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Convergence between species and entire clades can occur due to shared environmental conditions and shared resource use. Comparisons of biogeography between convergent clades and taxa may reveal some of these properties unique to each taxon. We sought to characterize and compare the global scale biogeography of hummingbirds (family Trochilidae), which possess unique adaptations for nectar feeding, with sunbirds (family Nectariniidae), which also feed on nectar but are more generalist in their feeding ecology. We collected the latitudinal and elevational range of all species in both clades to create species distributions along those gradients by way of empirical cumulative distribution functions. We compared those distributions to see 1) if they differed, by way of minimum difference estimation and 2) how they differed, by way of non-linear regression. Hummingbirds are shown to extend into higher elevations and latitudes compared to sunbirds, and better maintain their species number in these more extreme environments. We provide possible reasons for these patterns including dispersal limitation, land area, diversity of resources, and climatic conditions. In one particularly interesting hypothesis, we propose that hummingbirds’ unique adaptations for nectar feeding allow them to exploit resources more efficiently, gain higher intrinsic fitness, and therefore speciate and spread into more extreme climates than less efficient nectar feeding sunbirds.

Abstract Due to their non-motile nature, plants rely heavily on mutualistic interactions to obtain resources and carry out services. One key mutualism is the plant–microbial mutualism in which a plant trades away carbon to a microbial partner for nutrients like nitrogen and phosphorous. Plants show much variation in the use of this partnership from the individual level to entire lineages depending upon ecological, evolutionary and environmental context. We sought to determine how this context dependency could result in the promotion, exclusion or coexistence of the microbial mutualism by asking if and when the partnership provided a competitive advantage to the plant. To that end, we created a 2 × 2 evolutionary game in which plants could either be a mutualist and pair with a microbe or be a non-mutualist and forgo the partnership. Our model includes both frequency dependence and density dependence, which gives us the eco-evolutionary dynamics of mutualism evolution. As in all models, mutualism only evolved if it could offer a competitive advantage and its net benefit was positive. However, surprisingly the model reveals the possibility of coexistence between mutualist and non-mutualist genotypes due to competition between mutualists over the microbially obtained nutrient. Specifically, frequency dependence of host strategies can make the microbial symbiont less beneficial if the microbially derived resources are shared, a phenomenon that increasingly reduces the frequency of mutualism as the density of competitors increases. In essence, ecological competition can act as a hindrance to mutualism evolution. We go on to discuss basic experiments that can be done to test and falsify our hypotheses. Plants frequently partner with microbes to obtain essential nutrients. Plants show variation in this mutualistic partnership, particularly with ecological and environmental context. We created a model of individual plant fitness given an ecological background to see how competition between plants over microbially derived resources affects this mutualism’s evolution. Our results show that such competition can hinder the evolution which may be relevant for some partnerships (e.g. mycorrhizal fungi) but not others (e.g. rhizobia). Our model also points to simple experiments which could be used to falsify our hypothesis.

The evolution of ecological specialization can be summed up in a single question: why would a species evolve a more-restricted niche space? Various hypotheses have been developed to explain the promotion or suppression of ecological specialization. One hypothesis, competitive diversification, states that increased intraspecific competition will cause a population to broaden its niche breadth. With individuals alike in resource use preference, more individuals reduce the availability of preferred resources and should grant higher fitness to those that use secondary resources. However, recent studies cast doubt on this hypothesis with increased intraspecific competition reducing niche breadth in some systems. We present a game-theoretic evolutionary model showing greater ecological specialization with intraspecific competition under specific conditions. This is in contrast to the competitive diversification hypothesis. Our analysis reveals that specialization can offer a competitive advantage. Largely, when facing weak competition, more specialized individuals are able to acquire more of the preferred resources without greatly sacrificing secondary resources and therefore gain higher fitness. Only when competition is too great for an individual to significantly affect resource use will intraspecific competition lead to an increased niche breadth. Other conditions, such as a low diversity of resources and a low penalty to specialization, help promote ecological specialization in the face of intraspecific competition. Through this work, we have been able to discover a previously unseen role that intraspecific competition plays in the evolution of ecological specialization. Competing Interest Statement The authors have declared no competing interest.

