Gnathiid isopods are one of the most common fish ectoparasites, and are found in both temperate and tropical oceans. On coral reefs, gnathiids are most active at dusk and dawn, and contribute significantly to trophic dynamics, as they are a prey resource for cleaner fish and parasitize numerous fishes. Gnathiids also inhabit temperate intertidal waters, but their activity patterns and contribution to intertidal trophic dynamics remain unstudied. To provide the first ecological data on temperate intertidal gnathiid activity patterns, 172 gnathiid-free Clinus superciliosus were set in an intertidal system in Tsitsikamma National Park, South Africa, during early morning, morning, afternoon, early evening, and evening, high and low tide, and within the inter- and infra-tidal zone to examine gnathiid infestation levels. After exposure, gnathiids from each fish were identified to the species level, counted, and their developmental stage was recorded. All gnathiids were identified as Gnathiia africana. On average, 1 ± 5SD gnathiids were collected from each fish, and the majority of gnathiids collected were stage 1. Significantly more gnathiids were collected during morning and afternoon compared with all other time periods. The number of gnathiids collected was not influenced by the fish's exposure to high or low tide, or placement within the tide zone. Although G. africana is free from cleaner fish predation because cleaner fish do not reside in temperate intertidal habitat, G. africana abundance is surprisingly small. Future studies should examine what regulates G. africana population size and the role they play in temperate intertidal food webs.

Disentangling trophic interactions among species is important for elucidating mechanisms underlying ecosystem functioning and services. Carabid beetles are an important guild of predators that may regulate pest populations in arable landscapes, but their generalist feeding behavior hinders predictions about their actual contribution to pest control. In order to assess carabids’ potential for pest control, we simultaneously analyzed the carbon and nitrogen stable isotope ratios of a community of 45 co-occurring species in wheat and oilseed rape fields. With the expectation to identify distinct trophic groups based on the mean and the variance of carabid isotopic signatures, we observed a high degree of overlap in trophic positions between species. However, we also observed that species could be successfully categorized into two groups according to whether or not their carbon signatures varied independently from variations in the crop baseline. We interpret these results as differential primary resource uptake or by differential mobility aptitude in foraging. Accordingly, we propose that the isotopic signal can inform us on the presence/absence of links between generalist predators and cultivated plants through the trophic networks they belong to, and consequently on their potential role as pest natural enemies. We therefore suggest the complementarity of stable isotope analysis for obtaining a time-integrated assessment of carabid trophic behavior that may be combined with more direct molecular diet analysis allowing the simultaneous quantification of specific trophic links within agricultural landscapes.

Ecologists examine diet composition in order to assess the spatial and temporal variations in interactions between species, the impact of different species traits on the ecological network structure, and the long-term effects of the removal of different species by small-scale fisheries. In this study, our goal was to compare the diets of silky sharks (Carcharhinus falciformis) and scalloped hammerhead sharks (Sphyrna lewini) off the south-west coast of Mexico in order to infer their diet preferences and spatial distributions. We sampled 164 S. lewini (96 stomachs had food, 68 were empty) and 183 C. falciformis (30 stomachs had food, 153 were empty) in Puerto Madero, Chiapas in 2011. The large number of empty stomachs may be the result of using longline fishing gear, which causes high stress resulting in regurgitation. Based on the index of relative importance (%IRI), the fish Chloroscombrus orqueta (IIR = 27.7%) was the most important species in the diet of S. lewini, while the squid Dosidicus gigas (IIR = 34%) was the primary prey of C. falciformis. Levin's index (Bi) and Shannon's index (H′) confirm that both sharks are generalists, as in other regions. The trophic levels of S. lewini (TL = 4.1) and C. falciformis (TL = 4.2) are characteristic of tertiary consumers; meanwhile, the Morisita–Horn index indicates low interspecific overlap between all categories. These results confirm that these two sharks have different foraging preferences or movement patterns; thus, there is no trophic overlap between species as they play unique roles in the ecological network off the south-west coast of Mexico.

The diets of marine predators are a potential source of information about range shifts in their prey. For example, the short-finned squid Illex argentinus, a commercially fished species on the Patagonian Shelf in the South Atlantic, has been reported in the diet of grey-headed, Thalassarche chrysostoma; black-browed, T. melanophris; and wandering, Diomedea exulans, albatrosses breeding at Bird Island, South Georgia (54°S 28°W) in the Southern Ocean. Tracking data suggest that these birds may feed on I. argentinus while foraging in Southern Ocean waters during their breeding season. This led to the hypothesis that I. argentinus may occur south of the Antarctic Polar Front. To test this hypothesis, we used stable isotope analyses to assess the origin of I. argentinus. We compared I. argentinus beaks from the diets of the three albatross species with beaks of cephalopod species endemic to the Patagonian Shelf and others from the Southern Ocean. Our results show that I. argentinus from the diet of albatrosses at Bird Island have δ13C values in the range −18.77 to −15.28‰. This is consistent with δ13C values for Octopus tehuelchus, a typical species from the Patagonian Shelf. In contrast, Alluroteuthis antarcticus, a Southern Ocean squid, has typically Antarctic δ13C in the range −25.46 to −18.61‰. This suggests that I. argentinus originated from warmer waters of the Patagonian Shelf region. It is more likely that the albatross species obtained I. argentinus by foraging in the Patagonian Shelf region than that I. argentinus naturally occurs south of the Antarctic Polar Front.

