The influence of prey identity and size on selection of prey by two marine fishes

Laboratory experiments were conducted with two predatory fishes, Lagodon rhomboides (Linnaeus) and Syngnathus floridae (Jordan & Gilbert), to determine if prey selection was a result of predator preference or prey accessibility. Prey consisted of two species of caridean shrimp, Tozeuma carolinense (Kingsley) and Hippolyte zostericola (Smith), that commonly inhabit seagrass meadows. Natural diets of both predators revealed that selection ofTozeuma and Hippolyte was not related to their field densities. My experiments demonstrated that natural prey selection was a consequence of prey accessibility, not predator preference. Experiments examining the role of prey size in predator preference revealed that large individuals were significantly preferred over small individuals. Observations of prey behavior indicated that prey motion affected predator choice. These results suggest that predator preference was primarily determined by prey visibility and that the combined effects of prey size and motion contributed to the visibility of these prey.     

The influence of diel cycle,tidal direction and trawl alignment on beam trawl catches in an equatorial estuary

Synopsis Using a 3 m beam trawl, catch variation in the fish and prawn assemblage of the Labu estuary, Papua New Guinea was investigated during July and December 1981 and September 1984. About six times more organisms, three and a half times the biomass and twice as many species were caught per trawl at night than during the day. The greatest number of species, individuals and biomass were caught just after dusk. With the exception ofSecutor ruconius, there was no significant difference in the catches trawled at ebbing and flooding tides. Over twice as many individuals ofS. ruconius were caught during ebbing tides. Alignment of trawl direction in relation to the tidal current did not have a significant effect on the fish catch, but affected the prawn (Metapenaeus demani) catch. It is postulated that most species are not carried to and fro by tidal currents, but maintain their position in the estuary with respect to the substratum. Only prawns appeared to be carried by the currents. This study indicates that the most representative trawl results in terms of species diversity and abundance in shallow estuaries may be obtained at night and, that in estuaries with a small tidal range, tidal direction and velocity have little influence on catch. It also indicates that analyses of demersal nekton assemblages from daytime only estuarine trawl surveys must be approached with caution.Lizard Island Research Station     

The influence of prey size and abundance, and individual phenotype on prey choice by the three-spined stickleback, Gasterosteus aculeatm L.

Prey selection behaviour of three-spined sticklebacks, Gasterosteus aculeatus L., was studied in two experiments. Where possible, the experimental apparatus satisfied the assumptions of the simplest optimal diet model (the basic prey model); prey were presented sequentially, the fish could not search for and handle prey at the same time, and net energy gain, handling time and encounter rate were fixed. Experiment 1 presented fish with a range of Asellus sizes so that pursuit ( p ) and handling ( h ) time could be related to prey size. Published energy values of Asellus together with pursuit and handling times were used to calculate E /( p+h ) for Asellus measuring 3,4,5,6,7 and 9 mm. Pursuit times did not differ with prey size but handling times did. E /( p+h ) was very variable particularly at the larger prey sizes. Experiment 2 presented fish with two sequences of prey differing in the encounter rate with the most profitable prey sizes. Fish did not select the diet predicted by the basic prey model tending to always ignore the largest prey even when net energy gain would have been maximized by including them in the diet. Further analysis showed that the probability of a prey size being taken was a function of prey size, fish stomach fullness and encounter rate. It is concluded that the basic prey model is too simple to capture the behaviour of the fish. One of its main faults is that the changing state of the fish through the feeding bout is ignored.     

