Dynamics of Reintroduced Populations of Oedipoda Caerulescens (Orthoptera, Acrididae) Over 21 Years

View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by edoc Journal of Insect Science (2017) 17(1): 10; 1–7 doi: 10.1093/jisesa/iew102 Research article Dynamics of Reintroduced Populations of Oedipoda caerulescens (Orthoptera, Acrididae) over 21 Years Bruno Baur,1,2 G. Heinrich Thommen,1,* and Armin Coray3 1Department of Environmental Sciences, Section of Conservation Biology, University of Basel, St. Johanns-Vorstadt 10, 4056 Basel, Switzerland, 2Corresponding author e-mail: [email protected], and 3Natural History Museum, Augustinergasse 2, 4001 Basel, Switzerland Subject Editor: Konrad Fiedler *deceased 28 June 2013 Received 20 September 2016; Editorial decision 20 October 2016 Abstract Conservation programs increasingly involve the reintroduction of animals which otherwise would not recolon- ize restored habitats. We assessed the long-term success of a project in which the Blue-winged grasshopper, Oedipoda caerulescens (L., 1758), was reintroduced to a nature reserve in Northwestern Switzerland, an alluvial gravel area where the species went extinct in the 1960s. In summer 1995, we released 110 individuals (50 females and 60 males) and 204 individuals (101 females and 103 males) into two restored gravel patches with sparse vegetation. We used a transect count technique to assess the population size of O. caerulescens in the years 1995–2004 and 2015–2016 and recorded the area occupied by the species. At both release sites, the populations persisted and increased signiﬁcantly in size. Individuals that followed a newly created corridor estab- lished four new subpopulations. Seven years after reintroduction, O. caerulescens had reached a high abundance around the release sites and in the four colonized patches, indicating a successful project. At the same time, the dispersal corridor became increasingly overgrown by dense vegetation. Surveys 20 and 21 yr after introduction showed that the abundance of the Blue-winged grasshopper had strongly declined in the estab- lished subpopulations and moderately in the original release sites, owing to natural succession of the habitat and lack of disturbances, which reduced the area suitable for the species by 59%. Our study shows that reintroductions are unlikely to succeed without integration of long-term habitat management (in the present case maintenance of open ground). Key words: habitat restoration, propagule size, reintroduction, succession Restoration of a site, especially in highly fragmented landscapes, populations have become locally extinct (Bajomi et al. 2010, Swan mostly benefits mobile generalist species (Samways 1994, Baur et al. 2016). Examples of successful reintroductions were reported 2014). For less mobile species, reintroductions, i.e., the intentional for Lepidoptera (Thomas 1989, Marttila et al. 1997), Orthoptera movement and release of plants and animals inside their indigenous (Pearce-Kelly et al. 1998, Sherley 1998, Hochkirch et al. 2007) and range from which they have disappeared, are an increasingly used beetles (Drag and Cizek 2015), although some projects were not suc- tool to re-establish populations in restored habitats (IUCN/SSC cessful (e.g., Wagner et al. 2005). 2013). Reintroduction projects frequently focus on keystone species In this article, we assessed the long-term success of a project in related to particular functions in the ecosystem, or alternatively, on which the Blue-winged grasshopper Oedipoda caerulescens (L., rare and/or endangered species, as well as charismatic species, which 1758) was reintroduced to a nature reserve, a locality where the spe- have public acceptance and receive financial support (Fischer and cies went extinct in the 1960s. The Blue-winged grasshopper is a Lindenmayer 2000). The approach is valuable to rescue particular xerothermophilous species living in stony and sandy habitats with species from extinction, both at the local and global scale, and to in- sparse vegetation (Detzel 1998, Straube 2013). Matching habitat crease local biodiversity (Harris and van Diggelen 2006, Thomas suitability is the crucial step in any reintroduction project. Suitable et al. 2009). habitat should meet the candidate species’ total biotic and abiotic Invertebrates constitute a substantial proportion of both the bio- needs through space and time and for all life stages (Samways mass and species richness of ecosystems and play a significant role in 2005). The importance of habitat quality for population viability ecosystem functioning (New 1995, Samways 2005). Invertebrate and patch occupancy dynamics has repeatedly been shown in diverse species become increasingly frequent reintroduction targets once the insect taxa (Baur et al. 2002, Fleishman et al. 2002, Franze´n and VC The Authors 2017. Published by Oxford University Press on behalf of Entomological Society of America. 