Understanding Ecology and the Interdependence of Life

34.1 THE BIOSPHERE IS THE GLOBAL ECOSYSTEM

What is Ecology?

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

Ecology can be studied at many levels.

INDIVIDUAL

POPULATION

COMMUNITY

ECOSYSTEM

BIOME

BIOSPHEREAll the portions of the planet in which life exists (land, water, & atmosphere)

A group of ecosystems that have the same climate and similar dominant communities

All the organisms that live in an area together with their physical environment

Groups of populations live together in a defined area

A group of the same species living in a defined area

Species interbreed and produce fertile offspring

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

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

Chapter 35: Population and Community Ecology

35.1 A POPULATION IS A LOCAL GROUP OF

ORGANISMS OF ONE SPECIES

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.

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.

Sampling TechniquesQuadrants: 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.