BIOL1007 Lecture Notes - Lecture 20: Lemna, Exponential Growth, Logistic Function

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19 May 2018
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Multiple organisms occupying a common space
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Can be ephemeral or consistent
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Can be social, indirect (share common resource) or accidental (random chance)
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Benefits outweigh the costs
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Groups
Number of organisms of the same species in a defined geographical area
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Number of individuals or pop size
Age structure
Sex ratio
Properties
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Help understand factors that shape and drive the diversity of life
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Distrbution and abundance of individuals
Density
Ecology
Populations of organisms evolve, not individuals
Gene flow
Evolution
Invasive species
Defining threat status of taxa
Translocations and restoration
Conservation and management
Essential for
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e.g. land and water
Sessile and motile
Composition and structure influenced by life history, mobility and habitat
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Populations
How to determine population? Predict how many animals/plants there will be next year
compared to this year
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Group -> population (when does a group become a population, where to draw the line?)
Populations consist of a number of individuals, which grow, survive and reproduce
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Form is determinate
Development and growth predictable
Unitary
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Grow by addition of modules e.g. leaf and length of stem
Individuals highly variable in number of modules
e.g. Lemna sp.
Modular
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Genet - organism developed from a zygote. Defines the genetic individual in modular
organisms
Ramet - offshoot or module formed by vegetative growth that is potentially
physiologically independent
What is an individual?
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Addition of modules tends to lead to a branched form
Removal of modules may harm an organism but not kill it
Modularity may lead to natural cloning
Natural cloning arises when a genet fragments and the ramets establish in to
physiologically independent parts
Consequences of modular growth
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Individuals
L20 - groups and populations
Thursday, 12 October 2017
9:04 AM
mod 4 - ecology and ecosystems Page 1
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physiologically independent parts
Screen clipping taken: 12/10/2017 9:17 AM
Be able to describe and understand exponential and logistic models
of population growth.
Understanding temporal dynamics of pops e.g. boom and bust cycles, predator and prey
fluctuate up and down as prey consumed, predator-prey cycle show multispecies iteration
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Understand spatial distribution of pops
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Natural selection occurs within pops
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Importance of population biology
Accurately predict number of individuals in given area overtime
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May be exponential at first, but as resources become limiting, groth slows until they may
reach the carrying capcity, such growth is typically described by a logistic curve
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Populations change in number over time - can be positive or negative
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Birth
Fundamental to pop growth
Balance between additions and losses determines growth rates
Inherent to all types of population growth models
Birth and death rates
Death
Emigration (leaving pop)
Immigration (number entering pop)
Growth (individual)
Age at maturity
Sex ratio
Demographic rates (drives growth)
Rate = change/unit time, populations grow at different rates due to…
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Population growth
Only births and deaths affect population ie. No emigration/immigration e.g. isolated areas,
islands
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Pop growth rate = change in numbers of inds over time
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Nt= no. of inds in pop at time t
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Screen clipping taken: 12/10/2017 9:26 AM
Population growth in closed systems
mod 4 - ecology and ecosystems Page 2
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Document Summary

Can be social, indirect (share common resource) or accidental (random chance) Number of organisms of the same species in a defined geographical area. Help understand factors that shape and drive the diversity of life. Composition and structure influenced by life history, mobility and habitat e. g. land and water. Group -> population (when does a group become a population, where to draw the line?) Predict how many animals/plants there will be next year compared to this year. Populations consist of a number of individuals, which grow, survive and reproduce. Grow by addition of modules e. g. leaf and length of stem. Individuals highly variable in number of modules e. g. lemna sp. Ramet - offshoot or module formed by vegetative growth that is potentially physiologically independent. Addition of modules tends to lead to a branched form. Removal of modules may harm an organism but not kill it.

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