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"Life History Patterns"

By Wes Cianchette


Reproduction is the major drive for all living things

"Fitness" The ability of one organism to transmit its genetic characteristics to another.

Involves survivorship, physiological adaptations and modes of reproductions.

Section 12.1
"Reproduction may be sexual
or asexual"

Two Categories for Reproduction: Sexual and Asexual

Asexual is when the offspring produced is genetically the same as the parent

Examples are Parameciums, strawberry plants and aphids.


Sexual reproduction

Common to multicellular organisms.

When two organisms mate, they’re chromosomes come together to form a new organisms.

This offspring is a combination of genes from both the parents.

Examples are mammels, reptiles, some insects, species of fish.

Sexual Reproduction takes on several forms

Most common form, two organisms mate of the opposite sex.

Hermaphroditic= Some organisms posses both male and female organs for procreation.(Common in Flowers)

Monoecious = Only in plants, when males and females on the same stem




Some animals are known as "hermaphrodites". They are one sex at a young age, then when they mature they change into another sex. Most prominate in fish species.

This is due usually to the fact of a loss of one of the sex’s in a social group. If a group of coral fish lose all of they’re females, some males will then go on to change sex to fill in the gaps.

12.3 Mating strategies take several forms

The ability to attract a mate is know as a mating system.

Monogamy = system that is adopted by species in which the offspring need to be taken care of for a long time, by two present parents

Polygamy = Acquisition of an individual of two or more mates, none of which is mated to other individuals. Has several sub categories

Polygyny = Male gains two or more females

Polyandry = Female gains two or more males

Promiscurity = Females and males mate with no intended long standing bond

12.4 Acquisition of a mate involves sexual selection

Males are not as selective as females. Females are, due to need for high energy investment in young.

Much selection is done by competition for the female.

Sexual selection = Selecting a mate from among competing mates on the basis of some specific characteristics during courtship.

12.5 Females attempt to acquire mates with the highest fitness

Selection is found in two forms. Intrasexual selection and Intersexual selection.

Intrasexual selection = involves male to male (sometimes female to female) competition for a mate. Leads to exaggerated secondary sexual characteristics. (Ex. Antlers on deer and bright plumage on birds.)

Intersexual selection = Female choice of a male

Females choose a mate upon his characteristics, habitat, things that will improve her fitness.

Some scientists believe that superior looks on a male, also attract a female, this is believed to be that the male as superior genetic abilities, thus siring good bodies offspring.

12.6 In polygamy, females have limited information for mate choice

In polygamy environments, females usually must choose males from within a close circle of a pack or a close environment. Shown in such packs as elk and seals.

Females, in these situations, are shown to a male for mating by the dominate male of their pack. Though not of choice, the future of the pack is sealed with the best possible genetic choice for that female, as shown by the dominate male.

Other females choose males on leks or an arena. A lek is a small area which a male defends and also shows off by colors or high vocal pitches that attract a female. The female chooses her mate from these leks then moves on.


Also a way for other females to choose is known as hot spot choice. Males congregate at an area where female encounter is very high.

A third way is the hotshot model. When a dominate male enters a lek he is sought by all of the females within that area. He may perform over 90% of the copulation's that occur. This model is the most abundant way a male exhorts his dominance over others.

12.7 Organisms budget time and energy to reproduction

Reproductive effort = To achieve optimal fitness, an organism has to budget its energy and time in reproduction.

Semelparity = An organism expending all of its energy in one suicidal act of reproduction. Employed by fish and insects.

Iteroparous = Organisms that choose to spawn fewer young, and wish to sire offspring more in their life.

Optimal lifetime reproductive success = The ability of an organism to reproduce fully in its lifetime.

12.8 Parental investment relates to the number of young

Amount of attention paid to offspring depends on size of litter.

To ensure the achievement of the well off offspring, parents will pay more attention to those that will succeed, and simply forget about others that will not

Altricial = Animals that need considerable parenting

Precocial= Offspring that are able to look after themselves when they are born.

12.9 Environmental conditions influence the number of young

The number of young that can survive will be the ones who can adapt to such environmental that they live in.

Organisms with a lot of offspring can afford losses of young, most prominate in plants. Seedlings can number in the thousands.

12.10 Food supply affects the production of young

In certain regions, production of offspring reflects abundance of food in area.

Yet parents cannot predict food availability so only some of they’re offspring can live. The others are taken care of by siblicide. The killing of one sibling by another.

Early born young are much more well off, because when they become a little older, begging for food becomes much more prominate. Therefore parents are left with dealing the older siblings more then the younger ones. The younger ones usually die from this type of treatment.

12.11 The number of offspring may vary with latitude

Many animals at higher latitudes have larger amount of offspring then they do at other levels.

Due to the fact that food is much more abundant for them and predators are scarce where they are.

Population density is regulated by offspring mortality in winter.

12.12 Fecundity relates to age and size

Fecundity = Potential ability of an organism to produce eggs or young

Fecundity and size of litter rely on age and size of parents.

Examples in plants, smaller plants produce less seeds. Also in fish, as they mature, ability to sire offspring grows, also do sizes of litters.

The ability to produce offspring also rely’s heavily on the mothers body size. Females with larger body weights produce more offspring and more of them survive to adulthood.

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