Predator dispersal determines the effect of connectivity on prey diversity

Linking local communities to a metacommunity can positively affect diversity by enabling immigration of dispersal-limited species and maintenance of sink populations. However, connectivity can also negatively affect diversity by allowing the spread of strong competitors or predators. In a microcosm experiment with five ciliate species as prey and a copepod as an efficient generalist predator, we analysed the effect of connectivity on prey species richness in metacommunities that were either unconnected, connected for the prey, or connected for both prey and predator. Presence and absence of predator dispersal was cross-classified with low and high connectivity. The effect of connectivity on local and regional richness strongly depended on whether corridors were open for the predator. Local richness was initially positively affected by connectivity through rescue of species from stochastic extinctions. With predator dispersal, however, this positive effect soon turned negative as the predator spread over the metacommunity. Regional richness was unaffected by connectivity when local communities were connected only for the prey, while predator dispersal resulted in a pronounced decrease of regional richness. The level of connectivity influenced the speed of richness decline, with regional species extinctions being delayed for one week in weakly connected metacommunities. While connectivity enabled rescue of prey species from stochastic extinctions, deterministic extinctions due to predation were not overcome through reimmigration from predator-free refuges. Prey reimmigrating into these sink habitats appeared to be directly converted into increased predator abundance. Connectivity thus had a positive effect on the predator, even when the predator was not dispersing itself. Our study illustrates that dispersal of a species with strong negative effects on other community members shapes the dispersal-diversity relationship. When connections enable the spread of a generalist predator, positive effects of connectivity on prey species richness are outweighed by regional extinctions through predation.     

Scale- and intensity-dependent disturbance determines the magnitude of opportunistic response

Opportunistic, fugitive or pioneer species are species that posses life-history characteristics that allow them to respond quickly to disturbances. Their abundance during the early stages of succession is central to ecological models of benthic soft-sediment succession and these species can play important roles in affecting subsequent successional trajectories. Nevertheless, numerous studies have demonstrated seemingly random patterns of opportunistic responses following disturbance, questioning the generality of currently accepted successional models. In this paper we provide examples from two case studies and argue that the spatial scale or magnitude of disturbance is key to the development of opportunistic responses, and that the scale of disturbance may be particularly important in determining (a) the levels of resources made available and (b) the magnitude of release from competitive interactions, which permit opportunists to flourish.     

Conspecific density determines the magnitude and character of predator-induced phenotype

The benefits in survival gained from predator-induced phenotypes often come at a cost to other components of fitness. Therefore, the level of expression of an induced phenotype should mirror the level of risk in the environment. When a predator exhibits a saturating functional response the risk of mortality to a given prey decreases as prey density increases. Therefore, for a given predator threat, investment in defense should be lower in prey at high density relative to those at low density. In this study, I test whether the magnitude of predator-induced morphological plasticity decreases with increasing conspecific density by exposing pine woods tree frog (Hyla femoralis) tadpoles at three different densities to predators (present or absent) in a factorial experiment. Tadpole morphology was not affected by changes in density in the absence of predators. However, predators had a significant, density-dependent effect on tadpole morphology. Specifically, the magnitude of morphological response was graded and larger for animals in the low density (high risk) environment. This study demonstrates that tadpoles can modulate phenotypic plasticity in response to mortality risk as a function of both the density of conspecifics and chemical cues from predators, which suggests that they are able to detect and respond to fine-scale changes in the threat environment. In addition, this study highlights the need for analytical approaches that allow morphological plasticity studies to elucidate allometric relationships in addition to simply quantifying size-corrected traits. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Previous agonistic experience determines both foraging behavior and territoriality in the limpet Lottia gigantea (Sowerby)

Lottia gigantea, the owl limpet, is an algal gardener. Territorial individuals actively defend gardens, which consist of clearedareas in the intertidal zone upon which a thick algal filmdevelops and upon which the territory holder feeds. Smaller,nonterritory holders raid these gardens and graze the algalfilm. Territorial individuals must obtain an adequate ration without compromising the productivity of the garden. In contrast,a nonterritory holder grazing on another limpet's territorymust obtain an adequate ration before it contacts the territoryholder and is driven off. In the laboratory, replicate setsof 10 limpets were trained to behave territorially and nonterritorially.Training mimicked natural encounters between territorial andnonterritorial L. gigantea. Limpets given territorial trainingleft significantly (t = -4.92, df = 9, p =.00041) more algalcover behind when grazing (on average 71%) than did limpetstrained to be nonterritorial (on average 50%). Territorial limpets seldom grazed over the same area more than once (4% of the grazedarea). In contrast, nonterritorial limpets frequently foragedover an area more than once; of the area grazed, 20% had beenvisited more than once. Previous agonistic experience determinesboth territorial behavior and foraging strategies, two of thecritical behaviors necessary for successful gardening behavior.Nonterritorial limpets maximize consumption per unit area, whereas territorial limpets appear to forage prudently, leaving a significantly greater proportion of the plant biomass behind.     

