Araneae Biodiversity in the Amazonian Foothills: An analysis of family and guild presence across habitat types

The activity of the order Araneae within ecosystems is often considered an ecological mystery. Considered top-level trophic predators, spiders act as regulators of insect populations and have influence upon the foundation of the trophic web. In the Ecuadorian Amazonian foothills, it is important to address the lack of knowledge of the biodiversity of spiders in the region. Conducting biodiversity studies across land use gradients can begin to characterize anthropogenic impacts on neotropical spider species. This study quantifies the araneae biodiversity in the transition between the Cloud and Amazon forests in Ecuador. Populations in primary forest, secondary forest, cultivated fields and cave systems were analyzed to identify the families and guilds present in the ecosystems. The biodiversity of spider families and guild type were found to diminish with increasing land use impact and the decrease of vegetation complexity. Resumen La actividad del orden Araneae entre los ecosistemas frecuentemente se considera un misterio. Considera depredadores importantes arañas son reguladores de las poblaciones de insectos y tienen influencia sobre la base de la red trófica. Por las estribaciones de la Amazonia, es importante a enfocar en la falta de información de la biodiversidad de arañas en el región. La realización de más estudios entre los gradientes del uso de la tierra puede empezar a caracterizar los impactos humanos en las arañas de los alotrópicos. Este estudio cuantificó la biodiversidad de araneae en la transición del Bosque Nublado y la Amazonian de Ecuador. Las poblaciones de bosque primario, bosque secundario, campos cultivados, y los sistemas de cuevas fueron analizados a identificar las familias y losgremios que se presenten en los ecosistemas. La biodiversidad de las familias y los gremios de arañas se encontraron a disminuir con el crecimiento del uso de tierra y con el decrecimiento de la complejidad de la vegetación. Acknowledgements The author would like to extend gratitude to Germania Estevez for advisement and guidance throughout the study, to Alex Bentley for advisement in the field and Ana Maria Ortez, Xavier Silva and Diana Serrano for aid throughout the development and completion of the study. To the staff of Sumak Kawsay in Situ and the fellow Anzu team researchers, Renee Heller, Teo Carr, and Zane Libke for their companionship, their resilience and their constant ability to inspire even in the hardest conditions. To all the representatives of SIT study abroad. Introduction Spiders represent a megadiverse order within the arthropod phylum, with 48,262 currently described species (The World Spider Catalog 20.5). Spiders pose a taxonomic challenge, as morphological variation within species is abundant and can be due to genetic deviation or geographical difference (Coddington & Levi 1991). The current number of described species is speculated to only constitute 35% of the total spider species present on earth. In comparison to other non-invertebrate groups, spiders and other arachnids represent both a lack of research and an area for new discovery (Pinzon 2010, Brooks 2004.) While research into the ecological importance of spiders is increasing, only an average of 605 new species are described each year. At this rate of description, it would take more than 150 years to develop a sufficient database on the planet’s spider biodiversity (Platnick 2013). In the neotropics, where biodiversity is notably higher than temperate regions, research into spider biodiversity is needed and presents a frontier for the discovery and description of new species. Spiders of tropical regions such as in Ecuador, present an under-explored world of ecological and physiological potential (Basset 2012.) Spider venom contains neurotoxins that are becoming important in neurobiological innovation, studies into properties of spider web for fiber research, and also in the development of less environmentally damaging insecticides (Coddington & Levi 1991). Spiders may benefit the effectiveness of pest control in agroforestry. Increased diversity of spider populations has been found to benefit the mitigation of pest impact on crops. A range of species from different guilds creates an effective network to target pests across their lifecycles. This promotes land management with less chemical impact and focuses on harnessing the natural ecosystem to promote crop productivity (Marc & Conrad 1997). In order to quantify the impact of land use, spider populations must be thoroughly surveyed. The most effective technique for spider collecting is “nocturnal hand collecting. ” This is due to higher probability of encounters in the night hours when many species are more likely to be hunting. This study focused on hand collecting as the main sampling method as advised by Rego (2009) when other methods are not available. This method was the focus of the study in order to encounter a