There is significant concern about potential ecological effects of introduced organisms, including non-indigenous species and those created by genetic modification. This paper presents an Ecopath with Ecosim modelling approach, designed to examine long-term trophic effects of growth hormone (GH) transgenic coho salmon should they ever escape to a coastal salmonid ecosystem, namely the Strait of Georgia in British Columbia (Canada). The model showed that the effects of introduced GH transgenic coho salmon varied with their biomass, diet, structure of the invaded ecosystem, and environmental conditions. Occasional escapes of non-reproductive salmon did not have a significant impact on the example ecosystem. However, effects of GH coho salmon varied with their diet when large numbers of these fish were present in the simulated ecosystem (for example, when they constituted 20% of total current aquaculture production in the area). Further, climate-driven changes in the biomass of low trophic levels (bottom-up effects) could have a greater impact on the ecosystem than the introduction of large numbers of GH coho salmon. A new version of Ecopath with Ecosim's Monte Carlo approach showed that the model predictions were robust to GH coho salmon's Ecopath parameters, but more sensitive to vulnerabilities of prey to GH coho salmon. Modelling ecosystem effects of genetically modified organisms provides a complementary approach for risk assessments when data from nature are not readily obtainable.

Cephalopods (Mollusca: Cephalopoda) play an important role as keystone invertebrates in various marine ecosystems, as well as being a valuable fisheries resource. At the World Malacological Congress, held 21–28 July 2013 in Ponta Delgada, Azores, Portugal, a number of cephalopod experts convened to honour the contribution of the late Malcolm R. Clarke, FRS (1930–2013) to cephalopod research. Endorsed by the Cephalopod International Advisory Council (CIAC), the meeting discussed some of the major challenges that cephalopod research will face in the future. These challenges were identified as follows: (1) to find new ways to ascertain the trophic role and food web links of cephalopods using hard tissues, stable isotopes and novel concepts in theoretical ecology; (2) to explore new approaches to the study of cephalopod morphology; (3) to further develop cephalopod aquaculture research; (4) to find new ways to ascertain cephalopod adaptation and response to environmental change; (5) to strengthen cephalopod genetics research; and (6) to develop new approaches for cephalopod fisheries and conservation. The present paper presents brief reviews on these topics, followed by a discussion of the general challenges that cephalopod research is bound to face in the near future. By contributing to initiatives both within CIAC and independent of CIAC, the principle aim of the paper is to stimulate future cephalopod research.

The study focuses on the question, how a seamount in the oligotrophic eastern Mediterranean affects the zooplankton community, as compared to the open water. Zooplankton samples were taken with 333 µm nets at two sites, the Rhodes Basin and the Anaximenes Mountain, in December 2006. The samples were sieved into size fractions, and the composition, biomass, abundance and stable isotope signatures were analysed. In general, biomass and abundance of zooplankton were low, reflecting the oligotrophic character of the eastern Mediterranean, but zooplankton standing stocks were higher at the Rhodes Basin than at the Anaximenes Mountain. Stable isotope signatures showed, at a generally low level, enrichment in zooplankton taxa along the food chain within the different pelagic zones and from the surface to the deep-sea, but no significant differences between Rhodes Basin and the seamount were evident in the food web structure. The zooplankton community in the Anaximenes Mountain region in the northern Levantine Basin seems not to be influenced by a local seamount effect, despite the difference in standing stocks between the seamount and the Rhodes Basin. This seems to be driven by larger-scale upwelling and downwelling structures of cyclones and anticyclones, dominating the circulation in the area.

Silicon (Si) is known to have a role in constitutive plant defence against arthropod pests, and recent work has illustrated involvement in induced plant defences. The present tri-trophic study tested the hypothesis that Si increases natural enemy attraction to pest-infested plants and improves biological control. Cucumber plants treated with potassium silicate (Si+) and untreated control plants (Si−) were maintained in separately vented glasshouse compartments. Y-tube olfactometer studies showed that adult Dicranolaius bellulus were significantly more attracted to Si+ plants upon which Helicoverpa armigera larvae had fed compared with Si−, pest-infested plants. Predators were not significantly more attracted to Si+ plants when comparing uninfested cucumbers. In a field experiment, we placed H. armigera-infested and uninfested Si+ and Si− cucumber plants in a lucerne stand. Removal rates of H. armigera egg baits showed predation was greater for Si+ infested plants than for other treatments. Results suggest that Si applied to plants with a subsequent pest infestation increases the plants' attractiveness to natural enemies; an effect that was reflected in elevated biological control in the field.

