Spatial Distribution Of Organisms Research Articles

Artificial light at night bans Chaoborus from vital epilimnetic waters

Artificial light at night (ALAN) is known to affect organisms in terrestrial ecosystems and adjacent litoral habitats. In the present study, we tested the effect of ALAN on the spatial distribution of organisms in open waters, using the insect larvae of Chaoborus flavicans as an example. During the day C. flavicans typically hide from visually hunting fish in deep, dark, anoxic waters. On safer nights, they forage in rich subsurface waters. Nighttime field tests revealed that light from an HPS street lamp mounted on a boat anchored in open water attracted planktivorous fish, but deterred planktonic Chaoborus from rich but risky surface waters. Chaoborus did not descend to the safest, anoxic hypolimnion, but remained in hypoxic mid-depth metalimnion, which does not appear to be a perfect refuge. Neither light gradient nor food distribution fully explained their mid-depth residence under ALAN conditions. A further laboratory test revealed a limited tolerance of C. flavicans to anoxia. Half of the test larvae died after 38 h at 9 °C in anoxic conditions. The trade-off between predation risk and oxygen demand may explain why Chaoborus did not hide in deep anoxic waters, but remained in the riskier metalimnion with residual oxygen under ALAN conditions.

Advancing bioenergetics-based modeling to improve climate change projections of marine ecosystems

Climate change has rapidly altered marine ecosystems and is expected to continue to push systems and species beyond historical baselines into novel conditions. Projecting responses of organisms and populations to these novel environmental conditions often requires extrapolations beyond observed conditions, challenging the predictive limits of statistical modeling capabilities. Bioenergetics modeling provides the mechanistic basis for projecting climate change effects on marine living resources in novel conditions, has a long history of development, and has been applied widely to fish and other taxa. We provide our perspective on 4 opportunities that will advance the ability of bioenergetics-based models to depict changes in the productivity and distribution of fishes and other marine organisms, leading to more robust projections of climate impacts. These are (1) improved depiction of bioenergetics processes to derive realistic individual-level response(s) to complex changes in environmental conditions, (2) innovations in scaling individual-level bioenergetics to project responses at the population and food web levels, (3) more realistic coupling between spatial dynamics and bioenergetics to better represent the local- to regional-scale differences in the effects of climate change on the spatial distributions of organisms, and (4) innovations in model validation to ensure that the next generation of bioenergetics-based models can be used with known and sufficient confidence. Our focus on specific opportunities will enable critical advancements in bioenergetics modeling and position the modeling community to make more accurate and robust projections of the effects of climate change on individuals, populations, food webs, and ecosystems.

Weathering the hunt: The role of barometric pressure in predator insects' foraging behaviour.

Abiotic factors strongly influence ecological interactions and the spatial distribution of organisms. Despite the essential role of barometric pressure, its influence on insect behaviour remains poorly understood, particularly in predators. The effect of barometric pressure variation can significantly impact biological control programs involving entomophagous insects, as they must efficiently allocate time and energy to search for prey in challenging environments. We investigated how predatory insects from different taxonomic groups (Coleoptera, Dermaptera and Neuroptera) adapt their foraging behaviour in response to variations in barometric pressure (low, medium and high). We also examined the response of different life stages to changes in pressure regimes during foraging activities. Our results showed that the searching time of Doru luteipes (Dermaptera: Forficulidae) was faster in a favourable high-pressure regime, whereas Chrysoperla externa (Neuroptera: Chrysopidae) and Eriopis connexa (Coleoptera: Coccinellidae) had similar searching times under varying pressure regimes. Although no differences in prey feeding time were observed among the studied species, the consumption rate was influenced by low barometric pressure leading to a decrease in the number of preyed eggs. Moreover, we provide novel insights into how hemimetabolous (D. luteipes) and holometabolous (E. connexa) species at different life stages respond to barometric pressure. Doru luteipes nymphs and adults had similar consumption rates across all pressure regimes tested, whereas E. connexa larvae consumed fewer eggs under low barometric pressure, but adults were unaffected. This highlights the importance of investigating how abiotic factors affect insects foraging efficiency and predator-prey interactions. Such studies are especially relevant in the current context of climate change, as even subtle changes in abiotic factors can have strong effects on insect behaviour. Barometric pressure is a key meteorological variable that serve as a warning signal for insects to seek shelter and avoid exposure to weather events that could potentially increase their mortality. Understanding the effects of barometric pressure on predatory insects' behaviour can help us develop more effective pest management strategies and promote the resilience of agroecosystems. We provide new insights into the complex relationship between barometric pressure and predator-prey interactions.

