Arthropod diversity in epiphytic bryophytes of a Neotropical cloud forest

S. P. Yanoviak and N. M. Nadkarni

The Evergreen State College; Olympia, WA 98505 USA

Tropical montane forests typically support high diversity and abundance of epiphytic plants. For example, the forests in and around Monteverde, Costa Rica, contain several hundred species of epiphytic orchids alone. Bryophytes (mosses and leafy liverworts) are the most conspicuous epiphytes in the Monteverde forests, and form a nearly continuous covering on the woody portions of trees from the ground to the tips of the highest branches. Few ecological studies have specifically focused on these plants. Moreover, unlike the fauna of temperate bryophytes, almost nothing is known of the arthropods and other invertebrates that live in association with epiphytic bryophytes in tropical forests. Here we present preliminary results from the first half of a two-year study of arthropods living in epiphytic bryophytes of the Monteverde Cloud Forest Preserve, Costa Rica. The Preserve is mostly primary forest with a few small (2-5 ha) secondary forest inclusions. The results presented here address two questions from the larger project: 1) What kinds of arthropods live in the bryophytes of the Preserve? and 2) Does arthropod diversity and abundance in these epiphytes differ between secondary (~ 40 yr old) and primary (> 200 yr old) forest types? We collected small patches of bryophytes (each ca 300 ml in volume) from crowns (15-30 m) of various tree species in primary and secondary forests. Arthropods were extracted from epiphyte samples using Tullgren funnels, counted, and assigned to morphospecies. Mites (Acarina), Collembola, and Coleoptera (especially Curculionidae and Staphylinidae) were consistently the most diverse and most abundant groups collected. Ants (Hymenoptera: Formicidae) were very numerous in many samples, and were proportionally more abundant in secondary forest. In general, arthropod morphospecies composition in epiphytic bryophytes was very similar between forest types. The average number of arthropod morphospecies collected was significantly higher in primary forest bryophytes than in secondary forest, whereas arthropod abundance was greater in secondary forest than in primary forest. This is attributed to the large number of ants in the secondary forest samples; mean arthropod abundance did not differ between forest types when ants were removed. Changes in average morphospecies richness and abundance over time suggest that the structure of arthropod assemblages in epiphytic bryophytes varies seasonally.