27Adaptations can be thought of as evolutionary technologies that allow organisms to 28 exploit their environment. Like human technologies, adaptations can be 'progressive', increasing 29 in their ability to accomplish a task. Progressive adaptations which also fundamentally alter the 30 rules of trade-offs are known as key adaptations. Key adaptations allow a taxon to expand its 31 niche space thereby radiating to larger species numbers and spread beyond its original range. If 32 so, then of two otherwise ecologically equivalent taxa, the one with the greater geographical 33 range may have a key adaptation. We tested this hypothesis by comparing the global 34 biogeographic patterns of hummingbirds (Trochilidae) and sunbirds (Nectariniidae), ecologically 35 equivalent families with distinct evolutionary technologies. Though many species of both 36 families feed on nectar, hummingbirds also possess adaptations permitting hovering flight. We 37 analyzed each family's species diversity with latitude and elevation, charting how they decline 38 with movement towards poles and peaks. Hummingbirds persist into higher elevation and more 39 extreme latitudes than sunbirds, reaching their 50% species richness value at 22.14º and 2087 m 40 versus 18.92º and 2533 m for sunbirds. Looking at morphology, the evolution of hovering is 41 likely the constraint breaking adaptation that allowed hummingbirds to radiate into more species 42 and inhabit more extreme climes than sunbirds. Comparing the biogeography of ecologically-43 equivalent taxa has the potential to reveal insights into the species adaptations and niche 44 expansion.

Questions: Can resource-resource trade mutualism offer a competitive advantage to plants? If so, what are the conditions that give mutualism an advantage especially with regard to the size of the neighborhood? Hypothesis: We hypothesized that mutualism could offer a competitive advantage if the benefits outweighed the costs. We also hypothesized that this competitive advantage could lead to coexistence between mutualist and non-mutualist strategies within the same population. We also hypothesize that local neighborhood size (the number of competitors at a given moment) would change this response, though the specific direction of change was unclear to us. Method: We created an evolutionary game theoretic model in which a plant could either be a mutualist or non-mutualist that incorporated nutrients freely available to the plant, nutrients obtained only through mutualism with microbes, the cost of producing roots, the cost of trade with microbes, and neighborhood size. We sought ESS solutions as defined by the Nash equilibrium criterion. Key Assumptions: 1) Costs and benefits are fixed for all plants. 2) Freely available nutrients are equally shared between all competing plants in a local neighborhood. 3) Microbially obtained nutrients are shared equally between mutualistic plants in the local neighborhood. Conclusion: We found that mutualism could offer a competitive advantage if the net benefit was positive. Coexistence between mutualist strategies in our model happens because of competition between mutualists over the microbially available nutrient. Coexistence was more likely with greater neighborhood size but at the expense of mutualist fixation.