Predator Species Richness Research Articles

Long-term ecological footprints of a man-made freshwater discharge onto a sandy beach ecosystem

Sandy shores comprise one of the coastal ecosystems most vulnerable to human impacts, and they are increasingly affected by a variety of stressors. Local-scale drivers such as man-made freshwater discharges have changed the salinity, temperature and nutrient regimes, leading to the degradation of sandy beaches. However, there is still little understanding about the effects of salinity changes on the structure and functioning of sandy shores at the ecosystem level of ecological organization. This study seeks to identify the main spatial and long-term variations in a sandy beach ecosystem due to salinity changes induced by a freshwater discharge using a trophic network approach and thus linking anthropogenic pressures with functional and structural ecosystem changes. The trophic networks of nine scenarios involving three sampling sites representing different salinity stress regimes and three study phases established between 1987 and 2015 were modelled and compared. The results showed important space-time variations that were reflected at the community and ecosystem levels. A more complex trophic structure was developed with longer distances to the freshwater inflow, with higher biomass, species richness and number of predators. The highly disturbed and undisturbed sites occupied discrete, contrasting and clearly distinguishable states over time, whereas the moderately disturbed site showed a variable pattern over time. Recent trends in ecosystem indicators reflected a more fragile state, characterized by a greater organization (Ascendency) and a lower adaptive potential (Overhead) to address unexpected disturbances. Ecosystem indicators were sensitive enough to distinguish among sites and long-term phases in the ecosystem, where different organization states can persist over time. Future studies aimed at assessing press disturbances on sandy beach ecosystems should emphasize a longer time scale in order to assess the recovery capacity of these systems that are increasingly threatened by long-lasting stressors.

Landscape composition, configuration, and trophic interactions shape arthropod communities in rice agroecosystems

Abstract Increasing landscape heterogeneity of agroecosystems can enhance natural enemy populations and promote biological control. However, little is known about the multiscale effects of landscape heterogeneity on arthropod communities in rice agroecosystems, especially in combination with trophic interactions. We examined for the first time how landscape heterogeneity, measured by four independent metrics of landscape composition and configuration at three spatial scales, affected species abundance and species richness of rice arthropods within four functional groups and the abundance of the most common species at 28 sites in the Philippines. We additionally examined the influence of trophic interactions among these functional groups. We found that both the compositional and configurational landscape heterogeneity in combination with trophic interactions determined the structure of rice‐arthropod communities. Herbivore abundance decreased with increasing landscape diversity. The abundance of parasitoids and species richness of both parasitoids and predators increased with the structural connectivity of rice bunds. Fragmentation of the rice landscape had a clear negative effect on most arthropod groups, except for highly mobile predatory arthropods. Abundance of common predators and detritivore species decreased with increasing complexity in the shape of rice patches. Trophic interactions, measured as the abundance of prey, outweighed the importance of landscape heterogeneity for predators. In contrast, parasitoids responded positively to configurational landscape heterogeneity but were unaffected by prey abundance. Synthesis and applications. Our research shows how landscape heterogeneity and trophic interactions have different effects on different functional groups. While predator abundance was solely driven by the availability of prey, all other functional groups in the rice‐arthropod community were significantly affected by the composition and configuration of surrounding landscape features. Landscape management aiming to improve biodiversity and biological control in rice agroecosystems should promote a diversity of land uses and habitat types within 100–300 m radii to reduce the presence of pests. Management practices should also focus on maintaining smaller rice patches and the structural connectivity of rice bunds to enhance populations of the natural enemies of rice pests. Future research should focus on the temporal and spatial manipulation of rice fields to maximize the effects of biological control.

Functional diversity positively affects prey suppression by invertebrate predators: a meta-analysis.

