Implications of the evolution of agriculture and resource foraging for the maintenance of species diversity and community structure

Agriculture - cultivation of plants, algae, fungi and animal herding - is found in numerous taxa such as humans, but also ants, beetles, fishes and even bacteria. Such niche construction behaviours have evolved independently from hunter/predation behaviours, though many species remain primarily predators. We here investigate when such a transition from predation/hunter behaviour to agriculture is favoured. In these systems where a consumer has a positive effect on its resource, we can expect an allocative cost of agriculture for the farmer, hence modifying the selective pressures acting upon it. The management of the resource may have a negative effect on its consumption: for instance, when the consumer defends the resource against other predators (exploitation cost). In other situations, the cost may occur on the foraging of alternative resources, for instance if the consumer spends more time nearby the farmed resource (opportunity cost). Here, we develop a simple three-species model constituted by a farmer species that consumes two resource species, one of them receiving an additional positive effect from the consumer. We consider two trade-off scenarios based on how the cost of agriculture is implemented, either as an exploitation cost or as an opportunity cost. We use an adaptive dynamics approach to study the conditions for the evolution of the investment into agriculture and specialization on the two resources, and consequences on the ecological dynamics of the community. Eco-evolutionary dynamics generate a feedback between the evolution of agriculture and specialization on the helped resource, that can lead to varying selected intensity of agriculture, from generalist strategies with no agriculture, to farmer phenotypes that are entirely specialized on the farmed resource, with possible coexistence between those two extreme strategies.