Stonefly nymphs use hydrodynamic cues to discriminate between prey

Summary Playback experiments conducted in a Rocky Mountain, USA, stream determined whether predatory stonefly nymphs (Kogotus modestus; Plecoptera: PerlodiMae) used hydrodynamic cues to discriminate prey species from nonprey species. In the laboratory we recorded pressure wave patterns associated with swimming escape behavior of Baetis bicaudatus (Baetidae), the favored mayfly prey species, and those of a nonprey mayfly, Ephemerella infrequens (Ephemerellidae). We video taped the responses of 24-h starved Kogotus to Baetis playbacks, Ephemerella playbacks or no playbacks made by oscillating (or not) live mayflies (Ephemerella) or clear plastic models placed within in situ flow-through observation boxes. The probability of attacks per encounter with Baetis playbacks was highest and independent of the model type used, but Kogotus also showed an unexpected high probability of attacks per encounter when Ephemerella playbacks were made through live Ephemerella. Thus, Kogotus discriminated between Baetis and Ephemerella swimming patterns but only when playbacks were made through the plastic model. Kogotus never attacked motionless mayflies or motionless plastic models. We allowed some Kogotus to successfully capture one small Baetis immediately before playbacks, which resulted in a much higher probability of attacks per encounter with Baetis playbacks on either model and a heightened discrimination of prey versus nonprey playbacks. The probability of attacks per encounter by Kogotus with live Baetis swimming under similar experimental conditions was strikingly similar to its response to Baetis playbacks made by oscillating the plastic model after a successful capture. Order of playback presentation (Baetis first or Ephemerella first) did not influence predatory responses to mayfly swimming patterns. This study is the first to document the use of hydrodynamic cues by stream-dwelling predators for discrimination of prey from nonprey and provides a mechanism to explain selective predation by stoneflies on Baetis in nature.     

Foraging distribution overlap and marine reserve usage amongst sub-Antarctic predators inferred from a multi-species satellite tagging experiment

Satellite telemetry data was used to predict at sea spatial usage of five top order and meso-predators; Antarctic fur seals (Arctocephalus gazella), macaroni penguins (Eudyptes chrysolophus), king penguins (Aptenodytes patagonicus), black browed albatross (Diomedea melanophrys), and light mantled albatross (Phoebetria palpebrata). All were tagged at Heard Island in the Southern Ocean over a single summer season collecting over 5000 tracking days for 178 individuals. We aimed to predict areas of likely high foraging value from tracking environmental data and also to quantify overlap in foraging range between species. Hidden Markov models were used to differentiate between bouts of Area Restricted Search (ARS) assumed to be associated with areas of higher foraging value, and transit behaviours. Oceanographic and distance metrics associated with ARS activity were then used to calculate a habitat electivity index. A combined bootstrap/Monte Carlo scheme was employed to propagate uncertainty from the Hidden Markov models into the habitat prediction scheme. Distinct differences were predicted in the spatial distribution of foraging locations in different species, reflecting different dispersive abilities and foraging strategy. The extent of usage and foraging distribution was largely contained within Australian the Economic Exclusion Zone (EEZ). In comparison, the smaller Australian Commonwealth Marine Protected Areas (MPAs) contained <20% of the predicted foraging distributions.     

Trophic niche overlap between sympatric harbour seals (Phoca vitulina) and grey seals (Halichoerus grypus) at the southern limit of their European range (Eastern English Channel)

Sympatric harbour (Phoca vitulina) and grey seals (Halichoerus grypus) are increasingly considered potential competitors, especially since recent local declines in harbour seal numbers while grey seal numbers remained stable or increased at their European core distributions. A better understanding of the interactions between these species is critical for conservation efforts. This study aimed to identify the trophic niche overlap between harbour and grey seals at the southern limit of their European range, in the Baie de Somme (BDS, Eastern English Channel, France), where numbers of resident harbour seals and visiting grey seals are increasing exponentially. Dietary overlap was identified from scat contents using hierarchical clustering. Isotopic niche overlap was quantified using δ¹³C and δ¹⁵N isotopic values from whiskers of 18 individuals, by estimating isotopic standard ellipses with a novel hierarchical model developed in a Bayesian framework to consider both intraindividual variability and interindividual variability. Foraging areas of these individuals were identified from telemetry data. The three independent approaches provided converging results, revealing a high trophic niche overlap due to consumption of benthic flatfish. Two diet clusters were dominated by either small or large benthic flatfish; these comprised 85.5% [CI95%: 80.3%–90.2%] of harbour seal scats and 46.8% [35.1%–58.4%] of grey seal scats. The narrower isotopic niche of harbour seals was nested within that of grey seals (58.2% [22.7%–100%] overlap). Grey seals with isotopic values similar to harbour seals foraged in coastal waters close to the BDS alike harbour seals did, suggesting the niche overlap may be due to individual grey seal strategies. Our findings therefore provide the basis for potential competition between both species (foraging on benthic flatfish close to the BDS). We suggest that a continued increase in seal numbers and/or a decrease in flatfish supply in this area could cause/amplify competitive interactions and have deleterious effects on harbour seal colonies.     

