Predator-prey Ratios Research Articles

Evaluating the relative importance of habitat filtering and niche differentiation in shaping the food web of dung-inhabiting predators

Investigation into the mechanisms responsible for community assembly (habitat filtering, niche differentiation) is essential for understanding the processes maintaining coexistence of species rich natural communities. Studies of such mechanisms have up to now been almost exclusively limited to communities of primary producers or consumers, and very few are focused on coexistence of predatory communities. Top-down regulation by predators is on the other hand essential in structuring communities of primary consumers. We therefore present a study focusing on coexistence and assembly in a species rich community of dung-inhabiting predators, investigating the potential effect of their temporal trends (succession, seasonality) on lowering their negative interactions (competition and intra-guild predation). We used field derived predator-prey co-occurrence data in combination with previous observations of trophic interactions and morphological constraints to describe the potential food web of dung-inhabiting insects. We used that food web to establish all combinations of negative interactions among individual species. We then analyzed whether interaction between species successional and seasonal optima could lower or eliminate their negative interactions. The predator prey ratio increased throughout dung pat succession, remaining constant among seasons. We found that the predator size decreased along the successional gradient, while similarly sized predators were evenly distributed across seasons. The succession of dung-inhabiting predators therefore displayed potential for environmental filtering. In contrast, seasonality niche differentiation seems to promote coexistence of species co-occurring along succession. The interaction of both species temporal patterns should significantly reduce or even eliminate the potential negative interactions between dung-inhabiting predators and thus promote high species richness in communities of dung-inhabiting insects.

Life-cycle complexity in helminths: What are the benefits?

Parasitic worms (i.e., helminths) commonly infect multiple hosts in succession. With every transmission step, they risk not infecting the next host and thus dying before reproducing. Given this risk, what are the benefits of complex life cycles? Using a dataset for 973 species of trophically transmitted acanthocephalans, cestodes, and nematodes, we tested whether hosts at the start of a life cycle increase transmission and whether hosts at the end of a life cycle enable growth to larger, more fecund sizes. Helminths with longer life cycles, that is, more successive hosts, infected conspicuously smaller first hosts, slightly larger final hosts, and exploited trophic links with lower predator-prey mass ratios. Smaller first hosts likely facilitate transmission because of their higher abundance and because parasite propagules were the size of their normal food. Bigger definitive hosts likely increase fecundity because parasites grew larger in big hosts, particularly endotherms. Helminths with long life cycles attained larger adult sizes through later maturation, not faster growth. Our results indicate that complex helminth life cycles are ubiquitous because growth and reproduction are highest in large, endothermic hosts that are typically only accessible via small intermediate hosts, that is, the best hosts for growth and transmission are not the same.

Neighbourhood effect of faba bean (Vicia faba L.) on density of vegetation-dwelling natural biocontrol agents in winter wheat

Legume crops such as faba bean (Vicia faba L.) have been underrepresented in conventional cropping systems in Europe for decades for economic reasons, even though faba bean is a native crop and suitable to diversify local cropping systems. While the environmental benefits that go along with faba bean cropping are well established, there is a gap of knowledge on the effects faba bean may have on biodiversity and associated ecosystem services, such as natural biocontrol in agricultural landscapes.The aim of the present field study was to quantify neighbourhood effects of faba bean on densities of vegetation- dwelling natural biocontrol agents and herbivores in adjacent winter wheat. Densities of predators, herbivores, parasitized aphids (mummies) and leaf damage by the cereal leaf beetle (CLB) were assessed by repeated visual counts in conventionally managed winter wheat crops. In winter wheat adjacent to faba bean, total predator density was higher than in wheat adjacent to winter wheat, independent of the observation period. This effect was not reflected in the predator-prey ratio though. The total density of mummies and parasitism rate were not affected by the neighbouring faba bean crop. Predator density decreased towards the field centre. CLB leaf damage and yield were not affected by the neighbouring crop. All densities were affected by the observation period. The effects were measurable in spite of the external management such as insecticide application, which had a negative effect on both predator and herbivore densities. The present study sheds first light on faba bean effects on natural biocontrol agents in conventionally managed agro-ecosystems. While few, effects were measurable, which shows the need for further research on the association of faba bean cropping with the ecosystem service natural biocontrol.

Retraction.

