Jacques Tassin’s research while affiliated with Cirad - La recherche agronomique pour le développement and other places

On oceanic islands, strong human impacts on habitats, combined with introductions of exotic species, modify the composition of terrestrial bird assemblages and threaten their ecological functions. In La Réunion, an oceanic island located in the Madagascan region, a national park was established in 2007 to counter the ecosystem-level effects of three centuries of habitat conversion, native species destruction and exotic species introductions. Here, we investigated how bird assemblages were structured in these human-modified landscapes, 10 years before the national park set out its first conservation measures. We used a combination of multivariate statistics and generalized additive models to describe variations in the taxonomic and functional composition and diversity of 372 local bird assemblages, encompassing 20 species, along gradients of habitat composition and configuration. We found that native species were tied to native habitats while exotic species were associated with urban areas and man-modified landscape mosaics, with some overlap at mid-elevations. Species' trophic preferences were segregated along habitat gradients, but ecological traits had an overall weak role in explaining the composition of species assemblages. Hence, at the time of the survey, native and exotic species in La Réunion formed two spatially distinct species assemblages with contrasting ecological trait suites that benefited from antagonistic habitat compositions and dynamics. We conclude that our results support the analysis of historical data sets to establish reference points to monitor human impacts on insular ecosystems. K E Y W O R D S ecological traits, habitat changes, insular birds, Mascarenes, oceanic islands, species introductions T A X O N O M Y C L A S S I F I C A T I O N

This article explores possible histories of plant exchanges and plant naming tied to the slave trade between East Africa, Madagascar and the Mascarene Islands. The subsequent 'marronnage' of slaves on these islands - their escape from captivity, sometimes to live in mountain hideouts - continues to inspire cultural references. Inspired by the use of the adjective 'marron/marronne' for a number of plants on Reunion Island, we compile evidence of plant exchanges and plant naming from ecological records, historical accounts and the use of descriptive, emotive or symbolic vernacular names as clues for deepening our knowledge of historical societies and environments. The evidence from the Mascarenes opens a window into the role of the African diaspora in plant introduction, diffusion, domestication and cultivation. We document that maroons relied on a variety of wild, escaped and cultivated plants for their subsistence. We also highlight the role of marronnage in the popular and literary imaginary, with the result that many plants are named 'marron/marrone' in a metaphorical sense. Finally, we identify a few plants that may have been transported, cultivated, or encouraged in one way or another by maroons. Along the way, we reflect on the pitfalls and opportunities of such interdisciplinary work.

Biological and structural factors of the invading vine Merremia peltata in forested habitats in Mayotte. — Lianas are hyperdynamic elements of tropical vegetation that strongly react to changes in forest structure. In Mayotte (Western Indian Ocean), the indigenous vine Merremia peltata (Convolvulaceae) greatly expanded its range in recent decades and sometimes causes the collapse of the forest canopy. Surveys were conducted in 52 4 m-radius plots arranged in Voundzé forest and Bénara Monts Departmental Forest, along an ecological gradient of invasion of M. peltata from free to very strongly invaded areas. The propagation modes of the liana, the vertical structure of forest stands, but also topographic parameters, were identified and quantified. No plantlet resulting from germination was observed. The creeping stems, present in high density (1.9 stems / m) were systematically layered in the ground. A set of 37 native plant species have been recorded as supports, the most common one being Grisollea myrianthea. From the primary host, which has an average diameter of 6.0 ± 4.9 cm at 1.30 m above ground, the creeper joins another support remote of a mean distance of 97 cm. The index of colonization and the index of forest structure which were used, which sum the rate of vegetation cover at different heights, were negatively correlated (n = 52, Pearson coefficient r = -0.319, P < 0.05). Natural forests, which show a complex vertical structure, were actually less colonized than secondary forests, which have a poorer vertical structure. The negative correlation between the same index of colonization and altitude (n = 35, Pearson coefficient r = -0.439, P < 0.05) is interpreted as a relationship confused with the previous, as natural forests are located at altitude unlike secondary forests. The colonization of forest ecosystems by M. peltata is facilitated by a high aptitude for vegetative propagation, coupled with higher propensity of secondary forests to be colonized by lianas. Uncertainty remains about the future of the sites where this vine has led to the collapse of forest stands. However, only new ecosystems mixing indigenous and alien species, are expected to emerge.

