A membership society whose goal is to advance and to diffuse knowledge of organic evolution and other broad biological principles so as to enhance the conceptual unification of the biological sciences.
Posted on
by
Brian A. Lerch, Reinhard Bürger, and Maria R. Servedio: Read the article
Lerch et al unify ecological perspectives on coexistence with evolutionary perspectives on speciation to study how diversification results from a complex interplay of both ecological and evolutionary constraints
The vast and diverse ecosystems of the world support a limited number of species, and biologists have been intrigued for years by what determines this number. Spurred on in their inquiries by the now classic manuscript, “Homage to Santa Rosalia” by G. E. Hutchinson, researchers have worked to understand the processes underlying these biodiversity patterns.
The initial ecological approaches focused on niche availability and competition as the dominant forces driving biodiversity patterns. While the rise of speciation genetics has engendered greater emphasis on microevolutionary factors involved in the creation and maintenance of biodiversity, the field has remained relatively siloed from ecological perspectives. This issue can be problematic, as the rate-limiting constraint on the number of species could be the generation of those species or their survival, depending on the circumstances. A synthesis of ecological and population genetic approaches can clarify when different kinds of constraints are important for the generation and maintenance of species.
To contribute to merging ecological and genetic viewpoints, the authors, Lerch et al., constructed a diploid, three-locus, population genetic model simulating diversification and persistence. They varied the strength of mating preferences for more similar or different genotypes, the degree to which species competed with all other species or those most similar to themselves, and the shape of the resource distribution (resulting in different amounts of niche space and fitness differences). In addition, they created a version of the model with only asexual reproduction. Comparing the outcomes of these two models allowed the authors to isolate the effects of ecological factors. More specifically, if a species arose and went extinct in the sexual model but was present at equilibrium in the asexual model, incomplete reproductive isolation (allowing hybridization) contributed to the extinction. If the species was lost from the asexual model as well as the sexual model, competitive exclusion was sufficient for extinction to occur.
This model indicates that assortative mating promotes speciation by preventing hybridization, and narrow resource distributions prevent speciation by limiting the amount of available niche space. They also demonstrated many cases in which speciation occurred, followed by species loss at equilibrium, or “ephemeral speciation.” In these cases, competitive exclusion was a much more common cause of extinction than hybrid collapse. The authors highlight that competitive exclusion can instigate species loss even after the evolution of reproductive barriers in sympatric speciation. Furthermore, Lerch et al. predict that a skewed or broad resource distribution and intense competition results in ecological limits on speciation. Genetic limits, they predict, arise from competition between similar phenotypes and weak assortative mating.
In summary, this model contributed valuable insight into the central question of “Homage to Santa Rosalia,” representing a step towards aligning disparate approaches to biodiversity research 65 years later. Future interdisciplinary ventures will further reconcile the processes investigated by Lerch et al.
Nikka Malakooti is a PhD Candidate in the labs of Marm Kilpatrick and Kristy Kroeker at UC Santa Cruz. She is researching the population dynamics of an important kelp forest grazer, including the effects of global change, predation, and disease. Outside of the lab she likes to go to concerts, rock climb, and host her friends for tea.