In order to understand how marine ecosystems function, it is essential to study the trophic interactions among the community members, particularly from poorly known regions. In this study, the feeding ecology and diet of conger eels, Conger conger, an abundant fish species with commercial interest, was examined in the north-east Atlantic, off Algarve (southern Portugal) between May 2005 and August 2006. The diet was characterized by species composition, size and mass of prey. Conger eels are opportunistic feeders, cannibalistic, feeding on benthopelagic/pelagic prey (67% by mass and 71% by number) but also benthic prey (32% by mass and 29% by number). Fish (67.8±4.7% in mass) are the main prey of conger eels, followed by cephalopods (16.5±3.8%) and crustaceans (15.6±3.7%). The most numerous (identifiable) fish consumed were Capros aper, occurring in 90% of the stomach samples that contained food and representing 1.4% in mass, and Scomber japonicus, the most important fish in mass (21.1%), which occurred in 4.2% of the stomach samples that contained food. The present study shows that octopodids can play a more important role in the diet of conger eels than previously thought. Of the species preyed upon by conger eels, six species (21% of the total prey taxa) are caught commercially (Trachurus trachurus, Scomber japonicus, Micromesistius poutassou, Helicolenus dactylopterus and Conger conger) by local fisheries. As discards by local trawl and longline fisheries do not correspond with the diet of C. conger, it is likely that most prey of C. conger in rocky areas were caught actively in that study region.

Predation on parasitized hosts can significantly affect natural enemy communities, and such intraguild predation may indirectly affect control of herbivore populations. However, the methodological challenges for studying these often complex trophic interactions are formidable. Here, we evaluate a DNA-based approach to track parasitism and predation on parasitized hosts in model herbivore-parasitoid-predator systems. Using singleplex polymerase chain reaction (SP-PCR) to target mtDNA of the parasitoid only, and multiplex PCR (MP-PCR) to additionally target host DNA as an internal amplification control, we found that detection of DNA from the parasitoid, Lysiphlebus testaceipes, in its aphid host, Aphis fabae, was possible as early as 5 min. post parasitism. Up to 24 h post parasitism SP-PCR proved to be more sensitive than MP-PCR in amplifying parasitoid DNA. In the carabid beetles Demetrias atricapillus and Erigone sp. spiders, fed with aphids containing five-day-old parasitoids, parasitoid and aphid DNA were equally detectable in both predator groups. However, when hosts containing two-day-old parasitoids were fed to the predators, detection of parasitoid prey was possible only at 0 h (immediately after consumption) and up to 8 h post consumption in carabids and spiders, respectively. Over longer periods of time, post-feeding prey detection success was significantly higher in spiders than in carabid beetles. MP-PCR, in which parasitoid and aphid DNA were simultaneously amplified, proved to be less sensitive at amplifying prey DNA than SP-PCR. In conclusion, our study demonstrates that PCR-based parasitoid and prey detection offers an exciting approach to further our understanding of host-parasitoid-predator interactions.

A model (DALIS 1.0) of pelagic zone trophic interactions was developed using long-term, comprehensive data sets of theSulejow Reservoir. We calibrated the model using observations from the pelagic zone of the Sulejow Reservoir made between1999 and 2001. The model performed well in the description of Daphnia sp. – L. kindtii interactions when hydrologicalconditions were stable. A discrepancy between observed and simulated results was found when water inflows were high, whichwashed out the biota. We suggested that the hydrological impacts should be coupled in the updated DALIS model. Using DALIS,we also tested two scenarios: the food web model (A) without Leptodora; and (B) without YOY fish, under both good and badfood conditions for Daphnia. Results indicated that Leptodora would have a more significant impact on the reduction of Daphniabiomass than juvenile fish during some periods. As the maintenance of high Daphnia densities is recognised as a key factor intop-down effects, the DALIS model may provide frameworks that support ongoing empirical work. It is therefore recommendedthat the model be incorporated into the programme of the Sulejow Reservoir restoration.

Krill are thought to be predominantly herbivorous, but a heterotrophic diet might be crucial for their growth and survival. To compare the influence of herbivory and carnivory on krill we conducted a nine month feeding trial. We examined lipid composition of the hepatopancreas, abdomen and remaining body portions of krill fed diatoms at bloom condition levels, and diatoms with the addition of pellets or minced clam meat to simulate a partly carnivorous diet. Mortality, dry mass and lipid content were similar among treatments. We examined lipid class and fatty acid profiles, with emphasis placed on the ratio of storage (triacylglycerol) to structural (polar lipid) lipid and key essential omega 3 polyunsaturated fatty acids: 20:5ω3 and 22:6ω3. The triacylglycerol : polar lipid ratio increased in krill fed on the mixed diet as did the 20:5ω3 : 22:6ω3 ratio. Overall these findings indicate that provision of clam in the diet improved krill condition, and further suggest that carnivory may aid krill growth in the wild under certain environmental conditions.