Soil moisture, no-tillage and predator effects on southern corn rootworm survival in peanut agroecosystems

Experiments examined the effects of no-tillage (NT) and conventional-tillage (CT) and increased soil moisture (irrigation) on southern corn rootworm (SCR), Diabrotica undecimpunctata howardi Barber (Coleoptera: Chrysomelidae), oviposition and survival and SCR below-ground predators in peanut (Arachis hypogeae L.) agroecosystems. No-tillage systems without irrigation had significantly greater soil moisture than CT systems without irrigation in 1987, but not in 1988. Both moist soil and the presence of an organic residue increased the number of southern corn rootworm eggs in a system. The same 17 species of predatory arthropods were found in all systems. However, their activity in the top 10-cm of soil which increased in NT systems, determined how effective they were as predators. Only 7 predators significantly reduced SCR immature stages, and of these 7, only one, Formicidae, preyed on all stages of SCR. Southern corn rootworm first instars and eggs had the greatest overall percent mortality, with second and third instars the lowest. Peanut yields and pod quality were equal between NT and CT systems. Overall return per ha showed NT, no-irrigation systems with the greatest return. Abiotic parameters dominated SCR survival in CT systems, while biotic parameters had the greatest influence on SCR survival in NT systems.

---

Résumé Des expériences ont été entreprises pour examiner l'influence de labours classiques ou de leur absence et de l'augmentation de l'humidité du sol (irrigation) sur la ponte et la survie de D. undecimpunctata howardi Barber (Coleo. Chrysomelidae) et sur ses prédateurs souterrains dans des agrosystèmes à arachide. L'humidité du sol s'est montrée significativement plus élevée dans les parcelles irriguées pendant les deux années, 1987 et 1988, mais, en 1987 et non en 1988, l'humidité du sol a été significativement plus élevée dans le sol non labouré pourtant non irrigué que dans le sol labouré et irrigué. La présence de sol humide et de résidus organiques augmente le nombre d'ufs émis. Les mêmes 17 espèces d'arthropodes prédateurs dateurs souterrains ont été rencontrés dans toutes les sols non labourés et parfois dans les sols labourés irrigués; leur activité détermine leur efficacité comme prédateur. 7 espèces réduisent les effectifs de larves, mais une seule d'entre elles, une Formicidae, (Lasius spp. et Pheidole spp.) s'est révélée prédatrice de tous les stades de la chrysomèle. La plus forte mortalité de D. u. howardi a été observée sur les ufs et les larves de premier stade, la plus faible sur les larves de deuxième et troisième stade. La récolte et la qualité des arachides sont identiques avec ou sans labour. Ainsi, la rentabilité financière par ha était supérieure dans les systèmes sans labour non irrigués. Il découle de cette étude que les paramètres physiques dominent la survie de la chrysomèle dans les systèmes avec labour, tandis que les paramètres biologiques influent le plus sur la survie dans les systèmes sans labour.

     

Presence of Cuckoo reliably indicates high bird diversity: A case study in a farmland area

Here we studied the occurrence of Cuckoo Cuculus canorus and top predators as indicators of biodiversity in agro ecosystems of Western Poland, to identify local hotspots. Bird species richness and land-use diversity were used as measures of biodiversity. The relationship between the presence of Cuckoos and four avian top predators with biodiversity measures were examined using Generalized Linear Mixed Models.Cuckoos were mainly distributed on sites with greater species richness, but were absent from the low species richness sites, while the top predators were distributed uniformly. The performance of the best models using the presence of Cuckoo was 27% higher than the best models using top predators. Our results highlight the predictive capacity of Cuckoos as an indicator of bird species richness than top predators and the usefulness of this species in biodiversity studies. The cookoo is charismatic, widespread across the main types of landscapes, and is easy to detect from its song. Importantly, our findings propose that cookoo can be used as effective and cheap tool to monitor the high bird diversity in different European countries.     

Insect predation on pike fry

Laboratory tests evaluated the predatory impact of the macroinvertebrates Erythromma najas larvae (Odonata, Zygoptera: Coenagrionidae), Notonecta glauca (Heteroptera: Notonectidae), Ilyocoris cimicoides (Heteroptera: Naucoridae), Libellula depressa larvae (Odonata, Anisoptera: Libellulidae), Dytiscus marginalis larvae (Coleoptera: Dytiscidae) and Anax imperator larvae (Odonata, Anisoptera: Aeshnidae) on 3-, 12-, 21- and 30-day-old pike fry Esox lucius . All these insect predators captured and ate pike fry during the test, although the numbers killed varied among species. Dytiscus marginalis, Anax imperator and Notonecta glauca were the most Voracious predators.     

