Pierre-Yves Henry, Sandrine Pavoine, Éric Guilbert, Marc Théry, Dario Zuccon, Marianne Elias, Jean-François Ponge
Species traits have been hypothesized by one of us (Ponge, 2013) to evolve in a correlated manner as species colonize stable, undisturbed habitats, shifting from “ancestral” to “derived” strategies. We predicted that generalism, r-selection, sexual monomorphism, and migration/gregariousness are the ancestral states (collectively called strategy A) and evolved correlatively toward specialism, K-selection, sexual dimorphism, and residence/territoriality as habitat stabilized (collectively called B strategy). We analyzed the correlated evolution of four syndromes, summarizing the covariation between 53 traits, respectively, involved in ecological specialization, r-K gradient, sexual selection, and dispersal/social behaviors in 81 species representative of Fringillidae, a bird family with available natural history information and that shows variability for all these traits. The ancestrality of strategy A was supported for three of the four syndromes, the ancestrality of generalism having a weaker support, except for the core group Carduelinae (69 species). It appeared that two different B-strategies evolved from the ancestral state A, both associated with highly predictable environments: one in poorly seasonal environments, called B1, with species living permanently in lowland tropics, with “slow pace of life” and weak sexual dimorphism, and one in highly seasonal environments, called B2, with species breeding out-of-the-tropics, migratory, with a “fast pace of life” and high sexual dimorphism.
Our results provide a strong support to r-selected traits, sexual monomorphism, and migratory/gregarious behavior (strategy A) as ancestral in the fringillid family (true finches). Opposite traits (strategy B), associated with predictability of the environment, should be subdivided in B1 (sexually dimorphic, r-selected, and migratory/gregarious), associated with harsh habitats (mountain and boreal habitats), mostly out of the tropics, and B2 (sexually monomorphic, K-selected, and resident/territorial), associated with most benign habitats, mostly in lowland tropics. Both habitats of B-organisms are predictable, although in B1 the high seasonality forces species to migrate seasonally (either altitudinal or latitudinal migration) while in B2 the ancestral migratory behavior has been lost, being unnecessary.