Resurrecting the Work of Gordon Alexander: Grasshopper Communities and our Changing Climate

Dr. César Nufio has examined a vast number of grasshoppers to understand the impacts of climate change on insects in the Rocky Mountains of Colorado. To be precise, the number of specimens he has captured and processed over the last 10 years has exceeded 180,000 from grassland communities found along a high plains to subalpine gradient. Nufio’s National Science Foundation funded research combines extensive field surveys with comparisons of museum collections, weather data, and laboratory and field experiments.  The entire project started with his discovery of a collection of 25,000 pinned and label grasshopper specimens and three data notebooks at the University of Colorado’s Natural History Museum. These pinned specimens and notebooks, which are part of the Gordon Alexander Collection, were part of several field studies conducted over 50 years ago.

Gordon Alexander and assistants at the subalpine field site Brainard Lake (Roosevelt National Forest, 3200 m in elevation) on August 17th, 1958. Photo courtesy of The Gordon Alexander Project.

Dr. Gordon Alexander (1901-1973) was a professor at the University of Colorado and chair of the Biology Department for over 20 years. In the springs and summers of 1958-1960, Alexander conducted field surveys of grasshoppers found across the Front Range of Colorado. He was interested in determining which species were present where and when, and how grasshoppers adapted to living on mountains.  Four of these surveyed sites, which were associated with high prairie, lower montane, upper montane, and subalpine meadows, were sampled on a weekly basis. During each of these surveys, Alexander record the species, and life stage of all grasshoppers that were captured. Fortuitously, each of these sites were associated with weather stations that have been collecting data since 1953.  Despite the importance of Alexander’s surveys and data collections for serving as a baseline for addressing how insect development and communities have been affected by climate change   over the last 50 years, the potential for such a collection was nearly forgotten.

In 2006, Nufio began resurveying the same sites that Alexander had nearly half a century ago. Nufio wanted to understand how climate had changed along the gradient and how this change might impact the timing of grasshopper life history events (when they hatched and how fast they developed), their elevational ranges and demography (population size, longevity, reproductive rates), and body sizes. All of these questions could be addressed comparing his recent findings to the observations made by Alexander.  

To Nufio’s surprise, the sites had not warmed equally across the elevational gradient. Temperatures in the high prairie had not significantly changed since the 1950s but the montane and sub-alpine sites had warmed a great deal (more on temperature: Article). As such it was not surprising that the grasshoppers appeared to hatch and reach adulthood at roughly the same time they did 50 years prior at the lowest site. At the higher sites, however, temperatures had warmed by  ~1.5°C during Nufio’s initial resurvey (2006-2008) and consequently, the grasshopper communities were found to have hatched and became adults much sooner than they did during Alexanders time by 2-4 weeks! (more on phenology: Article).  During 2009 to 2011, seasonal temperatures across the mountains declined and the grasshoppers across the mountain no longer hatched early or reached adulthood earlier than they previously had. However, in 2012 which was the second warmest year in the last 118 years in Colorado, the communities at all of the sites advanced their development by nearly a month. One population even matured 52 days earlier than previously recorded!  Interestingly, a second study examining flowering times at one of the sites showed that the grasshoppers have changed their timing to adulthood by twice as much as the plants had changed their flowering times. As grasshoppers are herbivores, changes in a plants phenology can have major impacts on the grasshoppers. For example, if a grasshopper population prefers a certain plant and they emerge before the plant is available then the grasshoppers will most likely experience starvation.  

Grasshoppers go through five nymph stages (instars) (top five sketches) before becoming an adult. Generally nymphs and adults look similar in shape with the exception that adults have fully developed wings (bottom sketch). Some grasshopper species the nymphs and adults have strikingly different colors or patterns. Image: Utah State University

In addition to examining phenology, Nufio more recently was interested in the demographic changes among species over the elevational gradient. He observed that species with short wings showed a reduction in body length with no change in reproductive output with increasing elevation. Conversely, grasshoppers with long wings showed no change in body size but a reduction in reproductive output. Nufio also examined changes in weight, longevity, and reproduction over time in response to temperature using a caged field experiment. During a warm year, he found that females tended to be heavier, live longer, and laid more eggs (more on demography: Article).  While these subalpine grasshoppers appear to be benefiting from warming, his surveys suggest that those at the bottom of the mountain may be negatively affected by warm years.
   

Grasshoppers in the historical collection assembled by Dr. Gordon Alexander. (Photos courtesy of Dr. Cesar Nufio)

Living grasshopper as part of Dr. Nufio's current research. Photo credit to Jeff Mitton.

Grasshoppers in the historical collection assembled by Dr. Gordon Alexander. (Photos courtesy of Dr. Cesar Nufio)