1 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact [email protected] 2 Journal of Insect Science, 2017, Vol. 17, No. 1 Nilsson 2010, Pasinelli et al. 2013). The long-term success of a re- second half of July. The density of adults reaches a peak at the introduction can be influenced by temporal changes in both habitat beginning of August, and individuals can be found until the end of quality and the abundance of competitors and predators. In many October (Appelt and Poethke 1997). Grasses including Lolium per- cases, reintroduction success may also be affected by societal condi- enne, Dactylis glomerata, and Agropyron repens and herbs such as tions, such as local public support and socio-political considerations Rumex acetosella and Hieracium pilosella are the preferred food (IUCN/SSC 2013). (Merkel 1980). Despite recent efforts to develop the science of reintroduction biology (Seddon et al. 2007, Armstrong and Seddon 2008), there is Selection of Reintroduction Sites still no general and broadly accepted definition of reintroduction Criteria used in the choice of the two reintroduction sites were 1) success (Robert et al. 2015). Long-term viability of the introduced similarity of the habitats to that of remnant populations in terms of population is the ultimate target of any translocation action. Here, soil structure, cover and composition of vegetation, and climate; 2) population size can be used as a relevant indicator (although subject avoidance of uncontrolled disturbance; and 3) accessibility for man- to considerable uncertainty) of the viability of the reintroduced agement. Reinacherheide, a 1.7 km-long and 300-m wide nature populations and thus as a proxy for reintroduction success (Fischer reserve (47 290 5000 N; 7 360 1800 E; elevation 280 m a.s.l.) situated and Lindenmayer 2000). An important issue is also the quantifica- 10 km south of Basel, Switzerland, was chosen. In this nature reserve tion of the roles of the various intrinsic, environmental and manage- O. caerulescens went locally extinct in the 1960s. The site of the ment factors on the reintroduction success of a species. Sarrazin source population (see Source Population) and the nature reserve are (2007) proposed to split the dynamics of successful reintroductions 20 km apart separated by unsuitable habitat. Both have similar cli- into three main phases, namely establishment, growth and regula- mate, soils, and vegetation. In this region, the annual temperature tion, and to focus on the regulation phase to assess the ultimate suc- averages 10.4C and the annual precipitation is 780 mm (Meteo cess of any reintroduction action. The success criteria should, Swiss 2013). The nearest-situated recent population of O. caerules- therefore, focus on the regulation phase during which population cens is approximated 10 km apart from the reintroduction sites. dynamics critically depend on the interactions among species and habitat characteristics to draw reliable conclusions about long-term History and Preparation of Reintroduction Sites population persistence (Robert et al. 2015). Major parts of the nature reserve Reinacherheide are situated on The aim of our project was to re-establish viable populations of alluvial gravel (Eglin and Moor 1981). In the past centuries, the O. caerulescens at two sites in a nature reserve in Switzerland. The river Birs represented a natural, up to 700-m wide river system with distribution of the Blue-winged grasshopper ranges from North branches and slow-flowing meanders associated with sand and Africa (Morocco) in the south, to Denmark and Southern Sweden in gravel flats. In the section of the release sites, the Birs was trans- the north, and to Southwest Asia in the east. In Germany, O. caeru- formed into a 30-m wide channel between 1847 and 1855 (Lu¨ thi lescens is considered in the Red List as near threatened (Maas et al. 2003). As a consequence, the riverbed deepened by 3 m. The alluvial 2011), as it is in the Red List of Switzerland (Monnerat et al. 2007), gravel interspaced with patches covered by a thin layer of nutrient- and in both countries as elsewhere in Europe the species is protected poor, dry and sandy soil allowed the development of species-rich by law. The causes of its decline and local extinction include the de- plant and invertebrate communities. In the 19th century, this area struction and degradation of xerothermous

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