In this lecture, we review the processes in natural systems that cause diversity to grow initially and then collapse as systems get more mature (and this collapse in diversity can lead to the release and reorganization, as in the Adaptive Cycle). We use a Pareto-based multi-objective framework to conceptualize what is going on in ecological communities. In this framework, Pareto improvements correspond to expansion of diversity (virtuous cycle) that ends up slowing down as the community approaches the Pareto frontier (limits to growth). Once on the frontier, competitive exclusion and genetic drift lead to sparsification of the community (success to the successful). In other words, the initial process generates a diverse set of niches, but the later processes collapse each niche to a very small set of individuals that dominate that niche. We explain how genetic drift causes diversity to collapse even when diverse individuals have equal fitness. We also talk about how we can measure diversity using the Shannon index, which measures both richness as well as evenness. This whole explanation sets up for an introduction of the Adaptive Cycle (r/growth phase, K/conservation phase, omega/release phase, and alpha/reorganization phase). Overall, the adaptive cycle links topics from earlier in the semester (systems archetypes) with more recent topics (chaotic dynamics) and helps provide a framework for understanding how exogenous/slow variables change over time (and thus how stability regimes change over time). Change is inevitable, and sustainability is about surviving change; sustainability is not about preventing change.
Whiteboard notes for this lecture can be found at: https://www.dropbox.com/s/te0c37iet0roxa3/SOS220-LectureF2-2023-03-14-The_Adaptive_Cycle_and_Panarchy.pdf?dl=0
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