B12 - Reproductive strategies of weedy flowering plants in tropical rainforest transformation systems
The project aims to study the mode of reproduction of frequent weeds in the understory of tropical rainforest transformation systems. The biological factors for weedy and even invasive behaviour in human-influenced landscapes are still poorly understood. We want to test the hypothesis that asexual reproduction via seed (apomixis) is one of the key factors for introduced weeds to reach rapidly dominance in the understory vegetation of plantations, and to invade natural rainforest systems. Uniparental reproduction after long distance dispersal may explain the superior colonization ability of apomictic plants (Baker’s law). We will focus on two model systems of widespread invasive species with facultative apomixis (Melastomataceae: Clidemia hirta, and Poaceae: Panicoideae). To test the hypothesis that apomictic weeds have a major impact on tropical rainforest transformation systems, we will quantify apomictic vs. sexual seed formation by using pollen-exclusion experiments population genetic studies and molecular progeny arrays with microsatellite markers, microscopic histological investigation plus flow cytometric seed screening. Sampling will follow the general project scheme in two landscapes, with each four plots in palm oil, rubber plantations and in jungle rubber; for natural rainforests we will analyse marginal populations. Coverage of the respective species will be recorded and correlated to canopy and understory coverage, overall taxonomic biodiversity, and abiotic measures of the selective plots from other subprojects to get information on the impact of these invaders on the ecosystem. These data will support modelling rainforest transformations at a landscape scale. Chemical and mechanical control will be analysed in collaboration with economic subprojects to understand the socioeconomic relevance of weed management. Long term perspectives focus on functional studies on the respective species to understand better the causality of invasiveness within tropical transformation systems and the threat for remnants of tropical rainforests. International collaborations are planned for phylogeographic studies to understand the origin and the causality of the worldwide geographical range expansion of the selected species.