By Timur Katsnelson, Neurobiology, Physiology, and Behavior ‘19
Conservation biology has always been an interesting field to me. After having previously submitted two neuroscience-related articles to the Aggie Transcript, I decided to explore a new topic. The bear-sighting on campus last spring was on my mind, mainly because I began to wonder about the status of bears in our state. Given their symbolic status in California, I imagined that their conservation would be well-documented. This article serves as a brief report of the black bear’s current status in California, and the population genetics methods used by researchers keeping track of the animal.
Shortly before 6 a.m. on June 4, 2019, a very rare occurrence captured the attention of the entire Aggie community. A young, male black bear was spotted wandering near the UC Davis Arboretum’s Redwood Grove . The campus police and fire departments, in conjunction with California’s Department of Fish and Wildlife (CDFW), worked to tranquilize the straggler and release him to the nearest habitat west of the city of Davis. This moment of excitement on campus sparked the curiosity of many who care about wildlife and conservation. According to CDFW, black bear populations have been on the rise over the past quarter-century, so what are the challenges the species face and how do biologists keep track of populations? It is also important to evaluate the evolutionary track of the species to understand if it can withstand changing environments, so what is the genetic diversity of the state’s population of black bears?
California’s history with bears is complicated. Many sports teams in the state are fondly named after them and, most notably, a prominent grizzly roams a patch of grass on the state’s flag. While it is a cherished symbol of the state, the grizzly faced a savage end to its reign as apex predator. The Spanish threw the bears in fights to the death against bulls and dogs, and later American settlers hunted them into oblivion. The last California grizzly was seen in 1924 and has since been extinct . Nearly one hundred years later, environmentalists are aspiring to reintroduce the grizzly bear through back-breeding, cloning, or genetic engineering . Many might consider these to be aspirational long-term goals, and in the meantime have focused on the current population of bears in the state. What is known for sure is that the absence of the grizzly in the state has opened up more room for a different population to flourish .
The real challenge in the many decades since the last grizzly has been observing and managing the population of California black bears. Unlike their phylogenetic cousins, black bear populations still exist in the state and are relatively stable. The department estimates that between 25,000 and 30,000 black bears occupy 52,000 square miles in California. There are three subpopulations of the bears which are recognized as the North Coast/Cascade, Sierra, and Central Western/Southwestern regions. Unsurprisingly, about half of the state-wide population of black bears resides in the North Coast/Cascade region .
In 2016, a population genetics study of California Black Bears was published by the CDFW in conjunction with the Wildlife Population Health and Genetics Laboratory at the UC Davis School of Veterinary Medicine. The study analyzed the Central Western subpopulation, specifically in Monterey and San Luis Obisbo counties and compared genetic samples to bears in Mono County, which is between Yosemite National Park and the border with Nevada. Research of this sort evaluates abundance of the species and the genetic diversity of small populations to predict migrating patterns, check for genetic bottlenecking and inbreeding, and to examine the overall strength of the genetic pool .
One way researchers acquired genetic material was through a hair sampling technique. Two rungs of barbed wire were tied around a circle of trees. At the center of this sample area was fish bait and a sweet scent bait made of honey and berries. As bears approached the bait, their hair would get caught in the wires. The spacing of each sample station was strategically determined from a grid design that considered habitable ranges for the bears and safe distances from human-related dangers such as roads and watch points. DNA extraction and further genotyping was used to identify unique individual bears. From there, most of the work came from computer-programmed statistical tests such as Bayesian genetic clustering algorithms to evaluate the population structure for each data range .
Researchers have come to believe that the central coastal population of bears has been in the region for about 50 years and are descendants of the population in the Sierra region that have migrated towards the coast. The report concluded that there are very few bears populating in Monterey County because there has not been enough time for them to disperse adequately within the coastal region. A potential reason for their slow migration towards Monterey County could be urbanization and the construction of highways that provide real physical barriers .
A 2009 study (Brown et al.) by researchers at the UC Davis School of Veterinary Medicine also analyzed the population genetics of California’s black bears, this time on a statewide scale. Using historical documents to track translocations of bears by humans, but also the analysis of microsatellite DNA from subpopulations of the bears, the researchers came to similar conclusions as the aforementioned CDFW report. It is believed that the extinction of the California grizzly, which roamed a significant portion of the state’s central coast, made room for the black bear to begin to inhabit regions such as Monterey and San Luis Opisbo . Brown et al. used genetic samples from 540 bears, which were collected between 1990 and 2004 throughout the state. To determine the genetic structure of the California populations, the group used a computer program that “groups individuals into clusters based on genotype without consideration of sampling geography.” Following this, the determined clusters were tested for Hardy-Weinberg equilibrium, one of a handful of tests for genetic populations. This is an evaluation method that assumes no evolutionary changes are taking place in the genetic pool. Doing this makes it possible to simply analyze the allelic frequencies within the population without accounting for potential changes.
Wildlife management is an increasingly important and difficult operation for any organization. Urbanization and global climate change will certainly become more prominent issues in black bear conservation. This is not even considering the laws on hunting or other policy-related challenges that may arise. The CDFW, in conjunction with researchers from around the state, has made a concerted effort to observe this population. If we are to learn a lesson from the past, it would be to not take for granted the abundance of the bear population in California. There has been a lot of excitement about the black bear’s proliferation, but our state will need to be attentive if we are to keep the health of our wildlife in balance.
- California Department of Fish and Wildlife “Black Bear Biology” https://www.wildlife.ca.gov/Conservation/Mammals/Black-Bear/Biology
- Los Angeles Times “Column: Will the California Grizzly Make a Comeback?” https://www.latimes.com/opinion/op-ed/la-oe-arellano-grizzlies-20180718-story.html
- Sherman et al., “Population Genetics Study of California’s Black Bears” https://lpfw.org/wp-content/uploads/2017/02/Sherman-Ernest-CDFW-Final-Report-Population-Genetics-Study-of-California%E2%80%99s-Black-Bears.pdf
- UC Davis “Bear Caught in the Morning, Freed 5 Hours Later” https://www.ucdavis.edu/news/bear-caught-morning-freed-5-hours-later/
- Brown et al., “Black Bear Population Genetics in California: Signatures of Population Structure, Competitive Release, and Historical Translocation” Journal of Mammalogy https://doi.org/10.1644/08-MAMM-A-193.1