We all know that living things need resources in order to survive. We often, however, don't make the connection that the amount of available resources dictates the size of a population – 
that a population will grow when resources are in surplus, decline when resources are scarce, and stabilize when the population is at the maximum level that can be sustained. It smoothes out generally like the S-curve here (right).
There are a number of complex variables, but the results are understandable. Continuous growth depends on unlimited resources. Equilibrium comes with a balance of population and resources. Overshoot and oscillation occurs with fluctuating resource events like drought and flood and marketplace upheavals. Collapse comes when resources are used and not renewed.
Human population is on a steep J-curve rise based on our aggressive exploitation of resources. We're bringing water, food, power, raw materials in at an accelerating pace, and population responds accordingly, particularly urban population.
It's not a smooth path across the globe. Oscillations occur regionally with drought and flood, earthquake and marketplace upheavals, things that interrupt the flow of resources. The world's rich don't feel the inherent distress others do. The poor are affected the most.
Do we know what resources will be available to support human population? Do we know which ones are not being replaced at an adequate rate to support our current consumption? Of course we do.
Change is certain.
- Caught in the Crosshairs: Wildlife Faces the Population Challenge
- Demographic Facts of Life
- Fishing for a Solution to the Population Problem
- Population: 7 Billion
- Population and Climate Change: A Clear Link
- Seeing the Forest for the Trees: Population and Deforestation
- Ten Population and Environment Connections
- The Perfect Disaster: Man vs. Nature
- The Thirsty Billion: Population and Water
- Unsustainable Suburban Sprawl
- Wildlife Feeling the Population Squeeze