Ecology of a tidal marsh corixid,Trichocorixa verticalis (Insecta,Hemiptera)

The high marsh panne ecosystem at Adam's Point, N. H. provides a particular opportunity for holistic, yet autecological approach to the natural history of Trichocorixa verticalis var. sellaris (Corixidae). This area was dominated by physical and chemical factors associated with highly variable salinities (1 to 160) and temperatures (–1 to 40°C) caused by irregular tidal flooding and neap tidal dry periods. Trichocorixa verticalis reach a maximum density of 26,914/m² (x = 3,909.6/m²) in open shallow pannes, where eggs hatch in staggered sequence, allowing population replenishment after drought and reflooding. Winter eggs hatched between salinities of 0 to 30 at 20°C and 0 to 20 at 10°C. Summer eggs hatched between salinities of 0 to 55 at variable temperatures (20 to 36°C). All instars showed a similar higher summer and lower fall tolerance; immatures were more tolerant than adults. Body molt measurements of the 6 instars are given here.Aside from being herbivores and detritivores, T, verticalis feed on chironomid larvae and oligochaetes. They are food for invertebrates and vertebrates, and provide substantial food for migratory shorebirds.The experimental work was based on a thesis submitted to the Graduate School of the University of New Hampshire in partial fulfillment of the requirements for the degree of Doctor of Philosophy.     

The life cycle of Trichocorixa verticalis interiores Sailer (Hemiptera, Corixidae) with special reference to diapause

SUMMARY. The life cycle of Trichocorixa verticalis interiores was studied in six Saskatchewan saline lakes. A detailed study of the timing of the stages in the life cycle showed that T. v. interiores has a life cycle which differs from that of all other Corixidae. This species overwinters solely in the egg stage. Females oviposit in the late summer and all adults die in the fall. The eggs, which remain in a pre-blastokinesis stage of embryonic development until the following spring, are prevented from developing in late summer by diapause which lasts approximately 2 months. Although diapause terminates in October, embryonic development does not occur in cold water during the winter months. Experimental results indicate that exposure to cold is not necessary to break diapause.     

Spatially varying density dependence drives a shifting mosaic of survival in a recovering apex predator (Canis lupus)

Understanding landscape patterns in mortality risk is crucial for promoting recovery of threatened and endangered species. Humans affect mortality risk in large carnivores such as wolves (Canis lupus), but spatiotemporally varying density dependence can significantly influence the landscape of survival. This potentially occurs when density varies spatially and risk is unevenly distributed. We quantified spatiotemporal sources of variation in survival rates of gray wolves (C. lupus) during a 21‐year period of population recovery in the Upper Peninsula of Michigan, USA. We focused on mapping risk across time using Cox Proportional Hazards (CPH) models with time‐dependent covariates, thus exploring a shifting mosaic of survival. Extended CPH models and time‐dependent covariates revealed influences of seasonality, density dependence and experience, as well as individual‐level factors and landscape predictors of risk. We used results to predict the shifting landscape of risk at the beginning, middle, and end of the wolf recovery time series. Survival rates varied spatially and declined over time. Long‐term change was density‐dependent, with landscape predictors such as agricultural land cover and edge densities contributing negatively to survival. Survival also varied seasonally and depended on individual experience, sex, and resident versus transient status. The shifting landscape of survival suggested that increasing density contributed to greater potential for human conflict and wolf mortality risk. Long‐term spatial variation in key population vital rates is largely unquantified in many threatened, endangered, and recovering species. Variation in risk may indicate potential for source‐sink population dynamics, especially where individuals preemptively occupy suitable territories, which forces new individuals into riskier habitat types as density increases. We encourage managers to explore relationships between adult survival and localized changes in population density. Density‐dependent risk maps can identify increasing conflict areas or potential habitat sinks which may persist due to high recruitment in adjacent habitats.     

Life tables of Moina macrocopa (Straus) in successive generations under food and temperature adaptation

Life tables of Moina macrocopa (Straus) cultured at seven foodconcentrations (FC) (Scenedesmus sp., 1.49–1490 mg wet weightl^-1, 10⁴–10⁶ cellml^-1) were investigated for animals of the first generation(nonadapted animals) and for animals of the third generation (adaptedanimals) cultivated at these FC. Adapted animals showed a trophicpreferendum, i.e. a narrow FC-range at which maximal R_ovalues were observed in comparison with nonadapted animals. In adaptedanimals, the maximal R_o was 115.3 individual, observed at 20°C and a FC of 74.5 mg wet weight l^-1.     

