Devils Postpile invertebrate inventory

This inventory investigated fauna throughout the riparian corridor of the Middle Fork of the San Joaquin River within Devils Postpile National Monument. We sampled riffle and pool habitats in the river and both flooded and dry portions of meadows.

We documented 77 taxa from dry meadow habitat, 29 from flooded meadow habitat, and 51 from the San Joaquin River. The 77 taxa from dry meadow habitat represented eleven orders and 50 families, the highest diversity overall. In contrast, the 29 taxa from flooded meadow habitat were from six orders and fifteen families, and the 51 taxa from the river represented six orders and 27 families. Virtually all taxa from the meadows were new records for the Monument. About 40% of the river fauna were new records for Devils Postpile. Family richness was high for Diptera across all three habitats. In addition, family richness was high within the Coleoptera, Hymenoptera, and Araneae in the dry meadow and within Ephemeroptera, Trichoptera, and Plecoptera in the river.

Groups for which richness was high at the genus level varied among the three habitats. In the dry meadow, richness was greatest in the Cicadellidae and Delphacidae (two families of leafhoppers), the Formicidae (Hymenoptera), and the Chloropidae (Diptera). In the flooded meadow, Dytiscidae (Coleoptera), Hydrophilidae (Coleoptera), and Culicidae (Diptera) had the highest richness. In the river, we found the greatest richness in Ephemerellidae (Ephemeroptera) and Chironomidae (Diptera).

Wet meadow habitat and riffles each harbored about 800 animals per square meter, versus about 200 per square meter in the dry meadow habitat. The substrate samplers yielded a striking 87,000 animals per cubic meter. Pools and other low-flow habitats appear to represent a significant resource. Both meadow and river fauna demonstrated a relatively high level of dominance. There were greater numbers of meadow fauna present in early season than in late season. It is possible that invertebrate assemblages are even more sensitive than flora to grazing impacts in early season but more resistant to disturbance in late season. In contrast, riffle abundances were about twice as high in late season as in early season.