Lab #5 – Oct. 9-10

GENERAL LAB INTRODUCTION

Interactions between species in a community is a fundamental focus of ecological research.  There are many ways in which species, populations, and individuals interact with each other, including competition, parasitism, and predation.  Competitive interactions are nearly a “fight” for some mutually desired/needed resource.  Resources include, but are not limited to, food (organic matter for animals, nutrients for plants), water, space, and mates.  Parasitism is a form of predation in which the goal of the predator--the parasite—is to avoid killing its prey—the host that is providing it with needed resources.  Predator-prey species interactions have received the attention of ecologists for this entire century.  Lotka, in his classic work on lake food chains, recognizing the critical importance of food and food supply to the survival of individuals, populations, species, and ecosystems.  G.Evelyn Hutchinson (arguable THE father of modern ecology as we know it), noted that:  “In any study of evolutionary ecology, food relations appear as one of the most important aspects of the system of animate nature.  There is quite obviously much more to living communities than the raw dictum ‘eat or be eaten’, but in order to understand the higher intricacies of any ecological system, it is most easy to start from this crudely simple point of view.”  The ecological definitions of “food” and “eat” are easy for animals.  However, as animals must take in organic sustenance (aka.  Food), plants must take up, or “eat”, nutrients.  Classic experiments on competitive interactions between species have been conducted using nutrient limitation and fertilization experiments with plants.  However, these studies take a great deal of time—time that we do not have this semester!  Therefore, we will focus our investigations of interspecies interactions on animal interactions.

The effects of, and degree to which, predation occurs in nature has been the focus of a number of studies in community ecology.  Models of predator-prey dynamics have been around for nearly 80 years, beginning with the infamous Lotka-Volterra model from the 1920s.  Previous studies have suggested that predation rates vary depending on a several factors, including:  1) the relative abundances of predators and prey; 2) the relative sizes of predators and prey; 3) the gender of the predator; 4) physical characteristics of the prey (e.g. cryptic coloration, elusiveness), and; 5) habitat heterogeneity (as a measure of places for both predators and prey to hide).  Predation experiments lend themselves well to the laboratory since the relative size of individuals, the relative numbers of individuals, environmental conditions, and even habitat heterogeneity can be manipulated while easily measuring the number of prey consumed under controlled conditions.  Our lab today will involve quantifying the predator-prey interspecies interactions between Gambusia holbrooki andArtemia sp. (brine shrimp) under varying conditions.  Your fish will have been collected from three different [and very familiar!] aquatic settings on campus:  1) in the shallow wetland region of Hennington Pond; 2) in the deeper lake areas of Hennington Pond, and; 3) the FIU Gym Pond.  Your prey will have been laboratory raised brine shrimp.  You will be investigating controls on interspecific relationships between these two species by such variables as:  1) predator size; 2) prey size; 3) the relative numbers of predators and prey; 4) predator gender, and 5) habitat heterogeneity.  Your dependent variable—the parameter you will measure—will be predation rate, as # prey consumed per predator per unit time.

 LAB INSTRUCTIONS

1.  Generate several testable hypotheses as a class that you can test with today’s exercise.  Use the controls on predator-prey interactions listed above as helpful hints, and think about key differences between the 3 habitats where you will be catching your predators.

2.      Divide into groups and work as teams in the lab.  Work should be divided up so that all team members get to experience each aspect of the exercise.  In other words, don’t make one person record data for the entire lab exercise!

3.      Prepare your group’s lab area with a holding beaker for your brine shrimp and an experimental beaker.  Organize yourself so that your experimentation will go smoothly.  Be sure you have a watch with a second hand.

4.      Based on the hypotheses you developed, write down the different treatments of predator number, prey number, predator gender, predator size (note that you can assume a consistent prey size today).  Keep your number of experiments reasonable, but be sure you have enough manipulations to actually test your hypotheses.  NOTE:  It may actually be more efficient to split up the hypothesis-testing responsibilities through the class, so that a given test may have more treatments.  Discuss this with your TA.

5.      Be sure that you let all of your experiments run for at least 5 minutes.  It is preferable to run them until all prey have been consumed, but this may not always be possible.  Remember the units of your dependent variable.

6.      Once you have conducted an experiment with a predator, or predators, place them in the “USED” aquarium.  Since predators were starved for 24 hours before today’s experiment, there would be a bias if fish that had just eaten were used in another experiment.