Food limitation and demography of a migratory antelope,the white-eared kob

Summary Although it is commonly presumed that many populations of large-herbivores are limited by food availability, supporting evidence is scarce. This hypothesis was investigated in a population of over 800,000 white-eared kob in the Boma National Park region of the southern Sudan. Food availability, body condition, and mortality rates of adults and calves were measured during the dry seasons of 1982 and 1983. Sampled age distributions from both the live population and carcasses were used to calculate age-specific rates of mortality. In 1982, food supplies during the dry season were augmented by substantial rainfall, which produced regrowth of grass in areas that ordinarily had little green forage. As a result, fat reserves declined little, and rates of adult mortality showed no increasing trend. Total adult mortality was 5%. In 1983, there was no rainfall during the dry season and food intake was insufficient to meet the estimated energy requirements of kob. As a result, fat reserves declined and adult mortality rates increased fourfold. Total adult mortality was 10% (equivalent to the recruitment rate of yearling into the population). Calf mortality during the dry season was similar in both years (50%), based on field estimates of mortality rates and calf/female ratios. Lactation throughout the dry season possibly provided a buffer for calves against variations in food availability. The age structure of the live population in 1983 suggests that a drought in 1980 reduced kob numbers by 40%. These results suggest that adult survival is influenced strongly by the availability of food during the dry season. However, the duration of the dry season also plays an important role. During the dry season, declining fat reserves make an increasing proportion of the population vulnerable to mortality. As a result, even moderate droughts may lead to substantial changes in population numbers.     

Environmental correlates of gastrointestinal parasitism in montane and lowland baboons in Natal,South Africa

We compared the gastrointestinal parasites of the baboon,Papio cynocephalus ursinus, living in montane (altitude, >1800 m) and coastal lowland (altitude, 100–200 m) habitats in Natal, South Africa, using fecal analysis. While the montane animals harbored a smaller number of species, helminth egg-output rates were higher in them than in the lowland animals. The decrease in parasite diversity with increasing altitude was expected, but the difference in helminth egg output was not. It may be due to a combination of food shortage, which characterizes the montane environment, especially at the end of winter, and the high proportion of soil-contaminated items in the diets of the montane animals.     

围栏封育和自由放牧对克氏针茅草原植被空间异质性的影响

群落组成结构的异质性是群落动态的主要属性。本研究采用样线、样方调查方法,基于物种频度与幂函数法则,分析了内蒙古克氏针茅草原围栏封育和自由放牧条件下群落物种结构与空间异质性的变化。结果表明:在围栏外和围栏内不同利用方式下,物种均呈现集中分布;从水分生态型、生活型、生育型、种子传播型和植物科属等不同功能群类别来看,旱生植物和中旱生植物广泛分布,生活型以多年生草本植物为主,依靠重力传播种子的植物占有相对较大的比例,达到60%以上,禾本科、百合科、菊科和豆科等适牧植物具有相对优势;在围栏保护状态下,物种多样性增加,群落异质性降低,放牧退化草原开始向群落状况良好的草原类型演替。     

Coexistence of drosophilid flies: Aggregation, patch size diversity and parasitism

We carried out field experiments to investigate the coexistence of Drosophila species in domestic and forest areas on the basis of the aggregation model. Three cosmopolitan species Drosophila simulans Sturtevant, Drosophila melanogaster Meigen and Drosophila immigrans Sturtevant, and a native species, Drosophila auraria Peng, emerged abundantly from banana placed at the domestic station, while Drosophila immigrans and five native species, Drosophila lutescens Okada, Drosophila rufa Kikkawa and Peng, Drosophila bizonata Kikkawa and Peng, Drosophila sternopleuralis Okada and Kurokawa and Scaptodrosophila coracina (Kikkawa and Peng), were abundant at the forest station. The present analysis suggests that their coexistence was facilitated by the aggregation mechanism. In the cosmopolitan species, the density of individuals that emerged from patches increased with the increase of patch size, but the relationship between fly density and patch size was not clear in the native species. This difference in distribution patterns between the cosmopolitan and native species is likely to be due to the difference in the female visiting behavior. In the present analysis, however, it was not clear whether patch size diversity facilitated their coexistence or not. The effect of patch size diversity may have been masked, because the effect of aggregation was more prominent. The rate of parasitism by wasps was high in October at the domestic station, and in May and June at the forest station. The present result suggests that the rate of parasitism was density-dependent, at least at the domestic station, and therefore parasitism facilitates the coexistence of drosophilid species in domestic areas.     

