Natural selection and the structure, dynamics, and diversification of mutualistic assemblages

Author(s)

Rafael Luís Galdini Raimundo

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB)
• Defense date: 2015-04-16

Examining board members

Paulo Roberto Guimaraes Junior; Marcus Aloizio Martinez de Aguiar; Mario Almeida Neto; Márcio Silva Araújo; Rodrigo Cogni

• Advisor: Paulo Roberto Guimaraes Junior

Abstract

Adaptation and diversification in species-rich systems are increasingly recognized as relevant processes to improve our understanding on biodiversity. Our aim was to investigate how natural selection related to ecological interactions shapes the structure, dynamics and diversification of mutualistic assemblages. First, we modeled how mutualism and intraspecific competition generate antagonistic selective regimes that define patterns of diversification. Ours models predict that in low intimacy mutualisms, in which each organism has various individual partners, extreme phenotypes experience trait mismatches in mutualistic interactions that oppose the diversifying effects of intraspecific competition and constrain speciation. In high intimacy systems, in which mutualistic interactions have a higher impact on fitness and each organism has fewer partners, such stabilizing selection is reduced, favoring diversification. However, low intimacy mutualisms are richer than high intimacy mutualisms in nature. Under low interaction intimacy, additions of non-related species involved in trait convergence dynamics are a plausible explanation for such a discrepancy. In high intimacy systems, restrictions to species additions imposed by tight coevolutionary histories could explain lower richnesses despite of a higher potential for adaptive diversification. In a subsequent study, we evaluated whether the adaptive rewiring of ecological interactions explain the structural variation of mutualistic networks. Using an eco-evolutionary model, we show that selection favoring continuous interaction switching that maximizes species abundances changes network properties, increasing nestedness and decreasing stability. Our models overestimated nestedness in high intimacy mutualisms, probably because we did not consider forbidden links imposed by morphology or phenology. However, simulated networks reproduce nestedness and modularity of low intimacy mutualism, in which interactions are more flexible. Under competition for mutualists, rewires continue in an endless dynamics, even when the structure and stability reach asymptotic levels at the network level, which could explain the empirical variation of interactions in networks showing temporally constant structures. In a third study, we modeled effects of different modes of speciation on mutualistic network properties. If speciation results in niche width expansion and emerging species become more connected, nestedness increases and modularity decreases, often resulting in unstable networks. If speciation causes niche width retractions and emerging species become less connected, both nestedness and modularity increase, promoting stability. Different rules of niche overlap between emerging rules did not change these results. Therefore, niche retractions via adaptive divergence, such as character displacement in sympatric speciation, can generate species that will enter local networks without destabilizing them. However, niche width expansions due to adaptation to additional resources in allopatry should destabilize networks if secondary contact between emerging species occur. High magnitude potential effects of a single speciation event show that studies relating diversification and dynamics are relevant to the debate on complexity and stability of ecological networks. We concluded that the mechanistic understanding of biodiversity origins and maintenance relies on the integration between ecological and evolutionary theories based on empirical data, as wed did here by modeling the adaptive dynamics of ecological interactions using information on the structure and natural history of mutualistic assemblages (AU)

• FAPESP's process: 11/13054-6 - Natural selection and the structure, dynamics, and diversification of mutualistic assemblages
• Grantee: Rafael Luís Galdini Raimundo
• Support Opportunities: Scholarships in Brazil - Doctorate