Natural abundances of the stable isotopes, 15N/14N (δ15N) and 13C/12C (δ13C), were used to study temporal host-parasite relationships of the wild rabbit, Oryctolagus cuniculus (L.). During the 12-month sampling period, temporal isotopic shifts in δ15N were noted for dietary vegetation, host rabbit faeces and fur, but not for muscle or stomach contents. δ15N varied temporally for the parasitic cestode species, Mosgovoyia pectinata but not for Cittotaenia denticulata. Similarly, intestinal parasitic nematodes had apparent species-specific δ15N patterns. Only rabbit fur and intestinal parasitic nematodes did not exhibit temporal shifts in δ13C. Overall, host faeces and stomach contents were isotopically indistinct as a likely consequence of coprophagy. Relative to their host, parasitic nematodes were 15N-enriched, consistent with an increase in trophic level status. Conversely, cestodes were 15N-depleted. Isotopically, each parasite reflected a species-specific relationship with their rabbit host. This technique could be utilized to integrate parasites into food-web studies.

An individual-based model named OSMOSE (Object-oriented Simulator of Marine Ecosystems Exploitation) is used to investigate the dynamics of exploited marine fish communities. It allows the representation of age- and size-structured populations comprised of groups of individuals that interact within a spatialized food web. Within each group, which constitutes the basic interaction entity (the ‘super-individual’ in individual-based modelling terminology), fish belong to the same species, have similar biological parameters and behaviour rules. Somatic growth, reproduction, predation and starvation processes are modelled. Two rules apply for the predation process: for a given fish group, prey selection depends both on the spatial and temporal co-occurrence of the predator and its prey, and on the respective lengths of the prey versus the predator. Thus, fish feed regardless of the taxonomy of their prey. The strength of both predation and competition relationships therefore vary according to changes in relative species abundance. Preliminary investigations are conducted on a theoretical community comprising seven interacting species. The simulation results show how community stability can emerge from variability in species biomass. It is thus suggested that size-based trophic interactions, along with the existence of multiple weak links and species redundancy, favour community persistence and stability.

We shall examine the impact of Charles S. Elton's 1924 article on periodic fluctuations in animal populations on the development of modern population ecology. We argue that his impact has been substantial and that during the past 75 years of research on multi-annual periodic fluctuations in numbers of voles, lemmings, hares, lynx and game animals he has contributed much to the contemporary understanding of the causes and consequences of population regulation. Elton was convinced that the cause of the regular fluctuations was climatic variation. To support this conclusion, he examined long-term population data then available. Despite his firm belief in a climatic cause of the self-repeating periodic dynamics which many species display, Elton was insightful and far-sighted enough to outline many of the other hypotheses since put forward as an explanation for the enigmatic long-term dynamics of some animal populations. An interesting, but largely neglected aspect in Elton's paper is that it ends with speculation regarding the evolutionary consequences of periodic population fluctuations. The modern understanding of these issues will also be scrutinised here. In population ecology, Elton's 1924 paper has spawned a whole industry of research on populations displaying multi-annual periodicity. Despite the efforts of numerous research teams and individuals focusing on the origins of multi-annual population cycles, and despite the early availability of different explanatory hypotheses, we are still lacking rigorous tests of some of these hypotheses and, consequently, a consensus of the causes of periodic fluctuations in animal populations. Although Elton would have been happy to see so much effort spent on cyclic populations, we also argue that it is unfortunate if this focus on a special case of population dynamics should distract our attention from more general problems in population and community dynamics.

Empirical models were established, which link the biomasses or productions of the successive planktonic trophic levels in lakes of different depth and trophic status. Published data on 56 lakes were analysed, using both least-square and reduced-major-axis regressions. Reduced-major-axes regression technique was used in order to take into account variability due to both bottom-up and top-down forces. In shallow lakes, the energy transfer efficiency between phytoplankton and zooplankton decreases with increasing trophy. An inverse tendency appears in deep lakes. However, when considering only the oligo- and mesotrophic temperate lakes, the mean primary and secondary productivities per unit of area are about the same in shallow and in deep sites. On the other hand, shallow water bodies are characterized by a smaller mean size of the crustacean species, a lower mean biomass of zooplankton and a higher P zoo/B zoo ratio than deep lakes, probably as a response to the predation by fish. While the consumers seem to have a strong influence on the size structure and biomass of plankton, the energy flows between the trophic levels could be largely controlled by bottom-up forces.