SEE-U 2000: Biosphere 2 - Module 4:Exercise 4

Exercise Contents:

• | Your Questions
• | Background
• | Your Assignment
• | Objectives
• | Key Skills
• | Timetable
• | Procedural Notes
• | Materials Needed

Exercise Contents:
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# Biosphere 2 Center ## Exercise 4: Animal Trapping and Population Size Estimation Module 4: Growth and Competition: Population and Metapopulation Dynamics
Printer format ### Your Questions How can the size of an animal population be measured? What influences the growth of a population? What methods are used by conservation biologists to predict the dynamics of a population? ### Background #### Factors that Influence Populations To manage a species, whether common or rare, one needs to have a firm understanding of the factors that influence population size. Ecologists achieve this by monitoring population size, understanding the factors limiting the population, and using mathematical models to predict the future dynamics of a population. A population is a collection of individuals from the same species that occupies some specified area. Populations change in abundance due to intraspecific interactions (interactions between individuals of the same species—competition for example), interspecific interactions (interactions between individuals of different species—predation and herbivory for example), and environmental factors such as temperature, rainfall, and nutrient availability. Populations also undergo random fluctuations—this is especially important for small populations. As presented in the Module Introduction, changes in population size can also be thought of as density independent (changes occur independent of the size of the population—for example, weather-induced population declines) or density dependent (changes are a function of the size of the population itself—for example when a population gets so large that it reduces the availability of a needed resource, and thus declines). In a density-dependent situation, mortality, reproduction and other factors may change concurrently with changes in population density, such that as population density becomes more extreme (high or low) a greater proportion of the population is influenced. #### Estimating Population Size Ideally, a measure of the size of a population would be obtained by counting all the individuals, with the knowledge that none are missed in such a count. For many organisms, however, estimates of population size by direct counts are impractical. For mobile or secretive animals, for example, it is difficult to obtain direct estimates of population density, even in very small areas. However, animal population estimates can also be made using a variety of indirect techniques such as counting signs of animals (e.g. tracks, feces, vocalizations) and by estimates derived from observing a subset of animals and extrapolating to estimate the size of the entire population. Transect estimates and mark, release, recapture techniques are examples of the later. The mark and recapture technique can provide a robust estimate of population size by marking a segment of the population on one occasion and then resampling the population at a later time (often more than one occasion) to quantify numbers of previously marked plus new unmarked animals. The ratio of marked to unmarked animals is used to estimate total population size. #### Modeling Populations Many variables interact to determine the size of a population and its persistence. Often the only way to gain insight is to develop a mathematical model of the population and use it to perform a Population Viability Analysis, or PVA. PVA’s are models that relate a dependent variable (in our case, population size) to the independent variables that influence it (for example, mortality, harvesting, and weather). PVA estimates the probability of a population persisting in an environment. It is a form of risk analysis in which one is interested not only in the average size of a population at some time in the future, but perhaps more importantly in the range of possible future values. A robust PVA incorporates density-dependent and density-independent events, as well as the role of random fluctuations. Read more about PVA and the importance of population size in the protection and management of endangered species in the Wilson and Perlman CD (“Population Viability” and other topics under Main Menu/Conservation Practice/Small Populations). Follow Exploration and Further Thought elements of these pages. ### Your Assignment Your assignment involves the following tasks: In the evenings, bait and set small mammal traps along line transects in the vicinity of B2C, checking the traps early morning over 2 days. Animals are marked and released.(2 hrs to set and bait traps night before Day 1, 2 hrs Day 1 morning to mark captured mammals, 1 hr Day 1 eve to reset traps, and 2 hrs am Day 2 to record recapture rate and to pull line) Population Viability Analysis lab/digital exercises: Following Exercise 4 in Gibbs et al. (Day 2, 3 hrs), explore the elements of PVA through a coin-flipping exercise Follow exercise as laid out in Gibbs et al and as on the web page: http://rainbow.ldgo.columbia.edu/ees/life/labs/lab8.population.html (from Matt Gompper) Using the interactive population models in Wilson and Perlman, formulate and address your questions concerning management of an endangered species. These models are under “Population Viability” (Main Menu/Conservation Practice/Small Populations/ Population Viability). (Optional) For further exploration of PVA models, you can exercise another simple PVA model for Bandicoots: Continue to follow Gibbs et al.’s Ex. 4. Download the PC-executable file for the Bandicoot model (bandcoot.exe) at: http://research.amnh.org/biodiversity/center/webdoc4.htm Plot the results in Excel (or other spreadsheets) of varying of parameters to address the effects of various management policies. Write-up and discuss results. (2 hr Day 2 afternoon) In your journals address the following questions using your results: What problems arise in estimating populations of organisms (both plants and animals) especially for rare and endangered species? What issues do these bring to preservation and management of threatened species? What is the effect of initial small population size on the viability of a population? What is the interaction of population size and low allele frequency in maintaining genetic diversity? ### Objectives Understand the factors that regulate population size. Knowledge of the different types of population growth, how they differ, and when they tend to occur in nature. Understand the theoretical underpinnings involved in population size estimates. Recognize the flaws and assumptions inherent in estimation methods and how these flaws could impact conservation biology methods. Understand the basis of population viability estimation. ### Key Skills Dexterity with trapping small mammals and other organisms with a similar lifestyle. Ability to extrapolate trapping data that the students collect to other organisms with different lifestyles. Familiarity with several of the main population size estimation methods and ability to use them on a given set of data. Ability to predict population growth. Ability to perform a simple PVA. ### Timetable Total elapsed time to perform the experiment : Two days Set-up, field work, data analysis and population estimation, and report should all be done in two days (because of the lag time in the recapture event) Total elapsed hands-on time : approximately Nine hours Layout of experiment, designing excel formulae, researching alternative species = 1.5 hours First day of field work = 2.5 hours Second day of field work = 1.5 hours Analysis and extrapolation to other species and methods = 1 hours Preparation of oral presentation and presenting it = 2.5 hours ### Procedural Notes Trap setting Set the traps one day ahead of time. Space traps 5-15 meters apart, in lines that run through areas of high cover or near arroyos. Set next to features that might be frequently used as cover or runway, like grass clump, shrub/tree trunk, rocks. Bait with a ball of rolled oats and peanut butter. Create a short path to trap with a line of oats. The PVA program (shareware written by James Gibbs in Gibbs et al. Problem-solving in conservation biology and wildlife management) should be down-loaded in advance. It is a PC-based program, but will (should) run on Mac’s in Softwindows. ### Materials Needed Computer and printer Need Excel or some other data base and statistical analysis package Need Gibbs program (bandcoot.exe) for PVA. On Macintosh, this also requires Softwindows Other PVA programs available as shareware includes ALEX (available from Ian Davies at: Ian.Davies@anu.edu.au). Field materials: mammal traps bait — rolled oats (regular—non-instant non-flavored), peanut butter quick-drying waterproof paint field guides for species identification.