will be influenced by the anisotropic advection/mixing properties and large-eddy structures prevalent in the surface mixed layer. This paper presents the results of the coupling of a large-eddy simulation (LES) model of the mixed layer with an advection-diffusion system of coupled equations for nitrate-phytoplankton-zooplankton (NPZ) concentration, incorporating sub-grid parameterizations of the biological processes. Typically these include phytoplankton growth due to light levels and ambient nitrate concentration, offset by grazing losses due to the presence of zooplankton. The primary goal of this work is to investigate how the characteristics of the mixed layer turbulence influence the observed distribution of phytoplankton. One novel feature is the incorporation of a 'vortex-force' term in the LES code in order to generate Langmuir circulations. It has been speculated that the enhanced mixing rates associated with 'Langmuir turbulence' play a significant role in regulating planktonic activity. Results derived from the coupled LES-NPZ model, run with and without the presence of Langmuir circulations, are presented in order to investigate these ideas.

Computer Simulation↗

PubMed2001

Population dynamics of sand flies (diptera: psychodidae) at two foci of leishmaniasis in Texas.

Sand flies were collected at a focus of leishmaniasis in Medina County, TX, from April through October 1997 and at a focus in Bexar County, TX, from April 1998 through December 1999. Lutzomyia diabolica (Hall) were collected from April through November with peak abundance in July. The male:female ratio of Lu. diabolica was 1:6.2. Almost all female Lu. diabolica in the collections were unfed. One gravid Lu. diabolica contained 49 ova. Female Lu. anthophora (Addis) were active from February through December with three peaks in abundance suggestive of successive generations. Unfed and gravid Lu. anthophora were collected in about equal numbers. Gravid females contained from 1 to 64 ova per female. The male:female ratio was 1:1.8, with male Lu. anthophora collected in all months. One female Lu. anthophora was found infected with Leishmania in July 1999. Lutzomyia texana (Dampf) were collected from April through October with peak abundance in April during 1997. The male:female ratio was 1:1.4, with most females unfed. Two gravid Lu. texana contained 32 and 102 ova. An undescribed species of Lutzomyia was found only at the Medina County site from May through September 1997. Trapping sites four times per month versus two times per month in 1999 did not appear to adversely affect the abundance of Lu. diabolica or Lu. anthophora. There were marked differences in the species composition and relative abundance at the different sites, indicating that the spatial distribution of sand flies is patchy in nature.

Animals↗

PubMed2006

Population dynamics of nematode parasites of reindeer in the sub-arctic.

Nematode parasite infections of semi-domestic reindeer grazing in their natural habitat in northern Finland were monitored for approximately 2 years. This was achieved by monthly faecal egg counts of male and female calves and adult females from an experimental reindeer herd, in addition to estimating the acquisition of nematode infection from pasture using tracer reindeer calves. The most abundant parasite was Ostertagia gruehneri in the worm counts of tracer animals and in faecal egg counts of adult female reindeer. Capillaria sp. eggs were detected in calves and adults, but Nematodirinae eggs were only recovered from calves. Faecal egg counts showed variations between months for each nematode species, with male and female calves shedding similar numbers of eggs. During each year, calves shed more Capillaria sp. eggs than adult female reindeer, but similar numbers of O. gruehneri eggs. Egg counts of O. gruehneri were more abundant in late summer-autumn (July-September), whereas Capillaria sp. and the Nematodirinae dominated the winter months (November-February). The seasonal trends of adult worm burdens of O. gruehneri in the tracers paralleled the egg count patterns. Capillaria sp. was not detected in tracer worm counts. Tracer worm burdens showed that the proportion of inhibited larvae of O. gruehneri and Nematodirinae steadily increased from spring to early winter, followed by a decline and a commensurate increase in the number of adult parasites in the second summer. This investigation showed that parasite transmission occurs continuously throughout the year for nematode parasites of reindeer in northern Finland.

Animals↗

PubMed2001

Population dynamics and antagonistic potential of enterococci colonizing the phyllosphere of grasses.

AIMS: To investigate the spatial and temporal dynamics of enterococci colonizing forage grass and their ability to produce bacteriocins. METHODS AND RESULTS: Enterococci could be detected on above-ground plant parts throughout the growing season, with high continuity but low cell numbers (2.60 x 101-6.16 x 104 cfu g-1 fresh matter). A total of 750 strains were isolated and identified by their whole-cell protein patterns as Enterococcus faecalis (7.9%), Ent. mundtii (7.9%), Ent. casseliflavus (5.5%), Ent. faecium (5.2%) and Ent. sulfureus (0.1%). The vast majority of the strains (69.7%) formed a homogeneous 16S rDNA genotype that differed from those of known enterococci. A screening for antagonistic activity using an agar spot test revealed that 18.4% of all isolates were potential antagonists. Partially-purified proteins extracted from cell-free culture supernatant fluids of various species were characterized as pH- and heat-stable bacteriocins active against a wide range of lactic acid bacteria, clostridia and Listeria. The producing strains were antagonistically active even on 'phylloplane agar' at temperatures between 4 and 37 degrees C. CONCLUSION: Enterococci are a common part of the epiphytic microflora of grasses, displaying probably some antagonistic activity. SIGNIFICANCE AND IMPACT OF THE STUDY: The results provide new information on the distribution, species diversity and antagonistic potential of enterococci in the phyllosphere.