The use of pesticides within agricultural ecosystems has led to wide concern regarding negative effects on the environment. One possible alternative is the use of predators of pest species that naturally occur within agricultural ecosystems. However, the mechanistic basis for how species can be manipulated in order to maximize pest control remains unclear. We carried out a meta‐analysis of 51 studies that manipulated predator species richness in reference to suppression of herbivore prey to determine which components of predator diversity affect pest control. Overall, functional diversity (FD) based on predator's habitat domain, diet breadth and hunting strategy was ranked as the most important variable. Our analysis showed that increases in FD in polycultures led to greater prey suppression compared to both the mean of the component predator species, and the most effective predator species, in monocultures. Further analysis of individual traits indicated these effects are likely to be driven by broad niche differentiation and greater resource exploitation in functionally diverse predator communities. A decoupled measure of phylogenetic diversity, whereby the overlap in variation with FD was removed, was not found to be an important driver of prey suppression. Our results suggest that increasing FD in predatory invertebrates will help maximize pest control ecosystem services in agricultural ecosystems, with the potential to increase suppression above that of the most effective predator species.

Interference competition pressure predicts the number of avian predators that shifted their timing of activity.

Being active at different times facilitates the coexistence of functionally similar species. Hence, time partitioning might be induced by competition. However, the relative importance of direct interference and indirect exploitation competition on time partitioning remains unclear. The aim of this study was to investigate the relative importance of these two forms of competition on the occurrence of time-shifting among avian predator species. As a measure of interference competition pressure, we used the species richness of day-active avian predator species or of night-active avian predator species (i.e. species of Accipitriformes, Falconiformes and Strigiformes) in a particular geographical area (assemblage). As an estimate of exploitation competition pressure, we used the total species richness of avian predators in each assemblage. Estimates of the intensity of interference competition robustly predicted the number of Accipitriformes species that became crepuscular and the number of Strigiformes species that became day-active or strictly crepuscular. Interference competition pressure may depend on body size and on the total duration of the typical active period (day or night length). Our results support—to some extent—that smaller species are more likely to become time-shifters. Day length did not have an effect on the number of time-shifter species in the Accipitriformes. Among the large Strigiformes, more time-shifter species occur in areas where nights are shorter (i.e. where less of the typical time resource is available). However, in the small Strigiformes, we found the opposite, counterintuitive effect: more time-shifters where nights are longer. Exploitation competition may have had an additional positive effect on the number of time-shifters, but only in Accipitriformes, and the effect was not as robust. Our results thus support the interference competition hypothesis, suggesting that animals may have shifted their time of activity, despite phylogenetic constraints on the ability to do so, to reduce the costs of direct interactions. Our findings also highlight the influence of body size as a surrogate of competitive ability during encounters on time partitioning, at least among avian predators.

Species richness of thrips and whiteflies and their predators in mustard fields

With a view to assessing the effect of temperature (ºC) and locations on species richness of thrips and whiteflies and their natural enemies (NEs), predatory Geocoris bug and Asian lady bug beetle (LBB) in mustard field of BARI Sarisha 16, the experiment was carried out at the farmers’ fields in two specific locations of Southern Bangladesh, Rupsha, Khulna and Abhaynagar, Jessore during November, 2015 to March, 2016. The studies were laid out with randomized complete block deign (RCBD) maintaining four replicates. The results depicted that there was a significant variation in mean population abundance of thrips, whitefly and their predators across the observation dates, which principally resulted from the variation of temperature along the various observation dates in each location and between locations along with phenological characters of host plants. Initially, population of thrips and whitefly, and their predators were very low in both locations at first observation date of 20 November, 2015 which gradually colonized and reached the peak in 19 March, 2016 with temperature of 27.8°C and 71% RH in Khulna and 26.1ºC and 61% RH in Jessore. Notably, temperature ranging from 22–27°C during mid-February to March, 2016 considerably favors the species richness of both insect pests, thrips and whiteflies, and their predators, Geocoris bug and Asian lady bug beetle in both places. By contrast relative low temperature of 16–20°C from December 20, 2015 to January 29, 2016 affected the species richness of predators and pest as well. The yield of mustard, BARI Sarisha 16 was significantly higher in Jessore (1365.75 kgha–1) due to lower pest population and higher predator population relative to Khulna region (1277.25 kgha–1). Ecological factors especially temperature appeared as major striking factor of species richness and played crucial role in getting up and down of mustard insect pests and NEs population across various date of observations and between places.J. Bangladesh Agril. Univ. 15(1): 7-14, January 2017