Previous article FreeRetractionChristopher E. Oufiero, Leticia Avilés, and Susan E. RiechertChristopher E. Oufiero1. Department of Biological Sciences, Towson University, Towson, Maryland 21252 Search for more articles by this author , Leticia Avilés2. Department of Zoology, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada Search for more articles by this author , and Susan E. Riechert1. Department of Biological Sciences, Towson University, Towson, Maryland 21252 Search for more articles by this author 3. Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee 37996Original articleIterative Evolution of Increased Behavioral Variation Characterizes the Transition to Sociality in Spiders and Proves Advantageous.Full TextPDF Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinked InRedditEmailQR Code SectionsMoreThe article “Iterative Evolution of Increased Behavioral Variation Characterizes the Transition to Sociality in Spiders and Proves Advantageous,” published in the October 2012 issue of The American Naturalist (pp. 496–510), is retracted by The American Naturalist and the authors of this retraction. Investigation by the journal, which was fully examined by all authors, revealed duplicate ratios of spider mass to prey mass, which was often an exact value (e.g., 0.3, followed by 0.33 and 0.34 exactly). Similar anomalies, with redundant predator-prey mass ratios, were also found for other size categories. These anomalies in data collection by Jonathan N. Pruitt could not be explained, undermining the credibility of the article’s results. On this basis, the authors of this statement regretfully retract the article. Previous article DetailsFiguresReferencesCited by The American Naturalist Volume 197, Number 3March 2021 Published for The American Society of Naturalists Article DOIhttps://doi.org/10.1086/713144 Views: 4504 HistoryPublished online January 19, 2021 © 2021 by The University of Chicago. All rights reserved. Crossref reports no articles citing this article.Related articlesIterative Evolution of Increased Behavioral Variation Characterizes the Transition to Sociality in Spiders and Proves Advantageous.17 Jul 2015The American Naturalist

Establishment of the predator Laricobius nigrinus, introduced as a biological control agent for hemlock woolly adelgid in Virginia, USA

Laricobius nigrinus Fender (Coleoptera: Derodontidae), a predatory beetle native to western North America, has been released since 2003 for management of hemlock woolly adelgid (HWA), Adelges tsugae Annand (Hemiptera: Adelgidae), a non-native pest killing hemlocks in eastern North America. Over 420,000 L. nigrinus have been released in the eastern USA from field and lab-reared sources, 14,000 of which were deployed in the Commonwealth of Virginia, USA. In order to determine the establishment rates of L. nigrinus in Virginia, surveys were conducted in 2017 and 2018 at all release sites within this state. During the study, stand-level HWA densities were estimated, and hemlock tree health and predator–prey ratios were quantified. The identification of Laricobius spp. recoveries were made using microsatellite analysis. During the period of the study, L. nigrinus were found to have established at 82% of Virginia release sites and were the primary species recovered (80%). Both Laricobius rubidus (18%) and hybrids (2%) were also recovered. Stand-level HWA densities varied greatly over sites and years but showed a general decline in year two of the study. Establishment at such a high percentage of release sites suggests that the climate in Virginia is suitable for the predator and the insect is adaptable to the wide variety of site conditions where hemlocks typically grow.

Observations on feeding habits of the common dolphinfish,Coryphaena hippurus(Linnaeus 1758) from the western Bay of Bengal

Coryphaena hippurusis a large pelagic species and constitutes an important by-catch in drift gillnet, trolling and long-line fishing gears operated along the Bay of Bengal, northeastern Indian Ocean. The present study, first from the region, is aimed at deciphering the feeding dynamics from 1150 individuals collected from 2017 to 2019. 32.17% of the fishes had empty stomachs or was with food traces, 45.57% had partially-full stomachs and 22.26% had full stomachs. The feeding intensity was inferred through stomach filling and predator-prey weight ratio, which was higher in May and lower in January, and increasing as increase in the fish size.Coryphaena hippurusis considered a piscivorous pelagic predator as pelagic teleosts contribute more than half of the prey species. Major prey species were big-eye scad (27.3%), squid (10.3%), crabs (9.3%), Indian mackerel (7.2%), Indian scad (5.9%), whitebaits (5.7%) and sardines (5.4%). Scads and crabs were abundantly preyed during summer and winter, while clupeids and engraulids in monsoon; however, no significant variations were observed in prey composition between sizes. Trophic Level was 4.22 ± 0.15 and Levins Standardized Niche Breadth Index was 0.30. Dietary niche breadth was higher during summer (0.48) and monsoon (0.33) and in fishes measuring 60.0–74.9 cm (0.51) and below 45.0 cm (0.48) indicating generalised feeding. This primary study from Bay of Bengal is the first comprehensive report on trophodynamics for the species and would contribute to its management using trophic interactions.

