Generalist Predator Species Research Articles

Terrestrial generalist predators have larger isotopic niches but rely less on aquatic prey at a natural compared to a post-mining lakeshore

The flooded pits from former opencast mining (post-mining lakes) are young aquatic ecosystems often with low primary productivity due to the high acidity. The limited availability of nutrients and simplified aquatic food webs in these artificial lakes may affect the matter fluxes towards food webs in adjacent terrestrial habitats. To understand the impact of emerging prey from a post-mining lake on terrestrial food webs and associated arthropod communities, we compared the emergence and activity of arthropods as well as the isotopic niches of generalist predators and their potential prey between lakeshores of a post-mining and a natural lake. We used aquatic and terrestrial emergence tents to sample potential prey that emerged locally (Collembola and Diptera) and pitfall traps to sample terrestrial arthropod predators (Carabidae and Araneae) from lakeshores. Community and stable isotope (δ13C and δ15N) analyses were performed to compare diversity and isotopic niches of generalist arthropod predators between the natural and post-mining lakeshores. The number of emerging aquatic and terrestrial prey did not differ significantly between lakes, but the δ15N values of aquatic emerging dipterans differed between the two lakes. Predator community diversity did not differ significantly between lakeshores, but generalist predator species from the natural lakeshore generally had larger isotopic niche sizes than the same species at the post-mining lakeshore indicating a more diverse diet. Additional estimates of diet composition suggest that predators at the natural lakeshore utilized aquatic prey to a lesser degree than at the post-mining lake, but still had a more diverse diet.

Complex Habitats Boost Predator Co-Occurrence, Enhancing Pest Control in Sweet Pepper Greenhouses

Sweet pepper is a crop that benefits from phytosanitary treatments with low environmental impact, especially the successful control of pests through the introduction of biological control agents in greenhouses. However, predators that naturally occur in these surroundings often enter greenhouses. The precise roles of these natural predators and their interactions with the introduced predatory insects and mites are often unknown. This study investigated the relationships between Nesidiocoris tenuis, which is naturally present, and Amblyseius swirskii and Orius laevigatus, which are two species of generalist predators released for the control of multiple pests. This study was conducted for two years on 13 commercial sweet pepper crops in various types of greenhouses (tunnels and traditional greenhouses) in Sicily. The environmental complexity value (ECV) for each site was estimated based on 18 points detected around the site according to the different habitats that occurred at each coordinate. The results showed that the occurrence of N. tenuis in greenhouses, independently of their typology (tunnel or traditional greenhouse), was mainly promoted by the greater diversification of habitats immediately surrounding the pepper crops (in a circular area with a diameter of 500 mt), with an increase in its density during the crop season. Moreover, N. tenuis–O. laevigatus’s co-occurrence in flowers suggested that they were not impacted by each other’s presence and that their co-occurrence had a significant effect on pest reduction, although their co-occurrence was density-dependent. As an intraguild predator, N. tenuis competed with O. laevigatus for Frankliniella occidentalis when many predators were present. In addition, N. tenuis also competed with A. swirskii when they both occurred in flowers at a higher density. This study highlights the importance of pepper plant flowers in promoting a higher occurrence of juvenile forms of N. tenuis within flowers. Amblyseius swirskii colonized the plants in 3 weeks, distributing itself almost uniformly over the leaves with a clear control action against not only Bemisia tabaci but also F. occidentalis when present on the flowers. Thus, this concurrent analysis of several commercial pepper sites within the same production area suggests that, even with similar pest control plans, the diverse variability in the presence of natural enemies must be considered when selecting control strategies for pepper crop pests and that N. tenuis, favored by complex surrounding habitats, contributes actively to pest reduction.

Predatory Arthropods Associated with the Invasive Tipu Psyllid, Platycorypha nigrivirga, in Southern Spain.

