Abstract
Concerns regarding the long-term viability of threatened and endangered plant species are increasingly warranted given the potential impacts of climate change and habitat fragmentation on unstable and isolated populations. Orchidaceae is the largest and most diverse family of flowering plants, but it is currently facing unprecedented risks of extinction. Despite substantial conservation emphasis on rare orchids, populations continue to decline. Spiranthes parksii (Navasota ladies' tresses) is a federally and state-listed endangered terrestrial orchid endemic to central Texas. Hence, we aimed to identify potential factors influencing the distribution of the species, quantify the relative importance of each factor and determine suitable habitat for future surveys and targeted conservation efforts. We analysed several geo-referenced variables describing climatic conditions and landscape features to identify potential factors influencing the likelihood of occurrence of S. parksii using boosted regression trees. Our model classified 97 % of the cells correctly with regard to species presence and absence, and indicated that probability of existence was correlated with climatic conditions and landscape features. The most influential variables were mean annual precipitation, mean elevation, mean annual minimum temperature and mean annual maximum temperature. The most likely suitable range for S. parksii was the eastern portions of Leon and Madison Counties, the southern portion of Brazos County, a portion of northern Grimes County and along the borders between Burleson and Washington Counties. Our model can assist in the development of an integrated conservation strategy through: (i) focussing future survey and research efforts on areas with a high likelihood of occurrence, (ii) aiding in selection of areas for conservation and restoration and (iii) framing future research questions including those necessary for predicting responses to climate change. Our model could also incorporate new information on S. parksii as it becomes available to improve prediction accuracy, and our methodology could be adapted to develop distribution maps for other rare species of conservation concern.
Highlights
Conservation biologists and natural resource managers are growing increasingly concerned about the manner in which climate change and accelerating habitat fragmentation may negatively affect the long-term viability of threatened and endangered plant species (Wilcove et al 1998; Pitman and Jorgensen 2002; Brigham and Swartz 2003)
Given the conservation concerns and limited availability of survey data for this species, we developed a species distribution model to aid in effective conservation of S. parksii
A suite of climatic variables and landscape features can be used to predict the distribution of the endangered terrestrial orchid, S. parksii which is endemic to central Texas
Summary
Conservation biologists and natural resource managers are growing increasingly concerned about the manner in which climate change and accelerating habitat fragmentation may negatively affect the long-term viability of threatened and endangered plant species (Wilcove et al 1998; Pitman and Jorgensen 2002; Brigham and Swartz 2003). To successfully prevent their extirpation, conservation efforts will require detailed studies of species population biology and life-history dynamics, more thorough assessments of the factors contributing to rarity, sophisticated land management and restoration strategies and the development of more robust predictive models that better identify both high-priority conservation locations as well as areas potentially suitable for plant reintroductions They have often been used as flagship species in conservation initiatives because of their uniqueness and rarity and are often touted as important early warning bioindicators for ecosystem health given their sensitivity to environmental degradation (Cribb et al 2003; Swarts and Dixon 2009)
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