1. 1. Population Dynamics: The Red Queen Effect and Attractors in Evolution Ted Carmichael SwarmFest July 11, 2015
2. 2. Outline Introducing the General Ecosystem model Assumptions of the model Demo: Stepped pattern of biomass accrual Considerations for field studies The Red Queen Hypothesis Predators: Effects of Effectiveness Impacts on Evolutionary Pressures
3. 3. The Marine Ecosystem Model Three trophic levels: Food Prey (Fish) Predators Model assumptions: Both predators and prey reproduce as a function of how much they eat. Completely homogeneous environment. The agents move randomly and eat once per turn if there is food available. All agents have a limited lifetime.
4. 4. The Marine Ecosystem Model Validation: Lotka-Volterra, Gause's Law, Paradox of Enrichment, Stepped pattern of biomass accrual Carmichael & Hadzikadic, Advances in Complex Systems, 2013
5. 5. The Marine Ecosystem Model Stepped pattern of biomass accrual Oksanen, et. al, 1981 Mathematical predictions of population changes based on changes in primary enrichment Model Assumption: prey have a constant supply of food. - what happens if the food supply changes? Demo: increasing the food supply to the prey. What happens? Will: 1) the prey population increase? 2) the predator population increase? 3) both prey and predator increase in population size?
6. 6. Considerations for Field Studies Average Age is an important attribute Can give us important inferences on existent populations Rarely collected systematically Replacement rate and equilibrium population
7. 7. The Red Queen Hypothesis Now, here, you see, it takes all the running you can do, to keep in the same place. -Through the Looking Glass Arms race between predators and prey Assuming the current state is a basin of attraction, and the arms race reaches a terminus, what accounts for the trade-offs that prevent further advancements? Diversity among prey old, young, sick, unlucky Prey sharing leads to cooperative strategies, which leads to free riders, which limits positive evolution Anything else?
8. 8. The Red Queen Hypothesis Another piece of the evolutionary puzzle the effects on predator and prey populations via two different methods of reducing predator effectiveness: Decrease the success rate of predators: i.e., sometimes the predators try to eat a prey but miss (the prey escapes) Reduce the turns per tick of the predators, from 6 to 4. Predators will live longer 600 turns across more ticks
9. 9. The Red Queen Hypothesis Success rate reduced by 1/3rd. Turns per tick reduced by 1/3rd.
10. 10. Conclusions: There are many non-intuitive results, even in a very simple model of population dynamics Average age for a population is important, and may help infer attributes (such as consumption rate) that cannot easily be gathered Not all efficiency gains produce population-level benefits, and some may even be detrimental to a species Some of these non-intuitive results may help explain evolutionary pressures on a species
11. 11. Conclusions: Thank you!
12. 12. The Competitive Exclusion Principle The competitive exclusion principle states that two (or more) species competing for the same resources, and sharing the same predators, cannot continually co- exist if all other ecological factors are constant.