Abstract. Large-scale environmental gradients have been invaluable for unraveling the processes shaping the evolution and maintenance of biodiversity. Environmental gradients provide a natural setting to test theories about species diversity and distributions within a landscape with changing biotic and abiotic interactions. Elevational gradients are particularly useful because they often encompass a large climatic range within a small geographical extent. Here, we analyzed tree communities in plots located throughout Arunachal Pradesh, a province in northeast India located on the southern face of the Eastern Himalayas, representing one of the largest elevational gradients in the world. Using indices of species and phylogenetic diversity, we described shifts in community structure across the landscape and explored the putative biotic and abiotic forces influencing species assembly. As expected, species richness and phylogenetic diversity decreased with increasing elevation; however, contrary to predictions of environmental filtering, species relatedness did not show any clear trend. Nonetheless, patterns of beta diversity (both taxonomic and phylogenetic) strongly suggest lineage filtering along the elevational gradient. Our results may be explained if filtering is driving the assembly of species from distinct evolutionary lineages. New metrics exploring community contributions to regional taxonomic and phylogenetic beta diversity provided additional evidence for the persistence of unique communities at high elevations. We suggest that these patterns may be consistent with filtering on glacial relicts, part of once more diverse clades with convergent traits suited to climates at the last glacial maximum, resulting in random or over-dispersed community assemblages at high elevations. We propose that these high-elevation sites with evolutionarily distinct species represent possible regions for conservation priority that may provide refugia for species threatened by current warming trends.
1. Phylogenetic tools have increasingly been used in community ecology to describe the evolutionary relationships among co-occurring species. In studies of succession, such tools may allow us to identify the evolutionary lineages most suited for particular stages of succession and habitat rehabilitation. However, to date, these two applications have been largely separate. Here, we suggest that information on phylogenetic community structure might help to inform community restoration strategies following major disturbance. 2. Our study examined phylogenetic patterns of succession based on a chronosequence of three abandoned subarctic mine spoil heaps (waste piles) dating from the early 1970s, mid-1970s and early 1980s. The vegetation at each mine site was compared to the surrounding vegetation, and community structure on mines was explored assuming species pools at nested spatial scales. 3. We found that the adjacent vegetation was more phylogenetically clustered than the vegetation on the mines, with mines demonstrating weaker phylogenetic community structure. Using simulation models, we showed that phylogenetic dissimilarity between mine sites did not depart from null expectations. However, we found evidence for species sorting along abiotic gradients (slope and aspect) on the mine sites that had been abandoned for the longest. 4. Synthesis and applications. Understanding the trajectory of succession is critical for restoration efforts. Our results suggest that early colonizers represent a phylogenetically random subset of species from the local species pool. Over time, there appears to be selection for particular lineages that come to be filtered across space and environment. The species most appropriate for mine site restoration might, therefore, depend on the successional stage of the community and the local species composition. For example, in later succession, it could be more beneficial to facilitate establishment of more distant relatives. Our findings can improve management practices by providing relatedness information for known successful colonizers and by informing seeding decisions with knowledge of the surrounding and regional species pools. The application of phylogenetics to restoration ecology and succession is relatively new, but it has the potential to provide novel insight into the dynamics of changing community structures during succession.
Solidago canadensis is a self-incompatible perennial species indigenous to North America that reproduces asexually via rhizomes and sexually via seeds. It is the favoured host of the gall fly, Eurosta solidaginis. Sexual reproduction leads to faster rates of adaptation in stressful environments and may be advantageous in the maintenance of host-parasite coevolution. The effect of infection by the gall fly on pollinator visitations at the patch and at the ramet level was assessed as a proxy for the ability to sexually reproduce. The study was conducted by analyzing pollinator preference at both the patch level and individual ramet level through successive observations of pollinator visitations. Though the variation in the number of pollinator visitations could be accounted for by time of day and median bloom stage, the percentage of infected ramets in a patch was not a significant explanatory variable. This suggests that gall formation does not affect pollinator preference and that the capacity to sexually reproduce is likely not reduced because of the host-parasite interaction. Broadly, this study served as an example of how pollinator preference may be utilized as a measure of fitness, and to further understand how selective pressures affect plant populations that reproduce both sexually and asexually.
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