ALBERT

Description: The link between ecology and reproductive isolation constitutes the cornerstone of the ecological hypothesis of speciation. Such a link can arise when traits under ecologically based selection are also used as cues for mating (‘magic traits’) or as a by-product of habitat choice when mating takes place within habitats. Here, we propose that behavioural syndromes may also constitute such a link. We illustrate this mechanism in the butter hamlet, Hypoplectrus unicolor, a reef fish from the wider Caribbean, with aggressive mimicry as the focal ecological trait. Aggressive mimicry is of particular interest in hamlets since it has been proposed to play a key role in the radiation of Hypoplectrus. Individuals from a natural population in Bocas del Toro, Panama, were tagged and their diurnal and spawning behaviours observed over 2 years. The results indicate that aggressive mimicry behaviour differed consistently between individuals and formed two discrete behavioural types that also differed with respect to territoriality. Differences in territoriality between the two behavioural types translated into different use of space in spawning contexts, which generated a tendency for assortative mating by behavioural type. This case study illustrates how behavioural syndromes may form a link between ecologically relevant behavioural traits and mate choice, suggesting that they might play an underappreciated role in the early stages of speciation.

Description: Highlights • Records of hard-bottom communities show regional differences in community dynamics. • Regionally, signs of regime shift were detected. • Shift can be explained by the decline of the foundation species Mytilus sp. • Modelling process revealed three environmental variables explaining the decline. • Regional differences in larval dispersal could explain contrary Mytilus recoveries. Abstract Ecological processes modulate ecosystem functioning and services. Foundation species are those exerting intense control on such processes as both their existence and loss have profound implications on the structure of ecological communities. For the distinction between random fluctuations and directional regime shifts in community composition, long-term records are of strategic need. In this study we present the monitoring of benthic hard-bottom communities over 11 years along seven stations in the SW Baltic Sea. Regional differences were found between the communities of Kiel and Lübeck bights, with the former area displaying signs of regime shift. The decline and near disappearance of the foundational species Mytilus edulis from settlement panels deployed in Kiel Bight correlated with three environmental variables: sea surface temperature, water current speed and chlorophyll a concentration. Thus, low spring temperatures, in some cases reinforced by local maxima of chlorophyll a, correlated with reduced recruitment of Mytilus. Moreover, regional differences of larval dispersal and population connectivity could explain the rapid recovery after disturbance of the mussel populations in Lübeck Bight in contrast to Kiel Bight. Our findings underscore the relevance of long-term monitoring programmes to detect the interactive impacts of global climatic and regional environmental drivers.

Description: Highlights: • A social-ecological system (SES) is analyzed through a multilayer network approach. • The social-ecological network represents the value chain of different fisheries. • The multi-layer network considers the transfers of biomass and money as link types. • Network position reflects individual vulnerability towards external disturbance. • Understanding SES linkages is crucial for designing meaningful management measures. Coastal marine resources provide livelihoods to human communities around the world. The interactions in respective social-ecological systems are usually of complex nature, due to a wide range of different fisheries interacting with the ecosystem. Understanding connectivity within these systems (i.e. among social and ecological actors) helps in establishing meaningful management strategies for sustainable use of marine resources. This work uses the value chain analysis of different fisheries sectors to construct a qualitative social-ecological network (SEN) model of the Sechura Bay in North Peru. Here, a diverse ensemble of small-scale fisheries co-exists with a flourishing mariculture sector, though the respective production chains partially overlap. Directed and unweighted links between actors were defined based on the transfer of biomass (trophic interactions) and money (economic interactions). Several analytical network tools were applied (e.g. degree centrality, dominator tree) to identify the most important nodes of the social-ecological network and to understand interdependencies. Results of the network analysis suggest position of system's components being related to their vulnerability in the face of external disturbances. Fisher groups with a high specialization with respect to fisheries target species were stronger impacted by the last strong El Niño event (the Coastal El Niño 2017), with drastic consequences for actors of the respective production chains. The present approach is envisioned to be applicable beyond this particular case study and to nourish on-going scientific discussions on the use of social-ecological network analysis to describe human-nature interactions. This study allows (i) estimating node (actor) susceptibilities to natural and anthropogenic disturbances, and (ii) reconciling sustainable resource use and nature conservation by enhancing the understanding of the functionality of the respective social-ecological system.

