Populations 1 Population Parameters Population growth

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Populations 1-Population ParametersPopulation
growth
Readings Chapters 9 10 (pp 133-136 only) Krebs
Ecology
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Populations 1 - Population Parameters I.
Definition of Population II. Key Population
Parameters III. Measuring Populations 1.
Density 2. Natality 3. Mortality 4.
Immigration and emigration
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I. Definition of Population

• A population is a group of organisms of the same
  species that occupy a particular space at a
  particular time
• Deme the breeding population

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What defines a population?
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Individuals vs. Populations
Light, water, temperature
Habitat
Competition
Chemical factors
Individuals - each genetically different
Dispersal
Natural Selection
Population range of genetic characteristics
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Phenotype (bill size)
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Populations 1 - Population Parameters I.
Definition of Population II. Key Population
Parameters III. Measuring Populations 1.
Density 2. Natality 3. Mortality 4.
Immigration and emigration
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Population Parameters

• Density Number of organisms per unit space
  (area or volume)
• Natality the reproductive output of a
  population per unit time
• Mortality the number of deaths in a population
  per unit time
• Immigration the number of individuals moving
  into the area occupied by the population per
  unit time
• Emigration the number of individuals moving
  out of the area occupied by the population per
  unit time

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II. Key Population Parameters
Births (Natality)

Density (individuals per unit area)
Emigration
Immigration
-

-
Deaths (mortality
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Population Equation

• Change in Population (Density) in a stated time
• (Natality Immigration) Per unit time
• -
• (Mortality Emigration) Per unit time

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Populations 1 - Population Parameters I.
Definition of Population II. Key Population
Parameters III. Measuring Populations 1.
Density 2. Natality 3. Mortality 4.
Immigration and emigration
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1. Density

• Unitary versus modular organisms
• Modular organisms
• Some modular organisms are part of a single
  organism unit, others are not
• Ramets modular organisms that can exist
  independent of a modular form
• Genets individuals that are represented by
  original zygotes have the same genetic
  signatures

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Porcupine Caribou Herd
Population of unitary organisms
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Modular organisms
Genet
Ramets
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Modular animals
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Aspen (Populus tremeloides) in boreal forest
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Aspen (Populus tremeloides) in boreal forest
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Counting Populations

• Total counts
• Sampling methods
• Use of quadrats
• Catch and release

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Issues in using quadrats

• Individuals vs. modules
• Distribution of populations and individuals
• Adequate quadrat size
• Adequate sample size
• Random sampling
• Studying populations over time

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Quadrat sampling of grassland

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Point quadrat sampling of grassland
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Quadrat sampling of grassland

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Mean Standard Deviation Chestnut
oak 1000 241 Sugar maple 242
69 American beech 667 69
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Catch and Release Approach
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Catch and Release Approach
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Estimating Population Sizethrough
capture/recapture

• N actual size of the study population
• M total number of individuals caught in the
  first capture, marked and released
• n total number of individuals in the second
  capture
• m total number of marked individuals in the
  second capture
• M/N m/n or N Mn/m

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Capture/Recapture Example

• Sampling of trout in small lakes
• Can mark trout by clipping a fin
• M 109 fish caught in first sample and marked
• n 177 caught in second sample
• M 57 marked fish in second sample
• N Mn/m 109177/57 338 trout

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Northern Humpback Whale

• N actual size of the study population
• M total number of individuals caught in the
  first capture, marked and released
• n total number of individuals in the second
  capture
• m total number of marked individuals in the
  second capture
• M/N m/n or N Mn/m

• Whale studies in Frederick Sound, Alaska
• Two sample periods July 31 to August 3 1986 and
  August 29 to September 1 1986
• M 72, n 78, m 22
• N 7278/22 255

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Assumptions for Capture/Recapture Models

• Marked and unmarked animals are captured randomly
• Marked animals are subject to the same mortality
  as unmarked animals (Petersen model assumes no
  mortality between samples)
• Marked animals are neither lost nor overlooked

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Relative Density Indices

• Traps number of individuals caught in a trap
  per day
• Fecal pellets know number of pellets produced
  per individual per day
• Vocalization frequency used for birds
• Pelt records population size changes in animals

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Relative Density Indices

• Catch per unit fishing effort
• Number of artifacts e.g., number of nests, egg
  shells, etc.
• Questionaires
• Relative plant cover
• Feeding capacity consumption of bait
• Roadside counts common for birds
• Sightings
• Vovalization
• Faecal counts
• Tracks

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Populations 1 - Population Parameters I.
Definition of Population II. Key Population
Parameters III. Measuring Populations 1.
Density 2. Natality 3. Mortality 4.
Immigration and emigration
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2. Natality

• Natality refers to the production of new
  individuals
• birth, hatching, germination, or fission
• Fecundity and fertility are important aspects of
  natality

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3. Mortality

• Rate at which individual organisms die
• Issues with respect to mortality
• Why do individuals die?
• Why do individuals die at different ages?
• What influences longevity?

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Measuring mortality

• Direct Monitor the death rates of actual
  individuals through direct observation or
  capture/recapture methods
• Indirect monitor the abundance of successive
  age groups

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4. Immigration/Emigration

• In most populations studies, it is assumed that
  immigration emigration

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Important characteristics of populations

• In addition to counting numbers of individuals,
  population studies also look at characteristics
  of the individuals
• Most common are age, size, and sex of individuals
• Other characteristics are often measured as well

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Populations 1 - Population Parameters I.
Definition of Population II. Key Population
Parameters III. Measuring Populations 1.
Density 2. Natality 3. Mortality 4.
Immigration and emigration IV. Life Tables 1.
Diagrammatic and tabular 2. Static and cohort
life tables 3. Dynamic population parameters
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Life Tables Reading Chapter 10, Krebs.
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Number of individuals dying

• dx the number of individuals dying during the
  age interval from x to x1
• dx nx nx1

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Example cohort life table sparrows
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Mortality rate

• qx per capita rate of mortality during the age
  interval of x to x1
• qx dx / nx

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Example cohort life table sparrows
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Patterns of survivorship

• Pearl was the ecologist who introduced life
  tables to ecology
• Showed three patterns of mortality
• 1. Low early in life, high later in life
• 2. Constant mortality
• 3. High early in life, low later in life

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Static Life Table

• Another form of a life table is the static life
  table
• In this case, a group of cohorts is not sampled,
  but instead a life table is created by sampling a
  population for number of individuals in each age
  group (nx) and the deaths in each age group (dx)
• Use these data to estimate mortality rate (qx)

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Why use a static life table?

• It is not always possible to follow a population
  of cohorts throughout their entire lifetime
• Examples
• migrating fish (salmon)
• humans

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Do cohort and static life tables give the same
information?

• Only if the conditions to which the population is
  exposed that influence mortality and survivorship
  stay constant