A cohort is a group of organisms of the same species that are born during the same year. The term is used most frequently when describing the population dynamics of a species. Organisms that live longer, have more cohorts and have more interaction between multiple aged individuals (Demography n.d.).
Knowledge of cohorts are important in invasive biology as they may provide clues for the species introduction and establishment history. Long lived organisms that are represented with only one cohort were obviously established during that one year, however may be wiped out more easily than populations with a greater number of cohorts. In essence, more cohorts corresponds to greater population stability over time (DeAngelis et al. 1993).
DeAngelis, D. L., Rose, K. A., Crowder, L. B., Marschall, E. A., & Lika, D. (1993). Fish cohort dynamics: application of complementary modeling approaches. American Naturalist, 604-622.
Demography. (n.d.) In Wikipedia. Retrieved April 12th, 2015, from http://en.wikipedia.org/wiki/Demography#Generational_cohorts