1. Image: Encyclopedia of Life Flickr
“On average, ants monopolize 15 – 20% of the terrestrial animal biomass.” – Schultz (2000) PNAS
Image: Encyclopedia of Life Flickr
Ants rule the world

2. What controls population size?
Trophic efficiency
Not everyone can be a human/eagle/tuna
Age structure
Density-dependent (bottom-up)
Limiting resource: food, growing space
Predation (top-down)
Density-independent
Fire, cold winter

3. Recall: ~10x the biomass of lower trophic level to support consumer
Image: biologycorner.com

4. Energy is released

5. Age structure
How many individuals fall into particular age categories (i.e. cottonwood data)
Predict how fast a population can grow
Reproductive age females
In some species, egg production increases with body size/age

6. Density-independent
Same effect on individual’s survival probability at any population size
Cold winter kill birds or freeze ponds
High temperatures kill coral or frogs
mountain pine beetle

7. Density-dependent: limiting resource
Bottom-up control
Density-dependent: individual’s survival probability depends on size of population
Recall carrying capacity: limit based on necessary resources.
Resource in short supply is the limiting resource
Limiting resource can be water, nutrient, food, space, light

8. Logistic growth

9. Food webs exert both top-down and bottom-up population controls
Phytoplankton are marine autotrophs, use nutrients (like N, P, S) to make organic material
Primary consumers are zooplankton
Coastal food web, image: USGS

10. Simple ecosystem model
The size of the circle represents the amount of nitrogen through the plankton populations.
Nitrogen is often a limiting resource.
Arrows represent fluxes between the N reservoirs.
Sliders let you control model parameters. Z
decomposition
Uptake N P

11. Human population 7 Billion and still climbing… but slower
Kolkata street, National Geographic
7 Billion and still climbing… but slower

12. What is the percentage increase?
United Nations Population Division
Population size
Annual increase / increment
% increase = (new - old) / old

13. Human population
National
Population
Immigration
Emigration
Birth
Death
Population explosion: accelerating rate of increase after Industrial Revolution
Mortality rates fall as living conditions improve
Growth rate probably topped out ~1970 at ~2% per year, perhaps 1000x faster than early human history
Now at ~1% per year growth and falling