EcologyChapters 2-4

•Ecology is the study of interactions that take place between organisms and their environment

• The nonliving parts of an environment are the abiotic factors.–air currents, temperature, moisture, light, and soil.

The nonliving environment: Abiotic factorsThe nonliving environment: Abiotic factors• This graph shows how the plant’s glucose

(food) production is affected by temperature.

5

10

15Food Production in Salt Bush

10 20 30 40 50Temperature (°C)

Food

pro

duct

ion

(mg

of g

luco

se/h

r)

•All the living organisms that inhabit an environment are called biotic factors

I. Levels of Organization

• A population is a group of organisms of the same species which live in the same area.

Levels of Organization

• A community is made up of interacting populations

Levels of Organization

• An ecosystem is a community plus the abiotic components of that area.

• A habitat is the place where an organism lives out its life.

• A niche is the role or position a species has in its environment—how it meets its specific needs

Symbiotic relationships

• Mutualism: both benefit– E. coli in digestive tract– In termite’s guts– In grazer’s guts– In flashlight fish

• Commensalism: one benefits, other unaffected (rare)– Orchids on trees

• Parasitism: one benefits (parasite), one hurt (host)– Pathogenic bacteria, (make you sick)

II. Energy Flow

• The ultimate source of the energy for life is the sun.– Utilized by

producers (autotrophs) in photosynthesis

• Consumers are heterotrophs– Herbivores: eat producers– Carnivores: eat other consumers– Omnivores: eat both plants and

animals– Scavengers: eat food already dead– Decomposers: absorb nutrients

from decaying organisms

Herbivores: eat producers

Carnivores: Eat other consumers

Scavengers: eat dead animals

Decomposers: absorb decaying organisms

Energy Flow

• A food chain shows how matter and energy move through an ecosystem

• Berries mice snake• Each organism in a food chain

represents a feeding step, or trophic level

• Available energy decreases with each trophic level

•Some lost as feces•Some lost in cellular respiration as

heat•Only 10% passed on

Energy and trophic levels: Ecological pyramidsEnergy and trophic levels: Ecological pyramids

• The pyramid of energy: available energy decreases at each succeeding trophic level.

Pyramid of Energy

Heat

Heat

Heat

Heat

0.1% Consumers

1% Consumers

10% Consumers

100% Producers

Parasites, scavengers, and

decomposers feed at each

level.

Cycles in Nature

• Energy flows, it does NOT cycle• Water cycle

– Evaporation condensation precipitation

• Carbon Cycle– Photosynthesis fixes atmospheric CO2 into living

matter

– Respiration by organisms returns CO2 to atmosphere

– Carbon in dead organisms returns to atmospheric CO2 through combustion or decomposer respiration

Cycles in Nature

• Nitrogen Cycle

• Phosphorus Cycle

IV. Population Growth

• The graph of a growing population starts out slowly, then begins to resemble a J-shaped curve.

How fast do populations grow?How fast do populations grow?Population Growth of Houseflies

1 million

500,000

100One year

Pop

ula

tion

siz

e

• A limiting factor restricts the existence, numbers, reproduction, or distribution of organisms.

Common Limiting Factors

Sunlight

ClimateAtmospheric gases

Temperature

WaterNutrients/Food

FireSoil chemistrySpaceOther organisms

Limiting factorsLimiting factors

• Limiting factors may cause population growth to slow and stabilize in an S-shaped growth curve.

What can limit growth?What can limit growth?Characteristics of Population Growth

Exponential growth

Carrying capacity

J curve S curve

Pop

ula

tion

Time0

DIS

EA

SE

SPA

CE

PR

ED

A-

TO

RS

FO

OD

Carrying Capacity (K)

• The number of organisms of one species that an environment can support

Predation affects population sizePredation affects population size• The data in this graph reflect the number of

hare and lynx pelts sold to the Hudson’s Bay Company in northern Canada from 1845 through 1935.

Lynx and Hare Pelts Sold to the Hudson’s Bay Company

Num

ber

of o

rgan

ism

s(in

tho

usan

ds)

Times (in years)

LynxHare

VI. Life History Strategies• R Strategy: (Rapid)

– small body size– mature rapidly– short life span– Live in a changeable or

unpredictable environment– Large “litter”– Little to no parental care– Tend to overshoot carrying

capacity before falling back to carrying capacity

Life History Strategies

• K Strategy:

– Large body

– Mature slowly

– Long-lived

– live in stable environments

– Few, well cared for young

– Population maintained at or near K

Types of Limiting Factors

• Density Dependent factors– Increased effect as population size increases

• Disease• Competition• Food

• Density Independent Factors– Affect population regardless of size

• Storms• Floods• pollution

V. Competition

• Gause (1934) hypothesized that two species with the same niche requirements cannot live together– Tested with paramecium– Grown separately, both species reach K– Grown together, one reaches K, the other

becomes extinct

•Competitive exclusion principle

VII. Biodiversity

• Def: the variety of species in a specific area– Ex. Cornfield has less biodiversity than equal

area of rainforest

• Increases as you near the equator– Hectare of Amazon rainforest ~300 tree species– Hectare of temperate deciduous forest ~30

tree species

• Increases with increasing primary productivity– Supports more “links” in food chain due to

higher energy base

Importance of Biodiversity

• Beauty• Interdependence of nature

– Food chain links– Symbiotic relationships– Abiotic changes as the result of species loss– Resources for humans

• Genetic – to produce new food varieties• Medical – quinine, cyclosporine, penicillin• Raw materials

Rosy periwinkle, the source of drugs for Hodgkin’s disease and leukemia

Invasive (Exotic) Species

• Def: species that are not native (introduced) to a community– Ex. Goats on Santa Catalina Island– Ex. Sea lamprey in Great Lakes

• Population grows exponentially at first due to absence of predators and ability to outcompete native species

• May drive native species to extinction