Environmental heterogeneity and clonal growth: a study of the capacity for reciprocal translocation in Glechoma hederacea L.

Clonal fragments of Glechoma hederacea L. (Lamiaceae) were subjected to environments in which light and nutrients were supplied with a strictly negative association in space, i.e. when one of these resources was in ample supply the other was scarce. Treatments were chosen to simulate environments in which clones grew either within homogeneous conditions or across patch types (heterogeneous conditions). The hypothesis was tested that reciprocal translocation (i.e. exchange of both nutrients and assimilates) between connected groups of ramets would increase biomass production of clones growing under heterogeneous conditions compared to that of clones growing in homogeneous conditions. A cost-benefit analysis was carried out to test this hypothesis. Results suggested that reciprocal translocation did not occur at the structural scale considered in this experiment; no evidence was found for a significant effect on whole clone biomass of assimilate and/or nutrient translocation between clone parts experiencing contrasting levels of resource supply. It is suggested that predominantly acropetal movement of resources and the pattern of integrated physiological unit formation in G. hederacea are the main properties responsible for the lack of mutual physiological support between connected clonal fragments growing in differing habitat conditions. These properties are expected to promote clonal expansion and the exploitation of new territory, rather than sustaining clone parts in sub-optimal patches of habitat for prolonged periods of time.     

Misting and nitrogen fertilization of shoots of a saltmarsh grass: effects upon fungal decay of leaf blades

We conducted a 12-week field manipulation experiment in which we raised the nitrogen availability (ammonium sulfate fertilization to roots) and/or water potential (freshwater misting) of decaying leaf blades of a saltmarsh grass (smooth cordgrass, Spartina alterniflora) in triplicate 11-m² plots, and compared the manipulated plots to unmanipulated, control plots. The ascomycetous fungi that dominate cordgrass leaf decomposition processes under natural conditions exhibited a boosting (>2-fold) of living standing crop (ergosterol content) by misting at the 1 st week after tagging of senescent leaves, but afterwards, living-fungal standing crop on misted blades was equivalent to that on control blades, confirming prior evidence that Spartina fungi are well adapted to natural, irregular wetting. Misting also caused 2-fold sharper temporal declines than control in instantaneous rates of fungal production (ergosterol synthesis), 5-fold declines in density of sexual reproductive structures that were not shown by controls, and 2-fold higher rates of loss of plant organic mass. Extra nitrogen gave a long-term boost to living-fungal standing crop (about 2-fold at 12 weeks), which was also reflected in rates of fungal production at 4 weeks, suggesting that saltmarsh fungal production is nitrogen-limited. Although bacterial and green-microalgal crops were boosted by manipulations of nitrogen and/or water, their maximal crops remained 0.3 or 2% (bacteria or green microalgae, respectively) of contemporaneous living-fungal crop. The fungal carbon-productivity values obtained, in conjunction with rates of loss of plant carbon, hinted that fungal yield can be high (>50%), and that it is boosted by high availability of nitrogen. We speculate that one partial cause of high fungal yield could be subsidy of fungal growth by dissolved organic carbon from outside decomposing leaves.     

