45.2 Life Histories and Natural Selection

Humans and most mammals have a survivorship curve because death occurs in the older years.
Birds have a curve of death at any age.
People are more likely to survive after a certain age, which is why trees have a type III curve.

Energy is required by all living organisms for their growth, maintenance, and reproduction; at the same time, energy is often a major limiting factor in determining an organisms survival.

Plants use the sun's energy to grow, maintain health, and produce energy-rich seeds to produce the next generation.
Animals have to use some of their energy reserves to get food.
Some animals need to care for their offspring.

fecundity is how many offspring can be produced if an individual has as many as possible, repeating the reproductive cycle as soon as possible after the birth of the offspring.

fecundity is related to the amount of parental care given to an individual offspring.
Many marine invertebrates that produce many offspring don't provide much care for their offspring because they don't have the energy or the ability to do so.
Their energy budget is used to produce many tiny offspring.
At a very early age, animals with this strategy are often self-sufficient.
The organisms have made tradeoffs to maximize their evolutionary fitness.
Because their energy is used for producing offspring instead of parental care, it makes sense that they have the ability to move within their environment and find food and shelter.
The production of many offspring allows enough of them to survive despite their small size, as they are vulnerable to predation.

During a reproductive event, animal species that have few offspring usually give extensive parental care, devoting much of their energy budget to these activities, sometimes at the expense of their own health.

Plants with low fecundity produce few energy-rich seeds, like coconuts and chestnuts, with each having a good chance to grow into a new plant.

Plants with high fecundity usually have many small, energy-poor seeds, like orchids, that have a relatively poor The energy tradeoff of the orchid is very effective, even though coconuts and chestnuts have a better chance of surviving.
For large numbers of seeds or for fewer seeds with more energy, it's a matter of where the energy is used.

Organisms that reproduce at an early age have a greater chance of producing offspring, but this is usually at the expense of their growth and health.

When organisms start reproducing later in life, they have greater fecundity or are better able to provide parental care, but they risk not surviving to reproductive age.

In fishes, examples of this can be seen.
guppies use their energy to reproduce quickly, but never reach the size that would give them defense against some predator.
The risk of dying before they can reproduce or at least reproduce to their maximum is why larger fish use their energy to attain a large size.
Understanding the evolution of each species is dependent on different energy strategies and tradeoffs.
Some species blow it all and use most of their energy reserves to reproduce early before they die.
Other species delay having reproduction to become stronger, more experienced individuals and to make sure that they are strong enough to provide parental care if necessary.

fecundity, timing of reproduction, and parental care can be grouped together into general strategies that are used by multiple species.

The species use most of their resources during a single reproductive event, sacrificing their health to the point that they do not survive.
Bamboo flowers once and then dies, and the Chinook salmon uses most of its energy reserves to migrate from the ocean to its freshwater habitat, where it reproduces and dies.
There are differing explanations for the evolutionary advantage of the postreproduction death of the Chinook, including a programmed suicide caused by a massive release of hormones, or a simple exhaustion caused by the energy demands of reproduction.

An example of an animal that goes into a seasonal estrus cycle is the pronghorn antelope.
The estrus phase of the cycle is when females of these species mate.
Humans and Chimpanzees may attempt reproduction at any time during their reproductive years, even though their menstrual cycles make pregnant only a few days per month.

During the reproductive life of the pronghorn, it mates at specific times of the year.
Humans and Chimpanzees can mate on any day of the week.