Environmental gradients and the evolution of successional habitat specialization: a test case with 14 Neotropical forest sites

Abstract

Summary Successional gradients are ubiquitous in nature, yet few studies have systematically examined the evolutionary origins of taxa that specialize at different successional stages. Here we quantify successional habitat specialization in Neotropical forest trees and evaluate its evolutionary lability along a precipitation gradient. Theoretically, successional habitat specialization should be more evolutionarily conserved in wet forests than in dry forests due to more extreme microenvironmental differentiation between early and late‐successional stages in wet forest. We applied a robust multinomial classification model to samples of primary and secondary forest trees from 14 Neotropical lowland forest sites spanning a precipitation gradient from 788 to 4000 mm annual rainfall, identifying species that are old‐growth specialists and secondary forest specialists in each site. We constructed phylogenies for the classified taxa at each site and for the entire set of classified taxa and tested whether successional habitat specialization is phylogenetically conserved. We further investigated differences in the functional traits of species specializing in secondary vs. old‐growth forest along the precipitation gradient, expecting different trait associations with secondary forest specialists in wet vs. dry forests since water availability is more limiting in dry forests and light availability more limiting in wet forests. Successional habitat specialization is non‐randomly distributed in the angiosperm phylogeny, with a tendency towards phylogenetic conservatism overall and a trend towards stronger conservatism in wet forests than in dry forests. However, the specialists come from all the major branches of the angiosperm phylogeny, and very few functional traits showed any consistent relationships with successional habitat specialization in either wet or dry forests. Synthesis. The niche conservatism evident in the habitat specialization of Neotropical trees suggests a role for radiation into different successional habitats in the evolution of species‐rich genera, though the diversity of functional traits that lead to success in different successional habitats complicates analyses at the community scale. Examining the distribution of particular lineages with respect to successional gradients may provide more insight into the role of successional habitat specialization in the evolution of species‐rich taxa.

Resilience of tropical dry forests – a meta‐analysis of changes in species diversity and composition during secondary succession

“…These rapid structural changes provide suitable micro‐environmental conditions (increased shading and decreased temperature) for the establishment of species associated with later stages of succession (Lebrija‐Trejos et al , Chazdon et al ). This is consistent with the study of Letcher et al () showing a lower rate of habitat specialisation of species in TDF than in wet forests, allowing old‐growth forest species to arrive earlier in succession. However, this result could also be an artefact of only one study being analysed for the shorter‐duration class, and it needs to be retested once a greater number of studies become available.…”

“…Derroire et al () showed evidence that facilitation is more important in drier sites. These differences all suggest more differentiation between the species composition of early and late successional communities in TDF where precipitation is higher, in line with the findings of Letcher et al () that successional habitat specialisation is stronger for tropical wet forests than TDF.…”

“…This trend can also be explained by the generalist species, able to establish throughout succession and then persist. Rozendaal and Chazdon () found that such species were abundant in successional tropical wet forests, which is also likely to be the case in TDF where the environmental gradient during succession is less strong (Letcher et al ).…”

“…During TDF succession, there is an extensive change in environmental conditions from hot and water‐limited early stages towards more shaded later stages (Lebrija‐Trejos et al ), suggesting an important role of facilitative biotic interactions (Callaway and Walker , Derroire et al ). However, the strength of the light gradient is lower in TDF than in wet forests due to smaller differences in light conditions between the early and late stages of succession (Ewel , Letcher et al ), suggesting a faster recovery of old‐growth forest species. Furthermore, difference in precipitation regimes among TDF can affect successional processes.…”

Higher survival drives the success of nitrogen‐fixing trees through succession in Costa Rican rainforests

“… Habitat classification from Letcher et al . (), based on Chazdon et al . (), which had four options: generalist, second growth (SG) specialist, old growth (OG) specialist, too rare to classify.…”