Creation of an Ecological Corridor in Southwestern Ecuador
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Restoring connectivity in a fragmented landscape: Creation of an ecological corridor in southwestern Ecuador Thesis submitted in partial fulfillment of the requirements of the degree Dr. rer. nat. of the Faculty of Environment and Natural Resources, Albert-Ludwigs-Universität Freiburg by Claudia Stefanie Hermes Freiburg im Breisgau, Germany 2017 Dean: Prof. Dr. Tim Freytag Supervisor: Prof. Dr. Gernot Segelbacher 2nd Supervisor: Dr. H. Martin Schaefer 2nd Reviewer: Prof. Dr. Jürgen Bauhus June 2017 Date of Thesis’ Defense: Contents 1 Introduction 1 2 Thesis Structure 7 3 Habitat requirements and population estimate of the endangered Ecuadorian Tapaculo Scytalopus robbinsi 9 4 Effects of forest fragmentation on the morphological and genetic structure of a dispersal-limited, endangered bird species 31 5 Projected impacts of climate change on habitat availability for an endangered parakeet 51 6 A framework for prioritizing areas for conservation on tropical mountains 69 7 The ecological corridor Pagua - Cerro Azul - Buenaventura Puyango 89 8 Synthesis – 101 9 Summary 107 10 Zusammenfassung 111 11 Acknowledgements 115 12 Bibliography 117 13 List of Figures 135 14 List of Tables 139 Chapter 1 Introduction TROPICAL FORESTS IN A CHANGING WORLD Global biodiversity is declining at an unprecedented rate (Pimm et al. 1995). Anthropogenic land-use change is causing a severe loss in habitat, accompanied by a drastic increase of the extinction rates of animal and plant species (Sala et al. 2000, Butchart et al. 2010, Pereira et al. 2010). Likewise, anthropogenic climate change puts global biodiversity under serious strain, as global warming can alter species distribution ranges and reduce habitat availability, thus aggravating the extinction risk for several species (Thomas et al. 2004, Malcolm et al. 2006). Among the areas most prone to biodiversity loss are the so- global biodiversity hotspots (Mittermeier et al. 1998, Myers et al. 2000). Biodiversity hotspots are areas called where an extraordinarily high concentration of endemic species is threatened by an extraordinarily high loss of habitat (Myers et al. 2000). To date, 34 biodiversity hotspots have been identified worldwide, mostly located in tropical regions. Each of these hotspots harbors more than 1500 endemic plant species, while at least 70 % of the original habitat within each hotspot is already lost (Brooks et al. 2002). The most imminent threat to pristine habitat in the tropical hotspots is deforestation and land- use change. Between 1990 and 1995, tropical biodiversity hotspots have lost on average 1.6 % of their forested area annually (Brooks et al. 2002). Throughout the tropical hotspots, pristine forests are converted into cropland or cattle pasture. Due to the severe loss and degradation of forests in the tropics, the formerly continuous cover of primary forest has given way to a heterogeneous landscape of scattered forest fragments in various successional stages, separated by large areas of open land. Under current deforestation rates, the clearance of tropical forests is 1 Chapter 1 - Introduction expected to drive 15 % of forest-dependent species to extinction (Pimm and Raven 2000, Brook et al. 2008). Forest fragmentation aggravates the extinction risk of species though habitat loss, as it isolates populations from each other with increasing disconnection between forest patches (Kareiva and Wennergren 1995). Isolation between forest fragments largely reduces migration and gene flow between populations (Coulon et al. 2006), which can lower the genetic diversity within a population and make it vulnerable to environmental and demographic stochasticity as well as to inbreeding effects, such as reductions in fitness and disease resistance (Ellstrand and Elam 1993, Keller and Waller 2002, Dixo et al. 2009). Furthermore, lower genetic diversity may also lead to reduced evolutionary responses on the long- term, as the potential of a population to adapt to future environmental changes is restricted (Keller and Waller 2002, Beissinger et al. 2008). Thus, a decrease in genetic diversity caused by declines in population size and migration rates can severely threaten the survival of populations. In the cloud forests on tropical mountains, the aforementioned negative impacts of habitat loss and fragmentation are worsened by climate change. The biodiversity of these forests heavily depends on a humid, cool environment created by frequent immersion in the cloud bank (Foster 2001). With ongoing climate change, the lower zones are becoming increasingly dry and hot, shifting the level of cloud formation to higher elevations (Still et al. 1999). Following the cloud bank, the species also shift their distribution