Niche partitioning in Hawaiian web-building Tetragnatha spiders

Hawaiian Tetragnatha spiders have undergone a spectacular adaptive radiation, and as such, present a priceless opportunity to study evolutionary ecology in an island system. Our study seeks to define the ecological niches occupied by five sympatric web-building Tetragnatha species in Waikamoi Preserve in East Maui, using data on both the physical placement (site choice) and the geometry (architecture) of the spiders’ orb webs. Quantifying niche differences among these species is important for understanding how they can coexist in a relatively small geographical area. Such studies may also illuminate the ecological factors involved in the recent divergence of taxa from their common ancestor, expanding our knowledge of rapid evolutionary processes. Thus, we used field measurements and digital photography to quantify interspecific variation in both site choice and web architecture, as well as to measure the extent to which various biotic (spiders’ local species richness and density) and abiotic (temperature, humidity, elevation, and time) factors affect these aspects of the niche. While there was no significant effect of either biotic or abiotic variables on site choice or web architecture, there was a significant species effect on both site choice and architecture, particularly in the density (length per unit area) of sticky capture silk in the webs. This strongly suggests niche partitioning, and differences in foraging strategy, among the five species. Future work will include stable isotope analysis of the five species in order to characterize the trophic levels and taxonomic assemblages of their respective prey.