Role of parthenogenetic natality and emergence from diapausing eggs in the dynamics of some rotifer populations

There are few quantitative data on the role of emergence from diapausing eggs in population dynamics of natural populations of zooplankton species; to our knowledge, all these concern copepods and cladocerans. We present here direct estimates of emergence from bottom resting eggs for another important category of freshwater zooplankton, namely rotifers. Three populations of rotifers of the genus Brachionus were studied in a lake. During the study period 10 population increases, each corresponding to an individual sampling interval, were detected. For each interval, emergence from immediately hatching, parthenogenetic eggs calculated on the basis of the Edmondson-Paloheimo model and emergence from diapausing bottom eggs determined in short-term experiments were estimated and compared to each other. We found that three of the population increases observed are entirely explained by parthenogenetic natality. In contrast, emergence from diapausing eggs can, on its own, account for none of population increases. For two population increases, however, it accounts for that part of population growth which remains unexplained by the parthenogenetic natality. For rotifer populations studied, emergence from diapausing eg eggs is generally less important than parthenogenetic births, when both are regarded as an immediate cause of population growth. This is in sharp contrast to the data available for some crustaceans (De Stasio, 1990) where the role of emergence from diapausing eggs in population dynamics has been clearly shown.     

Polymorphism and Food Limitation in Three Daphnia carinata Populations

The annual cycles of Daphnia carinata in three fish-free ponds in southern New Zealand (Quarry, Taieri and Raupo Ponds) are described. Although breeding was continuous, the populations were frequently dominated by distinct cohorts and there was a sexual phase in spring. Growth rates, particularly in Quarry Pond, were often slow, and clutch sizes generally small. Egg and neonate sizes changed seasonally, but changes were not closely related to clutch sizes and body lengths. In Taieri Pond and Raupo Pond some D. carinata grew to 6.14 mm and carried clutches of up to 154 eggs. The potentially high fecundity associated with large size makes D. carinata a good coloniser, but our studies showed that it also survives well in poor food conditions by growing slowly and producing only 1–2 eggs per clutch. D. carinata showed marked seasonal polymorphism in tailspine length and development of head crests. In winter, crests were absent and tailspines were short and varied little with body length. Crests were first apparent, and tailspines began to elongate, in early spring, before the first appearance of a notonectid, Anisops wakefieldi. By midsummer, tailspines had increased markedly with body length but the slope of the relationship declined in autumn. Laboratory trials showed that both tailspine length and crest development increased in the presence of Anisops. These increases may be due to water-soluble factor(s) produced by Anisops.     

Temperature impact on the midsummer decline of Daphnia galeata: an analysis of long-term data from the biomanipulated Bautzen Reservoir (Germany)

1. The influence of water temperature on occurrence and duration of a midsummer decline (MSD) of Daphnia galeata was studied in the biomanipulated Bautzen Reservoir in Germany. The proportion of piscivores in the fish community of the reservoir has been enhanced experimentally since 1981. As a consequence, Daphnia galeata has dominated the zooplankton. Over 18 years of study (1981–1998), a long‐lasting MSD (longer than 30 days) occurred in 7 years, whereas a short MSD (shorter than 30 days) was observed in 6 years. During the remaining 5 years, an MSD was not observed.
2. Two hypotheses were examined to explain the observed patterns. First, we postulated that high water temperature during winter and early spring (January–April) leads to an MSD after an early and high spring peak of daphnids. On the other hand, low temperature during winter and early spring should not cause an MSD owing to a slower increase of the population, resulting in a later peak of daphnids. Second, we hypothesized that the mean water temperature during early summer (May and June) influences the occurrence of an MSD (by controlling young‐of‐the‐year (YOY) fish predation on daphnids).
3. The water temperature during winter and early spring explains 83%, and the early summer water temperature 55%, of interannual variation in the occurrence of an MSD.
4. The interannual variation in duration of an MSD was neither explained by temperature during winter and early spring nor by early summer temperature alone, but in 14 of the 18 years (78%) by a combination of both.
5. We conclude that water temperature during winter and early spring had a strong impact on Daphnia mortality by influencing height and timing of the spring peak which, in turn, influenced the extent of overexploitation of their food resources. By contrast, the water temperature during early summer probably influenced the mortality of daphnids caused by predation of YOY fish. The relative timing of both sources of mortality, which depends on the temperature regime during the first 6 months of the year, is the key process in controlling the occurrence and duration of an MSD. A long‐lasting MSD, therefore, is likely in Bautzen Reservoir only if temperatures are high during winter and early spring, as well as during early summer.
6. As a consequence of climate warming, recent climate records reveal warming during winter, spring and early summer in middle Europe, rather than an increase in mean annual temperatures. If our findings and conclusions are related to this regional and temporal pattern of climate warming, an increasing frequency of years with a long‐lasting MSD and, consequently, a decreasing efficiency of biomanipulation can be predicted.     