Conserving herbivorous and predatory insects in urban green spaces

Insects are key components of urban ecological networks and are greatly impacted by anthropogenic activities. Yet, few studies have examined how insect functional groups respond to changes to urban vegetation associated with different management actions. We investigated the response of herbivorous and predatory heteropteran bugs to differences in vegetation structure and diversity in golf courses, gardens and parks. We assessed how the species richness of these groups varied amongst green space types, and the effect of vegetation volume and plant diversity on trophic- and species-specific occupancy. We found that golf courses sustain higher species richness of herbivores and predators than parks and gardens. At the trophic- and species-specific levels, herbivores and predators show strong positive responses to vegetation volume. The effect of plant diversity, however, is distinctly species-specific, with species showing both positive and negative responses. Our findings further suggest that high occupancy of bugs is obtained in green spaces with specific combinations of vegetation structure and diversity. The challenge for managers is to boost green space conservation value through actions promoting synergistic combinations of vegetation structure and diversity. Tackling this conservation challenge could provide enormous benefits for other elements of urban ecological networks and people that live in cities.

Predator diversity reduces habitat colonization by mosquitoes and midges.

Changes in predator diversity via extinction and invasion are increasingly widespread and can have important ecological and socio-economic consequences. Anticipating and managing these consequences requires understanding how predators shape ecological communities. Previous predator biodiversity research has focused on post-colonization processes. However, predators can also shape communities by altering patterns of prey habitat selection during colonization. The sensitivity of this non-consumptive top down mechanism to changes in predator diversity is largely unexamined. To address this gap, we examined patterns of dipteran oviposition habitat selection in experimental aquatic habitats in response to varied predator species richness while holding predator abundance constant. Caged predators were used in order to disentangle behavioural oviposition responses to predator cues from potential post-oviposition consumption of eggs and larvae. We hypothesized that because increases in predator richness often result in greater prey mortality than would be predicted from independent effects of predators, prey should avoid predator-rich habitats during colonization. Consistent with this hypothesis, predator-rich habitats received 48% fewer dipteran eggs than predicted, including 60% fewer mosquito eggs and 38% fewer midge eggs. Our findings highlight the potentially important links between predator biodiversity, prey habitat selection and the ecosystem service of pest regulation.

Contrasting predation services of predator and omnivore diversity mediated by invasive ants in a tropical agroecosystem

Invasive natural enemies are known to either strengthen or weaken the suppression of herbivorous arthropods. However, the impact of invasive species on the predation service provided by natural enemy diversity remains largely unexplored. Here, we tease apart the roles of invasive ants as providers of a predation service and a potential disservice, i.e. reducing the diversity of natural enemies. In mango orchards on Reunion Island, we evaluated the predation service in 20 open fields by simultaneously monitoring the predation on bait eggs and arthropod communities in two strata: the ground surface and the mango tree canopy. Our results show that the predation on bait eggs was limited to the ground surface. This stratum is dominated by three invasive omnivorous ants: Pheidole megacephala and Solenopsis geminata strongly increased the predation rate of bait eggs, whereas Brachymyrmex cordemoyi was responsible for only a small decrease in predation rate. Predation rate was positively related to predator species richness, and was negatively related to omnivore species richness. The negative relationship between the predation rate and omnivore species richness is caused by the most dominant invasive ant, P. megacephala, which reduces omnivore richness and seems to strongly prey on eggs. This study demonstrates, for the first time, the distinct influence of the diversity of two trophic groups on the predation service and how these effects can be mediated by invasive ant species.