Organohalogen compounds of emerging concern in Baltic Sea biota: Levels, biomagnification potential and comparisons with legacy contaminants

While new chemicals have replaced major toxic legacy contaminants such as polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDT), knowledge of their current levels and biomagnification potential in Baltic Sea biota is lacking. Therefore, a suite of chemicals of emerging concern, including organophosphate esters (OPEs), short-chain, medium-chain and long-chain chlorinated paraffins (SCCPs, MCCPs, LCCPs), halogenated flame retardants (HFRs), and per- and polyfluoroalkyl substances (PFAS), were analysed in blue mussel (Mytilus edulis), viviparous eelpout (Zoarces viviparus), Atlantic herring (Clupea harengus), grey seal (Halichoerus grypus), harbor seal (Phoca vitulina), harbor porpoise (Phocoena phocoena), common eider (Somateria mollissima), common guillemot (Uria aalge) and white-tailed eagle (Haliaeetus albicilla) from the Baltic Proper, sampled between 2006 and 2016. Results were benchmarked with existing data for legacy contaminants. The mean concentrations for ΣOPEs ranged from 57 to 550 ng g−1 lipid weight (lw), for ΣCPs from 110 to 640 ng g−1 lw for ΣHFRs from 0.42 to 80 ng g−1 lw, and for ΣPFAS from 1.1 to 450 ng g−1 wet weight. Perfluoro-4-ethylcyclohexanesulfonate (PFECHS) was detected in most species. Levels of OPEs, CPs and HFRs were generally similar or higher than those of polybrominated diphenyl ethers (PBDEs) and/or hexabromocyclododecane (HBCDD). OPE, CP and HFR concentrations were also similar to PCBs and DDTs in blue mussel, viviparous eelpout and Atlantic herring. In marine mammals and birds, PCB and DDT concentrations remained orders of magnitude higher than those of OPEs, CPs, HFRs and PFAS. Predator-prey ratios for individual OPEs (0.28–3.9) and CPs (0.40–5.0) were similar or somewhat lower than those seen for BDE-47 (5.0–29) and HBCDD (2.4–13). Ratios for individual HFRs (0.010–37) and PFAS (0.15–47) were, however, of the same order of magnitude as seen for p,p′-DDE (4.7–66) and CB-153 (31–190), indicating biomagnification potential for many of the emerging contaminants. Lack of toxicity data, including for complex mixtures, makes it difficult to assess the risks emerging contaminants pose. Their occurence and biomagnification potential should trigger risk management measures, particularly for MCCPs, HFRs and PFAS.

Predation Efficacy of Rove Beetle (Coleoptera: Staphylinidae) Adults in Response to Western Flower Thrips (Thysanoptera: Thripidae) Pupal Stage, Predator–Prey Ratio, and Searchable Area

AbstractThe rove beetle, Dalotia coriaria (Kraatz) (Coleoptera: Staphylinidae), is a soil-dwelling predator that preys upon insect pests residing in growing media. Minimal information exists addressing its predation on western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), below-ground life stages. Two laboratory experiments were conducted to assess the effects of western flower thrips pupal stage, predator–prey ratio, and searchable area on predation efficacy of rove beetle adults. In Experiment 1, predation was recorded in response to two thrips pupal stages (prepupae and pupae); three predator–prey ratios (1:5, 1:10, 1:15) and predator–prey ratios that were 2, 3, and 4 times greater. Experiment 2 was designed to assess predation in response to those predator–prey ratios along with searchable areas in 15.2- and 11.5-cm-diameter containers. Response was measured by capturing thrips adults on yellow sticky cards (YSC) as they emerged from pupation. The estimated mean probability of thrips adults captured on the cards was significantly higher for the 1:5 (61.1%) than for the 1:10 (39%) and 1:15 (34.7%) predator–prey ratios. The estimated mean probability of thrips adults captured on the cards for 2 times the predator–prey ratio (57%) was significantly higher than 3 times (37.2%) and 4 times (40.6%) the ratios. A significantly higher estimated mean probability of thrips adults was captured on the cards in the 15.2-cm-diameter containers than in the 11.5-cm-diameter containers. We conclude that a predator–prey ratio of 1:15 would result in fewer rove beetle adults needed to reduce western flower thrips prepupae/pupae stages and subsequent adult populations.