The ‘generalism’ debate: misinterpreting the term in the empirical literature focusing on dietary breadth in insects

We here attempt to show, using three broad insect groups – Lepidoptera (mainly leaf‐chewing larval herbivores and nectar‐sucking adults), parasitic Hymenoptera (mainly endoparasitoids, especially of other insects) and aphids (sap‐sucking plant parasites) – how the terms ‘generalist’, usually equated with levels of phagy (oligo‐ and polyphagy), and ‘specialist’ (monophagy), still in widespread parlance, have often been misrepresented. Probably, the reality of generalism, be that herbivorous, predatory and parasitic, can only be demonstrated by detailed empirical field observations plus the use of high‐resolution molecular (DNA) markers, including sequencing, and thereby determining whether the organism in question is really a homogeneous species population over a wide geographical range, or rather comprises a series of morphologically similar/identical cryptic, host‐adapted specialist populations. In the case of insects, the largest group of terrestrial animals on the planet, even if it can be shown that certain species are indeed polyphagous and feed on a variety of plant hosts (herbivores) or prey species (predators and parasitoids), nevertheless, the range of these food items may be highly selective and restricted, depending on morphological–genetical (biochemical/chemical)–behavioural constraints. In the end, while some animals appear to be generalist, this situation may well be illusory. Our present recognition of the term is at best inappropriate, and at worse, inaccurate, as we demonstrate in the examples given, mostly insects. In the meantime, we suggest that the terms used should be re‐defined as four broad classes of specialism–generalism, although the apparent ‘generalism’ is itself conditional on proof following further empirical analyses.     

Benthic organic matter and detritivorous macroinvertebrates in two intermittent streams in south-eastern Australia

Temporal changes in coarse (> 1 mm), fine (< 1 mm, > 250 m), and woody benthic organic matter (BOM), and densities of detritivores in pools and riffles were monitored at three sites on two intermittent streams (Werribee and Lerderderg Rivers) in Victoria, Australia during a drought year followed by a wetter year. Standing stocks of BOM peaked in both habitats during summer when discharge ceased and eucalypt leaf fall was greatest. During high winter and spring discharges, concentrations of BOM were low. Floods did not always scour BOM from the pools and riffles; after floods in October, standing stocks rose when BOM was imported from upstream or mobilized from the riparian zone. Densities of benthic detritivores, collector-gatherers, and shredders also varied seasonally, usually peaking in summer. Correlations between detritivore feeding group densities and amounts of putative food resource were habitat-specific. There were few significant correlations in depositional habitats, even after incorporating lag-times of two and four weeks into the analysis. However, detritivore densities in riffles, especially in the Lerderderg River, were strongly positively correlated with the amounts of BOM. Possibly, physico-chemical conditions in riffles are more conducive to litter conditioning and invertebrate colonization and breakdown of leaf material than are those in pools.     

High Predation Pressure by an Introduced Flatworm on Land Snails on the Oceanic Ogasawara Islands1

The introduction of a predatory flatworm, Platydemus manokwari, has been considered a cause of the decline of endemic land snails on the tropical oceanic islands. To clarify the effect of P. manokwari on land snail survival in the field, we examined survival rates of snails experimentally placed in areas where snails are absent (i.e., P. manokwari is present) on Chichijima, Ogasawara (Bonin) Islands. We found that over 50 and 90 percent of the snails were dead after 3 and 11 d, respectively, and that the main cause of mortality was predation by P. manokwari.     

Spatial variability in the abundance of pelagic invertebrate predators in relation to depth and turbidity

The abundance of pelagic invertebrate predators in relation to turbidity and depth gradients in Lake Hiidenvesi (southern Finland) were studied. In the shallow (<5 m) and the most turbid (up to 75 NTU) part of the lake, the community of invertebrate predators consisted of cyclopoid copepods (max biomass >500 μg dw l⁻¹) and Leptodora kindtiii (Focke) (17 μg dw l⁻¹), while in the less turbid (10–40 NTU) stratifying area Chaoborus flavicans (Meigen) dominated (max 146 μg dw l⁻¹). In the temporarily stratifying and moderately turbid basin Chaoborus and small-bodied invertebrate predators co-existed. Mysis relicta (Lovén) occurred only in the stratifying area (max 15 μg dw l⁻¹). The results suggested that both water depth and turbidity contributed to the community structure of Chaoborus flavicans. Depth great enough for stratification was of special importance and its effect was amplified by elevated turbidity, while high turbidity alone could not maintain chaoborid populations. Mysis relicta also requires a hypolimnetic refuge but is more sensitive to low oxygen concentrations and may therefore be forced to the epilimnion where it is vulnerable to fish predation. Cyclopoids as rapid swimmers can take advantage at elevated turbidity levels and coexist in high biomass with fish even in shallow water. Leptodora kindtii can form high biomass despite planktivorous fish providing that turbidity exceeds 20 NTU. The results demonstrated that depth and water turbidity can strongly regulate the abundance and species composition of invertebrate predators. These factors must thus be taken into account when applying food web management, which aims to reduce phytoplankton biomass by depressing planktivorous fish.