Seasonal variation in the effect of landscape structure on ground-dwelling arthropods and biological control potential

Landscape ecology has highlighted the role of the surrounding landscape in structuring arthropod communities at a given place. Previous studies have confirmed that non-crop habitats in agricultural landscapes increase the abundance and diversity of natural enemies in crop fields, which can generate a positive impact on pest control. However, landscape structure may differentially affect generalist predator communities within a year. Our knowledge about how such intra-annual variation affects the biological control of pests is still scarce. In this study, we surveyed predator carabid and spider assemblages and estimated biological control potential using experimentally added aphids in 21 winter wheat fields from mid-March until harvest. We investigated whether landscape structure differentially affected predator activity density, species richness and species composition across months, as well as how the relationship between biological control potential and landscape structure changed over time. We also investigated whether different time steps (15-day sampling period vs. whole sampling season) influenced the detection and significance of landscape effects. Spider assemblages benefit from fine-grained landscapes in spring, but this effect disappeared later in summer. For carabids, species richness was the only biodiversity measure related to grain size, and the relationship was strongest when considering the whole sampling season. No relationship was found between landscape structure and biological control potential. Our study showed that the influence of landscape structure can be inconsistent across taxa, biodiversity measures and time. The results demonstrate the importance of time steps and seasonality in the relationship between landscape structure and biodiversity.

English

The effects of intercropping of Brassicaceae with coriander (Coriandrum sativum), dill (Anethum graveolens), African marigold (Tagetes erecta) and calendula (Calendula officinalis) on the abundance, species richness and diversity of predators and parasitoids of Lipaphis erysimi have been assessed. The numbers of aphids, parasitized aphids and natural enemies were determined during two consecutive phases. The first period comprised the vegetative phase of companion plants up to the onset of flowering and the development of kale up to the start of harvesting, while the second period encompassed the late flowering of companion plants up to senescence and the complete harvesting phase of kale. The establishment of L. erysimi and its natural enemies during the first period was enhanced by the climatic conditions and the additional nutritional resources offered by companion plants. Over the complete 13 week period, the abundance of natural enemies in kale intercropped with African marigold, calendula, coriander and dill increased by factors of 3.1, 2.1, 2.0 and 1.6, respectively, compared with the kale monoculture, while species richness increased by 1.8-fold in kale/African marigold intercrop and by a factor of 2.7 in the other treatments. The predominant predators were Syrphidae larvae and Hippodamia convergens whereas the predominant parasitoid was Diaeretiella rapae. The diversity of natural enemies was similar in all crops owing to the high proportion of syrphids in relation to the other groups of insects. The improved resources offered by companion plants can be exploited in the conservative biological control of insect pests. Key words: Conservation biological control, natural enemies, insect seasonality, Hemiptera, Aphididae, Asteraceae, Apiaceae, Lipaphis erysimi, abundance, richness, Syrphidae, ladybird, kale

Biotic interactions mediate patterns of herbivore diversity in the Arctic

AbstractAimUnderstanding the forces shaping biodiversity patterns, particularly for groups of organisms with key functional roles, will help predict the responses of ecosystems to environmental changes. Our aim was to evaluate the relative role of different drivers in shaping the diversity patterns of vertebrate herbivores, a group of organisms exerting a strong trophic influence in terrestrial Arctic ecosystems. This biome, traditionally perceived as homogeneous and low in biodiversity, includes wide variation in biotic and physical conditions and is currently undergoing major environmental change.LocationThe Arctic (including the High Arctic, Low Arctic and Subarctic)MethodsWe compiled available data on vertebrate (birds and mammals) herbivore distribution at a pan‐Arctic scale, and used eight variables that represent the most relevant hypotheses for explaining patterns of species richness. We used range maps rasterized on a 100 km × 100 km equal‐area grid to analyse richness patterns of all vertebrate herbivore species combined, and birds and mammalian herbivores separately.ResultsOverall, patterns of herbivore species richness in the Arctic were positively related to plant productivity (measured using the normalized difference vegetation index) and to the species richness of predators. Greater species richness of herbivores was also linked to areas with a higher mean annual temperature. Species richness of avian and mammalian herbivores were related to the distance from the coast, with the highest avian richness in coastal areas and mammalian richness peaking further inland.Main conclusionsHerbivore richness in the Arctic is most strongly linked to primary productivity and the species richness of predators. Our results suggest that biotic interactions, with either higher or lower trophic levels or both, can drive patterns of species richness at a biome‐wide scale. Rapid ongoing environmental changes in the Arctic are likely to affect herbivore diversity through impacts on both primary productivity and changes in predator communities via range expansion of predators from lower latitudes.