Influence of intra- and interspecific variation in predator-prey body size ratios on trophic interaction strengths.

Predation is a pervasive force that structures food webs and directly influences ecosystem functioning. The relative body sizes of predators and prey may be an important determinant of interaction strengths. However, studies quantifying the combined influence of intra‐ and interspecific variation in predator–prey body size ratios are lacking.We use a comparative functional response approach to examine interaction strengths between three size classes of invasive bluegill and largemouth bass toward three scaled size classes of their tilapia prey. We then quantify the influence of intra‐ and interspecific predator–prey body mass ratios on the scaling of attack rates and handling times.Type II functional responses were displayed by both predators across all predator and prey size classes. Largemouth bass consumed more than bluegill at small and intermediate predator size classes, while large predators of both species were more similar. Small prey were most vulnerable overall; however, differential attack rates among prey were emergent across predator sizes. For both bluegill and largemouth bass, small predators exhibited higher attack rates toward small and intermediate prey sizes, while larger predators exhibited greater attack rates toward large prey. Conversely, handling times increased with prey size, with small bluegill exhibiting particularly low feeding rates toward medium–large prey types. Attack rates for both predators peaked unimodally at intermediate predator–prey body mass ratios, while handling times generally shortened across increasing body mass ratios.We thus demonstrate effects of body size ratios on predator–prey interaction strengths between key fish species, with attack rates and handling times dependent on the relative sizes of predator–prey participants.Considerations for intra‐ and interspecific body size ratio effects are critical for predicting the strengths of interactions within ecosystems and may drive differential ecological impacts among invasive species as size ratios shift.

Temporal variation of the effects of landscape composition on lacewings (Chrysopidae: Neuroptera) in vineyards

Abstract Increasing landscape heterogeneity, both in terms of composition and configuration, can promote natural enemies and biological control in agricultural landscapes. However, relatively poor information exists about the effects of landscape heterogeneity on lacewings, which are a major group of predators. Furthermore, temporal changes of landscape effects on natural enemy dynamics remain largely unexplored. Here, we investigated how landscape composition and configuration affect lacewings and their biological control potential on leafhoppers. Lacewings and leafhoppers were sampled from April to July in 10 vineyards located in southwestern France. The vineyards were selected along a gradient of a proportion of semi‐natural habitats in the landscape. The proportion of semi‐natural habitats positively affected the abundance of adults and eggs, as well as species richness, of lacewings, alone or in interaction with the sampling month. Landscape configuration was never found to enhance abundance or species richness of lacewings. Finally, the predator–prey ratio increased through time but did not respond to landscape composition or configuration. Our study highlights that the proportion of semi‐natural habitats increases both abundance and diversity of lacewings in vineyard landscapes but that this effect varies over time. This result indicates the need to assess the variability of landscape effects over time to maximize biological pest control services in agricultural landscapes.

Role of Stethours gilvifrons (Mulsant) as Biological Control Agents of the Two Spotted Spider Mite Tetranychus urticae Koch

Predaceous insects is an effective important biological control agents of feeding on Tetranychus urticae Koch and decreasing the number during 2018 season to study the optimal predator: prey ratios for the release of Stethours gilvifrons (Mulsant) sacond larvae and adult stage for controlling the T. urticae on cottonplants Gossypium burbadense L. The obtained results showed that the effective control was gained after 12 days from released the second larvae and adult of the S. gilvifrons predatorwhen the predator: prey ratios were 1:15and1:25 respectively. The regression analysis between predator: prey ratios of S. gilvifrons (larvae and adults) reduction percentages cleared that there were negatively high relationship of larvae and adult predators and prey ratios, which means that the reduction rate was increased with lower predator : prey ratios and vice versa .The results assured that the best control of T.urticae populations under semi field conditions was cleared by using the lower predator prey ratios (1:15 and 1:25) . Finally the predators can be used as biological control agents for T.urticae in cotten plantation under field conditions. The regression analysis between P: p ratios of S. gilvifrons adults and reduction percentage of the T.urticae mites , data showed there were negatively highly relationship of both predators larvae and adult which means that the reduction rate was increased with lower P: p ratios and vice versa.

