Comparative Thermal Physiological Ecology of Syntopic Populations of Cacama valvata and Tibicen bifidus (Homoptera: Cicadidae): Modeling Fitness Consequences of Temperature Variation

SYNOPSIS. This paper develops a model based on egg-laying ratesand female oviposition temperature preferences in two speciesof cicada, Cacama valvata and Tibicen bifidus, from a centralNew Mexico desert grassland habitat. Output from the model indicatesthat C. valvata achieves maximal daily egg production (eggsfemale^–1 day^–1) on days when maximum shade ambienttemperatures reach 41°C; the corresponding value for T.bifidus is 33°C. These differences correlate with the thermalregime experienced by each species in its respective typicalhabitat. Simulations of the effects of variation in mean habitatambient temperature on egg production demonstrated that knowndistributional limits for T. bifidus correspond to thermal conditionsthat reduce daily egg production by only about 5–10% relativeto long-term means at the study site. The same is true for C.valvata only in lower-ambient temperature habitats. In higher-temperaturehabitats, C. valvata exhibits an unusual plasticity in the timingof adult activity and reproduction that allows it to occupya much wider geographic range than T. bifidus. Contrary to expectations,frequency distributions of predicted daily egg production rateswere negatively skewed in each species' respective ‘typicalhabitat’, and Gaussian only in thermally marginal habitats.The findings are discussed in the context of attempts to modelpopulation- and community-level effects of climatic change.