Platycorypha nigrivirga Burckhardt (Hemiptera: Psyllidae) is a neotropical invasive species strictly associated with the tipu tree, Tipuana tipu (Benth.) Kuntze (Fabaceae: Papilionoideae). This psyllid has rapidly spread to several temperate areas of Spain and Portugal causing considerable problems in urban landscapes. The aim of this study was to determine the arthropod predator complex of this exotic insect and report the possibility of its biological control. Three urban green areas were surveyed in southern Spain during 2018 and 2019. Platycorypha nigrivirga populations increased during the spring months and reached a maximum level between late May and mid-June, declining greatly during the summer. A large complex of generalist predator species was found to exert a certain natural control on the pest, belonging to Anthocoridae (68.53%), Coccinellidae (18.39%), Chrysopidae (5.67%), Miridae (4.39%) and Araneae (3.02%). Anthocoris nemoralis (Fabricius) (Hemiptera: Anthocoridae) was the most abundant predatory species, followed by Orius laevigatus (Fieber) (Hemiptera: Anthocoridae) and Scymnus laetificus Weise (Coleoptera: Coccinellidae). High levels of abundance of anthocorids coincided with the highest abundance of the pest, showing a significant relationship with the psyllid density. Anthocoris nemoralis seems to be a promising candidate to control P. nigrivirga in the urban green areas of southern Spain, but more studies are needed to define the optimum management strategies.

Why aren't warning signals everywhere? On the prevalence of aposematism and mimicry in communities.

Warning signals are a striking example of natural selection present in almost every ecological community - from Nordic meadows to tropical rainforests, defended prey species and their mimics ward off potential predators before they attack. Yet despite the wide distribution of warning signals, they are relatively scarce as a proportion of the total prey available, and more so in some biomes than others. Classically, warning signals are thought to be governed by positive density-dependent selection, i.e. they succeed better when they are more common. Therefore, after surmounting this initial barrier to their evolution, it is puzzling that they remain uncommon on the scale of the community. Here, we explore factors likely to determine the prevalence of warning signals in prey assemblages. These factors include the nature of prey defences and any constraints upon them, the behavioural interactions of predators with different prey defences, the numerical responses of predators governed by movement and reproduction, the diversity and abundance of undefended alternative prey and Batesian mimics in the community, and variability in other ecological circumstances. We also discuss the macroevolution of warning signals. Our review finds that we have a basic understanding of how many species in some taxonomic groups have warning signals, but very little information on the interrelationships among population abundances across prey communities, the diversity of signal phenotypes, and prey defences. We also have detailed knowledge of how a few generalist predator species forage in artificial laboratory environments, but we know much less about how predators forage in complex natural communities with variable prey defences. We describe how empirical work to address each of these knowledge gaps can test specific hypotheses for why warning signals exhibit their particular patterns of distribution. This will help us to understand how behavioural interactions shape ecological communities.

Can Generalist Predators Control Bemisia tabaci?

Simple SummaryWhiteflies are major insect pests on a global scale. The use of insecticides is the primary tool for controlling them, but there are many problems relying on this strategy. However, natural enemies like predators and parasitic insects that attack whiteflies can help provide a sustainable pest management approach. This paper focuses on predators that feed on whiteflies as well as other insect pests and are called generalist predators. We provide a comprehensive view of generalist predator contributions and review the currently recognized generalist predators of whiteflies. There are many generalist predators in agricultural cropping systems that help control whiteflies. We highlight the need for conservation biological control programs through habitat management strategies and the use of selective insecticides, with an aim for more sustainable management of whiteflies in crops.The whitefly, Bemisia tabaci, has developed resistance to many insecticides, renewing interest in the biological control of this global pest. Generalist predators might contribute to whitefly suppression if they commonly occur in infested fields and generally complement rather than interfere with specialized natural enemies. Here, we review literature from the last 20 years, across US cropping systems, which considers the impacts of generalist predators on B. tabaci. Laboratory feeding trials and molecular gut content analysis suggest that at least 30 different generalist predator species willingly and/or regularly feed on these whiteflies. Nine of these predators appear to be particularly impactful, and a higher abundance of a few of these predator species has been shown to correlate with greater B. tabaci predation in the field. Predator species often occupy complementary feeding niches, which would be expected to strengthen biocontrol, although intraguild predation is also common and might be disruptive. Overall, our review suggests that a bio-diverse community of generalist predators commonly attacks B. tabaci, with the potential to exert substantial control in the field. The key challenge will be to develop reduced-spray plans so that generalist predators, and other more specialized natural enemies, are abundant enough that their biocontrol potential is realized.

