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Ecology 1 - Population Dynamics

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Jed Doyle

on 7 May 2014

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Transcript of Ecology 1 - Population Dynamics


Where Are We?
Ecology is the study of organism interactions with each other and the enviornment.

Ecological processes occur at multiple levels of organization on Earth.

Each level of organization emerges from the processes of the level below it
Big Questions:
Make Sure You Can
How Populations Grow
Human Population Growth
All members of a species in a contiguous area.

Populations are dynamic.
Organisms enter a population in 2 ways:

Organisms leave a population in 2 ways:
Model 1: Exponential Growth
Model 2: Logistic Growth
The growth of a population continues indefinitely.
Assumes no resource limitation.

Can be described by:

change in number of individuals (
change in time (

): the "
per capita rate of increase
", how many offspring per individual in the population
As long as (r) is a positive value, a population will continue to increase at an exponential rate.

Higher (r) values will lead to faster rates of increase.

if (r) is 0, the population will not increase or decrease.

if (r) is negative, the population will decrease.
The growth of a population decreases as the population approaches the "
carrying capacity
" (
) of the environment.

Models resource limitations.

The effect of (K) on (r) becomes greater as (N) approaches (K)
How are real populations structured?
How do real populations grow?
How does evolution effect life history traits?
How does the environment affect population growth?
Measuring Population Size
Population Distribution
Population Demographics
It can be difficult to estimate population size accurately.

": 1 common method
Capture and mark members of the population.
Release them.
Recapture members of the population.

Number of marked individuals Recaptured marked individuals
Total population size Total recaptured individuals
Individuals tend to be distributed in three major patterns:
Demographics: The study of a population's vital statistics and how they change over time.
Demographic Data can be arranged in tables (e.g.
life tables
reproductive tables
), or graphs (e.g.
survivorship curves
There are 3 major types of survivorship curves demonstrated in real populations:
Exponential Growth
Typically occurs in small populations, well below the carrying capcity of the environment.
Logistic Growth
Much more common. Typically populations oscillate around the carrying capacity.
Life History Traits
Any trait that affects an organism's life table.

Costs and benefits of all adaptations.
Reproductive stategies
Parental Care
: Produce a lot of offspring, once.

: Produce a few offspring, repeatedly
Number of babies varies inversely with amount of parental care
Selection for traits that maximize reproductive success at low-population densities
Selection for traits that maximize reproductive success at high population densities
The effect of population density on population growth
Density Dependent Population Regulation
Intrinsic Factors
The underlying root of all
ecological problems

Historical Human Growth Rate
The human population has been in a period of accelerated exponential growth since the industrial revolution...

...that growth rate is slowing
The decrease in growth rate is not uniform accross the globe.
As countries industrialize, various changes in demographics occur (the "
demographic transition
It is, as of yet, unclear what the global carrying capacity for the human population is.
How are populations structured?

How are populations affected by the environment?
Explain how populations can be mathematically modeled.

Describe the relationships among all terms in population models.

Compare ideal populations to real-world populations.

Explain patterns of life-history, distribution, and survivorship.

Explain the costs and benefits of particular life-history characteristic adaptations and strategies.

Describe historical and current trends in the human population.
A comparison of the exponential and logistic growth models for a population
N = ~1,100
The Agave Plant: Semelparous
Elephants (and all mammals): Iteroparous
Data showing parental survivorship as a function of brood size in kestrels.
"Age-Structure Pyramids"
Human Population Growth
Full transcript