Target density estimation of mesopelagic fish using a towed, broadband, split-beam, acoustic scattering system

The ocean mesopelagic zone (200–1000 m) features a complex temporal and spatial distribution of organisms which may play an important role in ocean biogeochemical cycles. Yet a quantitative account of the abundance, biomass and migration behaviors of mesopelagic inhabitants is still lacking. Shipboard echosounders are limited by acoustic attenuation at higher frequencies constraining the usable frequency band for investigating deep sound scattering layers, as well as large acoustic sampling volumes, a result of the large depths associated with the deep scattering layers, combined with the inherent complexity of mesopelagic communities. Deep-See, a towed platform carrying multiple broadband sonars, focuses on individual targets in the deep scattering layers, to help interpret shipboard data. Target density estimation is the first step towards determining biomass in the mesopelagic zone. Two methods are investigated and applied to a summer 2019 dataset collected using two broadband split-beam echosounders (5.5–18.5 kHz, 18–47 kHz) on Deep-See in the slope waters off the New England Continental Shelf. The echo-counting method utilizes echo magnitude and phase information to determine singe targets while echo-statistics involves comparison of data to a physics-based numerical simulation to predict the statistics of broadband echoes from which target density can be extracted.

Ecological niche modeling of the pantropical orchid Polystachya concreta (Orchidaceae) and its response to climate change

Climate is the dominant control factor on the spatial distribution of organisms on a global scale and global warming is predicted to become a major cause of species extinctions. In our study ecological niche modeling (ENM) was used to estimate the effect of projected future climate changes on the pantropical orchid Polystacha concreta as well as to reconstruct changes in the distribution of the suitable climatic niches of this species since the Last Glacial Maximum (LGM). The study revealed small differences in the niches occupied by populations of P. concreta recorded in various continents; however, these alterations will become more significant in regard to future climatic change. While losses of suitable habitats of the studied orchid will occur in the Americas and Africa, global warming will be favorable for Asian populations. Our study suggests a significant loss of niches since the LGM which indicates that the currently observed loss of habitats is not only the result of human activity but also of natural changes of the Earth’s climate. From the obtained models we identified the areas that will be the most resistant regarding the modifications caused by climate change.

IMPLICACIONES ECOLÓGICAS DE LA EVASIÓN COMO RESPUESTA A LA CONTAMINACIÓN: UN ANÁLISIS CRÍTICO CON EL COBRE

Los estudios de evasión espacial en sistemas multicompartimentado han demostrado la habilidad de algunos organismos para detectar la contaminación y huir hacia zonas menos contaminadas. Esta respuesta previene efectos adversos a nivel individual, aunque lleva a una pérdida local de especies, lo que podría provocar problemas a nivel ecosistémico. La evasión es estudiada mediante sistemas de ensayos con una exposición que simula un gradiente de contaminación y permite que los organismos elijan las zonas más favorables. Debido a que hay pocos estudios en comparación con las respuestas ecotoxicológicas tradicionales, es crucial saber cuán sensible es la respuesta de evasión frente a las demás respuestas ampliamente usadas. El presente trabajo se centró en comparar la sensibilidad de la evasión espacial con las respuestas ecotoxicológicas tradicionales mediante tres herramientas: representación del perfil de sensibilidad por grupos biológicos, creación de la distribución de las especies en función de la sensibilidad y finalmente calculándose la concentración de riesgo a 5% de las especies. El estudio ofrece una visión de la sensibilidad de la respuesta de evasión para especies de agua dulce y marinas como una señal del potencial riesgo asociado a la contaminación y discute la relevancia ecológica de dicha respuesta. Se ha observado que la evasión es una respuesta muy sensible al ser comparada con otras respuestas ecotoxicológicas y se constata la importancia de incluir dicha respuesta para evaluar los riesgos ecológicos de los contaminantes sobre la dispersión de los organismos. Palabras clave: evasión espacial; sistema multicompartimentado; exposición no forzada; cobre; HC5, SSD.

