1. The study of the interactions of organisms with their environment
Ecology
The study of the interactions of organisms with their environment

2. The “control of nature” is a phrase conceived in arrogance, born of the Neanderthal age of biology and philosophy, when it was supposed that nature exists for the convenience of man. - Rachel Carson, Silent Spring

3. Definitions
Population – a group of individuals of a single species that occupies the same general area.
Exponential growth model – the rate of expansion of a population under ideal conditions
Population-limiting factors – hunting, amount of space suitable for breeding, restricted population growth, food availability
Logistic growth model – idealized population
growth slowed by limiting factors as the population size increases
Carrying capacity – the maximum population size that an environment can support at a particular time with no degradation to the habitat

4. Exponential growth of bacteria

5. Logistic growth and exponential growth compared

6. Growth of a population of fur seals

7. What does the logistic growth model suggest about real populations in nature?
A population’s growth rate will be small when the population size is either small or large and highest when the population is at an intermediate level relative to the carrying capacity.
Limiting factors make the birth rate decrease, the death rate increase or both
Eventually the population will stabilize at the carrying capacity when the birth rate equals the death rate
These are mathematical models and no population fits either perfectly

8. Sparrow Population
Some populations remain fairly stable in size close to carrying capacity
Most populations fluctuate as seen at the left
This graph shows song sparrow populations, with periodic catastrophic reductions due to severe winter weather

9. Boom and bust cycles
Hare cycles may be caused by increasing food shortages during winter caused by overgrazing
They may be due to predator-prey interactions
Cycles could be affected by a combination of food resource limitation and excessive predation
Predators reproduce more slowly than their prey so they always lag behind prey in population growth.

11. Exponential growth of the human population
Throughout human history parents had many children but only two on average survived to adulthood
Estimates that by 2025 the world will have to double food production, 2/3 of the available fresh water on earth will be in use, 60,000 plant species will be lost to support the population
Issues: overgrazing, rivers running dry, decrease in groundwater, energy?

12. How to achieve population stability?
Zero population growth – when birth rates equal death rates
Two ways to reach ZPG. High birth and death rates or low birth and death rates.
Demographic transition is moving from the first to the second. Most developed countries have made the transition
See the demographic transition in Mexico at the left.

15. Growth to a Stable Population

16. Limiting Factors
Limiting factors are things that prevent a population from growing any larger
Limiting factors are very closely tied to carrying capacity
Examples of Limiting factors
Disease
Predators
Food
Water
Hunting
Climate Change
poor reproductive success
damage to the habitat

17. Growth to a Stable Population
Logistic growth
Environmental resistance

19. Collapse of northern cod fishery – estimates of stocks to high
Renewable resource management – harvesting crops without damaging the resource
Maximum sustainable yield – harvest at a level that produces a consistent yield without forcing a population into decline
Can be just as tricky to reduce population sizes

20. Potential Effects of Global Climate Change
1) Continent-wide synchronization of cycles may disrupt food webs
“If climate change results in … more shallow and icy snow pack, this will probably … expose small mammals to predators, … and thereby prevent peak abundances of lemmings and voles. For nomadic predators whose life history tactic is based on asynchronous lemming populations at a continental scale, [frequent large-scale] climatic anomalies that [induce] continental-wide synchrony is very likely to have devastating effects.”
–Callaghan et al. (2004)
Actually a lemming
Kaikusalo and Angerbjorn (1995)
The pictures illustrate the point. Callaghan et al. refer to these data and suggests that declines in arctic foxes and snowy owls may be caused by this “Moran effect,” or more generally an overall decline in lemming and vole abundances at their peaks. (They refer both to lemmings and voles, even though the data here are for voles only.)
Lemmus lemmus
Picture from
Picture from