Refined Approaches to Improving Efforts to Conserve Plant Biodiversity

Most mega-biodiverse countries have low to upper middle incomes (Fisher and Christopher 2007), resulting in a shortage of funding and expertise to implement conservation actions in these biodiversity hotspots. Creating conservation guidelines can help developing countries comply with international conventions and, in some cases, result in poverty reduction by ensuring the protection of natural resources (Fisher and Christopher 2007). Distinguishing species that require immediate conservation actions to prevent extinction of species that are rare but demographically stable can help make conservation decisions when resources are scarce. To date, only 5% of all species known to science have been evaluated for risk of extinction (IUCN 2016), and of those listed as critically endangered, endangered, or vulnerable, a greater proportion are plant species than animal species (IUCN 2016). Generating data to evaluate extinction risk based on data on population dynamics for all species under these categories would take too much time, and decisions must often be made quickly. However, there are databases that contain demographic and functional trait data for hundreds of species of plants, that can, in principle, be used to identify traits that characterize species that are demographically stable and distinguish them from species in danger of imminent extinction. Yenni et al. (2012) proposed that strong self-limitation would enable some rare species to persist at low abundance (Yenni et al. 2012). Focusing on low abundance and its natural causes could help identify key characteristics that would help direct conservation efforts to the species at greatest risk of extinction. I conducted intraspecific competition experiments in the field for related pairs of common and low abundance but persisting herbaceous plant species in the understory of longleaf pine savannas to test the hypothesis that low abundance persisting taxa experience stronger self-limitation. I found that low abundance species were taller and experienced less herbivory damage than their respective closely related common species. However, I did not find evidence of stronger self-limitation in low abundance species compared to closely related common species. To further examine the hypothesis that some low abundance species can persist naturally at low abundance due to strong self-limitation, I took advantage of global databases of demographic and trait data. I used information from these databases to designate 336 herbaceous plant species as common or low abundance. For species with trait data, I classified them as either demographically stable or increasing (50 common, 17 low abundance) or declining (31 common, 11 low abundance). I compared trait values for these groups focusing on those expected to be related to competitive ability. I was expecting traits associated with strong competitive ability could provide a tool to identify rare taxa that are at lower risk of extinction. I found that low abundance species regardless of their population growth rates had trait values consistent with greater competitive ability when compared to common species. However, I was unable to identify any trait that could distinguish low abundance herbaceous plant for which stable or increasing population growth rates were measured. In the face of projected human population growth, an alternative approach for preserving biodiversity is to preserve entire communities that encompass substantial biodiversity rather than assessing individual species. For this approach, there are different ways to assess biodiversity, one of them is to measure phylogenetic diversity, these measures can determine which areas will maximize future options for diversification. I examined the effects of human activities on phylogenetic diversity and structure in the longleaf pine savannas. I found that even after 100 years of continuous restoration efforts after plowing, phylogenetic diversity does not recover to the overall evolutionary history of undisturbed plant communities. Species that did not return after anthropogenic disturbance were not a random subset of species. One explanation for this clustering is that abiotic filtering influences recovery after disturbance. Although I did not find a successful way to distinguish species at higher risk of extinction from those that are not, I wouldn't discourage the approaches I used because species representation was small for the field experiments, and the overlap of species for which both demographic and trait data were available was limited. Natural history information in species descriptions was brief and sometimes non-existent in many demographic papers, which limits the power to identify plant traits that are associated with risk of extinction. There is potential for more synthetic approaches to help conservation decision making, however those efforts would be more successful after we address this data deficit. An initial step towards resolving this data gap would be to prioritize the collection of trait data for species for which demographic data already exist.