Studies of invasive species have shown that introduced species have great potential for rapid adaptation. This explains how many introduced species are able to establish and become invasive in new environments. In addition, the rate at which an invasive species can spread can be difficult to ascertain by biologists since population growth occurs geometrically, rather than linearly. When bottlenecks and founder effects cause a great decrease in the population size and may constrict genetic variation, the individuals begin to show additive variance as opposed to epistatic variance. This conversion can actually lead to increased variance in the founding populations which then allows for rapid adaptive evolution. Following invasion events, selection may initially act on the capacity to disperse as well as physiological tolerance to the new stressors in the environment. Adaptation then proceeds to respond to the selective pressures of the new environment. These responses would most likely be due to temperature and climate change, or the presence of native species whether it be predator or prey. Adaptations include changes in morphology, physiology, phenology, and plasticity.