Abstract
Lemurs, the diverse, endemic primates of Madagascar, are thought to represent a classic example of adaptive radiation. Based on the most complete phylogeny of living and extinct lemurs yet assembled, I tested predictions of adaptive radiation theory by estimating rates of speciation, extinction and adaptive phenotypic evolution. As predicted, lemur speciation rate exceeded that of their sister clade by nearly twofold, indicating the diversification dynamics of lemurs and mainland relatives may have been decoupled. Lemur diversification rates did not decline over time, however, as predicted by adaptive radiation theory. Optimal body masses diverged among dietary and activity pattern niches as lineages diversified into unique multidimensional ecospace. Based on these results, lemurs only partially fulfil the predictions of adaptive radiation theory, with phenotypic evolution corresponding to an ‘early burst’ of adaptive differentiation. The results must be interpreted with caution, however, because over the long evolutionary history of lemurs (approx. 50 million years), the ‘early burst’ signal of adaptive radiation may have been eroded by extinction.
Highlights
The ecological limits hypothesis posits that species diversity is limited by resource availability, creating a diversity carrying capacity [1]
I assessed the impact of changes in the topology and branch lengths on the results by conducting analyses with the following alternate trees: the maximum clade credibility (MCC) tree, 100 trees randomly selected from the posterior distribution, the MCC tree with an alternative placement of the subfossil genus Megaladapis following [31], the MCC tree of extant species only, the MCC tree comprised of only taxa accepted under a more conservative taxonomy, given some skepticism in the recent increase in species richness [32], and the strepsirrhine tree based on mitochondrial genomes with extinct lemurs [31]
There was partial support for the prediction that lemur lineage diversification was higher than lorisiform rates—lemur speciation rates were twice that of lorisiforms, though a significant shift in diversification dynamics was not detected across the whole strepsirrhine tree
Summary
The ecological limits hypothesis posits that species diversity is limited by resource availability, creating a diversity carrying capacity [1]. As diversity increases and reaches the carrying capacity, speciation rates decrease and/or extinction rates increase, leading to a diversity equilibrium [1]. Diversity equilibria can change over time, as exemplified by mass extinction events and adaptive radiations [1]. Adaptive radiations perturb equilibrium dynamics by changing the carrying capacity for species able to exploit unique ecological opportunities; e.g. invading a novel habitat and diversifying owing to open niches and competitive release [2,3].
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