The influence of ecological infrastructures adjacent to crops on their carabid assemblages in intensive agroecosystems.

BackgroundConserving biodiversity and enhancing ecosystem services of interest in intensive agroecosystems is a major challenge. Perennial ecological infrastructures (EIs), such as hedges and grassy strips, and annual EI under Agri-Environment Schemes appear to be good candidates to promote both. Our study focused on carabids, an indicator group responding both at the species and functional trait level to disturbances and supporting pest control and weed seed consumption services.MethodsWe compared carabid assemblages at the species and functional traits levels, sampled via pitfall trapping, in three types of EIs (hedges, grassy strips and annual flower strips) and crops. We also tested via GLMs the effect of (1) the type of EI at the crops’ border and (2) the distance from the crops’ border (two meters or 30 meters) on carabid assemblages of crops. Tested variables comprised: activity-density, species richness, functional dispersion metrics (FDis) and proportions of carabids by functional categories (Diet: generalist predators/specialist predators/seed-eaters; Size: small/medium/large/very large; Breeding period: spring/autumn).Results and DiscussionCarabid assemblages on the Principal Coordinate Analysis split in two groups: crops and EIs. Assemblages from all sampled EIs were dominated by mobile generalist predator species from open-land, reproducing in spring. Assemblages of hedges were poor in activity-density and species richness, contrarily to grassy and annual flower strips. Differences in carabid assemblages in crops were mainly driven by the presence of hedges. The presence of hedges diminished the Community Weighted Mean size of carabids in crops, due to an increased proportion of small (<5 mm) individuals, while distance from crops’ border favoured large (between 10–15 mm) carabids. Moreover, even if they were attracted by EIs, granivorous carabid species were rare in crops. Our results underlie the importance of local heterogeneity when adapting crops’ borders to enhance carabid diversity and question the relevance of hedge implantation in intensive agrolandscapes, disconnected from any coherent ecological network. Moreover, this study emphasizes the difficulty to modify functional assemblages of crops for purposes of ecosystem services development, especially for weed seed consumption, as well as the role of distance from the crops’ border in the shaping of crop carabid assemblages.

Woolly Apple Aphid Generalist Predator Feeding Behavior Assessed through Video Observation in an Apple Orchard

Generalist predators are considered effective biological control agents in many agroecosystems. However, characterizing the behavior of different generalist predator species in realistic field settings is difficult due to challenges associated with directly observing predation events in the field. Here we video recorded woolly apple aphid (Erisoma lanigerum) (Hemiptera: Aphididae) colonies to directly observe the feeding behavior of their generalist predators during the day and night. To observe European earwigs (Forficula auricularia) (Dermaptera: Forficulidae), which are thought to be key woolly apple aphid predators but were not present at our study location, we released earwigs into the study area. Across 1413 h of video recorded over 4 weeks, earwigs made the most attacks on woolly apple aphid colonies, but coccinellid larvae spent more total time attacking because their individual attacks were longer. Antagonistic interactions between predators were rare, and earwigs never antagonized other predators. However, ants commonly antagonized earwigs, and incidence of ant-earwig antagonistic interactions was negatively correlated with earwig-aphid attack rates. Overall, these results suggest that coccinellid larvae and earwigs differ in their feeding behavior in the field, and provide new evidence that ants may hinder aphid biological control by antagonizing earwigs.

