Climate change has caused warming temperatures in the Pacific Northwest, leading some insect species to expand their range into the oak savannahs more north, according to new research from Binghamton University, State University of New York.
Side by side, Dylan Jones posted images of two oak leaves. One, healthy and green, dotted with occasional galls, a framework made by a herbivorous species of oak gall wasp. The other leaf was yellowed and tattered, the victim of a population of insects with no predatory checks and balances. Climate change has caused warming temperatures in the Pacific Northwest, leading species such as Neurotereus saltatorius to expand their range into the oak savannahs further north.
“In the native range, you may find a handful of galls on a single leaf. In the expanded range, you sometimes find thousands of them on a single tree,” said Kirsten Prior, assistant professor of biological sciences. “It’s pretty prevalent all over Vancouver Island.”
Jones, a PhD student in biological sciences at Binghamton University and Clifford D. Clark Diversity Fellow, is the lead author of a research write-up recently published in the Journal of Animal Ecology on the condition. The co-authors of “The Latitudinal Gradient in Species Diversity Offers High Market Opportunities for a Growing Phytophagous Insect” include Prior, field technician Julia Kobelt, then undergraduate student Jenna Ross and assistant professor of science biological Thomas Powell.
Oak savannahs are grassy, shrubby areas where oaks are the dominant tree species. The dilemma oak species – Quercus garryana – requires a dry environment. As a result, oak savannahs are often found in the rain shadow of the West Coast Mountain Range, Prior explained. Ecologically important throughout North America, oaks are home to a wide diversity of insect species, such as oak gall wasps. These wasp species form growths called galls that can be striking in their various shapes, from those that look like large apples to others with colorful spikes reminiscent of sea urchins.
Interestingly, Alfred Kinsey – yes, that Kinsey – studied oak wasps before shifting his field of study to human sexuality.
“Biologists and hobbyists have long fascinated this group of species because they are quite charismatic,” Prior said. “You can go into an oak tree and see all those buildings on it.”
In addition to their herbivorous creators, these galls host other species of insects, including a dazzling variety of parasitoid wasps, one of the most diverse and ecologically important groups in the animal kingdom, the latter for their role in controlling insect pests. The parasitoid wasps lay their eggs in the gall after hatching, their larvae then eat the oak gall wasp larvae.
Oak gall wasps are very diverse in North America, but their evolutionary relationships are not well documented and even the identification of some species remains unknown. A consortium of scientists across the continent is working to change that Jones and Prior are part of this hard work.
“It is important to continue to document biodiversity. We still haven’t described much of the biodiversity on Earth, especially with insects,” Prior said. ecosystem
The researchers checked their study web-sites three times during this summer. Some were quite remote, involving travel on dirt logging roads, or located on Bureau of Land Administration property or on reservations associated with Indigenous communities. Others were suburban, located a short distance from cities.
Due to urbanization, few oak savannahs remain on Vancouver Island those that remain are highly documented and maintained by landowners.
“We have had long relationships with many landowners there who allow us to work on their property,” Prior said. “Some of them are so excited to have researchers there.”
Biodiversity tends to operate on a latitudinal gradient, Jones added: closer to the equator, the more species you have. A similar situation is true when dealing with higher altitudes. When a species can expand its range due to warming temperatures, it can move into areas with no diversity of predators and competitors, eventually overwhelming the ecosystem.
The case of oak gall wasps highlights the importance of biodiversity and the potential long-term ramifications of climate change, the researchers point out.
“Biodiversity can be very important in potentially protecting areas from invasive species,” Jones said. “If we have strong competitors and predators, it could make areas less susceptible to invasive species.”