Both dust and silica phytoliths have been shown to contribute to reducing tooth volume during chewing. However, the way and the extent to which they individually contribute to tooth wear in natural conditions is unknown. There is still debate as to whether dental microwear represents a dietary or an environmental signal, with far-reaching implications on evolutionary mechanisms that promote dental phenotypes, such as molar hypsodonty in ruminants, molar lengthening in suids or enamel thickening in human ancestors. By combining controlled-food trials simulating natural conditions and dental microwear textural analysis on sheep, we show that the presence of dust on food items does not overwhelm the dietary signal. Our dataset explores variations in dental microwear textures between ewes fed on dust-free and dust-laden grass or browse fodders. Browsing diets with a dust supplement simulating Harmattan windswept environments contain more silica than dust-free grazing diets. Yet browsers given a dust supplement differ from dust-free grazers. Regardless of the presence or the absence of dust, sheep with different diets yield significantly different dental microwear textures. Dust appears a less significant determinant of dental microwear signatures than the intrinsic properties of ingested foods, implying that diet plays a critical role in driving the natural selection of dental innovations.

We propose an approach to texture characterization and comparison that directly uses the information of digital images of the earth surface without requesting a prior distinction of structural ‘patches'. Digital images are partitioned into square ‘windows' that define the scale of the analysis and which are submitted to the two-dimensional Fourier transform for extraction of a simplified textural characterization (in terms of coarseness) via the computation of a ‘radial' power spectrum. Spectra computed from many images of the same size are systematically compared by means of a principal component analysis (PCA), which provides an ordination along a limited number of coarseness vs. fineness gradients. As an illustration, we applied this approach to digitized panchromatic air photos depicting various types of land cover in a semiarid landscape of northern Cameroon. We performed ‘textural ordinations' at several scales by using square windows with sides ranging from 120 m to 1 km. At all scales, we found two coarseness gradients (PCA axes) based on the relative importance in the spectrum of large (> 50 km−1), intermediate (30–50 km−1), small (10–25 km−1) and very small (<10 km−1) spatial frequencies. Textural ordination based on Fourier spectra provides a powerful and consistent framework to identifying prominent scales of landscape patterns and to compare scaling properties across landscapes

International audienceIn West Africa, climate variations and droughts have always affected livelihoods but have also triggered adaptation strategies. A better understanding of the impacts of drought and the responses of West African populations is indispensable for researchers and decision makers in the current and future context of multiple socioeconomic and environmental changes, including climate change. We conducted a systematic review of the literature on drought in West Africa. In this paper, we highlight controversial issues and identify knowledge gaps. Although drought has been widely considered as a major problem in West Africa, there is a need to frame it within a set of multiple threats faced by local populations and to understand how droughts act as a trigger in economic, societal, and environmental contexts. The literature on responses to drought focuses on agricultural and individual responses, while diversification, migration, and tree-based or livestock-based responses are less frequently addressed. More research is needed on the effectiveness and on the unexpected effects of responses of populations, states, and NGOs, as well as on the interactions between different responses. To understand the complexity of impacts and responses, the context in which they occur and how individual and collective actions interact within households or communities needs to be taken into account. Ecosystems and agriculture offer many goods and services that are suitable for adaptation and the different landscape components should be analyzed together. Such historical, contextual, and integrated analyses would better inform new policies and projects for adaptation to climate change

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