Contemporary issues,current best practice and ways forward in soil protist ecology

Soil protists are increasingly studied due to a release from previous methodological constraints and the acknowledgement of their immense diversity and functional importance in ecosystems. However, these studies often lack sufficient depth in knowledge, which is visible in the form of falsely used terms and false- or over-interpreted data with conclusions that cannot be drawn from the data obtained. As we welcome that also non-experts include protists in their still mostly bacterial and/or fungal-focused studies, our aim here is to help avoid some common errors. We provide suggestions for current terms to use when working on soil protists, like protist instead of protozoa, predator instead of grazer, microorganisms rather than microflora and other terms to be used to describe the prey spectrum of protists. We then highlight some dos and don'ts in soil protist ecology including challenges related to interpreting 18S rRNA gene amplicon sequencing data. We caution against the use of standard bioinformatic settings optimized for bacteria and the uncritical reliance on incomplete and partly erroneous reference databases. We also show why causal inferences cannot be drawn from sequence-based correlation analyses or any sampling/monitoring, study in the field without thorough experimental confirmation and sound understanding of the biology of taxa. Together, we envision this work to help non-experts to more easily include protists in their soil ecology analyses and obtain more reliable interpretations from their protist data and other biodiversity data that, in the end, will contribute to a better understanding of soil ecology.     

Effect of temperature on life table parameters of Podisus nigrispinus (Het., Pentatomidae) fed with Alabama argillacea (Lep., Noctuidae) larvae

Abstract: The influence of temperature on life table parameters of Podisus nigrispinus (Dallas) (Het., Pentatomidae) fed with Alabama argillacea (Hübner) (Lep., Noctuidae) larvae was studied. This predator was kept at constant temperatures of 20, 23, 25, 28, 30 and 33±0.2°C, at relative humidity of 60±10% and photoperiod of L : D 14 : 10. Gross (GRR) and net ( R ₀) reproductive rates of P. nigrispinus ranged from 1.6 to 366.6 and from 0.02 to 189.5 females/female at temperatures of 33 and 28°C, respectively; generation time ( T  ) ranged from 33.3 (33°C) to 85.5 (20°C) days; doubling time ( D ) from 0.82 (33°C) to 17.8 (20°C) days; intrinsic rate of increase ( r _m ) from −0.13 (33°C) to 0.12 (28°C) per day; and the finite rate of increase ( λ ) from 0.88 (33°C) to 1.12 (28°C) females/female added to the population per day. The ideal age to release P. nigrispinus should be when this predator presents higher reproductive values (VR _x ); that is, its adults are about 7 days old, independent of prevailing temperature. Population growth of P. nigrispinus was affected by temperature with maximum numerical response between 28 and 30°C. The negative population growth shown at 33°C may not occur in natural conditions due to milder microclimate in the cotton agroecosystem and due to oscillations of temperature in the course of the day.     

Free—living fathead minnows rapidly learn to recognize pike as predators

Individuals from a natural population of approximately 20 000 fathead minnows from a pike–free pond did not respond with appropriate anti–predator behaviour upon encountering pike odour in laboratory tests. However, 14 days after 10 pike were stocked into the pond, minnows had acquired recognition of pike odour. Laboratory studies have indicated several possible mechanisms for acquiring predator recognition in fathead minnows. This study indicates that these, or similar processes, can produce major changes in predator recognition in the wild.     

Density- and frequency-dependent predation of artificial bird nests

Predators are often expected to vary their relative predation rates according to the frequency of prey types in the environment (frequency-dependent predation). The underlying cause for this must lie in some dependency of absolute predation rates on the density of prey types in the environment (density-dependent predation). However, frequency-dependent predation may either be caused by 'simple' density-dependent predation, in which the absolute predation rate on a given prey type depends purely on the density of that type, or by more complex responses in which absolute rates depend also on the density of other prey types. It is usually difficult to distinguish the underlying cause of frequency-dependent predation, because frequencies tend to change as densities change. Here, we describe the results of an experiment conducted to disentangle these phenomena under two prey richness (low and high) conditions. We used artificial bird nests (placed on shrubs and on saplings) baited with quail eggs placed in natural forests as models of natural bird nests. Our results indicate that both the absolute and relative predation rates on the prey types may vary in complex ways. Predation rates depend on a complex interaction between the prey's own density, other prey density and the diversity of prey in the environment. Neglecting to include, or consider, these complexities into analyses may lead to erroneous conclusions in studies of absolute or relative predation rates.     

