Population Ecology

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Populations CANT consist of

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several species

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Phrases that can characterize a population

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Interaction individuals
Age structure
Density
Boundaries

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Population ecology

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the study of populations in relation to the environment: including environmental influences on population density and distribution, age structure, and variations in population size

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Population

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a group of individuals of the same species living in the same general area

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Abundance

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the total number of individuals in a population

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Density

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the number of individuals per unit area

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THREE ways to estimate density and abundance

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1. Count
2. Sampling techniques
3. Mark-recapture

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Count

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count all individuals within boundaries of population (e.g. sea stars in tide pools)

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Sampling techniques

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to ESTIMATE population size (e.g. oak trees in 10x100 m plots)

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Mark-recapture

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trap, mark, and recapture animals (eg. dolphins, prarie dogs)

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The fundamental law of population dynamics

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there are ADDITIONS: births, immigration (combine to form population size)

and...

SUBTRACTIONS: emigration and deaths

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Equation for fundamental law of population dynamics

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change in N = (B + I) - (D + E)

B=births
I=immigration
D=deaths
E=emmigration

N=population size

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demography

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study of the statistics of populations and how they change over time

FOCUS on birth rates and death rates

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Change in population size during time interval=

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BIRTHS during interval-DEATHS during interval

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Equation from above

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[Change in N/Change in Time]=B-D

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Per capita birth rate (b)=

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average # births per individual during a specific time interval (ex. year)

if population = 1000 individuals, births 34/yr,
b= 34/1000=.034

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Per capita death rate

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average # deaths per unit time per individual

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The change in population size N in an interval of time (using per capita birth and death rates)=

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change in N/change in T = bN-dN

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"r" =

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per capita rate of increase: r=b-d

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If r>0...

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population is GROWING

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If r<0...

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population is DECLINING

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Expontential growth occurs when

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resources are unlimited and the rate of increase is at its maximum

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In a J curve...

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rate of increase is constant, but population accumulates more individuals when it is large than when it is small

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Exponential growth tends to occur when:

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1. Populations are INTRODUCED to the new environment
2. Populations are REBOUNDING from a population crash

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Populations do not

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increase forever

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Carrying capacity (K)

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maximum population size that a particular environment can support

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Rate of population growth __________ as population size (N) approaches carrying capacity (K)

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slows