1. Understanding Ecology and the Interdependence of Life
34.1 THE BIOSPHERE IS THE GLOBAL ECOSYSTEM

2. What is Ecology?
Ecology is the scientific study of the INTERACTIONS among organisms and organisms and their environment.

3. Ecology can be studied at many levels.
INDIVIDUAL
POPULATION
COMMUNITY
ECOSYSTEM
BIOME
BIOSPHERE
A group of the same species living in a defined area
Species interbreed and produce fertile offspring
Groups of populations live together in a defined area
All the organisms that live in an area together with their physical environment
A group of ecosystems that have the same climate and similar dominant communities
All the portions of the planet in which life exists (land, water, & atmosphere)

4. The biosphere is made up of BIOTIC and ABIOTIC factors
BIOTIC FACTORS: Living factors such as prokaryotes, protists, animals, plants, and fungi in the environment

5. ABIOTIC FACTORS: Nonliving physical and chemical conditions
The KEY abiotic factors in an ecosystem are:
Sunlight: provides light, heat, and energy
Water: essential to all life on earth
Temperature: most life is tolerant of temperatures between 0◦C and 50◦C
Soil: the structure and chemical make-up of the soil controls what type of plants will grow
Wind: winds move clouds and rain as well as disperse seeds
Severe Disturbances: wildfires, hurricanes, tornadoes, droughts, floods, and volcanic eruptions

6. Chapter 35: Population and Community Ecology
35.1 A POPULATION IS A LOCAL GROUP OF
ORGANISMS OF ONE SPECIES

7. Defining Populations
The researcher must define the population’s geographic boundaries
Ex: Edges of a lake for a trout study, a state for coyote, a Petri dish of bacteria, etc.

8. Population Density
The number of individuals of a particular species per unit area or volume 
Ex: In a forest measuring 50 km2, a researcher counted 1000 birch trees. What is the population density?
PD = 1000 birch trees = 20 trees/km2
50 km2
Population density is useful measurement to compare populations in two or more locations.

9. Sampling Techniques
Quadrants: Researchers mark off an area and count the number of individuals in that area (or quadrant). They repeat the procedure in several locations and average the results to estimate the total population size.
Indirect Counting: counting nests, burrows, or tracks instead of actual organisms
Mark-Recapture: Researcher traps animals, marks them, and releases them. Later, they capture animals again.
Total Population = # in 1st capture × # in 2nd capture
# of marked animals recaptured
All of these methods have limits to accuracy. Many assumptions are made about the population. If the assumptions are invalid, the estimate will not be accurate.