Evidence Against MacArthur’s Latitude–Niche Breadth Hypothesis

According to Robert MacArthur, the realized niche breadth of species is positively associated with latitude (cf. MacArthur’s latitude-niche breadth hypothesis), namely niches in highly diverse tropical regions near the equator are narrower than in less diverse boreal and polar regions (MacArthur, 1972). If you want to know more on this hypothesis, I highly recommend to read the paper from Vázquez & Stevens (2004) who deeply discuss the concept behind this hypothesis and made a thorough meta-analysis of the evidence for or against the latitude-niche breadth hypothesis, concluding that the null hypothesis (i.e, that there is no correlation between latitude and niche width) cannot be rejected. According to Klaus Rohde (see his post on MacArthur’s latitude-niche breadth hypothesis), a priori assumptions of this hypothesis are flawed: “The latitude-niche breadth hypothesis makes equilibrium assumptions, implicitly and explicitly assuming that niche space is more or less saturated with species. However, there is much evidence for an overabundance of vacant niches and that most ecological including tropical systems are far from saturation” (for a discussion and examples see Rohde 2005).

In a recent paper published by Safaa Wasof who will soon defend her PhD, we tested the niche conservatism hypothesis among distant populations of the same species and for a fairly large number (n = 888) of native European vascular plant species occurring in both the Alps (central Europe) and Fennoscandia (northern Europe). In addition to that, we also compared the realized niche breadth between populations from the Alps and populations from Fennoscandia, assuming that niche breadth would be wider for populations thriving in Fennoscandia than for those thriving in the Alps according to MacArthur’s latitude-niche breadth hypothesis. Well, we found the opposite pattern: populations from central Europe in the Alps have, on average, a wider climatic niche breadth than populations from northern Europe in Fennoscandia, thus contradicting MacArthur’s latitude-niche breadth hypothesis. Although we compared only two regions and did not cover the entire latitudinal gradient from the Tropics to the North Pole, our result is cristal clear.

If you want to know more about this result, you are very welcome to read Safaa’s paper (Wasof et al., 2015). However, this result was not the central message of Safaa’s paper which we twisted on the niche conservatism hypothesis and its relevance for species distribution models. Here I would like to focus more specifically on MacArthur’s latitude-niche breadth hypothesis and the result we found. This is also a nice opportunity for me to present a slightly different set of analyses that we ran together with Safaa but which did not get into the manuscript or the appendices (Safaa’s paper is just the tip of the iceberg).

So, instead of using growing degree days (GDD) and the aridity index (AI) solely to capture species realized climatic niche, like we did in Safaa’s paper, we here used a larger set of bioclimatic variables (8 out of the 19 bioclimatic variables from WorldClim: BIO2, BIO5, BIO6, BIO7, BIO8, BIO15, BIO18, BIO19) that we subsequently reduced to a bi-dimensionnal climatic space by using a Principal Component Analysis (PCA). We used the 1-km resolution bioclimatic grids that we each clipped to the two study regions (see Figure 1A for an example based on BIO5) before running the PCA (Figure 1B). The resulting first (PC1: Figures 1C and 1D) and second (PC2: Figures 1E and 1F) PCA axes captured 49% and 24%, respectively, of the total inertia. Note that Figures 1C, 1D, 1E and 1F are showing the spatial distribution of the PC1 and PC2 variables of the analog climatic space solely (cf. purple point cloud in Figure 1B).

Study region and climatic space

Figure 1: Study area and climatic space

Focusing on the analog climatic space solely to make climatic niches comparable between the two regions (cf. same reference), we used a set of 440 species, out of the 888 species belonging to the common species pool, for which we had enough data to compute the climatic niche breadth across both regions and along both PC1 and PC2 axes. Figure 2 shows an example of the realized climatic niche of Corydalis cava across the PC1-PC2 bi-dimensionnal climatic space for both the Alps (on the right) and Fennoscandia (on the left).

Corydalis cava

Figure 2: Realized climatic niche of Corydalis cava across the PC1-PC2 bi-dimensionnal climatic space for both the Alps (in red) and Fennoscandia (in blue).