Intraspecific nest parasitism in the grey starling (Sturnus cineraceus)

We studied intraspecific nest parasitism in the grey starling (Sturnus cineraceus) in 1992 and 1993. We used three criteria to detect nest parasitism: (i) the appearance of more than one egg per day while the host was laying; (ii) the appearance of extra eggs after the host completed its clutch; and (iii) the appearance of eggs which were of a different shape, size and color to other eggs in the clutch. There were 290 nests (157 nests in 1992; 133 nests in 1993) in which the clutch was completed early (clutches initiated before May 10). Twenty-nine (1992) and 32 (1993) nests contained at least one parasitic egg. Parasitic eggs hatched if they were laid during the laying period and early in the incubation period of their host, and a few of them fledged. Fledging success of parasitic eggs was not different from that of eggs in non-parasitized nests if parasitic eggs were laid during the host's laying period. However, fledging success of all parasitic eggs was fewer than that of eggs in non-parasitized nests. By comparison, fledging success of parasitized nests was not a great as that of non-parasitized nests.     

Comparative demography of sympatric populations of Lacerta vivipara and Lacerta agilis

Summary A mark-recapture study was carried out in sympatric populations of Lacerta agilis and Lacerta vivipara in the Netherlands from 1976 to 1982. In most years the age structure of both populations was pyramidal. For both species life expectation of females was higher and on average they did live longer. Hence the sex ratio for adults deviated significantly from 1.0 in favour of females. Maximum age for Lacerta vivipara was 8 years (female) and for Lacerta agilis 12 years (male). The density of both species fluctuated around 100/ha. The biomass of Lacerta agilis was twice that of Lacerta vivipara. In Lacerta vivipara the 3rd and 4th calendar year class supplied 78% of total net reproduction; in Lacerta agilis the 4th, 5th, and 6th calendar year classes supplied 68%. In both populations the population replacement rate was 2. Population turnover time was 4.83 years for Lacerta agilis and 2.81 for Lacerta vivipara. The life history strategy of the Lacerta vivipara population is compared with six other European Lacertavivipara populations.     

Different demography of friends and strangers: an experiment on the impact of kinship and familiarity in Clethrionomys glareolus

Summary We examined demographic effects of familiarity and relatedness in the bank vole Clethrionomys glareolus (Schreber) in four 0.5-ha enclosures in Central Finland. In two enclosures were mature voles which had overwintered together and some of their mature off-spring (hereafter referred to as Friends), and in the other two individuals of the same species captured from different localities near the study area (Strangers). The experiment lasted from June to September. The populations of Friends reached densities twice as high as those of Strangers with a significantly higher rate of recruitment and survival of the young. This may have been due to mutual familiarity decreasing antagonism towards the juveniles. The conflicting results obtained from studies of Clethrionomys and Microtus are discussed. We believe that these genera represent behavioural adaptations to different habitats and ways of life. Most behavioural population regulation hypotheses are based on studies of Microtus. We conclude that these results should be applied with great caution to other rodent genera.     

The effects of oxalates produced by Salsola tragus on the phosphorus nutrition of Stipa pulchra

Oxalic acid is produced by some species of plants and mycorrhizal fungi and it may solubilize unavailable soil phosphorus (P) bound by cations (Ca⁺⁺, Al⁺⁺, Fe⁺⁺⁺). Field and greenhouse experiments were conducted to show whether oxalate produced by the annual Salsola tragus or added oxalic acid would solubilize P from the inorganic-bound soil P pool, making it available for uptake by Stipa pulchra. Oxalate could be leached in the laboratory from the senescent canopy of Salsola, and leaching by rainfall was hypothesized to be a source of potential increased soil P under the Salsola canopy. Both oxalate leached from the canopy of Salsola and added oxalic acid increased the availability of soil P in greenhouse experiments. The source of the increase in available soil P in the greenhouse experiment was shown to be the inorganic-bound P pool, as the total P concentration of the soil decreased with increasing oxalate. There were significant increases in Stipa shoot P in response to Salsola leachates and in response to added oxalate in the greenhouse studies. These results suggest an important role for oxalate in P cycling. On disturbed sites where Salsola invades it may act to facilitate the establishment of later seral species like Stipa by creating a nutrient island of available P.     

