Giovanni Strona

University of Helsinki

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Paolo Galli

University of Milano-Bicocca

Simone Fattorini

University of L'Aquila

Simone Montano

University of Milano-Bicocca

Davide Seveso

Marine Research Centre

Corey J. A. Bradshaw

Flinders University

Achille Mauri

ETH Zurich

John Llewelyn

Flinders University

Frédérik Saltré

Flinders University

Valériano Parravicini

Centre National de la Recherche Scientifique

Jesús San-Miguel-Ayanz

Joint Research Centre

Cooperative Institutions

University of Helsinki

Joint Research Centre

European Commission

Centre National de la Recherche Scientifique

John Wiley & Sons (United States)

Consejo Superior de Investigaciones Científicas

University of Milano-Bicocca

Ecological Society of America

University of Milan

Finnish Environment Institute

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A new measure of ecological network structure based on node overlap and segregation

Methods in Ecology and Evolution (2015)

Giovanni Strona Joseph A. Veech

Summary Despite substantial recent progress, ecologists continue to search for methods of measuring the structure of ecological networks. Several studies have focused on nestedness, a pattern reflecting the tendency of network nodes to share interaction partners. Here, we introduce a new statistical procedure to measure both this kind of structure and the opposite one (i.e. species' tendency against sharing interacting partners) that we call ‘node segregation’. In addition, our procedure provides also a straightforward measure of modularity, that is, the tendency of a network to be compartmented into separated clusters of interacting nodes. This new analytical measure of network structure assesses the average deviation between the observed number of neighbours shared by any pair of nodes (species), and the expected number, that is computed using a probabilistic approach based on simple combinatorics. The measure can be applied to both bipartite networks (such as plant–pollinators) and unimode networks (such as food webs). We tested our approach on several sets of hypothetical and real‐world networks. We demonstrate that our approach makes it possible to identify different kinds of non‐random network configurations (nestedness, node segregation and modularity). In addition, we show that nestedness in ecological networks is less common than previously thought, and that most ecological networks (including the majority of mutualistic ones) tend towards patterns of segregated associations. Our analyses show that the new measure of node overlap and segregation can efficiently identify different structural patterns. The results of our analyses conducted on real networks highlight the need to carefully reconsider the assumption that ecological networks are stable due to their inherent nestedness.

Nestedness

Ecological network

Modularity

10.1111/2041-210x.12395

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Citations (43)

Extinction Sequences

Fascinating life sciences (2022)

Giovanni Strona

10.1007/978-3-030-86764-5_6

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Citations (0)

Correction: Corrigendum: A fast and unbiased procedure to randomize ecological binary matrices with fixed row and column totals

Nature Communications (2016)

Giovanni Strona Domenico Nappo Francesco Boccacci Simone Fattorini Jesús San-Miguel-Ayanz

Nature Communications 5: Article number: 4114 (2014); Published: 11 June 2014; Updated: 5 October 2016 Previous work by Verhelst describing an equivalent mathematical argument for analysing binary matrices, but with different implementation and reasoning, was inadvertently omitted from the referencelist of this Article and should have been cited in instances where multiple swap methods were mentioned.

10.1038/ncomms13086

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Citations (1)

Nestedness and Ecological Network Stability

Fascinating life sciences (2022)

Giovanni Strona

Nestedness

Ecological network

10.1007/978-3-030-86764-5_8

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Citations (1)

Biological Invasions

Fascinating life sciences (2022)

Giovanni Strona

10.1007/978-3-030-86764-5_12

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Citations (1)

A network approach for managing ecosystem services and improving food and nutrition security on smallholder farms

People and Nature (2022)

Thomas P. Timberlake Alyssa R. Cirtwill Sushil Baral Daya Ram Bhusal Kedar Devkota

Abstract Smallholder farmers are some of the poorest and most food insecure people on Earth. Their high nutritional and economic reliance on home‐grown produce makes them particularly vulnerable to environmental stressors such as pollinator loss or climate change which threaten agricultural productivity. Improving smallholder agriculture in a way that is environmentally sustainable and resilient to climate change is a key challenge of the 21st century. Ecological intensification, whereby ecosystem services are managed to increase agricultural productivity, is a promising solution for smallholders. However, smallholder farms are complex socio‐ecological systems with a range of social, ecological and environmental factors interacting to influence ecosystem service provisioning. To truly understand the functioning of a smallholder farm and identify the most effective management options to support household food and nutrition security, a holistic, systems‐based understanding is required. In this paper, we propose a network approach to understand, visualise and model the complex interactions occurring among wild species, crops and people on smallholder farms. Specifically, we demonstrate how networks may be used to (a) identify wild species with a key role in supporting, delivering or increasing the resilience of an ecosystem service; (b) quantify the value of an ecosystem service in a way that is relevant to the food and nutrition security of smallholders; and (c) understand the social interactions that influence the management of shared ecosystem services. Using a case study based on data from rural Nepal, we demonstrate how this framework can be used to connect wild plants, pollinators and crops to key nutrients consumed by humans. This allows us to quantify the nutritional value of an ecosystem service and identify the wild plants and pollinators involved in its provision, as well as providing a framework to predict the effects of environmental change on human nutrition. Our framework identifies mechanistic links between ecosystem services and the nutrients consumed by smallholder farmers and highlights social factors that may influence the management of these services. Applying this framework to smallholder farms in a range of socio‐ecological contexts may provide new, sustainable and equitable solutions to smallholder food and nutrition security. A free Plain Language Summary can be found within the Supporting Information of this article.

Provisioning

Resilience

10.1002/pan3.10295

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Citations (24)

Can additive beta diversity be reliably partitioned into nestedness and turnover components?