Comparison of learning in related generalist and specialist eucoilid parasitoids

Effects of learning in two microhabitat specialists, Leptopilina boulardia Barbotin et al. and L. fimbriata Kieffer were compared to previous and new results of learning in the microhabitat generalist L. heterotoma Thomson. Females were given one or more oviposition experiences on hosts in different types of substrate. In all species oviposition experience affected the choice for a substrate, although this effect of learning was considerably less in L. fimbriata compared to the other two species. Patch times, known to be highly determined by experience in the generalist L. heterotoma, were much less flexible in the specialists. L. boulardi and L. fimbriata have fixed patch times on their natural substrate and have variable patch times on other substrates only. In all three species one oviposition affected the choice for a substrate. Additional ovipositions showed no different effect. An accumulative effect of the number of ovipositions on patch times was found in L. heterotoma only. Retention of the learning effect was only studied in L. boulardi, and was shown to be similar to that reported for L. heterotoma, i.e. two to three days. Although learning was found in both the generalist and the specialist species studied, it seems to affect their foraging behaviour differently.     

Natural enemies ofPlutella xylostella (Lep.: Plutellidae) on crucifers in Honduras

Three primary parasitoids in three genera were reared fromPlutella xylostella (L.) larvae and pupae collected in various crucifer producing regions of Honduras. The ichneumonidDiadegma insulare (Cresson) was by far the most abundant species. TwoSpilochalcis species, facultative hyperparasitoids attackingP. xylostella andD. insulare, were encountered as well as eleven species in nine genera of obligate hyperparasitoids attackingD. insulare. Three vespid predators are noted as predating on larvae.      

Biology and comparative predation efficacy of three heteropteran species recorded as predators ofBemisia tabaci in Maharashtra

Two mirids,Deraeocoris sp. andCampylomma nicolasi Reuter and one lygaeid,Geocoris ochropterus Fieber were found preying onB. tabaci (Gennadius) for the first time in Maharashtra State of India during 1987–88. Their biology and predation capacity onB. tabaci were studied in detail under laboratory conditions. The nymphal stage ofDeraeocoris sp. passed through 6 instars, whereas 5 instars in case of the remaining species.G. ochropterus, Deraeocoris sp. andC. nicolasi consumed on an average 482.5, 275.3 and 128.8 nymphs of 57.3, 25.5 and 20.6 days, respectively. On the basis of consumption rate per day,Deraeocoris sp. proved to be a superior predator. Part of Ph. D. Thesis submitted to Marathwada Agricultural University, Parbhani 431402, India.     

The dicey dinner dilemma: Asymmetry in predator–prey risk‐taking,a broadly applicable alternative to the life‐dinner principle

Forty years ago, the ‘life‐dinner principle’ was proposed as an example of an asymmetry that may lead prey species to experience stronger selection than their predators, thus accounting for the high frequency with which prey escape alive from interaction with a predator. This principle remains an influential concept in the scientific literature, despite several works suggesting that the concept relies on many under‐appreciated assumptions and does not apply as generally as was initially proposed. Here, we present a novel model describing a very different asymmetry to that proposed in the life‐dinner principle, but one that could apply broadly. We argue that asymmetries between the relative costs and benefits to predators and prey of selecting a risky behaviour during an extended predator–prey encounter could lead to an enhanced likelihood of escape for the prey. Any resulting advantage to prey depends upon there being a behaviour or choice that introduces some inherent danger to both predator and prey if they adopt it, but which if the prey adopts the predator must match in order to have a chance of successful predation. We suggest that the circumstances indicated by our model could apply broadly across diverse taxa, including both risky spatial or behavioural choices.     

Anthropogenic noise reduces avian feeding efficiency and increases vigilance along an urban–rural gradient regardless of species’ tolerances to urbanisation

Anthropogenic noise can adversely impact urban bird populations by interfering with vocal communication. Less research has addressed if anthropogenic noise masks the adventitious sounds that birds use to aid predator detection, which may lead to increased vigilance and reduced feeding efficiency. We test this hypothesis using a controlled playback experiment along an urban–rural gradient in Sheffield (UK). We also test the related predictions that anthropogenic noise has the greatest impacts on vigilance and feeding efficiency in rural populations, and on species that are more sensitive to urbanisation. We focus on six passerines, in order from most to least urbanised (based on how urbanisation influences population densities): blue tit Cyanistes caeruleus, robin Erithacus rubeculla, great tit Parus major, chaffinch Fringilla coelebs, coal tit Periparus ater and nuthatch Sitta europaea. We used play-back of anthropogenic urban noise and a control treatment at 46 feeding stations located along the urban–rural gradient. We assess impacts on willingness to visit feeders, feeding and vigilance rates. Exposure to anthropogenic noise reduced visit rates to supplementary feeding stations, reduced feeding rates and increased vigilance. Birds at more urban sites exhibit less marked treatment induced reductions in feeding rates, suggesting that urban populations may be partially habituated or adapted to noisy environments. There was no evidence, however, that more urbanised species were less sensitive to the impacts of noise on any response variable. Our results support the adventitious sound masking hypothesis. Urban noise may thus interfere with the ability of birds to detect predators, reducing their willingness to use food rich environments and increase vigilance rates resulting in reduced feeding rates. These adverse impacts may compromise the quality of otherwise suitable foraging habitats in noisy urban areas. They are likely to be widespread as they arise in a range of species including common urban birds.