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Slide 2 of 27
Ecology
Def – Study of the interactions of organisms with their physical environment & with each other
Population – Group of individuals of one species living in one area who are able to interbreed and interact with each other
Community – All organisms living in one area
Ecosystem – all the organisms in a given area & the abiotic (non-living) factors with which they interact
Abiotic (non-living) – temperature, water, sunlight, wind, rocks, & soil
Biosphere – global ecosystem
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Biosphere
Ecosystem 1
Ecosystem 2
Ecosystem 3
Abiotic Factors
Pop 1
Pop 2Pop 3
Community
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Population Properties
5 Properties1. Size – Total number of individuals in a population
-- Typically represented by N
2. Density – The number of individuals per unit area/volume-- Here we are measuring not population size but how closely packed they are into an area-- For example: which population is more dense: Manhattan’s
or Weston’s?-- Sampling techniques used to estimate the number of organisms living in an area
-- One sampling technique is called mark & recapture
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Mark & Recapture Method
Sampling technique used to estimate population size
Organisms are captured, tagged, then released
Then at some future time, the process is repeated
Example: 1st catch: 50 whippets tagged
2nd catch: 100 whippets captured, but only 10 tagged
catchndrecapturesofNumber
catchndcapturedTotalcatchstmarkednumberN
2
)2()1(
50010
10050
N Population Estimate = 500
whippets
Slide 6 of 27
Population Properties (Page 2)
3. Dispersion – Pattern of spacing of individuals within the area the population inhabitsa) Clumped
-- Most common pattern of dispersion-- Pack animals
b) Uniform-- Animals that defend their territories -- Certain plants which secrete toxins that keep away
other plants that compete for the same resourcesc) Random
-- Spacing occurs in absence of any spatial factors-- Uncommon pattern in nature-- Tree spacing in a forest
Slide 8 of 27
Population Properties (Page 3)
4. Survivorship Curve (Mortality Curve)-- Show the size & composition of a population -- 3 basic types
a) Type I -- Low death rates in young & middle age-- High mortality in old age-- Humansb) Type II-- Constant death rate over entire life span-- Hydra, reptiles, & rodentsc) Type III-- High death rate among young, but then slows-- Fish & Invertebrates (external fertilization)
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Population Properties (Page 4)
5. Age Structure Diagrams-- Shows relative number of individuals at each age
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Age Structure Diagrams
Curve I – Afghanistan Pyramidal shape Bottom heavy or majority of population is young May indicate future population explosion Alternatively, may indicate population pressure
The majority of population will die young
Curve II – USA Stable population Experiencing little or zero population growth Birth & death rates are equal = numbers in each age group
is the same
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Population Growth
Biotic Potential Maximum rate at which a population could increase
under ideal conditions Maximum reproductive capacity of a population under
optimum environmental conditions.
As should be evident, this is probably never true If true, it will only exist briefly Used more for comparison to the actual situation
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Biotic Potential Factors
1. Age of reproductive opportunity onset
2. Reproductive Life span
3. Number of reproductive periods during lifetime
4. Number of offspring produced in each reproductive event
Also called Variables of Life History
-- The variables that affect an organism’s schedule of reproduction and survival
Slide 14 of 27
Exponential Population Growth
Simplest model for population growth is exponential growth Represents unrestrained growth Unlimited resources No predation/parasitism No competition No immigration/emigration
Example: introduction of a foreign organism into a stable ecosystem Humans have experienced exponential growth for ~300 yrs.
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Exponential Growth is Constrained
Populations grow exponentially at first, but then grows logistically S-shaped curve Highest growth rate is at intermediate population size
An example of constrained optimization
There is an environmental limit to population size Carrying Capacity – the population size that an
environment will permit Referred to as K
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Factors influencing Population Growth
2 main factors Density-dependent factors – factors that increase
directly as the population density increases K-selection (K = carrying capacity) Associated with logistic growth
Density-independent factors – factors that are independent of the density of a population r-selection (r = growth rate) Associated with exponential growth
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Different Life History Strategies
1. r-strategists Reproduce rapidly Small but numerous offspring Little or no parenting Insects
2. K-strategists Large but few offspring Intensive parenting Mammals (Chimps)
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Regulation of Population Growth
Density-dependent factors Competition for resources Territoriality Predation Infectious Disease
Density-independent factors Naturally occurring disasters, such as fires, floods,
earthquakes, & hurricanes (not The “U” type of hurricane, though they were a disaster last year)
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Typical Populations
Boom-and-bust cycles are common in populations over time Due to complex interactions between biotic and abiotic
factors
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Predator-Prey Relationships
--Exponential Growth then crash
-- Lynx population follows the hare pop.
-- Cycles in hare due to food availability (grass overgrazing), disease, or predation
-- Cycles in Lynx due to hare availability
Slide 24 of 27
Human Populations
Until 1650, human populations were very low growth
Humans have experienced high growth rates since about 1650
Since 1970s, population growth has decreased over time
Slide 25 of 27
Demographic Transition
Individual country populations vary widely in size and growth rates, but economic development leads to a demographic transition
From: high birth rates – high death rates = 0 growth
To: Low birth rates – Low death rates = 0 growth
Typically, death rate falls Fast population growth Due to medical care & Santiation
Too many people, so birth rates fall as well