Some aspects of Artemia biology affected by cestode parasitism

Artemia individuals from a wild population, bearing cestode cysticercoids (Hymenolepididae) were kept in the laboratory during four months to observe influences of the parasite on the host biology. No differences were found between parasitized and unparasitized shrimps regarding final adult size. The higher survival of parasitized animals suggests that parasitism is not pathogenic. The most dramatic effect was host castration. Parasitized individuals showed higher total lipid levels, probably linked to carotenoid pigments conveying a red color to parasitized shrimps.     

Spatial heterogeneity of daphniid parasitism within lakes

Spatially explicit models show that local interactions of hosts and parasites can strongly influence invasion and persistence of parasites and can create lasting spatial patchiness of parasite distributions. These predictions have been supported by experiments conducted in two-dimensional landscapes. Yet, three-dimensional systems, such as lakes, ponds, and oceans, have received comparatively little attention from epidemiologists. Freshwater zooplankton hosts often aggregate horizontally and vertically in lakes, potentially leading to local host–parasite interactions in one-, two-, or three-dimensions. To evaluate the potential spatial component of daphniid parasitism driven by these local interactions (patchiness), we surveyed vertical and horizontal heterogeneity of pelagic Daphnia infected with multiple microparasites in several north temperate lakes. These surveys uncovered little evidence for persistent vertical patchiness of parasitism, since the prevalence of two parasites showed little consistent trend with depth in four lakes (but more heterogeneity during day than at night). On a horizontal scale of tens of meters, we found little systematic evidence of strong aggregation and spatial patterning of daphniid hosts and parasites. Yet, we observed broad-scale, basin-wide patterns of parasite prevalence. These patterns suggest that nearshore offshore gradients, rather than local-scale interactions, could play a role in governing epidemiology of this open water host–parasite system. Electronic Supplementary Material Supplementary material is available for this article at     

Effects of parasitism by Praon pequodorum on age-specific fecundity and population growth of the pea aphid, Acyrthosiphon pisum

The effects of parasitism by Praon pequodorum Viereck (Hymenoptera: Aphidiidae) on the survival, development and reproduction of apterous pea aphids, Acyrthosiphon pisum (Harris) (Homoptera: Aphididae), were studied in the laboratory. Ten cohorts of aphids differing in age from 0.5 h to 9 days were tested. At 20°C, pea aphids survived an average of 7 days after parasitization. Parasitized first and second instars died before reaching the adult stage. Third instars died as adults but without producing any offspring. Parasitized fourth instars and adult aphids produced a variable number of offspring; their mean total fecundity increased as an exponential function of the age at parasitization. Host age did not significantly affect the period from the beginning of parasitism to the end of reproduction. Equations are provided to estimate the length of the reproductive period, the total fecundity, the intrinsic rate of increase, and the doubling time as functions of aphid age at parasitization. The data are discussed with regard to host population growth. It is shown that a parasite's potential impact on an aphid population is critically dependent on its preference for and successful oviposition in early host instars.