English

Coastal ecosystems are increasingly impacted by man-made disturbances including pollution from agriculture, aquaculture and municipal waste. This study employed multiple ecological indicators to assess environmental quality of the Densu Estuary and understanding of environmental controls on the spatial distribution of organisms. Physicochemical parameters were measured in situ. Water and sediment samples were collected from ten stations and analysed for nutrients, total suspended solids and organisms using standard methods. The water quality index for the Densu Estuary ranged from 359.5 to 484.4, suggesting an unhealthy ecosystem. The abundance of indicator species, e.g. faecal bacteria (Escherichia coli, Enterococcus species) and polychaetes (Capitella and Nereis species) varied significantly (p<0.05) among stations. Contaminated sites are located landwards with high human impacts. Faecal bacteria and polychaete abundance correlated significantly (p<0.05) with the respective physicochemical parameters. Canonical analysis (74.11%) showed the physicochemical influence on the spatial distribution of species. The pH significantly (p<0.05) controlled the spatial distribution of faecal bacteria and polychaetes in the Densu Estuary. The results suggest environmental pollution in the Densu Estuary, useful baseline information for effective legislation towards its sustainable management. Key words: Biological indicators, water quality index, pollution, estuarine ecology, Densu Estuary.

Spatiotemporal patterns of avian host-parasite interactions in the face of biogeographical range expansions.

Exploration of interactions between hosts and parasitic symbionts is important for our understanding of the temporal and spatial distribution of organisms. For example, host colonization of new geographical regions may alter levels of infections and parasite specificity, and even allow hosts to escape from co-evolved parasites, consequently shaping spatial distributions and community structure of both host and parasite. Here we investigate the effect of host colonization of new regions and the elevational distribution of host-parasite associations between birds and their vector-transmitted haemosporidian blood parasites in two geological and geographical settings: mountains of New Guinea and the Canary Islands. Our results demonstrate that bird communities in younger regions have significantly lower levels of parasitism compared to those of older regions. Furthermore, host-parasite network analyses demonstrate that blood parasites may respond differently after arriving to a new region, through adaptations that allow for either expanding (Canary Islands) or retaining (New Guinea) their host niches. The spatial prevalence patterns along elevational gradients differed in the two regions, suggesting that region-specific biotic (e.g., host community) and abiotic factors (e.g., temperature) govern prevalence patterns. Our findings suggest that the spatiotemporal range dynamics in host-parasite systems are driven by multiple factors, but that host and parasite community compositions and colonization histories are of particular importance.

Day and night in the subterranean: measuring daily activity patterns of subterranean rodents (Ctenomys aff. knighti) using bio-logging.

While most studies of the impacts of climate change have investigated shifts in the spatial distribution of organisms, temporal shifts in the time of activity is another important adjustment made by animals in a changing world. Due to the importance of light and temperature cycles in shaping activity patterns, studies of activity patterns of organisms that inhabit extreme environments with respect to the 24-hour cyclicity of Earth have the potential to provide important insights into the interrelationships among abiotic variables, behaviour and physiology. Our previous laboratory studies with Argentinean tuco-tucos from the Monte desert (Ctenomys aff. knighti) show that these subterranean rodents display circadian activity/rest rhythms that can be synchronized by artificial light/dark cycles. Direct observations indicate that tuco-tucos emerge mainly for foraging and for removal of soil from their burrows. Here we used bio-logging devices for individual, long-term recording of daily activity/rest (accelerometry) and time on surface (light-loggers) of six tuco-tucos maintained in outdoor semi-natural enclosures. Environmental variables were measured simultaneously. Activity bouts were detected both during day and night but 77% of the highest values happened during the daytime and 47% of them coincided with time on surface. Statistical analyses indicate time of day and temperature as the main environmental factors modulating time on surface. In this context, the total duration that these subterranean animals spent on surface was high during the winter, averaging 3h per day and time on surface occurred when underground temperature was lowest. Finally, transport of these animals to the indoor laboratory and subsequent assessment of their activity rhythms under constant darkness revealed a switch in the timing of activity. Plasticity of activity timing is not uncommon among desert rodents and may be adaptive in changing environments, such as the desert where this species lives.

