Insects Through the Ages

[This project was completed in collaboration with the River Basin Center at University of Georgia; to read the original post, click here].

Long before Atlanta became the thriving metropolis it is today, streams and rivers rich with biodiversity interwove ancient forests. Similar streams exist today, threaded between the concrete and asphalt of the city.

IRIS graduate student Denzell Cross, and his advisor Dr. Krista Capps, are  studying how time and changing environments have affected the aquatic ecosystems that inhabit those streams. Cross will incorporate research from the 1970s conducted in the same locations to examine how insect communities in urban streams have changed.

“I’m researching how urbanization affects aquatic insect communities over time, by incorporating a dataset that was conducted at my study sites in the 1970s, my study region being the greater Atlanta metropolitan area. I’m looking at changes in taxonomy as well as changes in trait diversity—so looking at the characteristics of these species, and how they’re able to persist in these environments,” Cross explained.

While many might write off insects as less interesting than the fish, reptiles and amphibians that inhabit Georgia’s streams, they serve as an important indicator for stream health.

“Insects are easy to sample and collect, they’re relatively easy to identify, and they indicate the health of the environment around them. The insects that persist in these environments are a good reflection of what’s happening around them. They’re a good metric of stream health,” Cross said.

He also will use maps to factor in whether the hallmarks of urbanization—increasing development and deforestation—have impacted insect life in the streams.

“By using geographic information systems (GIS), you can track changes in urban development, including factors like road density,” Cross said.

The key to successfully tracking changes in ecosystems over the years is to stay consistent—down to the exact location sampled. In order to successfully compare the streams between the years, Cross has to stand in the footsteps of past researchers.

“The past researchers sampled in 1975, and again in 2003. They used standardized methods that are easy to replicate. For measuring abundance I use benthic samplers that were also used in 1975 and 2003 to stay consistent. I’m also in the same exact space that they were. It’s really cool. I was looking at some of the hand drawn maps that they made in 2003 and I could pick up reference points with trees or rocks, and see that I was in exactly the same place,” Cross said.

Cross is also taking steps to ensure that this research can be replicated again down the line by simplifying and standardizing the methods used.

“In the 1970s the researchers sampled by hand, which is very subjective and user-specific. Sampling with a net helps standardize it so that anyone who wants to repeat this study and keep on this path, is able to,” Cross explained.

This fall, Cross completed sampling the streams. Next up, he has to identify the species found. While he expects to find resilient insect species—instead of some of the more sensitive ones—he won’t know for sure until he has finished sorting through all of his samples.

“I’m excited to see what’s there. There’s a chance I’ll find insects that weren’t there originally, but are in the streams now—this study really lends itself to looking at invasive species. By looking at what factors are linked to certain invasive species being present, we can begin to get a mechanistic understanding of how the landscape impacts stream health. We can look at the data and find linkages between habitat, the landscape, and the insect communities themselves,” Cross said.

Cross’s work gets at the heart of stream research:

“From providing the water we drink to recreational opportunities—swimming, fishing, kayaking—we rely on healthy streams for so many things, we may not even realize how much we need them. Streams and rivers are an important centerpiece of healthy ecosystems.”