Effects of temporal variation in temperature and density dependence on insect population dynamics

Authors: HARIDAS, CHIRAKKAL - University Of Nebraska; MEINKE, LANCE - University Of Nebraska; Hibbard, Bruce; SEIGFRIED, BLAIR - University Of Nebraska; TENHUMBERG, BRIGITTE - University Of Nebraska

Submitted to: Ecosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/8/2015
Publication Date: 5/31/2016
Publication URL: http://handle.nal.usda.gov/10113/62635
Citation: Haridas, C.V., Meinke, L.J., Hibbard, B.E., Seigfried, B.D., Tenhumberg, B. 2016. Effects of temporal variation in temperature and density dependence on insect population dynamics. Ecosphere. 7(5). doi: 10.1002/ecs2.1287.

Interpretive Summary: Mathmatical models can assist in our understanding of biological systems including insect population dynamics. Models including random factors for temperature, rainfall, population levels, etc., can increase the realism of the model versus models without random factors. Including population density-dependent factors (i.e., factors that depend on the size of the population and distribution of individulas within the population) into the model can also assist in achieving realistic model output for pests with such growth constraints. We developed a population model to study how density-dependent survival and random variation in soil temperature and other factors may influence the population dynamics of the western corn rootworm (WCR). In the model, survival was affected by population density, but only at relatively high population levels and in years with low population density, stable population dynamics are less likely. The general modeling framework provides a structure for future work and contributes to our basic understanding of the population dynamics of WCR major pest and how management strategies to control them will fare in the field.

Technical Abstract: Understanding effects of environmental variation on insect populations is important in light of predictions about increasing future climatic variability. In order to understand the effects of changing environmental variation on population dynamics and life history evolution in insects one would need models that integrate density-dependent vital rates with stochastic environmental drivers like temperature. In this work we determined the relationship between density and daily larval survival in a univolitne insect species using field-derived data. We used this relationship and the developmental time for completing the larval stage to develop a population model. We evaluated a deterministic model where the developmental time was fixed and a stochastic model where the developmental time varied annually depending on the random variation in soil temperature. Our results showed that density-dependence could be strong in the field and that stochastic variation in soil temperature could either enhance or diminish the effect of density. The deterministic model produced different dynamics, ranging from stable equilibrium to cycles and unstable dynamics, depending on model parameters. The results showed that the dynamics (stability, cycles etc.) of insect population densities would depend on both the mean as well as the variation in temperature. Stochastic variation in soil temperature produced large variation in predicted larval densities. Our work provides a general modeling framework to incorporate density-dependence and temporal environmental variation in insect vital rates based on field data and we showed that ignoring stochasticity in insect vital rates could lead to erroneous conclusions about population dynamics.