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Chapter 53

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

Biological Sciences
Course Code
Nancy Aguilar- Roca

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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
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
Random - is unpredictable , it just happens 9 wind blowing seeds)
Factors that affect population density are:
Ecological needs of a species
Structure of the environment
And interactions among individuals within the population
Demography - is the study of vital statistics of populations and how they change over
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
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