Corydalis cava

Corydalis cava (Source: Wikimedia Commons).

Niche breadth along both PC1 and PC2 was computed as the 95% confidence interval around the optimum value (cf. maximum density position). Figure 3 shows the result for all 440 studied species along PC1 (Figure 3A) and PC2 (Figure 3B). I guess statistical tests are useless here given the strength of the signal. For most European vascular plant species, populations from the Alps have wider realized climatic niche along both PC1 and PC2 than populations from Fennoscandia.

Niche breadth Alps vs Scandinavia

Figure 3: Realized climatic niche breadth for 440 vascular plant species occurring in both the Alps and Fennoscandia

This trend towards wider niches in the Alps than in Fennoscandia (Figure 3) invalidates MacArthur’s latitude–niche breadth hypothesis. In Safaa’s paper we discuss several potential drivers behind this result. My favorite one implies greater genetic diversity due to a diversity of refugia close to the Alps (Schönswetter et al., 2005), corresponding to greater habitat heterogeneity, thus increasing the likelihood for a species to widen its fundamental climatic niche in the Alps.

References

MacArthur (1972) Geographical ecology. Princeton University Press, Princeton

Rohde (2005) Nonequilibrium ecology. Cambridge University Press, Cambridge

Schönswetter et al. (2005) Molecular evidence for glacial refugia of mountain plants in the European Alps. Molecular Ecology, 14: 3547–3555.

Vázquez & Stevens (2004) The Latitudinal Gradient in Niche Breadth: Concepts and Evidence. The American naturalist, 164: E1–E19

Wasof et al. (2015) Disjunct populations of European vascular plant species keep the same climatic niches, Global Ecology and Biogeography, 24: 1401-1412

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The Niche Concept under Contemporary Climate Change

I’m proud to announce the forthcoming PhD defense of Safaa Wasof who did her PhD under my supervision at Jules Verne University of Picardie (UPJV) within the research unit “Ecologie et dynamique des systèmes anthropisés” (Edysan, FRE3498 CNRS-UPJV). Safaa’s PhD defense is scheduled on Friday 27 November at 9H00 am at the Faculty of Pharmacy (Pôle Santé Saint Charles, 1 Rue des Louvels, 80037 Amiens Cedex, France). If you are somewhere around at that time, you are welcome to join. Please find below a short summary written by Safaa. You can also read more on Safaa’s work by downloading her papers on (i) “Disjunct populations of European vascular plant species keep the same climatic niches” and (ii) “Ecological niche shifts of understorey plants along a latitudinal gradient of temperate forests in north-western Europe“, both published in Global Ecology and Biogeography.

Ecological niche under climate change: conservatism and role in the biodiversity-ecosystem functioning relationship

Abstract: The scientific literature has shown a revival of interest in the concept of the ecological niche for the recent decades. This interest was largely promoted by the increasing use of species distribution models (SDMs) to inform conservation and management strategies in relation to climate change. In this thesis, I studied and used the concept of the ecological niche to answer two research questions which are heavily debated in ecology: the niche conservatism hypothesis and the relationship between biodiversity and ecosystem functioning. The first part of my work provides the first large-scale (i.e. Europe) assessment of the niche conservatism hypothesis between distinct populations of the same species and for a large number of vascular plant species (389 species) in their native geographical range. Main results from this work suggest that niche conservatism of vascular plant species is a widespread phenomenon. However, we also found that regional differences in niche width and optimum are common suggesting that other processes including adaptive responses are at play. Hence, while we conclude positively on the legitimacy of SDMs for predicting future species distributions, our results nevertheless show the importance of considering regional variations in the key parameters of species’ realized niche (cf. niche width and optimum) as well as the key mechanisms governing them (e.g. local adaptation), in order to accurately predict how these regional subtleties within the ecological space translate into the geographical space. In the second part of my thesis, I incorporated the concept of the ecological niche into the relationship between biodiversity and the net production of aboveground biomass in understory plant communities of temperate deciduous forests in Northern France. For this purpose, we first built a new set of diversity indices capturing the idea of ecological-niche diversity and then used it as an alternative or a complementary facet of biodiversity to test its relative importance for standing biomass in comparison with other facets of biodiversity that are more commonly used in ecology (cf. taxonomic and functional diversity). Among other things, results from this work highlight the importance of considering the ecological niche of species (sensu Hutchison) as an alternative and complementary facet of biodiversity having an important impact on ecosystem functioning, particularly the net production of aboveground biomass within the forest herb layer. These new findings suggesting a strong niche conservatism and supporting the idea to use the concept of the ecological niche as a facet of biodiversity will improve our understanding and our predictions of the effect of climate change on biodiversity and therefore on ecosystem functioning.

