Philippine Journal of Science 150 (S1): 563-575, Special Issue on Biodiversity ISSN 0031 - 7683 Date Received: 30 Sep 2020 Collembola (Arthropoda: Hexapoda) Assemblages in the Canopy and Forest Floor along an Elevational Gradient at Mt. Makiling, Philippines Marnelli S. Alviola1*, Felipe N. Soto-Adames2, Cristian C. Lucañas3,4, Virginia C. Cuevas1, Juancho B. Balatibat3,5, and Ireneo L. Lit Jr.1,3 1Environmental Biology Division, Institute of Biological Sciences College of Arts and Sciences, University of the Philippines Los Baños, Philippines 2Florida State Collection of Arthropods, Division of Plant Industry Florida Department of Agriculture and Consumer Services, Gainesville, Florida, USA 3Entomology Section, University of the Philippines Los Baños Museum of Natural History, Philippines 4Graduate School, University of the Philippines Los Baños, Philippines 5Department of Forest Biological Sciences, College of Forestry and Natural Resources University of the Philippines Los Baños, Philippines Patterns of distribution and diversity of springtails along an elevational gradient in the canopy and forest floor of Mt. Makiling, Philippines were determined, this being the first study conducted on springtail diversity along an elevational gradient and also the first published report of canopy arthropods in the Philippines. Springtails were extracted from soil samples from the floor and those suspended in the canopy of three natural forests at different elevations (tropical lowland evergreen rainforest, lower montane rainforest, and tropical upper montane forest). We predict that elevation and forest strata will have significant effects on the springtail assemblages. A total of 2,287 springtails representing 31 morpho-species and eight families were collected from the study. Across the elevation gradient, mean species richness and mean abundance consistently decrease as elevation increases, but only the mean abundance of the lowland forest is significantly different from that of the lower and upper montane forests. Diversity t-test (p-values less than 0.05) revealed significant differences between different sites and strata. Clustering analysis using the Bray-Curtis similarity index revealed separate groupings of the lowland forests to those of the montane forests. Lastly, the results of PERMANOVA showed that both elevation and strata were found to have significant effects on the overall assemblage of springtails. This study suggests that forest floor species assemblages are closely related to each other unlike those of the canopy, where only the upper montane and lower montane are similar. The results of this study affirm our main hypothesis that springtails (as a group) respond significantly to both elevation and strata in a tropical forest in the Philippines. Keywords: forest strata, springtails, tropical rainforest, vegetation types *Corresponding Author: [email protected] 563 Philippine Journal of Science Alviola et al. Collembola Across Vol. 150 No. S1, Special Issue on Biodiversity Elevation and Forest Strata INTRODUCTION decaying plant matter (Hopkin 1997), which are abundant in the canopy of “closed” tropical rainforests (Basset et Explorations of the forest canopy have increased the global al. 2003). Addressing these hypotheses will increase our estimates of biodiversity by several folds (Greenslade et understanding as to how these organisms are structured al. 2016; Nakamura et al. 2017). The canopy has been along elevational and vertical gradients in a tropical considered as “the last biotic frontier” (Erwin 1983) due to ecosystem. Results of the study would also be of great the favorable habitat it provides for numerous organisms importance in studying the sensitivity of springtails, along that are rarely or never found on the forest floor. It also with other soil-inhabiting organisms, to climate change. serves as a “dynamic interface between organic nature This is the first study conducted on springtail diversity and the atmosphere,” which is a great avenue (in addition along an elevational gradient in the Philippines and also to the most-studied elevational gradients) for studying the first published report of canopy arthropods, especially how changes in the environment may affect biodiversity springtails, in the Philippine forests. (Nakamura et al. 2017). The arthropods make up most of the soil biodiversity, with the Collembola (springtails) and oribatid mites being the most dominant (Cassagne et al. 2006). The Collembola MATERIALS AND METHODS make up some of the most abundant and widespread soil This study was conducted in the northeastern side of Mt microarthropods in the world. They can be found in almost Makiling, a dormant volcano located on the border of the all types of terrestrial habitats where