Amphibia-Reptilia 41 (2020): 337-347 brill.com/amre Niche occupancy of two (congeneric) skinks in an islands environment Emilio Civantos1,3,∗, Rosa Arribas2, Jose Martín3 Abstract. Among the scincid lizards inhabiting the Mediterranean region, the Ocellated skink (Chalcides ocellatus)andthe little-known and endangered Chafarinas’ skink (Chalcides parallelus) co-occur in sympatry at the Chafarinas Islands (NW Africa). Although both species are present in the archipelago, C. ocellatus is spread in the three islands, but C. parallelus is present only in one island. What factors influence this distribution, and whether these two species show evidence for syntopy is unknown. In this study, we investigated spatial niche occupancy at the level of microhabitat of both skinks at the Chafarinas Islands. We tested for microhabitat differences between islands and then, we tested the null hypothesis of no differences between microhabitat used by each of these skink species and a set of locations chosen at random from the general habitat. Results showed that the distribution and abundance of available microhabitats were different among islands, thus each island has different spatial niches that may be important in distinguishing the areas occupied by these skinks. Results also revealed that C. ocellatus did not use available microhabitats at random, but preferentially selected particular microhabitats. However, C. parallelus used microhabitats according to their availability, although it showed some aspects of habitat selection similar to C. ocellatus. Our results showed that the inclusion of detailed microhabitat descriptors could be useful for understanding patterns of niche occupancy by these skinks species. Furthermore, to our knowledge this is the first study documenting the spatial niche selection of C. parallelus and provides novel ecological information that may be of major importance to develop management strategies that will help to conserve this endangered species. Keywords: Chafarinas Islands, Chalcides ocellatus, Chalcides parallelus, conservation, distribution, niche partition, sympatry. Introduction geographical area (Schleich et al., 1996; Ander- son, 1999; Kalboussi and Nouira, 2004; Baha Among the 25 species of scincid lizards of the genus Chalcides inhabiting the Mediterranean Eldin, 2006; Taylor et al., 2012). The Chafari- region, two related species co-occur in sympatry nas’ or Doumergue skink (C. parallelus) is a lit- in one island at the Chafarinas archipelago (NW tle known species that was first time described Africa): Chalcides ocellatus and C. parallelus by Doumergue (1901). Mateo et al. (1995) re- (Carranza et al., 2008; Civantos et al., 2013; described and named the species as C. par- García-Roa et al., 2014; Martín et al., 2017). C. alleus from the study of individuals from the ocellatus is the most widespread species and oc- Rey Francisco island at Chafarinas archipelago curs in a broad range of habitats across a large and from the coastal areas of Morocco in front of the archipelago. This species has been found 1 - CIBIO-InBIO | Research Centre in Biodiversity & Ge- only along a narrow coastal strip of approxi- netic Resources, University of Porto, Campus de Vairão, mately 250 km between Nador in northeastern Rua Padre Armando Quintas n° 7, 4485-661 Vairão, Vila do Conde, Portugal Morocco and Cape Carbon in northwestern Al- 2 - Facultad de Ciencias, Universidad Autónoma de geria (Geniez et al., 2008). Thus, the known dis- Madrid, Ciudad Universitaria de Cantoblanco, 28049 tribution of this species is limited to a very small Madrid, Spain 3 - Departamento de Ecología Evolutiva, Museo Nacional area. In the Chafarinas archipelago (Spain), the de Ciencias Naturales (CSIC), c/ José Gutiérrez Abas- species has only been found in the Rey Fran- cal, 2, E-28006 Madrid, Spain ∗Corresponding author; cisco island (Civantos et al., 2013; García-Roa e-mail: [email protected] et al., 2014) where it is an abundant species, Downloaded from Brill.com02/25/2021 10:38:58AM via Museo Nacional de Ciencias Naturales © Koninklijke Brill NV, Leiden, 2020. DOI:10.1163/15685381-bja10002 338 E. Civantos, R. Arribas, J. Martín however it is thought to be rare along its nar- One interesting aspect of the biogeography row coastal range (Geniez et al., 2008). The is- of C. ocellatus and C. parallelus is that, al- land and mainland populations are highly re- though both species co-occur at the Chafari- lated genetically (Martín et al., 2017), probably nas archipelago, C. ocellatus is spread in the due to the flow of individuals travelling on float- three islands, but C. parallelus is present only ing items over the sea surface between the island in one island (Civantos et al., 2013; García-Roa and the coastal populations (Thiel and Gutow, et al., 2014). What factors influence this distri- 2005). The Chafarinas’ skink is considered as bution, and whether these two species show evi- Endangered by the IUCN (Geniez et al., 2008), dence for syntopy is unknown. Extended obser- and it is therefore considered to be facing a very vations (Civantos, unpubl. data) suggest that