The influence of habitat and behavioural interactions on the local distribution of the wrasse,Pseudolabrus celidotus

Synopsis The temperate wrasse, Pseudolabrus celidotus (Labridae), was studied in a shallow rocky reef habitat to asses how ecological and behavioural factors influence its within habitat patterns of distribution. Emphasis was placed on examining the mechanisms underlying size/age related changes in dispersion and habitat use. Juveniles (< 100 mm SL) were found to be aggregated whereas adults tended to be more randomly dispersed. This pattern appeared to be a product of both (a) ecological, and (b) behavioural factors. (a) Juveniles were closely associated with shelter (macro-algae) which was located in patches throughout the habitat. Their local distribution was probably not related to the distribution of their major prey items. Shelter dependence appears to decrease with growth and fish switched from feeding on micro-crustaceans present in macro-algae to those associated with bare rock — coralline turf areas. Adults foraged throughout larger home ranges, but fed preferentially in microhabitats where their prey items (e.g. bivalves) were most abundant. (b) Juveniles tended to aggregate into loose foraging schools. This tendency declined with age and was associated with a corresponding increase in the rate of aggressive interactions among individuals of a cohort. Consequently, individuals of the same size became more spaced out as they grew. Between cohort association or aggression was rare and apparently unimportant in determining local patterns of distribution. Many interspecific foraging associations and aggressive interactions were recorded. However, with the probable exception of interspecific territoriality by the blenny Forsterygion varium, these behaviours probably had only a transitory influence on the distribution of the wrasse.     

The effect of two prey species, Chrysomphalusaonidum and Corcyra cephalonica, on the qualityof the predatory thrips, Aleurodothripsfasciapennis, reared in the laboratory

Periodic and augmentative releases of natural enemies are often required to enhance biological control and integrated pest management programs. One requirement for these programs to be practical is that natural enemies can be easily and economically mass-reared. This study assessed the effects of dieton the quality of the F₃ and F₄laboratory-reared generations of the predatory thrips,Aleurodothrips fasciapennis. Diets were eggs and crawlers of the diaspidid scale Chrysomphalusaonidum and eggs of the pyralid moth Corcyracephalonica. It was found that both the F₃ and F₄ generations were not viable when reared on the eggs and crawlers of C. aonidum due to very low fecundity and, in the F₄ generation, increased larval mortality. In contrast, thrips reared on the eggs of C. cephalonica were viable in both generations but an increase in larval mortality from the F₃ to the F₄ generation did result in are duction in viability. These results are discussed in terms of genetic, environmental and behavioural factors that may have influenced the quality of the thrips. It is concluded that genetic factors(inbreeding suppression, genetic drift or selection),the behaviour of scale crawlers and the predatory behaviour of thrips were probably of little value in explaining the results. The most likely explanation was that the diet supplied to thrips was of in adequatenutritional quality. It was not possible to distinguish whether this was due to low intrinsic quality of the prey or an indirect effect of experimental conditions on prey quality. This revised version was published online in July 2006 with corrections to the Cover Date.     

The effect of jasmonic acid on the accumulation of ABA,proline and spermidine and its influence on membrane injury under water deficit in two barley genotypes

Seedlings of two barley genotypes (‘Maresi’ and wild form of Hordeum spontaneum) were treated with jasmonic acid (JA 5 μM and 15 μM) for 24 h, and then subjected to water stress (PEG 6000 solution of − 1.5 MPa). JA caused an increase in the content of ABA but not in that of proline and spermidine in the two studied genotypes. The effect of the treatment did not depend on the applied JA concentration. The pre-stress treatment with JA changed plant response to water deficit with regard to membrane injury. Treatment with a lower JA concentration (5 μM) caused a substantial reduction of the stress-induced membrane damage in the both genotypes. A higher JA concentration (15 μM) caused the reduction of membrane injury only in H. spontaneum and was ineffective in ‘Maresi’. JA had no influence on the leaf water status in water-stressed plants. A possible role of JA in leaf ABA accumulation and alleviation of cell membrane injury under water deficit is discussed. The work was partly supported by the Polish Committee For Scientific Research, grant No 5 PO6A 036 18     

The influence of high levels of brief or prolonged supplementary far-red illumination during growth on the photosynthetic characteristics, composition and morphology of Pisum sativum chloroplasts

