Climate-induced effects on the meroplankton and the benthic-pelagic ecology of the North Sea

Analyses of long-term time series of North Sea plankton and sea surface temperature (SST) data reveal that the annual planktonic larval abundance of three benthic phyla, Echinodermata, Arthropoda, and Mollusca, responds positively and immediately to SST. Long-term outcomes for the planktonic abundance of these three phyla are different, however. The planktonic larvae of echinoderms and decapod crustaceans have increased in abundance from 1958 to 2005, and especially since the mid-1980s, as North Sea SST has increased. In contrast, the abundance of bivalve mollusc larvae has declined, despite the positive year-to-year relationship between temperature and bivalve larval abundance continuing to hold. We argue that the changes in meroplankton abundance, coincident with increased phytoplankton and declining holoplankton, reflect the synchronous effect of rising SST and related changes in the pelagic community on the reproduction and recruitment of many benthic marine invertebrates. Under this scenario, the long-term decline in bivalve mollusc larvae will reflect increased predation on the settled larvae and adults by benthic decapods. These alterations in the zooplankton may therefore describe an ecosystem-wide restructuring of North Sea trophic interactions.

Book Review: A Mechanistic Approach to Plankton Ecology

No abstract is available for this article.

Macro-ecology of plankton–seabird associations in the North Pacific Ocean

In conjunction with the North Pacific Continuous Plankton Recorder program, we conducted surveys of seabirds from June 2002 to June 2007. Here, we tested the hypotheses of (i) east–west variations in coupled plankton and seabird abundance, and (ii) that surface-feeding and diving seabirds vary in their relationships to primary productivity and mesozooplankton species abundance and diversity. To test these hypotheses, we developed statistical models for 20 species of seabirds and 12 zooplankton taxonomic groups. Seabird density was highly variable between seasons, but was consistently higher in the western than eastern North Pacific. Seabird diversity was greater in the east. Zooplankton abundance did not differ between regions. We found associations at the “bulk” level between seabird density and net primary productivity, but only one association between seabirds and total zooplankton abundance or diversity. However, we found many relationships between seabird species and the abundance of different zooplankton summarized at the genus or family level. Some of these taxonomic relationships reflect direct predator–prey interactions, while others may reflect zooplankton that serve as ecological indicators of other prey, such as micronekton, upon which the birds may feed. Surface or near-surface feeding, mostly piscivorous seabirds, did not differ systematically from diving, mainly planktivorous seabirds in their zooplankton associations. Seabirds apparently respond to zooplankton taxonomic groupings more so than bulk zooplankton characteristics, such as abundance or diversity. Macro-ecological studies of remote marine ecosystems using zooplankton and seabirds as ecological indicators provide a framework for understanding and assessing spatial and temporal variations in these difficult-to-study pelagic environments.

Scale-dependent foraging ecology of a marine top predator modelled using passive acoustic data

1.Understanding which environmental factors drive foraging preferences is critical for the development of effective management measures, but resource use patterns may emerge from processes that occur at different spatial and temporal scales. Direct observations of foraging are also especially challenging in marine predators, but passive acoustic techniques provide opportunities to study the behaviour of echolocating species over a range of scales. 2.We used an extensive passive acoustic data set to investigate the distribution and temporal dynamics of foraging in bottlenose dolphins using the Moray Firth (Scotland, UK). Echolocation buzzes were identified with a mixture model of detected echolocation inter-click intervals and used as a proxy of foraging activity. A robust modelling approach accounting for autocorrelation in the data was then used to evaluate which environmental factors were associated with the observed dynamics at two different spatial and temporal scales. 3.At a broad scale, foraging varied seasonally and was also affected by seabed slope and shelf-sea fronts. At a finer scale, we identified variation in seasonal use and local interactions with tidal processes. Foraging was best predicted at a daily scale, accounting for site specificity in the shape of the estimated relationships. 4.This study demonstrates how passive acoustic data can be used to understand foraging ecology in echolocating species and provides a robust analytical procedure for describing spatio-temporal patterns. Associations between foraging and environmental characteristics varied according to spatial and temporal scale, highlighting the need for a multi-scale approach. Our results indicate that dolphins respond to coarser scale temporal dynamics, but have a detailed understanding of finer-scale spatial distribution of resources.

