Alban Thomas

Morphology and genetics reveal an intriguing pattern of differentiation at a very small geographic scale in a bird species, the forest thrush Turdus lherminieri

Mobile organisms are expected to show population differentiation only over fairly large geographical distances. However, there is growing evidence of discrepancy between dispersal potential and realized gene flow. Here we report an intriguing pattern of differentiation at a very small spatial scale in the forest thrush (Turdus lherminieri), a bird species endemic to the Lesser Antilles. Analysis of 331 individuals from 17 sampling sites distributed over three islands revealed a clear morphological and genetic differentiation between these islands isolated by 40–50u2009km. More surprisingly, we found that the phenotypic divergence between the two geographic zones of the island of Guadeloupe was associated with a very strong genetic differentiation (Fst from 0.073–0.153), making this pattern a remarkable case in birds given the very small spatial scale considered. Molecular data (mitochondrial control region sequences and microsatellite genotypes) suggest that this strong differentiation could have occurred in situ, although alternative hypotheses cannot be fully discarded. This study suggests that the ongoing habitat fragmentation, especially in tropical forests, may have a deeper impact than previously thought on avian populations.

Phenotypic variation of Forest Thrushes Turdus lherminieri in Guadeloupe: evidence for geographic differentiation at fine spatial scale

AbstractSpatial differentiation in avian models has been extensively studied at a coarse scale for both theoretical and conservation purposes. Yet, studies at a finer spatial scale are also particularly relevant in birds because their dispersal ability may be much more reduced than expected. In the Forest Thrush Turdus lherminieri, we studied morphological characters commonly used to assess differentiation because they mirror both demographic and selective processes. The Forest Thrush is an endemic and vulnerable Antillean bird species which has dramatically declined in the last 15xa0years, and whose population functioning and structure remain unknown. We compared birds from 11 sites in Guadeloupe, which were distributed from 2 to 42xa0km apart over the two main geographic zones of the island (i.e. Grande-Terre and Basse-Terre). Using two synthetic descriptors (for body size and feather size), we detected a strong micro-geographic differentiation between Forest thrush populations for the body-size descriptor but not for the feather-size descriptor. Both males and females were significantly larger in Basse-Terre than in Grande-Terre despite the fine geographic scale. Several hypotheses could explain these results: (i) geographic isolation and differentiation caused by (1)absence of gene flow, (2) phenotypic plasticity, or (3) divergence with gene flow. Although further investigation is needed to identify the exact process generating phenotypic divergence, our study provides a first highlight to the high local variability of this species.ZusammenfassungPhänotypische Unterschiede bei AntillendrosselnTurdus lherminieriin Guadeloupe: Hinweis auf kleinräumige geographische Differenzierungn Räumliche Differenzierung in Vogelmodellen wurde in groben Rastern sowohl theoretisch, als auch für Schutzzwecke ausgiebig untersucht. Trotzdem sind kleinräumigere Untersuchungen bei Vögeln teilweise auch relevant, weil ihre Ausbreitungsmöglichkeiten stärker eingeschränkt sein könnten als erwartet. Wir untersuchten morphologische Merkmale bei der Antillendrossel, die üblicherweise verwendet werden um eine Differenzierung abzuschätzen, weil diese sowohl demographische als auch Selektions-Prozesse widerspiegeln. Die Antillendrossel ist eine endemische und gefährdete Vogelart der Antillen, die in den letzten 15 Jahren dramatisch abgenommen hat, und deren Aufbau und Strukturen der Population weiterhin unbekannt sind. Wir verglichen Vögel aus elf verschiedenen Gebieten von Guadeloupe, die im Abstand von zwei bis 42xa0km über die beiden geographischen Hauptzonen der Insel, Grande-Terre und Basse-Terre, verteilt lagen. Unter Verwendung zweier künstlicher Maße (für Körpergröße und Federgröße) fanden wir eine deutliche mikrogeographische Differenzierung zwischen Antillendrosseln für das Maß der Körpergröße, aber nicht für das Maß der Federgröße. Trotz des geringen geographischen Abstands waren sowohl Männchen als auch Weibchen signifikant größer in Basse-Terre als in Grande-Terre. Verschiedene Hypothesen könnten diese Ergebnisse erklären: (i) Geographische Isolation und Differenzierung durch einen fehlenden Gen-Austausch, (ii) phänotypische Plastizität oder (iii) eine Auseinanderentwicklung mit Gen-Austausch. obwohl weitere Untersuchungen nötig sind, um den genauen Prozess zu finden, der zur phänotypischen Divergenz führt, gibt unsere Untersuchung doch einen ersten Einblick in die hohe örtliche Variabilität dieser Art.

Economic modelling of agricultural production: past advances and new challenges

This paper is a methodological review focusing on the major advances in modelling issues in agricultural production economics that have been made over recent decades. Issues include the role of markets and international trade, structural and dynamic aspects of production, environmental impacts of production decisions and risk issues. We describe the main scientific developments and their implications for policy design and evaluation for each topic. We also provide a short conclusion on emerging issues, data and modelling requirements and perspectives for future research.

A dynamic model for water management at the farm level integrating strategic, tactical and operational decisions

Abstract Farming systems are complex and have several dimensions that interact in a dynamic and continuous manner depending on farmers management strategies. This complexity peaks in Indian semi-arid regions, where small farms encounter a highly competitive environment for markets and resources, especially unreliable access to water from rainfall and irrigation. NAMASTE, a dynamic computer model for water management at the farm level, was developed to reproduce interactions between decisions (investment and technical) and processes (resource management and biophysical) under scenarios of climate-change, socio-economic and water-management policies. The most relevant and novel aspects are i) system-based representation of farming systems, ii) description of dynamic processes via management flexibility and adaptation, iii) representation of farmers decision-making processes at multiple temporal and spatial scales, iv) management of shared resources. NAMASTEs ability to simulate farmers adaptive decision-making processes is illustrated by simulating a virtual Indian village composed of two virtual farms with access to groundwater.