Global Ecology and Biogeography (2019)

Thomas J. Matthews Thomas W. H. Aspin Werner Ulrich Andrés Baselga Yasuhiro Kubota

Abstract Aims Quantifying β‐diversity (differences in the composition of communities) is central to many ecological studies. There are many β‐diversity metrics, falling mostly into two approaches: variance‐based (e.g., the Sørensen index), or diversity partitioning (e.g., additive β‐diversity). The former cannot be used when species–sites matrices are unavailable (which is often the case in island biogeography in particular) and only species richness data are provided. Recently, efforts have been made to partition additive β‐diversity, a metric calculated using only α‐diversity and γ‐diversity, into nestedness and turnover components (termed here “richness‐only β‐diversity partitioning”). We set out to test whether this form of β‐diversity partitioning generates interpretable results, comparable with metrics based on species incidence β‐diversity partitioning. Location Global. Time period Present day. Major taxa studied Multiple taxa. Methods We first provide a brief review of β‐diversity partitioning methods, with a particular focus on the development of richness‐only β‐diversity partitioning. Second, we use 254 empirical incidence matrices (provided with the paper) sourced from the literature to measure turnover and nestedness using incidence β‐diversity partitioning, comparing the resulting values with those calculated using richness‐only β‐diversity. Results We provide an account of the emergence of β‐diversity partitioning, with particular reference to the analysis of richness‐only datasets, and to the definition and usage of the relevant metrics. Analytically, we report weak correlations between turnover and nestedness calculated using the two different approaches. We show that this is because identical values of α‐diversity and γ‐diversity can correspond to incidence matrices with a range of different structures. Main conclusions Our results demonstrate that the use of richness‐only β‐diversity partitioning to measure turnover and nestedness is problematic and can produce patterns unrelated to conventional measures of turnover and nestedness. We therefore recommend that more accurate definitions are adopted for these terms in future studies.

Nestedness

Gamma diversity

Diversity index

10.1111/geb.12921

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Citations (26)

Supplementary material from "Corals hosting symbiotic hydrozoans are less susceptible to predation and disease"

Simone Montano Simone Fattorini Valériano Parravicini Michael L. Berumen Paolo Galli

In spite of growing evidence that climate change may dramatically affect networks of interacting species, whether—and to what extent—ecological interactions can mediate species' response to disturbances is an open question. Here we show how a largely overseen association such as that between hydrozoans and scleractinian corals could be possibly associated with a reduction in coral susceptibility to ever-increasing predator and disease outbreaks. We examined 2450 scleractinian colonies (from both Maldivian and the Saudi Arabian coral reefs) searching for non-random patterns in the occurrence of hydrozoans on corals showing signs of different health conditions (i.e. bleaching, algal overgrowth, corallivory and different coral diseases). We show that, after accounting for geographical, ecological and co-evolutionary factors, signs of disease and corallivory are significantly lower in coral colonies hosting hydrozoans than in hydrozoan-free ones. This finding has important implications for our understanding of the ecology of coral reefs, and for their conservation in the current scenario of global change, because it suggests that symbiotic hydrozoans may play an active role in protecting their scleractinian hosts from stresses induced by warming water temperatures.

Coral bleaching

Hydrozoa

10.6084/m9.figshare.c.3946255.v2

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How to catch a parasite: Parasite Niche Modeler (PaNic) meets Fishbase

Ecography (2012)

Giovanni Strona Kevin D. Lafferty

Parasite Niche Modeler (PaNic) is a free online software tool that suggests potential hosts for fish parasites. For a particular parasite species from the major helminth groups (Acanthocephala, Cestoda, Monogenea, Nematoda, Trematoda), PaNic takes data from known hosts (maximum body length, growth rate, life span, age at first maturity, trophic level, phylogeny, and biogeography) and hypothesizes similar fish species that might serve as hosts to that parasite. Users can give varying weights to host attributes and create custom models. In addition to suggesting plausible hosts (with varying degrees of confidence), the models indicate known host species that appear to be outliers in comparison to other known hosts. These unique features make PaNic an innovative tool for addressing both theoretical and applied questions in fish parasitology. PaNic can be accessed at < http://purl.oclc.org/fishpest >.

Acanthocephala

10.1111/j.1600-0587.2012.07439.x

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Citations (7)

Relative demographic susceptibility does not explain the extinction chronology of Sahul’s megafauna

eLife (2021)

Corey J. A. Bradshaw Christopher N. Johnson John Llewelyn Vera Weisbecker Giovanni Strona

The causes of Sahul’s megafauna extinctions remain uncertain, although several interacting factors were likely responsible. To examine the relative support for hypotheses regarding plausible ecological mechanisms underlying these extinctions, we constructed the first stochastic, age-structured models for 13 extinct megafauna species from five functional/taxonomic groups, as well as 8 extant species within these groups for comparison. Perturbing specific demographic rates individually, we tested which species were more demographically susceptible to extinction, and then compared these relative sensitivities to the fossil-derived extinction chronology. Our models show that the macropodiformes were the least demographically susceptible to extinction, followed by carnivores, monotremes, vombatiform herbivores, and large birds. Five of the eight extant species were as or more susceptible than the extinct species. There was no clear relationship between extinction susceptibility and the extinction chronology for any perturbation scenario, while body mass and generation length explained much of the variation in relative risk. Our results reveal that the actual mechanisms leading to the observed extinction chronology were unlikely related to variation in demographic susceptibility per se, but were possibly driven instead by finer-scale variation in climate change and/or human prey choice and relative hunting success.

Megafauna

Extinction (optical mineralogy)

Chronology

Mammal

10.7554/elife.63870

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Citations (16)