Ch 12: Population Growth

Capacity for increase, geometric vs exponential growth, survivorship, logistic growth, density dependence, human demogr. trans life tables

Capacity for increase over time, darwin example with elephants

If an elephant starts breeding at 30, stops at 90, and has 6 calves it will and survive until 100, then in about 750 years there will be 19 million elephants descended from the first pair.

Increase in Northern Elephant Seal

Populations in central california and the channel islands (more isolated) had dramatic increases because more seals are giving birth

Discrete breeding

Having periods of abundance of when breeding occurs (during spring, fall, etc). Looking at when populations spike shows breeding season.

Growth Curves

Geometric growth when breeding only occurs during breeding season, it occurs during intervals. Exponential growth occurs when breeding is continuously

How can we measure changes in a population over a period of time?

When lambda is < 1 and r is < 0, population is declining. When lambda = 1 and r = 0, population is staying the same. When lambda is > 1 and r > 0, population is growing.

Peter and Rosemary Grant study

Looked at evolution of beak size with an increase in seed hardness. Mistnetted all medium ground finches on Daphne Island, banded them, then resampled each year for 15 years, specific example was cactus finch

Survivorship Curve Type I

Humans and bears, good survivorship through adult hood, most individuals die in older ages

Survivorship Curve Type II

Birds and squirrels, decline in the number of species remains steady (at any rate)

Survivorship Curve Type III

Insects and flowers, high mortality young in life but those that make it typically mature

Exponential vs logistic growth

Exponential growth has “K” which describes the ones that do well at carrying capacity and above the inflection point it levels off. Logistic growth does not account for carrying capacity

Human demographic transition

Countries across the world are at different stages of this transition. Pre-industrialization, birth and death rates are high, therefore population is stable. After industrialization,

Density dependence

refers to how environmental factors influence population growth rates, with the impact varying based on the population's size or density, In song sparrows, increase of territorial males also increases the number of “floating males” that arent reproducing.

Big project research question

How do pollinator amounts and individuals differ across campus in regards to flower richness?