Predatory beetles in cacao agroforestry systems in Brazilian Atlantic forest: a test of the natural enemy hypothesis

The natural enemy hypothesis predicts a positive correlation between plant species diversity and natural enemy control. This study aimed to evaluate the role of traditional cacao agroforests, known as “cabrucas,” on the conservation of the predatory beetle community compared to that of monodominant rubber agroforests. Predatory beetles were sampled in three habitats in Southeastern Bahia, Brazil: cabrucas and rubber agroforests and native Atlantic forests. In each habitat, 18 10 m2 plots were established, in which canopy cover was measured and beetles were sampled with a modified Malaise/window trap. Land use intensification did not affect the composition of predatory beetles, with the presence of widely distributed species that are also capable of colonizing simpler environments such as the rubber agroforest. Canopy cover had a positive effect on generalist predator diversity and we observed a reduction in the abundance and species richness of generalist predators with increasing habitat homogenization. Despite the simplified structure of the habitat, the remaining tree diversity and canopy cover in cabrucas supported a community of generalist predators similar to the one found in the native forest. Species diversity of bark beetle predators was higher in cabrucas, which may be due to the high diversity of bark beetles and the favorable abiotic conditions, whereas the low abundance of prey in the native forest and severe abiotic conditions in the rubber agroforest probably determined the lower diversity of generalist predators in these habitats. Cabrucas play an important role in the conservation, supporting a community of predatory beetles more similar to the one found in native forest and that is more effective at controlling populations of herbivores than in homogeneous rubber agroforests.

Responses of community-level plant-insect interactions to climate warming in a meadow steppe.

Climate warming may disrupt trophic interactions, consequently influencing ecosystem functioning. Most studies have concentrated on the temperature-effects on plant-insect interactions at individual and population levels, with a particular emphasis on changes in phenology and distribution. Nevertheless, the available evidence from the community level is limited. A 3-year field manipulative experiment was performed to test potential responses of plant and insect communities, and plant-insect interactions, to elevated temperature in a meadow steppe. Warming increased the biomass of plant community and forbs, and decreased grass biomass, indicating a shift from grass-dominant to grass-forb mixed plant community. Reduced abundance of the insect community under warming, particularly the herbivorous insects, was attributed to lower abundance of Euchorthippus unicolor and a Cicadellidae species resulting from lower food availability and higher defensive herbivory. Lower herbivore abundance caused lower predator species richness because of reduced prey resources and contributed to an overall decrease in insect species richness. Interestingly, warming enhanced the positive relationship between insect and plant species richness, implying that the strength of the plant-insect interactions was altered by warming. Our results suggest that alterations to plant-insect interactions at a community level under climate warming in grasslands may be more important and complex than previously thought.

Decadal effects of emulating natural disturbances in forest management on saproxylic beetle assemblages

Prescribed burning and retention forestry are used to bring the biological legacies of forest harvesting closer to those of natural disturbances. Although widely used, the effects of these methods on species assemblages in the longer term are still relatively unknown. In 2000, we established a large-scale replicated field experiment to explore the effects of prescribed burning and tree retention (four levels: 0, ten and 50m3ha−1 and unharvested control) on saproxylic beetles. Assemblages were monitored over 10 post-treatment years. Our results showed that species richness of predators was increased by burning of the forest stand. Early- and late-stage xylophagous species increased in the first post-harvest year. Increased logging intensity led to a decrease in mycetophagous, early-stage xylophagous and predator species richness over the ten year period. In the burned unharvested stands, the total species richness remained high after ten years, but decreased to the pre-treatment level in the stands with retention trees, and to even lower levels in the clear-cuts. Furthermore, the saproxylic beetle assemblages in the burned unharvested stands differed from the assemblages in any of the harvested stands. Burning increased pyrophilous and rare and red-listed (RRL) species richness. Over the ten year period, the richness of those species collapsed in the harvested stands, but increased in the burned unharvested stands. Our results emphasize the difference in tree stand legacies between logging and natural disturbance, but also indicates that prescribed burning and retention forestry have the potential to alleviate the negative effects of forest management on biodiversity in the longer term.

