Possible Combined Effects of Climate Change, Deforestation, and Harvesting on the Epiphyte Catopsis Compacta:A Multidisciplinary Approach Rafael F
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Possible combined effects of climate change, deforestation, and harvesting on the epiphyte Catopsis compacta:a multidisciplinary approach Rafael F. del Castillo1, Sonia Trujillo-Argueta1, Raul Rivera-Garcıa1, Zaneli Gomez-Ocampo 2 & Demetria Mondragon-Chaparro 1 1Instituto Politecnico Nacional, CIIDIR Oaxaca, Hornos 1003, Santa Cruz Xoxocotlan, Oaxaca 71239, Mexico 2Yale University, Yale Peabody Museum of Natural History, 170 Whitney Avenue, New Haven, Connecticut 06520 Keywords Abstract Altitudinal gradient, demography, edge effects, fragmentation, genetic diversity, Climate change, habitat loss, and harvesting are potential drivers of species harvesting, nontimber forest products, extinction. These factors are unlikely to act on isolation, but their combined plant cover dynamics. effects are poorly understood. We explored these effects in Catopsis compacta, an epiphytic bromeliad commercially harvested in Oaxaca, Mexico. We ana- Correspondence lyzed local climate change projections, the dynamics of the vegetation patches, Rafael F. del Castillo, Instituto Politecnico the distribution of Catopsis in the patches, together with population genetics Nacional, CIIDIR Oaxaca, Hornos 1003, Santa and demographic information. A drying and warming climate trend projected Cruz Xoxocotlan, Oaxaca 71239, Mexico. Tel: +52 (951) 5170610; by most climate change models may contribute to explain the poor forest Fax: +52 (951)5170400, ext. 82700; regeneration. Catopsis shows a positive mean stochastic population growth. A E-mail: [email protected] PVA reveals that quasi-extinction probabilities are not significantly affected by the current levels of harvesting or by a high drop in the frequency of wet years Funding information (2%) but increase sharply when harvesting intensity duplicates. Genetic analyses The authors thank Instituto Politecnico show a high population genetic diversity, and no evidences of population sub- Nacional, The European Commission division or a past bottleneck. Colonization mostly takes place on hosts at the (REFORLAN FP6-2004-INCO-DEV-3 032132) and FOSEMARNAT-2004-01-244 for funding. edges of the fragments. Over the last 27 years, the vegetation cover has being À À lost at a 0.028 years 1 rate, but fragment perimeter has increased 0.076 years 1. Received: 27 June 2013; Revised: 13 August The increases in fragment perimeter and vegetation openness, likely caused by 2013; Accepted: 14 August 2013 climate change and logging, appear to increase the habitat of Catopsis, enhance gene flow, and maintain a growing and highly genetically diverse population, in Ecology and Evolution 2013; 3(11): 3935– spite of harvesting. Our study evidences conflicting requirements between the 3946 epiphytes and their hosts and antagonistic effects of climate change and frag- doi: 10.1002/ece3.765 mentation with harvesting on a species that can exploit open spaces in the for- est. A full understanding of the consequences of potential threatening factors on species persistence or extinction requires the inspection of the interactions of these factors among each other and their effects on both the focus species and the species on which this species depends. Introduction species response to the combined effects of such factors is unlikely. For instance, habitat degradation and climate Climate change, land-use change, and harvesting are driv- change are likely to decrease habitat specialists and benefit ers of species extinction of global importance (Foley et al. some mobile and generalist species of British butterflies 2005; Beever and Belant 2012). Therefore, understanding (Warren et al. 2001). For exploited species, harvesting the effects of these factors is essential for the design of effects adds a further complication, which combined conservation, sustainable management, and restoration effects with other potential drivers of species extinction plans. In many cases, these factors act simultaneously on are yet to be explored. the species, but their combined effects need to be investi- Epiphytes comprise 10% of all vascular plants, and gated. The little evidence available reveals that a common some epiphyte species are among the most vulnerable ª 2013 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd. 3935 This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. Combined Anthropogenic Effects on an Epiphyte R. F. del Castillo et al. organisms to climate change, harvesting, and disturbance useful for assessing the effects of anthropogenic factors on (Benzing 1998; Ozanne et al. 2003). Climate change may populations. Harvesting, for instance, is one source