Rotifer population dynamics in response to increased bacterial biomass and nutrients: a mesocosm experiment

The impact of organic nutrients and massive addition of bacteria was followed in lake water mesocosms in a eutrophic lake. Increased DOM initiated a sequence of trophic responses indicated by rapid increases in bacterioplankton, protozoa, and algal biomass. The populations of Keratella cochlearis and Keratella quadrata showed a distinct response by rapid increase in birth rate followed by maxima of production and abundance. This succession clearly reflected the trophic position of these rotifer populations in the food chain. A reverse response was observed in Conochilus unicornis.     

Dynamics of an age‐structured population drawn from a random numbers table

I constructed age‐structured populations by drawing numbers from a random numbers table, the constraints being that within a cohort each number be smaller than the preceding number (indicating that some individuals died between one year and the next) and that the first two‐digit number following 00 or 01 ending one cohort’s life be the number born into the next cohort. Populations constructed in this way showed prolonged existence with total population numbers fluctuating about a mean size and with long‐term growth rate (r) ≈ 0. The populations’ birth rates and growth rates and the females’ per capita fecundity decreased significantly with population size, whereas the death rates showed no significant relationship to population size. These results indicate that age‐structured populations can persist for long periods of time with long‐term growth rates of zero in the absence of negative‐feedback loops between a population’s present or prior density and its birth rate, growth rate, and fecundity, contrary to the assumption of density‐dependent regulation hypotheses. Thus, a long‐term growth rate of zero found in natural populations need not indicate that a population’s numbers are regulated by density‐dependent factors.     

Ants on the Move: Resource Limitation of a Litter‐nesting Ant Community in Costa Rica1

The leaf litter of tropical wet forests is replete with itinerant ant nests. Nest movement may help ants evade the constraints of stress and disturbance and increase access to resources. I studied how nest relocation and environmental factors may explain the density, size, and growth of leaf litter ant nests. I decoupled the relationships among litter depth, food abundance, and nest availability in a 4‐mo manipulation of food and leaf litter in a community of litter‐nesting ants in a lowland wet forest in Costa Rica. Over 4 mo, 290 1 m² treatment and control plots were sampled without replacement. Nest densities doubled in response to food supplementation, but did not decrease in response to litter removal or stress (from litter trampling). The supplementation of food increased the utilization of less favored nesting materials. In response to food supplementation and litter trampling, arboreal ants established nests in the litter, and growth rates of the most common ants (Pheidole spp.) increased. Colony growth was independent of colony size and growth rates of the most abundant ants. In general, I conclude that litter‐nesting ant density is driven primarily by food limitation, that nest relocation behavior significantly affects access to resource and the demographic structure of this community, and that nest fission may be a method to break the growth–reproduction trade‐off.     

