Compléter ES Age Structure and Sex Ratios pp 108-109Version en ligne pages 108 and 109 of the textbook par rpedelty 1 single ages stable post ratio unbalanced age older distribution rapid growth quickly frequencies reproductive males pre females group numbers decline increase Different populations have different mixes of ages . Likewise , populations can vary in the proportion of and present . These differences can affect how a population grows . Populations almost always include individuals of different . Age structure , or age , describes the relative numbers of organisms of each age within a population . Age pyramids , or age structure diagrams , are visual tools scientists use to show the age structure of populations . The width of each horizontal bar in the diagram represents the relative size of each . Individuals capable of having offspring make up the group . Young individuals who have not yet reached the age where they can have offspring are called - reproductive . Older individuals past the age of having offspring are called - reproductive . Age structure diagrams can be effective tools when predicting population . A population with an even age distribution will likely remain as births keep pace with deaths . A population made up mostly of individuals past reproductive age will tend to over time . In contrast , a population of mostly reproductive or pre - reproductive individuals is likely to over time . Populations that are " bottom heavy " are capable of growth . In this respect , the wide base of an age pyramid is like an oversized engine in a sports car - the bigger the engine , the faster it accelerates . A population's age structure diagram shows relative of males and females in different age groups . Populations with more young , prereproductive individuals tend to grow . Populations with more , post - reproductive individuals tend to decline . A population's sex is its proportion of males to females . Age structure diagrams also give information about sex ratio by providing the relative of males and females in each age group . Sex ratio is an important characteristic for populations of organisms that reproduce sexually and have distinct male and female individuals . For example , in monogamous species ( in which each sex takes a mate ) , a 50 : 50 sex ratio is often ideal . If there are too many males or females , called an sex ratio , many individuals would be left without a mate - making it much harder for any given individual to reproduce and pass on genes .
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