SEE-U 2000: Black Rock Forest - Module 4:Exercise 4

## General Methadology for Instructors and TAs

## Exercise 4: Turtle Trapping And Population Size Estimation
Module 4: Growth and Competition: Population and Metapopulation Dynamics

1. Instructor gives the biological background during the lecture on population growth, population estimation methods, and why they are important for conservation biology
   - Lay the groundwork for the exercise quickly — talk about correctly estimating population size
     - describe the importance of this in conservation biology (estimating population sizes of endangered species, ability to project population sizes in the future)
     - in agriculture (estimating degree of infestation of pest species)
     - in ranching (ability to project the sizes of herds, and estimating degree of pest infestation)
     - in epidemiology (estimating current population size and future growth rates of illnesses in human population)
     - demography (estimating human and plant and animal population size)
   - Describe two main population growth types and talk about when they would exist in nature (Draw each curve and label the X axis, Y axis, and the significant points in the curve)
     - Exponential — unregulated growth, consistently exponentially increasing population size, apparently slow initially but rapid explosion eventually when growth is mapped out on the same graph
       - Occurs in nature when populations invade novel habitats (introduced species that become pests due to either human action or natural dispersal, e.g., rabbits into Australia or naturally dispersing organisms), when food supply suddenly outstrips population size (often due to human action, e.g., massive influx of fertilizers into a lake leading to rapid increase in the algae)
       - All organisms have the inherent capability to grow exponentially, although different species nonetheless increase at different rates as a function of their life history characteristics.
       - Difficult to naturally maintain, usually comes about as a consequence of environmental change
       - What is one of the very few species that has demonstrated continual exponential population growth of late? ANS: humans. Why? ANS: human innovations in health care, agriculture, transportation. Is this sustainable?
       - Although this is apparently unrestrained growth, there are forces that are at least slowing the growth — what are they? ANS: catastrophes, extreme weather, etc. Collectively referred to as Density Independent factors because they have the same proportionate effect irrespective of the population density
     - Logistic — a growth curve with three phases: initially slow, rapidly increasing (first two resemble exponential growth), stabilizing when population regulatory mechanisms (starvation, excessive competition, rapidly decreasing resources, cannibalism, parasite explosion) are engaged
       - These regulatory mechanisms are called Density Dependent Factors in that they increasingly affect populations as density increases
       - Most common form of population growth
       - Leveling off point in the curve is called the Carrying Capacity, because it is the maximum number of organisms of that species that that habitat can sustain
   - The numbers on the curve assume that we actually know the population sizes at each time slice — how do we know the population size that exists at each time slice?
     - Count every individual that exists (not very tractable, how do you know that you’ve surveyed EVERY individual? You cannot for most animals, but you could for most plants) — Other options for censusing animals?
     - Capture, Mark, Release, Recapture at some time in the future
   - Mark, Release, Recapture (MRR) and estimation methods
     - Jolly-Seber and Lincoln-Peterson methods—(note: Lincoln-Peterson is better for closed populations such as turtles in a pond. Jolly-Seber is better for open populations)
       - Assumptions:
       - Equation (encourage them to input this into Excel so that they needn’t recalculate it for each set of data)
   - Quick introduction to the basic biology of the species being studied
     - Describe where it lives
     - what it prefers to feed upon
     - its reproductive biology
     - its seasonality
     - have them brainstorm for other animals that have similar basic biology and to whom this MRR method would be applicable
       - Other species to which this would be applicable: other primarily herbivorous turtles, frogs
2. Students will be asked at the end of the lecture to begin thinking of how to answer the question: “How would differences in the basic biology of the organisms affect the population estimates?”
   - For example:
     - if a species tends to clump together due to resources or reproductive biology (e.g., lekking) and thus provide wildly erratic censuses
     - if a species evenly disperses over a range and thus provide tremendously consistent censuses with a solid censusing technique
     - if it experiences extreme seasonal differences in activity patterns
   - They will also be asked to design methods to get around these problems if it is known ahead of time that they could be problematic
3. Independent and Dependent variables in the experiment: pond size and population size
   - Students will break into several groups, with each group working on a different pond
4. After lecture, before the start of field time, the students will be asked to confer with their labmates and will be required to convert the above mark-recapture concepts to Excel formulae (to be checked against those of the instructor)
5. Possible field methodology
   - Go to field and capture animals from turtle traps. Traps set day before by TAs.
     - traps obviously need to be set so that the turtles can breathe and in areas that they tend to accumulate and can tolerate the nearby environmental extremes
   - Mark them with paint that is not water soluble in an area of the turtle where it won’t be scraped off during its normal activities in the next day
   - Release the animals in the same pond where they were collected and all from a single point (this should also be factored into the student analyses when discussing errors and flaws of the method)
   - Rebait and set the traps
   - Return to lab — do PVA coin and computer labs using data set from Gibbs et al. and http://rainbow.ldgo.columbia.edu/ees/life/labs/lab8.population.html
   - Second day: revisit traps, count number that were caught that were marked vs. those that were not marked — release all, and dismantle traps (or have TAs do so later in the day)
   - Return to computer lab
   - Come up with population estimates, share results, analyze relationship between population size and pond size
   - manipulate censuses in accordance with above question in point 2
   - address how these three phenomena would affect population estimates and how the sampling and estimation techniques could be modified to accommodate these situations if they are known ahead of time
6. Present the work as an oral or written report at the end of the second day