Description: Highlights: • Flow network indices signal directional changes during ecosystem development. • They showed linear trends in the evolution of a mountain lake. • The lake evolved to increase stability at the expense of efficiency in energy transfer. • Trends of the indices challenge current hypotheses about the directionality of ecosystem development. • Flow network indices from long term field data can help assessing ecosystem health. Empirical evidence of the theoretically expected trends of ecosystem development is scarce so far. In this research, we used long-term empirical data about the plankton community of a small mountain lake (Lake Santo, northern Apennines, Italy) to reconstruct its developmental trajectory during a period comprised between early 1970 s and 2010 s. We exploited these data to build yearly ecological networks and from their configuration of energy flows we computed network information indices. The trends of these indices enlighten about the developmental trajectory of this ecosystem during the period covered by the data set. In particular, they indicate that Lake Santo evolved in the direction of increasing stability at the expense of efficiency in energy transfer. We compared these results with current hypotheses about the directionality of ecosystem development, which are rooted in ecosystem theory, and discussed the possibility that, counter to some theoretical models of ecosystem development, Lake Santo followed an unimpeded direction of development rather than a trajectory typical of an ecosystem under stress. Finally, the long-term trends of flow network indices provided insights about the health status of the ecosystem.

Description: Highlights: • Microphytobenthos contributed to the particulate organic matter in both beaches. • Allochthonous materials provide relevant contributions to the POM in surf zones. • Estuarine subsidies' availability determines changes in consumers' isotopic niches. • Higher estuarine trophic subsidies resulted in narrower niches of dominant species. Abstract: Benthic invertebrates in the surf zone of exposed sandy beaches represent important links for energy circulation between benthic and pelagic food webs. This work assesses the trophic ecology of co-occurring epi- and hyper-benthic invertebrates inhabiting the surf zone of sandy beaches located close to an estuarine mouth. It illustrates that different sources of organic matter induce changes in resource utilization. The trophic positions, and the niche width and overlap of species were described using δ13C and δ15N stable isotope analysis. The contribution of different sources to the particulate organic matter was quantified through stable isotopes analysis and fatty acids profiles. Shifts in the trophic niches of dominant species reflected a decrease in the contribution of estuarine carbon to the diets along the coast. This change in contribution of estuarine carbon also influenced trophic niche properties: more diverse resources availability resulted in narrower niches without overlap while less diverse resources resulted in broad isotopic niches and a highest overlap. Results show that spatial variations in the availability of resources can modify carbon pathways and trophic interactions in coastal food webs. Whenever resources are abundant, species display a more specialized diet while food scarcity leads to broader diets, a pattern consistent with the optimal foraging theory. This resource maximization behavior commonly observed in nature is also occurring in surf zone ecosystems.

Description: Multiple stressors often act concomitantly on ecosystems but detection of species responses follows the “single species-single driver” strategy, and cumulative impacts are seldom considered. During 1990–2010, multiple perturbations in the Caspian Sea, led to the decline of kilka, sturgeon and Caspian seal populations. Specific causes for their collapse were identified but a cumulative assessment has never been carried out. Using loop analysis, a qualitative modelling technique suitable in poor-data contexts, we show how multiple drivers can be combined to assess their cumulative impact. We confirm that the decline of kilka, sturgeon and Caspian seal populations is compatible with a net effect of the concomitant perturbations. Kilkas collapse was certainly due to the outburst of M. leidyi and overfishing. In addition, the excess nutrient might have conspired to reduce these populations. The interplay between concurrent drivers produces trade-offs between opposite effects and ecosystem management must face this challenge