Biology subjects

Cherif, M.

Publications and source records attributed to Cherif, M..

3 recordsLinked to original sources

bioRxiv2025

Spatial variability of shade and its effects on cocoa trees productivity in agroforestry systems

The impact of intra-plot multi shading on cocoa tree productivity is a widely exploited aspect of agroforestry practice. This study, conducted on 1,000 m2 experimental plots at three agroclimatic sites in Cote dIvoire (Azaguie, Divo, Soubre), mapped the spatial heterogeneity of shade provision using light intensity measurements and then calculated cocoa productivity over two years of data collection. A geostatic approach (ordinary kriging) was used to analyze the shade in agroforestry plots, which revealed significant heterogeneity. This heterogeneity was primarily attributed to the phenological diversity of the companion trees. The analysis revealed that low shading levels (approximately 30%) emerged as thresholds where cocoa productivity was highest. However, it was observed that elevated shading levels, exceeding 60%, resulted in a significant decline in productivity. Among the companion trees, Ceiba pentandra, Eleais guineensis, and Persea americana offer light to moderate shade. Conversely, certain trees that provide heavy shade, such as Mangifera indica, are identified as less beneficial because they significantly reduce cocoa productivity.

ecology↗

bioRxiv2020

More than stoichiometry: the molecular composition of inorganic and organic substrates controls ammonium regeneration by bacteria

The mineralization of nitrogen (N) and especially the regeneration of ammonium are critical processes performed by bacteria in aquatic ecosystems. Quantifying these processes is complicated because bacteria simultaneously consume and produce ammonium. Here we use experimental data on the effects of the molecular composition of the supplied substrates, combined with a classical stoichiometric model of ammonium regeneration, to demonstrate how the quantification of these processes can be improved. We manipulated a batch culture experiment with an isolated bacterial community by adding three different types of N substrates: dissolved inorganic nitrogen (DIN, nitrate), dissolved organic nitrogen (DON, amino acid) and a mixture of DIN and DON. With such experiment set-up, the ammonium regeneration per se could be easily tracked without using complicated methods (e.g. isotope dilution). We compared the experimental data with the predictions of Goldman et al model (1987) as well as with a revised version, using the measured consumption carbon:nitrogen ratio (C:N ratio), rather than an estimated consumption ratio. We found that, for all substrates, and in particular, mixed substrates where C and N are partially dissociated between different molecules, estimates of ammonium regeneration rates can be improved by measuring the actual consumption C: N ratio. ImportanceMeasuring bacterial ammonium regeneration in natural aquatic ecosystem is difficult because bacteria in the field simultaneously consume and produce ammonium. In our experimental design, we used nitrate as the inorganic nitrogen substrate. This way, we could measure separately the uptake and excretion of inorganic nitrogen by bacteria without incorporating cumbersome methods such as isotope dilution. Our experiment allowed us to evaluate the accuracy of various stoichiometric models for the estimation of net bacterial nitrogen regeneration. We found that: O_LIThe exact distribution of C and N among the various molecules that make the bulk of DOM is a crucial factor to consider for bacterial net nitrogen regeneration. C_LIO_LIFor all substrates, and in particular, mixed substrates where C and N are partially dissociated between different molecules, estimates of net nitrogen regeneration rates can be improved by measuring the actual C: N ratio of bacterial consumption. C_LI

ecology↗

bioRxiv2018

The mechanics of predator-prey interactions: first principles of physics predict predator-prey size ratios

O_LIRobust predictions of predator-prey interactions are fundamental for the understanding of food webs, their structure, dynamics, resistance to species loss and invasions and role in ecosystem functioning. Most current food web models are empirically based. Thus, they are sensitive to the quality of the data, and ineffective in predicting non-described and disturbed food webs. There is a need for mechanistic models that predict the occurrence of a predator-prey interaction based on the traits of organisms and the properties of their environment.\nC_LIO_LIHere, we present such a model that focuses on the predation act itself. We built a Newtonian, mechanical model for the processes of searching, capture and handling of a prey item by a predator. Associated with general metabolic laws, we predict the net energy gain from predation for pairs of predator and prey species depending on their body sizes.\nC_LIO_LIPredicted interactions match well with data from the most extensive predator-prey database, and overall model accuracy is greater than the niche model.\nC_LIO_LIOur model shows that it is possible to accurately predict the structure of food webs using only a few ecomechanical traits. It underlines the importance of physical constraints in structuring food webs.\nC_LI

ecology↗