Our research follows the scientific method.
Click on each step of the scientific method to see how the Mitchell lab follows that step.
Make an Observation
An observation that sparked interest in the Mitchell lab is that infectious disease can be greater in communities with lower host species diversity. For example, in this figure, the number of humans with lymes is greatest when there are few small mammal species.
Ask a Question
After doing a lot of background research, we asked: "Is the community composition more important than the species richness?" Do you remember what composition and richness are? If not, click here for a reminder.
After asking a question we usually do a lot of background research, we read related papers written by other researchers, conduct preliminary experiments or make observations in nature. This helps us form a good hypothesis.
Form a Hypothesis
The Mitchell Lab decided to test the hypothesis that "Host species in ecosystems that have a high abundance of reservoir species have a greater risk of infection compared to ecosystems without reservoir species." A reservoir species is a species that is easily infected by a pathogen, and is also good at passing on the disease.
Test the hypothesis
We design an experiment very carefully to test our hypothesis. We change one condition of the experiment while keeping all the other conditions the same. Since we are interested in composition (i.e., reservoir species), we hold species richness constant and only vary the presence or absence of a reservoir species.
We replicate both types of grass communities (with reservoir species and without reservoir species) and average the results. If you wanted to know the average height of adults in North Carolina, and you chose just one random adult to measure, you might choose a college basketball player who is 7'1". Would this represent all adults in North Carolina? Of coarse not, but if you chose 100 random adults in Nort Carolina and take an average of their heights, that height would be more representative of the whole state. In the same way, if we make 10 replicates of each type of community we get a better representation of each type of community.
Analyze the data
We organize the data from our experiments so we can understand the results. We make charts and graphs, and perform complex statistical analysis to help us see patterns in the experimental observations.
Support or reject the hypothesis
Remember our hypothesis was "Host species in ecosystems that have a high abundance of reservoir species have a greater risk of infection compared to ecosystems without reservoir species". The data showed that in plots where Avena fatua, a good reservoir species, was present more plants were infected. This confirms our hypothesis!
This experiment partly answered our question and more information is needed to fully explain why decreasing biodiversity causes an increase in infectious disease. Other experiments in the lab are building on this result. We are currently investigating what makes some species good reservoirs while other species are not good reservoirs. We are also investigating how the presence of diseases can cause reservoir species to thrive while non-reservoir species die off.
Take a quiz to see if you understand experiments! Click on TEST YOURSELF.