Prey kills predator: Counter-attack success of a spider mite against its specific phytoseiid predator

Success of counter-attack by the spider mite,Schizotetranychus celarius (Banks), against its specific phytoseiid predator,Typhlodromus bambusae Ehara, was examined under experimental conditions. The success of counter-attack by prey females (mothers) against a predaceous larva depended upon the former's density per nest. About 30% of the predaceous larvae were killed when they intruded into a nest containing eight females and their offspring. On the other hand, the prey males (fathers) effectively killed the predators, i.e. one male in the nest killed ca. 40% of the predators while two or three males destroyed up to 80%.The presence of prey parents in a nest considerably enhanced the success of the counter-attack. One male and two young females could kill 70% of the predator's larvae, while two males and two females killed 90% of such larvae. This suggests a kind of cooperative brood defence amongstS. celarius parents.Although more robust, protonymphs of the predator also suffered damage by the prey's counter-attack. However, prey male and female could not destroy the predator's eggs and adult females, whilst the latter often killed spider mite adults.From these as well as previous experiments, it is concluded thatS. celarius has evolved some kind of biparental care for its offspring. It is further proposed that the predator—prey interactions observed in this study provide a unique contribution towards understanding predator—prey coevolution.     

Combined effects of food level and inoculation density on competition between Brachionus patulus (Rotifera) and the cladocerans Ceriodaphnia dubia and Moina macrocopa

Competition among cladocerans and rotifers is of considerable interest not only due to their close similarity in life history strategies, but also due to the considerable overlap they exhibit in their feeding habits. In tropical waterbodies, several genera of cladocerans, including Ceriodaphnia and Moina occur, simultaneously with rotifers. We tested over a period of 3 weeks the combined effects of food (0.5×10⁶ and 1.5×10⁶ cells ml^–1 of Chlorella) level and rotifer density on the competition between B. patulus and C. dubia and M. macrocopa using population growth experiments. For each cladoceran species we used 30 test jars of 50 ml capacity. The initial density of cladocerans was 0.2 ind ml^–1, while for B. patulus it was either 1 ind ml^–1 or 5 ind ml^–1. Neither the maximal population density nor the rate of population increase (r) of C. dubia was significantly affected by B. patulus. However, for M. macrocopa, both these variables were negatively affected by the rotifers. The combined effects of low food level and high initial density of B. patulus resulted in a 50% reduction in the peak population density of M. macrocopa. The population growth of B. patulus was negatively influenced by the presence of C. dubia and M. macrocopa. The results of the competition experiments conducted in the present study between cladocerans and rotifers suggest the existence of a more complex and delicate interaction than is generally thought.     

Predatory and toxic effects of the turbellarian (Stenostomum cf leucops) on the population dynamics of Euchlanis dilatata,Plationus patulus (Rotifera) and Moina macrocopa (Cladocera)

Catenulid turbellarians, common in shallow, tropical ponds, affect their rotifer prey via the production of toxins. There is, however, no quantitative information on their effect on the demography of their prey. Here, we test the impact of Stenostomum cf leucops on the population dynamics of the rotifers Euchlanis dilatata and Plationus patulus, and the cladoceran Moina macrocopa. Experiments were initiated with rotifers at 0.5 ind. ml⁻¹ and the cladoceran at 0.2 ind. ml⁻¹; growth patterns were compared in the absence and presence of worms (2 Stenostomum ind. per 50 ml). Results revealed that brachionids were most adversely affected: there was a lower growth rate of the rotifers in the presence of worms (P < 0.01, repeated measures ANOVA), although at the densities applied, the predator did not wipe out its prey. These littoral predators may therefore regulate rotifer prey in natural conditions. In Moina, the population evolved differently; initially, we found no difference between control and treatment, but after about 10 days, the population collapsed, irrespective of a direct or indirect contact with the predator. This delayed effect deserves more study, as it could represent flatworm toxin accumulation by the cladoceran.     

Climate and density shape population dynamics of a marine top predator

Long-term studies have documented that climate fluctuations affect the dynamics of populations, but the relative influence of stochastic and density-dependent processes is still poorly understood and debated. Most studies have been conducted on terrestrial systems, and lacking are studies on marine systems explicitly integrating the fact that most populations live in seasonal environments and respond to regular or systematic environmental changes. We separated winter from summer mortality in a seabird population, the blue petrel Halobaena caerulea, in the southern Indian Ocean where the El Niño/Southern Oscillation effects occur with a 3-4-year lag. Seventy per cent of the mortality occurred in winter and was linked to climatic factors, being lower during anomalous warm events. The strength of density dependence was affected by climate, with population crashes occurring when poor conditions occurred at high densities. We found that an exceptionally long-lasting warming caused a ca. 40% decline of the population, suggesting that chronic climate change will strongly affect this top predator. These findings demonstrate that populations in marine systems are particularly susceptible to climate variation through complex interactions between seasonal mortality and density-dependent effects.     