Competition is a fundamental ecological interaction, accounting for the origination, distribution, and extinction of species. It occurs at the smallest scales yet can also drive larger scale phenomena. It is most often studied at the local scale, either between individuals within a population or between populations.This focus on smaller scale competition can bias the perception of how competition operates at even higher scales. In my dissertation, I analyze competitive dynamics at multiple scales to reveal the unique processes that govern each scale. At the smaller scales, I analyze how individual competitive interactions with regard to resource use can affect population structure. At moderate scales, I analyze how the diversity of competing populations can affect their evolutionary dynamics. At larger scales, I show how the fundamental adaptations of clades competing over the same resource can lead to mutual suppression of diversity and speciation process. Through this, I hope to expose the unique dynamical process of competition at multiple eco-evolutionary scales.

Plants due to their non-motile nature rely heavily on mutualistic interactions to obtain resources and carry out services. One key mutualism is the plant-microbial mutualism in which a plant trades away carbon to a microbial partner for nutrients like nitrogen and phosphorous. Plants show much variation in the use of this partnership from the individual level to entire lineages depending upon ecological, evolutionary, and environmental context. We sought to determine how this context dependency could result in the promotion, exclusion, or coexistence of the microbial mutualism by seeing if and when the partnership provided a competitive advantage to the plant. To that end, we created a simple 2 × 2 evolutionary game in which plants could either be a mutualist and pair with a microbe or a non-mutualist and forgo the partnership. This model included 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 the size of the local competitive neighborhood. Not surprisingly, we found that mutualism could offer a competitive advantage if its net benefit was positive. Coexistence between strategies is possible though due to competition between mutualists over the microbially obtained nutrient. In addition, the greater the size of the local competitive neighborhood, the greater the region of coexistence but only at the expense of mutualist fixation (non-mutualist fixation was unaffected). Our model, though simple, shows that plants can gain a competitive advantage from using a mutualism depending upon the context and points to basic experiments that can be done to verify the results.

The concept of the evolutionary stable strategy (ESS) has been fundamental to the development of evolutionary game theory. It represents an equilibrial evolutionary state in which no rare invader can grow in population size. With additional work, the ESS concept has been formalized and united with other stability concepts such as convergent stability, neighborhood invasion stability, and mutual invisibility. Other work on evolutionary models, however, shows the possibility of unstable and/or non-equilibrial dynamics such as limit cycles and evolutionary suicide. Such \"pathologies\" remain outside of a well-defined context, especially the currently defined stability concepts of evolutionary games. Ripa et al. (2009) offer a possible reconciliation between work on non-equilibrial dynamics and the ESS concept. They noticed that the systems they analyzed show non-equilibrial dynamics when under-saturated and \"far\" from the ESS and that getting \"closer\" to the ESS through the addition of more species stabilized their systems. To that end, we analyzed three models of evolution, two predator-prey models and one competition model of evolutionary suicide, to see how the degree of saturation affects the stability of the system. In the predator-prey models, stability is linked to the degree of saturation. Specifically, a fully saturated community will only show stable dynamics, and unstable dynamics occur only when the community is under-saturated. With the competition model, we demonstrate it to be permanently under-saturated, likely showing such extreme dynamics for this reason. Though not a general proof, our analysis of the models provide evidence of the link between community saturation and evolutionary dynamics. Our results offer a possible placement of these evolutionary \"pathologies\" into a wider framework. In addition, the results concur with previous results showing greater evolutionary response to less biodiversity and clarifies the effect of extrinsic vs. intrinsic non-equilibrial evolutionary dynamics on a community.

Adaptations can be thought of as evolutionary technologies which allow an organism to exploit environments. Among convergent taxa, adaptations may be largely equivalent with the taxa operating in a similar set of environmental conditions, divergent with the taxa operating in different sets of environmental conditions, or superior with one taxon operating within an extended range of environmental conditions than the other. With this framework in mind, we sought to characterize the adaptations of two convergent nectarivorous bird families, the New World hummingbirds (Trochilidae) and Old World sunbirds (Nectariniidae), by comparing their biogeography. Looking at their elevational and latitudinal gradients, hummingbirds not only extend into but also maintain species richness in more extreme environments. We suspect that hummingbirds have a superior key adaptation that sunbirds lack, namely a musculoskeletal architecture that allows for hovering. Through biogeographic comparisons, we have been able to assess and understand adaptations as evolutionary technologies among two convergent bird families, a process that should work for most taxa. Footnotes * Updated manuscript with newer figures