Keywords: community ecology, ecological niche, climate change, niche conservatism, biodiversity, vascular plants, forest.

Supervisors: Dr. Jonathan Lenoir & Prof. Guillaume Decocq, UR “Ecologie et dynamique des systèmes anthropisés” (Edysan, FRE 3498 CNRS), Jules Verne University of Picardie.

Exam committee: Prof. Antoine Guisan, Department of Ecology & Evolution, University of Lausanne; Prof. Martin Diekmann, Institute of Ecology, University of Bremen; Prof. Jean-Claude Gégout, UR “Laboratoire d’étude des resources forêts bois” (UMR 1092 LERFoB), AgroParisTech-ENGREF.

Importance du Concept de Niche Ecologique en Contexte de Changement Climatique

Je suis fier d’annoncer que Safaa Wasof, étudiante en thèse à l’Université de Picardie Jules Verne (UPJV) dans l’unité de recherche “Ecologie et dynamise des systèmes anthropisés” (Edysan, FRE3498 CNRS-UPJV), soutiendra sa thèse publiquement le 27 Novembre prochain, à 9H00, en salle des thèses de la Faculté de pharmacie (Pôle Santé Saint Charles : 1 rue des Louvels, 80037 Amiens Cedex 1). Si vous êtes de passage dans les environs vous êtes la/le bienvenu(e). Ce fût un réel plaisir pour moi de travailler aux côtés de Safaa durant ces quatre dernières années (Octobre 2011 – Octobre 2015) et de co-encadrer son travail de thèse dont vous trouverez un résumé écrit par Safaa ci-dessous. Vous trouverez également plus d’informations sur les travaux de Safaa en lisant ses articles intitulés (i) “Disjunct populations of European vascular plant species keep the same climatic niches” et (ii) “Ecological niche shifts of understorey plants along a latitudinal gradient of temperate forests in north-western Europe“, tout deux publiés dans la revue Global Ecology and Biogeography.

La niche écologique en contexte de changement climatique : conservatisme et rôle dans la relation biodiversité-fonctionnement de l’écosystème