Evaluating functional diversity conservation for freshwater fishes resulting from terrestrial protected areas

Abstract Protected areas are one of the hammers in conservation toolkits, yet few protected areas exist that were designed to protect freshwater ecosystems. This is problematic as freshwater ecosystems are among the most threatened systems on earth. Nonetheless, terrestrial protected areas (TPAs) may afford spill‐over benefits to freshwater ecosystems included within their boundaries, but evaluations of these potential benefits for the protection of freshwater fish diversity are lacking. Using fish community data from 175 lakes inside, outside, or bordering TPAs in Ontario, Canada, we sought to determine if TPAs preserve fish functional diversity. We focused on functional diversity because previous work indicated no taxonomic differences between these lakes, but a difference in normalised‐length size‐spectra slopes inside versus outside TPAs (indicator of unique predator–prey ratios and trophic energy transfer). We expected that communities inside TPAs would show greater functional diversity (i.e. functional dispersion and functional richness) and have more extreme trait combinations (i.e. functional divergence) than communities outside or bordering TPAs. We also tested for differences in the rarity of species‐specific functional traits between fish communities inside, outside, or bordering TPAs, between thermal guilds, and across average body size and overall prevalence of the species. Our results indicated no significant differences in functional diversity among lake fish communities inside, outside, or bordering TPAs. However, fish communities inside TPAs had more extreme trait combinations than outside TPAs because abundant species in lake communities outside TPAs had more ubiquitous trait combinations than abundant fishes inside TPAs. Small‐bodied species showed greater functional rarity than large‐bodied species, indicating that small‐bodied fishes fill functionally unique roles while the most prevalent, large‐bodied species possess a more generalist set of traits. Overall, the similarity of functional diversity metrics for lake fish communities inside, outside, or bordering TPAs in Ontario suggests that TPAs capture the functional diversity of Ontario's lake fish communities. However, we encourage similar evaluations in regions where environmental conditions and stressors are more distinct across TPA boundaries than they are in Ontario, as these types of evaluations will inform guidelines for the design of freshwater protected areas and monitoring of their effectiveness in the future.

Structure and nutrient transfer in a tropical pelagic upwelling food web: From isoscapes to the whole ecosystem

Little is known about ecosystem structure and nutrient flux in the pelagic zone of seasonal upwelling systems in the tropics, despite their global importance to marine production. The Tropical Eastern Pacific (TEP) is responsible for around 10% of global ocean productivity, largely due to wind-driven seasonal upwelling areas between Mexico and Panama. The Gulf of Panama has a detectable outflow for hundreds of kilometres into the Pacific Ocean and the upwelling system there is an important productivity source in the TEP. In this study, we aim to determine the spatio-temporal patterns in variability of carbon and nitrogen stable isotope composition throughout the pelagic ecosystem of the Bay of Panama in upwelling and non-upwelling conditions, and how these patterns are recorded throughout the ecosystem from primary producers to apex predators. We characterise the stable isotope composition of basal production in the ecosystem to quantify spatial variability during the non-upwelling season. We use the δ15N composition outside of upwelling season as an ecosystem baseline and quantify the overall δ15N separation between all trophic levels (TL) from primary producers to apex predators (e.g. yellowfin tuna and mahi mahi) within the pelagic ecosystem (2.9 ± 0.1‰ per TL). The ecosystem has a relatively simple, linear structure with size-based TL increase. We calculate the predator-prey mass ratio of this ecosystem (c. 113:1 for fishes, 376:1 for the whole ecosystem, uncertainty range: 77:1–1272:1). These values are low for existing estimates in other marine ecosystems, although within the expected range for animals of the mass sampled. The calculated predator-prey mass ratios and maximum TL indicate that this pelagic ecosystem may have a relatively long trophic chain, with inefficient nutrient transfer from low to high TLs.Using a monthly time series of stable isotope values of resident, planktivorous fishes and co-occurring sea surface temperature measurements, we determine nutrient transfer time between primary production and TL3 fish. We calculate a rapid nutrient turnover time within this ecosystem as 0.5–1 month per TL. The incorporation of upwelled nutrients, which are enriched in the 13C, leads to higher consumer δ13C values. Carbon isotopes can therefore be used to track timing, duration, and use of upwelling zones. Our findings give novel, empirical insights into the functional ecology of the pelagic ecosystem in the Gulf of Panama, and provide a baseline for comparison and quantification of ecosystem structure and dynamics in the tropics, and in other pelagic upwelling systems.