Implications of streamlining theory for microbial ecology

Whether a small cell, a small genome or a minimal set of chemical reactions with self-replicating properties, simplicity is beguiling. As Leonardo da Vinci reportedly said, 'simplicity is the ultimate sophistication'. Two diverging views of simplicity have emerged in accounts of symbiotic and commensal bacteria and cosmopolitan free-living bacteria with small genomes. The small genomes of obligate insect endosymbionts have been attributed to genetic drift caused by small effective population sizes (Ne). In contrast, streamlining theory attributes small cells and genomes to selection for efficient use of nutrients in populations where Ne is large and nutrients limit growth. Regardless of the cause of genome reduction, lost coding potential eventually dictates loss of function. Consequences of reductive evolution in streamlined organisms include atypical patterns of prototrophy and the absence of common regulatory systems, which have been linked to difficulty in culturing these cells. Recent evidence from metagenomics suggests that streamlining is commonplace, may broadly explain the phenomenon of the uncultured microbial majority, and might also explain the highly interdependent (connected) behavior of many microbial ecosystems. Streamlining theory is belied by the observation that many successful bacteria are large cells with complex genomes. To fully appreciate streamlining, we must look to the life histories and adaptive strategies of cells, which impose minimum requirements for complexity that vary with niche.

Scaling laws of ambush predator 'waiting' behaviour are tuned to a common ecology

The decisions animals make about how long to wait between activities can determine the success of diverse behaviours such as foraging, group formation or risk avoidance. Remarkably, for diverse animal species, including humans, spontaneous patterns of waiting times show random ‘burstiness’ that appears scale-invariant across a broad set of scales. However, a general theory linking this phenomenon across the animal kingdom currently lacks an ecological basis. Here, we demonstrate from tracking the activities of 15 sympatric predator species (cephalopods, sharks, skates and teleosts) under natural and controlled conditions that bursty waiting times are an intrinsic spontaneous behaviour well approximated by heavy-tailed (power-law) models over data ranges up to four orders of magnitude. Scaling exponents quantifying ratios of frequent short to rare very long waits are species-specific, being determined by traits such as foraging mode (active versus ambush predation), body size and prey preference. A stochastic–deterministic decision model reproduced the empirical waiting time scaling and species-specific exponents, indicating that apparently complex scaling can emerge from simple decisions. Results indicate temporal power-law scaling is a behavioural ‘rule of thumb’ that is tuned to species’ ecological traits, implying a common pattern may have naturally evolved that optimizes move–wait decisions in less predictable natural environments.

Shark personalities? Repeatability of social network traits in a widely distributed predatory fish. Behavioral Ecology and Sociobiology, 68, 1995-2003.

Interest in animal personalities has generated a burgeoning literature on repeatability in individual traits such as boldness or exploration through time or across different contexts. Yet, repeatability can be influenced by the interactive social strategies of individuals, for example, consistent inter-individual variation in aggression is well documented. Previous work has largely focused on the social aspects of repeatability in animal behaviour by testing individuals in dyadic pairings. Under natural conditions, individuals interact in a heterogeneous polyadic network. However, the extent to which there is repeatability of social traits at this higher order network level remains unknown. Here, we provide the first empirical evidence of consistent and repeatable animal social networks. Using a model species of shark, a taxonomic group in which repeatability in behaviour has yet to be described, we repeatedly quantified the social networks of ten independent shark groups across different habitats, testing repeatability in individual network position under changing environments. To understand better the mechanisms behind repeatable social behaviour, we also explored the coupling between individual preferences for specific group sizes and social network position. We quantify repeatability in sharks by demonstrating that despite changes in aggregation measured at the group level, the social network position of individuals is consistent across treatments. Group size preferences were found to influence the social network position of individuals in small groups but less so for larger groups suggesting network structure, and thus, repeatability was driven by social preference over aggregation tendency.