range of spiders across guilds and vegetation types, as well as to observe each individual’s ecological interactions and behavior while in their natural environments. Night collecting sessions were a vital component of the study as spiders are often observed in higher quantity in hours of no light in the neo-tropics, with some species exclusively recorded as nocturnally active (Green 1999). This is often due to spider’s main predators being active during day light hours, and in order to hunt spiders must put themselves at risk. Building a web or ambush hunting demands high levels of energy and requires individuals to leave locations where they are safe from predators (Venner 2005). Hunting in low or no light hours decreases the risk of predation and also increases the individual’s potential for catching unsuspecting insects who may not be able to detect the spider’s presence as well at night (Rypstra 1986). Spiders are considered top level trophic predators within their habitats. Spiders fill the ecological regulator role within their ecosystems, with the capacity to dictate the composition and balance of insect populations (Martin 1982). Throughout the planet’s ecosystems, predators are distinguished as keystone components in overall health. The disproportionate lack of research into spider’s impact on ecosystem functionality draws a stark comparison to predators on larger trophic levels. While small in physical size, spiders have the capacity to act as important control agents in the balance of insect populations (Silva 1992). Spider families present a diverse range of guilds. Guilds are classified as groups of species who compete for the same resources in an ecosystem. Identifying the guilds present in an ecosystem can lead to a better understanding of the ecological impact spider communities are having on the trophic web. Classifying guilds can also develop an understand of the impact of land use in a habitat. The descriptions of spider guilds by Cardoso et al (2011) characterized spider guilds by 8 definitions: sensing web weavers, sheet web weavers, space web weavers, orb web weavers, specialists, ambush hunters, ground hunters and other hunters. The stratospheric range of a spider can help identify the taxonomy as well as the guild it belongs to (Yanoviak 2013). Spiders that rely on specific vegetation structure for web building or for hunting will be more vulnerable to changes in vegetation. Spiders who rely on camouflage for hunting may also be negatively impacted by changes in vegetation type (Thery 2002). Spiders will utilize vegetation structure to build webs, forage, or use ambush hunting. Web building spiders will elect locations of higher insect traffic, in locations where they can attract specific individuals, or locations where they can utilize surprise to entrap prey (Venner 2005). This study collected specimens across four distinct habitats. Within each habitat a 200m transect oriented around a body of water and a 200m transect in a dry region were sampled. The four ecosystems sampled were primary forest, secondary forest, cultivated fields, and subterranean caves. The first three ecosystem types were selected in order to compare the biodiversity gradient across the region with increasing anthropogenic impact. The cave transects were selected in order to observe the impacts of the ecological pressures of subterranean ecosystems on spider diversity (Mammola & Isaia 2017). The primary forest transects were considered regions unaltered by anthropogenic activity, with little to no disturbance. The first transect selected was situated in a valley and cut through the path of a stream. The second transect selected was situated along the ride of the same valley, and cut through the forest. Both transects had little to no human impact except for collecting reasons. The structure of vegetation has a significant impact on spiders. As they rely heavily on infrastructure for hunting, areas with more diverse flora will often provide the foundation for diverse spider populations (Schüpbach 2013). The secondary forest transects were defined as areas were primary forest had been cleared, but had then been abandoned and successional growth was permitted. The first transect selected was oriented close to a river along a stream tributary. The second transect cut through the forest, and crossed the dry portion of the first transects stream. Secondary forest growth is denser while less diverse than primary forests, and if found adjacent to primary forests will often present ideal conditions for spider diversity (Floren & Deeleman-Reinhold 2005). The cultivated transects were characterized as areas where primary forest had been removed to open the land for agricultural activity. The transects selected were dominated by grasses and some successional forest flora. Cultivated habitats often exhibit patchwork like regions, with the altercations of land causing fragmentation of habitats for the species present. Spiders are adaptive predators, often exhibiting resilience w