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Chapter 53

BIO SCI 94 Chapter Notes - Chapter 53: Survivorship Curve, Exponential Growth, Carrying Capacity


Department
Biological Sciences
Course Code
BIO SCI 94
Professor
Nancy Aguilar- Roca
Chapter
53

Page:
of 2
Chapter 53 Population Ecology
Wednesday, March 5, 2014
10:21 PM
Density and Dispersion
Density- number of individuals pre unit area or volume
Dispersion - pattern of spacing among individuals
Density: A dynamic Perspective
Sometimes we could al individuals, other times , not so much .
Instead ecologists use formulas to estimate
Or use number of nests , burrows and tracks
Mark recapture method -estimate size of wildlife populations
Density isn't a static property, it changes when individuals are added or subtracted from a
population
Immigration - when an individual moves into a population
Emigration - when an individual "peaces out"
Patterns of Dispersion
Clumped- individuals live in patches
Uniform - evenly spaced out ( this seems quite subjective)
This might result from competition for resources
Territoriality - defense of bounded physical space against encroachment by other
individuals
Random - is unpredictable , it just happens 9 wind blowing seeds)
Demographics
Factors that affect population density are:
Ecological needs of a species
Structure of the environment
And interactions among individuals within the population
THESE ALSO INFLUENCE OTHER CHARACTERISTICS OF POPULATIONS
Demography - is the study of vital statistics of populations and how they change over
time.
birth rater and death rates
Life tables
Life tables are age specific summaries of the survival pattern of a species
you can go about making a life table by tracking down the lives of a cohort
Or a group of individuals that are the same age, from birth to death
Survivorship Curves
Survivorship curve- Graphic method of representing some of the data in a life table plot
of proportions of cohorts still alive
Type one curve -curve is flat at the start , low death rates early in life and then drops once
someone gets somewhat old
Type 3 drops right at the beginning , babies die fast but flattens out
Type 2 is a 1x slope, so the is constant death everywhere
Exponential Growth Models describes population growth in an idealized unlimited environment
Without dying , a species can reproduce a huge amount with inhibitions
Per capita rate of increase
Increase with every birth , decreases with every death
Number of offspring produced per unit time by an average member of populatiion
Per capita death rate - how many deaths per unit time
Ecologists are interested in the difference between death and birth rate
Zero population growth- when death and birth rates are at equilibrium
Exponential growth- population increase under ideal conditions
53.3 Logistic model describes how a population grows more slowlt as it nears its carrying
capacity
Carrying capacity , max population size an evironment can carry
Crowding and lack of resources slow down population rate
Life History
3 variables
When reproduction begins
How often the organism reproduces
And how many offspring are produced