SEE-U 2000: Black Rock Forest - 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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# Black Rock Forest ## Exercise 4: Turtle 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 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. 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. 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-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 and unmarked animals is used to estimate total population size. 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). A 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. ### Your Assignment Your assignment involves the following tasks: Bait and set turtle traps at designated ponds at BRF, checking the traps in the morning over 2 days. Animals are marked and released.(3 hrs am day 1 to mark captured turtles and 3 hrs am day to recapture turtles) To understand the elements of PVA through a coin-flipping exercise and to perform a PVA using computer software to address questions concerning management of an endangered species. (3 hrs day 1 afternoon). Write-up and discuss results. (2 hr day 2 afternoon) ### 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 turtles 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 turtle 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 Writing oral presentation and presenting it = 2.5 hours ### Procedural Notes The TAs would have to initially set the turtle traps one day ahead of time so that the students could just go out and mark those that were in the traps, release them, reset the traps, and then repeat it the next day Is one day enough for the turtles to be recaptured in the traps or would they require more time to be attracted to the baited traps? Baited traps would be preferable over unbaited traps in that it introduces some experimental error (good for analyses of flaws of methods), but also ensures that more turtles will be captured (good for data analyses) The PVA program (shareware written by James Gibbs in Gibbs et al. Problem-solving in conservation biology and wildlife management) should be downloaded in advance. It is a PC-based program, but will run on Mac’s in Softwindows. Writing the excel formulae alone could take about a half an hour before the students could finish things ### 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 Field materials: turtle traps, baits, quick-drying waterproof paint, field guides for species identification.