Effects of Tree Genotypic Diversity and Species Diversity on the Arthropod Community Associated with Big‐leaf Mahogany

AbstractDespite potential interactive effects of plant species and genotypic diversity (SD and GD, respectively) on consumers, studies have usually examined these effects separately. We evaluated the individual and combined effects of tree SD and mahogany (Swietenia macrophylla) GD on the arthropod community associated with mahogany. We conducted this study within the context of a tree diversity experiment consisting of 74 plots with 64 saplings/plot. We sampled 24 of these plots, classified as monocultures of mahogany or polycultures of four species (including mahogany). Within each plot type, mahogany was represented by either one or four maternal families. We surveyed arthropods on mahogany and estimated total arthropod abundance and species richness, as well as abundance and richness separately for herbivorous and predatory arthropods. Overall tree SD and mahogany GD had positive effects on total arthropod species richness and abundance on mahogany, and also exerted interactive effects on total species richness (but not abundance). Analyses conducted by trophic level group showed contrasting patterns; SD positively influenced herbivore species richness but not abundance, and did not affect either predator richness or abundance. GD influenced predator species richness but not abundance, and did not influence herbivore abundance or richness. There were interactive effects of GD and SD only for predator species richness. These results provide evidence that intra‐ and inter‐specific plant diversity exert interactive controls on associated consumer communities, and that the relative importance of SD and GD may vary among higher trophic levels, presumably due to differences in the underlying mechanisms or consumer traits.

Ants in citrus: impact on the abundance, species richness, diversity and community structure of predators and parasitoids

Ants can act as plant biotic defenses, however, in agricultural ecosystems they are often associated with outbreaks of honeydew-producing pests mainly due to the protection they offer to the plant feeders in exchange for honeydew. In this interaction ants may alter the abundance, diversity and community structure of predators and parasitoids. In the present study, we conducted ant-exclusion experiments in three commercial citrus orchards, each one dominated by one ant species (Pheidole pallidula, Lasius grandis or Linepithema humile) during two consecutive years. We then compared the abundance, species richness, diversity and community structure of predators and parasitoids between the ant-allowed and ant-excluded treatments. A total of 176,074 natural enemies belonging to 81 taxa were captured and identified. The abundance of the natural enemies showed a species specific response between treatments. When examining functional groups of natural enemies the abundance of generalist predators decreased while that of parasitoids increased in the ant-allowed treatment. The species richness was significantly lower for predators and higher for parasitoids in the ant-allowed treatment. The Shannon diversity index was not different between treatments for predators, whereas parasitoid diversity was significantly higher in the ant-allowed treatment. Finally, the community structure of predators and parasitoids was not significantly different between treatments. These results suggest that ants in citrus are not associated with a dramatic decrease in natural enemy abundance or biodiversity; on the contrary ants were associated with increased parasitoid species richness and diversity. On the other hand, ants negatively affected the abundance of specific natural enemy species, mainly generalist predators. The impact on these predators might explain the higher pest densities associated with ants in citrus.

Predators indirectly reduce the prevalence of an insect-vectored plant pathogen independent of predator diversity.

A widely cited benefit of predator diversity is greater suppression of insect herbivores, with corresponding increases in plant biomass. In the context of a vector-borne pathogen system, predator species richness may also influence plant disease risk via the direct effects of predators on the abundance and behavior of herbivores that also act as pathogen vectors. Using an assemblage of generalist insect predators, we examined the relationship between predator species richness and the prevalence of the aphid-vectored cereal yellow dwarf virus in wheat. We found that increasing predator richness enhanced suppression of the vector population and that pathogen prevalence was reduced when predators were present, but the reduction in prevalence was independent of predator species richness. To determine the mechanism(s) by which predator species richness contributes to vector suppression, but not pathogen prevalence, we evaluated vector movement and host plant occupancy in response to predator treatments. We found that pathogen prevalence was unrelated to vector suppression because host plant occupancy by vectors did not vary as a function of vector abundance. However, the presence of predators reduced pathogen prevalence because predators stimulated greater plant-to-plant movement by vectors, which likely diminished vector feeding time and reduced the transmission efficiency of this persistent pathogen. We conclude that community structure (i.e., the presence of predators), but not predator diversity, is a potential factor influencing local plant infection by this insect-vectored pathogen.