C. high risk of extinction in the wild. ocellatus and C. parallelus maybeverysimi- Islands environments are thought to be less lar in most aspect of their ecology as, for ex- complex than mainland ones, with lower num- ample, their similar diets (Çiçek and Göçmen, bers of predators and competitors and lower 2013; Civantos et al., 2013). We hypothesized that their differential distribution at Chafarinas diversity of habitats (Warren et al., 2015). archipelago could be explained by differences Thus, islands are good study areas to research in their spatial niche preferences. To minimize the mechanisms of co-existence of congeneric interspecific interactions, sympatric and closely species with similar ecological requirements related lizard species can often partition their (Schluter, 1988; Warren et al., 2015), which is niche and differentiate their microhabitat use still an ongoing area of research in ecology. (Huey and Webster, 1976; Harmon et al., 2007; When closely related species occur together, Corbalán et al., 2013). However, both skink they nearly always separate on at least one of species may also simply conserve their respec- three niches axes: food, time, or space (Pianka, tive ancestral habitat selection patterns existing 1974, 1976, 1986). In the case of lizards, species in the mainland populations (Arnold, 1987). that share the same habitat often have to ei- In this study, we investigated spatial niche se- ther differentiate their thermal or diet prefer- lection at the microhabitat level of C. ocellatus ences, or select different microhabitats (Arnold, and C. parallelus skinks at the Chafarinas Is- 1987; Scheers and Van Damme, 2002; Mur- lands. We tested for microhabitats differences ray et al., 2016). Many reptiles exploit avail- between islands and then we tested the null hy- able microhabitats according to their require- pothesis of no differences between microhabitat ments for thermoregulation (Christian et al., used by each of these skink species and a set 1983; Scheibe, 1987; Paulissen, 1988), forag- of locations chosen at random from the general ing (Paulissen, 1988), or predator avoidance habitat. We aimed to determine whether differ- (Stamps, 1983). Thus, for example, the selec- ences in microhabitat use may help to under- tive use of certain microhabitats allows many stand niche occupancy of these skinks in the reptiles to maintain body temperatures within archipelago. We also aim to provide novel eco- a range that optimizes physiological capacities logical information about the little known Cha- and ultimately ecological performance (Huey, farinas’ skink. 1991). In addition, some microhabitats may supply better refuges against predators or pro- vide more or higher-quality food (Martín and Materials and methods Salvador, 1992; Martín and López, 1998), and We conducted field work at the Chafarinas Islands (Spain). therefore, microhabitat use may influence sur- This archipelago is located in the southern-western area of the Mediterranean sea (35°1100N-2°2535W), 2.5 vival (Civantos et al., 1999; Civantos and Fors- nautical miles to the north of the Moroccan coast (Ras el man, 2000). Ma, Morocco) and 27 miles to the east of the Spanish city of Downloaded from Brill.com02/25/2021 10:38:58AM via Museo Nacional de Ciencias Naturales Microhabitat use by two sympatric skinks 339 Melilla. It consists of three islands named Congreso, Isabel area surrounding the skink (i.e., number of contacts with II (the only inhabited) and Rey Francisco. Congreso is the each substratum and vegetation type, and with vegetation westernmost, largest (25.6 ha) and the highest island (137 at each height). The sampling of multiple points to charac- meters above sea level), Isabel II (15.1 ha; 35 m. a.s.l.), terise surfaces near the skink rather than only measuring the located between Congreso (at 1 km) and Rey Francisco (at particular point at the skink location allowed a better char- 175 m) is the most oriental, smallest (13.9 ha) and lowest acterisation of the microhabitat in a skink’s home range (for (31 m. a.s.l.) island of the three. The islands present a a similar sampling methodology see (Scheibe, 1987). Given Mediterranean dry and warm climate very influenced by that we avoided walking routes taken previously, the proba- the dominant winds from east and west. The vegetation is bility of repeated sampling on the same individual was close conditioned by the aridity of the climate (average annual to null. We therefore treated all measurements as indepen- precipitation = 300 mm), the higher salinity and the guano dent. accumulation from numerous seabirds colonies (García et Availability of microhabitats in the three islands was al., 2002). The current vegetation is dominated by plants estimated along a series of random transects (3 in each adapted to the salinity and the drought such as species of island) located at least 50 m apart from each other and Atriplex, Lycium, Suaeda and Salsola bushes. In general, distributed for covering most of the vegetated surface of the the soils of the islands are little developed and immature, islands and the whole general habitat.