While a number of plants, animals, and insects in Madagascar have been called ’invasive’, the topic of invasive species has until recently received less attention here than in other island contexts. Some species, often alien to Madagascar and introduced by humans, have expanded their range rapidly and have had both negative and positive effects on landscapes, on native biodiversity, and on livelihoods. Examples include the prickly pear (raketa), the silver wattle (mimosa), and, recently, the Asian common toad (radaka boka). Building on a conceptual approach to ’invasive species’, this paper emphasizes the importance of inclusive and deliberative site- and population - specific management of invasive species. It analyses three separate concepts commonly used in definitions of invasion: the origin, behaviour, and effects of particular species. It places these concepts in their broader social and ecological context, with particular attention to local perspectives on invasive species. We illustrate these concepts with Malagasy examples and data. The examples demonstrate that while invasions can have dramatic consequences, there can be multiple, often competing, interests as well as site - specific biophysical, environmental, and cultural considerations that need to be taken into account when designing policy and management interventions. We conclude with a number of lessons learned. - RÉSUMÉ : Contrairement à la plupart des autres îles, et en dépit du quali­ficatif ‘invasif’ rattaché depuis longtemps à certaines espèces qui s’y sont naturalisées, les réflexions autour de l’approche des espèces invasives à Madagascar demeurent récentes. L’opuntia (Opuntia spp.) figure certes parmi les plus anciens exemples d’espèces traités dans la littérature sur les invasions biologiques. Mais ce n’est vraiment qu’avec le retentissement médiatique autour de la détection en 2011 de la présence du crapaud masqué (Duttaphrynus melanostictus) et la recherche d’une parade appropriée que s’est affirmée la nécessité de traiter cette question des espèces invasives en tant que telle. Une posture nativiste et uniforme qui ignorerait la spécificité des contextes biophysiques et socio - économiques locaux, mais aussi la pluralité des formes d’invasion biologique et des définitions qui s’y rattachent, ne saurait être privilégiée. L’article montre qu’il s’agit de situer les réflexions dans un contexte insulaire socio - économique dans lequel les espèces allogènes tiennent depuis longtemps une large place. Il défend en outre la nécessité d’envisager les espèces invasives non pas selon une forme de perception unique et autoritariste, mais selon une diversité de points de vue, conforme aux conflits d’intérêts qui se manifestent parfois, et mettant plutôt en avant le caractère exogène des espèces invasives, leurs effets (négatifs, mais aussi positifs) sur le milieu, ou leur mode de fonctionnement (dispersion, dominance) dans des contextes spécifiques et locaux. Il convient en particulier d’observer qu’aux coûts générés par les invasions biologiques peuvent s’ajouter des bénéfices économiques, et que les impacts écologiques néfastes peuvent se combiner avec des incidences heureuses, y compris auprès d’espèces indigènes en situation critique. En outre, le point de vue des populations humaines, leur connaissance d’espèces invasives quotidiennement rencontrées, leur réticence à scinder le vivant en espèces indigènes et allogène, mais aussi leur vision pragmatique, ne sauraient être mésestimés, et moins encore oubliés. Enfin, l’article invite à prendre du recul face aux effets rhétoriques liés aux discours conventionnels sur les invasions biologiques, à éviter les amalgames et les généralisations excessives, à tenir compte des contraintes environnementales mais aussi des aspirations socio - économiques des populations locales, et à prendre en compte la diversité des spécificités locales, qu’elles soient biophysiques ou sociales. En conclusion, il est sans doute heureux que Madagascar n’ait rejoint que très récemment la mouvance internationale des reflexions sur les espèces invasives : cela lui permet en effet d’être en mesure de disposer d’une position équilibrée, déjouant certains discours catastrophistes, et préférant une approche résolument contextualisée, à l’échelle nationale comme aux échelles régionales.

Seed passage through the gut of vertebrates is critical for endozoochorous seed dispersal because it may influence seed germination and seed dispersal. Seed retention time in the gut may improve or decrease the seed germination. In Madagascar, extinct giant tortoises were potential seed dispersers of the baobab species. We used the related species Aldabrachelys gigantea, kept in the Tsimbazaza Zoological and Botanical Park (Antananarivo), to test the effect of gut retention time on seed germination in Adansonia rubrostipa. Seed retention time ranged from 15 to 23 days, and almost 87% of defecated seeds remained viable. Germination percentage of defecated seeds did not differ Gut passage (T1) enhanced seed germination percentage compared with that of seeds not extracted from the pulp (T2) but did not differ significantly from pulp removal (T3). The mean retention time (i.e. 17 or 18 days) ensured the most efficient seed dispersal, optimizing the germination rate and allowing a long dispersal distance.

We aimed to characterize the altitudinal variation of species richness of maquis on New Caledonia (South Pacific Ocean). Data were collected from altitudinal maxima and minima mentioned in Flore de Nouvelle-Calédonie, reported from herbarium samples of the Herbarium of Nouméa, New Caledonia. Using interpolation between minimum and maximum altitude, the altitudinal range of 577 phanerogam species within 34 families was documented. The variation of species richness of maquis species showed a linear regular decline with altitude. The effect of area of each 100 m altitudinal band on the pattern of variation of species richness is low, compared to the major effect of altitude. Direct biophysical or historical factors are still to be identified to explain the pattern. This altitudinal pattern can be explained by a long—term accumulation of species and an important refugee effect of New Caledonian mountains, which could have favoured the migration of species towards low altitudes following the last glaciation event.