Larval dispersal drives trophic structure across Pacific coral reefs.

Top predators are a critical part of healthy ecosystems. Yet, these species are often absent from spatially isolated habitats leading to the pervasive view that fragmented ecological communities collapse from the top down. Here we study reef fish from coral reef communities across the Pacific Ocean. Our analysis shows that species richness of reef fish top predators is relatively stable across habitats that vary widely in spatial isolation and total species richness. In contrast, species richness of prey reef fish declines rapidly with increasing isolation. By consequence, species-poor communities from isolated islands have three times as many predator species per prey species as near-shore communities. We develop and test a colonization-extinction model to reveal how larval dispersal patterns shape this ocean-scale gradient in trophic structure.

No detectable effect of lionfish (Pterois volitans and P. miles) invasion on a healthy reef fish assemblage in Archipelago Los Roques National Park, Venezuela

There is an increasing concern that invasive lionfish will have dramatic impacts on native reef fish assemblages in the Caribbean. However, the intensity and speed of such changes will probably depend on the initial structure of each assemblage and on the lionfish population characteristics. The species composition of native fishes, diet and size structures were analyzed on a protected Venezuelan reef, through visual census on zones with and without lionfish, 1 and 3 years after the first sighting of Pterois (lionfish). Lionfish mean density ± SD increased from 30 ± 83.5 (n = 22) to 121 ± 164 ind ha−1 (n = 22), with an important increase in lionfish over 30 cm and the near absence of juveniles. Native species richness and densities remained stable through time. No significant change of native fish assemblage structure, species richness and density of potential Pterois prey, predators and competitors was found over time, but zones with lionfish had significantly higher levels of prey and predators, and significantly different fish assemblage structures. Most importantly, there was no interaction between time and the presence of Pterois on these metrics. Our results may suggest that: 1—a healthy composition of the initial structure of the reef fish assemblage may moderate the early impact of lionfish, and the observed lionfish densities (mean ± SD = 121 ± 164 ind ha−1, n = 22) were not sufficient to induce a significant change in the assemblage; and 2—lionfish probably select zones where species richness and density of prey are the highest.

Effects of shrub presence and shrub species on ground beetle assemblages (Carabidae, Curculionidae and Tenebrionidae) in a sandy desert, northwestern China

Shrub presence has an important effect on the structuring of ground beetles in desert ecosystems. In this study, in order to determine how shrubs and different species influence ground beetle assemblages in a sandy desert scrubland dominated by two different shrub species, namely Calligonum mongolicum and Nitraria sphaerocarpa, we sampled the ground beetles using pitfall traps during spring, summer and autumn in 2012. At the community level, the activity density of the ground beetles was shown to be significantly higher under shrubs than in intershrub bare habitats in spring; but an opposite pattern occurred in autumn, suggesting the presence of season-specific shrub effects on the activity density of the ground beetles. Meanwhile, at the trophic group level, the activity density and species richness of predators were significantly greater under shrubs than in intershrub bare habitats in spring, whereas an opposite trend occurred on the activity density in autumn. N. sphaerocarpa shrubs had a positive effect on the activity density of herbivores in the three seasons, and C. mongolicum shrubs had a positive effect on the activity density of detritivores in spring and autumn. At the species level, more Microdera sp. was captured under shrubs than in intershrub bare habitats in spring. During the same time, we also found that C. mongolicum shrubs had a positive effect on Blaps gobiensis in spring, Carabus sp. in autumn, and Tentyria sp. in spring and autumn, and N. sphaerocarpa shrubs had a positive effect on Cyphogenia chinensis, Sternoplax setosa in spring and summer, and Curculionidae sp. 1 in summer and autumn. The study results suggest that shrub presence, shrub species and season variation are important factors for ground beetle assemblages in this desert ecosystem, but the responses of beetles differed among trophic and taxonomic levels.