# BISC 102 Lecture Notes - Lecture 16: Logistic Function, Local Extinction, Anthropocene

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Individuals in a population use common resources, cope with similar environmental

factors, and interact with one another and with their environment.

Population Ecology: Variation in space

● Population ecologists describe populations and ask questions about how

individuals vary through space

○ Demography: The statistical study of how population size/structure change

over time. (Population Structure)

■ Life Table: A summary of deaths/survivors at various age classes for

a population

● Population characteristics

○ Range: Geographic area a population resides in

○ Dispersion: Pattern of spacing between individuals

■ Clumped: Individuals aggregated into patches

■ Uniform or Regular: Individuals evenly spaced (maintain individual

distance)

■ Random: Unpredictable spacing of individuals. It occurs when biotic

and abiotic conditions are relatively homogenous

○ Size: number of individuals

■Small populations can be counted directly

■Larger populations are estimated using sampling

● Sampling: counting a proportion of the population to estimate

the total number of individuals per unit area

■ Quadrat sampling: Organisms that are sessile (e.g. plants,

barnacles) or slow moving (e.g. sea stars)

● Quadrat: Sampling area of any size or shape (e.g. 1 m2 )

● q/Aq = N/Ap

○q = average # individuals per quadrat

○Aq = area of the quadrat (cm2 , m2 )

○Ap = area inhabited by the population (same units!)

○N = estimated population size

■ Mark recapture sampling: Used to estimate the population of mobile

animals.

○ Density: number of individuals per unit area

○ Age structure: number of individuals of different ages

○ Sex ratio: ratio of males to females

Survivorship curves (logx )

●Survival patterns can be tabulated using life tables, and presented as survivorship

curves

○ Type 1: mortality increases with age

○ Type 2: mortality is constant over time

○ Type 3: mortality decreases with age

Correlated life history traits: Survivorship is often correlated with other aspects of life

history.

● Strategy A

○Breed young

○Many small babies

○Little parental care

○Die young