53 Revista Ibérica de Aracnología, nº 30 (30/06/2017): 53–60. ARTÍCULO Grupo Ibérico de Aracnología (S.E.A.). ISSN: 1576 - 9518. http://www.sea-entomologia.org ABUNDANCE AND RICHNESS OF ORB-WEB SPIDERS (ARACHNIDA: ARANEAE) IN A SECONDARY HIGH-ANDEAN FOREST OF COLOMBIA German Antonio Villanueva-Bonilla 1 , Alexander García García 2 , Antonio Domingos Brescovit 3 & João Vasconcellos-Neto 4 1 Departamento de Biologia Animal, Instituto de Biologia. Universidade Estadual de Campinas, Campinas, São Paulo, Brazil. — germanvillanueva9@gmail.com 2 Universidad Distrital Francisco José de Caldas, Bogotá, Colombia. 3 Laboratório Especial de Coleções Zoológicas, Instituto Butantan, São Paulo, SP, Brazil. 4 Departamento de Biologia Animal, Instituto de Biologia. Universidade Estadual de Campinas, Campinas, São Paulo, Brazil. Abstract: We compared the species richness and abundance of orb-web spiders in a secondary high-Andean forest in Colombia in the dry and wet seasons at two altitudes (3100 and 3300 m a.s.l.). We identified six species, four belonging to Araneidae and two to Tetragnathidae. The abundance of Araneidae and Tetragnathidae decreased with increasing altitude, which was mainly due to the harsh climatic conditions (e.g. low temperature) which are in fact a limiting factor in the establishment and survival of spiders. Yet, the orb-web spider community appeared to be adapted to major variation in precipitation between the dry and wet season, with no significant change in spider abundance between these two periods. Apparently, disturbed forest, along with the high altitude, would explain the low number of spider species recorded in this study and high dominance observed of the genus Chrysometa (Tetragna- thidae). Key words: Araneae, Araneidae, Tetragnathidae, Chrysometa, biodiversity, high altitude ecosystems, Andes, Colombia. Abundancia y riqueza de arañas orbiculares (Arachnida: Araneae) en un bosque alto andino secundario de Colombia Resumen: Se comparó la riqueza de especies y abundancia de arañas orbiculares entre las estaciones seca y húmeda a dos alti- tudes (3100 y 3300 m.s.n.m.) en un bosque secundario alto andino en Colombia. Se identificaron seis especies, cuatro de Aranei- dae y dos de Tetragnathidae. La abundancia de Araneidae y Tetragnathidae disminuyó con el aumento de altitud, posiblemente debido a las duras condiciones climáticas (por ejemplo, baja temperatura), que son de hecho un factor limitante en el estableci- miento y la supervivencia de las arañas. Sin embargo, la comunidad orbicular pareció adaptada a la variación en la precipitación entre la estación seca y húmeda, pues no se registró ningún cambio significativo en la abundancia de araña entre estos dos perío- dos. Aparentemente, un bosque perturbado, junto con la gran altitud, explicaría el bajo número de especies de arañas registrado en este estudio y alta dominancia observada del género Chrysometa (Tetragnathidae). Palabras clave: Araneae, Araneidae, Tetragnathidae, Chrysometa, biodiversidad, ecosistemas de elevada altitud, Andes, Colom- bia.     Introduction In spiders, a decrease in diversity and abundance with in- creasing altitude has been reported, although more complex patterns such as humpback relationships between species richness and altitude have also been found (Otto & Svensson, 1982; Greenstone, 1984; Olson, 1994; Chatzaki et al., 2005; Lee et al., 2012; Foord & Dippenaar-Schoeman, 2016). In high altitude environments, abiotic factors are the principal components affecting the abundance and distribution of biota (Chatzaki et al., 2005; Almeida-Neto et al., 2006). Two main abiotic factors have been suggested to cause these patterns: climatic conditions and habitat heterogeneity. McCoy (1990) proposed that “ends are bad” to explain the low diversity on different groups of invertebrates (e.g. ants, spiders, parasi- toids) in high altitude environments. According to McCoy (1990), the climatic severity and resource scarcity are the principal factors affecting the distribution of various groups of invertebrates. Probably, harsh conditions (e.g. low tempera- ture) is the limiting factor that can explain the distribution of spiders at high altitude environments (Chatzaki et al., 2005; Lee et al., 2012; Foord & Dippenaar-Schoeman, 2016) The decrease in habitat heterogeneity is another abiotic factor that affects spider richness and abundance (Greenstone, 1984; Riechert & Gillespie, 1986; Wise, 1993; Gunnarsson, 1996). The hypothesis of habitat heterogeneity mentions that the more complex the habitat, the more niches are available and, therefore, the greater the species richness (Tews et al., 2004). Habitat structure and, more specifically, vegetation complexity, has been frequently recognized as one of the most important factors in determining the presence of spider species, as well as their richness and composition (Uetz, 1991; Wise, 1993). Therefore, vegetation type may be an important factor in determining spider associations due to their relationship to vegetation structure (Greenstone, 1984; Urones & Puerto, 1988). Then changes in habitat (e.g. forest fragmentation or loss, deforestation) can greatly affect the composition of the spider community because the local vege- tation complexity decreases affecting the availability and variety of insect populations which affects spider community (Denno et al., 2005; Prieto-Benítez & Méndez, 2011). Spiders are usually classified based on hunting strate- gies and predatory habits, such behaviors range from active search and ambushing prey ("sit and wait") to the use of vari- ous types of traps (e.g. orb-webs) (Uetz, 1977; Foelix, 2011; Elias et al., 2011; Cardoso et al., 2011). Orb web spiders are one of the most diverse and abundant guilds, representing from 15% to over 50% of total richness and abundance in tropical (Basset, 1991; Silva & Coddington, 1996; Brescovit et al., 2004; Villadiego et al., 2013) and subtropical forest environments (Avalos et al., 2009). In Colombia, patterns of species richness and abundance in orb-web spiders have been