Dynamics in agrarian systems of Uruguay and Argentina present some positive aspects as well as other potentially devastating. Traditional producers have a production strategy based on looking for a balance between cattle and agriculture production, alternating pasture and crops. A new actor: investment-fund-managers rent the land for agriculture production, and from our team¿s discussions emerged that they follow a strategy similar to that of financial capital: decide what to do in terms of the expected net profit. Economical, ecological and social consequences could be expected. Modeling and simulating with Multi-Agent-Systems was used for exploring the system¿s evolution with the objective of improving our understanding of the agrarian system and to contribute to the envision of possible effects on land use caused by changes in product prices and/or policy changes. The model considers the soil resource as having productive potential and assumes that each traditional producer annually decides whether to change or not its production activity over 25% of its land units or to rent to investment fund managers. A six year database with historical production activity revenues and product¿s prices was used for the simulation, where each simulated year randomly chooses from this database. The first results of these simulations generate questions about the dynamics of the natural resources, challenge the survival of traditional farmers and anticipate landscape changes associated to economic, ecological and social changes. A strong variability was observed from year to year in respect to land use. Results show that if the current price structure is maintained as well as the relation between net profits of agriculture and cattle, then a tendency to expand Investment Fund Managers¿ lands will occur. We conclude that the newly arrived Investment Fund Managers tend to induce a rent activity in traditional producers as well as a substantial increase in agricultural activities (de