<p class="Body">Effect of pollen with different predator release ratios on biological control of Tetranychus urticae by the predaceous mite Kampimodromus aberrans

The purpose of this study was to examine the impact of birch pollen (Betula pendula Roth.) on the efficacy of the predatory mite Kampimodromus aberrans (Oudemans) (Acari: Phytoseiidae) as a biological control agent for the two spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae) at different predator release ratios. The experiments were conducted on apple cv. Golden Delicious at 1:5, 1:15 and 1:30 predator-prey release ratios in a climate room (25±2°C, 65±10% RH and 16:8 L:D). The predatory mites were also offered pollen grains daily (0.5-0.10 mg/leaf) on the apple seedling during the experiments. One week after the release of K. aberrans, significant reductions in T. urticae density were observed at a ratio of 1:5; and the density remained at low levels thereafter, especially in the pollen experiments. The highest mean numbers of T. urticae in the control group (no predator release) were observed in week 3 with 4067 mites per leaf and 4922 mites per leaf, respectively for the pollen and no pollen application plots. This study demonstrates the potential of K. aberrans to effectively control T. urticae at ratios of 1:5 and 1:15 within three weeks, especially at a ratio of 1:5 when the pollen was added. Furthermore, releasing K. aberrans at the appropriate time and ratio enabled more successful control of T. urticae populations and plant damage, and subsequently kept the mites at low levels.

Predator traits determine food-web architecture across ecosystems.

Predator-prey interactions in natural ecosystems generate complex food webs that have a simple universal body-size architecture where predators are systematically larger than their prey. Food-web theory shows that the highest predator-prey body-mass ratios found in natural food webs may be especially important because they create weak interactions with slow dynamics that stabilize communities against perturbations and maintain ecosystem functioning. Identifying these vital interactions in real communities typically requires arduous identification of interactions in complex food webs. Here, we overcome this obstacle by developing predator-trait models to predict average body-mass ratios based on a database comprising 290 food webs from freshwater, marine and terrestrial ecosystems across all continents. We analysed how species traits constrain body-size architecture by changing the slope of the predator-prey body-mass scaling. Across ecosystems, we found high body-mass ratios for predator groups with specific trait combinations including (1) small vertebrates and (2) large swimming or flying predators. Including the metabolic and movement types of predators increased the accuracy of predicting which species are engaged in high body-mass ratio interactions. We demonstrate that species traits explain striking patterns in the body-size architecture of natural food webs that underpin the stability and functioning of ecosystems, paving the way for community-level management of the most complex natural ecosystems.

Impact of vineyard agrochemicals against Panonychus ulmi (Acari: Tetranychidae) and its natural enemy, Neoseiulus californicus (Acari: Phytoseiidae) in Brazil

Grapevines are attacked by diseases and pests, and strategies used by wine makers for the control of these involve the use of agrochemicals, causing in balancing of predator-prey ratios. The spider mite Panonychus ulmi causes damage to grapevines in the South of Brazil, whereas Neoseiulus californicus is the most frequently used predatory mite in biological control of tetranychids in Brazil. The effects of 13 agrochemicals used in the wine growing sector and their effect on P. ulmi and N. californicus were evaluated. A residual contact method by air-brush spraying was used. The corrected mortality rate and the effect of products on mite reproduction were evaluated and eggs were monitored until larval hatching to evaluate viability. Products were classified according to the total effect caused, in toxicity classes proposed by the IOBC/WPRS Working Group “Pesticides and beneficial organisms”. Lambda-cyhalothrin was the product that caused the highest mortality rate of P. ulmi: 76% within 24 h after spraying, reaching 100% mortality within 72 h. The other products caused mortality between 50% and 60% at 96 and 120 h. None of the products fitted into the harmless category; however, the fungicides azoxystrobin, metiram + pyraclostrobin, copper hydroxide and mancozeb showed low toxicity to the pest and predator. So, it is probably they can be used for doses management without disrupting the mite biocontrol. The products recommended which were harmful to the predator were cymoxanil + mancozeb, tetraconazole, lambda-cyhalothrin, famoxadone + mancozeb. These results can be used to develop guidelines on the best products to be used in the field, thus creating pest management practices that preserves predatory mite populations in vineyards.

Prey body mass and richness underlie the persistence of a top predator.