Spiders feeding on earthworms revisited: consumption of giant earthworms in the tropics

Predation on earthworms is common in some generalist predator species, as for example several ground beetle species (Coleoptera: Carabidae) that frequently feed on earthworms. In spiders (Araneae), however, such behavior is far less well documented. A survey of reports on spiders feeding on earthworms yielded a total of 44 naturally occurring predation events. Spiders from 14 families were observed feeding on earthworms in nature, and species from two additional families consumed earthworm prey in captivity. Earthworm predation by spiders has been observed in temperate, subtropical, and tropical regions in 18 different countries. Tropical spiders from the families Theraphosidae (Mygalomorphae) and Ctenidae (Araneomorphae) accounted for 59% of the reported predation events. Reports from French Guiana document the capture of giant earthworms (0.6–1 m in length) by the giant tarantula, Theraphosa blondi (Latreille, 1804). Predation on giant earthworms by large tarantulas has also been observed in rainforest habitats in Brazil, Ecuador, Peru, and Venezuela. Wandering spiders (Ctenidae) are known to feed on earthworms in Belize, Brazil, Costa Rica, French Guiana, Guyana, and Singapore. Quite obviously, larger-sized mygalomorph and araneomorph spiders in humid tropical rainforests are predators with broad feeding niches—including earthworms and vertebrate prey in addition to arthropod prey—and this is presumed to improve the survival of these spiders. By comparison, reports of earthworm predation in temperate climate are rarer, and recent molecular studies of the diet composition of lycosid and linyphiid spider species in Swedish arable fields suggest that earthworms are not a common prey of these species.

Temporal variation in habitat use, co-occurrence, and risk among generalist predators and a shared prey

Generalist predators typically have broad diets, but their diets may become constrained when one species of prey becomes disproportionately available. Yet there is poor understanding regarding whether generalist predators exhibit stereotypic relationships with pulsed prey resources. We used telemetry data from 959 woodland caribou (Rangifer tarandus caribou (Gmelin, 1788); 146 adult females, 813 calves), 61 coyotes (Canis latrans Say, 1823), and 55 black bears (Ursus americanus Pallas, 1780) to investigate how two generalist predators interacted with caribou neonates on the island of Newfoundland. We examined the similarity of patterns of habitat use between caribou and their predators across time and related this similarity to interspecific spatiotemporal co-occurrence and mortality risk for caribou neonates. The similarity in habitat use between coyotes and caribou mirrored variation in juvenile hazard risk, but had weak association with actual co-occurrence with caribou. Bears and caribou exhibited less similarity in habitat use during the calving season than coyotes and caribou. The relationship between habitat use of bear and caribou did not correspond with either co-occurrence patterns or overall risk for caribou neonates. Our work illustrates how risk for a prey species can be shaped differently based upon differences between the behavioural strategies of generalist predator species.

Quantifying Avian Predation on Fish Populations: Integrating Predator‐Specific Deposition Probabilities in Tag Recovery Studies

AbstractAccurate assessment of specific mortality factors is vital to prioritize recovery actions for threatened and endangered species. For decades, tag recovery methods have been used to estimate fish mortality due to avian predation. Predation probabilities derived from fish tag recoveries on piscivorous waterbird colonies typically reflect minimum estimates of predation due to an unknown and unaccounted‐for fraction of tags that are consumed but not deposited on‐colony (i.e., deposition probability). We applied an integrated tag recovery modeling approach in a Bayesian context to estimate predation probabilities that accounted for predator‐specific tag detection and deposition probabilities in a multiple‐predator system. Studies of PIT tag deposition were conducted across three bird species nesting at seven different colonies in the Columbia River basin, USA. Tag deposition probabilities differed significantly among predator species (Caspian terns Hydroprogne caspia: deposition probability = 0.71, 95% credible interval [CRI] = 0.51–0.89; double‐crested cormorants Phalacrocorax auritus: 0.51, 95% CRI = 0.34–0.70; California gulls Larus californicus: 0.15, 95% CRI = 0.11–0.21) but showed little variation across trials within a species or across years. Data from a 6‐year study (2008–2013) of PIT‐tagged juvenile Snake River steelhead Oncorhynchus mykiss (listed as threatened under the Endangered Species Act) indicated that colony‐specific predation probabilities ranged from less than 0.01 to 0.17 and varied by predator species, colony location, and year. Integrating the predator‐specific deposition probabilities increased the predation probabilities by a factor of approximately 1.4 for Caspian terns, 2.0 for double‐crested cormorants, and 6.7 for California gulls compared with traditional minimum predation rate methods, which do not account for deposition probabilities. Results supported previous findings on the high predation impacts from strictly piscivorous waterbirds nesting in the Columbia River estuary (i.e., terns and cormorants), but our findings also revealed greater impacts of a generalist predator species (i.e., California gulls) than were previously documented. Approaches used in this study allow for direct comparisons among multiple fish mortality factors and considerably improve the reliability of tag recovery models for estimating predation probabilities in multiple‐predator systems.Received August 1, 2014; accepted November 11, 2014

