Environmental Engineering Reference
In-Depth Information
Figure 5.3.
Examples of different survivorship curves exhibited by species. A Type I
curve is representative of species that have high newborn and juvenile survival.These are
typically species such as birds and mammals that engage in extended parental care. A
Type II curve indicates that mortality rate is fairly constant across all age classes. A Type
III curve applies to species with very high newborn and juvenile mortality rates and low
adult mortality. These are typically species such as lizards and amphibians that produce
many offspring in one breeding period and allow the offspring to survive the vagaries
of the environment on their own.
count for sex ratio biases.The interested reader can consult Caswell for in-
sight into building such complexity into structure population models.
In light of the above information, forecasting the numbers of individu-
als in each age or stage class from year to year requires that we know two
things: (1) number of offspring produced by a female of a given age or life-
cycle stage, (2) the probability that an individual will survive from one age
or stage class to the next.There are two ways to get these data.
1. A longitudinal study in which a cohort of newborns is followed
from their time of birth through their entire life. Age- or stage-
specific survival and offspring reproduction is estimated from this
cohort directly.This is impractical for long-lived organisms.