they often dominate provinces of Laguna and Batangas, Luzon, Philippines the soil community (Deharveng and Bedos 2004). Gapud [Makiling Center for Mountain Ecosystems (MCME) (1968) considered the Collembola to be one of the most Collection Permit S.N. 27 January 2018]. The reserve has neglected insect orders in the Philippines. Handschin a total land area of 4,224 ha and is located at 14°8′ north (1926, 1930) pioneered in Collembola taxonomy and and 121°12′ east spanning parts of Los Baños, Bay, and recorded 18 species, including seven that are endemic to Calamba in Laguna province, and Sto. Tomas in Batangas the Philippines. Gapud (1968, 1969, 1971) expanded the province. The average rainfall, temperature, and humidity in knowledge on the Philippine Collembola as he reviewed Los Banos, Laguna during the date of collection (August– the two suborders Arthropleona and Neoarthropleona by September 2018) were 195.895 mm, 27 °C, and 84.5%, examining museum specimens and new collections. Most respectively (source: World Weather Online). of the species collected were either new to science or new Philippine records. Three natural forests (Fernando et al. 2008) at different elevations (tropical lowland evergreen, lower montane, Canopy science in the Philippines is a relatively new and tropical upper montane rainforests) were selected field. At present, there have been no published scientific (Figure 1). The first site, lowland evergreen rainforest articles on the canopy fauna of the country. The present (LL), is composed of early to late secondary growth forest study was conducted to determine patterns of distribution at an elevation between 442–655 masl. The second site, the and diversity of springtails along an elevational gradient lower montane rainforest (LM), spans from 760–899 masl, in the canopy and forest floor of Mt. Makiling, a well- with vegetation consisting of natural stands of old-growth documented biodiversity area in the Philippines (Pancho forests with prominent vines and lianas; human activities, 1973; Abraham et al. 2010). aside from hiking of mountaineers, are limited in the We hypothesized that springtails would respond strongly area. The last site is the upper montane rainforest (UM) to both elevation and strata as these parameters possess a located at the peak of Mt. Makiling starting from 900m distinct set of environmental conditions that could have asl and where trees are significantly shorter and covered discernable effects on springtail assemblages (Paoletti with thick layers of mosses. The mean temperature et al. 1991; Maunsell et al. 2013; Basset et al. 2015; during the time of collection was 26.23, 23.09, and 22.30 Bokhorst et al. 2018). Specifically, we hypothesized °C in the lowland, lower montane, and upper montane that species diversity increases with increasing altitude, forests, respectively. Soil pH decreases with increasing following the same pattern of springtail studies in elevation (LL: 7.23; LM: 6.43; UM: 5.76). On the other Mexico (Cutz-Pool et al. 2010), Sweden (Bokhorst et hand, relative humidity was highest in the lowland forest al. 2018), and China (Sun et al. 2020). We also expect (75.83%), followed by upper montane forests (72.67%) that a clear distinction between forest floor and canopy and lower montane forests (69.75%). species exists (Rodgers and Kitching 1998, 2011). Lastly, At each of the three study sites, a 20-m transect line was we hypothesized that species abundance and richness established based on rapid assessment of suspended soil are higher in the canopy than in the forest floor since presence and accessibility from the trail. Four collection the majority of springtails feed on fungal hyphae and trips were done due to an inadequate number of available 564 Philippine Journal of Science Alviola et al. Collembola Across Vol. 150 No. S1, Special Issue on Biodiversity Elevation and Forest Strata Figure 1. Location of three study sites at three elevations in the northeastern side of Mount Makiling, Philippines. Berlese-Tullgren funnels. The dates of the collection were slides and identification of springtails were done at the 16 and 30 Aug, 11 Sep, and 26 Sep 2018. Florida State Collection of Arthropods, Department of Plant Industry, Gainesville, Florida, USA. Lastly, the springtails Twelve suspended soil samples and 12 forest floor samples were identified to the species or morpho-species with the were collected in each vegetation/elevational type. Each use of dichotomous keys and/or illustrations provided sample ideally consisted of around 1 kg. For the whole by Christiansen and Bellinger (1980), Fjellberg (2007), study, 36 canopy (suspended soils) and 36 forest floor Gapud (1968, 1969, 1971), Zhang and Deharveng (2014), samples were collected representing three