Life Theory: The Key To Life History Theory

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Townsend et al. (2008) 1. Most animals are unitary organisms; they are both genetically and physiologically separate and therefore these individuals can be easily recognised or set apart. Unitary organisms develop from zygote to adult with determinant form – not modified by environmental conditions. On the other hand, modular organisms form new functional modules (ramets – subunit of the genet that is physiologically viable as an autonomous fragment) from a single genetically unique individual (the genet). Modular organisms grow by repeated interactions (through asexual reproduction) of its parts (modules) into an adult of indeterminate form (coral, poison oak). When the ramets are physiologically independent, they can be counted as individuals,…show more content…
The life history theory states that the schedule and duration of key events in an organism 's lifetime are governed by natural selection to produce the largest possible number of surviving offspring thus increasing the chances of an individual to pass on its genetic material through generations to come. These events are noted in juvenile development, age of sexual maturity, first reproduction, number of offspring and level of parental investment, senescence and death, depend on the physical and ecological environment of the organism. The theory depends on evolutionary biology and ecology principles. Life history characteristics are traits that affect the life-span of an organism, and are the various investments they made in growth, reproduction, and survivorship. The key to life history theory is that there are limited resources available. Major life history characteristics include age at first reproductive event, reproductive lifespan and ageing and lastly the number and size of…show more content…
Organisms that are r-selected have a high growth rate (r) and tend to produce a high number of offspring with the least amount of parental care compared to k-s lected organisms; their lifespans also tend to be shorter whilst k-selected organisms tend to have a longer life-span. R-selected organisms are suited to life in unstable environments, because they reproduce quickly after their own birth, early, and reproduce abundantly and allowing for low survival rate of offspring due to low or no parental care. K-selected organisms occur near the carrying capacity of their environment (K), and produce a relatively low numbers of offspring over a longer period of time, and show very high parental care. They are more suited to life in stable environments in which they can rely on a long lifespans and low mortality rates thus allowing them to reproduce multiple times in their own lifetime with a high offspring survival rate. Some organisms that are very r-selected are semelparous – reproducing once before death. Semelparous organisms may be short-lived. However, some semelparous organisms are relatively long-lived. Organisms with longer lifespans are usually iteroparous, reproducing more than once in their lifetime. However, iteroparous organisms can be more r-selected than K-selected, such as a sparrow, which gives birth to several times

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