Co-adaptations of feeding behaviours and gut modulation as a mechanism of co-existence

Question: How do foods differing in bulk, energy content, and ease of digestion influence diet choice, gut characteristics, community organization, and species co-existence? Mathematical method: Application of evolutionary game theory to a consumer-resource model. We let the consumer species choose their optimal diets, and we seek the ESS values for each species' gut volume and gut throughput time. Key assumptions: Gut physiology of consumers influences diet through differences in gut size and throughput time, and both of these gut characteristics can adjust evolutionarily to differences in food properties. Foods differ in key properties, including energetic reward, handling time, ease of absorption, and bulk. Consumer species encounter two food types simultaneously and may choose to forage selectively or partially selectively on one food type or opportunistically on both food types. Conclusions: Evolutionary co-adaptation of behaviour and gut physiology results in different communities of consumers depending upon properties of the available foods. Foods can differ along a quantitative or a qualitative niche axis, although most changes in food properties result in quantitative niche axes. When foods possess similar digestive properties, a single generalist species foraging opportunistically forms the ESS. Along a quantitative niche axis (with all consumers ranking food similarly), sufficiently different foods produce communities of a selective specialist on the rich resource and an opportunistic or partially selective generalist feeding on both resources. The specialist will evolve a smaller gut size than the generalist. The relative throughput times of these strategies will depend on the nature of the food. Simultaneously, increasing the bulk and the absorption rate between two foods produces a qualitative niche axis. Such foods can select for an ESS community of two selective specialists. The specialist on the bulkier resource evolves a shorter throughput time than the specialist on the less bulky resource.