Partitioning beta diversity in a Neotropical forest Opiliones assemblage (Cusuco National Park, Honduras.)

Background/Question/Methods

Partitioning diversity among hierarchal levels permits researchers to draw inferences about the processes that structure local communities.  These nested levels may show that different levels contribute to the overall regional diversity differently than other levels with in the same region.  Opiliones (harvestmen) have a near-cosmopolitan distribution, and are especially diverse in the tropics.  In this study we collected 20 harvestmen morphospecies using a nested hierarchical design.  This study occurred at Cusuco National park in Honduras, which is dominantly a cloud forest, with elevations ranging from sea level to over 2000 m asl.  We sampled three nested levels with in the park; 18 sampling efforts within nine sites within six camps within the park (samples within sites within camps). This study predicted that at the highest level (camp), beta diversity would contribute more to overall regional diversity than the lower hierarchal levels (sampling efforts, and sites), due to more habitat heterogeneity at the camp level.  We also predicted that species richness would be higher at the lowest elevation camps due to more favorable environment, such as wet lowland habitat.  We collected harvestmen using timed sampling along transects and in enclosed quadrats.  Hierarchal data analysis was completed using the software program PARTITION.

Results/Conclusions

We collected 4.4 ± 0.66 SE) morphospecies per sampling effort, 5.3 ± 0.94), per site, and 6.3 ± 1.4 per camp.   The observed beta diversity at the camp level was more than what would be expected if all the individuals were randomly distributed  (p <0.001). Beta diversity at the site level did not differ from expected (p =0.59), and the observed beta diversity and alpha diversity were significantly lower than expected.   Camps with the lowland wet forest habitat did not contain the most morphospecies.  The two camps with the most morphospecies were at elevations higher than 1400 m asl.  Efforts to find new species for the park should focus on sampling new areas within the park instead of more intensive sampling at existing camps.  We recorded more morphospecies than the number of Opiliones species documented in all of Honduras, suggesting the nation’s Opilionid diversity is poorly-characterized.