Increased control of thrips and aphids in greenhouses with two species of generalist predatory bugs involved in intraguild predation

The combined release of species of generalist predators can enhance multiple pest control when the predators feed on different prey, but, in theory, predators may be excluded through predation on each other. This study evaluated the co-occurrence of the generalist predators Macrolophus pygmaeus Rambur and Orius laevigatus (Fieber) and their control of two pests in a sweet pepper crop. Both predators consume pollen and nectar in sweet pepper flowers, prey on thrips and aphids, and O. laevigatus is an intraguild predator of M. pygmaeus. Observations in a commercial sweet pepper crop in a greenhouse with low densities of pests showed that the two predator species coexisted for 8months. Moreover, their distributions in flowers suggested that they were neither attracted to each other, nor avoided or excluded each other. A greenhouse experiment showed that the predators together clearly controlled thrips and aphids better than each of them separately. Thrips control was significantly better in the presence of O. laevigatus and aphid control was significantly better in the presence of M. pygmaeus. Hence, combined inoculative releases of M. pygmaeus and O. laevigatus seem to be a good solution for controlling both thrips and aphids in greenhouse-grown sweet pepper. The predators are able to persist in one crop for a sufficiently long period and they complement each other in the control of both pests. This study also provides further evidence that intraguild predation does not necessarily have negative effects on biological control.

Cryptocephaline Egg Case Provides Incomplete Protection from Generalist Predators (Coleoptera: Chrysomelidae)

The egg case ofCryptocephalus rufipes(Goeze) is described and illustrated. In laboratory trials, eggs of field-collectedC. rufipeswere observed for larval emergence (untreated control) or exposed to two species of generalist predators,Chrysoperla carnea(Stephens) orXylocoris flavipes(Reuter) in no-choice experiments. The behaviour of the predators upon contact with theC. rufipeseggs was observed. The number of hatching larvae was counted and compared. In the presence of each of the two species of predators, larval emergence was significantly reduced. Eggs that were not protected by an egg case were completely consumed by the predators.C. rufipeseggs were therefore incompletely protected from the studied generalist predators. This is the first study showing experimentally the protective function of cryptocephaline egg case.