Changes in the behaviour of Moina macrocopa (Crustacea: Cladocera) under the influence of Gurleya sp. (Microsporidia: Gurleyidae)

It is established, that infestation with Gurleya sp. (Microsporidia, Gurleyidae) changes the behaviour of its host Moina macrocopa (Straus, 1820), a crustacean inhabiting pools. Heavily infested host individuals attach to surface film of water before their death by senescence. As a consequence, their dead bodies filled with spores of the parasite adhere to objects dipped in water that probably facilitates the transfer of spores by birds and cattle to other pools. Weakly infested or uninfested individuals drown after the end of their ontogenesis. Distribution of the microsporidian spores by two different ways (with attached dead bodies of the hosts or with bottom sediments) makes invasion of a new host more probable.     

The infection of Moina macrocopa by a colonial peritrich, Epistylis daphniae, and its effects on the host

• 1 The effects of infection by Epistylis daphniae on its host, Moina macrocopa, were studied in the laboratory at 28°C by comparing the growth, reproduction and survival between infected and uninfected hosts.
• 2 Infestation by epizoites had little or no effect on the survival of the dadoceran hosts when adequate food was present.
• 3 The infected cladocerans had lower growth rates as juveniles, lower net reproduction rates as adults, and smaller body size at death than uninfected hosts.
• 4 The index of infection at different stages in the life cycle was related to the durations of intermoult period. Ranked in order of both index of infection and intermoult duration, the development stages were: old adult > young adult > juvenile.

     

Prey choice by facultative predator larvae of Chrysomya albiceps (Diptera: Calliphoridae)

In this study we investigated predation rates on third instar larvae of Chrysomya putoria and C. megacephala by third instar larvae of C. albiceps in a two-choice situation. The highest predation rate occurred on C. putoria larvae and this result is compared to previous experiments, in which C. macellaria larvae were present. Our results suggest that, when C. macellaria is absent C. albiceps larvae attack more C. putoria than C. megacephala larvae. Prey choice decisions and its implications for introduced and native blowflies are discussed.     

温度和盐度对蒙古裸腹Sou种群内禀增长能力的影响

报道了蒙古裸腹Sou(Moina mongolica)在20℃-33℃温度和5－40ppt盐度条件下和种群内禀增长率（rm),结果表明,20℃-30℃范围内蒙古裸腹Sourm随温度升高,超过30℃后继续升高,rm显著降低,在低盐度下蒙古裸腹Sou的种群增长能力相对较强,盐度为10ppt时rm最高,20－40ppt范围内Sou的rm差别不明显,本实验表明,25℃-30℃和10ppt分别是蒙古裸腹Sou种群增长较快的温度和盐度条件,在海水中长期培养对蒙古裸腹Sou的种群增长能力不会产生明显的不良影响。     

The artificial infection of the cladoceran Moina macrocopa (Crustacea: Phyllopoda) with the microsporidia Gurleya sp. (Microsporidia: Gurleyidae)

Microcrustaceans Moina macrocopa (Straus, 1820) have been collected in a small vernal pond and cultured under laboratory conditions. The infection of this culture with the microsporidia Gurleya sp. was detected and high virulence of this microsporidian species allowed us to carry out the transmission experiments. Horizontal transmission, the high host specificity and maximal spore production in the hypodermal and fat body cells through 5-6 days after per oral experimental infection have been revealed. Histological investigations demonstrated that Gurleya sp. reduces drastically host reproductive success without a considerable influence on the microcrustaceans' mortality.     

Cadmium uptake and oxidative-stress-induced DNA alterations in the freshwater cladoceran Moina macrocopa (Straus 1820) following consecutive short-term exposure assessments

Limnology - Moina macrocopa is a toxicologically less explored, yet widely distributed freshwater cladoceran found worldwide. The present study is aimed at determining the cadmium (Cd) uptake and...     