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Résumé Les effets du parasitisme par P. pequodorum Viereck (Hym.: Aphidiidae), sur la survie, le développement et la reproduction des aptères de A. pisum, ont été examinés au laboratoire. L'étude a porté sur 10 cohortes de pucerons dont les âges différaient de 0,5 heure à 9 jours. A 20°C, les pucerons parasités ont survécu en moyenne pendant 7 jours après avoir été parasités. Leur évolution ultérieure dépend au stade auquel ils ont été parasités: au premier et second stades, ils sont morts avant de devenir adultes; au troisième stade, ils sont morts adultes avant de se reproduire; au quatrième stade et adultes, ils ont donné un nombre variable de descendants. La fécondité totale moyenne a crû comme une fonction exponentielle de l'âge au moment où ils avaient été parasités. L'âge de l'hôte n'a pas modifié significativement la durée de la période entre le moment où ils ont été parasités et la fin de la phase de reproduction. Des équations ont été établies en fonction de l'âge des pucerons au moment où ils ont été parasités, pour estimer la longueur de la période de reproduction, la fécondité totale, le taux intrinsèque d'accroissement et le temps de doublement des cohortes de pucerons. Les résultats sont discutés sous l'angle de la dynamique de la population. On en déduit que l'impact potentiel d'un parasite sur une population de pucerons dépend d'abord de ses préférences pour les premiers stades de l'hôte et du succès de sa ponte sur ces stades.

     

Food preferences and nematode parasitism in mycophagousDrosophila

Food preferences and nematode parasitism were studied in natural populations of mycophagousDrosophila in and near Sapporo, northern Japan. Species which preferred fresh mushrooms showed species-specific responses toPleurotus mushrooms:D. pirka bred only onPleurotus cornucopiae, D. trivitata onP. cornucopiae andP. ostreatus, D. trilineata on these twoPleurotus mushrooms and some other mushrooms, whileD. sexvittata bred on a wide variety of mushrooms but seldom onPleurotus mushrooms. Species which preferred decayed mushrooms (D. quadrivittata, D. histrioides, D. testacea and species of thequinaria species-group) showed host preferences different from those of the above species. The rate of parasitism by nematodes was generally higher in species which prefer decayed mushrooms than in species which prefer fresh mushrooms. Among species which prefer fresh mushrooms, onlyD. trilineata was parasitized frequently by nematodes. It was not clear what factors determine the rate of parasitism in these mycophagousDrosophila. D. pirka, D. trivittata andD. trilineata passed through three or four generations per year and entered reproductive diapause in early September in and near Sapporo. Bionomics of Drosophilidae (Diptera) in Hokkaido, IX.     

Phylogeny of marine Gregarines (Apicomplexa)--Pterospora, Lithocystis and Lankesteria--and the origin(s) of coelomic parasitism

Gregarines constitute a large group of apicomplexans with diverse modes of nutrition and locomotion that are associated with different host compartments (e.g. intestinal lumena and coelomic cavities). A broad molecular phylogenetic framework for gregarines is needed to infer the early evolutionary history of apicomplexans as a whole and the evolutionary relationships between the diverse ultrastructural and behavioral characteristics found in intestinal and coelomic gregarines. To this end, we sequenced the SSU rRNA gene from (1) Lankesteria abbotti from the intestines of two Pacific appendicularians, (2) Pterospora schizosoma from the coelom of a Pacific maldanid polychaete, (3) Pterospora floridiensis from the coelom of a Gulf Atlantic maldanid polychaete and (4) Lithocystis sp. from the coelom of a Pacific heart urchin. Molecular phylogenetic analyses including the new sequences demonstrated that several environmental and misattributed sequences are derived from gregarines. The analyses also demonstrated a clade of environmental sequences that was affiliated with gregarines, but as yet none of the constituent organisms have been described at the ultrastructural level (apicomplexan clade I). Lankesteria spp. (intestinal parasites of appendicularians) grouped closely with other marine intestinal eugregarines, particularly Lecudina tuzetae, from polychaetes. The sequences from all three coelomic gregarines branched within a larger clade of intestinal eugregarines and were similarly highly divergent. A close relationship between Pterospora schizosoma (Pacific) and Pterospora floridiensis (Gulf Atlantic) was strongly supported by the data. Lithocystis sp. was more closely related to a clade of marine intestinal gregarines consisting of Lankesteria spp. and Lecudina spp. than it was to the Pterospora clade. These data suggested that coelomic parasitism evolved more than once from different marine intestinal eugregarines, although a larger taxon sample is needed to further explore this inference.     

