Understanding Resource Limitation in Moose

A major goal for many management and conservation efforts is to understand if food limitation is responsible for poor reproduction and subsequently poor or negative population growth rates. The point at which a habitat can no longer support additional population growth is known as the “carrying capacity”. Despite numerous examples of food limitations and low reproductive rates occurring at or near carrying capacity, managers and ecologists continue to struggle to find effective methods for identifying food limitations even though the importance of doing so has been recognized for over 80 years. Recent advancements in the understanding of nutritional ecology, however, provide a new means for identify the proximity of a population to carrying capacity. For example, reproductive success can now be predicted by simply understanding the nutritional condition (amount of body fat) of an animal. Because the amount of fat animal has reflects the climatic and habitat conditions an animal is experiencing, we can now understand how reproductive success is linked to changes in habitat condition and climatic factors. Further, we now understand that the amount of fat an animal has influences their diet selection because individuals search for new foods when high-quality foods become scarce. We are using a variety of field and lab techniques to understand how measures of habitat condition, climate, body fat levels, diet quality, diet selection, and pregnancy rates signal resource (food) limitation in moose and other large herbivores. Such a newfound understanding of resource limitation will result in a number of valuable tools for identifying proximity to carrying capacity, and will therefore aid managers in their decision making process.

Fig 1. Map depicting the locations and boundaries of our eight study populations.

With the goal of understanding resource limitation and developing management tools, we set out to measure the habitat and climatic conditions, body fat levels, diet selection, diet quality and pregnancy rates of moose in Wyoming and Colorado. In collaboration with the Wyoming Game and Fish Department and Colorado Parks and Wildlife we identified eight populations (Fig. 1) that span the range of recruitment rates—an indicator of population growth or decline—found across the Intermountain West (Fig. 2). Specifically, we are measuring the condition of willow shrubs in areas where moose focus their foraging activities, we are characterizing autumn fat levels using a kidney fat index, and, from feces, we are estimating diet quality (winter and summer), diet composition, (winter and summer), pregnancy (winter), and hormones (winter) indicative of nutritional condition. Preliminary data summaries indicate that willow condition determines autumn nutritional condition, nutritional condition can be measured using fecal hormone concentrations, and that moose from populations with higher offspring recruitment rates spend more time foraging in willow habitats (see project photo gallery). These results suggest that some of our populations are suffering from resource limitation, and that metrics of habitat condition, nutritional condition, and foraging behavior will provide tools for assessing resource limitation in moose.

Fig 2. Percentage (mean +/- standard error) of females recruiting young into late winter from 2011-2013.

In addition to understanding the population-level signals of resource limitation, we are also interested in how individual animals vary in their strategies for coping with resource limitation. We are working to understanding if individual diet selection is a better predictor of resource limitation than population-level diet use. Further, we are addressing how individual moose may use different migratory and movement strategies to reduce the effects of drought on their forage (energy and nutrient) intake. By understanding these individual strategies we will provide further, and possibly more accurate, tools for identifying resource limitation, which will aid managers in making science-based management decisions.

Gallery

Willow bottoms like this one are where moose spend much of their time foraging

We measure the condition of willows to understand how much willow browse (food) is available to moose in each of our eight study populations.

The condition of willows varies across the different moose populations. In some populations, the willows are so heavily browsed that many of the stems die.

We also search for moose feces in the willows and in a variety of other habitats that moose use. The feces provide us with a lot of valuable information (continue the slide show to learn more).

Summer vegetation grows high and thick, especially in the willows. We use specially trained dogs to seek out moose feces. Here, Wicket is sitting and alerting us to a fresh pile of feces.

Orbee is always very proud of his finds.

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We collect fresh feces from which we extract DNA to tell which pile of feces belongs to which individual moose and its sex. From the summer feces we also analyze diet composition and diet quality.

During winter, we also search for feces so that we can not only learn about moose diet during this time of year, but we can also determine whether or not individual females are pregnant by analyzing the hormones in their feces.

To find feces in winter we snowshoe and ski in search of moose tracks, which lead us to our prize.

The fecal sample is nicely preserved (frozen) by the snow and cold temperatures of winter in Wyoming and Colorado.

There is a lot of organization and preparation of the feces before we can begin extracting DNA and analyzing diet composition, diet quality, and pregnancy.

In the lab we harvest the outer 'skin' or mucous of the fecal pellets. This is were we find the sloughed intestinal cells that provide the DNA needed to identify individuals and their sex.

A series of chemical reactions and cleaning steps allows us to turn the fecal mucous into a concentrated source of DNA that we can then analyze.

When we finish analyzing the DNA we get a graph like this one. The peaks here combine to represent a "fingerprint" for each moose.

Working with hunters throughout Wyoming we collected over 600 sets of moose kidneys. We weigh the fat and the kidney separately after we carefully remove the fat as seen here. This allows us to assess how much total body fat each moose has during autumn.

Understanding how much fat a moose has allows us to understand the quality of habitat they experienced during the preceding summer. For females, the amount of fat they have during autumn strongly predicts whether or not they will become pregnant.

Willow condition is strongly correlated with the amount of autumn kidney fat across six moose populations where we were able to collect kidneys (i.e., Wyoming). We expect kidney fat to strongly predict population-level pregnancy rates (analysis underway).

Reports & Publications

Jesmer, B. R., J. R. Goheen, K. L. Monteith, and M. J. Kauffman. In Review. State-dependent foraging alters endocrine-energy relationships in a large herbivore. Functional Ecology.

Annual Report 2013

Annual Report 2014

Contact

Brett Jesmer
Wyoming Cooperative Fish and Wildlife Research Unit
Program in Ecology
Department of Zoology and Physiology
University of Wyoming
[email protected]
(315) 420-2890

Goheen Research Group

Working Dogs for Conservation

Project Lead

Brett Jesmer

Brett completed his Ph.D. in ecology at the University of Wyoming in 2018, moving on to a post-doctoral position at Yale University. He grew up in the St. Lawrence river valley of northern New York state and attended the State University of New York, College of Environmental Science and Forestry at Syracuse University (SUNY ESF).

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Timeline

Field work was completed for this project in March 2015. We are currently working in the lab to finalize genetic analyses of feces to identify individual moose and their sex prior to further analyzing feces for diet composition, diet quality, and hormone concentrations (nutritional condition and pregnancy). Also, we are currently working to assess drought conditions across our study areas using remotely-sensed data (i.e., satellite data). We anticipate completion of all data analyses during spring 2016 and finalized products and reports by spring 2017. This project page will be updated periodically as new results are obtained, so please come back and visit the Understanding Resource Limitation in Moose page again!

Funding & Partners

Wyoming Game and Fish Department

Wyoming Governors Big Game License Coalition

Colorado Parks and Wildlife

NASA Wyoming Space Grant Consortium

University of Wyoming- National Park Service Research Station

University of Wyoming- Department of Zoology and Physiology

Alces Society