ranges uphill (Pounds et al. 1999, Chen et al. 2001, Raxworthy et al. 2008, Feeley et al. 2011). As many cloud forest species occur in very narrow ranges or close to mountain tops (Foster 2001), the upslope displacement of their ranges can be accompanied by severe reductions in range size and thus an increased extinction risk (Rull and Vegas-Vilarrúbia 2006, Raxworthy et al. 2008). Moreover, an upslope shift of distribution ranges can disrupt connectivity among populations confined to different mountains. Taken together, the effects of forest loss and climate change CONSERVATION OF TROPICAL BIODIVERSITY Habitat loss due to deforestation, forest degradation and fragmentation can be counteracted by sound conservation actions, e.g. the reforestation of open land and the improvement of forest quality. However, conservation measures on tropical mountains should not merely alleviate forest loss, but also account for climate change impacts in order to provide habitat and connectivity for cloud forest species in the long-term. Consequently, a major aspect in biodiversity management is the protection 2 Chapter 1 - Introduction of remaining habitat and the restoration of connectivity between populations (Hess and Fischer 2001, Chetkiewicz et al. 2006). A priority approach for the conservation of biodiversity is the establishment of dispersal corridors. Dispersal corridors can mitigate the negative effects of habitat loss on the genetic diversity and population size by enhancing migration and dispersal among populations (Caro et al. 2009). In general, a corridor, or linkage, can among populations in disconnected habitat patches, or ction by fulfill a conduit function by enabling or facilitating the movement and gene flow providing habitat and facilitating dispersal (Lindenmayer and Nix 1993, Hess and a habitat fun Fischer 2001). In fragmented tropical forests, linear forest remnants or riparian corridors, i.e. forested corridors close to watercourses, up to 500 m wide can provide habitat for small mammals, understory birds and amphibians (Laurance and Laurance 1999, Lima and Gascon 1999, Gillies and St Clair 2008), while enabling dispersal for larger mammals like jaguars (Rabinowitz and Zeller 2010). Live fences, i.e. tree rows demarking pasture edges, or scattered trees on pastures serving as stepping stones, highly enhance dispersal of canopy birds and bats (Gillies and St Clair 2008, Fischer et al. 2010), but do not necessarily provide habitat. Therefore, which of the two functions is mainly fulfilled largely depends on the design of the corridor. A large number of studies have already proven the positive effects of ecological corridors in conservation practice (e.g. Beier and Noss 1998, Levey et al. 2005; Damschen et al. 2006, Lees and Peres 2008). Corridors can provide a variety of benefits to biodiversity. The restoration of connectivity between habitat patches prevents the declines of genetic diversity and population size, as immigration and gene flow from other patches are possible. Moreover, the total area and diversity of habitats increase with connection to other patches (Caro et al. 2009). Likewise, corridors can allow the colonization of new habitat. In tropical montane cloud forests, where climate change is driving species uphill, this feature takes on an important position. A corridor designed to account for climate change impacts should therefore facilitate migration upslope in order to enable evasion into higher elevations. THE BIODIVERISITY HOTSPOT TUMBES-CHOCÓ-MAGDALENA A biodiversity hotspot in need for urgent conservation measures is the Tumbes- Chocó-Magdalena hotspot on the western flanks of the Andes. This hotspot covers an area of more than 250,000 km² from Panama and Colombia to Ecuador and northern Peru, and harbors a high diversity of ecosystems, including tropical dry forests, wet 3 Chapter 1 - Introduction and humid forests, and mangroves. This variety of ecosystems makes the Tumbes- Chocó-Magdalena hotspot one of the most species-rich areas on Earth, with over 2500 plant and 400 vertebrate endemic species (Myers et al. 2000). The extraordinary biodiversity of the Tumbes-Chocó-Magdalena hotspot, however, is heavily threatened by deforestation and climate change. Projections suggest that the hotspot will lose over 90 % of its original habitat until the year 2100 (Jantz et al. 2015), which ranks the Tumbes-Chocó-Magdalena area among the hotspots most prone to species extinction in the near future. CREATION OF AN ECOLOGICAL CORRIDOR IN SOUTHWESTERN ECUADOR In the premontane cloud forests on the foothills of the Andes in the El Oro province of southwestern Ecuador, the two main ecoregions of the Tumbes-Chocó-Magdalena hotspot, the dry Tumbesian forests of northern Peru and the wet Chocó forests of Colombia and Ecuador, are intermingling. The resulting