捕食者对空心莲子草叶甲种群的生物胁迫

Generalist predators are often applied in biological control of pests. Sine generalist predators often prey on herbivorous insects unselectively,they also influence biological control of weeds with herbivorous insects. The alligator weedflea beetle,Agasicles hygrophila( Coleoptera: Chrysomelidae) is acted as a specific biological control of the alligator weed Alternanthera philoxeroides( Amaranthacese: Alternanthera),and it had been introduced to China from Florida,USA. It has performed a good control effect on A. philoxeroides since the beetle was released in the areas invaded by A. philoxeroides. Although the population of A. hygrophila had been established and spread to adjacent regions from the release sites,the population abundance of the beetle maintains only a lower level. Thus,it can not suppress effectively the population expansion and spread of A. philoxeroides. We found that many generalist predator species such as spiders and predatory insects live in the habitat of A. philoxeroides. Whether the generalist predators are a biotic stress factor for suppressing the population expansion of the beetle? To demonstrate this problem,a predator-prey system including predators,i. e. lady beetle Propylaea japonica( Coleoptera: Coccinellidae),spider Oxyopes sertatus( Araneae: Oxyopidae) and Pirata subpiraticus( Araneae: Lycosidae),and host preys,i. e. egg,1st—3rdinstar larva and adult of A. hygrophila was built. Then the daily eating number of the above three predators on different immature stages and adults of A. hygrophila was observed in the laboratory. This aim to understand the biotic stress of predators on A. hygrophila in a natural ecosystem that may evaluate objectively the biological control efficiency of A. hygrophila on A. philoxeroides in the field. The results showed that P. japonica,O. sertatus and P. subpiraticus could feed on eggs as well as 1st—2ndinstar larvae of A. hygrophila. Both O. sertatus and P. subpiraticus could feed on 3rdinstar larvae of A. hygrophila. The predatory capacities of P. japonica, O. sertatus and P. subpiraticus to eggs and larvae of A. hygrophila increased,but searching efficiency of the predators decreased with the increasing densities of prey. However,the three predators did not prey on adult A. hygrophila in this experiment. The predatory function responses of P. japonica and P. subpiraticus on eggs,1st—2ndinstar larvae,and of O. sertatus on eggs,1st—3rdinstar larvae of A. hygrophila fitted to the disc equation of Holling II. With the exception of the predatory function response of P. subpiraticus on 3rdinstar larvae of A. hygrophila,there were a significant correlation between predator and host prey that were fitted by the disc equation of Holling II. The maximum theoretical number of eggs, 1stinsar and 2ndinsar larvae of A. hygrophila captured by O. sertatus,P. subpiraticus and P. japonica per day was 10.9,6.2 and 5.6 eggs,17.1,35.8 and 10.4 1stinsar larvae,and 6.6,11.2 and 2.9 2ndinsar larvae,respectively. The maximum theoretical number of 3rdinsar larvae of A. hygrophila captured by O. sertatus and P. subpiraticus was 12.3 and 1.1 larvae, respectively. The results of our present study suggest that the predation of predators can decrease the population density of A. hygrophila,which weakens the control efficiency of A. hygrophila on A. philoxeroides in the field. Therefore,the predators are an important biotic stress factor that affects survival and development of A. hygrophila in the field. Another further study should focus on how the biocontrol efficiency of A. philoxeroides are enhanced via increasing the population density of A. hygrophila in the field.

The brown-world role of insectivores: Frogs reduce plant growth by suppressing detritivores in an alpine meadow

Predators of plant-suppressing herbivores have long been known to indirectly enhance plant biomass, while more recent work has revealed that predators of plant-facilitating detritivores can have the opposite effect on plant biomass. Generalist predators, such as frogs that typically facilitate plant growth in green food webs, may potentially negatively affect plant growth by consuming prey from brown food webs. In a marshy Tibetan alpine meadow, we tested the hypothesis that the locally abundant frog Rana kukunoris could negatively affect plant growth through suppression of dung-decomposing detritivores that promote plant growth by enhancing nutrient recycling. We conducted a factorial experiment (presence/absence of predators×presence/absence of dung) using replicate field enclosures over a growing season. Where dung was present, frogs significantly reduced the number of dung-feeding beetles and dung-feeding flies (including fly eggs and maggots) per dung pat, thereby decreasing dung mass loss and, indirectly, aboveground plant biomass (by 22%) surrounding dung pats. Where dung was absent, frogs did not affect plant biomass. Moreover, the number of dung beetles was positively associated with dung mass loss and soil soluble N concentration (but not total N concentrations), which in turn positively correlated with aboveground plant biomass. These results indicate that a generalist predator species standing in green food webs may play a contrasting role in brown food webs and indicate that a more nuanced appreciation of the functional role of predators in tri-trophic systems is required to accurately predict their cascading effects. Future studies must assess the relative strength of cascading effects mediated through brown and green channels in order to assess the net cascading effects of generalist predators in natural food webs.

Predator hunting mode influences patterns of prey use from grazing and epigeic food webs

Multichannel omnivory by generalist predators, especially the use of both grazing and epigeic prey, has the potential to increase predator abundance and decrease herbivore populations. However, predator use of the epigeic web (soil surface detritus/microbe/algae consumers) varies considerably for reasons that are poorly understood. We therefore used a stable isotope approach to determine whether prey availability and predator hunting style (active hunting vs. passive web-building) impacted the degree of multichannel omnivory by the two most abundant predators on an intertidal salt marsh, both spiders. We found that carbon isotopic values of herbivores remained constant during the growing season, while values for epigeic feeders became dramatically more enriched such that values for the two webs converged in August. Carbon isotopic values for both spider species remained midway between the two webs as values for epigeic feeders shifted, indicating substantial use of prey from both food webs by both spider species. As the season progressed, prey abundance in the grazing food web increased while prey abundance in the epigeic web remained constant or declined. In response, prey consumption by the web-building spider shifted toward the grazing web to a much greater extent than did consumption by the hunting spider, possibly because passive web-capture is more responsive to changes in prey availability. Although both generalist predator species engaged in multichannel omnivory, hunting mode influenced the extent to which these predators used prey from the grazing and epigeic food webs, and could thereby influence the strength of trophic cascades in both food webs.