Analysis of environmental and species effects on the magnitude of biomass investment in the reproductive effort of annual pasture plants

Summary In annual pastures utilized for grazing, the amount and quality of the standing dry matter in the dry season is of importance for the performance of the animals. Often both characteristics decline at the end of the green season. It is shown, that dispersal of the reproductive structures of the vegetation may be the main reason for this phenomenon. Determination of the reproductive effort of the annuals indicates that the proportion of their total production invested in reproductive tissue may be as high as that of cultivated species. It is shown that the harvest index (or seed ratio) of annual species is closely related to nutrient (mainly nitrogen) transfer from vegetative organs to the reproductive organs in the period between flowering and maturity, when in most cases, additional uptake of nitrogen from the soil is negligible. The effect of environmental and genetic effects on these processes is discussed.Present address: Laboratory of Soils and Fertilizers, Agricultural University, P.O. Box 14, Wageningen, The Netherlands     

Growth in field and laboratory populations of Wood mice (Apodemus sylvaticus)

Intrinsic growth rate and asymptotic body weight parameters were estimated for two laboratory and three field populations of the Wood mouse, Apodemus sylvaticus , using a logistic model fitted by an ordinary least squares method. The data upon which the growth equations were based were differences in body weight for individual animals between sampling occasions. Suckling mice in one of the laboratory studies suffered high mortalities and poor body growth which was related to disturbance to the mothers and their young during examination. Growth in weaned mice appeared normal and was compared with growth in autumn and winter populations of wild mice with poor and good natural seed supplies. Males tended to have higher growth rates, and to a lesser extent, higher body weight asymptotes than females in all groups. Growth rates were highest in the autumn field population with a good seed supply; differences between the other groups were less marked. These results are discussed and it is suggested that, despite the approximations inherent in the method, the method will be a useful tool for studying the the productivity of wild populations of small mammals.     

Consumptive and non-consumptive effects of an invasive marine predator on native coral-reef herbivores

Invasive predators typically have larger effects on native prey populations than native predators, yet the potential roles of their consumptive versus non-consumptive effects (CEs vs. NCEs) in structuring invaded systems remains unclear. Invasive lionfish (Pterois volitans) may have ecosystem-level effects by altering native fish grazing on benthic algae that could otherwise displace corals. Lionfish could reduce grazing by decreasing the abundance of herbivorous fishes (CEs), and/or the predation risk posed by lionfish could alter grazing behavior of fishes (NCEs). To test for these CEs, we manipulated lionfish densities on large reefs in The Bahamas and surveyed fish populations throughout June 2009–2011. In July 2011, NCEs of lionfish were measured by observing fish grazing behavior on algal-covered substrata placed in microhabitats varying in lionfish presence at different spatial scales, and quantifying any resulting algal loss. Lionfish reduced small herbivorous fish density by the end of the 2010 summer recruitment season. Grazing by small and large fishes was reduced on high-lionfish-density reefs, and small fish grazing further decreased when in the immediate presence of lionfish within-reefs. Lionfish had a negative indirect effect on algal loss, with 66–80 % less algae removed from substrata in high-lionfish-density reefs. Parrotfishes were likely driving the response of herbivorous fishes to both CEs and NCEs of lionfish. These results demonstrate the importance of considering NCEs in addition to CEs of invasive predators when assessing the effects of invasions.     

Ranking the magnitude of crop and farming system effects on soil microbial biomass and genetic structure of bacterial communities

Biological soil characteristics such as microbial biomass, community structures, activities, and functions may provide important information on environmental and anthropogenic influences on agricultural soils. Diagnostic tools and detailed statistical approaches need to be developed for a reliable evaluation of these parameters, in order to allow classification and quantification of the magnitude of such effects. The DOK long-term agricultural field experiment was initiated in 1978 in Switzerland for the evaluation of organic and conventional farming practices. It includes three representative Swiss farming systems with biodynamic, bio-organic and conventional fertilization and plant protection schemes along with minerally fertilized and unfertilized controls. Effects on microbial soil characteristics induced by the long-term management at two different stages in the crop rotation, i.e. winter wheat after potato or corn, were investigated by analyzing soil bacterial community structures using analysis of PCR-amplified rRNA genes by terminal restriction fragment length polymorphism and ribosomal intergenic spacer analysis. Application of farmyard manure consistently revealed the strongest influence on bacterial community structures and biomass contents. Effects of management and plant protection regimes occurred on an intermediate level, while the two stages in the crop rotation had a marginal influence that was not significant.     