Sexual selection by the seashore: the roles of body size and weaponry in mate choice and competition in the maritime earwig (Anisolabis maritima)

The spatial distribution of organisms can provide insight into their mating systems, either revealing mating preferences (intersexual selection for ornaments), competition for mates (intrasexual selection for armaments), or both. Teasing apart the relative contributions of these selective forces is a critical step in understanding mating systems, particularly given the potential combinations and complexities that arise when both sexes possess weaponry. We examined the mating system of the maritime earwig Anisolabis maritima, an insect well suited for studies of sexual selection because males differ markedly from females in body size (males are more variable in size, and sometimes substantially larger, than females) and weaponry (males possess asymmetrical, curved forceps, whereas females have straight forceps). We varied sex, body size, and forceps asymmetry among trios of earwigs and examined their spatial distribution under conditions where movement was restricted to promote either intersexual choice or intrasexual competition. Our results indicate strong sexual selection for larger sizes through both competition and choice in both sexes. However, females had no preference for males based on forceps asymmetry. We discuss how the competition and cohabitation patterns provide insight into the mating system, including how the possession of weaponry by both sexes could operate in intrasexual competitive battles as well as serve as a basis for assessing the quality of a potential mate. Sexually dimorphic traits are often the result of either intersexual selection, where one sex chooses the other based on phenotypic qualities, or intrasexual selection, where members of one sex compete with each other for mating opportunities. Although many mating systems lie squarely on one end of this spectrum, it is often less clear which selection forces shape mating systems when both sexes possess weaponry. We monitored cohabitation patterns to examine the relative roles of mate choice and competition in Anisolabis maritima, an earwig in which males have asymmetrical, curved pincers, whereas females have symmetrical, straight pincers. By restricting the movement of certain individuals within trios, we found that large size but not forceps asymmetry was important in both mate choice and competition. Our results indicate that weaponry and aggression may significantly affect both sexes and contribute to the complexity of the mating system.

Habitat selection and reproduction of newts in networks of fish and fishless aquatic patches

The spatial distribution of organisms in patchy environments can be determined by the relationship between habitat quality and animal behaviour. In species with complex life cycles, such as pond-breeding amphibians, the selection of a suitable wetland is crucial. While the traditional view of amphibian ecology suggests strong site fidelity and low vagility, more recent research highlights mechanisms involving active site choice through avoidance behaviour and bet-hedging strategies in heterogeneous environments. The introduction of fish to the aquatic environment is one of the factors that may alter site selection and lead to local dispersal. In this context, we investigated the habitat choice of Alpine newts, Ichthyosaura alpestris, in networks of fish (Carassius auratus) and fishless aquatic patches. Using a laboratory design consisting of aquaria divided into two water tanks connected by a terrestrial platform, we assessed newt distribution and movement between patches. During the breeding period, we compared the reproductive success of individuals in two types of networks. We found that newts escaped fish by rapidly changing aquatic patches and then aggregating in safe aquatic patches that were free of fish. In the fish network, newts maintained reproduction, but the high local abundance resulted in decreased sexual activity and egg production and increased use of the terrestrial habitat. However, in the fishless network, newts moved between aquatic patches several times, exhibited more courtship behaviour and laid more eggs than they did in the fish networks. Our results showed both adaptive habitat switching due to environmental risks in the fish network and habitat supplementation (i.e. use of alternative resources) in the fishless network. Such studies on movement behaviour and habitat selection have conservation implications in showing that the persistence of native species in invaded networks depends on the rescue effect, with immigration to fish-free habitats potentially preventing local extinction.

Making up for lost time: Biophysical constraints on the temporal abundance of two fiddler crabs in wet-dry tropical mangroves

