Biodiversity and Vulnerability of Aquatic Insects in California

Winter 2015 Ecesis, Volume 25, Issue 4

Photograph of a widow skimmer (Libellula luctuosa) specimen, taken as part of the UC Berkeley Calbug project to digitize insect specimen data from California’s entomology collections.

Photograph of a widow skimmer (Libellula luctuosa) specimen, taken as part of the UC Berkeley Calbug project to digitize insect specimen data from California’s entomology collections.

As practitioners tasked to plan or evaluate restoration projects and meet permit requirements in freshwater habitats, we often neglect non-listed species. Review studies of biodiversity in California have found that only 6% of known freshwater species (within groups that have been evaluated) are formally protected by the state or federal government (Ball et al. 2013; Howard et al. 2015). However, half of all freshwater species in California are considered to be vulnerable to extinction (Howard et al. 2015), and extinction rates in freshwater ecosystems are 4 to 5 times higher than those of terrestrial systems (Ricciardi and Rasmussen 1999). 

What about species that have not yet been evaluated? It turns out that when including hyper-diverse groups, such as insects and diatoms, only 2 to 4% of known freshwater species have been assessed for conservation status (Ball et al. 2013; Howard et al. 2015). Most of these unassessed species belong to the most diverse animal group — invertebrates. No aquatic insects are currently included in state or federal lists of endangered species in California, yet they make up 40% of total known species in streams (Ball et al. 2013). Aquatic insects also include some of the most sensitive indicators of overall ecosystem health, such as the Ephemeroptera, Plecoptera, and Trichoptera orders (EPT: mayflies, stoneflies, and caddisflies). For example, a study of stoneflies in Illinois found that 22 out of 77 species have been extirpated, and of the remaining species, 25% are considered to be imperiled. This meets or exceeds imperilment rates of amphibians, which are known as the most vulnerable animal group (e.g. Hoffman et al. 2015). 

If our goal is to protect and restore ecosystems and biodiversity, we should also address hyper-diverse groups, such as insects. These invertebrates are essential components of food webs, provide important ecosystem services, and are some of the most sensitive indicators of ecosystem health. 

One problem is that we do not currently have enough data on the distribution and ecology of most insects to perform conservation assessments or to understand how to protect individual species and their habitats. A UC Berkeley-based project, known as Calbug, began filling this data gap in 2010 for insects by digitizing specimen data from entomology collections throughout California. One of the priority groups was Odonata (dragonflies and damselflies), and the project successfully digitized all specimens from the major collections throughout the state, as well as enthusiast observations from recent years. The result was a database of over 32,000 georeferenced and vetted occurrence records spanning the period of 1879 through 2013 (Ball-Damerow et al. 2015).

Scientists, practitioners, and the general public can use such historical species databases as a data discovery tool. For example, conservation biologists might identify promising datasets for further study, or identify species that may be in decline. Looking at the distributions of records over time, there are distinct peaks in collections that correspond to the activities of individual Odonatologists. One such peak occurred in the early 1900s as a result of work done by Clarence Hamilton Kennedy across central California and Nevada. For part of my doctoral dissertation work, I conducted a resurvey study of 45 sites throughout this region that were originally sampled by Kennedy in 1914-1915 (Kennedy 1917; Ball-Damerow et al. 2014). 

Kennedy was the first to carry out a comprehensive census of dragonflies in the western United States. While working on a graduate degree in entomology from Stanford, he travelled by railroad as far north as Chico; as far east as Carlin, Nevada; and as far south as Los Angeles. He compiled lists of species at specific sites along with notes on environmental conditions. During that time — although many naturalists were documenting biodiversity throughout the country, finding and describing new species — detailed historical information for insect communities is rare. Kennedy’s work is a valuable source of information on freshwater habitats and insect communities at a time when widespread urban development was beginning, and more than 50 years before anyone thought of human-caused global warming. 