Résumé : Ces dernières décennies le concept de niche écologique a connu un véritable regain d’intérêt dans la littérature scientifique. Cet intérêt a été largement promu par l’utilisation croissante des modèles de distribution d’espèces (SDMs) pour informer sur les défis de conservation et de gestion liés aux changements globaux. Dans cette thèse, j’ai étudié et utilisé ce concept de niche écologique pour répondre à deux questions de recherches faisant l’objet d’importants débats en écologie : le conservatisme de la niche écologique et la relation entre biodiversité et fonctionnement de l’écosystème. Le premier volet de mes travaux a ainsi fournit une première estimation globale de l’hypothèse de conservation de la niche entre des populations distinctes de la même espèce et ce chez un grand nombre d’espèces vasculaires (389 espèces) dans leur aire géographique d’indigénat. Cette partie a permis de mettre en évidence que le conservatisme de la niche climatique réalisée est un phénomène répandu. Toutefois, des différences régionales dans les paramètres synthétiques de la niche (cf. l’amplitude et l’optimum de la niche) étaient fréquentes laissant la possibilité d’une adaptation locale potentielle des populations végétales au sein de chaque région. Ces résultats renforcent la légitimité des SDMs, mais ils montrent néanmoins l’importance de considérer les variations régionales de l’amplitude et de l’optimum de la niche réalisée des espèces, ainsi que les mécanismes clés qui les régissent (comme l’adaptation locale), dans les prédictions des SDMs quand il s’agit de traduire ces subtilités régionales dans l’espace géographique. Dans le deuxième volet de ma thèse, je me suis ensuite intéressée à utiliser le concept de niche écologique au service de l’étude de la relation entre biodiversité et un aspect particulier du fonctionnement des écosystèmes : la production nette de biomasse aérienne au sein de la strate herbacée forestière. Nous avons pour cela développé et intégré, pour la première fois, la notion de diversité des niches écologiques comme facette alternative ou complémentaire de la biodiversité et avons comparé son importance vis-à-vis des autres facettes de la biodiversité utilisées plus communément en écologie (cf. diversité taxonomique et fonctionnelle). Entre autres choses, cette partie a permis de démontrer l’importance de considérer la niche écologique des espèces (sensu Hutchison) en tant que facette de la biodiversité ayant un rôle important dans le fonctionnement de l’écosystème, plus particulièrement la production nette de biomasse aérienne des communautés végétales du sous-bois forestier. Dans un contexte de changement climatique, évaluer et étudier les conséquences éventuelles d’un degré élevé de conservatisme de la niche vis-à-vis des conditions climatiques sur la distribution des espèces et donc sur la biodiversité, ainsi que de comprendre la relation entre biodiversité et le fonctionnement de l’écosystème sont deux étapes incontournables pour améliorer notre compréhension ainsi que nos prédictions de l’effet du changement climatique sur la biodiversité et donc sur le fonctionnement des écosystèmes.

Mots-clés : biomasse, biodiversité, changement climatique, conservation de la niche, écologie des communautés, écologie fonctionnelle, écologie végétale, écosystème forestier, niche écologique, plantes vasculaires, productivité.

Encadrants : Dr. Jonathan Lenoir & Prof. Guillaume Decocq, UR “Ecologie et dynamique des systèmes anthropisés” (Edysan, FRE 3498 CNRS), Université de Picardie Jules Verne.

Membres du jury : Prof. Antoine Guisan, Department of Ecology & Evolution, University of Lausanne; Prof. Martin Diekmann, Institute of Ecology, University of Bremen; Prof. Jean-Claude Gégout, UR “Laboratoire d’étude des resources forêts bois” (UMR 1092 LERFoB), AgroParisTech-ENGREF.

A Call for a Post-Doc Position in Ecoinformatics and Vegetation: Combining Remote Sensing and Field Data in a Toolbox to Map Non-Native Plant Distribution

Project aim:

IMAG3774

Saplings of Prunus seronita, a non-native plant, in a mixed Oak-Beech forest stand in Compiègne (France)

This postdoctoral position is part of a BiodivERsA project entitled “Detection of invasive plant species and assessment of their impact on ecosystem properties through remote sensing (DIARS)”. By combining field data together with two aircraft remote sensing technologies (hyperspectral imaging and light detection-and-ranging), DIARS aims at monitoring and modelling spread and risk assessment of invasive plant species at fine spatial resolution. Both remote sensing and field data are already available within the DIARS consortium for three different study sites (Belgium, France and Germany). The postdoc will develop a toolbox in a Free and Open Source environment (cf. R or GRASS GIS) to help end-users to combine both remote sensing and field data in a modelling framework that will allow mapping the invasion dynamic of non-native plants. More specifically, the toolbox will handle hyperspectral data preprocessing and classification, LiDAR data processing, species distribution modeling based on spatial proxies as well as field occurrences, and spatial representation of the uncertainty related to statistical modeling procedures. There will be many opportunities for independent and collaborative research in related areas of ecoinformatics.

Canopy_density

Canopy density derived from LiDAR data at 50-cm resolution across the entire Compiègne forest (144 km2) in northern France (Tarek Hattab)

The candidate is expected to have the following qualifications:

  • A Ph.D. in environmental sciences, computer sciences, statistics or mathematics;
  • Cutting-edge expertise in modeling and advanced statistical analyses;
  • Coding skills in Free and Open Source environments (R or GRASS GIS);
  • Basic knowledge and interest in plant ecology and biological invasions;
  • Experience in remote sensing;
  • Strong collaborative skills;
  • Proven abilities to publish at a high International level;
  • Good oral and written communication skills in English;
  • Ability to self-manage European project under European Commission, e.g. FP7.