Influence of climate and community composition on the population demography of pasture species in semi-arid Australia

Substantial recruitment of Callitris glaucophylla in woodland, Sclerolaena birchii in cleared woodland, and Astrebla lappacea in grassland is related to catastrophic events of the past century in the form of interactions between climate, the impact of European land use (sheep, cattle, rabbits) and the rabbit myxoma epizootic. The direct effect of rainfall on the demography of these species and its indirect effect through competition via suites of accompanying plant species are examined. Major long-term changes in plant populations are generated by extreme sequential events rather than by random isolated events. One of the most potent climatic agents for change in eastern Australia is the El Niño/Southern Oscillation phenomenon.     

The demography of the lion-tailed macaque (Macaca silenus) in rain forest fragments in the Anamalai Hills, South India

We examined demographic consequences of habitat fragmentation in the lion-tailed macaque in the Anamalai Hills in southern Western Ghats. The parameters examined were group size, age/sex composition, and birth rate, in relation to various habitat parameters. Demographic parameters were estimated for 11 groups in 8 rain forest fragments, during January to May 1996. Area, tree density, canopy cover, canopy height, and tree basal area were estimated for these fragments. As fragment area decreased, there was a decline in birth rate and proportion of immatures in the group, and an increase in the number of adult males, and the variability in group size and adult sex ratios. A similar pattern was also observed with decreasing values of other habitat variables. Differences in the founder population size and age structure, demographic randomness, and history of poaching have caused greater variability in group size and adult sex ratios in the small fragments. The lack of dispersal in the small fragments is another reason for the high variability.     

The correlation between demography and metabolic rate: a test using the beach vole (Microtus breweri) and the meadow vole (Microtus pennsylvanicus)

Summary This study examines the hypothesis that mammalian species with wide fluctuations in population size will have greater metabolic rates than species with smaller population fluctuations. We tested this hypothesis using two microtine rodents — the beach vole (Microtus breweri) and the meadow vole (M. pennsylvanicus). Although these species experience similar climatic regimes, eat similar foods, and have a very close phylogenetic relationship, they show marked differences in demography. Microtus pennsylvanicus is prone to large supraannual fluctuations in population size, while M. breweri is essentially acyclical. Metabolic rate (oxygen consumption) of each species was measured using open-flow respirometry at ambient temperatures ranging from 2 to 34° C. Basal metabolic rate of M. pennsylvanicus (1.81 ml O₂ g^–1 h^–1) was significantly greater than that of M. breweri (1.39 ml O₂ g^–1 h^–1). The lower critical temperature, estimated by continuous two-phase regression, was 28.9° C for M. pennsylvanicus and 29.8° C for M. breweri. Regression lines below thermoneutrality did not differ in slope, but the elevation for M. pennsylvanicus was significantly higher. Thus, M. pennsylvanicus has a higher metabolic rate at all temperatures examined. These results support the hypothesis that metabolic rate is positively correlated with the extent of population fluctuation. We suggest that further evidence for, or against, this hypothesis should be found by comparing closely matched species pairs, rather than resorting to confounded allometric comparisons of ecologically and phylogenetically diverse taxa.     

The scale of demographic heterogeneity in a population of Peromyscus leucopus

Summary The patterns of spatial heterogeneity in density and demography were studied in a population of Peromyscus leucopus inhabiting a deciduous forest in west-central Indiana. A series of 9 live-trapping grids sampled densities from 3 spatial scales: 3 ha, 80 ha and 350 km². We found high levels of variation within all three spatial scales. There was as much variation within a single, large grid as within the entire Sugar Creek Valley (350 km²). The patterns of density variation were not temporally stable and thus represent variation in demographic processes rather than simply differences in habitat quality. We suggest that the Sugar Creek Valley represents a metapopulation of Peromyscus leucopus composed of a number of temporally unstable subpopulations. This structure provides considerable demographic variation that dispersing animals can exploit.