-Survivorship is key to understanding life tables, and, as a result, the changes in a population over time.
-For example, if individuals in a particular species have several thousand offspring, you would believe that the environment would be overrun in a short time, they would consume all the resources available to them, the population would crash, and maybe the community would suffer as well.
- However, if few of these offspring survived long enough to consume many resources, you would expect a dramatically different outcome.
Remember, survivorship is the proportion of offspring produced that survive to a particular age.
-it's an example of General Adaption Syndrome and Intraspecific competition
a. In the summer of 2012, much of the NE U.S. saw a significant increase in the gypsy moth (Porthetria dispar). As the summer wore on, the larvae (caterpillars) pupated; the hatched adults mated, and the females
b. laid masses of eggs (each mass containing several hundred eggs) on virtually every tree in the region.
c. In May/June of 2013, the young caterpillars that hatched from these eggs began feeding and molting.
d. The results were dramatic: Large patches of forest began to take on a winter appearance with their skeletons of bare branches. For example, in a documented 72-hour period, a 50-ft beech tree and a 25-ft white pine tree were completely defoliated (gypsy moth caterpillars really don't do well developmentally when eating white pine). In fact the infestation was so heavy that many trees were completely defoliated before the caterpillars could complete their larval development.
e. The result: a massive die-off of the animals; very few succeeded in completing metamorphosis.
f. Here, then, was a dramatic example of how competition among members of one species for a finite resource — in this case, food — caused a sharp drop in population size.
g. The effect was clearly density-dependent. In comparison, the lower population densities of the previous summer had permitted most of the animals to complete their life cycle.