The Catastrophic Decline of Tortoises at a Fenced Natural Area

Agassiz’s desert tortoise (Gopherus agassizii), a threatened species of the southwestern United States, has severely declined to the point where 76% of populations in critical habitat (Tortoise Conservation Areas) are below viability. The potential for rapid recovery of wild populations is low because females require 12–20 years to reach reproductive maturity and produce few eggs annually. We report on a 34-year mark-recapture study of tortoises initiated in 1979 at the Desert Tortoise Research Natural Area in the western Mojave Desert, California, USA, and provide substantive data on challenges faced by the species. In 1980, the United States Congress designated the Research Natural Area and protected the land from recreational vehicles, livestock grazing, and mining with a wildlife-permeable fence. The 7.77-km² study area, centered on interpretive facilities, included land both within the Natural Area and outside the fence. We expected greater benefits to accrue to the tortoises and habitat inside compared to outside. Our objectives were to conduct a demographic study, analyze and model changes in the tortoise population and habitat, and compare the effectiveness of fencing to protect populations and habitat inside the fence versus outside, where populations and habitat were unprotected. We conducted surveys in spring in each of 7 survey years from 1979, when the fence was under construction, through 2012. We compared populations inside to those outside the fence by survey year for changes in distribution, structure by size and relative age, sex ratios, death rates of adults, and causes of death for all sizes of tortoises. We used a Bayesian implementation of a Jolly Seber model for mark-recapture data. We modeled detection, density, growth and transition of tortoises to larger size-age classes, movements from inside the protective fence to outside and vice versa, and survival. After the second and subsequent survey years, we added surveys to monitor vegetation and habitat changes, conduct health assessments, and collect data on counts of predators and predator sign. At the beginning of the study, counts and densities for all sizes of tortoises were high, but densities were approximately 24% higher inside the fence than outside. By 2002, the low point in densities, densities had declined 90% inside the fence and 95% outside. Between 2002 and 2012, the population inside the fence showed signs of improving with a 54% increase in density. Outside the fence, densities remained low. At the end of the study, when we considered the initial differences in location, densities inside the fence were roughly 2.5 times higher than outside. The pattern of densities was similar for male and female adults. When evaluating survival by blocks of years, survivorship was higher in 1979–1989 than in 1989–2002 (the low point) and highest from 2002 to 2012. Recruitment and survival of adult females into the population was important for growing the population, but survival of all sizes, including juveniles, was also critical. Major events and activities driving the decline in populations both inside and outside the fence included illegal collecting, upper respiratory tract disease, and hyperpredation by the common raven (Corvus corax) on juvenile tortoises. Other sources of death were gunshots, vehicles, and predation by mammals. Outside the fence, fragmentation and deterioration of habitat was a critical driver. Between the first and last surveys, 2 different ecosystem processes were underway: recovery of vegetation and soils from grazing and vehicles inside the fence and continued deterioration outside the fence. Habitat outside the fence became increasingly denuded of shrubs and fragmented by roads and trails, and habitat fragments increased 50-fold. Outside the fence, biomass of non-native annual plants was higher and the cover of shrubs was lower, a reflection of ongoing deterioration. These changes and losses of habitat resulted in loss of shrub cover and sites for burrows, reduction in preferred food plants, and greater exposure to predators and extremes in temperature. Overall, the tortoise population and habitat inside the fence appeared to benefit from protection and showed signs of recovery at the end of the study. Fencing, control of vehicular access, and removal of livestock grazing were among several recommended management actions for critical habitat in the first recovery plan in 1994. At the end of the study, the Natural Area remained as 1 of 2 fenced, official protected areas for the species in the geographic range. We attribute fencing to continuing higher densities of adults inside the fence compared with outside the fence and promising signs of recovery. Densities of adults at the Natural Area also were 2.3 to 5.5 times higher than in 16 of the 17 Tortoise Conservation Areas (critical habitat units) within the geographic range. © 2020 The Authors. Wildlife Monographs published by Wiley Periodicals, LLC on behalf of The Wildlife Society.     

Field Investigations and Model Simulation of the Dynamics of Zooplankton Populations in Fresh Waters

The main parameters characterizing the dynamics of a population were determined by field investigations at the Saidenbach reservoir and by means of an ecological model. The results obtained by both methods involving totally different procedures were in good agreement. The gross growth rates obtained by both methods ranged up to 0.14 d^−1, and the net growth rates vary between 0.1 d⁻¹ and 0.2 d⁻¹. Field investigations revealed zooplankton mortality rates during summer of about 0.1 compared with 0.08 d⁻¹ for the model. Comparison of the two methods shows how practical investigations may be improved and gives a better insight into the dynamics of zooplankton populations in waters.     

