Ecological Limits on Diversification of the Himalayan Core Corvoidea

Abstract

Within regions, differences in the number of species among clades must be explained by clade age, net diversification rate, or immigration. We examine these alternatives by assessing historical causes of the low diversity of a bird parvorder in the Himalayas (the core Corvoidea, 57 species present), relative to its more species rich sister clade (the Passerida, ∼400 species present), which together comprise the oscine passerines within this region. The core Corvoidea contain ecologically diverse species spanning a large range of body sizes and elevations. Despite this diversity, on the basis of ecological, morphological, and phylogenetic information, we infer that the best explanation for the low number of species within the Himalayan core Corvoidea is one in which ecology limits diversification and/or immigration. Within the core Corvoidea, body size is correlated with elevation: large species are found at high elevations, and small species at lower elevations. This contrasts with the presence of many small‐bodied species spanning all elevations in the Passerida and many large bodied species at low elevations in the other orders of birds (the nonpasserines). Cladogenetic events leading to ecological differences between species in body size and shape mostly occurred millions of years ago, and the rate of evolutionary change has declined toward the present. Elevational distributions have been evolutionarily more labile, but are also associated with ancient cladogenetic events. We suggest the core Corvoidea occupy a restricted volume of ecological space in competition with other bird species, and this has limited in situ diversification and/or immigration.

A genome-wide assessment of stages of elevational parapatry in Bornean passerine birds reveals no introgression: implications for processes and patterns of speciation

“…In the context of the proposed tempo and mode of diversification, the marginal morphological differentiation is not that unusual. Other studies have shown that elevational differences between recently diverged species generally evolve before differences in body size or feeding ecology (Kennedy et al, 2012; Price et al, 2014; Richman & Price, 1992). More broadly, these results indicate that any species concept that attempts to predict interbreeding potential simply on the basis of perceived morphological differences (Tobias et al, 2010) likely underestimates species diversity.…”

The phylogenetic relationships of Przevalski's FinchUrocynchramus pylzowi, the most ancient Tibetan endemic passerine known to date

“…from the Hemphillian (Steadman , Steadman & McKitrick , Kennedy et al . , node: Cyanocompsa and Passerina ), (iii) a fossil tentatively identified as Parulidae from the early Miocene (Kennedy et al . , Mayr , node: Parulidae, Icteridae, Emberizidae and Passerellidae), and (iv) the earliest fossil representing the crown group Passeriformes for time to most recent common ancestor (tmrca) of the root separating Acanthisitta from other passerines (Mayr , the normal prior interval was defined using the separation of New Zealand from Australia as a soft minimum; see Kennedy et al .…”

Evolutionary history of passerine birds (Aves: Passeriformes) from the Qinghai–Tibetan plateau: from a pre-Quarternary perspective to an integrative biodiversity assessment

“…Recent ecological community analyses of Himalayan passerines have shed some light on adaptive processes and niche evolution. Differences among species in body size and shape as well as in foraging and feeding strategies had apparently already evolved in the early stages of SE Asian passerine radiations long before ancestors of extant species occupied their elevational niches in the respective Sino-Himalayan vegetation belts (Price 2010;Kennedy et al 2012;Price et al 2014). …”