🪲 How temperature affects ectotherms competition🌡️
My first research project concerned how temperature affects coexistence in ectotherms (e.g., insects, reptiles, amphibians, fish). I performed this research with Dr. Priyanga Amarasekare.
In this project, we first built a mathematical model of ordinary differential equations describing exploitative competition between two ectotherm consumers sharing a single resource (see “The model” in the below figure and see the paper for more details). Importantly, key vital rates of ectotherms exhibit well-characterized responses to temperature (e.g., consumer attack rate / birth rate and mortality rate; see “thermal response of parasitoids”, panels a-d for an example). We then asked the question: “if we include seasonal temperature variation, when might the two consumer species coexist?” and derived conditions under which we expect deterministic coexistence in the model.
The left-hand equations show the system of ordinary differential equations describing the dynamics of the Resource (\(R\)), Consumer 1 (\(C_1\)) and Consumer 2 (\(C_2\)). a-d show the thermal responses of the two egg parasitoids (Trissolcus murgantiae and Ooencyrtus johnsonii). a and b show how per capita egg attack rates respond to temperature; c and d show how temperature affects mortality. e and f are plots depicting the region of coexistence for the parasitoids; the blue point shows the model parameterized with the the data in a-d. g and h show the time series from (g) the parameterized model and (h) data from the field. Link to article published in The American Naturalist
We then applied the model to a naturally occurring insect community: the harlequin bug (Murgantia histrionica) and its two egg parasitoids (Trissolcus murgantiae and Ooencyrtus johnsonii) which compete in the wild (see the above figure, panels a-d for visualizations of how temperature affects the parasitoids’ vital rates). We find that the conditions for coexistence in the model are realized when parameterized with the measured temperature response of parasitoids (see the blue dot in panels e-f). Furthermore, the parameterized model gives a time series output for the parasitoids abundances (panel g) that is very similar to the parasitoid abundances measured in the field (panel h).