Supervisors and collaborators:

The main supervisors are Dr. Jonathan Lenoir and Dr. Duccio Rocchini who are Associate Professor in Biostatistics and Researcher in Geographical Modeling and Spatial Ecology, respectively. The postdoc will work in close collaboration with Tarek Hattab, who is a Post-Doctoral fellow involved in DIARS, and will benefit from interactions with researchers in remote sensing (Dr. Ben Somers, Dr. Feilhauer Hannes, Prof. Sebastian Schmidtlein and Prof. Gregory Asner), conservation ecology (Prof. Olivier Honnay) and biological invasions (Prof. Guillaume Decocq).

Where:

Ecologie et Dynamique des Systèmes Anthropisés (EDYSAN), Jules Vernes University of Picardie, Amiens, France. EDYSAN is a young, diverse, vibrant and international research community with strong collaborative interdisciplinary ties within and beyond Amiens. More information about the people and research activities of the group can be here.

When:

The postdoctoral position should start at the latest on January 1st 2016. For further information, please contact: Dr. Jonathan Lenoir (jonathan.lenoir@u-picardie.fr).

Duration:

One year

Net salary:

2 100 EUR/month

Application deadline:

Please send your CV, including a list of publications, together with a cover letter and the contact information of 3 references to Jonathan Lenoir (jonathan.lenoir@u-picardie.fr). The application deadline is November 23rd 2015.

DIARS is funded by the ERA-Net BiodivERsA, with the national funders BelSPO,
DFG and ANR, part of the 2012-2013 BiodivERsA call for research proposals.

BiodivERsAANR

Plant Invasion in Mountain Ecosystems

I have just spent several days in the breathtaking mountain landscapes of the Nahuel Huapi National Park (San Carlos de Bariloche, Argentina) together with Ann Milbau, Jonas LembrechtsAnibal Pauchard and Martin Nuñez talking about plant invasion at high altitudes and latitudes. I’m still very much a novice in the field of plant invasions and thus this post might sound pretty naive to those of you who are plant-invasion geeks. Anyway, I think that I’m learning a lot by hanging around Ann, Jonas, Anibal and Martin who all know a great deal on this topic and thus I’m giving it a try. Please, correct me if I’m saying anything stupid here. One thing that I have rapidely understood is that although these cold and harsh environments are among the least invaded ecosystems in the world, nonnative plants are becoming increasingly common in these environments (Pauchard et al., 2009) and will be even more with future climate change, posing a threat to native plant species. Within the Nahuel Huapi National Park, up to 130 invasive plants have been recorded so far. Nahuel Huapi National Park Shortly after landing in San Carlos de Bariloche, I could easily grasp the phenomenon and see by myself how important are plant invasions in mountain ecosystems such as in the Nahuel Huapi National Park and its surroundings. The Lodgepole pine (Pinus contorda), native from the western part of North America, has already rapidly expanded into the dry steppes surrounding Bariloche’s airport at the foothill of the Patagonian Andes. Lodgepole pine invasion into the dry steppes surrounding Bariloche’s airport at the foothill of the Andes As we were heading towards Bariloche, I could not miss the bright yellow colors of the Scotch broom (Cytisus scoparius) along the road. This European fellow is simply everywhere on the roadsides. Scoth broom on the shore of Nahuel Huapi lake From the lakeshore, close to Bariloche, we climbed uphill within the impressive Coihue forest (Nothofagus dombeyi) which understorey was covered by a carpet of dead Caña coihue (Chusquea coleou) after a massive die-off happening some years ago. This native bamboo is flowering on a thirty-year basis, on average, triggering mice population explosions the following years due to large seed supplies. Bamboo native from Latine America As we moved up along the trail, I encountered plenty of our little European plant fellows playing hide and seek in the clearings, among others: Prunus avium, Sorbus aucuparia, Juniperus communis, Rosa rubiginosa, Rubus idaeus and Taraxacum officinale. Prunus invasion As we kept climbing upward it got less crowded with European plants and once we reached the vegetation belt of the Lenga forest (Nothofagus pumilio), only few individuals were standing here and there along the trail (Rosa rubiginosa, Taraxacum officinale and Hieracium pilosella), barely visible. Lenga forest Finally, once we reached the treeline, at the doorstep of the alpine vegetation belt when Lenga trees rapidly decreases in size (see the two pictures below with Martin for the scale), then I did not see any of our European fellows anymore but maybe these little guys were just hiding very well and I was just too tired after the hike. Lenga tree before the treeline Treeline Or, most likely, I was just too much distracted by the most beautiful native alpine plant of the area (Ranunculus semiverticillatus) to see any nonnative plant… ranunculus semiverticillatus Thank Ann, Jonas, Anibal and Martin for the great discussions and for letting me discover a wonderful country (@Martin: you look great on the two pictures, very professional). For more information on plant invasions into mountain areas in general, have a look at the website of the outstanding mountain invasion research network (MIREN). Last but not least, I highly recommend to visit Jona’s blog which is just amazing and full of beautiful pictures, enjoy.