Partitioning the non-consumptive effects of predators on prey with complex life histories

Non-consumptive effects (NCEs) of predators on prey can be as strong as consumptive effects (CEs) and may be driven by numerous mechanisms, including predator characteristics. Previous work has highlighted the importance of predator characteristics in predicting NCEs, but has not addressed how complex life histories of prey could mediate predator NCEs. We conducted a meta-analysis to compare the effects of predator gape limitation (gape limited or not) and hunting mode (active or sit-and-pursue) on the activity, larval period, and size at metamorphosis of larval aquatic amphibians and invertebrates. Larval prey tended to reduce their activity and require more time to reach metamorphosis in the presence of all predator functional groups, but the responses did not differ from zero. Prey metamorphosed at smaller size in response to non-gape-limited, active predators, but counter to expectations, prey metamorphosed larger when confronted by non-gape-limited, sit-and-pursue predators. These results indicate NCEs on larval prey life history can be strongly influenced by predator functional characteristics. More broadly, our results suggest that understanding predator NCEs would benefit from greater consideration of how prey life history attributes mediate population and community-level outcomes.     

Performance of marking techniques in the field and laboratory for Diabrotica speciosa (Germar) (Coleoptera: Chrysomelidae)

A reliable marking technique was needed for a mark–release–recapture experiment with adults of Diabrotica speciosa (Germar). Four marking techniques, acrylic paint (spattered or brushed on the surface of the insect); and fluorescent pigments (dusted on surfaces or mixed with diet to produce an ingested marker), were tested. Fluorescent pigment durability for the dusting and ingested techniques was evaluated for laboratory conditions and under simulated field conditions. The impact of the techniques on beetle survival was also assessed. Both acrylic paint techniques caused mobility problems in the beetles, and neither technique lasted for more than 48 h. Both fluorescent pigment techniques were more reliable, but the dusting technique showed a significantly higher mortality than the control, and duration variations between laboratory and field conditions. Use of fluorescent pigments added to the diet was the most reliable technique. This technique allowed the manipulation of the marking period, and provided reliable timing of marker persistence in the field.     

Temperature response and flowering of white clover (Trifolium repens) varieties in controlled environments and the field

Floral initiation of 10 white clover varieties growing in three controlled day/night temperature regimes, 22“/10°C, 20°/10°C, 17°/10°C, was recorded. Effects of artificial soil heating on floral initiation of the same plants subsequently transferred to the field were also examined. In the controlled environments only a slight increase in day temperature (2–5°C) was necessary to significantly increase flowering. Defoliation at the three temperatures had contrasting effects on subsequent flower production. Results from the soil heating experiment suggested that increased temperature might compensate for short daylengths, by bringing forward reproductive bud initiation by 1 month. Soil heating increased the total number of inflorescences produced.     

Analogous effects of arbuscular mycorrhizal fungi in the laboratory and a North Carolina field

Although arbuscular mycorrhizal (AM) fungi are ubiquitous symbionts of plants, the mutualism has rarely been tested in nature. In experiments designed to explore the ecological relevance of associations between different fungal and plant species in a natural environment, plant species were infected with different species of fungi and grown in separate trials in the laboratory and a North Carolina (USA) field. The benefits to plants varied dramatically as plant species were grown with different species of AM fungi. Effects of mycorrhizal fungi in nature were generally correlated to effects in the growth chamber, suggesting that laboratory data do reflect dynamics between plants and AM fungi in the field. Initial size at transplant and experimental block were also significant predictors of plant growth in the field. Correlation statistics between laboratory and field data were weaker when analyses involved plant species less responsive to infection by any AM fungus, suggesting that the response of a species to inoculation is a good predictor of its sensitivity to specific AM fungi in the field. AM fungal identity appears to influence the growth and reproduction of plants in the field.     

椰甲截脉姬小蜂野外种群与实验种群差异性比较

通过随机抽样,比较了椰甲截脉姬小蜂Asecodes hispinarum Bou(c)ek林间种群与室内种群的雌雄比、出蜂量、未出蜂量、怀卵量的差异.t检验表明这些参数在2个种群间均存在显著的差异.野外种群和室内种群雌蜂比例分别占81.63%±2.54%和65.34%±1.80%,出蜂量分别是(25.13±1.17)头...     