温度和盐度对蒙古裸腹氵蚤种群内禀增长能力的影响

报道了蒙古裸腹氵蚤 (Moinamongolica)在 2 0℃～ 33℃温度和 5～ 40 ppt盐度条件下的种群内禀增长率(rm) .结果表明 ,2 0℃～ 30℃范围内蒙古裸腹氵蚤rm 随温度升高而升高 ,超过 30℃后继续升温 ,rm 显著降低 ;在低盐度下蒙古裸腹氵蚤的种群增长能力相对较强 ,盐度为 10 ppt时rm 最高 ,2 0～ 40 ppt范围内 氵蚤的rm 差别不明显 .本实验表明 ,2 5℃～ 30℃和 10 ppt分别是蒙古裸腹 氵蚤种群增长较快的温度和盐度条件 ,在海水中长期培养对蒙古裸腹氵蚤的种群增长能力不会产生明显的不良影响     

Prey: predator ratio dependence in the functional response of a freshwater amphipod

1. First known for their shredding activity, freshwater amphipods also behave as active predators with consequences for prey population regulation and amphipod coexistence in the context of biological invasions. 2. A way to quantify predation is to determine the average consumption rate per predator, also known as its functional response (FR). 3. Although amphipods are gregarious and can display social interactions that can alter per capita consumption rates, previous studies using the FR approach to investigate amphipod predation ignored such potential mutual interference because they did not consider variations in predator density. 4. We investigated the FR of Echinogammarus berilloni feeding on dipteran larvae with joint variations in prey and predator densities. This bivariate experimental design allowed us to estimate interference and to compare the fits of the three main classes of theoretical FR models, in which the predation rate is a function of prey density alone (prey‐dependent models), of both prey and predator densities (predator‐dependent models) or of the prey‐to‐predator ratio (ratio‐dependent models). 5. The Arditi–Ginzburg ratio‐dependent FR model provided the best representation of the FR of E. berilloni, whose predation rate showed a decelerating rise to a horizontal asymptote as prey abundance increased. 6. Ratio dependence means that mutual interference between amphipods leads to prey sharing. Mutual interference is likely to vary between amphipod species, depending on their level of aggressiveness.     

Prey naivety in the behavioural responses of juvenile Chinook salmon (Oncorhynchus tshawytscha) to an invasive predator

1. Non‐native predators might inflict proportionally higher mortality on prey that have no previous experience of them, compared to species that have coexisted with the predator for some time. 2. We tested whether juvenile Chinook salmon (Oncorhynchus tshawytscha) were less able to recognise a non‐native than a native predator, by investigating behavioural responses to the chemical cues of the invasive smallmouth bass (Micropterus dolomieu) and the native northern pikeminnow (Ptychocheilus oregonensis) in both laboratory and field experiments. 3. Laboratory results demonstrated strong innate antipredator responses of individual juvenile Chinook salmon to northern pikeminnow; fish spent 70% of time motionless and exhibited 100% greater panic response than in controls. By contrast, antipredator responses to the chemical cues of smallmouth bass did not differ from controls. 4. These results were supported by similar differences in recognition of these predator odours by groups of juvenile Chinook salmon in fully natural conditions, though responses reflected a greater range of antipredator behaviours by individuals. In field trials, responses to northern pikeminnow odour resulted in increased flight or absence, reductions in swimming and foraging, and increased time spent near the substratum, compared to smallmouth bass odour. 5. Given that survival of juvenile fish is facilitated by predator recognition, our results support the hypothesis that naivety may be an important factor determining the effect of non‐native predators on prey populations. Efforts to manage the effect of native and non‐native predators may benefit by considering complex behavioural interactions, such as these at the individual and group levels.     

Effect of population density and feeding rate on the fathead minnow (Pimephales promelas)

Juvenile fathead minnows ( Pimephales promelas ) were stocked in tanks at different densities and different ration levels, in two experiments, to determine effects on final population density, growth and fecundity. Length and weight of fish increased with increased food availability. Egg size was exponentially related to growth and perhaps directly to ration level. High population density appeared to limit growth and gamete development regardless of food abundance. Additionally, water volume appeared to limit numbers (tolerance density) of fish which can be supported in a specific volume of water.     

Prey or predator: 0+ perch (Perca fluviatilis) in the trade-off between food and shelter

The 0+ cohort of perch can split into a slow-growing planktivorous and a fast-growing piscivorous cohort during their first months of life. Both cohorts are, however, vulnerable to predation by piscivorous fish. Laboratory experiments were performed to test the behavior of 0+ perch as a predator of cyprinids, and in the trade-off between food and shelter from the threat of predators. In the foraging trials, 0+ perch attacked bream faster than they did carp, and vegetation hampered the aggression against bream. In the second experiment, the habitat selection of two size classes of 0+ perch under the threat of predation was monitored. Overall, vegetation structures were preferred by both size classes of 0+ perch. When small fish were offered to the 0+ perch as food, the open water becomes more attractive. The results of the habitat use trials further show that the two size cohorts of 0+ perch may also differ in their behavior, in that the availability of fish as food becomes more important than the shelter of vegetation structures for the larger perch.