Biophysical models are used to predict the spatial distributions of organisms. Nevertheless, understanding factors influencing the temporal distributions of animals may often be additionally required. It is expected that intertidal macrofauna of the wet–dry tropics face a multitude of temporal challenges because there is not only seasonal drying but also variation in surface moisture over the circatidal cycle. Activities of fiddler crabs (Uca spp.) depend on adequate surface moisture being available for feeding and respiration. A recent study monitored crab abundance during spring tides and found that one Uca species in the mangroves of Darwin Harbour, Australia, U. flammula, is most abundant in the wet season, while another, U. elegans, is most abundant in the dry season. We hypothesized here that these seemingly contradictory abundance patterns are driven by temporal variation in the availability of soil moisture within each species habitat. We thus monitored crab abundance and measured soil moisture content across four types of habitat (low gap centres, low gap edges, mid-height gap centres and high gap centres) seasonally and across the circatidal cycle. We found that crab abundance and soil moisture both varied over time among habitat types. We used a log-linear model to show that habitat type influenced soil moisture and this in turn influenced crab abundance. Sampling across the circatidal cycle showed that U. flammula was more abundant in the wet season, as reported previously, while the abundance of U. elegans did not vary between seasons. Our model suggested that U. elegans ‘makes up for lost time’ in the dry season by undertaking all activities during spring tide low water as only at this time is the substratum moist enough for feeding and respiration. We highlight the importance of measuring multiple variables across habitats over small and large scales when assessing temporal abundance patterns of intertidal tropical organisms.

Isolation by distance and non-identical patterns of gene flow within two river populations of the freshwater fish Rutilus rutilus (L. 1758).

The spatial distribution of organisms is maintained by a combination of in situ reproduction and dispersal of conspecifics from elsewhere within its habitable range. The determination of dispersal origin and sub-population connectivity has a vital role to play in forming effective management policies. The common roach (Rutilus rutilus) is an important component of the economically and socially valuable recreational fishery and represents a well-studied member of the Cyprinidae. Microsatellite allele data were used to investigate hypothetically variant levels of microevolutionary structuring and isolation-by-distance (IBD) in in the Rivers Stour and Thames. A strong signal of IBD was found in the Stour, probably due to the limited capacity for unrestricted bidirectional dispersal in this river compared with the Thames. A weak inference of IBD in the Thames is likely erroneous and effected by a strong localised genetic signal from a recent stocking event. Whilst we found significantly genetically divergent upstream areas in the River Stour, a strong signal of IBD remained when the headwater sub-population was removed, suggesting that that the signal is not biased by non-equilibrium conditions in upstream reaches. We discuss these results with reference to the management of aquatic bioresources and emphasise the idiosyncrasy that aquatic biota and hydrological complexity may imprint upon patterns of biodiversity within any given system.Electronic supplementary materialThe online version of this article (doi:10.1007/s10592-016-0828-3) contains supplementary material, which is available to authorized users.

Adaptive movement and food-chain dynamics: towards food-web theory without birth–death processes

Population density can be affected by its prey [resource] and predator [consumer] abundances through two different mechanisms: the alternation of birth [or somatic growth] or death rate and inter-habitat movement. While the food-web theory has traditionally been built on the former mechanism, the latter mechanism has formed the basis of a successful theory explaining the spatial distribution of organisms in the context of behavioral and evolutionary ecology. Yet, few studies have compared these two mechanisms, leaving the question of how similar (or different) predictions derived from birth–death-based and movement-based food-web theories unanswered. Here, theoretical models of the tri-trophic (resource–consumer-top predator) food chain were used to compare food-web patterns arising from these two mechanisms. Specifically, we evaluated the response of the food-chain structure to inter-patch differences in productivity for movement-based models and birth–death-based models. Model analysis reveals that adaptive movements give rise to positively correlated responses of all trophic levels to increased productivity; however, this pattern was not observed in the corresponding birth–death-based model. The movement-based model predicts that the food chain response to productivity is determined by the sensitivity of animal movement to the environmental conditions. More specifically, increasing sensitivity of a consumer or top predator leads to smaller inter-patch variance of the resource or consumer density, while increasing inter-patch variance in the consumer or resource density. In conclusion, adaptive movement provides an alternative mechanism correlating the food-web structure to environmental conditions.

A Mixed Modeling Approach to Predict the Effect of Environmental Modification on Species Distributions

Human infrastructures can modify ecosystems, thereby affecting the occurrence and spatial distribution of organisms, as well as ecosystem functionality. Sustainable development requires the ability to predict responses of species to anthropogenic pressures. We investigated the large scale, long term effect of important human alterations of benthic habitats with an integrated approach combining engineering and ecological modelling. We focused our analysis on the Oosterschelde basin (The Netherlands), which was partially embanked by a storm surge barrier (Oosterscheldekering, 1986). We made use of 1) a prognostic (numerical) environmental (hydrodynamic) model and 2) a novel application of quantile regression to Species Distribution Modeling (SDM) to simulate both the realized and potential (habitat suitability) abundance of four macrozoobenthic species: Scoloplos armiger, Peringia ulvae, Cerastoderma edule and Lanice conchilega. The analysis shows that part of the fluctuations in macrozoobenthic biomass stocks during the last decades is related to the effect of the coastal defense infrastructures on the basin morphology and hydrodynamics. The methodological framework we propose is particularly suitable for the analysis of large abundance datasets combined with high-resolution environmental data. Our analysis provides useful information on future changes in ecosystem functionality induced by human activities.