Food limitation of planktonic rotifers: field experiments in two mountain ponds

1. Resource competition is thought to be important in controlling zooplankton population dynamics and structuring zooplankton communities. Resource competition requires that resources are limiting. Ten field experiments were conducted to determine the presence and intensity of resource limitation of herbivorous planktonic rotifers in two mountain ponds. The intensity of food limitation was measured as Δ r , the difference between population growth rates in food supplemented versus control enclosures.
2. Rotifers were significantly food limited (Δ r  > 0) in most experiments. The intensity of food limitation varied between species. In Grady Lake, mean Δ r was 0.26 day⁻¹ for Polyarthra vulgaris and 0.43 day⁻¹ for an unidentified Synchaeta sp. In L1 Pond, mean Δ r was 0.07 day⁻¹ for Keratella cochlearis and 0.28 day⁻¹ for S. oblonga . The frequent and intense food limitation suggests that edible phytoplankton in both ponds were often present at low densities, were of low nutritional quality, or both. The intensity of food limitation often changed rapidly over time, indicating rapid temporal variation in resource availability.
3. For P. vulgaris , Δ r was not correlated with its population growth rate in Grady Lake. Thus, although food limitation was common, population dynamics may have been more strongly affected by other factors. For K. cochlearis , Δ r increased as population density increased, suggesting the existence of intraspecific resource competition that may regulate population dynamics.     

The longitudinal distribution and community dynamics of zooplankton in a regulated large river: a case study of the Nakdong River (Korea)

The longitudinal distribution and seasonal dynamics of zooplankton were examined along a 200-km section of the middle to lower Nakdong River, Korea. Zooplankton was sampled twice a month from January 1995 to December 1997 at five sites in the main river channel. There was considerable longitudinal variation in total zooplankton abundance (ANOVA, p < 0.001). All major zooplankton groups (rotifers, cladocerans, copepodids and nauplii) increased significantly with distance downstream along the river. There also were statistically significant seasonal differences in zooplankton abundance at the sampling sites (ANOVA, p < 0.01). Zooplankton abundance was high in spring and fall and low in summer and winter. The seasonal pattern of rotifers was similar to that of total zooplankton. This reflected the fact that rotifers (Brachionus calyciflorus, B. rubens, Keratella cochlearis and Polyarthra spp.) strongly dominated the zooplankton community at all locations. Among the macrozooplankton, small-bodied cladocerans (e.g. Bosmina spp.) dominated; the abundance of large-bodied cladocerans (e.g. Daphnia) was negligible (0–5 ind. l^–1). Among the environmental variables considered, partial residence time seemed to play the most important role in determining characteristics of the river zooplankton community.     

The Relative Role of Interference Competition in Regulation of a Rotifer Community during Spring Development in a Eutrophic Reservoir

The relative importance of interference and exploitative competition from Daphnia was tested in contrast to known role of Cyclops vicinus predation, influencing the rotifer community in Římov Reservoir during spring period. The abundances of five dominant rotifer species and their birth and death rates were analysed, together with changes in chl‐a concentration, HNF, bacteria biomass and the abundances of predator and competitor species, from high frequency sampling. Development of loricated species (Keratella cochlearis, K. quadrata and Kellicottia longispina) was driven predominantly by food availability. The dominant soft‐bodied species Polyarthra spp. and Synchaeta lakowitziana were affected predominantly through C. vicinus predation. The role of mechanical interference from D. galeata, although may be important in a limited periods was overclouded by predation and exploitative competition in general. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The influence of mesozooplankton on phytoplankton nutrient limitation: a mesocosm study with northeast Atlantic plankton

We used marine phytoplankton from mesocosms seeded with different zooplankton densities to study the impact of mesozooplankton on phytoplankton nutrient limitation. After 7 d of grazing (copepod mesocosms) or 9 d (appendicularian mesocosms) phytoplankton nutrient limitation was studied by enrichment bioassays. After removal of mesozooplankton, bioassay bottles received either no nutrients, phosphorus or nitrogen alone, or a combination of nitrogen and phosphorus and were incubated for 2 d. Phytoplankton reproductive rates in the bottles without nutrient addition were calculated after correction for grazing by ciliates and indicated increasing nitrogen limitation with increasing copepod abundance. No nutrient limitation was found in the appendicularian mesocosms. The increase of nutrient limitation with increasing copepod density seems to be mainly the result of a trophic cascade effect: Copepods released nanoplankton from ciliate grazing pressure, and thereby enhanced nitrogen exhaustion by nanophytoplankton and reduced nitrogen excretion by ciliates. Nitrogen sequestration in copepod biomass, the mechanism predicted by the ecological stoichiometry theory, seems to have been a weaker effect because there was only little copepod growth during the experiment.     