of affect epiphytes directly and indirectly. As some of these mortality, which affects the population vital rates and plants obtain nutrients and water from the atmosphere, may increase the extinction risks in epiphytes (Mon- changes in climate, in particular in temperature and dragon 2009; Mondragon and Ticktin 2011). Finally, the humidity, affect their water and nutrient supplies (Obreg- consideration of the epiphyte ecosystems and its dynamics ona et al. 2011). Climate change affects epiphytes indi- may help to interpret the observed population character- rectly by affecting the host plants on which they live (Hsu istics of epiphytes in ecosystems affected by anthropo- et al. 2012). Global warming, for instance, is expected to genic activities. Forest dynamics, in particular, is expected promote uphill displacements and range contractions of to play a crucial role in epiphyte abundance as shown in populations inhabiting mountain ranges (Wilson and simulation models (e.g., Hsu et al. 2012). Vegetation Gutierrez 2012). Such changes may benefit the epiphytes dynamics usually alter the distribution of epiphytes’ at certain altitudes and harm at others. The hosts are microhabitats (Zartman 2003). likely to be affected as well, although not necessarily with Despite their importance, comprehensive studies on the same effects observed in the epiphytes. epiphytes that include population genetics, demography, Land-use change usually reduces the abundance of host and the dynamics of the specific portions of the landscape trees and, consequently, is expected to decrease the abun- at which the studied population dwells are lacking. As dance and diversity of epiphytes. Disturbances associated part of a long-term project aiming at fomenting the con- with land-use change frequently result in higher solar servation of native forests and their species in southern radiation, temperature and wind velocity, and lower Mexico, we conducted a multidisciplinary study on Catop- humidity compared with the original conditions, resulting sis compacta in Santa Catarina Ixtepeji, Oaxaca. Deforesta- in a gradual substitution of mesic epiphytes by more tion is significant, and the current climatic conditions xerophytic epiphytes (Cascante-Marın et al. 2006). appear to be displaced to higher altitudes. Furthermore, Epiphyte harvesting is very common in certain geographi- this epiphyte is subjected to extraction. Because of cal regions (Flores-Palacios and Valencia Dıaz 2007), but harvesting, habitat fragmentation, and climate change, we its consequences are poorly known. Harvesting may expect a declining and subdivided population of Catopsis endanger some populations (Borba et al. 2007). However, in Santa Catarina with low genetic diversity, inbreeding, harvesting effects may depend on human culture and and declining population size. Our objectives were as taxonomic groups and may allow a higher degree of follows: (1) to assess the status of the population through biodiversity conservation, compared with other land-use demographic and population genetic analyses; (2) to iden- alternatives, such as the conversion of forest to pastures tify the patterns of distribution of C. compacta within the (Ruiz-Perez 1997). forest fragments; and (3) to assess the patterns of defores- Assessing the mechanisms underlying the impacts of tation in the vegetation that host C. compacta using satel- human activities on epiphytes such as harvesting requires lite images and GIS, and use this information to explain the inclusion of multiple ecological levels ranging from the demographic and genetic results obtained in (1). genes to ecosystems (Ticktin 2004). Population genetic studies are useful to detect the genetic diversity of popu- Materials and Methods lations. Theory predicts that the capability of populations to respond to environmental changes depends on their The study system genetic diversity. This appears to be the case for climate change in aquatic plant species (Ehlers and Reusch 2008), Catopsis compacta (Schult. & Schult. F.) Mez. is a herba- and for fragmentation in tropical tree species (del Castillo ceous epiphytic bromeliad from southern Mexico (Fig. 1). et al. 2011). Human activities have yielded conflicting The leaves are compactly arranged in a tubular, 30–60 cm results in epiphyte genetic diversity. Harvesting has been tall, upright rosette. A white wax covers the leaves and associated with decreases in genetic diversity (Cruse-Sand- makes them shine when hit by the light. The flowers are ers and Hamrick 2004), but some epiphytes maintain bee-pollinated, and arranged in panicles with green-yel- considerable levels of genetic diversity in fragmented lowish or yellow sepals and white petals. The species is habitats (Avila Diaz and Oyama 2007). In addition to dioecious,