Antibiosis↗

PubMed1992

Experimental population dynamics of Rhabdias bufonis (Nematoda) in toads (Bufo bufo): density-dependence in the primary infection.

Density-dependence in worm establishment, numbers, biomass and larval production were examined in primary infections of 0, 10, 40, 80 and 160 larvae of the lung nematode, Rhabdias bufonis in the common toad, Bufo bufo. The infection procedure established 4 non-overlapping levels of infection which persisted until 6 weeks post-infection (p.i.), after which there was an overall decline up to 12 weeks p.i. Worm numbers had no direct effect on adult worm survival but temporal changes in worm weight were density-dependent. Adult worm establishment in the lungs declined significantly as the numbers of worms in the lungs increased. At the lowest exposure dose, 86% of the larvae administered reached maturity in the lungs while at the highest, only 37% did so. Also, the numbers of immature larvae outside the lungs increased as adult worm numbers increased. Both features provide evidence for a threshold limit to the numbers of worms maturing in the lungs. Worm numbers also affected larval output per host and per capita fecundity. A significant positive relationship between per capita fecundity and per capita worm weight suggested that density-dependence acted primarily to constrain the growth of individual worms. Finally, the constraints imposed on worm growth and fecundity were apparently relaxed when worm density decreased, providing evidence for density-dependent flexibility in per capita fecundity. Density-dependence in worm establishment and per capita fecundity are mechanisms which may potentially regulate this host-parasite interaction in the field. Both mechanisms may be functionally related to physical space limitations in the lungs, within which worms must compete for finite nutrients.

Analysis of Variance↗

PubMed2006

Population dynamics of malaria vectors in western Kenya highlands.

Studies were carried out at three sites in the highlands of western Kenya (Iguhu and Mbale in Kakamega and Vihiga districts, respectively, and Marani in Kisii district) and at one site in the western Kenya lowlands (Kombewa in Kisumu district) to determine the spatial-temporal dynamics of malaria vectors and intensity of malaria transmission from June 2003 to June 2004. At the highland sites, Anopheles gambiae Giles predominated, constituting >80% of the vector species, whereas An. funestus Giles made up <20%. In contrast, at the lowland site, An. funestus made up 68% of the vector species. The mean annual indoor resting densities of An. gambiae at Iguhu were 5.0 female mosquitoes per house per night, 14.2- and 26.3-fold greater than those at Mbale and Marani. During the main transmission season, the indoor resting densities of An. gambiae increased 4.1-, 10.1-, and 5.0-fold over the dry season period in Iguhu, Mbale, and Marani, respectively. The estimated annual entomological inoculation rate (EIR) at Iguhu was 16.6 infectious bites per person per year (ib/p/yr), 1.1 at Mbale, and 0.4 at Marani. This suggests high spatial variation in vector abundance and malaria transmission intensity. At the lowland site, Kombewa, the total annual EIR was 31.1 ib/p/yr and the indoor resting densities during the transmission season increased 7.1-fold in An. funestus and 18.5-fold in An. gambiae sensu lato over the dry season. The low level of transmission in the highlands suggests that it may be disrupted by vector control methods such as residual spraying.

Animals↗

PubMed1986

Population dynamics of some Pakistan mosquitoes: changes in adult relative abundance over time and space.

Time series and spatial changes in the relative abundance of 14 mosquito species were described from weekly or biweekly collections at nine localities in Punjab province, Pakistan, from January 1976 to June 1980. Comparisons between indoor aspirator catches and outdoor mechanical sweeper collections enabled mosquito resting habits to be classified as: (1) endophilic (Anopheles culicifacies, An. fluviatilis, An. stephensi, An. subpictus); (2) partially exophilic (An. annularis, An. pulcherrimus, An. nigerrimus, Culex bitaeniorhynchus, Cx, pseudovishnui, Cx, quinquefasciatus, Cx. tritaeniorhynchus), or exophilic (Cx. fuscocephala, Aedes caspius, Mansonia uniformis). Temporal abundance patterns were grouped by seasonality, overwintering strategies and the magnitude of fluctuation. Seasonal patterns were: (1) unimodal-spring (Cx. quinquefasciatus, Ae. capius); (2) unimodal-monsoon (An. nigerrimus, An. subpictus, Cx. bitaeniorhynchus, Cx. fuscocephala); (3) bimodal-spring dominant (An. annularis, An. culcifacies, An. stephensi), and (4) bimodal-monsoon/post-monsoon dominant (An. fluviatilis, An. pulcherrimus, Cx. pseudovishnui, Cx. tritaeniorhynchus, Ma. uniformis). Mosquito overwintering strategies included: (1) adults with slowed reproductive activity (An. annularis, An. culicifacies, An. fluviatilis, An. pulcherrimus, An. stephensi, Cx. quinquefasciatus); (2) females with interrupted reproductive activity (An. nigerrimus, Cx. fuscocephala, Cx. pseudovishnui, Cx. tritaeniorhynchus); (3) immature stages (Ae. caspius, Ma. uniformis) and (4) annual extinction and re-introduction (An. subpictus). The magnitude of seasonal change was classified by the number of standard deviations from the overall mean exhibited by the annual maxima or minima: (1) stationary, less than 1 standard deviation (An. culicifacies, An. fluviatilis, Cx. bitaeniorhynchus, Ae. caspius), (2) fluctuating moderately, one to two standard deviations (An. annularis, An. nigerrimus, An. pulcherrimus, An. stephensi, Cx. fuscocephala, Cx. quinquefasciatus, Ma. uniformis) and (3) markedly fluctuating greater than two standard deviations (An. subpictus, Cx. pseudovishnui, Cx. tritaeniorhynchus). The seasonal increases of An. culicifacies and An. stephensi abundance did not closely parallel the periods of maximal malaria transmission. Temporal patterns exhibited by several culicine species indicated that the period of greatest West Nile virus activity would probably occur during the post-monsoon season.

