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Lecture 6

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University of Toronto Scarborough
Biological Sciences
Marc Cadotte

Lecture 6: Life History Analyses Introduction ▯ - An organismʼs life history is a record of events relating to its growth, development, reproduction, and survival ▯ - When does it grow? When it does it reproduce? ▯ - Life History Strategy: timing and division of resources ▯ - Organisms do things in order to maximize benefit Life History Diversity ▯ - Phenotypic plasticity: one genotype may produce different phenotypes under different environmental ▯ conditions ▯ - Animals change they way they look, behave, depending on the context ▯ - Phenotypic plasticity may produce a continuous range of growth rates; or discrete types-morphs ▯ - Polyphenism: a single genotype produce several distinct morphs ▯ - Produce 2 very different looking individuals depending on the environment ▯ - Organisms use different strategies to optimize benefit in different environments ▯ - Organisms have evolved many different modes of reproduction ▯ - Asexual reproduction: simple cell division- all prokaryotes and many protists ▯ - Some multicellular organisms reproduce both sexually and asexually (eg. corals) ▯ - Some use both strategies in order to maximize benefits of asexual and sexua reproduction ▯ - Asexual reproduction is much faster than sexual reproduction ▯ - The pros of sexual reproduction: ▯ ▯ - individuals can take advantage of more complex environments ▯ ▯ - produce different offsprings which increases the chances of being fit to varying environments unlike ▯ ▯ through asexual reproduction (all the same, only fit to one environment)▯ ▯ - Comple life cycles: involve at least two distinct stages that may have different body forms and live in different ▯ habitats ▯ - Transition between stages may be abrupt ▯ ▯ - There is often an important shift in juvenile and adult ▯ ▯ - They donʼt look like eachother ▯ ▯ - The difference in how they look is based on the habitat they occupy ▯ ▯ - Due to this difference in habitats they utilize difference resources ▯ - Metamorphosis: abrupt transition in form from the larval to the juvenile stage ▯ - In complex life cycles, they may look different due to the fact that they donʼt consume the same resources. ▯ They are not competing with the adults since they are utilizing different environments ▯ - In simple life cycle, the young looks like the adult, just a smaller version (like elephants, ▯humans) ▯ - Complex life cycle allows utilization of different resources Life History Continua ▯ - Reproductive patterns can be categorized along several continua ▯ - Semelparous: species reproduce only once ▯ ▯ - Species include: ▯ ▯ ▯ - Annual plants: want to reproduce quickly, take advantage quickly ▯ ▯ ▯ - Aggave: vegetative growth can last up to 25 years. It also produces clones asexually. ▯ ▯ ▯ Accumulate resources until itʼs a really good year (moist year), to give its offspring the best ▯ ▯ ▯ chance ▯ ▯ ▯ - Giant Pacific octopus: a female lays a single clutch of eggs and broods them for 6 months, ▯ ▯ ▯ dying after they hatch. Accumulates resources, nutrients, and reproduce at the best, also ▯ ▯ ▯ gives its offspring the best chance ▯ - Iteroparous: species can reproduce multiple times ▯ ▯ - Species include: ▯ ▯ ▯ - Trees such as pines and spruces ▯ ▯ ▯ - Most large mammals. Make decisions about when to reproduce, depending on their ▯ ▯ ▯ environment and other factors ▯ - r-selection and K-selection describe two ends of a continuum of reproductive patterns ▯ ▯ - dN/dt = rN ( 1 - N/K) ▯ ▯ - r = intrinsic rate of increase, how quickly it increases ▯ ▯ - K = carrying capacity, how many individuals an environment can substain ▯ - r is the intrinsic rate of increase of a population ▯ ▯ - r-selection is selection for high population growth rates, in uncrowded environments, newly disturbed ▯ ▯ habitats, etc ▯ ▯ - Short life spans, rapid development, early maturation, low parental investment, high rates of ▯ ▯ reproduction▯ ▯ - K is the carrying capacity for a population ▯ ▯ - K-selection is selection for slower growth rates in populations that are a or near K, crowded ▯ ▯ conditions, intense competition, efficient reproduction is favoured ▯ ▯ - Long-lived, develop slowly, delayed maturation, invest heavily in each offspring, and low rates of ▯ ▯ reproduction ▯ ▯ - for example, female mammals lactate, using their own energies to help offsprings ▯ - A classification scheme for plant life histories is based on stress and disturbance ▯ - Different environments = different strategies ▯ - Stress: any factor that reduces vegetative growth (eg. cold temperature) ▯ - Disturbance: any process that destroys plant biomass ▯ - Grimeʼs Triangular Model: Competive plants, Ruderal plants, and Stress-tolerant plants ▯ ▯ - Competitive plants: usually good at capturing light, live a long time, invest lots of resources into
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