A Call for a Post-Doc Position in Ecoinformatics and Vegetation: Fine-Grained Modeling of Invasive Plants by Remote Sensing

Digital surface model of the tree canopy from the southern part of the forest of Compiègne (France). Emilie Gallet-Moron2-yr postdoc position in ecoinformatics: fine-grained modeling of biological invasions

This is a call for a PhD who is interested in either biological invasions, remote sensing or species distribution modeling. Applications are invited for a 2-yr postdoc position starting in late 2014 or beginning of 2015 in the research team “Ecologie et Dynamique des Systèmes Anthropisés (EDYSAN)”, based at Jules Vernes University of Picardie, Amiens, France. EDYSAN is a young, diverse, vibrant and international research community with strong collaborative interdisciplinary ties within and beyond Amiens. More information about the people and research activities of the group can be found here.

The successful applicant will be tightly involved in the BiodivERsA project entitled “Detection of invasive plant species and assessment of their impact on ecosystem properties through remote sensing (DIARS)”. By combining two aircraft remote sensing technologies (hyperspectral imaging and light detection-and-ranging), DIARS aims at monitoring and predicting spread and risk assessment of invasive plant species at fine spatial resolution. Focusing on three different study sites in Southern France, Belgium and Western Germany, the postdoc will use LiDAR-derived data to assess current and future distributions of three invasive plants: one moss (Campilopus introflexus); one perennial herb (Oxalis pes-caprae); and one tree (Prunus serotina). The postdoc will also be involved in an ecoinformatics initiative designing a toolbox to facilitate the use of remote sensing data for assessing and characterizing the ecosystem impacts of invasive plants in a Free and Open Source environment. There will be ample opportunity for independent and collaborative research in related areas of ecoinformatics.

The candidate is expected to have:

  • A Ph.D. in environmental sciences, computer sciences, statistics or mathematics;
  • Cutting-edge expertise in modeling and advanced statistical analyses;
  • Programming skills in Free and Open Source environments (R and GRASS);
  • Basic knowledge and interest in ecology;
  • Strong collaborative skills;
  • Proven abilities to publish at a high International level;
  • Good oral and written communication skills in English.

Experience in remote sensing, species distribution modeling, plant ecology or biological invasions would also be an advantage for the position.

The main supervisors are Dr. Jonathan Lenoir and Dr. Duccio Rocchini who are Associate Professor in Biostatistics and Researcher in Geographical Modeling and Spatial Ecology, respectively. The postdoc will benefit from interactions with researchers in remote sensing (Dr. Ben Somers, Dr. Feilhauer Hannes, Prof. Sebastian Schmidtlein and Prof. Gregory Asner), conservation ecology (Prof. Olivier Honnay) and biological invasions (Prof. Guillaume Decocq).

Please send your CV, including a list of publication, together with a cover letter and the contact information of 3 references to Jonathan Lenoir – jonathan.lenoir@u-picardie.fr