Predators and prey often differ in body mass. The ratio of predator to prey body mass influences the predator's functional response (how consumption varies with prey density), and therefore, the strength and stability of the predator-prey interaction. The persistence of food chains is maximized when prey species are neither too big nor too small relative to their predator. Nonetheless, we do not know if (i) food web persistence requires that all predator-prey body mass ratios are intermediate, nor (ii) if this constraint depends on prey diversity. We experimentally quantified the functional response for a single predator consuming prey species of different body masses. We used the resultant allometric functional response to parametrize a food web model. We found that predator persistence was maximized when the minimum prey size in the community was intermediate, but as prey diversity increased, the minimum body size could take a broader range of values. This last result occurs because of Jensen's inequality: the average handling time for multiple prey of different sizes is higher than the handling time of the average sized prey. Our results demonstrate that prey diversity mediates how differences between predators and prey in body mass determine food web stability.

Limb Regeneration and Interference Competition Consequences on Foraging Efficiency of Coccinella undecimpunctata and Hippodamia variegata (Coccinellidae: Coleoptera) to Their Prey, Aphis craccivora (Hemiptera: Aphididae).

Regeneration of limbs lost during development has been recorded in a large number of species of hexapoda including many Coccinellids. Although regeneration has obvious survival and fitness benefits, it has also been demonstrated to impose costs on development, reproduction, and behavior. To investigate consequences of regeneration on foraging behavior, Coccinella undecimpunctata L. and Hippodamia variegata (Goeze) larvae were treated to remove one limb, allowed to pupate and regenerate and then prey searching ability assessed. Different densities of adults were placed in Petri dishes with aphid prey and consumption assessed over a 24-h period. Amputation/regeneration, predator species, and predator density significantly affected the total number of aphids consumed. Aphid consumption rates and predation efficiency of both regenerated and control beetles significantly increased as predator density increased. Although there were significant differences in consumption between ablated/regenerated and control C. undecimpunctata at each predator densities, H. variegata did not. Further, mutual interference was significantly higher for regenerated compared with control C. undecimpunctata but not so for H. variegata. This is the first demonstration of an effect of ablation/regeneration on foraging behavior of C. undecimpunctata and suggests that H. variegata demonstrates an adaptive phenotypic response to limb regeneration. Coccinellids are widely used as biological agents and these findings concerning the impact of variation in predator density have clear implications for the management of predator-prey ratios in order to maximize efficiency of pest consumption.

Coexisting large carnivores: spatial relationships of tigers and leopards and their prey in a prey-rich area in lowland Nepal

ABSTRACTIn the Shuklaphanta National Park (Nepal), we sampled the spatial distributions and diel activity patterns of tigers and leopards during three winter (dry) seasons. Densities of both predators were similar and rather low (≤ 3/100 km2), but total prey base was high (> 150 animals/km2). From camera trapping, 20 different tigers and leopards were identified. While leopards (9) were confined to areas along the reserve border, tigers (11) were located significantly farther inside, where the abundance of large-sized wild prey was higher and that of small-sized prey lower than closer to the border. In the inter-specific spatial overlap zones, the two species were never photographed at the same locations. Diel activity patterns did not differ. Normally, leopards avoid tigers owing to social interference. In our study, the spatial segregation was interpreted to be due to low predator-prey ratios (e.g., food not limiting for either species), with each species distributed in areas with highest densities of their preferred prey. Social interference behavior ‒ although probably occurring ‒ played a minor role. The concentration of leopards along the reserve border, coupled with a diet that included domestic dogs, suggest that different behavioral adaptations to anthropogenic factors might also have played a role.

Prey Limitation Drives Variation in Allometric Scaling of Predator-Prey Interactions

Ecologists have long searched for a universal size-scaling constant that governs trophic interactions. Although this is an appealing theoretical concept, predator-prey size ratios (PPSRs) vary strikingly across and within natural food webs, meaning that predators deviate from their optimal prey size by consuming relatively larger or smaller prey. Here we suggest that this unexpected variation in allometric scaling of trophic interactions can be predicted by gradients of prey limitation consistent with predictions from optimal foraging theory. We analyzed >6,000 trophic interactions of 52 populations from four tropical frog species along a gradient of prey limitation. The mean of PPSR and its variance differed up to two orders of magnitude across and within food webs. Importantly, as prey availability decreased across food webs, PPSR and its variance became more size dependent. Thus, trophic interactions did not follow a fixed allometric scaling but changed predictably with the strength of prey limitation. Our results emphasize the importance of ecological contexts in arranging food webs and the need to incorporate ecological drivers of PPSR and its variance in food web and community models.