In general, as large regions become urbanized or converted to agriculture, the diversity of aquatic habitats and organisms declines. Results from the resurvey study showed that dragonfly communities reflect this habitat homogenization, and have also become more similar across individual sites. Habitat generalists thrive and have expanded, because they can survive as long as there is water and some aquatic vegetation. Habitat specialists have declined in abundance or in the extent of their distribution with the loss of their particular type of bog or stream habitat. We found that the average percentage of habitat generalists at each site increased by 18%, while habitat specialists declined. Species with an overwintering diapause — a trait to withstand cold winter temperatures — also declined. These species may have experienced higher mortality with warmer winter temperatures and increased temperature variation, which may trigger egg hatch at inopportune times. In contrast, migratory species are more warm-adapted and have increased over time; these migrants experience higher larval growth rates and a longer reproductive period with warmer temperatures. 

This work provides a glimpse into data sources that may be used to determine the conservation status of aquatic insects, such as dragonflies. Including our most diverse animal group in conservation efforts would help protect a wider and more representative variety of freshwater diversity and habitats. This will only happen on a large scale if aquatic insects are included in state and federal lists of threatened and endangered species. The next step is to formally assess the status of habitat specialists and other sensitive groups and petition for species to be listed, which will take time. Until then, dragonflies and other aquatic insects would be a valuable consideration for restoration planning and monitoring efforts. Insects are sensitive indicators with shorter life cycles and flight, which allows a relatively quick response to habitat improvements. 

Despite the homogenization that has occurred across freshwater communities, a small patch of stream or lake habitat surrounded by an urban landscape can still harbor many dragonflies. Species found in urban areas are most often fairly tolerant to habitat change and pollution—but they are still charismatic and important components of ecosystems. Dragonflies can be an eye-catching sign that life carries on in urban streams, as long as certain habitat needs are met. Good urban habitat for dragonflies includes vegetation on the banks and in the water channel, with some areas of open canopy that allow sunshine to warm the water. The vitality of ecosystems in many urban areas is limited, and they will never be the same as in the past. But a good starting point to restoring urban streams is converting concrete-covered water drainage systems back in to habitat for these vibrant insect predators. It helps that humans can relate to the big eyes and personalities of dragonflies, and can enjoy their activity on a stroll through the park. All the while, the charming red, blue, orange, white, spotted, green, and purple individuals dart through the sky, and from reed to reed, eating mosquitoes. — by Joan E. Damerow, Wildlife Biologist, WRA Environmental Consultants, Inc.

References
Ball, J.E., L.A. Bêche, P.K. Mendez & V.H. Resh. 2013. Biodiversity in Mediterranean-climate streams of California. Hydrobiologia 719 (1) 187-213. 
Ball-Damerow, J.E., L.K. M’Gonigle &V.H. Resh. 2014. Changes in occurrence, richness, and biological traits of dragonflies and damselflies (Odonata) in California and Nevada over the past century. Biodiversity and Conservation 8: 2107–2106. 
Ball-Damerow, J.E., P.T. Oboyski & V.H. Resh. 2015. “California dragonfly and damselfly (Odonata) database: temporal and spatial distribution of species records collected over the past century.” Zookeys 482: 67-89. 
Hoffman, M., C. Hilton-Taylor, A. Angula, et al. 2015. The Impact of Conservation on the Status of the World’s Vertebrates. Science 330: 1503-1509.
Howard J.K., K.R. Klausmeyer, K.A. Fesenmyer, J. Furnish, T. Gardali, T. Grantham, et al. 2015. Patterns of Freshwater Species Richness, Endemism, and Vulnerability in California. PLoS ONE 10(7): e0130710. doi:10.1371/journal.pone.0130710
Kennedy, C.H. 1917. Notes on the life history and ecology of the dragonflies (Odonata) of central California and Nevada. Proceedings of the United States National Museum 52: 483–635. 
Ricciardi, A. & J.B. Rasmussen. 1999. Extinction rates of North American freshwater fauna. Conservation Biology. 13:1220–1222.