In a factorial microcosm experiment, we parsed the components of propagule pressure by fixing the total number of individuals introduced (20) and varying the number of introduction events (1, 2, 4, or 5 events) into a novel environment that is either stable or fluctuating through time (Koontz et al., 2018). We found that several, small introductions lead to greater colonization success compared to fewer, larger introductions in by reducing extinction probability and delaying time to extinction. We proposed that this was likely due to sustained immigration alleviating genetic load. We also suggested that sustained immigration might have affected how adaptation occurred, if at all. If both adaptation and genetic load affected populations, their influences on population fitness may cancel out and be undetectable without further experimentation.

Koontz, Michael J., Meagan F. Oldfather, Brett A. Melbourne, and Ruth A. Hufbauer. 2018. Parsing propagule pressure: Number, not size, of introductions drives colonization success in a novel environment. Ecology and Evolution. 8 (16): 8043-8054. https://doi.org/10.1002/ece3.4226