The yellow-bellied marmots of the
Rocky Mountain Biological Laboratory
|Marmot Minutes (a research blog)|
|Yellow-bellied marmots (Marmota flaviventris) are one of the 14 recognized species of marmots--cat-sized, ground squirrels found throughout the Northern Hemisphere. The yellow-bellied marmot is widely distributed through the Rocky Mountains, the Intermountain West and the Sierra Nevada and White Mountains in California. At this point, it's neither threatened nor endangered and thus makes a good species for detailed study of its population biology and behavior. The long-term database accumulated since 1962 makes this a priceless system for studying factors that drive changes in population size.|
The behavior and population biology of the marmots of the Rocky Mountain Biological Laboratory (RMBL), a private, non-profit field station in the Rocky Mountains near Crested Butte, Colorado, have been continuously studied since 1962. In 2011, we will celebrate 50 years of continuous marmot research. Kenneth B. Armitage (now a Distinguished Professor Emeritus in the Department of Ecology and Evolutionary Biology at the University of Kansas) started this long-term study in 1962 and led it through 2001. Over the years he supervised a number of PhD and MS students who worked on the marmot project. In 2001, Daniel T. Blumstein, Professor and Chair of the Department of Ecology and Evolutionary Biology at UCLA, took over the day-to-day management of the marmot project. Ken and Dan collaborate widely with others who bring a diversity of skills and interests to the study of the RMBL marmots.
Ken's initial goals were to test the idea that populations were regulated by intrinsic mechanisms rather than by extrinsic factors. Social behavior was proposed as the major intrinsic factor that could affect reproduction and dispersal. Yellow-bellied marmots were chosen for this research because they live in social groups and are diurnal. Thus their behavior could be directly observed and its effect on population dynamics quantified. Such long-term studies are both rare and valuable.
Most ecological studies last about 2-3 years; the duration of fieldwork for a MS or PhD student. With only two or three years of study, we must select our questions carefully and we are not typically able to gain insights into the population biology (the growth and decline of populations) for species, like marmots, that may live up to 16 years in the wild. Long-term studies of individually marked animals provide priceless insights into how animals adapt to environmental variation and allow us to identify those factors that influence population dynamics, including extinction. They allow us to study evolutionary dynamics in nature. They become increasingly productive over time because there is a detailed knowledge base on which to expand upon.
Over the years, the marmots have taught us a lot. Some key findings include:
The basis of sociality: Yellow-bellied marmot social organization is based on closely related female kin groups. These kin groups consist of mother-daughter-sister associations that may continue for several generations as matrilines. Social behavior is strongly affected by kinship. Females that are sisters are more likely to engage in amicable or cohesive behavior, while cousins and half sisters engage in more agonistic behavior. Familiarity is important too because; sisters from different litters are more likely to engage in agonistic interactions. Female matrilines are characterized by both cooperation and competition. Competition is strongly expressed as reproductive suppression of younger adults by older adults. This suppression also occurs between mothers and daughters and is most common when the younger female is two or three years old. The patterns of cooperation and competition indicate that kin selection (cooperation with non-descendent kin) is not important and that females attempt to maximize fitness by producing offspring. Assisting kin (indirect fitness) does not compensate for the loss of reproduction; thus females the reproduce have a higher inclusive fitness. Males disperse from their natal site and seek out females with whom they can associate. Males associate with as many females as possible, thus they are polygynous, but in many cases may be monogamous. Male reproductive success is directly related to the number of females with whom a male associates and not how long he maintains a territory. Read more about this in Armitage 1991, 2003, 2004.
The relationship between sociality and population dynamics: Social behavior, expressed through reproductive suppression, affects population dynamics. Reproductive suppression increases the age of first reproduction, which is a major factor reducing population growth rate. Such findings are important for understanding how social behavior more generally influences ppulation dynamics. Read more about this in Oli & Armitage 2003, 2008.
Extinction: Predation plays a very important role in population extinction. Marmots living in dangerous location are more likely to go extinct, while those in safer locations have persisted for almost 50 years. Safety, from a marmot's perspective is all about rocks, and big rocks provide safety from burrowing predators. Remarkably, food, as we measured it, had no significant effect on where we find marmots, or where marmots persisted over time. Read more about this research in Blumstein et al. 2006.
Climate change: The Springs at the RMBL are warmer now than they used to be and marmots, true hibernators, must gain sufficient mass to survive a winter spent in deep torpor. We know that they now emerge earlier than they have in the past. Such plasticity in emergence date is, itself, not a problem. But what appears to be a problem is that the marmots seem to use air temperature as a cue to time their emergence. Yet, in some years, there is considerable spring snowfall. Emerging earlier, through a large snowpack, leads to high rates of spring mortality through both starvation and predation (marmots are especially vulnerable between when they emerge and when the snow melts and uncovers their many escape burrows. Nevertheless, over the decade starting in 2000, our population has exploded; we have 3x more marmots than during the previous 30-odd years. We attribute this to earlier emergences being associated with longer growing seasons. Marmots are in better body condition, and this leads to an increase in the survival of breeding age females. Read more about our climate change research in Inouye et al. 2000; Blumstein et al. 2004; Blumstein 2009; and the 22 July 2010 Nature cover story--Ozgul et al. 2010.
Antipredator behavior: Marmots have become a model system for studying antipredator behavior--the things animals do to avoid predation. We know that they have a sophisticated set of abilities to reduce the risk of predation while foraging, and that they are able to detect predators using olfactory, acoustic, and visual cues. We also know from this study, and others, that animals may maintain antipredator behavior for extinct predators if they are exposed to extant predation risk. Read more about our antipredator research in Bednekoff & Blumstein 2009; Blumstein et al. 2008a,b, 2009.
Communication: Our studies of marmots have allowed us to test fundamental questions in the study of antipredator communication. We know that marmots emit alarm calls, potentially risky signals that may increase exposure to predators, to warn vulnerable offspring. We know that a considerable amount of information is contained in these calls that includes information about the caller's identity, age, sex, and the degree of risk the caller experiences when calling. We are also beginning to learn about what acoustical attributes communicate fear. Read more about this work in Blumstein 2007 and Blumstein & Récapet 2009.
Reliability assessment: Individuals of many species vary in their reliability--some individuals provide valuable information while others may not be so reliable. In other species, people have suggested that animals should ignore unreliable individuals--following the story of the 'Boy who cried wolf'. However, marmots have taught us that there is a different way that unreliable individuals may influence others: by encouraging them to acquire more information about the risk of predation. Such findings have implications for human security policies. Read more about reliability assessment in Blumstein et al. 2005 and the implications for Darwinian Security in Blumstein 2008.
Exciting new research directions focus on understanding reproductive suppression in females, coalitionary alliances in males, factors that maintain variation in personality types, the consequences of social relationships, and the importance of 'stress' in reproduction and health.
A special thanks to major sponsors and research facilitators...
Some of this material is based upon work supported by the National Science Foundation under Grant Number (DEB-1119660 and other grants issued to the RMBL). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
Last modified: 24 May 13