The response of the tidepool sculpin, Oligocottus maculosus, to hypoxia in laboratory, mesocosm and field environments

Animals living in the intertidal zone experience regular, predictable fluctuations in physical parameters including temperature, oxygen and salinity and rely on behavioural, physiological and biochemical mechanisms to cope with environmental variation. In the present study, behavioural strategies induced by aquatic hypoxia (e.g. emergence) were performed at similar oxygen tensions across laboratory, mesocosm and field environments; the number of individuals performing these behaviours at any one time was similar in mesocosms and the field. The use of aquatic surface respiration (ASR) was more plastic than emergence behaviour, occurring at a lower oxygen tension in juveniles than adults and being influenced by the addition of alarm substance. Oxygen uptake was lower in air than in water in adults but, in contrast, oxygen uptake was not influenced by the respiratory medium in juveniles. In the laboratory, 72 h of forced emergence did not affect whole body concentrations of lactate but when ASR and emergence were prevented within mesocosm environments there was a significant elevation of lactate. The present study highlights the benefits of transcending traditional laboratory/field boundaries allowing the responses of laboratory-held animals to environmental fluctuation to be integrated with how these animals perform in their natural environment.     

A field and laboratory study of the parasites of the triclad Phagocata vitta (Duges)

SUMMARY. 1. Over 13 months, fifty Phagocata vitta were collected from a smalt tributary of the Afon Anafon (Wales) and the occurrence of the ciliate Tetrahymena pyriformis and an unnamed nematode studied.
2. During the study, prevalence ranged from 5% to 22% and mean intensity from two to twenty-nine ciliates per infected triclad, whilst relative density never exceeded three per triclad. There was a trend for these values to be highest in summer and lowest in winter, but a significant positive correlation with field temperature was only found for mean intensity. The mean values of mean intensity and relative density were not significantly correlated with triclad size.
3. For the nematode, prevalence varied from 2% to 6% and relative density from 0.02 to 0.08 individuals per triclad, whilst mean intensity remained about one per infected triclad. No significant correlations between seasonal fluctuations of any of these values and field temperature were obtained.
4. In laboratory experiments lasting 5 weeks, triclads which had been initially fed tubificid worms infected with T. pyriformis and kept in uninfected water had much higher prevalence and mean intensity values than triclads fed uninfected tubiticids and kept in infected water. The main source of infection by the ciliate in the field seems likely to be through the ingestion of infected food. In infected triclads cultured at either 5, 10, 15 or 20°C, prevalence, mean intensity and relative density values increased with rising temperatures, whilst mortality was negligible at the two lowest temperatures and substantial at the two highest. Laboratory findings are related to field events.
5. It is concluded that the ciliate and nematode parasites may not cause significant mortality in the fieid population of P. vitta .     

Feeding responses of Asplanchna brightwelli (rotifera): laboratory and field studies

Laboratory-reared A. brightwelli were offered 16 different prey rotifer species from the genera Anuraeopsis, Brachionus, Epiphanes, Filinia, Hexarthra, Lecane, Lepadella, Pompholyx, Proalides and Trichocerca. Feeding responses (prey encounter, escape, capture, rejection and ingestion) were recorded. In general, the predator's ingestion time was positively correlated with prey length. B. falcatus and H. intermedia were never captured. Once captured, smaller rotifer species were ingested. Gut contents of field-collected A. brightwelli revealed increased occurrence of prey numbers when concentrated plankton samples were preserved after some delay.     

Variation between field and laboratory populations of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae)

Rates of development and pupal weights were compared between seven field populations and two laboratory strains of Tribolium castaneum. Rates of development did not differ significantly between field populations, but pupal weights did vary. Laboratory strains were both slower to develop and heavier than the field populations. The data support the hypothesis that field populations undergo selection for fast development in transient habitats. The findings are discussed in the context of r and K selection in field populations and laboratory cultures.     

Effect of herbivory on growth and biomass allocation of Brazilian peppertree (Sapindales: Anacardiaceae) seedlings in the laboratory

Brazilian peppertree (Schinus terebinthifolius Raddi), native to South America, is invading many ecosystems in south and central Florida. The defoliating tortricid moth Episimus unguiculus Clarke was selected as a potential biocontrol agent of Brazilian peppertree in Florida. The objective of this study was to examine the effect of different levels of herbivore damage on growth and biomass allocation of Brazilian peppertree seedlings in the laboratory. Three treatments were established: (1) no herbivory (control), (2) low herbivory (~4 larvae/plant), and (3) high herbivory (~12 larvae/plant). High levels of herbivory significantly reduced the number of leaflets, plant height, foliar biomass, foliar relative growth rate (RGR) and shoot: root ratio of Brazilian peppertree seedlings. Moreover, plants were not able to recover from herbivory after 2 months. The performance of Brazilian peppertree subjected to low herbivory levels did not differ from the control plants (no herbivory). The potential effectiveness of the biocontrol agent E. unguiculus to suppress this noxious weed is examined.