Potential Role of Spruce Budworm in Range-Wide Decline of Canada Warbler

ABSTRACT The Canada warbler (Wilsonia canadensis) is one of many common neotropical migrants whose populations are in decline across their range. Influences of habitat loss and degradation on breeding or wintering grounds have been postulated as possible causes, but few empirical data exist to support a specific cause. Based on previous studies linking abundances of Canada warbler and spruce budworm (Choristoneura fumiferana), we hypothesized that the Canada warbler may be influenced by a persistent decline in spruce budworm throughout the bird's breeding range, a hypothesis that has received little attention. This hypothesis makes 5 predictions: 1) budworm outbreaks and warbler detections should be spatially and temporally coincident; 2) the relationship between Canada warbler and spruce budworm outbreaks should be similar to relationships for other warblers known to be spruce budworm associates; 3) the relationship should be stronger than for warblers lacking an association with spruce budworm; 4) because temporal trends of both spruce budworm and Canada warblers have varied throughout Canadian provinces, declines in Canada warblers should be seen only in provinces where spruce budworm also declined; and 5) variation in Canada warbler abundance should reflect variation in supply of preferred habitat for the spruce budworm if habitat rather than budworm abundance is the key. Our analyses supported predictions 1–4, suggesting that Canada warbler may be even more closely associated with spruce budworm than are known associated species, a phenomenon noted in the literature but previously unexplained. Prediction 5 was not supported, because budworm habitat (area of mature and older balsam fir [Abies balsamea] and white spruce [Picea glauca]) remained constant in Ontario while warbler abundance declined. Although the correlative nature of these results precludes inference of a causal relationship between the declines of the Canada warbler and spruce budworm, we postulate that potential links may exist directly, where spruce budworm outbreaks provide elevated levels of insect prey items for breeding Canada warblers, or indirectly through changes in forest structure and composition following outbreaks. These results have implications when considering long-term trends in Canada warbler populations, because it may be impossible to alter population trends for species linked to the timing and magnitude of spruce budworm outbreaks.     

人口老龄化对卫生资源配置的影响研究

为探索人口老龄化对卫生资源配置的影响,本文在整群抽样调查法获取相关资料的基础上,运用卫生服务需求法测算出老年人群对床位配置、卫生人力的需求量。结果发现在2030年青岛市老年人口所占比重达到31.89%,因老年人口增加导致的床位配置、卫生人力的增加量分别为:2219、3093。面对巨大的老年医疗需求群体如何更合理的配置卫生资源,本文提出了相关的建议。     

The population decline of the New Zealand sea lion Phocarctos hookeri: a review of possible causes

• 1 The New Zealand (NZ) sea lion Phocarctos hookeri is NZ's only endemic pinniped and is listed as ‘nationally critical’. The species breeds in the NZ sub‐Antarctic: 71% of the population at the Auckland Islands (2010 pup production: 1814 ± 39) and the remaining 29% on Campbell Island (726 pups in 2010).
• 2 Pup production at the Auckland Islands has declined by 40% since 1998 (1998: 3021 pups produced): only 1501 pups were born in 2009. This decline is directly linked to philopatric females not returning to breeding areas. While the Auckland Island population has declined, the Campbell Island population appears to be increasing slowly.
• 3 Potential reasons for the decline in the Auckland Island population, but not in the Campbell Island population, include non‐anthropogenic factors: (i) disease epizootics, (ii) predation, (iii) permanent dispersal or migration, (iv) environmental change; and anthropogenic impacts: (v) population ‘overshoot’, (vi) genetic effects, (vii) effects of contaminants, (viii) indirect effects of fisheries (i.e. resource competition) and (ix) direct effects of fisheries (i.e. by‐catch deaths). Of the nine potential reasons examined here, six can be discounted (ii–vii). Bacterial epizootics (i) occur in the NZ sea lion population, but their impact has predominantly increased pup mortality, which is unlikely to cause the severe decline observed, as pup mortality throughout the species is naturally high and variable.
• 4 The most plausible hypotheses, based on available evidence, are that the observed decline, in particular, the decreasing number of breeding females in the Auckland Island population, is caused by (viii) fisheries‐induced resource competition and (ix) fisheries‐related by‐catch. By‐catch is the main known anthropogenic cause of mortality in the species. Competition with fisheries resulting in resource competition, nutrient stress and decreased reproductive ability in NZ sea lions should be a priority area for future research.