Spatial signatures of resilience

Predicting when the dynamics of a complex system will undergo a sudden transition is difficult. New experiments show that the spatial distribution of organisms can indicate when such tipping points are near. See Letter p.355 The behaviour of complex systems near tipping points, where a small change can lead to a large shift in the state of the system, is notoriously difficult to predict. Recent studies have identified temporal factors such as recovery time and changes in size and timescale of fluctuations that precede some tipping points. Lei Dai et al. grew populations of the budding yeast that were spatially connected through controlled dispersal between nearest neighbours, and looked for spatiotemporal patterns that anticipated population collapse after perturbation — the introduction of sucrose solution more highly diluted than its surroundings. As the distance from the diluted patch increased, yeast population density increased towards a steady state. The distance required for recovery by connected populations was much greater when populations were close to collapse. This work introduces the concept of 'recovery length' as a spatial counterpart to recovery time, and as boundaries between regions of different quality are ubiquitous in nature, many systems in the oceans and on land might be expected to be subject to such spatial instability.

Large-Scale Natural Disturbance Alters Genetic Population Structure of the Sailfin Molly,Poecilia latipinna

Many inferences about contemporary rates of gene flow are based on the assumption that the observed genetic structure among populations is stable. Recent studies have uncovered several cases in which this assumption is tenuous. Most of those studies have focused on the effects that regular environmental fluctuations can have on genetic structure and gene flow patterns. Occasional catastrophic disturbances could also alter either the distribution of habitat or the spatial distribution of organisms in a way that affects population structure. However, evidence of such effects is sparse in the literature because it is difficult to obtain. Hurricanes, in particular, have the potential to exert dramatic effects on population structure of organisms found on islands or coral reefs or in near shore and coastal habitats. Here we draw on a historic genetic data set and new data to suggest that the genetic structure of sailfin molly (Poecilia latipinna) populations in north Florida was altered dramatically by an unusually large and uncommon type of storm surge associated with Hurricane Dennis in 2005. We compare the spatial pattern of genetic variation in these populations after Hurricane Dennis to the patterns described in an earlier study in this same area. We use comparable genetic data from another region of Florida, collected in the same two periods, to estimate the amount of change expected from typical temporal variation in population structure. The comparative natural history of sailfin mollies in these two regions indicates that the change in population structure produced by the storm surge is not the result of many local extinctions with recolonization from a few refugia but emerged from a pattern of mixing and redistribution.

Community Spectrum, Seasonality and Diel Vertical Movements of Zooplankton in a Tropical Freshwater Fish Farm, South East Nigeria

Zooplankton communities of Little Stream Farm, South-East Nigeria, were studied from March 2008 to February 2009 spanning a period of 12months. A total of 38 species belonging to 24 genera were identified. Rotifera were the most abundant with 16 species, followed by Cladocera with 9 species, while Copepoda and Protozoa recorded 8 species and 7 species respectively. The relative abundance of the different groups revealed 57.4% for Rotifera, 40.42% for Cladocera, while Copepods and protozoa contributed 3.36% and 2.30% respectively. Analysis of variance showed no significant difference (p &gt; 0.05) in Taxa occurrence between the adjacent stream and the fish ponds, whereas a highly significant variation (p &lt; 0.05) in species abundance was observed between the stations. Spatial distribution of organisms between the ponds indicated occurrence of larger individuals in the deeper layers indicating greater sinking rate of these size classes. Correlation coefficient (r = 0.817; p &lt; 0.05) showed highly significant relationship between sinking rate and zooplankton size. Diurnal vertical movements of Calanoid Copepods related strongly (r = 0.924; p &lt; 0.05) with corresponding movements of Cladocerans. A significant relationship (r = 0.879; p &lt; 0.05) was also observed between zooplankton abundance and physico-chemical parameters.