Looking backwards to look forwards: the role of natural history in temperate reef ecology

Temperate reefs are superb tractable systems for testing hypotheses in ecology and evolutionary biology. Accordingly there is a rich history of research stretching back over 100 years, which has made major contributions to general ecological and evolutionary theory as well as providing better understanding of how littoral systems work by linking pattern with process. A brief resumé of the history of temperate reef ecology is provided to celebrate this rich heritage. As a community, temperate reef ecologists generally do well designed experiments and test well formulated hypotheses. Increasingly large datasets are being collected, collated and subjected to complex meta-analyses and used for modelling. These datasets do not happen spontaneously – the burgeoning subject of macroecology is possible only because of the efforts of dedicated natural historians whether it be observing birds, butterflies, or barnacles. High-quality natural history and old-fashioned field craft enable surveys or experiments to be stratified (i.e. replicates are replicates and not a random bit of rock) and lead to the generation of more insightful hypotheses. Modern molecular approaches have led to the discovery of cryptic species and provided phylogeographical insights, but natural history is still required to identify species in the field. We advocate a blend of modern approaches with old school skills and a fondness for temperate reefs in all their splendour.

Spatio-temporal Bayesian network models with latent variables for revealing trophic dynamics and functional networks in fisheries ecology

Ecosystems consist of complex dynamic interactions among species and the environment, the understanding of which has implications for predicting the environmental response to changes in climate and biodiversity. However, with the recent adoption of more explorative tools, like Bayesian networks, in predictive ecology, few assumptions can be made about the data and complex, spatially varying interactions can be recovered from collected field data. In this study, we compare Bayesian network modelling approaches accounting for latent effects to reveal species dynamics for 7 geographically and temporally varied areas within the North Sea. We also apply structure learning techniques to identify functional relationships such as prey–predator between trophic groups of species that vary across space and time. We examine if the use of a general hidden variable can reflect overall changes in the trophic dynamics of each spatial system and whether the inclusion of a specific hidden variable can model unmeasured group of species. The general hidden variable appears to capture changes in the variance of different groups of species biomass. Models that include both general and specific hidden variables resulted in identifying similarity with the underlying food web dynamics and modelling spatial unmeasured effect. We predict the biomass of the trophic groups and find that predictive accuracy varies with the models' features and across the different spatial areas thus proposing a model that allows for spatial autocorrelation and two hidden variables. Our proposed model was able to produce novel insights on this ecosystem's dynamics and ecological interactions mainly because we account for the heterogeneous nature of the driving factors within each area and their changes over time. Our findings demonstrate that accounting for additional sources of variation, by combining structure learning from data and experts' knowledge in the model architecture, has the potential for gaining deeper insights into the structure and stability of ecosystems. Finally, we were able to discover meaningful functional networks that were spatially and temporally differentiated with the particular mechanisms varying from trophic associations through interactions with climate and commercial fisheries.

Compound-specific isotope analysis of amino acids: A tool to unravel complex symbiotic trophic relationships

Carbon and nitrogen stable isotope ratios of amino acids (δ13CAA and δ15NAA) have been recently used to unravel trophic relationships in aquatic and terrestrial environments. However, none have studied the specific case of a symbiotic relationship. Here we use the stable isotope ratios of amino acids (AAs) to investigate the link between a scarab larva (Pericoptustruncatus) and its mite guest (Mumulaelaps, Mesostigmata: Laelapidae: Hypoaspidini). Five scenarios for the relationship between larva and mite were proposed and δ13CAA and δ15NAA respective data and patterns helped eliminate those that were inconsistent. The calculated gap of two trophic levels ruled out a parasitic trophic relationship scenario. The trophic relationship between P. truncatus was shown to most likely be commensalistic with the mites feeding on the larva's castings. Alongside this study, a comparison with the stable isotope bulk analysis method was made and demonstrated that the AA method brings a significant refinement to the results by providing a means of determining absolute tropic level without the need for prior knowledge of the isotopic composition of primary source material.