Abstract. Peas were grown in controlled environments (12h white fluorescent light. ∼47 μmol photons m^-2 s 1/12 dark, 25 °C), using (1) 15-min far-red illumination at the end of each photoperiod (brief FR) to simulate the increase in the far-red/red ratio near the end of the day, and (2) high levels of supplementary far-red light (red:far-red ratio=0.04) during the entire photoperiod (long-term FR) to simulate extreme shade conditions under a plant canopy. Brief FR illumination led to marked morphological effects attributable to phytochrome regulation, namely, an increase in internodal length, but a decrease in leaflet area, chloroplast size and chlorophyll content per chloroplast compared with the control. Significantly, brief FR illumination had little or no effect on the amounts of the major chloroplast components (ribulose 1.5-biphosphate carboxylase, adenosine triphosphate synthase, cytochrome b/f complex and Photosystem II) relative to chlorophyll or Photosystem I, and the leaf photosynthetic capacities per unit chlorophyll were similar. In contrast, supplementing high levels of far-red light during the entire photoperiod not only led to the phytochrome effects above, but there was also a marked increase in leaf photosynthetic capacity per unit chlorophyll. due to increased amounts of the major chloroplast components relative to chlorophyll or Photosystem I. We hypothesize that supplementary far-red light, absorbed by Photosystem I, induced an increase in the major chloroplast components by a photosynthetic feedback mechanism. In fully greened leaves, we propose that the two photosystems themselves, rather than phytochrome, may be the predominent sensors of light quantity in triggering modulations of the stoichiometries of chloroplast components, which in turn lead to varying photosynthetic capacities.     

The influence of sublethal deposits of agricultural mineral oil on the functional and numerical responses of <Emphasis Type="Italic">Phytoseiulus persimilis</Emphasis> (Acari: Phytoseiidae) to its prey, <Emphasis Type="Italic">Tetranychus urticae</Emphasis> (Acari: Tetranychidae)

Occasional pesticide application in integrated pest management to at least part of a crop requires that any biological control agents must re-invade previously sprayed areas in order that resurgent pests can be constrained. The ability of the phytoseiid predatory mite Phytoseiulus persimilis to feed on adult two-spotted spider mite (TSSM) Tetranychus urticae on excised leaf discs in both control conditions and in a treatment with a sub lethal residue of agricultural mineral oil (AMO) was assessed. The predator exhibited a Type II functional response with the asymptote significantly higher in the AMO conditions due to the fact that the prey grew slower and reached a smaller size in this treatment. In terms of prey volume eaten, the satiation level of the predator was unchanged by the AMO deposits. The numbers of eggs produced by adult P. persimilis females at densities of 4, 8 and 16 TSSM adult females/disc in the control were significantly higher than those in the AMO treatment, but were similar for the higher density levels, 32 and 64 prey per disc. Thus the functional response in terms of volume of prey eaten explained the numerical response in terms of predator eggs produced. The presence of AMO deposits when the prey were at high density had no effect on predator efficiency (volume eaten) but resulted in a lower intake than that in control conditions when there was a greater distance between prey.     

The influence of two endoparasitic wasps, <Emphasis Type="Italic">Hyposoter didymator</Emphasis> and <Emphasis Type="Italic">Chelonus inanitus</Emphasis>, on the growth and food consumption of their host larva <Emphasis Type="Italic">Spodoptera littoralis</Emphasis>

The influence of parasitism by Hyposoter didymator (Thunberg; Hymenoptera: Ichneumonidae) and Chelonus inanitus (Linnaeus) (Hymenoptera: Braconidae) on the growth and food consumption of their host Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) was studied in the laboratory. Parasitised larvae consumed significantly less artificial diet than unparasitised ones. Egg parasitisation by C. inanitus affected host larval consumption from the second day after emergence and it was significantly different from that of unparasitised ones. H. didymator, however, started to reduce larval consumption 4 days after parasitisation on the third instar host larvae. The overall reduction achieved by the larval endoparasitoid H. didymator is higher than that caused by the egg-larval endoparasitoid C. inanitus. The final body weight of a parasitised host larva by H. didymator and C. inanitus was only 6.7 and 13.0% of the maximum weight of an unparasitised sixth instar larva respectively. Moreover, parasitised larvae never reached the last instar. Results indicated that parasitised larvae might cause considerable less damage to the host plant than unparasitised ones.