Change in the meiofauna community structure of sandy beaches of the Nuevo Gulf (Chubut, Argentina)

The composition and distribution of the benthic meiofauna assemblages of the Nuevo Gulf (Chubut, Argentina) are described in relation to abiotic variables. The meiofauna and sediment samples were collected in the intertidal zone of four sandy beaches with different anthropic disturbances in June 2005. The samples were obtained at 20 sampling sites using a 2.5 cm diameter core tube at a depth of 10 cm. A total of 13 meiofauna taxa were identified, with the meiofauna being primarily represented by nematodes, gastrotrichs, ciliates and polychaetes and the meiofauna abundances ranging from 1.5 × 10³ to 6.5 × 10³ ind. 10 cm‑2. Univariate (one-way ANOVA test) and multivariate (ANOSIM/MDS test) analyses showed clear dissimilarities in community structures between sites with anthropic effects and those in pristine condition, revealed by the significant differences were found between beaches near to and far way from a city with port activity. The meiofaunal assemblage varied in abundance and diversity, and these changes in the community structure may have been related to environmental gradients on the shore. The BIO‑ENV analysis showed that the redox potential discontinuity depth might be the main factor in the spatial distribution of organisms.

陕西省栎黄枯叶蛾蛹的空间分布

Trabala vishnou gigantina Yang(Lepidoptera: Lasiocampidae) is one of the most important defoliators in China.Larvae of T.vishnou gigantina feed on tender leaves primarily causing damage to the crown layer.In the last few years,the use of single species plantations combined with poor management and a lack of adequate monitoring and early warning has allowed populations of this pest to erupt and cause serious damage in Hippophae rhamnoides L.forest stands in Wuqi County,Shaanxi Province,China. Spatial distribution is one of the most important properties of insect populations.It provides dynamic information about insect populations,describes individual associations,and allows the prediction of variations in spatial distribution patterns.Geostatistical methods provide very powerful tools for explaining the spatial distribution of many species.These methods allow both the direct measurement of spatial distribution of organisms and tracking of changes in distribution over time because the exact location of the species has been documented at a specific point in time. To further investigate spatial distribution and effectively control this pest species,spatial distribution patterns of T.vishnou gigantina pupae were analyzed using geostatistical methods in pure H.rhamnoides forests with different slopes and densities.Results show high levels of pupating occurred mainly in mid-August.Also,males pupated 3.7 days earlier than females.Pupae were also widely distributed on southeastern facing shady slopes,and on west and north facing sunny slopes.Pupae gathered mainly at heights of 30—75 cm on trees.Analysis of isotropic variograms indicated T.vishnou gigantina pupae spaced themselves 95.609,47.379,79.238,and 42.415 m apart in densely forested shady slopes,open forests on shady slopes,densely forested sunny slopes,and open forests on sunny slopes,respectively,while the intensity of local spatial continuity was 0.760,0.561,0.649,and 0.407,respectively,in the above stands.Also,semivariogram analysis revealed the Gaussian model had the best fit to T.vishnou gigantina pupae distributional patterns in dense forests,implying an intense spatial aggregation pattern,while the linear model fitted best with the open forest,implying a random distribution.As the maps with Kriging interpolation described,T.vishnou gigantina pupae exhibited an edge effect and an obvious directional distribution;the pupae had a clustered distribution at the edge of the plantation and occurred in point locations scattered inside the plantation.Numbers of clustered plaque gradually declined toward the center of the forested area.This was reflected in the tendency of the pupae to cluster together on a spatial scale,and in the direction of their proliferation. Currently,T.vishnou gigantina infestations are most commonly controlled using chemical pesticides.However,H.rhamnoides is an economically and ecologically important plant,so residues need to be considered when spraying pesticides.Based on the spatial distribution characters,we suggest picking the pupa manually on the sunny slopes and especially on the edges of seabuckthorn plantations at a height of 30—75 cm to limit reproduction of this pest species.Research results demonstrate the spatial distribution patterns of T.vishnou gigantina pupae in pure H.rhamnoides forests,providing a theoretical basis and practical guidance for controlling populations of this insect pest.This research will provide a meaningful foundation for integrated pest management.