Lecture 15 - Life History

Life history

the major events relating to an organism’s growth, development, reproduction, and survival

Life history strategy

the overall pattern in average timing and nature of life history events

Isogamy

Gametes are equal in size

Simple life cycles

lack abrupt transitions between ages or forms

Complex life cycles

have at least two stages with different body forms that live in different habitats and eat different foods

Alternation of generations

multicellular diploid sporophyte alternates with a multicellular haploid gametophyte

Semelparous

species reproduce only once

Iteroparous

species can reproduce multiple times

Allocation

energy to one function or aspect of life-history compromises energy available to other functions

Life history trade-offs

no organism has an infinite amount of energy and resources to invest

Dormancy

state of suspended growth and development in which an organism can survive unfavorable conditions

r-selected

– Selection for high population growth rates

– Short life spans, rapid development, early maturation, low parental investment, high reproduction rates

– Advantage in disturbed habitats, uncrowded conditions

– Most insects, small vertebrates (mice), weedy plants

K-selected

– Selection for lower growth rates in pops near carrying capacity

– Advantage in crowded conditions; efficient reproduction is favored

– Long-lived, develop slowly, late maturation, invest heavily in each offspring, low reproduction rates

– Large mammals, reptiles (tortoises, crocodiles), longlived plants