Animals↗

PubMed1999

Parasites, biodiversity, and population dynamics in an ecosystem in the high arctic.

The abomasa of 163 Svalbard reindeers (Rangifer tarandus platyrhynchus) from Nordenskiöld Land, Spitsbergen (78 degrees N, 15 degrees E) were examined for adult and juvenile nematodes. Spitsbergen has midnight sun from late April to late August, arctic night from late October to mid-February, permafrost, and snow cover from October to June. Plant growth is restricted to 6-8 weeks, usually starting mid-June. In the reindeer calves, which are born in June prevalence and intensity of infection increased over the winter. All young (1 year) and adult (older than 1 year) reindeers were infected. Variations in worm burden, fraction of adult nematodes, male to female ratio in the nematodes, number of adult nematodes, number of juvenile nematodes, and distribution of juvenile nematodes on length groups were analysed for relationships with sex and age of host, and time of the year. The material was further analysed for relationships between the reindeer's content of stored fat and worm burden and its elements. It is concluded that transmission of nematodes to the reindeer continues over the winter and that arrested larval development has not been strongly selected for in this High Arctic locality. Infection continued to increase in adult males but not in adult females with age. This is explained as a balance between gain and loss of worms in the females connected to levelling off of food intake at end of somatic growth. In adult male reindeers there was a negative trend between stored fat and infection at all seasons. In reproducing females there were significant negative relationships in winter-spring, while in yeld females no significant relationship was found. The nematodes belonged to the following taxa: Ostertagia gruehneri m. gruehneri, O. gruehneri m. arcticus, Marshallagia marshalli m. marshalli, M. marshalli. m. occidentalis, Teladorsagia circumcincta m. circumcincta, T. circumcincta. m. trifurcata, and T. circumcincta. m. davtiani. There appears not to be any specially adapted species among the helminth parasites of reindeer (Rangifer tarandus) and muskoxen (Ovibos moschatus) in the High Arctic. In the Low Arctic Uminmakstrongylus pallikuukensis of muskoxen may be an example of such adaptation.

Abomasum↗

PubMed2006

The distribution of eggs per host in a herbivorous insect--intersection of oviposition, dispersal and population dynamics.

1. The dynamics of parasitic organisms depend critically upon the frequency distribution of parasite individuals per host. However, the processes giving rise to this frequency distribution have rarely been modelled and tested for organisms with complex host selection behaviour. 2. In this study Microrhopala vittata, a chrysomelid beetle, was used to investigate how oviposition behaviour, movement and density of host plants interact in shaping the frequency distribution of egg clusters per host in the field. 3. Enclosures were stocked with two different host species and different beetle densities and various stochastic process models were fitted to egg cluster count data obtained from these enclosures. The different models were derived considering different scenarios, in particular whether or not plant density limits oviposition rate, whether or not ovipositing females actively seek out the most attractive plant within their perception radius and whether a female's oviposition rate is determined by plant intrinsic factors, the plant's egg cluster load or the surrounding beetle density. 4. The model parameters fitted to cage data were used to describe the frequency distribution of egg cluster counts obtained in a release experiment in the field. A total of 220 beetle pairs were released at five locations in a field where this beetle was not observed previously. Each release point was at a border between the two host species. 5. One model predicted for the preferred host species the egg cluster count frequencies in the field from parameters estimated in the cages. This model assumed that egg clusters present on a plant increased subsequent oviposition on this plant. All other models could not describe the distribution of egg cluster counts for either of the two host species. 6. The results suggest that females seek out attractive hosts actively and the attractiveness of a plant increases with its egg cluster load. This behaviour creates a frequency distribution of egg clusters per host that depends only on beetle density but not on plant density. This conclusion has important implications for modelling insect-plant interactions.

Animals↗