Hyperpredation by generalist predatory mites disrupts biological control of aphids by the aphidophagous gall midge Aphidoletes aphidimyza

Biological control of different species of pest with various species of generalist predators can potentially disrupt the control of pests through predator-predator interactions. We evaluate the impact of three species of generalist predatory mites on the biological control of green peach aphids, Myzus persicae (Sulzer) with the aphidophagous gall midge Aphidoletes aphidimyza (Rondani). The predatory mites tested were Neoseiulus cucumeris (Oudemans), Iphiseius degenerans (Berlese) and Amblyseius swirskii Athias–Henriot, which are all commonly used for pest control in greenhouse sweet pepper. All three species of predatory mites were found to feed on eggs of A. aphidimyza, even in the presence of abundant sweet pepper pollen, an alternative food source for the predatory mites. In a greenhouse experiment on sweet pepper, all three predators significantly reduced population densities of A. aphidimyza, but aphid densities only increased significantly in the presence of A. swirskii when compared to the treatment with A. aphidimyza only. This stronger effect of A. swirskii can be explained by the higher population densities that this predator reached on sweet pepper plants compared to the other two predator species. An additional experiment showed that female predatory midges do not avoid oviposition sites with the predator A. swirskii. On the contrary, they even deposited more eggs on plants with predatory mites than on plants without. Hence, this study shows that disruption of aphid control by predatory mites is a realistic scenario in sweet pepper, and needs to be considered when optimizing biological control strategies.

Changes over a decade in fish assemblages exposed to both environmental and fishing constraints in the Sine Saloum estuary (Senegal)

To investigate the changes in the fish assemblage of the Sine Saloum estuary (Senegal) over a 10-year period, it was surveyed during a complete hydrological cycle (three principal hydro-climatic seasons) first in 1992 and then in 2002–2003. The sampling protocol for the two surveys was identical, using the same sampling technique, the same collection periods, and the same sampling stations. The Sine Saloum is an inverse estuary in terms of its salinity gradient. It is affected by the intense drought that has occurred in this biogeographic region for more than 50 years. The estuary is also subjected to high fishing pressure. The second data-collection period followed a few years of higher recorded rainfall (approximately 35% higher than in 1992) and was characterized by increased fishing pressure (over 50% higher than in 1992). For the two study periods, the same set of indicators were calculated, including fishing indicators (catches, density, yields), size-based indicators (size structures, mean length, maximum observed length, size spectra), ecological indicators (richness, species diversity, K-dominance models, ABC curves, ecological categories) and trophic indicators (mean trophic level, trophic composition of catches). Overall, the main changes in the estuary's fish assemblage between 1992 and 2002 were (1) a loss in total biomass (40% less) for an equivalent species richness (approximately 55 species); (2) a decrease in the maximum observed lengths for many species (mean decrease of 17%); and (3) a decrease in the mean trophic level (more than 0.11 units). Analysis by bio-ecological and trophic category showed that the main species concerned were benthophagous species and, to a lesser degree, generalist predator species from marine origin that inhabit the estuary more or less permanently.

