Environmental Engineering Reference
In-Depth Information
Figure 5.1.
Depiction of life-cycle transitions and contributions of different stage class-
es to the overall population size and structure using loggerhead sea turtles as an exam-
ple.The figure depicts life-history transitions of six stage classes (Eggs/hatchlings, Small
juveniles, Large juveniles, Subadults, Novice breeders, and Mature adults). Horizontal
arrows indicate that individuals in one stage class grow older during the course of a sea-
sonal life cycle. Upward angled arrows identify those stage classes that produce offspring
at the beginning of a season. The parameter m with stage-specific subscript represents
stage specific reproduction; the parameter p with stage specific subscript represents
stage-specific survival.
sociated with the arrows represent parameter values.The p-values represent
the average probability that an individual will survive from the beginning
of one age class to the next age class, called age-specific survival.The m-val-
ues represent the average contribution of an individual of a specific age class
to the reproductive pool of the population, called age-specific fecundity.
Many analyses of population dynamics assume that here is one-year dif-
ference in age between the age classes in the population because many
species undergo annual breeding cycles. Considerations of population dy-
namics based on such age structure are called
age-structured population dynam-
ics
(Caswell 2001). Often, however, individuals from several different
breeding seasons could be considered to be in the same life-cycle stage. For
example, human teenagers comprise individuals from ages thirteen to nine-
teen; young adults are individuals say between the ages of twenty and thirty.
In such cases, all individuals within an age class (e.g., teenagers) do not all
become one age class older (e.g., young adults) over the course of a year.
