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Ecology = Scientific study of natural communities. Experimental and observational tests. are tested by. Process. provisionally accept, revise or reject. Predictions. begets. lead to. Hypotheses. Pattern. delimit. suggest. made of. Observations. Principles.

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ecology scientific study of natural communities
Ecology = Scientific study of natural communities

Experimental and observational tests

are tested by

Process

provisionally accept,

revise or reject

Predictions

begets

lead to

Hypotheses

Pattern

delimit

suggest

made of

Observations

Principles

types of terrestrial ecosystems
Types of Terrestrial Ecosystems
  • Biomes are major groupings of plant and animal communities defined by a dominant vegetation type.
  • Each biome is associated with a distinctive set of abiotic conditions.
  • The type of biome present in a terrestrial region depends on climate—the prevailing, long-term weather conditions found in an area.
  • Weather consists of the specific short-term atmospheric conditions of temperature, moisture, sunlight, and wind.
distinct biomes are found throughout the world
Distinct Biomes Are Found throughout the World

Barrow

Dawson

Chicago

Konza Prairie

Yuma

Belém

solar radiation per unit area declines with increasing latitude
Solar Radiation per Unit Area Declines with Increasing Latitude

North pole

Small amount of

sunlight per unit area

Low angle of

incoming sunlight

Moderate angle of

incoming sunlight

Sunlight directly

overhead

Large amount of

sunlight per unit area

global air circulation patterns affect rainfall
Global Air Circulation Patterns Affect Rainfall

Circulation cells exist at the equator …

Atmosphere (not to scale)

Hadley

cell

Warm air rises

and cools,

dropping rain

Hadley

cell

Cooled air is

pushed poleward

Dense, dry air

descends, warms,

and absorbs moisture

global air circulation patterns affect rainfall1
Global Air Circulation Patterns Affect Rainfall

… and at higher latitudes.

There are three

circulation cells in the

Northern Hemisphere

There are also three

circulation cells in the

Southern Hemisphere

(draw them in)

figure 50 12

Figure 50-12

Tropical wet forests are

extremely rich in species

figure 50 14

Figure 50-14

Saguaro cacti are a prominent

feature of the Sonoran Desert in

the southwestern part of

North America

figure 50 16

Figure 50-16

Grasses are the

dominant lifeform

in prairies and

steppes

figure 50 18

Figure 50-18

Temperate forests are

dominated by broad-

leaved deciduous trees

figure 50 20

Figure 50-20

Boreal forests are

dominated by

needled-leaved

evergreens, such

as spruce and fir

figure 50 22

Figure 50-22

Arctic tundra is dominated

by cold-tolerant shrubs,

lichens, and herbaceous

plants

how predictable are communities
How Predictable Are Communities?
  • Frederick Clements promoted the view that biological communities are stable, integrated, and orderly entities with a highly predictable composition.
  • Clements argued that communities develop by passing through a series of predictable stages dictated by extensive interactions among species, and that this development culminates in a stable final stage called a climax community.
  • “All the stages which precede the climax are stages of growth.”
  • ”As an organism the formation arises, grows, matures and dies.”
slide27

Figure 50.11

Old field

Disturbance ends, site is invaded by

short-lived weedy species.

Pioneering species

Weedy species replaced by

longer-lived herbaceous species

and grasses.

Early successional

community

Shrubs and short-lived trees begin

to invade.

Mid-successional

community

Short-lived tree species mature; long-

lived trees begin to invade.

Late-successional

community

Long-lived tree species mature.

Climax community

how predictable are communities1
How Predictable Are Communities?
  • Henry Gleason, in contrast, contended that the community found in a particular area is neither stable nor predictable.
  • According to Gleason, it is largely a matter of chance whether a similar community develops in the same area after a disturbance occurs.
  • Which viewpoint is more accurate?
disturbance and change in ecological communities
Disturbance and Change in Ecological Communities
  • Community composition and structure may change radically in response to changes in abiotic and biotic conditions.
  • A disturbance is any event that removes some individuals or biomass from a community.
  • The important feature of a disturbance is that it alters some aspect of resource availability.
disturbance and change in ecological communities1
Disturbance and Change in Ecological Communities
  • The impact of disturbance is a function of three factors:

(1) type of disturbance

(2) frequency of disturbance

(3) Severity of disturbance

  • Most communities experience a characteristic type of disturbance, and in most cases, disturbances occur with a predictable frequency and severity.
  • This is called a community's disturbance regime.
history of disturbance in a fire prone community
History of Disturbance in a Fire-Prone Community

Fire scars in the growth rings

Fire scars

Reconstructing history from fire scars

how do we measure diversity

Box 50.1, Figure 1

How do we measure diversity?

Community 1

Community 2

Community 3

A

B

C

Species

D

E

F

6

6

5

Species richness:

Species diversity:

0.59

0.78

0.69

simpson s index of diversity

Proportion of sample represented by species (pi)

Species A

Species B

Species C

Species D

Species E

Community 1

0.20

0.20

0.20

0.20

0.20

Community 2

0.50

0.30

0.10

0.07

0.03

Simpson’s Index of Diversity

D = 1 /  (pi)2

If you plug these numbers into the formula for Simpson’s Index, D = 5.00 for the community where all 5 species are at equal abundances (Row 3). In contrast, D = 2.81 for the community with the same 5 species at very unequal abundances (Row 4). As this example illustrates, Simpson’s index is more sensitive to changes in the abundant (rather than rare) species in a community.

slide38

Joseph Connell’s

Intermediate Disturbance Hypothesis