Comparison of Ground Beetle (Coleoptera: Carabidae) Assemblages in Rocky Mountain Savannas Invaded and Un-Invaded by an Exotic Forb, Spotted Knapweed

We compared ground beetle (Carabidae) assemblages between spotted knapweed (Centaurea maculosa Lam.) -invaded (invaded) and un-invaded (native) habitats in Rocky Mountain savannas. Carabids play important roles in biotic communities and are known as a good indictor group of environmental change. Carabid species activity-abundance and diversity were estimated, and environmental measurements were taken at four transects at each of six study sites in 1999 and 2000. Data on carabid trap captures were analyzed at both the species and functional group level. We found that species belonging to specialist predator and omnivore functional groups were more abundant on transects at invaded sites, whereas generalist predator species were more abundant within native sites. Carabid species richness was similar between invaded and native sites; however, evenness was greater at invaded compared to native sites. Greater species evenness in invaded versus native sites was primarily due to an increase in activity-abundance of species in the omnivore and specialist predator functional groups and a decrease in activity-abundance of dominant species belonging to the generalist predator functional group. Our results suggest that spotted knapweed invasion results in an alteration of carabid community structure and leads to the homogenization of carabid assemblages in Rocky Mountain savannas. Biotic homogenization, the increase in taxonomic similarity of once-diverse communities, is often a direct outcome of exotic invasions and an important concern currently facing biodiversity conservation.

Numerical and dietary responses of a predator community in a temperate zone of Europe

The generalist predation hypothesis predicts that the functional responses of generalist predator species should be quicker than those of specialist predators and have a regulating effect on vole populations. New interpretations of their role in temperate ecosystems have, however, reactivated a debate suggesting generalist predators may have a destabilizing effect under certain conditions (e.g. landscape homogeneity, low prey diversity, temporary dominance of 1 prey species associated with a high degree of dietary specialization). We studied a rich predator community dominated by generalist carnivores (Martes spp., Vulpes vulpes, Felis catus) over a 6 yr period in farmland and woodland in France. The most frequent prey were small rodents (mostly Microtus arvalis, a grassland species, and Apodemus spp., a woodland species). Alternative prey were diverse and dominated by lagomorphs (Oryctolagus cuniculus, Lepus europeus). We detected a numerical response among specialist carnivores but not among generalist predators. The dietary responses of generalist predators were fairly complex and most often dependent on variation in density of at least 1 prey species. These results support the generalist predation hypothesis. We document a switch to alternative prey, an increase of diet diversity, and a decrease of diet overlap between small and medium‐sized generalists during the low density phase of M. arvalis. In this ecosystem, the high density phases of small mammal species are synchronous and cause a temporary specializing of several generalist predator species. This rapid functional response may indicate the predominant role of generalists in low amplitude population cycles of voles observed in some temperate areas.

Influence of landscape characteristics on carnivore diversity and abundance in Mediterranean farmland

Predation is increasingly pointed out as one of the factors contributing to population declines of ground-nesting farmland birds, though it remains poorly understood how ongoing transformations of agricultural landscapes affect predator assemblages. This study addressed this issue, estimating the contribution of landscape composition and configuration to spatial variation in species richness and abundances of mammalian carnivores across a gradient of agricultural intensification in southern Portugal. The carnivore assemblage was diverse (10 species), but it was largely dominated by just three widespread and abundant species of generalist predators: domestic dog (Canis familiaris), red fox (Vulpes vulpes) and Egyptian mongoose (Herpestes ichneumon). The number of domestic carnivore species and the abundance of cats (Felis catus) increased along with farmland occupation by human dwellings, whereas dogs were not responsive to landscape variables. The species richness of wild carnivores was highest in landscapes with a patchwork of arable fields and semi-natural habitats such as forests and shrubland, though it was also high in irrigated landscapes with dense networks of irrigation channels and tree lines bordering agricultural fields. Irrigation was also positively associated with the abundance of otters (Lutra lutra) and mongooses. Cats, foxes, badgers (Meles meles), and total and wild carnivore abundances, were positively affected by increasing cover by eucalyptus and pine forest plantations. In general, results suggest that the highest diversity and abundance of carnivores in Mediterranean farmland may occur in mosaic landscapes with small agricultural fields, high cover by woody vegetation patches and corridors, and many human dwellings. Preventing scrub encroachment and afforestation may thus be necessary to maintain a low predation risk in open farmland habitats, which are often inhabited by ground-nesting birds of high conservation concern. Conversely, keeping shrubland and forest patches within farmed landscapes may be essential where carnivore persistence is a relevant conservation goal.