By: Michael Peterson
California was once home to the American Lion, short-faced bear, and dire wolf. Yet these large, exciting predators are now extinct. So, how do we know they ever existed? The hard structure of their bones and the right conditions produced petrified impressions of past animals known as fossils, which are found in the rock where they were preserved. Even more valuable are natural asphalt seeps, such as the La Brea Tar Pits in Los Angeles, which served as a bizarre trap for large animals and an ideal preservation environment. The abundance of fossils in this one spot, including over four hundred dire wolf skulls, has provided researchers with a treasure chest of evidence to reconstruct a past era of animal diversity.
Vertebrates, including birds and mammals, have large bones that increase the chances that they may be preserved, making it possible for us to find and describe the history of these creatures. But how do we know about the rest of the earth’s species? The little ones, the squishy ones, the ones that live in water and get washed away? How do we know what invertebrates, the spineless ones, once existed?
Many times, our best clues of extinct invertebrate biodiversity are provided by the investigations and notes left behind by earlier scientists. A variety of century-old biological surveys exist, as do species descriptions and fishing records. For more recent time periods, photos of wildlife or landscapes may exist. These records provide clues that enable a historical approach to ecology and how the richness of species may be changing over time.
One timely example of the importance of past natural history studies of invertebrates comes from California Odonates, better known as dragonflies and damselflies. These charismatic insects are known for their large size and beautiful coloration. C.H. Kennedy, from the University of California, Berkeley, was the first to thoroughly describe California dragonflies and damselflies by collecting them across much of California and northwest Nevada in 1914 and 1915. Many of his specimens were kept in insect drawers at museums all over the country, but even more importantly, Kennedy’s field notes were accessible at universities and museums in California, Michigan, and Florida. Time-stamped biodiversity baselines, such as Kennedy’s, are difficult to build, but creative approaches that leverage the field notes and collections of scientists long ago are making historical comparisons possible today.
Fast forward to 2011. Dr. Joan Ball, also from UC Berkeley, re-surveyed these sites again from 2011 – 2013. With a baseline from a 1914 study and new collections, Ball could compare the species found in California to infer the trajectory of biodiversity in these insect species. Ball found 67 species of the 80 Odonates represented in the historical study, demonstrating that California has probably lost some species from these sites. Interestingly, however, two species that were not found in Kennedy’s records were quite common in the resurvey effort. Changes in the landscape and climate of California may eliminate some species, while enabling others to disperse to new areas.
This type of analysis would not be possible without Kennedy’s massive field efforts nearly one-hundred years ago. His commitment to understanding the biodiversity of dragonflies and damselflies in California laid the groundwork for chronological comparisons. Current researchers like Ball are using collections of past field biologists, but also looking in other areas, including past photographs and thorough local surveys, to understand biodiversity in many types of animals.
In each case, good notes about the biological world can be imperative to know what species existed, how large or small they were, and how the past portfolio of species compares to that of the present. Historical ecology studies, such as this, do not provide the deep timelines of fossils or tar pits, but they do serve to help humans understand the trajectory of biodiversity over decades, even for small invertebrates like dragonflies. In the same way that Kennedy’s passion for field work and meticulous animal descriptions paved the way for researchers today, we can hope that field surveys today pave the way for a deeper understanding of the natural world in the future.
Essig Museum of Entomology, http://essig.berkeley.edu/
CalBug Project, http://calbug.berkeley.edu/
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