Population Ecology

What is a Population? An interbreeding group of the same species living in the same general area may be distinguished by natural or arbitrary boundaries

Population Density vs Dispersion the number of individuals per unit area or volume the pattern of distribution of individuals

Patterns of Dispersion What is the pattern for the population on the previous slide? On the title slide?

Population Dynamics

Demographics Life table: age-specific summary of survival pattern of a population Survivorship Curve

Survivorship Curves I – Fewer offspring and low mortality until old age due to parental care. III – Many offspring & high mortality in young due to lack of parental care. II – Death rate is relatively constant throughout the life span.

Reproductive Rates focus on females reproductive tables: age-specific summary

Semelparity vs Iteroparity reproduce once MANY offspring most offspring die offspring are “on their own” reproduce repeatedly FEW offspring most offspring survive Offspring are cared for

Population Growth Rate Births (B)Deaths (D) – = Change in population size per unit time (  N/  t) Per capita birth rate (b): average # offspring produced by individual Per capita death rate (m): used for expected # of deaths Per capita rate of increase (r) bN – mN =  N/  t rN =

r > 0 : population is growing r < 0 : population is shrinking r = 0 : zero population growth (ZPG) Simplifying the Population Growth Rate bN – mN =  N/  t rN = r = b – m

Exponential Growth r is steady & positive Maximal growth rate Abundance of resources J-Curve Growth

Logistic Growth Model carrying capacity (K): Max population size habitat can sustain

Logistic Model & Real Populations Growth rate decreases approaching K or Population size overshoots K, then decreases as a result

Trade-offs in life history Trade-off between reproduction and survival Invest in numbers of offspring or in provisions to offspring? K–selected competitive species r-selected opportunistic species

Regulation of Population Growth Density-independent factors: unrelated to population density

Density Dependent Factors: change in response to population density decrease birth rates and/or increase death rates closer to the carrying capacity

Density Independent vs Density Dependent Growth

Population Dynamics Fluctuate due to changes in weather & climate, resources, predator population size, pathogens

Human Population Growth

Why the Population Explosion? Industrial Revolution Medical & Biotechnology Revolution

Human Growth Rate is Decreasing

The Demographic Transition high birth & death rates high birth, low death rates (population expansion) low birth & death rates Key: education of women!

Age Structures useful for predicting future population growth

Ecological Footprint surface area required to sustain each person (at current levels of consumption)

Worldwide Energy Use

One person in the U.S. consumes more than 20 times the resources of a person living in an LDC.