     

风景园林与绿色基础设施在城市流域水资源规划中的重要作用

通过绿色基础设施途径,处理美国波士顿北部的马萨诸塞州城市流域的水资源规划问题。从多个尺度为风景园林师提供水资源规划的经验与启发,探究公众对新型绿色基础设施解决方案的态度与偏好,以及公众偏好对于整体规划设计的重要作用。     

The effect of prey morphology on the feeding behaviour and population growth of the predatory rotifer Asplanchna sieboldi: a case study using five species of Brachionus (Rotifera)

1. We investigated the numerical response, functional response and prey preference of Asplanchna sieboldi to five different prey brachionids. We also analysed the feeding behaviour of the predator in terms of encounters, attacks, capture and prey ingested per unit time. 2. The five prey species (Brachionus havanaensis, B. rubens, B. patulus, B. macracanthus and B. calyciflorus) differed in their body size and spine length. 3. The population growth rates of A. sieboldi ranged from 0.074 ± 0.03 to 0.431 ± 0.02 depending on prey type and density. There was a significant impact of the spine length rather than body size per se on the population growth rates of the predator. 4. The maximum number of prey consumed depended on both body size and spine length. In the functional response analyses, the plateau was reached at a prey density of 4–8 ind. mL^?1. 5. There was a significant impact of prey density on the prey preference of the predator.     

Long Term Effect of Cyprinid Fishes on Phytoplankton and Zooplankton Communities in a Shallow Water Protection Reservoir

The effects of fish kill and different fish stocks on the phytoplankton and zooplankton dynamics were studied in a shallow hypertrophic reservoir system. When fish stock was below 100 kg ha⁻¹, nutrient availability was not the main limiting factor for growth of phytoplankton. Consequently top‐down forces controlled phytoplankton. In the years with high fish stock (>100 kg ha⁻¹) the bottom‐up forces dominated as nutrient availability was the main limiting factor for growth of phytoplankton. We can conclude that significant water quality improvement can be achieved in the reservoir system by decreasing fish stock below 100 kg ha⁻¹. Although clear‐water phase could be stabilised temporary by macrophytes, stabilisation of good water quality requires continuous regulation of fish community. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

气孔限制在植物叶片光合诱导中的作用

用三种不同的气体交换分析方法研究了玉米、大豆等叶片光合诱导期间的气孔限制作用。发现有利于气孔开放的因素如良好的土壤水分状况、较高的空气湿度等,能够缩短叶片的光合诱导期;CO_2饱和条件下,叶片的光合诱导期比在普通空气条件下的诱导期短得多;在光合诱导后期细胞间隙CO_2度达到稳态值以后,气孔导度的增加伴随着光合速率的提高和气孔限制值的下降。而气孔导度的降低则会引起光合速率的降低和气孔限制值的上升。诱导期存在气孔限制,并在后期占优势。     

Absence of Recruitment Limitation in Restored Dune Slacks Suggests That Manual Seed Introduction Can Be a Successful Practice for Restoring Orchid Populations

Answering the question whether or not to introduce seeds of target species in restored habitats depends on the relative importance of dispersal and recruitment limitation. Especially in orchid species, recruitment limitation is expected to be important because of their dependence on mycorrhiza for germination. Using a large seed introduction experiment we investigated the relative importance of dispersal versus recruitment limitation in the failure of three rare orchid species to colonize restored habitat patches. For all species, seeds developed successfully into protocorms in both occupied and unoccupied habitats, and no significant differences in the number of protocorms per seed packet were found between occupied and unoccupied habitats. These results show that orchid species do not necessarily suffer from recruitment limitation when introduced in restored habitats, and that manual introduction of orchid seeds can be a successful and necessary ecological restoration practice.