Intraspecific Diversity and the Evolutionary Ecology of Competitive Coexistence: Experiments with Bruchid Beetles
Abstract
Understanding the mechanisms by which competing species coexist is fundamental to explaining nature’s biodiversity. One hypothesis is that intraspecific diversity promotes species coexistence. A number of ecological and evolutionary mechanisms have been identified through which intraspecific diversity can generate stabilizing mechanisms, those that increase the negative frequency-dependence of population growth. However, intraspecific diversity, can also increase a species’ competitive ability through a number of ecological and evolutionary mechanisms, altering equalizing mechanisms and potentially destabilizing coexistence. Modern coexistence theory provides a framework for understanding how these two suites of mechanisms interact: decreases in equalizing mechanisms must be compensated for by increases in stabilizing mechanisms to maintain the stability of coexistence.
In this thesis, I explore how intraspecific diversity affects stabilizing and equalizing mechanisms using a classic subject of competition and coevolution studies, bruchid beetles (Callosobruchus spp.). I explored the ecological consequences of intraspecific diversity for coexistence by assaying the coexistence (mutual invasibility) of populations of two competing species (Callosobruchus maculatus and C. chinensis) when each comprised one, three, or five genetically- and phenotypically-distinct lineages. Populations composed of five lineages were then experimentally evolved in sympatry or allopatry to explore the evolutionary consequences of intraspecific diversity. Through periodic assays of life-history traits I tested for ecological character displacement. After assaying each population’s phenotype, I assayed population-pairs for mutual-invasibility to explore how adaptive evolution alters species coexistence.
In both the short- and long-term, intraspecific diversity often inhibited coexistence, rather than promoting it. Intraspecific diversity promoted both ecological and evolutionary stabilizing mechanisms, but often had a negative effect on equalizing mechanisms. Intraspecific diversity increased species’ competitive abilities through a combination of ecological (e.g., niche complementarity) and evolutionary (e.g., selection effects) mechanisms. Similar increases in competitive ability by coexisting species maintained fitness equality and strengthened coexistence, due to a strengthening of stabilizing mechanisms, as predicted. However, species often experienced different gains in competitive ability, destabilizing coexistence. I review the mechanisms by which intraspecific diversity alters equalizing mechanisms and identify a need to better understand how these mechanisms interact.
Description
Keywords
Ecology
Citation
Hausch, S. (2015). Intraspecific Diversity and the Evolutionary Ecology of Competitive Coexistence: Experiments with Bruchid Beetles (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/26625