Abstract: Most invertebrate models incorporate only one environmental parameter like temperature or disturbance, judging one variable to be more important than the others. However, the interplay between temperature and disturbance regimes may be important for population dynamics, as species have evolved a specific life history in order to respond to variable temperature and disturbance regimes. Invertebrate species vital rates, including growth rate, maturation rate, and fecundity, are mediated by temperature regimes, seasonality, and pulse and press disturbances. Pulse disturbance events cause immediate mortality, followed by a population rebound, which is dependent on the magnitude, frequency, and duration of the pulse disturbance. Press disturbances cause consistent mortality throughout time, in response to suboptimal conditions. Invertebrate fecundity, growth, and maturation time are closely linked to temperature regimes. Our goal was to develop a novel time-varying stage-structured mechanistic matrix model that allows vital rates to change as a function of temperature regime and disturbance type, frequency, and magnitude. We parameterized the model with data from the literature for three aquatic invertebrates from the Colorado River ecosystem with different life-history syndromes: Potamopyrgus antipodarum, New Zealand Mud Snail, an ovoviviparous snail; a Hydropsyche spp, a univoltine net-spinning caddisfly, and a Baetidae spp, a multivoltine mayfly. In our model output, we detected an interaction between pulse timing temperature-mediated reproduction. In a high temperature dependent invertebrate (P. antipodarum), population rebounds were either dampened or amplified when seasonal timing of disturbance was changed, while organisms with a larger temperature threshold (i.e. Hydropsyche spp) had no response to changes in timing. Finally, we identified combinations of pulse magnitude timing and temperature regime where baetids species abundances fell below an extinction threshold, showing that some environmental scenarios could cause local extirpation. As anthropogenic climate change alters not only temperature and thermal gradients, but also disturbance event timing and magnitude, ecosystems will be exposed to novel environmental scenarios. Models can help us understand how these complex changes might play out and how organisms with different life histories could respond.
