Unraveling the Effects of Hurricane Maria on the Abundance and Composition of Harvestmen (Arachnida: Opiliones) Species Along an Elevational Gradient in Puerto Rico

Harvestmen exhibit substantial responses to environmental conditions, disturbances, and modifications of their habitat. We examined the abundance and species distribution of harvestmen along an elevational gradient in the Luquillo Experimental Forest (LEF) on Puerto Rico 6-12 weeks before and 9-10 months after Hurricane Maria passed over the island in September, 2017. This provided a unique opportunity to examine the effects of a major storm on litter-dwelling arthropod populations, as the storm led to a much greater abundance of leaf litter and downed branches. The abundance of harvestmen was measured in quadrat samples from 300 to 1,000 m elevation using Winkler samplers. We observed greater harvestmen abundance post-storm, which was similar to the results for most other arthropod groups. Pre-storm, harvestmen showed greater abundance in palm habitat, as compared to forests that were a mix of broadleaf and palm vegetation. Across all sampling periods, harvestmen were most abundant at low to medium elevations (300-600 m), especially for the two dominant taxa (Stygnomma spinula and Metacynortoides obscura obscura). Our findings are similar to results obtained from manipulative studies in the LEF several years prior to the hurricane. A challenge for the future is to understand the ways that the projected increase in storm severity due to climate change can affect various invertebrate groups such as harvestmen, and how tropical forests can remain resilient to such disturbances.