Population Ecology Notes

Population ecology studies the factors influencing the size, distribution, and other characteristics of natural populations.

Population: A group of organisms that interbreed more with each other than with other members of their species.
Population size: The total number of individuals in a population.
Population density: The number of individuals per unit area or volume.

Immigration:
- Movement of individuals into a population.
- Causes the population size to increase.
Emigration:
- Movement of individuals out of a population.
- Causes the population size to decrease.
Zero population growth:
- Occurs when the number of births equals the number of deaths in a population over a given interval.

For most of history, human population growth was very slow.
The growth rate began to increase approximately 10,000 years ago.
Population growth soared during the past two centuries.
Reasons for increased growth:
- Humans were able to migrate into new habitats and expand into new climate zones.
- Humans developed new technologies that increased the carrying capacity of existing habitats.

Links to websites providing real-time population statistics:
- http://www.worldometers.info/
- http://www.theworldcounts.com/counters/shockingenvironmen talfactsandstatistics/worldpopulationclock_live

People in highly developed countries use far more resources and generate more waste and pollution per capita than those in less developed countries.
Ecological footprint:
- The area of Earth’s surface required to sustainably support a particular level of development and consumption.
- People in China and India consume less than the average ecological footprint.
- The per capita footprint of the United States is more than three times the average.

The warming of Earth’s lower atmosphere and surface as a result of heat trapped by greenhouse gases.
Earth’s atmosphere reflects some sunlight energy back into space.
Some light energy reaches and warms Earth’s surface.

Earth’s warmed surface emits heat energy.
- Some heat escapes into space.
- Some heat is absorbed and emitted in all directions by greenhouse gases.

Human-induced increase in atmospheric greenhouse gases correlates with global climate change.
Current atmospheric $CO_2$ levels are the highest in 420,000 years and are still climbing.
Global climate change:
- A rise in temperature and shifts in other climate patterns.

Measurements of atmospheric carbon dioxide concentration (ppmv) at Mauna Loa, Hawaii, from 1960 to 2010, showing an annual cycle and increasing trend.

Graph depicting global temperature anomalies (°C) from 1860 to 2000, showing annual and five-year averages.

Minnesota is getting warmer and wetter.
Minnesota has warmed by $3.0$ degrees F between 1895 and 2020, while annual precipitation increased by an average of $3.4$ inches.
Most dramatic changes have occurred in recent decades.
Compared to 20th-century averages, almost all years since 1970 have been warm, wet, or both.
Each of the top-10 combined warmest and wettest years on record occurred between 1998 and 2020.
These increases are expected to continue throughout the 21st century.

Heavy rains are now more common and more intense in Minnesota than at any time on record.
Long-term observation sites have seen dramatic increases in 1-inch rains, 3-inch rains, and the size of the heaviest rainfall of the year.
Since 2000, Minnesota has seen a significant uptick in devastating, large-area extreme rainstorms.
Rains that historically would have been in the 98th percentile annually (the largest 2%) have become more common.
Climate projections indicate these big rains will continue increasing into the future.

The estimate of total duck abundance excluding scaup, was 387,000, which was 20% below last year's estimate, 35% below the 10-year average estimate, and 37% below the long-term average estimate.
The estimated number of Canada geese was 106,000 and 7% lower than last year and 31% below the long-term average estimate.